Pattern of fos activation in the ventral tegmental area (VTA) of male prairie vole's (Microtus ochrogaster) in response to infant-related stimuli.

Prairie voles are socially monogamous mammals that form pair bonds and display paternal care. This study was focused on the male prairie vole's neuronal responses to infant-related odors. Using the fos protein as a measure of neuronal activation, we examined the brain responses of males to infant-related odors. Prior to testing, the subjects had cohabited for two weeks with either a male sibling (Male-Cohabited) or an unrelated female (Female-Cohabited). Given that paternal behavior of male prairie voles is enhanced after two-weeks of cohabitation with a mate, we hypothesized that fos activation in brain regions involved in caring must be increased in response to infants or their odors but not in response to water or sub-adult odors. To test this hypothesis, we analyzed the pattern of fos expression in the ventral tegmental area (VTA) and the bed nucleus of the stria terminals (BNST) two hours after Male-Cohabited and Female-Cohabited males were exposed to either two live infants or to odors of infants, sub-adults or water. Results showed differences in fos expression within the VTA between Male-Cohabited and Female-Cohabited subjects that were exposed to infants and infant odors. The type of cohabitation had no effect on fos expression within the BNST, but the pattern of fos activation in this region differed by the type of odor to which the subjects were exposed. Together, the data indicate that female sensory cues during post-mating cohabitation may be processed within the VTA to direct the male prairie vole's responses towards infants.