Some seasonally-breeding animals are more aggressive during the short, "winter-like" days (SD) of the non-breeding season, despite gonadal regression and reduced circulating androgen levels. While the mechanisms underlying SD increases in 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 MEL in modulating seasonal transitions in aggressive behavior, we housed male hamsters in long days (LD) or SD, treated them with timed MEL (M) or saline injections, and measured aggression after 3, 6, and 9 weeks. 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-M and SD males exhibited similar physiological and behavioral responses to treatment. Specifically, both LD-M and SD males displayed higher levels of aggression than LD males and reduced circulating DHEA and T in response to an aggressive encounter, whereas LD males elevated circulating androgens. Interestingly, LD and SD males exhibited distinct relationships between circulating androgens and aggressive behavior, in which changes in serum T following an aggressive interaction (∆T) were negatively correlated with aggression in LD males, while ∆DHEA was positively correlated with aggression in SD males. Collectively, these findings suggest that SD males transition from synthesis to metabolism of circulating androgens following an aggressive encounter, a mechanism that is modulated by MEL.

中文翻译：

---

褪黑激素介导雄性西伯利亚仓鼠攻击行为和循环雄激素分布的季节性转变。


尽管性腺退化和循环雄激素水平降低，一些季节性繁殖的动物在非繁殖季节短暂的“类似冬天”的日子（SD）中更具攻击性。虽然SD增加攻击性的机制尚不清楚，但我们实验室之前的研究表明，松果体褪黑激素（MEL）和肾上腺雄激素脱氢表雄酮（DHEA）对于促进西伯利亚仓鼠（Phodopus sungorus）的非繁殖攻击性非常重要。为了表征 MEL 在调节攻击性行为季节变化中的作用，我们将雄性仓鼠圈养在长日照 (LD) 或 SD 中，对它们进行定时 MEL (M) 或盐水注射，并在 3、6 和 9 周后测量攻击性。此外，为了评估 MEL 是否介导性腺和肾上腺雄激素合成的季节性变化，在攻击前 36 小时和攻击后立即对血清睾酮 (T) 和 DHEA 浓度进行了定量。 LD-M 和 SD 男性对治疗表现出相似的生理和行为反应。具体来说，LD-M 和 SD 雄性都比 LD 雄性表现出更高水平的攻击性，并且在应对攻击性遭遇时减少了循环 DHEA 和 T，而 LD 雄性则升高了循环雄激素。有趣的是，LD和SD雄性在循环雄激素和攻击行为之间表现出明显的关系，其中攻击性相互作用后血清T的变化（ΔT）与LD雄性的攻击性呈负相关，而ΔDHEA与SD雄性的攻击性呈正相关。总的来说，这些发现表明，SD 雄性在遭遇攻击性遭遇后，循环雄激素从合成转变为代谢，这是一种受 MEL 调节的机制。