Photoperiod affects estrogen receptor a, estrogen receptor b and aggressive behavior

Estrogens have important effects on male and female social behavior. Despite growing knowledge of the anatomy and behavioral effects of the two predominant estrogen receptor subtypes in mammals (ERa and ERb), relatively little is known about how these receptors respond to salient environmental stimuli. Many seasonally breeding species respond to changing photoperiods that predict seasonal changes in resource availability. We characterized the effects of photoperiod on aggressive behavior in two species of Peromyscus that exhibit gonadal regression in short days. P. polionotus (old field mice) were more aggressive than P. maniculatus (deer mice) and both species were more aggressive in short days. We used immunocytochemistry and real-time polymerase chain reaction to characterize the effects of photoperiod on ERa and ERb expression. In both species ERa-immunoreactive staining in the posterior bed nucleus of the stria terminalis (BNST) was increased in short vs. long days. Both species had reduced ERb-immunoreactive expression in the posterior BNST in short days. In the medial amygdala ERb immunoreactivity was increased in long days for both species. Using real-time polymerase chain reaction on punch samples that included the BNST, we observed that ERa mRNA was increased and ERb mRNA was decreased in short days. These data suggest that the effects of photoperiod on ERa and ERb expression may thus have important behavioral consequences.