Effect of hypothalamic deafferentation on LH and sexual behaviour in ovariectomized ewe under hormonally induced oestrous cycle

Abstract

We have investigated the effect of surgical isolation of the mediobasal hypothalamus of ovariectomized ewes on LH secretion (basal level, rhythmicity and oestradiol- induced surge) and progesterone-oestradiol induced sexual receptivity. The disruption of the posterior inputs (just anterior to the mamillary bodies) was without any endocrine or beha- vioural consequence. The bilateral disruption of antero-dorsal inputs resulted in the suppression of OB-induced LH surge and damping of the mean basal level. This effect was observed both shortly after surgery, and 3 months later (2 artificial cycles in each case). The pulsatility of LH basal secretion remained evident regardless the drastic damping of the level. Such results suggest that antero-dorsal inputs, coming from preoptic-suprachiasmatic areas are required both for the positive feed-back of oestrogens on LH secretion, and for the mainte- nance of the basal level of secretion. The persistence of the pulsatile pattern of secretion suggests that the mechanism involved could be located in the medio-basal area. In 8 cases