OLFACTORY CONTRIBUTION TO FOS EXPRESSION DURING MATING IN INEXPERIENCED MALE HAMSTERS

Male hamsters are very dependent on chemosensory cues for normal matin g behavior. We have previously reported that central vomeronasal pathw ays are intensely and selectively activated during mating or pheromona l 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 in fusion of zinc sulfate or remained intact. Fos protein immunoreactivit y was analyzed in main olfactory and vomeronasal pathways of the zinc sulfate-treated, anosmic animals after mating with receptive females f or 45 min, and compared with Fos patterns seen in intact mating animal s, some of which have been described in a previous publication. The zi nc sulfate-treated anosmic males described here all mated when given a ccess to receptive females. Whether mated or unstimulated, anosmic mal es had little or no Fos expression in main olfactory pathways; signifi cantly less even than in unstimulated intact animals. Mating did not i ncrease Fos expression in main olfactory pathways of intact animals ov er that of unstimulated intact controls. However. Fos expression in ce ntral vomeronasal pathways was significantly higher in mating anosmic males, as in intact males, compared with appropriate non-mating contro ls. Fos expression was significantly different between intact and zinc sulfate-treated anosmic mating males in only one area studied. The ro stral anterior medial amygdala, known to receive a small olfactory ter minal field, had significantly lower Fos expression in zinc sulfate-tr eated anosmic males that mated when compared with intact-mating animal s. Thus, functional main olfactory input to the rostral vomeronasal am ygdala can be demonstrated but does not appear to be critical for mati ng behavior in previously inexperienced male hamsters with intact vome ronasal organs. Other main olfactory input appears to have a negligibl e contribution to Fos-patterns in such animals.