Immunocytochemistry of luteinizing hormone releasing hormone (LHRH) and gonadotropic hormones in the sheep after anterior deafferentations of the hypothalamus

Summary Using the immunoperoxidase method, the effect of the anterior deafferentations on the (1) LHRH-neuronal system in the hypothalamus and (2) gonadotropic cells in the adenohypophysis of the ewe were investigated. Two kinds of the anterior deafferentations were placed in the hypothalamus of cycling ewes. The first was performed at the level of caudal border of the chiasma opticum (CB deafferentation) and separated the medio-basal hypothalamus (MBH) from the anterior hypothalamic area (AHA). The second, was placed above the midline of the optic chiasma (MB deafferentation) and detached the AHA from the area praeoptica (AP). Estrous cycles and ovulation ceased in all CB-deafferentation. Immunocytochemical observations revealed a complete lack of LHRH-material both in the hypothalamic nuclei and in all parts of the median eminence (ME) and disappearance of LH-cells in the pituitary gland. In MB deafferented animals, only a diminished density of LHRH-material occurred in the rostral and central parts of the ME, but the ewes continued estrous cycles. Furthermore, numerous LHRH-axons and some LHRH-perikarya were visible in the regions of the AP and AHA. From these results the author is of the opinion, that in the ewe, principally AHA, but not MBH, retains the ability to produce LHRH. Difficulties in staining LHRH-perikarya suggest that in this species LHRH may be synthesized in an immunologically inactive (prohormonal) form.