UC Riverside

The mechanistic basis of paternal behavior in mammals is poorly understood. Assuming there are parallels between the factors mediating maternal and paternal behavior, it can be expected that the onset of paternal behavior is facilitated by reductions in stress responsiveness, as occurs in females of several mammalian species. This dissertation describes studies investigating the role of stress responsiveness in the expression of paternal behavior in biparental, monogamous California mice (Peromyscus californicus). I compared endocrine, neural, and behavioral responses to stress, as well as anxiety and neophobia, in males from different housing conditions, and between males that did or did not respond paternally to an unfamiliar pup. Results from the first study suggested that fatherhood attenuates behavioral responses, but does not influence corticosterone responses, to an acute predator-urine stressor. Cohabitation with a female mate, however, tended to reduce corticosterone responses to repeated predator-urine exposure. I next characterized neophobia, anxiety, and neuroendocrine responses to acute predator-urine exposure. Results indicated that being a father did not modulate neophobia, but did appear to be associated with reduced anxiety. Paternally responsive males exhibited more anxiety-related behavior than nonpaternally responsive males, but did not differ in levels of neophobia. Social isolation, but not fatherhood, modulated the neuroendocrine response to stress exposure, while no effect of paternal responsiveness was found. Finally, to determine whether fathers and nonfathers, or paternally responsive and nonpaternally responsive males, differentially perceive pups as stressful, I compared neural responses to 1-h exposure to a pup. No effect of fatherhood was found; however, paternally responsive virgin males showed lower Fos expression in the paraventricular nucleus of the hypothalamus and bed nucleus of the stria terminalis compared to nonpaternally responsive virgins. My findings suggest that fathers in this biparental species do not exhibit reductions in stress responsiveness similar to those in lactating females of several species. Nonetheless, paternally responsive males show reduced activation of stress-related brain areas in response to pup exposure, as well as altered patterns of neophobia and anxiety-related behavior, as compared to nonpaternally responsive males. These findings will further the understanding of the mechanistic basis of paternal behavior in mammals.