Libération intermittente de gonadolibérine (GnRH) par l'hypothalamus du rat in vitro

Hypothalamus were dissected from suprachiasmatic area to mamillary bodies in 50 days old male rats. These fragments were subsequently removed and incubated for 3 hours at 37 degrees C in Dulbecco Modified Eagle's medium supplemented with glucose and containing calcium (1.25 mM) and potassium (5.81 mM). Incubation medium was changed every 5 or 15 minutes and immediately collected at 4 degrees C for highly specific radioimmunoassay of GnRH using R 42 antiserum of Nett and Niswender. In these conditions, mean +/- 1 SD release of immunoreactive GnRH per 1 hour was 199 +/- 68 pg (n = 4) and 135 +/- 38 pg (n = 6) in medium collected every 5 and 15 minutes respectively. Furthermore GnRH release was found to be episodic, 3 to 5 peaks being observed during a period of 2 hours. It is concluded that, following deafferentation and isolation in vitro, mature hypothalamus remains capable of releasing GnRH in a spontaneous periodic manner, suggesting that this particular feature of neuroendocrine maturation can be initiated in the hypothalamus itself.