[Intermittent liberation of gonadoliberin (GnRH) by the rat hypothalamus 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.