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 o ther central structures shown to be important in mating behavior, incl uding the medial preoptic area (MPOA). In these experiments c-fos expr ession was used as a marker of neural activity to identify the contrib ution of vomeronasal sensory input during mating behavior in male gold en hamsters, either intact or with vomeronasal organs removed (VNX). I nexperienced hamsters were either stimulated with a receptive female a nd allowed to mate, exposed to female hamster vaginal fluid (HVF), whi ch 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 BN ST (pmBNST)] and a VN target area (MPOA). HVF-exposed animals showed F os expression in the AOB, Me, and BNST but not MPOA. Unstimulated anim als showed almost no activation. Most VNX animals exposed to females d id not mate, but performed intense chemoinvestigation. They had few Fo s-positive nuclei in any of these areas except the caudal pmBNST. A fe w VNX animals that did mate had patterns of Fos activation that were s imilar but less intense than those of intact mating animals, suggestin g a selective activation of VN central pathways during mating regardle ss of VN sensory input. The main olfactory system showed low levels of Fos expression in all animals (stimulated and unstimulated). Fos expr ession 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, regardles s of VN status or mating, suggesting that this region either directs o r responds to chemosensory investigation.