THE EFFECT OF HYPOTHALAMIC DEAFFERENTATION UPON PUBERTY IN THE FEMALE RAT

Abstract

ABSTRACT Neural connections of the medial basal hypothalamus (MBH) were completely or partially severed in 180 22-day-old female Sprague-Dawley rats by means of the Halàsz knife and the subsequent gonadal development studied. Surgical transection of all neural input (complete deafferentation) or of only the fibers reaching the MBH from anterior resulted in precocious vaginal opening followed immediately by the onset of persistent vaginal oestrus. Surgery which transected the lateral and posterior connections had no effect, while sham surgery delayed puberty slightly. Animals with anterior or complete deafferentation of the MBH failed to ovulate at puberty. Upon necropsy at 90 days of age, the ovaries of the latter animals contained large follicles but no corpora lutea and weighed less than control ovaries. The deafferented region associated with precocity and persistent vaginal oestrus extended from just behind the optic chiasm to the mamillary body and about 1.2 mm dorsally and laterally. Prepuberal injection of 25 IU PMS accelerated vaginal opening and ovulation in intact controls. Ovulation did not occur after PMS in animals with anterior deafferentation of the MBH although the ovaries at necropsy equalled in weight those of intact PMS-treated controls. It appears that the neurally isolated MBH can sustain precocious maturation due presumably to the removal of inhibitory influences, but it cannot support regular ovulatory cycles.