MATING AND AGONISTIC BEHAVIOR PRODUCE DIFFERENT PATTERNS OF FOS IMMUNOLABELING IN THE MALE SYRIAN-HAMSTER BRAIN

Previous work has shown that mating induces the expression of Fos prot ein within the chemosensory pathways of the male Syrian hamster brain. (37) However, it is not known if this pattern of labeling is specific to mating or the result of social interactions in general. To determin e the behavioral specificity of activation within these pathways, Fos immunostaining following mating was compared to that following agonist ic behavior. Both mating and agonistic behavior are dependent upon che mosensory cues(15,52,72) and gonadal steroids (reviewed in Refs 64, 65 ) and areas belonging to the olfactory and vomeronasal pathways proces s chemosensory and hormonal information (reviewed in Ref. 48). The res ults of this study demonstrate both similarities and differences in br ain activation patterns following these two social behaviors. Agonisti c behavior increased the number of Fos-immunoreactive neurons within m ost subdivisions of the medial amygdala, the anteromedial and posteroi ntermediate bed nucleus of the stria terminalis, the ventrolateral sep tum and the ventral premammillary nucleus of the hypothalamus in a pat tern comparable to that observed after mating. This pattern of activat ion common to mating and agonistic behavior may reflect an increase in an animal's general state of arousal during social interactions. In c ontrast, although mating and agonistic behavior both activated neurons within the caudal subdivision of the medial nucleus of the amygdala, the anterodorsal level of posteromedial bed nucleus of the stria termi nalis and the paraventricular and ventromedial nuclei of the hypothala mus, in these areas either the distribution and/or number of Fos-immun oreactive neurons differed. In addition, agonistic behavior selectivel y activated neurons within the anterolateral bed nucleus of the stria terminalis, the anterior nucleus of the hypothalamus and the dorsal pe riaqueductal gray, whereas mating alone activated neurons within the p osteroventral level of posteromedial bed nucleus of the stria terminal is and the medial preoptic area. No differences were found between dom inant and subordinate males following agonistic behavior. These observ ations along with results from other laboratories suggest that mating and agonistic behavior activate distinct neural circuits.