Effects of anterior and posterior hypothalamic deafferentation on gonadotrophin and prolactin secretion in ovariectomized ewes under hormonally induced oestrous cycles

Summary. Oestradiol benzoate (OB), when given to ovariectomized ewes under hormo- nally induced oestrous cycles, caused both negative and positive feedback effects, i. e. decreased FSH levels were followed by an FSH surge 15 to 18 hrs later concomitant with a preovulatory-like LH release. This injection also caused a prolactin surge with a spiking release pattern between 9 to 18 to 30 to 42 hrs later. Basal FSH levels, as well as those obtained after OB injection, progressively increased from December to April. Between December and February, no significant variations in prolactin secretion were detected, while later on (February to April) both basal prolactin levels, and those obtained after OB injection rose significantly. These long-term variations of both FSH and prolactin secretion indicate seasonal effects. After anterior deafferentation of the mediobasal hypothalamus (MBH), FSH levels decreased drastically, but remained detectable. The OB-induced surges were totally sup- pressed in some animals, while in others they showed a very small residual response at the time of the residual LH release. Thus, FSH secretion could be regulated by the same hypo- thalamic hormone as LH secretion, i. e. LH-RH. The tonic and/or cyclic regulation was located in the part of the brain anterior to the cut, probably in the septopreoptic-anterior hypothalamic areas. Residual secretion could be dueto the activity of the mediobasal areas,