Specific expression pattern of Fos in the accessory olfactory bulb of male mice after exposure to soiled bedding of females.

The heterogeneous structure of the accessory olfactory bulb (AOB) has been demonstrated immunocytochemically. In this study, we analyzed the expression of an immediate-early gene protein, c-Fos, as a marker of neuronal activity in response to chemosensory cues was analyzed. The number of c-Fos-immunoreactive (Fos-ir) cells was measured in the rostral and caudal zones of the AOB in male ICR mice after exposure to the soiled bedding of female mice. The results revealed no significant difference in the number of Fos-ir cells in the caudal zone of the AOB between exposure to the soiled bedding of female ICR mice (ICR group) and exposure to that of female Balb mice (Balb group). In the rostral zone, however, the number of Fos-ir cells in the glomerular layer and granule cell layer was larger in the ICR group than in the Balb group. The difference in the expression of c-Fos in response to different pheromonal stimuli between the rostral and caudal zones in the mouse AOB has been shown for the first time in this study. These results strongly suggest that the heterogeneous structure of the AOB has an important role in the perception and processing of pheromones.