Acute effect of hypothalamic deafferentation on progesterone-induced ovulating hormone release in the rats.

Abstract

A study was made to analyze the facilitatory effect of progesterone on ovulating hormone (OH) release in proestrous rats. Neural connections to the medial basal hypothalamus (MBH) or to the preoptic-suprachiasmatic (POA-SC) region of the hypothalamus were transected on the morning of proestrus with a curved knife or with an Lshaped knife. After the recovery from the surgical anesthesia, the rats were injected subcutaneously with progesterone, 1 mg per rat, and anesthetized again with pentobarbital during the time corresponding to the critical period for OH release in the intact rat. Facilitation by progesterone of OH release was confirmed in the next morning by counting the ova in the oviducts. Posterior deafferentation of the hypothalamus at the level of the mammillary body did not block the progesterone-induced ovulation. Anterior deaowqfferentation at the retrochiasmatic level completely blocked the ovulation. Progesterone-induced ovulation was also blocked by more rostral or broad dorsal deafferentation with a large curved or an L-shaped knife, the operation of which did not provide any damage on the structures of the POA-SC region. It is concluded that the facilitation of OH release by exogenous progesterone is due to the increase in the responsiveness of MH to the ovulatory stimulus coming from the higher CNS via the POA-SC region, rather than due to the direct stimulation of the hypothalamus to secrete releasing factor (s).