Download Investigating how parvocellularTRH neuronscontrol TSH secretion

Investigating how parvocellularTRH neuronscontrol TSH secretion in conscious mice.
Pauline Campos, Ombeline Hoa, PierreFontanaud, Anne Guillou, Patrice Mollard
Institut de Génomique Fonctionnelle, Team « Networks and rhythms in endocrine glands »,
CNRS UMR 5203, INSERM U1191 – Université de Montpellier, France
Hypothalamus-pituitary-thyroid (HPT) axis homeostasis is indispensable for normal growth,
metabolism, reproduction and intelligence. Parvocellularhypophysiotropic thyrotropin-releasing
hormone (TRH) neurons of the paraventricular nucleus (PVN) play a primary role in the
regulation of thyroid hormone production through release of TRH in the median eminence to
stimulate the pituitary TSH release. TSH then stimulates the thyroid gland to produce the thyroid
hormones (THs) T3 and T4. THs, in turn, regulates the activity of TRH neurons in the
hypothalamus by a negative feedback pathway. Despite the fact thatthe involvement of TRH
neurons in the control of THs levels is undoubtable, nothing is known about TRH neurons
function in vivo. We developed a system in which we can specifically monitor the activity of
TRH neurons using calcium imaging in awake mice. We used a Cre-dependant adeno-associated
virus (AAV) in transgenic TRH-Cre mice to target the genetically encoded calcium indicator,
GCamp6s, to the TRH neuronal phenotype. Taking advantage of the retrograde transport
properties of AAVs, we injected the AAV into the median eminence to target expression of
GCamp6s to only hypophysiotropic TRH neurons. Mice were then implanted with GRIN
(gradient-index) lensesin the PVN and TRH neurons were imaged in situ, either in a head-fixed
configuration, or freely moving with a miniature microscope. The preliminary results showed that
hypophysiotropic TRH neurons are likelyinteracting with each other within local networks and
are modulating their activities throughout the day. Using tail blood sampling and an in house
TSH ultra-sensitive ELISA, we are currently able to correlate the TRH neuron population activity
with the level of TSH secreted by pituitary thyrotrophs.The results of this work would shed light
about how parvocellular TRH neurons function in health and disease, namely during
subclinical/overt hypothyroidism.
This work is supported by grants from FRM (DEQ20150331732) and IPAM-BioCampus
Montpellier.