Olfactory contribution to Fos expression during mating in inexperienced male hamsters.

Male hamsters are very dependent on chemosensory cues for normal mating behavior. We have previously reported that central, vomeronasal pathways are intensely and selectively activated during mating or pheromonal stimulation. The contribution of main olfactory sensory input to the patterns of c-fos activation was investigated in this study. Sexually inexperienced male hamsters were either made anosmic by intranasal infusion of zinc sulfate or remained intact. Fos protein immunoreactivity was analyzed in main olfactory and vomeronasal pathways of the zinc sulfate-treated, anosmic animals after mating with receptive females for 45 min, and compared with Fos patterns seen in intact mating animals, some of which have been described in a previous publication. The zinc sulfate-treated anosmic males described here all mated when given access to receptive females. Whether mated or unstimulated, anosmic males had little or no Fos expression in main olfactory pathways; significantly less even than in unstimulated intact animals. Mating did not increase Fos expression in main olfactory pathways of intact animals over that of unstimulated intact controls. However, Fos expression in central vomeronasal pathways was significantly higher in mating anosmic males, as in intact males, compared with appropriate non-mating controls. Fos expression was significantly different between intact and zinc sulfate-treated anosmic mating males in only one area studied. The rostral anterior medial amygdala, known to receive a small olfactory terminal field, had significantly lower Fos expression in zinc sulfate-treated anosmic males that mated when compared with intact-mating animals. Thus, functional main olfactory input to the rostral vomeronasal amygdala can be demonstrated but does not appear to be critical for mating behavior in previously inexperienced male hamsters with intact vomeronasal organs. Other main olfactory input appears to have a negligible contribution to Fos-patterns in such animals.

Facilitation of mating behavior in male hamsters by LHRH and AcLHRH5-10: interaction with the vomeronasal system.

An intact vomeronasal organ is important for the reproductive physiology and behavior of many species. Vomeronasal sensory input is known to influence hormone levels especially LH, presumably by prior modulation of LHRH. LHRH has been shown independently to facilitate mating behavior in rodents of both sexes. In this study intracerebroventricular LHRH at a dose of 50 ng substantially relieved mating behavior deficits caused by prepubertal removal of vomeronasal organs from inexperienced male hamsters. Intranasal LHRH at a higher dose did not have this effect. Behavioral responses were recorded 30 mins after peptide or saline injection. The LHRH analog, AcLHRH5-10 which we demonstrate does not induce LH release, did facilitate mating behavior in these tests, suggesting that LHRH peptides may facilitate male mating behavior via an extra-pituitary mode of action.

c-fos expression in vomeronasal pathways of mated or pheromone-stimulated male golden hamsters: contributions from vomeronasal sensory input and expression related to mating performance.

The vomeronasal system projects to the accessory olfactory bulb (AOB), to the medial (Me) and posterior medial cortical nuclei (PMCN) of the amygdala, to the bed nucleus of the stria terminalis (BNST), and to other central structures shown to be important in mating behavior, including the medial preoptic area (MPOA). In these experiments c-fos expression was used as a marker of neural activity to identify the contribution of vomeronasal sensory input during mating behavior in male golden hamsters, either intact or with vomeronasal organs removed (VNX). Inexperienced hamsters were either stimulated with a receptive female and allowed to mate, exposed to female hamster vaginal fluid (HVF), which contains stimuli known to act through the VN system, or placed in a clean cage alone. Densely stained Fos-positive nuclei were evident in mated animals in the central VN pathway [AOB, Me, posterior medial BNST (pmBNST)] and a VN target area (MPOA). HVF-exposed animals showed Fos expression in the AOB, Me, and BNST but not MPOA. Unstimulated animals showed almost no activation. Most VNX animals exposed to females did not mate, but performed intense chemoinvestigation. They had few Fos-positive nuclei in any of these areas except the caudal pmBNST. A few VNX animals that did mate had patterns of Fos activation that were similar but less intense than those of intact mating animals, suggesting a selective activation of VN central pathways during mating regardless of VN sensory input. The main olfactory system showed low levels of Fos expression in all animals (stimulated and unstimulated). Fos expression in the MPOA and rostral pmBNST was seen only in mated animals, suggesting that these regions are concerned with mating performance or its consequences, rather than the chemosensory input that triggers it. Fos expression in the caudal encapsulated pmBNST was evident in all groups of animals that performed chemosensory investigation, regardless of VN status or mating, suggesting that this region either directs or responds to chemosensory investigation.