Vomeronasal neuroepithelium and forebrain Fos responses to male pheromonesin male and female mice

Male urinary pheromones modulate behavioral and neuroendocrine function in mice after being detected by sensory neurons in the vomeronasal organ (VNO) neuroepithelium. We used nuclear Fos protein immunoreactivity (Fos-IR) as a marker of changes in neuronal activity to examine the processing of male pheromones throughout the VNO projection pathway to the hypothalamus. Sexua lly naive male and female Balb/c mice were gonadectomized and treated daily with estradiol benzoate (EB) or oil vehicle for 3 weeks, Subjects were the n exposed to soiled bedding from gonadally intact Balb/c males or to clean bedding for 90 min prior to sacrifice and processing of their VNOs and fore brains for Fos-IR, Male pheromones induced similar numbers of Fos-IR cells in the VNO neuroepithelium of oil-treated male and female subjects; however , EB-treated females had significantly more Fos-IR neurons in the VNO than any other group. There was an equivalent neuronal Fos response to male odor s in the mitral and granule cells of the anterior and posterior accessory o lfactory bulb of males and females, regardless of hormone treatment. In cen tral portions of the VNO projection pathway (i,e,, bed nucleus of the stria terminalis, medial preoptic area) neuronal Fos responses to male pheromone s were present in female but absent in male subjects, regardless of hormone treatment. In a separate experiment, mating induced neuronal Fos-IR in the se brain regions at levels in gonadally intact male subjects which were equ al to or greater than those seen in ovariectomized females primed with estr ogen and progesterone. This suggests that neurons in the central portions o f the male's VNO pathway are capable of expressing Fos, Our results suggest that sexually dimorphic central responses to pheromones exist in mice that may begin in the VNO neuroepithelium, (C) 1999 John Wiley & Sons, Inc.