Sex differences in hormonal responses to social conflict in the monogamous California mouse

Abstract

Monogamous species are usually considered to be less likely to exhibit sex differences in behavior or brain structure. Most previous studies examining sex differences in stress hormone responses have used relatively sexually dimorphic species such as rats. We examined the stress hormone responses of monogamous California mice (Peromyscus californicus) to resident-intruder tests. We also tested males and females under different photoperiods, because photoperiod has been shown to affect both aggression and stress hormone responses. Females, but not males showed a significant increase in corticosterone levels immediately following a resident-intruder test. Males but not females showed elevated corticosterone levels under short days. Females tested in aggression tests also showed a significant increase in plasma oxytocin levels, but only when housed in long days. This was consistent with our observation that females but not males had more oxytocin positive cells in the paraventricular nucleus (PVN) when housed under long days. Our data show that sex differences in glucocorticoid responses identified in other rodents are present in a monogamous species.

Effects of reproductive status on behavioral and endocrine responses to acute stress in a biparental rodent, the California mouse (Peromyscus californicus)

“…Baseline CORT concentrations in California mice in this study were considerably lower than those in other studies of the same species (Glasper and Devries, 2005; Oyegbile and Marler, 2006; Trainor et al, 2010). Differences in methodology might explain this disparity.…”

“…Without this information, it is difficult to compare baseline CORT measures in the two studies. Predictably high baseline CORT levels were found by Oyegbile and Marler (2006) and Trainor et al (2010) shortly after lights out, corresponding to the rise in CORT around the time of waking in nocturnal rodent species (Dallman et al, 1993; Malisch et al, 2008; unpub. data).…”

Short photoperiod condition increases susceptibility to stress in adolescent male rats

“…The 3-week exposure to the short photoperiod condition alone was not sufficiently strong to induce anhedonia-like behavior, but it blunted the diurnal rhythmicity of CORT and significantly elevated plasma CORT levels, which is consistent with previous studies [14,31,32]. The plasma levels of both melatonin and NPY retained diurnal rhythmicity under the short photoperiod condition, although the peak phase of melatonin exhibited a phase inversion, and the peak phase of NPY was delayed.…”

Environmental Health Factors and Sexually Dimorphic Differences in Behavioral Disruptions

“…Acute responses of the HPA axis are more sensitive to social conflict in females than in males. Females show a significant increase in corticosterone following a resident–intruder test, and this increase is observed in both residents (winners [142]) and intruders (losers [143]). In contrast, neither male residents nor intruders show an increase in corticosterone.…”