* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download The Preoptic Nucleus in Fishes: A Comparative Discussion of
Transcranial direct-current stimulation wikipedia , lookup
Cognitive neuroscience wikipedia , lookup
Signal transduction wikipedia , lookup
Activity-dependent plasticity wikipedia , lookup
Single-unit recording wikipedia , lookup
Microneurography wikipedia , lookup
Neurolinguistics wikipedia , lookup
Central pattern generator wikipedia , lookup
Neural coding wikipedia , lookup
Causes of transsexuality wikipedia , lookup
Nervous system network models wikipedia , lookup
Neuroplasticity wikipedia , lookup
Electrophysiology wikipedia , lookup
Multielectrode array wikipedia , lookup
Development of the nervous system wikipedia , lookup
Neural oscillation wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Haemodynamic response wikipedia , lookup
Behaviorism wikipedia , lookup
Caridoid escape reaction wikipedia , lookup
Premovement neuronal activity wikipedia , lookup
Psychoneuroimmunology wikipedia , lookup
Neural correlates of consciousness wikipedia , lookup
Pre-Bötzinger complex wikipedia , lookup
Neuroethology wikipedia , lookup
Endocannabinoid system wikipedia , lookup
Neurostimulation wikipedia , lookup
Synaptic gating wikipedia , lookup
Neuroanatomy wikipedia , lookup
Metastability in the brain wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Neuroeconomics wikipedia , lookup
Sexually dimorphic nucleus wikipedia , lookup
Circumventricular organs wikipedia , lookup
Channelrhodopsin wikipedia , lookup
Stimulus (physiology) wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
AMER. ZOOL., 17:775-785 (1977). The Preoptic Nucleus in Fishes: A Comparative Discussion of Function-Activity Relationships R. E. PETER Department of Zoology, University of Alberta, Edmonton, Alberta T6G 2E9, Canada SYNOPSIS. The electrophysiological characteristics and the afferent inputs to the preoptic nucleus (PN) in fishes are reviewed. Information from teleosts indicates that PN neurons can be divided into different classes on the basis of their combined electrophysiological and anatomical charactenstics. Afferent input to the PN of teleosts has been demonstrated for the olfactory, optic, trigeminal, and vagus nerves, and the telencephalon and spinal cord. In teleosts the preoptic region, and the PN within it, are involved in the control of spawning behavior and the act of spawning. The neurohypophysial hormones (NH) may play a role in stimulation of the ovarian and oviduct musculature during spawning. The possible stimuli for NH secretion for osmoregulatory purposes in freshwater bony fishes are decreased plasma osmolality, or decreased concentration of some ion in the plasma, or expansion of either the extracellular or intracellular fluid volume. Decreased blood volume or blood pressure are also possible stimuli. Receptors on the outside of the animal may also play a role. Some results suggest that NH may be secreted during stress and that NH may be involved in stimulation of ACTH secretion in teleosts. In the mammals NH have some actions on the brain. Vasopressin aids retention of conditioned avoidance responses in rats. The various stimuli for secretion of NH in fishes and mammals are compared. than about that of the fishes, the mammalian literature is used as a model for Most of the contributions to this sym- comparison and the basis for speculation posium deal specifically with actions of the with regard to the fishes. neurohypophysial peptides. In this paper I will diverge from this theme somewhat to BONY FISHES discuss the preoptic nucleus-neurohypophysial system of fishes more in terms of its Electrophysiological activity of the preoptic nuneurophysiological activity. The intention cleus of the discussion is not to present neurophysiological information per se, but The classical electrophysiological study to try and relate what is known about the by Kandel (1964) on the preoptic nucleus neurophysiology of the system with the (PN) of goldfish demonstrated that the physiological actions of the hormones behaviour of neurosecretory neurons is produced by the system. This topic leads generally similar to that of other central itself to actions of the hormones on the neurons. Recordings by Kandel were innervous system, making it difficult to sepa- tracellular from the large PN cells belongrate neurophysiology from actions of the ing to the pars magnocellularis. Extension hormones. A great deal of literature is of the axons into the pituitary was available on the neurophysiology of the confirmed in 60% of the cells by antidrommagnocellular neuroendocrine system of ic stimulation by an electrode implanted in mammals and many excellent reviews have the pituitary gland. Such antidromically appeared recently on this topic (see Cross, identified neurons are supposedly endoI974a,b; Cross and Dyball, 1974; Cross et crine in function. The cells were found to al., 1975; Hayward, 1972, 19746). It is not have low rates of spontaneous firing. The my intention to review this literature again presence of inhibitory recurrent collaterals here. However, because there is much was shown by antidromic stimulation. This more known about the mammalian system provides a self-imposed system to decrease INTRODUCTION 775 776 R. E. PETER or damp out activity, and raises the question of neurotransmitter actions by the neurohypophysial peptides. Kandel also found that stimulation of the olfactory tract produced excitatory postsynaptic potentials and spikes in the PN neurons. Membrane hyperpolarization and inhibition of spontaneous firing activity occurred with perfusion of the mouth and gills with sea water diluted 100:1 with tap water. The response in the PN to mouth-gill perfusion with dilute sea water suggests some inhibitory input to the PN from such possible cranial nerves as the vagus, glossopharyngeal, facial or trigeminal. The specific origin of the input was, however, not identified. Hayward (1974a) extended the electrophysiological studies on the PN magnocellular neurons of goldfish to demonstrate the presence of three morphologically and electrophysiologically different cell types. The cells recorded from were antidromically identified and stained by electrophoretic injection of Procion Yellow via the intracellular recording electrode. Each cell type was found to have many fine dendritic branches within the PN itself. One cell was found to have more extensive dendritic branches laterally and to receive olfactory input, and another was found to have a special extension to the ependyma that in some cases actually made contact with the cerebrospinal fluid. Also, Hayward found evidence for invasion of the pituitary by multiple axon branches from some PN neurons. The general excitatory effect of olfactory afferents to the PN has been confirmed in goldfish by Jasinski et al. (1967), and Hayward (1974a), and in the goose fish by Bennetts al. (1968). Bennett and co-workers (1968) also found excitatory input from the trigeminal nerve. Also, after transection of the goose fish brain just posterior to the hypothalamus there was increased electrophysiological activity in the PN, suggesting some tonic inhibitory input from lower brain regions. Electrical stimulation of different regions of the telencephalon and simultaneous extracellular unit recording in the PN pars parvocellularis of the sunfishes Lepomis macrochirus and L. gibossus, demon- strated that PN cells can be activated by wide regions of the telencephalon (Hal\ow\tzet al., 1971). Unfortunately the units recorded were not identified as being en- • docrine neurons by antidromic activation by pituitary stimulation. However, the input from wide regions of the telencephalon does imply that a wide variety of sensory modalities could affect activity of PN neurons. As a somewhat unique means to demonstrate activity of PN neurons it was found by Jasinski et al. (1966, 1967) and confirmed by Peter and Gorbman (1968) that electrical stimulation of the olfactory tracts of goldfish leads to depletion of paraldehyde fuchsin stainable neurosecretion in the cell bodies and axons of the PN. Thus, electrical activity of PN neurons is associated with some change in their special staining characteristics. Similar results have been observed following olfactory tract stimulation of Heteropneustes fossilis (Prasada Rao, 1970) and Clarias batrachus (Prasada Rao and Dabhade, 1973), and after stimulation of the olfactory mucosa of Ophiocephalus punctatus (Chandrasekhar and Chacko, 1970). In addition, Peter and Gorbman (1968) found depletion of stainable neurosecretion in the goldfish PN following electrical stimulation of the retina, tenth cranial nerve, and spinal cord, demonstrating the existence of functional afferents to the PN from these sources as well. Stimulation of the lateral line nerve and the pineal stalk were without effect, however. Bennett et al. (1968) found that spike activity in the pituitary stalk of the goose fish was increased by stimulation of the spinal cord, and the trigeminal, optic, or olfactory nerves. Assuming the activity recorded in the stalk was due to the PNneurohypophysial system, these results support the findings of Peter and Gorbman (1968). In summary, the PN obviously has a wide range of afferents from which it can receive input. A ctivity-function relationships Involvement of neurohypophysial hormones in spawning behavior of the kil- PREOPTIC NUCLEUS ACTIVITY IN FISHES lifish, Fundulus heteroclitus, was proposed by Wilhelmi et al. (1955) when it was discovered that intraperitoneal injection of large doses of neurohypophysial hormone » preparations induced a "spawning reflex response." A full reflex response is described as an S-shaped flexure of the body, simultaneous with quivering of the body and flattening of the anal and dorsal fins to one side, ending with a quick and vigorous flick of the tail that darts the animal forward (Macey et al., 1974). This response can be elicited in killifish of either sex (Wilhelmi et al., 1955), after castration (Pickford, unpublished observations cited by Wilhelmi et al., 1955), or hypophysectomy (Pickford, 1952). A similar spawning reflex response occurs in response to exogenous neurohypophysial hormones in some closely related cyprinodontiform species: Oryzias latipes (Egami, 1959) and Gambusia sp. (Ishii, 1963). However, such a response is not elicited in the less-closely related cypriniforms: Carassius auratus (Pickford, unpublished results cited by Macey et al., 1974), Misgurnus fossilis (Egami and Ishii, 1962), and Heteropneustes fossilis (Sundararaj and Goswami, 1966). The PN has been directly implicated in the spawning reflex response off. heteroclitus by Macey et al. (1974). They found that complete or nearly complete destruction of the PN by electrolytic lesioning abolished or nearly abolished the reflex response to exogenous neurohypophysial hormone preparations, including the native hormone arginine vasotocin (AVT). If the lesions left more than about 6.5% of the PN cells intact, the response occurred at about a similar rate as in the sham control animals. Lesioning of a number of other forebrain regions also had no effect on the response. These results suggest involvement of the PN in spawning behavior of the killifish. As a mechanism to explain the occurrence of the spawning reflex response, Macey et al. (1974) suggested that activation of the PN was by action of the injected hormones on some brain center, perhaps directly on the PN itself. To test the effects of direct brain injection of neurohypophysial hormones on 777 spawning reflex behavior, a technique was developed by Peter and Knight (unpublished results) to chronically implant a cannula in the third ventricle of the brain of the killifish. In unpublished results by Pickford and Knight (personal communication) it was found that brain injection of an estimated dose of 5 mU arginine vasopressin (AVP)/g body weight gave no response in five trials. Injection of a higher dose, estimated at 100 mU/g body weight, gave a positive response in 5 out of 19 trials. Since the dose required to elicit a response by brain injection is similar to that required intraperitoneally, it seems likely that those fish that responded following a brain injection did so as a result of some peripheral action of the hormone. This situation is not likely a problem of specificity of the hormone used because large doses of AVT are also required when injected intraperitoneally. Furthermore, in view of the large doses normally required to elicit a spawning reflex response it seems that activation of a peripheral receptor by neurohypophysial hormones is probably not a part of the normal mechanism for triggering spawning behavior in teleosts. Given the above situation, does the PNneurohypophysial system have any role in spawning behavior in teleosts? Demski and Knigge (1971) observed that electrical stimulation of the preoptic region evoked courtship behavior in the male bluegill sunfish (L. macrochirus). In some cases in which a female was available for the stimulated male, actual spawning took place (Demski, personal communication). Nest building in the bluegill is evoked by stimulation of the dorsal area of the telencephalon (Demski and Knigge, 1971), suggesting that some aspects of the full sphere of reproductive behavior are not centered in the preoptic region. As mentioned previously, destruction of the PN abolishes the spawning reflex response of killifish (Macey et al., 1974). As a further demonstration of the involvement of the preoptic region in spawning, Demski et al. (1975) have shown by electrical stimulation and lesioning experiments on male green sunfish (L. cyanellus) that a pathway to 778 R. E. PETER evoke semen discharge originates in the preoptic region, and traverses lower brain regions into the rostral spinal cord. Unpublished observations by Demski, Bauer and Gerald (cited by Demski et al., 1975) indicate that sperm release in spermiated male goldfish and discharge of ovulated eggs in female goldfish may also be evoked by preoptic stimulation. Together all of these observations implicate the preoptic region in the act of gamete discharge during spawning and in spawning behavior of teleosts, but these results do not imply a role of the neurohypophysial hormones in this system. The possible involvement of the endocrine neurons of the PN would then be by their synaptic interconnections with other neurons rather than by their endocrine function. In spite of the above denials, a possible means for involvement of the neurohypophysial hormones in spawning may be via the abilities of the hormones to stimulate activity of oviduct and ovarian smooth muscles in teleosts (see Heller, 1972; LaPointe, 1977). Thus, the neurohypophysial hormones may serve as a part of the efferent system in spawning to accomplish stimulation of the oviduct and ovarian musculature, and perhaps also the sperm duct musculature, although there is no information available concerning the latter. Stacey and Liley (1974) demonstrated that an intra-ovarian mass of ovulated eggs must normally be present in order for female goldfish to show spawning behavior. On the other hand, spawning behavior can be induced in female goldfish in the absence of ovulated eggs by intraperitoneal injection of a large dose of prostaglandin F ^ (Stacey, 1976). Stacey also found that the spawning behavior usually induced by injection of ovulated eggs into the ovipore could be blocked by intraperitoneal injection of indomethacin, a blocker of prostaglandin synthesis. These results imply an effect of ovulated eggs, perhaps on the ovary or oviduct, to cause prostaglandin release which would in turn somehow initiate afferent stimuli involved in triggering spawning behavior in goldfish. At least a part of this afferent stimulus system involves the pituitary gland. Stacey (1976) found that hypophysectomy abolished the ability of PGF^ to induce spawning behavior in female goldfish, and that the behavior was restored by injection of a purified salmon gonadotropin preparation. This implicates gonadotropin as the particular pituitary factor involved in the afferent stimulus system. However, where and how gonadotropin acts is an open question. Of course stimuli other than those indicated above also impinge on this circuit, including such factors as the presence or absence of a mate and environmental conditions. For example, a pheromone from ovulated eggs and ovarian fluid of ovulated goldfish that attracts and induces spawning behavior in spermiated males has recently been demonstrated (Partridge et al., 1976). For all the various stimuli involved in evoking spawning behavior, the telencephalon may play an integrative role. This would particularly be true of olfactory information. Destruction of large amounts of the telencephalon, including total destruction, have, in fact, been noted to cause a marked decline or even extinction of certain aspects of reproductive behavior (see Aronson, 1970; Aronson and Kaplan, 1968). However, the major role of the telencephalon in fishes with regard to various behaviors is hypothesized to be more as an activator (Aronson, 1970; Aronson and Kaplan, 1968), rather than as an integrator. Unfortunately, the relationships between the telencephalon and preoptic region in the forebrain ablation experiments received little attention. Thus, for the moment it is assumed that the preoptic region is the main integrator for spawning behavior. If this were true it would complete the circuit of afferentefferent activity in relation to spawning behavior and egg and sperm release. A tentative model, encompassing all of the foregoing, to explain spawning and spawning behavior in female oviparous teleosts is shown in Figure 1. Not shown in the model is the possible action of the sex steroids or other hormones in priming the animal for reproductive behavior (see Liley, 1969, 1972; Liley and Wishlow, PREOPTIC NUCLEUS ACTIVITY IN FISHES SPAWNING BEHAVIOR FIG. 1. A tentative model describing the control of spawning and spawning behavior in an oviparous female teleost. Evidence for the various elements incorporated in the model are described in the text. 1974). Presumably the action of the sex steroids is on the brain, but the site of action has not yet been explored. In freshwater adapted bony fish, including the lungfish, the neurohypophysial hormones, particularly AVT, function as diuretic hormones (see Maetz and Lahlou, 1974; Pang, 1977; Perks, 1969; Sawyer, 1972; Sawyer and Pang, 1975) and possibly to stimulate sodium uptake by the gill (Maetz and Lahlou, 1974). Related to these actions are the vasopressor effects of the hormones, specifically to cause increased pressure in the dorsal and ventral aorta and the shunting of blood in the gill (see Chan, 1977; Maetz and Lahlou, 1974). The receptors that might subserve activation of the PN in relation to these functions may be located externally or internally. Extero-osmoreceptors may serve to detect changes in osmotic pressure or ion concentration changes of the external medium. The finding by Kandel (1964) that perfusion of the mouth and gills of goldfish with dilute sea water causes inhibition of activity in PN neurons suggests a mouth-gill location. The inhibition of PN activity and presumably concomitant decrease in secretion of hormone is a seemingly functional response in view of the osmoregulatory actions of the hormones. 779 On the other hand, perfusion of the olfactory epithelium of goldfish with NaCl solutions of various concentrations stimulates activity in the olfactory bulb and telencephalon (e.g., Hara and Gorbman, 1967; Oshima and Gorbman, 1966), and can also stimulate the activity of PN neurons in goldfish (Jasinski et al., 1967). Since activation would supposedly be associated with secretory activity of the PN-neurohypophysial system, it is difficult to resolve the functional significance of this response in terms of the osmoregulatory actions of the hormones. However, perfusion of the olfactory mucosa of a goldfish with NaCl solutions ranging from 10~2 M to 5 x 10~2 M (Hara and Gorbman, 1967) may be considered a general irritative stimulus, and not comparable to the sort of stimulus the goldfish might normally encounter. At this point there is no direct evidence for entero-osmoreceptors. However, indirect evidence for such receptors is provided by the observations that goldfish (Rourget etal., 1964) and lungfish (Sawyer, 1972) are able to compensate for intraperitoneal water and salt loading. As hypothesized by Sawyer (1972), the receptors could cue specifically to either a decrease in plasma osmolality or a decrease in concentration of a particular ion, such as sodium, or expansion of the extracellular fluid volume. Yet another possibility is that the receptors could cue to expansion of the intracellular fluid volume or osmoreceptor expansion. Expansion of the intracellular fluid volume would also occur with sodium depletion due to a shift of water to the intracellular space. These various possibilities and the supposed AVT secretion are illustrated in Figure 2. There are some suggestions that neurohypophysial hormones have involvement in stimulation of adrenocorticotropin (ACTH) secretion during stress responses in teleosts. Hawkins and Ball (1973) found that injection of arginine vasopressin into the molly, Poecilia latipinna, with an autotransplanted pituitary caused increased ACTH release. Stressful conditions, such as electric fishing and abrupt temperature or salinity changes, were noted to cause depletion of 780 R. E. PETER Absoluu hydration ECF ICF dehydration ECF —+• AV7+* ing, parturition, or other reproductive activities of elasmobranchs. ICF N.j CYCLOSTOMES ^ N , depletion Normal ulanc* Similar to the elasmobranchs no electrophysiological studies have been done on activation of the PN-neurohypophysial system in cyclostomes. However, exposure of larval lampreys to continuous light causes depletion, whereas continuous dark causes accumulation, of stainable neurosecretion in the cell bodies and axons of the PN N.+ (Oztan and Gorbman, 1960). This suggests that afferents to the PN may come from FIG. 2. A speculative scheme showing the changes light receptors located somewhere. No in extracellular fluid volume (ECF), and intracellular further studies have been done on the fluid volume (ICF) of enteroosmoreceptors in a freshwater teleost. The changes in osmotic balance mechanisms of activation of the PN in causing the alterations in ECF and ICF are given for cyclostomes. ECF ICF »> AVT» dohydratton Rtlativ hydration ECF ICF ICF ECF each situation, along with the supposed changes in arginine vasotocin (AVT) secretion. COMPARISON WITH THE MAMMALIAN MODEL stainable neurosecretion in the PN of the Electrophysiology European eel by Leatherland and Dodd The mammalian homologue of the (1969). Obviously further research is required to understand the role of the preoptic nucleus in fishes is the supraoptic neurohypophysial hormones in stimulat- nucleus (SON) and the paraventricular ing ACTH secretion and the response of nucleus (PVN). In those mammals (cat, the PN-neurohypophysial system during rat, rabbit, monkey) on which electrophysiological studies have been done, stressful situations. no exceptional characteristics of the SON and PVN neurons have been found (see CARTILAGENOL'S FISHES Cross I974a,b; Cross et al, 1975; Hayward, The electrophysiological characteristics 1972, 19746). As in the teleosts, the mamof PN neurons in elasmobranchs have not malian magnocellular neuroendocrine been studied. Likewise there is no infor- cells, identified as such by antidromic actimation available on the functional vation by pituitary stimulation, generally mechanisms of activation of the PN. Un- have low rates of spontaneous activity. fortunately, even the functions of the Also similar to the teleosts is the evidence hormones are poorly defined (see Maetz for inhibitory recurrent collaterals in some and Lahlou, 1974; Perks, 1969). Neurohy- antidromically identified SON and PVN pophysial hormones have been shown to neurons. Different from teleosts, however, have some ability to stimulate contraction is the finding of a significant portion of oviduct muscle in the dogfish (~20%) of neurons that have bursts of Scyliorhinus caniculus (Heller, 1972). This firing alternating with silent periods. may imply the presence of some sort of There have been no attempts to date to afferent input from the ovary and oviduct correlate electrophysiological activity of to the preoptic region, as is supposedly PN neurons in fishes with various suppresent in teleosts. However, since the posed states of secretory activity. However, reproductive process is so poorly under- much effort has been devoted to this in stood in elasmobranchs (see Dodd, 1975) mammals and a general correlation obit is highly tenuous to suggest a role of the tained (see Cross, 19746; Crossed al., 1975; PN-neurohypophysial system in egg lay- Hayward, 1972, 19746). For example, in PREOPTIC NUCLEUS ACTIVITY IN FISHES response to dehydration by substitution of a 2% NaCl solution for drinking water there is increased firing activity of rat SON and PVN neurons (Dyball and Pountney, 1973). The more direct, but perhaps more artificial, stimulus of intracarotid infusion of hypertonic saline or glucose solutions also causes increased firing activity of cells in and around the SON of the monkey (see Hayward, 19746). The PVN and SON neurons that show spontaneous bursting seem to be related to oxytocin release (Cross 1974a,b; Cross et al., 1975; Lincoln and Wakerly, 1974, 1975). During suckling in rats the bursting neurons specifically show increased burst frequency and more spikes per burst. This activity correlates with increased intramammary pressure and milk ejection. However, the bursting neurons of rats (Dyball and Pountney, 1973) and monkeys (Hayward, 1974ft) also show increased activity following intracarotid saline infusion. Thus, classification of the neurons as being vasopressinor oxytocin-secreting is difficult on the basis of electrophysiological findings. A ctivity-function relationships The actions of oxytocin on the uterine smooth musculature in mammals and the actions of neurohypophysial hormones on the oviduct and ovary musculature in fishes (see above) are analogous systems. Thus, although the neural pathways involved in oxytocin release in mammals have been investigated (see Cross and Dyball, 1974), a strictly homologous afferent and efferent system for the release of neurohypophysial hormones to stimulate oviduct and ovarian muscles in fish is unlikely. For reproductive behavior in mammals, the preoptic region has been implicated as a hormone-sensitive center that must be intact and primed by the sex steroids in order for the behavior to occur (see Lisk, 1973). This is similar to what we know about teleost fishes (see above), except that the role of the sex steroids in priming the preoptic region or some other brain region has not been explored. A major difference between the teleosts and mammals is that in the fishes the mag- 781 nocellular neuroendocrine system is apparently encompassed in the part of the preoptic region involved with spawning behavior. In the mammals there are no indications that the magnocellular neuroendocrine system is involved in reproductive behavior. The osmotic stimuli for neurohypophysial hormone secretion in the freshwater bony fishes (see above) are in general opposites to the stimuli for vasopressin secretion in mammals. Increased osmolality of the plasma due to saline infusion or dehydration by water deprivation, or infusion of hypertonic saline into the brain ventricular system all provide a hypertonic stimulus to evoke vasopressin secretion in mammals (see Anderson, 1972; Hayward, 1972; Moses and Millar, 1974; Share 1974). Each of these situations is associated with increased extracellular sodium concentration, although a change in sodium is not a necessary requisite for the osmotic stimulus. What seems to be the common element and may be the mechanism for detection of these osmotic stimuli is a decreased intracellular fluid volume, or supposed decrease in osmoreceptor volume. The osmoreceptors involved in detection of these changes may be endocrine neurons of the SON or PVN (see Cross, 1974ft; Cross et al., 1975; Hayward, 1972, 1974ft). However, it seems more likely that the osmoreceptors are interneurons in or adjacent to the SON and PVN since the cells that respond to osmotic stimuli in monkeys fall into two classes (Vincent et al., 1972). One class reacts monophasically with inhibition or excitation to intracarotid saline infusion and is not antidromically activated by pituitary stimulation. The second class responds biphasically to intracarotid saline infusion and is antidromically activated by pituitary stimulation. However, this categorization is not firm when other species are considered, because the types of responses to an osmotic stimulus can be quite varied (see Cross, 1974ft; Cross et al., 1975; Hayward, 1974ft). The entero-osmoreceptors of freshwater fishes may, as discussed above, respond to either a decrease in plasma osmolality, or a decrease in the plasma concentration of a 782 R. E. PETER particular ion such as sodium, or an increase in the extracellular fluid volume, or possibly an increase in the intracellular fluid volume (see Figure 2). The question of the location and the nature of the entero-osmoreceptors in freshwater fishes is open. Unlike mammals, fishes likely utilize information from extero-osmoreceptors to regulate neurohypophysial hormone secretion. Another important stimulus able to evoke vasopressin secretion in mammals is hypovolemia (see Hayward, 19746; Moses and Millar, 1974; Share, 1974). Such a stimulus occurs in the event of dehydration due to water deprivation, hemorrhage, or decreased blood pressure. While the first of these stimuli is able to also act via osmoreceptors, hypovolemia is detected variously by atrial stretch receptors, and aortic and carotid baroreceptors. Baroreceptors have been shown to be present in at least the bony fishes (for review see Randall, 1970), but involvement in stimulation of neurohypophysial hormone secretion has not been investigated. However, it seems likely that decreased blood volume due to hemorrhage and perhaps also decreased blood pressure would serve as stimuli for neurohypophysial hormone secretion in fishes for two reasons. First, the neurohypophysial hormones have vasopressor effects in the bony fishes, elasmobranchs and cyclostomes (see Maetz and Lahlou, 1974). Although the pressor effects may be more related to regulation of gill function, as suggested by Maetz and Lahlou (1974), involvement in regulation of blood pressure would imply that the hormones could be released in response to the appropriate signal to cause an increase in blood pressure. One such signal, similar to that seen in mammals, could be decreased blood pressure and/or hypovolemia. However, while this seems logical, it is contrary to the suggestion above and by Sawyer (1972) that expansion of the extracellular fluid volume may be a stimulus for neurohypophysial hormone secretion to prevent hydration. The second means by which hemorrhage may stimulate neurohypophysial hormone secretion in fishes is by the general stress response associated with it. In addition to hemorrhage, some other types of stress such as loud sounds, pain and intense emotion have also been found to cause vasopressin release in mammals (see Cross and Dyball, 1974; Hayward, 1972). Evidence cited above suggests that at least some stressors may also cause activity of the PN-neurohypophysial system in bony fishes. The release of neurohypophysial hormones as a result of a handling stress could also account for the commonly observed "laboratory diuresis" of freshwater teleosts. In relation to stress responses of mammals, the corticotropin-releasing hormone (CRH) activity of vasopressin has received much attention from researchers in the past (see Yates and Maran, 1974). At this point it is established that there is a hypothalamic CRH separate from vasopressin. Furthermore, the action of vasopressin in stimulating ACTH secretion seems to be primarily one of potentiating the action of hypothalamic CRH at the level of the pituitary (see Yates and Maran, 1974). In the experiments by Hawkins and Ball (1973) reviewed above it was found that vasopressin had ACTH releasing ability in the molly. In order to determine if a homologous system for stimulating ACTH secretion exists in fishes and mammals, research will have to be done on fishes using the native neurohypophysial hormones. Another sphere of action of oxytocin and vasopressin in mammals encompasses effects on the brain. This area is totally uninvestigated in fishes. In rats and rabbits it has been found that electrophoretically applied oxytocin causes excitation of a major portion of the antidromically identified neurons in the PVN, but that it has no action on the non-antidromically activated neurons of the PVN or on any neurons of the SON, thalamus or cerebral cortex (Moss et al., 1972). Electrophoretically applied vasopressin and intravenous oxytocin were also ineffective. In a similar study on cats by Nicoll and Barker (1971) it was found that electrophoretically applied vasopressin tended to excite cells in the cerebral cortex but inhibit antidromically PREOPTIC NUCLEUS ACTIVITY IN FISHES identified SON neurons and/or SON neurons showing recurrent inhibition. Higher amounts of applied hormone tended to have reverse effects. Thus, while these somewhat contrasting results suggest that the neurohypophysial hormones may have some transmitter activity, such a conclusion is not warranted without further investigation. The suggestion from the results by Nicoll and Barker (1971) that vasopressin may be the agent involved in recurrent inhibition does not seem tenable because homozygous Brattleboro rats, animals unable to synthesize vasopressin, still display recurrent inhibition (Dyball, 1974). Neurohypophysial hormones do have actions on the brain to influence certain behaviors. Retention of a conditioned avoidance response is very markedly aided by injections of Pitressin tannate in oil (de Wied and Bohus, 1966). This action is likely due to the vasopressin in the preparation, since subcutaneous injection of a single dose of lysine vasopressin (1 ng or 0.6 U) aids retention of a conditioned avoidance response in rats (Bohus et al., 1974; King and de Wied, 1974; de Wied, 1971). The avoidance behavior is affected only when the lysine vasopressin is given within about 1 hour before or after the training for the avoidance response. The retention of the avoidance response is up to a few days whereas saline treated control animals have extinction of the response within two days. Such hormones as oxytocin, 4~l0ACTH, angiotensin II, insulin or growth hormone do not have a similar effect. As further support for this action of vasopressin, homozygous Brattleboro rats are deficient in learning avoidance behavior (Bohus et al., 1974). The important implication from these studies is that vasopressin can alter the retention of the long-term memory of certain conditioned avoidance responses. A lesioning study by Wimersma Greidanus et al. (1974) indicates that at least some of the action of vasopressin in this regard involves the posterior thalamic region, particularly the parafascicular nuclei. When lesions were placed in this region higher doses of vasopressin were required 783 to prevent extinction of the avoidance reresponse; without vasopressin, lesions in this area accelerate extinction. What other brain regions may be involved remains to be determined. While these experiments clearly demonstrate some actions of vasopressin on a specific behavior, it is difficult to understand the context within which these results should be viewed. One notable problem with these studies is the very large dose of hormone usually administered. Also, lysine vasopressin has been used, rather than the hormone native to the rat, arginine vasopressin. Perhaps now that a brain region associated with the response has been located, smaller doses of the native hormone can be given directly into the brain. REFERENCES Andersson, B. 1972. Receptors subserving hunger and thirst. In E. Neil (ed.), Handbook of sensory physiology, Vol. III/l Enteroceptors, pp. 187-216. Springer-Verlag, New York, N.Y. Aronson, L. R. 1970. Functional evolution of the forebrain in lower vertebrates. In L. R. Aronson, E. Toback, D. S. Lehrman, and J. S. Rosenblatt (eds.), Development and evolution of behavior, pp. 75-107. W. H. Freeman, San Francisco, California. Aronson, L. R. and H. Kaplan. 1968. Function of the teleostean forebrain. In D. Ingle (ed.), The central nervous system and fish behavior, pp. 107-125. Univer- sity of Chicago Press, Chicago, Illinois. Bennett, M. V. L., M. Gimenez, and M. J. Ravitz. 1968. Synaptically evoked impulse activity of morphologically identified neurosecretory cells. Anat. Rec. 160:313-314. Bohus, B., R. Ader, and D. de Wied. 1972. Effects of vasopressin on active and passive avoidance behavior. Horm. Behav. 3:191-197. Bohus, B., Tj. B. van Wimersma Greidanus, W. de Jong, and D. de Wied. 1975. Behavioral, autonomic and endocrine responses during passive avoidance in rats with hereditary hypothalamic diabetes insipidus (Brattleboro strain). Exp. Brain Res. 23 (Suppl.):25. Bourguet, J., B. Lahlou, and J. Maetz. 1964. Modifications experimentales de l'equilibre hydromineral et osmoregulation chez Carassius auratus. Gen. Comp. Endocrinol. 4:563-576. Chan, D. K. O. 1977. Comparative physiology of vasomotor effects of neurohypophysial peptides in the vertebrates. Amer. Zool. 17:751-761. Chandrasekhar, K. and T. Chacko. 1970. Effect of electrical stimulation of the olfactory mucosa on the hypothalamo-hypophysial neurosecretory system in the fresh water teleostean fish, Ophiocephalus punctatus. Indian J. Zootomy 11:105-113. 784 R. E. PETER Cross, B. A. 1974a. Functional identification of hypothalamic neurons. In K. Lederis and K. E. Cooper (eds.), Recent studies of hypothalamic function, pp. 39-49. S. Karger, Basel, Switzerland. Cross, B. A. 1974i. The neurosecretory impulse. In F. Knowles and L. Vollrath (eds.), Neurosecretion—the final neuroendocrine pathway, pp. 115-128. Springer-Verlag, New York, N.Y. Cross, B. A. and R. E. J. Dyball. 1974. Central pathways for neurohypophysial hormone release. Handbook of Physiology, Sec. 7, Vol. IV, Pt. 1, pp. 269-285. American Physiological Society, Washington, D.C. Cross, B. A., R. E. J. Dyball, R. G. Dyer, C. W.Jones, D. W. Lincoln, J F. Morris, and B. T. Pickering. 1975. Endocrine neurons. Rec. Prog. Horm. Res. 31:243-294. Demski, L. S., D. H. Bauer, and J. W. Gerald. 1975. Sperm release evoked by electrical stimulation of the fish brain: A functional-anatomical study. J. Exp. Zool. 191:215-232. Demski, L. S. and K. M. Knigge. 1971. The telencephalon and hypothalamus of the bluegill (Lepomis macrochirus):Evoked feeding, aggressive and reproductive behavior with representative frontal sections. J. Comp. Neur. 143:1-16. Dodd, J. M. 1975. The hormones of sex and reproduction and their effects in fish and lower chordates: Twenty years on. Amer. Zool. 15 (Suppl. 1): 137-171. Dyball, R. E. J. 1974. Single unit activity in the hypothalamo-neurohypophysial system of Brattleboro rats. J. Endocrinol. 60:135-143. Dyball, R. E. J. and P. S. Pountney. 1973. Discharge patterns of supraoptic and paraventricular neurons in rats given a 2% NaCl solution instead of drinking water. J. Endocnnol. 56:91-98. Egami, N. 1959. Preliminary note on the induction of the spawning reflex and oviposition in Oryzias latipes by the administration of neurohypophysial substances. Annot. Zool. Japon. 32:13-17. Egami, N. and S. Ishii. 1962. Hypophysial control of reproductive functions in teleost fishes. Gen Comp. Endocrinol., Suppl. 1:248-253. Hallowitz, R. A., D. J. W. Woodward, and L. S. Demski. 1971. Forebrain activation of single units in preoptic area of sunfish. Comp. Biochem. Physiol. 40A:733-741. Hara, T. J. and A. Gorbman. 1967. Electrophysiological studies of the olfactory system of the goldfish, Carassius auratus L.— I. Modification of the electrical activity of the olfactory bulb by other central nervous structures. Comp. Biochem. Physiol. 21:185-200. Hawkins, E. F. and J. N. Ball. 1973. Current knowledge of the mechanisms involved in the control of ACTH secretion in teleost fishes. In A. Brodish and E. S. Redgate (eds.), Brain-Pituitary-Adrenal Interrelationships, pp. 293-315. S. Karger AG, Basel. Hayward, J. N. 1972. Hypothalamic input to supraoptic neurons. Progr. Brain Res. 38:145-162. Hayward, J. N. 1974a. Physiological and morphological identification of hypothalamic magnocellular neuroendocrine cells in goldfish preoptic nucleus. J. Physiol. 239:103-124. Hayward, J. N. 1974i. Neurohumoral regulation of neuroendocrine cells in the hypothalamus. In K. Lederis and K. E. Cooper (eds.), Recent studies of hypothalamic function, pp. 166-179. S. Karger, Basel, Switzerland. Heller, H. 1972. The effect of neurohypophysial ] hormones on the female reproductive tract of lower vertebrates. Gen. Comp. Endocrinol., Suppl. 3:703-714. Ishii, S. 1963. Some factors involved in the delivery of the young in the top-minnow, Gambusia affinis. J. Fac. Sci. Univ. Tokyo 10:181-187. Jasinski, A., A. Gorbman, and R. J. Hara. 1966. Rate of movement and redistribution of stainable neurosecretory granules in hypothalamic neurons. Science 154:776-778. Jasinski, A., A. Gorbman, and T. J. Hara. 1967. Activation of the preoptico-hypophysial neurosecretory system through olfactory afferents in fishes. In F. Stutinsky (ed.), Neurosecretion, pp. 100-123. Springer-Verlag, New York. Kandel, E. R. 1964. Electrical properties of hypothalamic neuroendocrine cells. J. Gen. Physiol. 47:691-717. King, A. R. and D. de Wied. 1974. Localized behavioral effects of vasopressin on maintenance of an active avoidance response in rats. J. Comp. Physiol. Psych. 86:1008-1018. La Pointe, J. L. 1977. Comparative physiology of neurohypophysial hormone action on the vertebrate oviduct-uterus. Amer. Zool. 17:763-773. Leatherland, J. F. and J. M. Dodd. 1969. Activity of the hypothalamo-neurohypophysial complex of the European eel (Anguilla anguilla L.) assessed by the use of an in situ staining technique and by autoradiography. Gen. Comp. Endocrinol. 13:45-59. Liley, N. R. 1969. Hormones and reproductive behavior in fishes. In W. S. Hoar and D. J. Randall (eds.), Fish physiology, Vol. I l l , pp. 73-116. Academic Press, New York, N.Y. Liley, N. R. 1972. The effect of estrogens and other steroids on the sexual behavior of tbe female guppy, Poeciha rettculata. Gen. Comp. Endocrinol., Suppl. 3:542-552. Liley, N. R. and W. Wishlow. 1974. The interaction of endocrine and experimental factors in the regulation of sexual behaviour in the female guppy, Poeciha reticulata. Behaviour 48:185-214. Lincoln, D. W. and J. B. Wakerley. 1974. Electrophysiological evidence for the activation of supraoptic neurons during the release of oxytocin. J. Physiol. 242:533-554. Lincoln, D. W. and J. B. Wakerley. 1975. Factors governing the periodic activation of supraoptic and paraventricular neurosecretory cells during suckling in the rat. J. Physiol. 250:443-461. Lisk, R. D. 1973. Hormonal regulation of sexual behavior in polyestrous mammals common to the laboratory. In Handbook of Physiology Sec. 7, Vol. II, Pt. 1, pp. 223-260. American Physiological Society, Washington, D.C. Macey, M. J., G. E. Pickford, and R. E. Peter. 1974. Forebrain localization of the spawning reflex response to exogenous neurohypophysial hormones in the killifish, Fundulus heterochtus. J. Exp. Zool. PREOPTIC NUCLEUS ACTIVITY IN FISHES 785 Sawyer, W. H. and P. K. T. Pang. 1975. Endocrine 190:269-280. adaptation to osmotic requirements of the enviMaetz, J. and B. Lahlou. 1974. Actions of neuroronment: Endocrine factors in osmoregulation by hypophysial hormones in fishes. In Handbook of PREOPTIC NUCLEUS lungfishes ACTIVITYand IN amphibians. FISHES Gen. Comp. Endocrin-785 physiology Sec. 7, Vol. IV, Pt. 1, pp. 521-544. Ameriol. 25:224-229. can Physiological Society, Washington, D.C. Moses, 190:269-280. A. M. and M. Miller. 1974. Osmotic influences Sundararaj, andand S. V. 1966. Effects of Sawyer, B. W.I. H. P.Goswami. K. T. Pang. 1975. Endocrine onMaetz, the release Handbook of mammalian adaptationhypophysial to osmotic hormones, requirementsplacental of the enviJ. and of B. vasopressin. Lahlou. 1974.In Actions of neurophysiology, Sec. hormones 7, Vol. IV,in Pt. 1, pp. 225-242. ofgonadotropins, gonadal hormones, and adrenal by ronment: Endocrine factors in osmoregulation hypophysial fishes. In Handbook American Physiological Society, Washington, D.C. Ameri-corticosteroids on ovulation andGen. spawning the lungfishes and amphibians. Comp.inEndocrinphysiology Sec. 7, Vol. IV, Pt. 1, pp. 521-544. hypophysectomized Moss, R. R. E. J. Dyball, andWashington, B. A. Cross.D.C. 1972. ol. 25:224-229. catfish, Heteropneustes fossilis canL., Physiological Society, J. Exp.B.Zool. Excitation antidromically neurosecreMoses, A.ofM. and M. Miller.identified 1974. Osmotic influences (Bloch.). Sundararaj, I. and161:287-296. S. V. Goswami. 1966. Effects of tory cells of the paraventricular nucleus In by oxytocin D. J. 1970. The circulatoryhormones, system. In W. S. on the release of vasopressin. Handbook Randall, of mammalian hypophysial placental applied iontophoretically. Exp. Neurol. and D. J. Randall (eds.),hormones, Fish physiology, Vol. physiology, Sec. 7, Vol. IV, Pt. 34:95-102. 1, pp. 225-242.Hoargonadotropins, gonadal and adrenal 133-172. Academic Press, New York, N.Y.in the Nicoll, American R. A. and J. L. Barker. Society, 1971. The pharmacol-D.C. IV, pp. Physiological Washington, corticosteroids on ovulation and spawning ogyMoss, of recurrent supraoptic L. 1974. Blood pressure, blood volume, and fossilis catfish, Heteropneustes R. L., R. E.inhibition J. Dyball, in andthe B. A. Cross. 1972.Share, hypophysectomized neurosecretory system. Brain Res.identified 35:501-511. of J. vasopressin. Handbook ofphysiology, (Bloch.). Exp. Zool. In161:287-296. Excitation of antidromically neurosecre- the release Sec. 7, Vol.D. IV, Pt. The 1, pp. 243-255.system. American Oshima, andof A. 1966.nucleus Olfactory retoryK.cells theGorbman. paraventricular by oxytocin Randall, J. 1970. circulatory In W. S. Physiological Washington, sponses in the forebrain of Exp. goldfish and 34:95-102. their applied iontophoretically. Neurol. Hoar andSociety, D. J. Randall (eds.),D.C. Fish physiology, Vol. Stacey, N. E. 1976. Effects of indomethacin and modification byand thyroxine treatment. IV, pp. 133-172. Academic Press, New York, N.Y. Nicoll, R. A. J. L. Barker. 1971.Gen. The Comp. pharmacolon the spawning behavior female and Endocrinol. ogy of 7:398-409. recurrent inhibition in the supraoptic prostaglandins Share, L. 1974. Blood pressure, bloodofvolume, goldfish. Prostaglandins 12:113-126. Oztan, neurosecretory N. and A. Gorbman. 1960. The hypophysis system. Brain Res. 35:501-511. the release of vasopressin. In Handbook ofphysiology, N. E.7, and R. Pt. Liley.1, 1974. Regulation of andOshima, hypothalamo-hypophysial neurosecretory sys- re-Stacey, Sec. Vol.N.IV, pp. 243-255. American K. and A. Gorbman. 1966. Olfactory behaviour in the Washington, female goldfish. tem of larval lampreys and their of responses light.their spawning Physiological Society, D.C.Nature sponses in the forebrain goldfishto and J. Morph. 106:243-262. Stacey, N. E. 1976. Effects of indomethacin and modification by thyroxine treatment. Gen. Comp. 247:71-72. Pang, P. K. T. 1977. Osmoregulatory functions of Vincent, J. D., E. Arnauld, A. Nicolescu-Catargi. prostaglandins on theand spawning behavior of female Endocrinol. 7:398-409. neurohypophysial hormones in fishes Osmoreceptors and neurosecretory Prostaglandins 12:113-126. cells in Oztan, N. and A. Gorbman. 1960.and Theamphibhypophysis 1972.goldfish. supraoptic the unanaesthetized ians. and Amer. Zool. 17:739-749. N. E. complex and N. R.of Liley. 1974. Regulation of hypothalamo-hypophysial neurosecretory sys- theStacey, Brain behaviour Res. 45:278-281. Partridge, N. lampreys R. Liley, and E. responses Stacey. 1976. spawning in the female goldfish. Nature tem B. of L., larval and N. their to light. monkey. D. 1971. Long term effect of vasopressin on The J.role of pheromones in the sexual behaviour of de Wied, 247:71-72. Morph. 106:243-262. maintenance a conditioned rethePang, goldfish. Anim. Behav.Osmoregulatory 24:291-299. P. K. T. 1977. functions of theVincent, J. D., E.ofArnauld, and A. avoidance Nicolescu-Catargi. sponses in rats. Nature 232:58-60. Perks, neurohypophysial A. M. 1969. The hormones neurohypophysis. S. in fishesIn andW.amphib1972. Osmoreceptors and neurosecretory cells in Hoarians. and Amer. D. J. Randall (eds.),, Fish physiology, Vol. de Wied, and B. Bohus. Longunanaesthetized term and the D. supraoptic complex1966. of the Zool. 17:739-749. II,Partridge, pp. 111-205. Academic Press,and NewN.York. term effects of a conditioned Brain on Res.retention 45:278-281. B. L., N. R. Liley, E. Stacey. 1976. shortmonkey. rats term by treatment with long on Peter, R. andofA.pheromones Gorbman. in 1968. Some behaviour afferent of avoidance de Wied,response D. 1971.inLong effect of vasopressin TheE.role the sexual actingthePitressin and a-MSH. Nature 212:1484pathways to the preoptic nucleus of the goldfish. maintenance of a conditioned avoidance rethe goldfish. Anim. Behav. 24:291-299. Neuroendocrinology Perks, A. M. 1969.3:229-237. The neurohypophysis. In W. S. 1486.sponses in rats. Nature 232:58-60. Pickford, G. E. of a spawning reflex Vol. Wilhelmi, A. E.,D.G.and E. Pickford, W. Long H. Sawyer. Hoar and1952. D. J.Induction Randall (eds.),, Fish physiology, de Wied, B. Bohus.and 1966. term and in hypophysectomized killifish.Press, Nature 1955.short Initiation the spawning reflex of responses in II, pp. 111-205. Academic New170:807York. term ofeffects on retention a conditioned 808. by theresponse administration and mammaavoidance in rats offish by treatment with long Peter, R. E. and A. Gorbman. 1968. Some afferent Fundulus neurohypophysial preparations and synthetic Prasadapathways Rao, P.toD.the1970. The nucleus effect ofof electrical Pitressin and a-MSH. Nature 212:1484preoptic the goldfish. lian acting oxytocin. stimulation of the olfactory tract on the nucleus 1486.Endocrinology 57:243-252. Neuroendocrinology 3:229-237. Greidanus, B., B. and Bohus, D. preopticus in E.the1952. catfish H eteropneustes fossdts Pickford, G. Induction of a spawning reflexvan Wimersma Wilhelmi, A. E., G. E. Tj. Pickford, W. and H. Sawyer. Differential localization of responses the in- in (Bloch). Experientia 26:1377-1378. in hypophysectomized killifish. Nature 170:807- de Wied. 1955. 1974. Initiation of the spawning reflex fluence of lysine and of ACTH 4-10mammaon Prasada808. Rao, P. D. and K. B. Dabhade. 1973. In situ Fundulus byvasopressin the administration offish and behavior: A study preparations in rats bearing demonstration changes in the preopticolian neurohypophysial andlesions synthetic Prasada Rao, of P. D. 1970. The effect of electrical avoidance parafascicular nuclei. 57:243-252. Neuroendocrinology neurohypophysial after electrical oxytocin. Endocrinology stimulation ofcomplex the olfactory tract on stimulathe nucleus in the tion preopticus of the olfactory in the catfish Clariasfossdts14:280-288. van Wimersma Greidanus, Tj. B., B. Bohus, and D. in thetract catfish H eteropneustes batarchus (Linn.). Z. Zellforsch 139:95-99. Yates, R. and J.1974. W. Maran. 1974.localization Stimulationofand de E. Wied. Differential the in(Bloch). Experientia 26:1377-1378. of of adrenocorticotropin release. In HandSawyer, W. H. and amphibians: fluence lysine vasopressin and of ACTH 4-10 on Prasada Rao,1972. P. D.Lungfishes and K. B. Dabhade. 1973. In situ inhibition book avoidance of physiology, Sec. 7,AVol. IV,inPt. 2, bearing pp. 367-404. Endocrine adaptationof and the transition from behavior: study rats lesions demonstration changes in the preopticoSociety, Washington, D.C. aquatic to terrestrial life.complex Fed. Proc. in thePhysiological parafascicular nuclei. Neuroendocrinology neurohypophysial after31:1609-1614. electrical stimula- American 14:280-288. tion of the olfactory tract in the catfish Clarias batarchus (Linn.). Z. Zellforsch 139:95-99. Yates, R. E. and J. W. Maran. 1974. Stimulation and inhibition of adrenocorticotropin release. In HandSawyer, W. H. 1972. Lungfishes and amphibians: book of physiology, Sec. 7, Vol. IV, Pt. 2, pp. 367-404. Endocrine adaptation and the transition from American Physiological Society, Washington, D.C. aquatic to terrestrial life. Fed. Proc. 31:1609-1614.