Neural responses to pup calls and pup odors in California mouse fathers and virgin males.

The onset of mammalian maternal care is associated with plasticity in neural processing of infant-related sensory stimuli; however, little is known about sensory plasticity associated with fatherhood. We quantified behavioral and neural responses of virgin males and new fathers to olfactory and auditory stimuli from young, unfamiliar pups in the biparental California mouse (Peromyscus californicus). Each male was exposed for 10minutes to one of four combinations of a chemosensory stimulus (pup-scented or unscented cotton [control]) and an auditory stimulus (pup vocalizations or white noise [control]). Behavior did not differ between fathers and virgins during exposure to sensory stimuli or during the following hour; however, males in both groups were more active both during and after exposure to pup-related stimuli compared to control stimuli. Fathers had lower expression of Fos in the main olfactory bulbs (MOB) but higher expression in the medial preoptic area (MPOA) and bed nucleus of the stria terminalis medial division, ventral part (STMV) compared to virgins. Lastly, males had higher Fos expression in MPOA when exposed to pup odor compared to control stimuli, and when exposed to pup odor and pup calls compared to pup calls only or control stimuli. These findings suggest that the onset of fatherhood alters activity of MOB, MPOA and STMV and that pup odors and vocalizations have additive or synergistic effects on males' behavior and MPOA activation.