Female-soiled bedding induced Fos immunoreactivity in the ventral part of the premammillary nucleus (PMv) of the male mouse

Previous studies have indicated that the ventral part of the premammillary nucleus (PMv) of rodents is involved in the regulation of aggressive and ma le mating behavior, although the precise physiological function of the PMv is still unclear. To analyze the physiological role of the PMv in male mati ng behavior, the effects of exposure to bedding soiled by female mice on Fo s immunoreactivity (Fos-ir), an early marker of neuronal activation, were s tudied in the PMv and some sex-related nuclei. We observed that exposure to female-soiled bedding induced Fos-ir expression in the PMv of the male mou se. Although Fos-ir positive cells were found in the posterodorsal part of the medial amygdaloid nucleus and in the posteromedial cortical amygdaloid nucleus, which are terminals of the neuronal projections from the main and accessory olfactory bulbs, the numbers of Fos-ir cells in those nuclei were not affected by exposure to female-soiled bedding. Moreover, Fos-ir was no t detected in the ventromedial hypothalamic nucleus. It is well established that soiled bedding is useful as a source of chemosensory substances, whic h include "pheromones," Thus, our findings, in agreement with previous beha vioral and anatomical data, suggest that the PMv plays a role in initiating male copulative behavior that is induced by a female mice pheromone(s). (C ) 1999 Elsevier Science Inc. All rights reserved.