Meeting Abstract
Some seasonally-breeding animals exhibit equivalent or increased levels of aggressive behavior during the short-day (SD) photoperiods of the non-breeding season, despite gonadal regression and reduced circulating androgen levels. While the mechanisms underlying SD increases in territorial aggression are not well understood, previous work from our lab suggests that pineal melatonin (MEL) and the adrenal androgen dehydroepiandrosterone (DHEA) are important in facilitating non-breeding aggression in Siberian hamsters (Phodopus sungorus). To characterize the role of melatonin (MEL) in modulating seasonal transitions in aggressive behavior, we housed male hamsters in long days (LD) or SD, treated them with either timed MEL or saline injections, and quantified aggression after 3, 6, and 9 weeks of photoperiodic housing. Furthermore, to assess whether MEL mediates seasonal shifts in gonadal and adrenal androgen synthesis, serum testosterone (T) and DHEA concentrations were quantified 36 h before and immediately following an aggressive encounter. LD hamsters administered MEL (LD-M) exhibited intermediate levels of aggression and basal T levels relative to LD and SD animals, and aggressive encounters reduced serum DHEA levels, yet increased serum T levels. Interestingly, LD and SD hamsters exhibited distinct relationships between circulating androgen profiles and aggressive behavior, in which changes in serum T following an aggressive encounter (∆T) were negatively correlated with aggression in LD and LD-M animals, while ∆DHEA was positively associated with aggression in SD animals. Collectively, these findings suggest that SD hamsters transition from synthesis to metabolism of circulating androgens following an aggressive encounter, a mechanism that is likely modulated by MEL.
