Poster Presentation The International Congress of Neuroendocrinology 2014

Postnatal defeminization of a neuroendocrine pulse generator in the rat hypothalamus. (#340)

Philippe Ciofi , Jean-Marc Israel , Jean-Marie Cabelguen , Gwendal Le Masson , Stéphane H Oliet

Whether electrophysiological activity in bursts, allowing release of a bolus of neurohormone, is intrinsic to neuroendocrine cells or driven by afferents is unclear. We evaluated this in anterohypothalamic organotypic cultures of neonatal rats where intracellular paired-recorded oxytocin (OT) neurons from the supraoptic nucleus (SON) have synchronized bursting activity identical to that seen in suckled dams in vivo, suggesting a drive by networks present at birth (JN 18:6641; EJN 17:2619). As lactation is a female-specific function, we reasoned that a specific network might be involved and that the development of this network should fit with mechanisms of sexual differentiation. OT neurons bursted in most (>90%) cultures from female neonates at postnatal day 5 (PN5), PN7, PN9 or PN12, and in cultures from males at PN5 (>90%), PN7 (50%) but not older (<10%), suggesting a defeminization by circulating androgens. Accordingly, bursting behavior in cultures harvested at PN9 was, rescued by orchidectomy at PN5, and abolished in females by testosterone given from PN5 to PN7. Applied for 72h to tissues harvested at PN5, testosterone abolished bursting irrespective of sex, and this was, blocked by the aromatase inhibitor letrozole or the pan-caspase inhibitor zVADfmk, and mimicked by the estrogen receptor (ER) alpha agonist PPT. The ERbeta agonist DPN and the AR agonist DHT had no effect.  In vivo, Hoechst labeling revealed a very low number of apoptotic-like cell nuclei in the SON with no sex-difference, and expression of ERalpha concentrated in the periventricular area (PeA). Removal of the PeA from tissue slices harvested at PN5 abolished bursting of OT neurons irrespective of sex. In the PeA, apoptotic-like cell nuclei were in both sexes equally abundant, declining after PN7. Seemingly, a periventricular network generates bursts in OT cells and is pruned postnatally in males.