Behaviors are shaped by hormones, which may act either by changing brain circuits or by modifying sensory detection of relevant cues. Pup-directed behaviors have been previously shown to change via action of hormones at the brain level. Here, we investigated hormonal control of pup-induced activity in the vomeronasal organ, an olfactory sensory structure involved in the detection of non-volatile chemosignals. Vomeronasal activity decreases as males switch from a pup-aggressive state to a non-aggressive parenting state, after they socially contact a female. RNA sequencing, qPCR, and in situ hybridization were used to identify expression, in the vomeronasal sensory epithelium, of candidate GPCR hormone receptors chosen by in silico analyses and educated guesses. After identifying that oxytocin and vasopressin receptors are expressed in the vomeronasal organ, we injected the corresponding hormones in mice and showed that oxytocin administration reduced both pup-induced vomeronasal activity and aggressive behavior. Conversely, injection of an oxytocin receptor antagonist in female-primed male animals, which normally exhibit reduced vomeronasal activity, significantly increased the number of active vomeronasal neurons. These data link oxytocin to the modulation of olfactory sensory activity, providing a possible mechanism for changes in male behavior after social experience with females.

Male mice undergo a striking behavioral switch after sexual experience: virgin males are infanticidal, but after sexual contact with a female they change their behavior towards the young, becoming non-aggressive, parenting individuals. In this project, our goal was to investigate the changes in olfactory sensory activity that accompany these behavioral changes. We used immunostaining to measure the activity levels in sensory neurons of one of the olfactory organs in the nasal cavity of mice, known as the vomeronasal organ. This approach was performed in virgin male mice and in males after varying periods of sexual contact and cohabitation with a female. As a result, we were able to correlate the olfactory sensory activity with the behavior in the same animal groups, and it became clear that, as mice become progressively less agressive during the switch, the sensory activity decreases.