Influence of male rats on the luteinizing hormone-releasing hormone neuronal system in female rats: role of the vomeronasal organ.

Olfactory information processed by the vomeronasal system is reported to influence reproductive functions in a variety of mammals. The present studies were designed to determine if male-associated cues affect the luteinizing hormone-releasing hormone (LHRH) neuronal system, and, if so, to determine the extent to which these cues are processed by the vomeronasal organ (VNO). Ovariectomized rats underwent VNO removal (VNX) or sham surgery (VN-Sham). Forty-eight hours after estrogen priming (5 micrograms), they were subjected to one of the following treatments: repeated mating, repeated exposure to male-soiled bedding or repeated exposure to clean bedding. In animals treated for 180 min, coronal brain sections were double labelled for Fos protein and LHRH. An intense Fos immunoreactivity was induced following mating in the majority of LHRH neurons in the VN-Sham females, whereas removal of the VNO significantly suppressed the mating-induced Fos staining. Exposure of female rats to male-soiled bedding or clean bedding did not induce appreciable Fos immunoreactivity in LHRH neurons. Following 90 min of mating or exposure to bedding, blood samples were assayed for luteinizing hormone (LH). Mating stimulated the release of LH in VN-Sham females, while the removal of the VNO significantly suppressed the mating-induced LH release. Exposure of the females to male-soiled bedding or clean bedding did not induce an LH surge. The present results demonstrate that male-originating sensory cues (i.e. repeated mating) can influence the LHRH neuronal system, as evidenced by the presence of Fos immunoreactivity in LHRH cell bodies, and indicate that this effect is mediated through the VNO to a certain extent.(ABSTRACT TRUNCATED AT 250 WORDS)