Variation in Aromatase Activity in the Medial Preoptic Area and Plasma Progesterone Is Associated with the Onset of Paternal Behavior

Abstract

The effects of aromatase within the brain on sexual behavior have been studied in a wide variety of species. Relatively few non-mating behaviors have been considered, despite evidence that estrogen affects many social behaviors. Testosterone promotes paternal behavior in California mouse (Peromyscus californicus) fathers, acting primarily via aromatization to estradiol. Virgin male California mice rarely exhibit paternal behavior, so we investigated whether aromatase in the brain changed with the onset of paternal behavior in California mouse fathers. In the medial preoptic area (MPOA), a brain area known to regulate parental behavior in rodents, we found that fathers had significantly more aromatase activity than mated males without pups, suggesting that an increase in estrogen production in this brain area contributes to the onset of paternal behavior. We also found that progesterone (P₄) levels were lower in fathers compared to sexually inexperienced males and that P₄ was negatively correlated with aromatase activity in the MPOA. These P₄ findings agree with a recent study that found an inhibitory effect of P₄ on paternal behavior. Overall, we found that aromatase activity and P₄ levels change in association with an important life history transition, and may provide a mechanistic basis for plasticity in paternal behavior.

Social environment modulates photoperiodic immune and reproductive responses in adult male white-footed mice(Peromyscus leucopus)

“…These data support previous findings that the presence of a female cagemate increases initial testosterone concentrations (1 h to 2 wk after cohabitation with a female) in Mus musculus and P. californicus (22,33). Suppression of reproductive parameters, on the other hand, by male-male pairings was evident in the present study but only statistically significant for testosterone concentrations of LD mice.…”

Social and photoperiod effects on reproduction in five species of Peromyscus

“…This raises a related hypothesis that species differences in T responses reflect motivation to mate (Macrides et al, 1975), and that after mating occurs, T subsides. In biparental P. californicus T increases 2 weeks after initial pairings and decreases 2 weeks after the birth of pups and post-partum estrus (Trainor et al, 2003). A similar pattern occurs in biparental Phodopus campbelli, T gradually increases prior to and including post-partum estrus and subsequently declines (Reburn and Wynne-Edward, 1999).…”

Non-genomic transmission of paternal behaviour between fathers and sons in the monogamous and biparental California mouse

“…California mouse fathers have significantly more aromatase activity in the MPOA compared with mated non-fathers, indicating that with fatherhood comes a regional increase in conversion of T to E2. Thus, the actions of E2 in the MPOA are also important for parental behaviour [26]. Future studies will need to examine whether epigenetic modifications to ER expression underlie transmission of HG behaviour across generations, as is the case for maternal behaviour.…”