Download Control of GnRH secretion: One step back - e

Frontiers in Neuroendocrinology xxx (2011) xxx–xxx
Contents lists available at ScienceDirect
Frontiers in Neuroendocrinology
journal homepage: www.elsevier.com/locate/yfrne
Review
Control of GnRH secretion: One step back
Iain J. Clarke ⇑
Department of Physiology, Monash University, P.O. Box 13F, Clayton, Victoria 3800, Australia
a r t i c l e
i n f o
Article history:
Available online xxxx
Keywords:
Gonadotropin releasing hormone
RF-amide peptide
Reproduction
Food intake
Hypothalamus
a b s t r a c t
The reproductive system is controlled by gonadotropin releasing hormone (GnRH) secretion from the
brain, which is finely modulated by a number of factors including gonadal sex steroids. GnRH cells do
not express estrogen receptor a, but feedback is transmitted by neurons that are at least ‘one step back’
from the GnRH cells. Modulation by season, stress and nutrition are effected by neuronal pathways that
converge on the GnRH cells. Kisspeptin and gonadotropin inhibitory hormone (GnIH) neurons are regulators of GnRH secretion, the former being a major conduit for transmission of sex steroid feedback. GnIH
cells project to GnRH cells and may play a role in the seasonal changes in reproductive activity in sheep.
GnIH also modulates the action of GnRH at the level of the pituitary gonadotrope. This review focuses on
the role that kisspeptin and GnIH neurons play, as modulators that are ‘one step back’ from GnRH
neurons.
Ó 2011 Elsevier Inc. All rights reserved.
1. Introduction
The original finding of Harris [53], that electrical stimulation of
the brain caused ovulation in the rabbit, instigated his lifelong mission to delineate the means by which pituitary gonadotropin secretion is stimulated. This culminated in the development of the
neurohumoral theory [54] which relies upon a unique anatomical
arrangement in the median eminence and a highly efficient conduit of multiple signals from various types of hypothalamic cells
to their respective target cells in the anterior pituitary. The early
work of Harris and others, which led to the formulation of the neurohumoral theory was well reviewed by Donovan [42] in an earlier
Harris Memorial Lecture.
Whereas it became apparent that neurohumoral factors were
produced by the hypothalamus and reached the anterior pituitary
gland by way of the hypophysial portal blood system, it was not
until the chemical identification of such factors that proof of such
‘messengers’ was obtained. The purification of thyrotropin releasing hormone (TRH) [14,16] from hypothalamic extracts was closely
followed by discovery of gonadotropin releasing hormone (GnRH)
[2,86,107]. Proof of secretion of GnRH into the portal system was
provided by the technically challenging studies of Fink and colleagues [106]. Original work in the non-human primate provided
evidence that the pattern of secretion of luteinizing hormone
(LH) was pulsatile [40]. Ultimately, the exact relationship between
the secretion of GnRH and that of LH from the pituitary was revealed with the creation of a model in sheep that allowed concomitant serial sampling of hypophysial portal blood and jugular
⇑ Fax: +61 3 9905 2547.
E-mail address: [email protected]
venous blood in conscious, sentient sheep [20,29]. This allowed
the full description of the hypothalamo-pituitary–gonadal (HPG)
axis, outlining how GnRH action is modulated at the level of the
pituitary gonadotrope and how feedback effects of gonadal hormones modulate the secretion of GnRH and the gonadotrophins
[23]. The measurement of GnRH secretion also allowed definition
of physiological and environmental factors that regulate reproduction at the level of the GnRH system. This included revelation of the
effects of gonadectomy [20], photoperiod/season [72], stress [92],
stress levels of cortisol [89], immune response [69] and gonadal
steroid feedback [25,71] on GnRH secretion. One of the most fundamental aspects of the operation of the HPG axis is the means
by which sex steroids act to modulate GnRH secretion and this
took some time to resolve. Since GnRH cells do not possess the relevant sex steroid receptors [57], significant efforts were made in
various laboratories and species over decades (1970s to 2003) to
identify steroid-receptive elements in the brain that relayed feedback information to the GnRH cells. Various cell types were found
to express estrogen, progesterone and androgen receptors, but evidence of a major conduit remained elusive [127]. A significant advance was the discovery that the kisspeptin receptor (and by
implication, its ligand, kisspeptin) was essential for normal reproduction [39,108]. Intense investigation over the past 7 years
strongly suggests that sex steroid feedback regulation of GnRH
cells is predominantly exerted via kisspeptin cells, although many
other cell types in the brain also play a role. These cells are at least
‘one step back’ from the GnRH cells, allowing for integration of
information of steroid feedback, season, stress, immune status,
nutritional status, etc. to be synthesized by the GnRH cells and
converted to a singular output of the brain that drives the reproductive system. Thus, serial and neuronal systems converge on
0091-3022/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved.
doi:10.1016/j.yfrne.2011.01.001
Please cite this article in press as: I.J. Clarke, Control of GnRH secretion: One step back, Front. Neuroendocrinol. (2011), doi:10.1016/j.yfrne.2011.01.001
2
I.J. Clarke / Frontiers in Neuroendocrinology xxx (2011) xxx–xxx
the GnRH cells to determine the output of these cells in terms of
secretion.
A major focus of this review is the role of kisspeptin in the regulation of the GnRH system, especially in relation to work done in
the ovine model. The reader is also referred to other recent reviews
on the function of kisspeptin [19,90,112]. Another recently recognized modulator of reproductive function is gonadotropin inhibitory hormone (GnIH). Whereas the prevailing view was that the
secretion of GnRH was the singular means by which the brain controls the reproductive system, the existence of an inhibitory system
was also entertained. Gonadal factors such as luteinizing hormone
release-inhibiting factor (LHRIF) [62] were proposed. Another
inhibitory factor, gonadotropin surge inhibiting factor (GnSIF)
[37], suppresses LH secretion with or without any effect on FSH.
This latter is a protein produced by ovarian follicles, not the brain
[83], but there was no convincing evidence of hypothalamic factor
that negatively regulated the reproductive axis until 2000. The discovery that GnIH was present in the hypothalamus of the quail
[131] and that it acted as a negative regulator of reproduction
was, therefore, an important advance in our knowledge. Whilst evidence that GnIH is an important facet of the HPG axis in mammals
has been tardy, work over the last few years has escalated its importance. Like kisspeptin, GnIH is an RF-amide peptide and it exerts
negative effects on GnRH cells [43] and, at least in some species,
the gonadotropes [33]. Recent and extensive reviews on the role
of GnIH in mammals are also available [32,77,111,129,130] and this
review will focus mainly on work in relation to GnIH function that
has been carried out in sheep. The following review will consider
the evidence that GnIH cells are also ‘one step back’ from GnRH cells
and play a major role in the regulation of GnRH secretion as well as
acting on the pituitary gonadotropes, in sheep at least, to negatively
regulate gonadotropin synthesis and secretion.
2. Inherent properties of GnRH cells
Andrew and Dudek [5] showed that magnocellular neuroendocrine cells possess inherent phasic firing patterns [5] and this was
extended to a demonstration of the same in GnRH cells when the
‘labeling’ of cells by incorporation of green fluorescent protein
genes through transgenics provided a means of recording from single units in vitro [79]. Others showed that multi-unit activity of the
hypothalamus correlated with pulsatile LH secretion in rats [74],
sheep [126] and non-human primates [138]. The work of Dudek
and colleagues suggested that all neuroendocrine may cells possess
an inherent phasic rhythm [4,5]. With the advent of transgenic mice
in which green fluorescent protein was genetically targeted to
GnRH neurons, it became possible to target individual cells, revealing that single units displayed bursting consistent with phasic
secretory activity [122]. This is translated into the secretory mode
as demonstrated by the phasic release of GnRH from cells of the fetal nasal placode of rhesus monkeys studied in culture [124].
One might envisage a model, based on modulation of such
inherent phasic activity of the hypophysiotropic cells. On the other
hand, based on the multi-unit activity generated by unknown elements in the basal hypothalamus, the concept of a ‘pulse generator’
continues to be embraced. For the reasons given above, pulse generation by neurons that are ‘upstream’ of neuroendocrine cells may
not be necessary if the neuroendocrine cells themselves have
inherent phasic rhythms. To achieve co-ordinate phasic rhythm
of a number of neurons, such that a pulsatile discharge of the hypophysiotropic hormone occurs at regular intervals, some means of
communication between the neurons would seem necessary. In
the case of GnRH neurons, this appears to be achieved by dendro-dendritic connections [17].
One could infer that neuronal elements that modulate GnRH
neurons are the ‘pulse generators’ and a wide range of neuronal inputs to the neurons are known; this is discussed in the next section. Irrespective of either model, it is clear that GnRH neurons
function in a phasic mode, leading to the ultradian pulse pattern
of GnRH secretion. In the free-running situation, unrestrained by
gonadal steroid feedback, the ultradian pulse rhythm of GnRH cells
(reflected in LH pulses) is roughly one hour, as well typified in nonhuman primates [40] and sheep [29,73]. It should be noted that, in
contrast to the pulse pattern of LH secretion, that of FSH secretion
does not rigidly reflect GnRH secretion [24]. This is because FSH
secretion does not depend directly on the secretagogue properties
of GnRH [28,30].
3. Regulation of GnRH cells by neuronal systems within the
brain
Given that GnRH cells operate in a phasic manner, the modulation of ultradian secretion becomes highly relevant, since this dictates reproductive function. Such a system allows for alterations
in frequency and amplitude with exquisite precision; variation in
these two parameters allows very fine tuning of GnRH output.
The question then becomes one of how such modulation is effected.
Afferents neurons that provide either direct or indirect input to
GnRH cell bodies are important in this regard, so a large number
of studies employing a variety of techniques have cataloged these.
Evidence exists for direct input to GnRH cells from brain stem noradrenergic cells [95,100] and the serotoninergic elements of the
raphe nucleus [76], as well as various cell types of the hypothalamus and the forebrain [63,93,95,96]. In order to exert fine control
over GnRH secretion, however, it is not necessary that upstream
neuronal systems form a direct pathway to the GnRH cells. Thus,
it is possible that pathways from regions such as the A1 noradrenergic field of the brainstem may involve inter-neuronal relays in the
bed nucleus of the stria terminalis (BNST) or preoptic regions in
close vicinity to the GnRH cells [91,93]. Anterograde and retrograde
neuronal tracing between the arcuate nucleus of the hypothalamus
(ARC) and the preoptic area of the ovine brain indicate that there is
very limited direct input to GnRH cells from the former [9,97]. Thus,
even though a case is made below for a predominant role of kisspeptin cells in the ARC in the regulation of GnRH cells, there is little
evidence of direct neuronal projections that subserve this [9]. One
caveat on this observation is that kisspeptin cells may project to
dendrites of GnRH cells that are not readily seen without special
techniques. On the other hand, kisspeptin cells in the lateral POA
of the ovine brain do appear to provide direct neuronal input to
GnRH cells [9]. The existence of multi-synaptic pathways to GnRH
neurons from various regions of the brain presumably allows even
further means of fine control of the reproductive system, incorporating information in relation to metabolic status, season, stress
state, immune status, olfactory stimuli, etc.
By 2002, various neuronal systems of the brain were known to
provide input to GnRH cells and the neuroanatomical framework
was reviewed [127]. Other reviews provided a description of sex
steroid responsive systems that might subserve feedback regulation of GnRH cells [57]. It is notable, however, that no single neuronal system could be ascribed a predominant role in the
modulation of GnRH cells by sex steroids. Noradrenergic cells of
the brain stem appear important for normal function, but it is also
likely that glutamatergic input plays a major role as a positive regulator of GnRH cells [35,79]. Certainly, GnRH cells in the sheep
brain receive a very high level of glutamatergic input, based on
confocal microscopic studies [95]. The other most common neurotransmitter in the hypothalamus is gamma amino butyric acid
(GABA) and GABAergic cells appear to be major negative regulators
Please cite this article in press as: I.J. Clarke, Control of GnRH secretion: One step back, Front. Neuroendocrinol. (2011), doi:10.1016/j.yfrne.2011.01.001
I.J. Clarke / Frontiers in Neuroendocrinology xxx (2011) xxx–xxx
of GnRH cells [56]. Notwithstanding this simplistic model, glutamatergic and GABAergic systems are known to have both positive
and negative effects on the firing patterns of GnRH cells, so much is
yet to be learned as to how neuronal function is translated into
pulsatile GnRH secretion. In 2003, our understanding of the neuronal circuits that are ‘one step back’ from GnRH cells received a major fillip with the revelation that kisspeptin cells are essential for
reproductive function.
4. Kisspeptin
As indicated above, the revelation that kisspeptins and the kisspeptin receptor GPR54 are essential for reproductive function was
a major advance in reproductive neuroendocrinology. Hereafter in
this review (unless stated otherwise), ‘kisspeptin’ will refer to the
10-amino acid form, although it is recognized that larger forms
of the post-translational product of the Kiss1 gene are equally
effective [65,75]. Mass spectrometry analysis of the arcuate nucleus of the sheep brain indicates the presence of kisspeptin-10,
but not larger forms of kisspeptin (Zeng, A.I. Smith and I.J. Clarke,
unpublished data).
There are two major groupings of kisspeptin cells in the mammalian brain, one being in the ARC and the other being in the rostral hypothalamus/POA. In rodents, the latter group of cells is
located in the anteroventral periventricular nucleus (AVPV) and
preoptic periventricular nucleus (PeV) [34,51,115,116]; this region
has also been called the rostral periventricular area of the third
ventricle (RP3V) [58]. In the female sheep, the two synonymous
populations of kisspeptin cells are in the ARC and in the lateral
POA [48]. How these two groups of kisspeptin cells regulate GnRH
cells has been the subject of intense study over the past 7 years.
4.1. Kisspeptin cells are major regulators of GnRH cells
Kisspeptin administration causes GnRH secretion, at least on the
basis of measurement of GnRH in cerebrospinal fluid following
intracerebroventricular infusion of kisspeptin-10 [87]. It remains
to be shown, however, that kisspeptin stimulates secretion into
the hypophysial portal blood. Supporting the notion that kisspeptin
exerts direct action on the GnRH cells, it has been shown that virtually all of these cells express the cognate receptor (GPR54) [52,64].
There is no good indication that kisspeptin has a direct effect on the
pituitary gonadotropes to cause LH release in sheep [119]. This is in
spite of the fact that at least some GPR54 expression can be detected in the pituitary gland by PCR [119]. Consistent with this, it
appears that kisspeptin does not exert hypophysiotropic function
because it is not secreted into the hypophysial portal blood in significant amounts [119]. Finally, in vivo studies on hypothalamopituitary disconnected, GnRH replaced sheep, kisspeptin infusion
did not affect the amplitude of LH pulses [119]. Interestingly, kisspeptin cells project to the median eminence, where varicose fibers
come into close apposition to GnRH fibers [99] and it is possible that
there is of axo-axonic regulation of GnRH secretion at this level. In
this regard, studies in the non-human primate, using push–pull
perfusion of the stalk-median eminence (SME) indicated concordance between patterns of secretion of kisspeptin and GnRH [75].
In addition, levels of both peptides in push–pull samples obtained
from the SME indicated a rise in associated with puberty. Furthermore, the administration of kisspeptin to the SME stimulated LH
secretion. Regarding the latter finding however, it is equivocal as
to whether kisspeptin acted on GnRH cell bodies in the mediobasal
hypothalamus or whether it acted on secretory terminals.
What is the exact link between kisspeptin and GnRH function?
In other words, is up-regulation or down-regulation of kisspeptin
function directly translated into a change in GnRH secretion?
3
One way of addressing this question is to prevent kisspeptin action
and measure GnRH/LH secretion. The development of a kisspeptin
antagonist was instructive in this regard. This peptide antagonist
blocks pulsatile LH secretion, with supporting electrophysiological
data as well as in vivo measurement of GnRH secretion from the
primate SME to show that the effect is exerted at the level of the
GnRH neuron [103]. In the ovine brain, kisspeptin cells of the lateral POA provide direct input to GnRH neurons, whereas kisspeptin
cells of the ARC may regulate GnRH neurons through a poly-synaptic pathway involving cells of another type [9]. The observation
that kisspeptin stimulates GnRH release from the mouse median
eminence [36] also supports the concept of a possible site of action
at the level of GnRH neuroterminals.
4.2. Kisspeptin cells transmit the feedback effect of sex steroids to
GnRH cells
One major reason for intense focus on the role of kisspeptin in
the control of reproductive function is that the kisspeptin cells express steroid receptors, whereas GnRH cells do not.
GnRH cells do not express estrogen receptor-a (ERa), or androgen receptors [59,61] yet it is clear that the function of secretion of
GnRH is regulated by sex steroids [23]. With respect to estrogen
feedback, more than 60% of kisspeptin cells in the AVPV of the female mouse brain express estrogen receptor-a (ERa), as demonstrated by in situ hybridization [118] and immunohistochemistry
[34,118]. In the AVPV/PeV of the female rat brain, approximately
90% of kisspeptin cells were shown express ERa, as assessed by
immunohistochemical staining [1]. In the ovine brain, virtually
all of the kisspeptin cells in the ARC express ERa, whereas only
50% of the population of cells in the lateral POA do so [48]. The
question arises as to what function is performed by the kisspeptin
cells that do not express steroid receptors; this may be to control
metabolic homeostasis as discussed below.
4.3. Kisspeptin cells produce the positive feedback effect of estrogen
Based on a range of criteria, including gene expression for Kiss1,
Fos activation by estrogen, immunohistochemically measured levels of kisspeptin and various studies with gene knockout and
replacement models, it is clear that the AVPV/PeV population of
kisspeptin cells is fundamentally involved in the positive feedback
effect of estrogen and the generation of the pre-ovulatory surge in
rats and mice [113,139]. It has been consistently shown across different laboratories and in both rats and mice that kisspeptin cells
are upregulated in the AVPV/PeV in the rat and mouse brain in
the pre-ovulatory (pro-estrous) period, whereas the arcuate kisspeptin cells are down-regulated at this time (reviewed in [110].
Thus, the AVPV/PeV kisspeptin cells are regarded as fundamental
to the propagation of the positive feedback effect that elicits the
pre-ovulatory surge in GnRH/LH in these species.
Whereas kisspeptin cells in the ovine brain exist as two major
groupings, as in rodents, the mode of estrogen positive feedback
appears to be quite different. Thus, in the ewe, this involves action
of estrogen within the mediobasal hypothalamus, based on studies
where micro-implants of estrogen were placed in this region
[13,18]. Concordant with this is a range of observations that
strongly suggest the fundamental role of arcuate nucleus kisspeptin cells in the positive feedback phenomenon. Evidence for this is
as follows:
1. Kisspeptin treatment causes ovulation in anestrous ewes [21].
The important principle that is demonstrated in this study is
that administration of this single neuropeptide leads to a surge
in LH secretion (and, by inference, a GnRH surge). This may,
however, be elicited by stimulation of basal pulsatile GnRH/
Please cite this article in press as: I.J. Clarke, Control of GnRH secretion: One step back, Front. Neuroendocrinol. (2011), doi:10.1016/j.yfrne.2011.01.001
4
2.
3.
4.
5.
6.
7.
I.J. Clarke / Frontiers in Neuroendocrinology xxx (2011) xxx–xxx
LH secretion, leading to a rise in estrogen levels that then elicits
a positive feedback effect. The positive feedback effect of estrogen may then be regarded as a secondary event, also at the level
of the mediobasal hypothalamus (most likely the arcuate
nucleus) in this species. More recent data also invoke a role
for preoptic kisspeptin neurons in the positive feedback event
in sheep [17] and non-human primates [121].
ARC and POA Kiss1 expression is upregulated in the follicular
phase of the estrous cycle [44,117]. The upregulation of Kiss1
in the caudal ARC is consistent with this region of the brain
being the site at which estrogen acts to cause positive feedback
in the sheep (vide supra). An effect of estrogen at this level
would necessarily be transmitted to GnRH cells by at least
one inter-neuronal link, which could be either the kisspeptin
cells in the latPOA or some other type of cell. The former would
explain the upregulation of the latPOA cells, although estrogen
could act directly on at least 50% of the latPOA kisspeptin cells
that express ERa. The latPOA kisspeptin cells project to GnRH
cells [9], so that this could be the direct conduit to GnRH cells
that subserves the positive feedback response.
Kisspeptin peptide levels are increased in cells of the caudal
ARC in the late follicular phase [117]. This substantiates the
observations on Kiss1 expression and also consolidates the
notion that this region of the brain is where estrogen acts to
cause positive feedback in the ewe.
Kisspeptin cells are acutely activated by estrogen as assessed by
Fos immunohistochemistry [117]. This particular study compared responses in ovariectomised ewes within 1 h after a challenge with estrogen, which is considered to be a transient signal
to activate the positive feedback mechanism [31]. This signal
activates a chain of events, leading to a time-delayed surge in
GnRH secretion [26]. This study contrasted the activational
state of kisspeptin neurons in the ARC in ovariectomised ewes
that were receiving chronic estrogen treatment as opposed to
a transient challenge. As such, it distinguished the two types
of feedback, with reduced Fos labeling in cells from animals
receiving chronic estrogen treatment and increased Fos labeling
in those receiving an acute challenge. Whether the same neurons are involved in both types of feedback or not is unknown,
but more detail on the negative feedback mechanism is given
below.
In the ewe brain, 90% of GnRH cells express GPR54, but there is
also a number of non-GnRH cells in the POA that express the
receptor and could act as relay cells for the effects of kisspeptin
to regulate GnRH secretion [117]. Further studies on the regulation of the receptor will prove informative in relation to the
positive feedback mechanism.
Response to kisspeptin in terms of LH secretion, is increased in
the follicular phase of the estrous cycle [120]. Presumably this
is preparatory to GnRH surge induction.
In the non-human primate, as in the ewe, it also appears that
the positive feedback phenomenon is associated with upregulation of kisspeptin in both the ARC and the POA, based on in situ
hybridization measures of Kiss1 [121]. This contrasts with the
repeated observation that AVPV/PeV kisspeptin cells are upregulated in the rodent brain by estrogen treatment or during the
pro-estrous period, with contemporaneous down-regulation of
the kisspeptin cells in the ARC (vide supra). This indicates a clear
cut difference between rodents on one hand and sheep/nonhuman primates on the other hand.
4.4. Kisspeptin cells mediate the negative feedback effect of ovarian
steroids
Kisspeptin cells appear to mediate negative feedback, as initially shown by upregulation of Kisspeptin cells following ovariec-
tomy, as assessed by immunohistochemistry [94]. Furthermore,
chronic treatment with estrogen alone reduces Fos in kisspeptin
cells in the ARC of ovariectomised ewes [117]. Virtually all kisspeptin cells in the ARC co-express dynorphin (DYN) and neurokinin B
(NKB) [50]. This has led to the naming of these cells as K (kisspeptin) N (neurokinin B) Dy (dynorphin) (KNDy) cells [22]. The KNDy
cells also express both ERa and progesterone receptor at a high level [46,48], providing the necessary machinery for these KNDy
cells to mediate both negative and positive feedback effects of
sex steroids. There is good evidence that dynorphin plays a role
in mediating the negative feedback effect of progesterone
[47,49], in addition to the evidence that chronic estrogen treatment downregulates the KNDy cells in OVX ewes [117]. Further
support for the notion that these cells participate in transmitting
the negative feedback effect to GnRH cells is the observation that
kisspeptin expression in the ARC is reduced in the luteal phase of
the estrous cycle [117]. This does not mean that other cells, such
as those that produce enkephalin, may not also participate in the
negative feedback regulation of GnRH secretion [136], but a major
role for the KNDy cells is most likely. As for the involvement of
these cells in the positive feedback mechanism, any transmission
from the ARC to the GnRH cells of the POA is likely to involve a
poly-synaptic pathway. KNDy cells may regulate a subset of GnRH
cells in the mediobasal hypothalamus, to exert the negative feedback effect [49].
4.5. Kisspeptin cells and non-reproductive functions
In spite of overwhelming evidence that kisspeptin cells exert
major control over GnRH cells, there is also a range of other regulatory neuronal systems. Kisspeptin cells in both the ARC and the
POA express the signaling form of the leptin receptor, ObRb, and
the former group are networked with appetite regulating cells
[9], allowing transmission of signals relating to metabolic state.
There are two reasons why this network is of significance. Firstly,
the expression of ObRb allows kisspeptin cells to respond to the
relative level of body fat and this could be transmitted to GnRH
cells. Reproductive function is shut down in low body condition,
but this can be counteracted by leptin administration [55], which
could be effected via kisspeptin cells. Second, kisspeptin cells in
the ARC are reciprocally connected with neuropeptide Y and proopiomelanocortin cells in the same nucleus [9]. The high level of
expression of sex steroid receptors in the kisspeptin cells may allow sex steroid regulation of appetite and energy expenditure via
the other two cell types, in which expression of ERa is much lower
[82,109]. Since estrogen is well known to influence metabolic function [6], this pathway could be important in this regard. Notably,
the reciprocal pathway is stronger for POMC/kisspeptin than for
NPY/kisspeptin [9] and in light of evidence that melanocortins
stimulate the reproductive axis [7], this could form part of a network that allows stimulatory effects via more than one neuronal
system, acting in concert.
5. Gonadotropin inhibitory hormone (GnIH)
GnIH was identified as an hypothalamic factor that inhibits the
HPG axis in the quail [131] and a large body of work has established this is as a bone fide regulatory peptide in avian species
[128]. Original work by Hinuma et al. [60] identified the GnIH gene
in mammals at the same time, but invoked a role in the control of
prolactin secretion. The presence of orthologues of GnIH in the
brains of various species as now been reported [32,111]. These
have been named RF-amide related peptides (RFRP), being members of the RF-amide family, but there seems no good reason
why the original nomenclature (GnIH) should not extend to all
Please cite this article in press as: I.J. Clarke, Control of GnRH secretion: One step back, Front. Neuroendocrinol. (2011), doi:10.1016/j.yfrne.2011.01.001
I.J. Clarke / Frontiers in Neuroendocrinology xxx (2011) xxx–xxx
species [32,111]. The GnIH gene encodes 3 peptides in birds [130]
and two peptides in mammals [77]. The issue of multiple forms of
nomenclature are clarified by Tsutsui et al. [130] and I have
adopted the same. Thus, in birds, the gene encodes GnIH, GnIHRP1 and GnIH-RP2, whereas the gene in mammals encodes GnIH1 (RFRP-1) and GnIH-3 (RFRP-3) [130].
Early work with a polyclonal antibody against avian GnIH [131],
identified immunoreactive cells in the diencephalon, pons and medulla of the mouse brain [134]. Within the hypothalamus, GnIHexpressing cells are concentrated in the dorsomedial hypothalamic
nucleus, with some also seen in the posterior hypothalamus between the ventromedial nucleus and the dorsomedial hypothalamic nucleus. In the rat brain, cells were visualized in the
dorsomedial nucleus and in regions surrounding the ventromedial
nucleus and in the tuberomammillary nucleus [67]. With a different antiserum against the rat GnIH precursor peptide immunoreactive cells were seen to be confined to the dorsomedial nucleus of
the rat brain [101]. Thus, it is important to consider these immunohistochemical findings against the possible variation in specificity
of the antibodies used and this is discussed in a recent review [32].
GnIH immunoreactive cells have also been localized to the
dorsomedial nucleus of the hypothalamus in hamsters, mice and
rats using an antibody against white crowned sparrow GnIH [78]
and this distribution was also observed with in situ hybridization
[78]. More recent in situ hybridization analysis reveals GnIH mRNA
expressing cells in the dorsomedial nucleus and dorsomedial parts
of the ventromedial nucleus, with cells extending rostral to the
anterior hypothalamus and the ventral perifornical area of the rat
brain [80]. In the sheep brain, in situ hybridization identified
GnIH-expressing cells in the ventral region of the paraventricular
nucleus and the dorsomedial nucleus [33,38,114], with a similar
distribution detected using immunohistochemistry, using either
the white crowned sparrow GnIH antiserum [78,114] or an antiserum raised in guinea pigs against human GnIH-3 [98]. The location
of GnIH cells in the dorsomedial nucleus in a range of species may
lend clues regarding the functional significance of the peptide. In
particular, dorsomedial nucleus plays a role in the regulation of energy balance (vide supra). In the male rhesus macaque, GnIH mRNA
and immunoreactive cell bodies are seen in the intermediate periventricular nucleus [133].
GnIH neurons have widespread projections within the hypothalamus, the amygdala, the bed nucleus of the stria terminalis
and the paraventricular nucleus of the thalamus [67]. In the rodent
and primate brain, GnIH terminal beds are also found in the preoptic area, septum and diagonal band of Broca [67,133], where GnRH
cells are located. Between 40% and 80% of GnRH cells show GnIHimmunoreactive varicose fibers in close proximity in the primate,
rat, sheep, hamster and mouse brain [67,78,98,114,133,140] as in
birds [11,135]. This provides a substrate by which GnRH cells
may be regulated either directly or indirectly by GnIH. GnIHimmunoreactive terminals have also been observed in the neurosecretory zone of the median eminence in hamsters, sheep, and primates [33,38,78,133], but similar projections have not been seen in
the rat [67,101]. On this basis, a role for GnIH in the regulation of
the pituitary gonadotrope is proposed for the sheep, as well as the
rat [88] with functional data supporting this (vide infra).
The GnIH receptor (GnIH-R) was originally identified by ligand
activation of an orphan G-protein coupled receptor as OT7T022
[60]. It is and is expressed at a high level in the hypothalamus, with
moderate levels of expression in other brain tissues, the eye and
the testis. The receptor is one of two previously named neuropeptide FF (NPFF) receptors. NPFF1 is the receptor for GnIH, whereas
NPFF2 is the receptor for NPFF, a RF-amide peptide family initially
proposed to modulate the actions of morphine [84,141]. GnIH-R
was also identified by Dockray [41] as GPR147 (named RFR-2).
GnIH-R has now been identified in range of species including the
5
rat [15], human [15] and sheep [38]. In the sheep brain, it is expressed in the suprachiasmatic, supraoptic nucleus and periventricular nuclei as well as the pars tuberalis. GnIH-R is expressed
by GnRH cells in the avian brain [12,132], but this has not yet been
shown in the brain of a mammal. It will also be important to identify other types of cell types that express GnIH-R, such as those regulating appetite (vide infra).
In spite of the earliest indications that GnIH was present in the
brains of mammals and that it negatively regulates reproductive
function [60], recognition that it is a significant regulatory peptide
in mammals has been unforthcoming until recently. The recent
description of the presence of GnIH orthologues and GnIH-R in
the brains of a range of mammalian species and the projections
of GnIH neurons to relevant neuroendocrine cells strongly suggest
a role in the regulation of reproduction and food intake. Functional
data now substantiate its significance.
5.1. GnIH input to GnRH cells and putative regulation of GnRH
secretion
Varicose fibers immunoreactive for GnIH are seen in close apposition to GnRH cells in the sheep [114] and the non-human primate
[121]. With this anatomical framework, functional evidence of direct action is offered by the demonstration that GnIH-3 administered by intracerebroventricular injection reduced plasma LH
secretion in ovariectomized (OVX) hamsters [78] and gonad-intact
rats [66,67]. Others, however, showed that icv administration of
GnIH-3 was not effective in reducing plasma LH levels in OVX,
estrogen treated rats [3] and OVX rats [88]. ICV administration of
GnIH an antisense oligonucleotide increased plasma LH levels to
pre-pubertal rats [66], but this did not cause advancement of puberty. Any regulation of GnRH cells by GnIH may be direct, predicated on the neuronal input to GnRH cells, but it could also be
indirect. In support of the latter, GnIH was shown to reduce neuronal activation in the anteroventral periventricular (AVPV) region as
well as in GnRH neurons (based on Fos labeling) with a surgeinduction protocol in rats [3]. In this study, however, the LH surge
was not significantly reduced in magnitude. These functional data
are consistent with observe projections of GnIH cells to GnRH cells
[98], as is other evidence of function, demonstrated by inhibition of
the firing rate of GnRH neurons in brain slices from male and female mice [43,140]. Whereas 43% of GnRH cells showed reduced
firing with GnIH treatment, 9% showed an increased firing rate
[43]. Further studies, including localization and quantification of
GnIH-R will elucidate the full significance of the peptide in the control of reproduction.
5.2. GnIH action on the pituitary gonadotropes
Intravenously (iv) administered GnIH-3 had no effect on basal
LH secretion in OVX rats and only minimal (albeit statistically significant) effects on GnRH-stimulated secretion [101]; was interpreted to mean that GnIH has no major effect on gonadotropes.
Others [88] showed a reduction in plasma LH levels in OVX rats
2 h after iv administration, with lack of effect of icv administration.
In OVX ewes, systemically administered GnIH-3 consistently reduces pulsatile LH secretion [33], without any effect on the plasma
levels of other pituitary hormones, such as growth hormone or
prolactin; similar results have also been obtained in the bovine
[68].
The dose-dependent reduction in GnRH-stimulated LH secretion that is seen in cultures of rat, sheep and bovine pituitary cells,
supports the notion of a direct effect of GnIH on gonadotropes
[33,68,88], although some contrary data have also been reported
in studies of effects on rat pituitary cells in vitro [3]. Such dissimilar
results may be due to variable culture conditions or may relate to
Please cite this article in press as: I.J. Clarke, Control of GnRH secretion: One step back, Front. Neuroendocrinol. (2011), doi:10.1016/j.yfrne.2011.01.001
6
I.J. Clarke / Frontiers in Neuroendocrinology xxx (2011) xxx–xxx
possible species differences in peripheral GnIH activity. Other lines
of evidence also suggest direct pituitary action of GnIH, in sheep, at
least. Firstly, GnIH-3 eliminates the GnRH-stimulated mobilization
of intracellular calcium in gonadotropes, which is considered mandatory for gonadotropin release [33]. Second, GnRH-stimulated
upregulation of LHb mRNA levels is also negated by GnIH, which
may be due to reduced phosphorylation of extracellular signalregulated kinase (ERK) [105]. These data indicate a direct action
of GnIH on the pituitary gonadotrope to reduce both synthesis
and secretion of LH. In vitro treatment of ovine pituitary cell
cultures also show an effect of GnIH-3 to reduce FSH secretion in
response to GnRH [33] as well as reducing FSHb mRNA levels
[105]. Thus, GnIH may inhibit the production/secretion of both
gonadotropins.
5.3. Effect of GnIH on food intake
GnIH cells project to appetite regulating cells within the lateral
hypothalamic area, ventromedial nucleus and arcuate nucleus in
the ovine brain [98], with similar projections also seen in the primate [133]. This suggests a functional role for GnIH in the regulation of food intake [67,88,123].
GnIH was originally shown to stimulate food intake in birds
[123] and similar data have now been obtained in rats
[66,67,88]. Thus ICV injections of GnIH increased food intake in
rats [66,67,88]. This is consistent with the role of the dorsomedial
nucleus in the regulation of appetite and energy balance [104], but
little was known of the cell types involved in energy balance within this nucleus. In sheep projections of GnIH cells to cells that produce neuropeptide Y or pro-opiomelanocortin in the arcuate
nucleus and those that produce orexin or melanin concentrating
hormone in the lateral hypothalamus [98] suggests a role in the
control of energy balance, but functional studies are required.
The dual function of GnIH in relation to reproduction and appetite
is similar to that of other peptides such as neuropeptide Y (which
stimulates food intake and negatively regulates reproduction in the
sheep [10,27]) and melanocortins (which reduce food intake and
stimulate reproduction [7,8,45,137]).
5.4. Kisspeptin and GnIH as key regulators in seasonal breeding
Sheep are seasonal breeders, being sexually active in response
to short day photoperiod [70,85]. Whereas it has been known for
some years that seasonality in sheep is due to alterations in the frequency of generation of GnRH/LH pulses [102], as well as an alteration in the negative feedback effect of ovarian steroids [81], there
was no identification of a neural substrate that changes with season and controls GnRH secretion accordingly. The A15 dopaminergic nucleus was identified as a key center in the control of
seasonality [125] but as to how this is connected to GnRH secretion
is not yet clear. With the revelation of key regulatory function of
kisspeptin and GnIH, it is hardly surprising that this has been
investigated in relation to seasonal breeding. In the ewe, kisspeptin
production (ARC) and input to GnRH cells is reduced in seasonal
anestrus and increases at onset of the breeding season [114]. Also
in the ewe, GnIH protein expression is higher during the nonbreeding season than in the breeding season [114]. Terminal projections from GnIH cells to GnRH neurons are increased during
the non-breeding season [114]. Thus, it appears that the activity
of GnIH may be a contributing factor to the inhibition of the reproductive system during the non-breeding season. Similarly, GnIH
gene expression in Soay ewes on long day photoperiod was higher
than in ewes on a short day protocol [38]. Nevertheless, when
these ewes were held on extreme long day photoperiods (20 h or
22 h light), the effect on GnIH gene expression was lost. It was concluded that GnIH may not play a major role in seasonality [38], but
the inhibitory effect may be amplified by an increase in input to
GnRH cells during the non-breeding season [114]. Further work,
including measurement of GnIHR expression in different seasons
may be informative. Reciprocal changes in kisspeptin activity indicate that both RF-amide peptides play a role in seasonal changes in
reproductive activity. Intervention studies such as reducing GnIH
function in the non-breeding season would be instructive.
6. Conclusions
In the last decade, the emergence of kisspeptin and GnIH as major neuroendocrine regulators of reproduction, the latter having
gained acceptance only in the last few years. This has led to a significant revision of our understanding as to how reproduction is
controlled by the brain, especially through the feedback effects of
gonadal steroids. The accumulated data on the role of kisspeptin
is far more extensive than that for GnIH and further work is required to understand the degree to which GnIH functions in normal physiology. There is a need to develop a reliable assay for
GnIH and to ascertain whether the peptide is secreted into hypophysial portal blood; this would substantiate the notion that GnIH
acts on the pituitary gonadotropes. A more detailed understanding
of the regulation of the receptors for these two peptides would be
informative.
As for the growth hormone axis, that is controlled by the opposing actions of somatostatin and growth hormone releasing hormone, it now appears that the reproductive system is also under
control of two peptides with opposing action. GnIH or relevant
analogs could potentially be developed for the treatment of diseases such as endometriosis, prostate cancer and precocious puberty; all conditions where reproductive function needs to be
down-regulated. Such agents could offer realistic alternatives to
the use of superactive GnRH agonists or antagonists to suppress
gonadal steroid levels. Kisspeptin may have some utility for the
induction of ovulation [19].
Whereas our knowledge of the neuroendocrine control of reproduction has been expanded by the recognition of the respective
roles of kisspeptin and GnIH, we should not lose sight of the fact
that many neuronal systems act to control GnRH secretion. The
output of GnRH neurons, as measured in the hypophysial portal
blood, is the sum of multiple inputs to the GnRH cells, being the
integration of neuronal systems transducing sex steroid feedback,
season, stress, immune status, nutritional status and mood. Nevertheless, the kisspeptin and GnIH systems appear to be only ‘one
step back’ from the GnRH neurons, providing important modulatory function.
References
[1] S. Adachi, S. Yamada, Y. Takatsu, H. Matsui, M. Kinoshita, K. Takase, H. Sugiura,
T. Ohtaki, H. Matsumoto, Y. Uenoyama, H. Tsukamura, K. Inoue, K. Maeda,
Involvement of anteroventral periventricular metastin/kisspeptin neurons in
estrogen positive feedback action on luteinizing hormone release in female
rats, J. Reprod. Dev. 53 (2007) 367–378.
[2] M. Amoss, R. Burgus, R. Blackwell, W. Vale, R. Fellows, R. Guillemin,
Purification, amino acid composition and N-terminus of the hypothalamic
luteinizing hormone releasing factor (LRF) of ovine origin, Biochem. Biophys.
Res. Commun. 44 (1971) 205–210.
[3] G.M. Anderson, H.L. Relf, M.Z. Rizwan, J.J. Evans, Central and peripheral effects
of RFamide-related peptide-3 on luteinizing hormone and prolactin secretion
in rats, Endocrinology 150 (2009) 1834–1840.
[4] R.D. Andrew, F.E. Dudek, Burst discharge in mammalian neuroendocrine cells
involves an intrinsic regenerative mechanism, Science 221 (1983) 1050–1052.
[5] R.D. Andrew, F.E. Dudek, Analysis of intracellularly recorded phasic bursting
by mammalian neuroendocrine cells, J. Neurophysiol. 51 (1984) 552–566.
[6] L. Asarian, N. Geary, Cyclic estradiol treatment normalizes body weight and
restores physiological patterns of spontaneous feeding and sexual receptivity
in ovariectomized rats, Horm. Behav. 42 (2002) 461–471.
[7] K. Backholer, M. Bowden, K. Gamber, C. Bjorbaek, J. Iqbal, I.J. Clarke,
Melanocortins mimic the effects of leptin to restore reproductive function
in lean hypogonadotropic ewes, Neuroendocrinology 91 (2010) 27–40.
Please cite this article in press as: I.J. Clarke, Control of GnRH secretion: One step back, Front. Neuroendocrinol. (2011), doi:10.1016/j.yfrne.2011.01.001
I.J. Clarke / Frontiers in Neuroendocrinology xxx (2011) xxx–xxx
[8] K. Backholer, J. Smith, I.J. Clarke, Melanocortins may stimulate reproduction
by activating orexin neurons in the dorsomedial hypothalamus and
kisspeptin neurons in the preoptic area of the ewe, Endocrinology 150
(2009) 5488–5497.
[9] K. Backholer, J.T. Smith, A. Rao, A. Pereira, J. Iqbal, S. Ogawa, Q. Li, I.J. Clarke,
Kisspeptin cells in the ewe brain respond to leptin and communicate with
neuropeptide y and proopiomelanocortin cells, Endocrinology 151 (2010)
2233–2243.
[10] M.L. Barker-Gibb, C.J. Scott, J.H. Boublik, I.J. Clarke, The role of neuropeptide Y
(NPY) in the control of LH secretion in the ewe with respect to season, NPY
receptor subtype and the site of action in the hypothalamus, J. Endocrinol.
147 (1995) 565–579.
[11] G.E. Bentley, N. Perfito, K. Ukena, K. Tsutsui, J.C. Wingfield, Gonadotropininhibitory peptide in song sparrows (Melospiza melodia) in different
reproductive conditions, and in house sparrows (Passer domesticus) relative
to chicken-gonadotropin-releasing ho, J. Neuroendocrinol. 15 (2003) 794–
802.
[12] G.E. Bentley, T. Ubuka, N.L. McGuire, V.S. Chowdhury, Y. Morita, T. Yano, I.
Hasunuma, M. Binns, J.C. Wingfield, K. Tsutsui, Gonadotropin-inhibitory
hormone and its receptor in the avian reproductive system, Gen. Comp.
Endocrinol. 156 (2008) 34–43.
[13] D. Blache, C.J. Fabre-Nys, G. Venier, Ventromedial hypothalamus as a target
for oestradiol action on proceptivity, receptivity and luteinizing hormone
surge of the ewe, Brain Res. 546 (1991) 241–249.
[14] J. Boler, F. Enzmann, K. Folkers, C.Y. Bowers, A.V. Schally, The identity of
chemical and hormonal properties of the thyrotropin releasing hormone and
pyroglutamyl-histidyl-proline amide, Biochem. Biophys. Res. Commun. 37
(1969) 705–710.
[15] J.A. Bonini, K.A. Jones, N. Adham, C. Forray, R. Artymyshyn, M.M. Durkin, K.E.
Smith, J.A. Tamm, L.W. Boteju, P.P. Lakhlani, R. Raddatz, W.J. Yao, K.L.
Ogozalek, N. Boyle, E.V. Kouranova, Y. Quan, P.J. Vaysse, J.M. Wetzel, T.A.
Branchek, C. Gerald, B. Borowsky, Identification and characterization of two G
protein-coupled receptors for neuropeptide FF, J. Biol. Chem. 275 (2000)
39324–39331.
[16] R. Burgus, T.F. Dunn, D. Desiderio, D.N. Ward, W. Vale, R. Guillemin,
Characterization of ovine hypothalamic hypophysiotropic TSH-releasing
factor, Nature 226 (1970) 321–325.
[17] R.E. Campbell, G. Gaidamaka, S.K. Han, A.E. Herbison, Dendro-dendritic
bundling and shared synapses between gonadotropin-releasing hormone
neurons, Proc. Natl. Acad. Sci. USA 106 (2009) 10835–10840.
[18] A. Caraty, C. Fabre-Nys, B. Delaleu, A. Locatelli, G. Bruneau, F.J. Karsch, A.
Herbison, Evidence that the mediobasal hypothalamus is the primary site of
action of estradiol in inducing the preovulatory gonadotropin releasing
hormone surge in the ewe, Endocrinology 139 (1998) 1752–1760.
[19] A. Caraty, I. Franceschini, G.E. Hoffman, Kisspeptin and the preovulatory
gonadotrophin-releasing hormone/luteinising hormone surge in the ewe:
basic aspects and potential applications in the control of ovulation, J.
Neuroendocrinol. 22 (2010) 710–715.
[20] A. Caraty, A. Locatelli, Effect of time after castration on secretion of LHRH and
LH in the ram, J. Reprod. Fertil. 82 (1988) 263–269.
[21] A. Caraty, J.T. Smith, D. Lomet, S. Ben Said, A. Morrissey, J. Cognie, B.
Doughton, G. Baril, C. Briant, I.J. Clarke, Kisspeptin synchronizes preovulatory
surges in cyclical ewes and causes ovulation in seasonally acyclic ewes,
Endocrinology 148 (2007) 5258–5267.
[22] G. Cheng, L.M. Coolen, V. Padmanabhan, R.L. Goodman, M.N. Lehman, The
kisspeptin/neurokinin B/dynorphin (KNDy) cell population of the arcuate
nucleus: sex differences and effects of prenatal testosterone in sheep,
Endocrinology 151 (2010) 301–311.
[23] I. Clarke, The hypothalamo-pituitary axis, in: S.G. Hillier, J.P. Neilson, (Eds.),
Scientific Essentials of Reproductive Medicine, WB Saunders, London, 1996,
pp. 120–133.
[24] I. Clarke, L. Moore, J. Veldhuis, Intensive direct cavernous sinus sampling
identifies high-frequency, nearly random patterns of FSH secretion in
ovariectomized ewes: combined appraisal by RIA and bioassay,
Endocrinology 143 (2002) 117–129.
[25] I.J. Clarke, Variable patterns of gonadotropin-releasing hormone secretion
during the estrogen-induced luteinizing hormone surge in ovariectomized
ewes, Endocrinology 133 (1993) 1624–1632.
[26] I.J. Clarke, The preovulatory LH surge: a case of a neuroendocrine switch.,
Trends Endocrinol. Metab. 7 (1995) 637–643.
[27] I.J. Clarke, K. Backholer, A.J. Tilbrook, Y2 receptor-selective agonist delays the
estrogen-induced luteinizing hormone surge in ovariectomized ewes, but y1receptor-selective agonist stimulates voluntary food intake, Endocrinology
146 (2005) 769–775.
[28] I.J. Clarke, K.J. Burman, B.W. Doughton, J.T. Cummins, Effects of constant
infusion of gonadotrophin-releasing hormone in ovariectomized ewes with
hypothalamo-pituitary disconnection: further evidence for differential
control of LH and FSH secretion and the lack of a priming effect, J.
Endocrinol. 111 (1986) 43–49.
[29] I.J. Clarke, J.T. Cummins, The temporal relationship between gonadotropin
releasing hormone (GnRH) and luteinizing hormone (LH) secretion in
ovariectomized ewes, Endocrinology 111 (1982) 1737–1739.
[30] I.J. Clarke, J.K. Findlay, J.T. Cummins, W.J. Ewens, Effects of ovine follicular
fluid on plasma LH and FSH secretion in ovariectomized ewes to indicate the
site of action of inhibin, J. Reprod. Fertil. 77 (1986) 575–585.
7
[31] I.J. Clarke, S. Pompolo, C.J. Scott, J.A. Rawson, D. Caddy, A.E. Jakubowska, A.M.
Pereira, Cells of the arcuate nucleus and ventromedial nucleus of the
ovariectomized ewe that respond to oestrogen: a study using Fos
immunohistochemistry, J. Neuroendocrinol. 13 (2001) 934–941.
[32] I.J. Clarke, Y. Qi, I. Puspita Sari, J.T. Smith, Evidence that RF-amide related
peptides are inhibitors of reproduction in mammals, Front. Neuroendocrinol.
30 (2009) 371–378.
[33] I.J. Clarke, I.P. Sari, Y. Qi, J.T. Smith, H.C. Parkington, T. Ubuka, J. Iqbal, Q. Li, A.
Tilbrook, K. Morgan, A.J. Pawson, K. Tsutsui, R.P. Millar, G.E. Bentley, Potent
action of RFamide-related peptide-3 on pituitary gonadotropes indicative of a
hypophysiotropic role in the negative regulation of gonadotropin secretion,
Endocrinology 149 (2008) 5811–5821.
[34] J. Clarkson, X. d’Anglemont de Tassigny, A.S. Moreno, W.H. Colledge, A.E.
Herbison, Kisspeptin-GPR54 signaling is essential for preovulatory
gonadotropin-releasing hormone neuron activation and the luteinizing
hormone surge, J. Neurosci. 28 (2008) 8691–8697.
[35] S. Constantin, C.L. Jasoni, B. Wadas, A.E. Herbison, Gamma-aminobutyric acid
and glutamate differentially regulate intracellular calcium concentrations in
mouse gonadotropin-releasing hormone neurons, Endocrinology 151 (2010)
262–270.
[36] X. d’Anglemont de Tassigny, L.A. Fagg, M.B. Carlton, W.H. Colledge, Kisspeptin
can stimulate gonadotropin-releasing hormone (GnRH) release by a direct
action at GnRH nerve terminals, Endocrinology 149 (2008) 3926–3932.
[37] D.R. Danforth, C.Y. Cheng, The identification of gonadotrophin surge
inhibiting factor and its role in the regulation of pituitary gonadotrophin
secretion, Hum. Reprod. 8 (Suppl. 2) (1993) 117–122.
[38] H. Dardente, M. Birnie, G.A. Lincoln, D.G. Hazlerigg, RFamide-related peptide
and its cognate receptor in the sheep: cDNA cloning, mRNA distribution in
the hypothalamus and the effect of photoperiod, J. Neuroendocrinol. 20
(2008) 1252–1259.
[39] N. de Roux, E. Genin, J.C. Carel, F. Matsuda, J.L. Chaussain, E. Milgrom,
Hypogonadotropic hypogonadism due to loss of function of the KiSS1-derived
peptide receptor GPR54, Proc. Natl. Acad. Sci. USA 100 (2003) 10972–10976.
[40] D.J. Dierschke, A.N. Bhattacharya, L.E. Atkinson, E. Knobil, Circhoral
oscillations of plasma LH levels in the ovariectomized rhesus monkey,
Endocrinology 87 (1970) 850–853.
[41] G.J. Dockray, The expanding family of-RFamide peptides and their effects on
feeding behaviour, Exp. Physiol. 89 (2004) 229–235.
[42] B.T. Donovan, Third Geoffrey Harris Memorial Lecture. The portal vessels, the
hypothalamus and the control of reproductive function, Neuroendocrinology
25 (1978) 1–21.
[43] E. Ducret, G.M. Anderson, A.E. Herbison, RFamide-related peptide-3, a
mammalian
gonadotropin-inhibitory
hormone
ortholog,
regulates
gonadotropin-releasing hormone neuron firing in the mouse, Endocrinology
150 (2009) 2799–2804.
[44] K.M. Estrada, C.M. Clay, S. Pompolo, J.T. Smith, I.J. Clarke, Elevated KiSS-1
expression in the arcuate nucleus prior to the cyclic preovulatory
gonadotrophin-releasing hormone/luteinising hormone surge in the ewe
suggests a stimulatory role for kisspeptin in oestrogen-positive feedback, J.
Neuroendocrinol. 18 (2006) 806–809.
[45] W. Fan, B.A. Boston, R.A. Kesterson, V.J. Hruby, R.D. Cone, Role of
melanocortinergic neurons in feeding and the agouti obesity syndrome,
Nature 385 (1997) 165–168.
[46] C.D. Foradori, L.M. Coolen, M.E. Fitzgerald, D.C. Skinner, R.L. Goodman, M.N.
Lehman, Colocalization of progesterone receptors in parvicellular dynorphin
neurons of the ovine preoptic area and hypothalamus, Endocrinology 143
(2002) 4366–4374.
[47] C.D. Foradori, R.L. Goodman, V.L. Adams, M. Valent, M.N. Lehman,
Progesterone increases dynorphin a concentrations in cerebrospinal fluid
and preprodynorphin messenger ribonucleic acid levels in a subset of
dynorphin neurons in the sheep, Endocrinology 146 (2005) 1835–1842.
[48] I. Franceschini, D. Lomet, M. Cateau, G. Delsol, Y. Tillet, A. Caraty, Kisspeptin
immunoreactive cells of the ovine preoptic area and arcuate nucleus coexpress estrogen receptor alpha, Neurosci. Lett. 401 (2006) 225–230.
[49] R.L. Goodman, L.M. Coolen, G.M. Anderson, S.L. Hardy, M. Valent, J.M.
Connors, M.E. Fitzgerald, M.N. Lehman, Evidence that dynorphin plays a
major role in mediating progesterone negative feedback on gonadotropinreleasing hormone neurons in sheep, Endocrinology 145 (2004) 2959–2967.
[50] R.L. Goodman, M.N. Lehman, J.T. Smith, L.M. Coolen, C.V. de Oliveira, M.R.
Jafarzadehshirazi, A. Pereira, J. Iqbal, A. Caraty, P. Ciofi, I.J. Clarke, Kisspeptin
neurons in the arcuate nucleus of the ewe express both dynorphin A and
neurokinin B, Endocrinology 148 (2007) 5752–5760.
[51] M.L. Gottsch, M.J. Cunningham, J.T. Smith, S.M. Popa, B.V. Acohido, W.F.
Crowley, S. Seminara, D.K. Clifton, R.A. Steiner, A role for kisspeptins in the
regulation of gonadotropin secretion in the mouse, Endocrinology 145 (2004)
4073–4077.
[52] S.K. Han, M.L. Gottsch, K.J. Lee, S.M. Popa, J.T. Smith, S.K. Jakawich, D.K.
Clifton, R.A. Steiner, A.E. Herbison, Activation of gonadotropin-releasing
hormone neurons by kisspeptin as a neuroendocrine switch for the onset of
puberty, J. Neurosci. 25 (2005) 11349–11356.
[53] G.W. Harris, The induction of ovulation in the rabbit, by electrical stimulation
of the hypothalamo-hypophysial mechanism, Proc. Roy. Soc. Ser. B 122
(1937) 374–394.
[54] G.W. Harris, Neural Control of the Pituitary Gland, Edward Arnold Ltd.,
London, 1955.
Please cite this article in press as: I.J. Clarke, Control of GnRH secretion: One step back, Front. Neuroendocrinol. (2011), doi:10.1016/j.yfrne.2011.01.001
8
I.J. Clarke / Frontiers in Neuroendocrinology xxx (2011) xxx–xxx
[55] B.A. Henry, J.W. Goding, A.J. Tilbrook, F.R. Dunshea, I.J. Clarke,
Intracerebroventricular infusion of leptin elevates the secretion of
luteinising hormone without affecting food intake in long-term foodrestricted sheep, but increases growth hormone irrespective of bodyweight,
J. Endocrinol. 168 (2001) 67–77.
[56] A.E. Herbison, Estrogen regulation of GABA transmission in rat preoptic area,
Brain Res. Bull. 44 (1997) 321–326.
[57] A.E. Herbison, Multimodal influence of estrogen upon gonadotropin-releasing
hormone neurons, Endocr. Rev. 19 (1998) 302–330.
[58] A.E. Herbison, Estrogen positive feedback to gonadotropin-releasing hormone
(GnRH) neurons in the rodent: the case for the rostral periventricular area of
the third ventricle (RP3V), Brain Res. Rev. 57 (2008) 277–287.
[59] A.E. Herbison, D.C. Skinner, J.E. Robinson, I.S. King, Androgen receptorimmunoreactive cells in ram hypothalamus: distribution and co-localization
patterns with gonadotropin-releasing hormone, somatostatin and tyrosine
hydroxylase, Neuroendocrinology 63 (1996) 120–131.
[60] S. Hinuma, Y. Shintani, S. Fukusumi, N. Iijima, Y. Matsumoto, M. Hosoya, R.
Fujii, T. Watanabe, K. Kikuchi, Y. Terao, T. Yano, T. Yamamoto, Y. Kawamata, Y.
Habata, M. Asada, C. Kitada, T. Kurokawa, H. Onda, O. Nishimura, M. Tanaka,
Y. Ibata, M. Fujino, New neuropeptides containing carboxy-terminal RFamide
and their receptor in mammals, Nat. Cell Biol. 2 (2000) 703–708.
[61] X. Huang, R.E. Harlan, Absence of androgen receptors in LHRH
immunoreactive neurons, Brain Res. 624 (1993) 309–311.
[62] J.C. Hwan, M.E. Freeman, A physiological role for luteinizing hormone releaseinhibiting factor of hypothalamic origin, Endocrinology 121 (1987) 1099–
1103.
[63] J. Iqbal, S. Pompolo, T. Sakurai, I.J. Clarke, Evidence that orexin-containing
neurones provide direct input to gonadotropin-releasing hormone neurones
in the ovine hypothalamus, J. Neuroendocrinol. 13 (2001) 1033–1041.
[64] M.S. Irwig, G.S. Fraley, J.T. Smith, B.V. Acohido, S.M. Popa, M.J. Cunningham,
M.L. Gottsch, D.K. Clifton, R.A. Steiner, Kisspeptin activation of gonadotropin
releasing hormone neurons and regulation of KiSS-1 mRNA in the male rat,
Neuroendocrinology 80 (2004) 264–272.
[65] C.N. Jayasena, G.M. Nijher, O.B. Chaudhri, K.G. Murphy, A. Ranger, A. Lim, D.
Patel, A. Mehta, C. Todd, R. Ramachandran, V. Salem, G.W. Stamp, M.
Donaldson, M.A. Ghatei, S.R. Bloom, W.S. Dhillo, Subcutaneous injection of
kisspeptin-54 acutely stimulates gonadotropin secretion in women with
hypothalamic amenorrhea, but chronic administration causes tachyphylaxis,
J. Clin. Endocrinol. Metab. 94 (2009) 4315–4323.
[66] M.A. Johnson, G.S. Fraley, Rat RFRP-3 alters hypothalamic GHRH expression
and growth hormone secretion but does not affect KiSS-1 gene expression or
the onset of puberty in male rats, Neuroendocrinology 88 (2008) 305–315.
[67] M.A. Johnson, K. Tsutsui, G.S. Fraley, Rat RFamide-related peptide-3
stimulates GH secretion, inhibits LH secretion, and has variable effects on
sex behavior in the adult male rat, Horm. Behav. 51 (2007) 171–180.
[68] H. Kadokawa, M. Shibata, Y. Tanaka, T. Kojima, K. Matsumoto, K. Oshima, N.
Yamamoto, Bovine C-terminal octapeptide of RFamide-related peptide-3
suppresses luteinizing hormone (LH) secretion from the pituitary as well as
pulsatile LH secretion in bovines, Domest. Anim. Endocrinol. 36 (2009) 219–
224.
[69] F.J. Karsch, D.F. Battaglia, Mechanisms for endotoxin-induced disruption of
ovarian cyclicity: observations in sheep, Reprod. Suppl. 59 (2002) 101–113.
[70] F.J. Karsch, E.L. Bittman, D.L. Foster, R.L. Goodman, S.J. Legan, J.E. Robinson,
Neuroendocrine basis of seasonal reproduction, Recent Prog. Horm. Res. 40
(1984) 185–232.
[71] F.J. Karsch, J.T. Cummins, G.B. Thomas, I.J. Clarke, Steroid feedback inhibition
of pulsatile secretion of gonadotropin-releasing hormone in the ewe, Biol.
Reprod. 36 (1987) 1207–1218.
[72] F.J. Karsch, G.E. Dahl, N.P. Evans, J.M. Manning, K.P. Mayfield, S.M. Moenter,
D.L. Foster, Seasonal changes in gonadotropin-releasing hormone secretion in
the ewe: alteration in response to the negative feedback action of estradiol,
Biol. Reprod. 49 (1993) 1377–1383.
[73] F.J. Karsch, D.L. Foster, E.L. Bittman, R.L. Goodman, A role for estradiol in
enhancing luteinizing hormone pulse frequency during the follicular phase of
the estrous cycle of sheep, Endocrinology 113 (1983) 1333–1339.
[74] M. Kawakami, T. Uemura, R. Hayashi, Electrophysiological correlates of
pulsatile gonadotropin release in rats, Neuroendocrinology 35 (1982) 63–67.
[75] K.L. Keen, F.H. Wegner, S.R. Bloom, M.A. Ghatei, E. Terasawa, An increase in
kisspeptin-54 release occurs with the pubertal increase in luteinizing
hormone-releasing hormone-1 release in the stalk-median eminence of
female rhesus monkeys in vivo, Endocrinology 149 (2008) 4151–4157.
[76] J. Kiss, B. Halasz, Demonstration of serotoninergic axons terminating on
luteinizing hormone-releasing hormone neurons in the preoptic area of the
rat using a combination of immunocytochemistry and high resolution
autoradiography, Neuroscience 14 (1985) 69–78.
[77] L.J. Kriegsfeld, E.M. Gibson, W.P. Williams 3rd, S. Zhao, A.O. Mason, G.E.
Bentley, K. Tsutsui, The roles of RFamide-related peptide-3 in mammalian
reproductive function and behaviour, J. Neuroendocrinol. 22 (2010) 692–700.
[78] L.J. Kriegsfeld, D.F. Mei, G.E. Bentley, T. Ubuka, A.O. Mason, K. Inoue, K. Ukena,
K. Tsutsui, R. Silver, Identification and characterization of a gonadotropininhibitory system in the brains of mammals, Proc. Natl. Acad. Sci. USA 103
(2006) 2410–2415.
[79] M.C. Kuehl-Kovarik, W.A. Pouliot, G.L. Halterman, R.J. Handa, F.E. Dudek, K.M.
Partin, Episodic bursting activity and response to excitatory amino acids in
acutely dissociated gonadotropin-releasing hormone neurons genetically
targeted with green fluorescent protein, J. Neurosci. 22 (2002) 2313–2322.
[80] K. Legagneux, G. Bernard-Franchi, F. Poncet, A. La Roche, C. Colard, D.
Fellmann, F. Pralong, P.Y. Risold, Distribution and genesis of the RFRPproducing neurons in the rat brain: comparison with melanin-concentrating
hormone- and hypocretin-containing neurons, Neuropeptides 43 (2009) 13–
19.
[81] S.J. Legan, F.J. Karsch, D.L. Foster, The endocrine control of seasonal
reproductive function in the ewe: a marked change in response to the
negative feedback action of estradiol on luteinizing hormone secretion,
Endocrinology 101 (1977) 818–824.
[82] M.N. Lehman, F.J. Karsch, Do gonadotropin-releasing hormone, tyrosine
hydroxylase-, and beta-endorphin-immunoreactive neurons contain estrogen
receptors? A double-label immunocytochemical study in the Suffolk ewe,
Endocrinology 133 (1993) 887–895.
[83] B.A. Littman, G.D. Hodgen, Human menopausal gonadotropin stimulation in
monkeys: blockade of the luteinizing hormone surge by a highly transient
ovarian factor, Fertil. Steril. 41 (1984) 440–447.
[84] Q. Liu, X.M. Guan, W.J. Martin, T.P. McDonald, M.K. Clements, Q. Jiang, Z. Zeng,
M. Jacobson, D.L. Williams Jr., H. Yu, D. Bomford, D. Figueroa, J. Mallee, R.
Wang, J. Evans, R. Gould, C.P. Austin, Identification and characterization of
novel mammalian neuropeptide FF-like peptides that attenuate morphineinduced antinociception, J. Biol. Chem. 276 (2001) 36961–36969.
[85] B. Malpaux, A. Daveau, F. Maurice-Mandon, G. Duarte, P. Chemineau,
Evidence that melatonin acts in the premammillary hypothalamic area to
control reproduction in the ewe: presence of binding sites and stimulation of
luteinizing hormone secretion by in situ microimplant delivery,
Endocrinology 139 (1998) 1508–1516.
[86] H. Matsuo, Y. Baba, R.M. Nair, A. Arimura, A.V. Schally, Structure of the
porcine LH- and FSH-releasing hormone. I. The proposed amino acid
sequence, Biochem. Biophys. Res. Commun. 43 (1971) 1334–1339.
[87] S. Messager, E.E. Chatzidaki, D. Ma, A.G. Hendrick, D. Zahn, J. Dixon, R.R.
Thresher, I. Malinge, D. Lomet, M.B. Carlton, W.H. Colledge, A. Caraty, S.A.
Aparicio, Kisspeptin directly stimulates gonadotropin-releasing hormone
release via G protein-coupled receptor 54, Proc. Natl. Acad. Sci. USA 102
(2005) 1761–1766.
[88] M. Murakami, T. Matsuzaki, T. Iwasa, T. Yasui, M. Irahara, T. Osugi, K. Tsutsui,
Hypophysiotropic role of RFamide-related peptide-3 in the inhibition of LH
secretion in female rats, J. Endocrinol. 199 (2008) 105–112.
[89] A.E. Oakley, K.M. Breen, I.J. Clarke, F.J. Karsch, E.R. Wagenmaker, A.J. Tilbrook,
Cortisol reduces gonadotropin-releasing hormone pulse frequency in
follicular phase ewes: influence of ovarian steroids, Endocrinology 150
(2009) 341–349.
[90] A.E. Oakley, D.K. Clifton, R.A. Steiner, Kisspeptin signaling in the brain, Endocr.
Rev. 30 (2009) 713–743.
[91] A. Pereira, J. Rawson, A. Jakubowska, I.J. Clarke, Estradiol-17beta-responsive
A1 and A2 noradrenergic cells of the brain stem project to the bed nucleus of
the stria terminalis in the ewe brain: a possible route for regulation of
gonadotropin releasing hormone cells, Neuroscience 165 (2010) 758–
773.
[92] B.N. Pierce, P.H. Hemsworth, E.T. Rivalland, E.R. Wagenmaker, A.D. Morrissey,
M.M. Papargiris, I.J. Clarke, F.J. Karsch, A.I. Turner, A.J. Tilbrook, Psychosocial
stress suppresses attractivity, proceptivity and pulsatile LH secretion in the
ewe, Horm. Behav. 54 (2008) 424–434.
[93] S. Pompolo, O. Ischenko, A. Pereira, J. Iqbal, I.J. Clarke, Evidence that
projections from the bed nucleus of the stria terminalis and from the
lateral and medial regions of the preoptic area provide input to gonadotropin
releasing hormone (GNRH) neurons in the female sheep brain, Neuroscience
132 (2005) 421–436.
[94] S. Pompolo, A. Pereira, K.M. Estrada, I.J. Clarke, Colocalization of kisspeptin
and gonadotropin-releasing hormone in the ovine brain, Endocrinology 147
(2006) 804–810.
[95] S. Pompolo, A. Pereira, T. Kaneko, I.J. Clarke, Seasonal changes in the inputs to
gonadotropin-releasing hormone neurones in the ewe brain: an assessment
by conventional fluorescence and confocal microscopy, J. Neuroendocrinol.
15 (2003) 538–545.
[96] S. Pompolo, A. Pereira, C.J. Scott, F. Fujiyma, I.J. Clarke, Evidence for estrogenic
regulation of gonadotropin-releasing hormone neurons by glutamatergic
neurons in the ewe brain: an immunohistochemical study using an antibody
against vesicular glutamate transporter-2, J. Comp. Neurol. 465 (2003) 136–
144.
[97] S. Pompolo, J.A. Rawson, I.J. Clarke, Projections from the arcuate/ventromedial
region of the hypothalamus to the preoptic area and bed nucleus of stria
terminalis in the brain of the ewe; lack of direct input to gonadotropinreleasing hormone neurons, Brain Res. 904 (2001) 1–12.
[98] Y. Qi, B.J. Oldfield, I.J. Clarke, Projections of RFamide-related peptide-3
neurones in the ovine hypothalamus, with special reference to regions
regulating energy balance and reproduction, J. Neuroendocrinol. 21 (2009)
690–697.
[99] S. Ramaswamy, K.A. Guerriero, R.B. Gibbs, T.M. Plant, Structural interactions
between kisspeptin and GnRH neurons in the mediobasal hypothalamus of
the male rhesus monkey (Macaca mulatta) as revealed by double
immunofluorescence and confocal microscopy, Endocrinology 149 (2008)
4387–4395.
[100] J.A. Rawson, C.J. Scott, A. Pereira, A. Jakubowska, I.J. Clarke, Noradrenergic
projections from the A1 field to the preoptic area in the brain of the ewe and
Fos responses to oestrogen in the A1 cells, J. Neuroendocrinol. 13 (2001) 129–
138.
Please cite this article in press as: I.J. Clarke, Control of GnRH secretion: One step back, Front. Neuroendocrinol. (2011), doi:10.1016/j.yfrne.2011.01.001
I.J. Clarke / Frontiers in Neuroendocrinology xxx (2011) xxx–xxx
[101] M.Z. Rizwan, R. Porteous, A.E. Herbison, G.M. Anderson, Cells expressing
RFamide-related peptide-1/3, the mammalian gonadotropin-inhibitory
hormone orthologs, are not hypophysiotropic neuroendocrine neurons in
the rat, Endocrinology 150 (2009) 1413–1420.
[102] J.E. Robinson, H.M. Radford, F.J. Karsch, Seasonal changes in pulsatile
luteinizing hormone (LH) secretion in the ewe: relationship of frequency of
LH pulses to day length and response to estradiol negative feedback, Biol.
Reprod. 33 (1985) 324–334.
[103] A.K. Roseweir, A.S. Kauffman, J.T. Smith, K.A. Guerriero, K. Morgan, J. PieleckaFortuna, R. Pineda, M.L. Gottsch, M. Tena-Sempere, S.M. Moenter, E.
Terasawa, I.J. Clarke, R.A. Steiner, R.P. Millar, Discovery of potent kisspeptin
antagonists delineate physiological mechanisms of gonadotropin regulation,
J. Neurosci. 29 (2009) 3920–3929.
[104] A. Sahu, Minireview: a hypothalamic role in energy balance with special
emphasis on leptin, Endocrinology 145 (2004) 2613–2620.
[105] I.P. Sari, A. Rao, J.T. Smith, A.J. Tilbrook, I.J. Clarke, Effect of RF-amide related
peptide-3 on LH and FSH synthesis and secretion in ovine pituitary
gonadotropes, Endocrinology 150 (2009) 5549–5556.
[106] D.K. Sarkar, S.A. Chiappa, G. Fink, N.M. Sherwood, Gonadotropin-releasing
hormone surge in pro-oestrous rats, Nature 264 (1976) 461–463.
[107] A.V. Schally, A. Arimura, Y. Baba, R.M. Nair, H. Matsuo, T.W. Redding, L.
Debeljuk, Isolation and properties of the FSH and LH-releasing hormone,
Biochem. Biophys. Res. Commun. 43 (1971) 393–399.
[108] S.B. Seminara, S. Messager, E.E. Chatzidaki, R.R. Thresher, J.S. Acierno Jr., J.K.
Shagoury, Y. Bo-Abbas, W. Kuohung, K.M. Schwinof, A.G. Hendrick, D. Zahn, J.
Dixon, U.B. Kaiser, S.A. Slaugenhaupt, J.F. Gusella, S. O’Rahilly, M.B. Carlton,
W.F. Crowley Jr., S.A. Aparicio, W.H. Colledge, The GPR54 gene as a regulator
of puberty, New. Engl. J. Med. 349 (2003) 1614–1627.
[109] D.C. Skinner, A.E. Herbison, Effects of photoperiod on estrogen receptor,
tyrosine hydroxylase, neuropeptide Y, and beta-endorphin immunoreactivity
in the ewe hypothalamus, Endocrinology 138 (1997) 2585–2595.
[110] J.T. Smith, Sex steroid control of hypothalamic Kiss1 expression in sheep and
rodents: comparative aspects, Peptides 30 (2009) 94–102.
[111] J.T. Smith, I.J. Clarke, Gonadotropin inhibitory hormone function in mammals,
Trends Endocrinol. Metab. 21 (2010) 255–260.
[112] J.T. Smith, I.J. Clarke, Seasonal breeding as a neuroendocrine model for
puberty in sheep, Mol. Cell. Endocrinol. 324 (2010) 102–109.
[113] J.T. Smith, D.K. Clifton, R.A. Steiner, Regulation of the neuroendocrine
reproductive axis by kisspeptin-GPR54 signaling, Reproduction 131 (2006)
623–630.
[114] J.T. Smith, L.M. Coolen, L.J. Kriegsfeld, I.P. Sari, M.R. Jaafarzadehshirazi, M.
Maltby, K. Bateman, R.L. Goodman, A.J. Tilbrook, T. Ubuka, G.E. Bentley, I.J.
Clarke, M.N. Lehman, Variation in kisspeptin and RFamide-related peptide
(RFRP) expression and terminal connections to gonadotropin-releasing
hormone neurons in the brain: a novel medium for seasonal breeding in
the sheep, Endocrinology 149 (2008) 5770–5782.
[115] J.T. Smith, M.J. Cunningham, E.F. Rissman, D.K. Clifton, R.A. Steiner,
Regulation of Kiss1 gene expression in the brain of the female mouse,
Endocrinology 146 (2005) 3686–3692.
[116] J.T. Smith, H.M. Dungan, E.A. Stoll, M.L. Gottsch, R.E. Braun, S.M. Eacker, D.K.
Clifton, R.A. Steiner, Differential regulation of KiSS-1 mRNA expression by sex
steroids in the brain of the male mouse, Endocrinology 146 (2005) 2976–
2984.
[117] J.T. Smith, Q. Li, A. Pereira, I.J. Clarke, Kisspeptin neurons in the ovine arcuate
nucleus and preoptic area are involved in the preovulatory luteinizing
hormone surge, Endocrinology 150 (2009) 5530–5538.
[118] J.T. Smith, S.M. Popa, D.K. Clifton, G.E. Hoffman, R.A. Steiner, Kiss1 neurons in
the forebrain as central processors for generating the preovulatory
luteinizing hormone surge, J. Neurosci. 26 (2006) 6687–6694.
[119] J.T. Smith, A. Rao, A. Pereira, A. Caraty, R.P. Millar, I.J. Clarke, Kisspeptin is
present in ovine hypophysial portal blood but does not increase during the
preovulatory luteinizing hormone surge: evidence that gonadotropes are not
direct targets of kisspeptin in vivo, Endocrinology 149 (2008) 1951–1959.
[120] J.T. Smith, S.N. Saleh, I.J. Clarke, Seasonal and cyclical change in the
luteinizing
hormone
response
to
kisspeptin
in
the
ewe,
Neuroendocrinology 90 (2009) 283–291.
[121] J.T. Smith, M. Shahab, A. Pereira, K.Y. Pau, I.J. Clarke, Hypothalamic expression
of KISS1 and gonadotropin inhibitory hormone genes during the menstrual
cycle of a non-human primate, Biol. Reprod. 83 (2010) 568–577.
9
[122] K.J. Suter, J.P. Wuarin, B.N. Smith, F.E. Dudek, S.M. Moenter, Whole-cell
recordings from preoptic/hypothalamic slices reveal burst firing in
gonadotropin-releasing hormone neurons identified with green fluorescent
protein in transgenic mice, Endocrinology 141 (2000) 3731–3736.
[123] T. Tachibana, M. Sato, H. Takahashi, K. Ukena, K. Tsutsui, M. Furuse,
Gonadotropin-inhibiting hormone stimulates feeding behavior in chicks,
Brain Res. 1050 (2005) 94–100.
[124] E. Terasawa, K.L. Keen, K. Mogi, P. Claude, Pulsatile release of luteinizing
hormone-releasing hormone (LHRH) in cultured LHRH neurons derived from
the embryonic olfactory placode of the rhesus monkey, Endocrinology 140
(1999) 1432–1441.
[125] J.C. Thiery, V. Gayrard, S. Le Corre, C. Viguie, G.B. Martin, P. Chemineau, B.
Malpaux, Dopaminergic control of LH secretion by the A15 nucleus in
anoestrous ewes, J. Reprod. Fertil. Suppl. 49 (1995) 285–296.
[126] J.C. Thiery, J. Pelletier, Multiunit activity in the anterior median eminence and
adjacent areas of the hypothalamus of the ewe in relation to LH secretion,
Neuroendocrinology 32 (1981) 217–224.
[127] A.J. Tilbrook, A.I. Turner, I.J. Clarke, Stress and reproduction: central
mechanisms and sex differences in non-rodent species, Stress 5 (2002) 83–
100.
[128] K. Tsutsui, A new key neurohormone controlling reproduction, gonadotropininhibitory hormone (GnIH): biosynthesis, mode of action and functional
significance, Prog. Neurobiol. 88 (2009) 76–88.
[129] K. Tsutsui, G.E. Bentley, G. Bedecarrats, T. Osugi, T. Ubuka, L.J. Kriegsfeld,
Gonadotropin-inhibitory hormone (GnIH) and its control of central and
peripheral reproductive function, Front. Neuroendocrinol. 31 (2010) 284–
295.
[130] K. Tsutsui, G.E. Bentley, L.J. Kriegsfeld, T. Osugi, J.Y. Seong, H. Vaudry,
Discovery and evolutionary history of gonadotrophin-inhibitory hormone
and kisspeptin: new key neuropeptides controlling reproduction, J.
Neuroendocrinol. 22 (2010) 716–727.
[131] K. Tsutsui, E. Saigoh, K. Ukena, H. Teranishi, Y. Fujisawa, M. Kikuchi, S. Ishii,
P.J. Sharp, A novel avian hypothalamic peptide inhibiting gonadotropin
release, Biochem. Biophys. Res. Commun. 275 (2000) 661–667.
[132] T. Ubuka, S. Kim, Y.C. Huang, J. Reid, J. Jiang, T. Osugi, V.S. Chowdhury, K.
Tsutsui, G.E. Bentley, Gonadotropin-inhibitory hormone neurons interact
directly with gonadotropin-releasing hormone-I and -II neurons in European
starling brain, Endocrinology 149 (2008) 268–278.
[133] T. Ubuka, H. Lai, M. Kitani, A. Suzuuchi, V. Pham, P.A. Cadigan, A. Wang, V.S.
Chowdhury, K. Tsutsui, G.E. Bentley, Gonadotropin-inhibitory hormone
identification, cDNA cloning, and distribution in rhesus macaque brain, J.
Comp. Neurol. 517 (2009) 841–855.
[134] K. Ukena, K. Tsutsui, Distribution of novel RFamide-related peptide-like
immunoreactivity in the mouse central nervous system, Neurosci. Lett. 300
(2001) 153–156.
[135] K. Ukena, T. Ubuka, K. Tsutsui, Distribution of a novel avian gonadotropininhibitory hormone in the quail brain, Cell Tissue Res. 312 (2003) 73–79.
[136] J.P. Walsh, A. Rao, R.C. Thompson, I.J. Clarke, Proenkephalin and opioid mureceptor mRNA expression in ovine hypothalamus across the estrous cycle,
Neuroendocrinology 73 (2001) 26–36.
[137] H. Watanobe, H.B. Schioth, J.E. Wikberg, T. Suda, The melanocortin 4 receptor
mediates leptin stimulation of luteinizing hormone and prolactin surges in
steroid-primed ovariectomized rats, Biochem. Biophys. Res. Commun. 257
(1999) 860–864.
[138] R.C. Wilson, J.S. Kesner, J.M. Kaufman, T. Uemura, T. Akema, E. Knobil, Central
electrophysiologic correlates of pulsatile luteinizing hormone secretion in
the rhesus monkey, Neuroendocrinology 39 (1984) 256–260.
[139] T.M. Wintermantel, R.E. Campbell, R. Porteous, D. Bock, H.J. Grone, M.G.
Todman, K.S. Korach, E. Greiner, C.A. Perez, G. Schutz, A.E. Herbison,
Definition of estrogen receptor pathway critical for estrogen positive
feedback to gonadotropin-releasing hormone neurons and fertility, Neuron
52 (2006) 271–280.
[140] M. Wu, I. Dumalska, E. Morozova, A.N. van den Pol, M. Alreja, Gonadotropin
inhibitory hormone inhibits basal forebrain vGluT2-gonadotropin-releasing
hormone neurons via a direct postsynaptic mechanism, J. Physiol. 587 (2009)
1401–1411.
[141] H. Yoshida, Y. Habata, M. Hosoya, Y. Kawamata, C. Kitada, S. Hinuma,
Molecular properties of endogenous RFamide-related peptide-3 and its
interaction with receptors, Biochim. Biophys. Acta 1593 (2003) 151–157.
Please cite this article in press as: I.J. Clarke, Control of GnRH secretion: One step back, Front. Neuroendocrinol. (2011), doi:10.1016/j.yfrne.2011.01.001