Reproductive response to photoperiod affects corticosterone and immunoglobulin G concentrations in prairie voles (Microtus ochrogaster)

Abstract

Nontropical rodent species display prominent breeding seasons mediated by photoperiod. Nonreproductive functions also exhibit seasonal changes; for example, fluctuations in adrenal activities may affect immune function and, ultimately, drive seasonal fluctuations in survival rates. The effects of photoperiod on adrenal and splenic masses and serum concentrations of corticosterone and immunoglobulin G (IgG) were evaluated in male prairie voles (Microtus ochrogaster). In one experiment, photoperiodic effects on adrenal and splenic masses and serum corticosterone and IgG levels were assessed in males that maintained "summer-like" reproductive systems after 8 weeks of short-day exposure. In a second experiment, the same parameters were examined in males in which testicular regression occurred after 8 weeks on short days. Voles that maintained reproductive organ size on short days failed to display other photoperiod-mediated differences in body, splenic, or adrenal masses or in serum corticosterone or IgG concentrations. In contrast, voles that underwent reproductive regression in response to short days decreased absolute adrenal mass and body mass compared with long-day animals, and also increased serum corticosterone concentrations and decreased IgG levels compared with their long-day counterparts. Taken together, these data indicate that reproductive responsiveness to day length may be linked to seasonal fluctuations in nonreproductive adaptations.