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：

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褪黑素介导了西伯利亚雄性仓鼠侵略行为和雄激素循环的季节性转变。

尽管性腺退化和雄激素水平降低，一些季节性繁殖的动物在非繁殖季节的短暂的“冬季样”日（SD）期间更具攻击性。尽管对SD侵略性增加的潜在机制尚不十分了解，但我们实验室的先前工作表明，松果褪黑激素（MEL）和肾上腺雄激素脱氢表雄酮（DHEA）在促进西伯利亚仓鼠（Phodopus sungorus）的非繁殖侵袭中很重要。为了表征MEL在调节侵略性行为的季节性转变中的作用，我们在长日（LD）或SD中收容雄性仓鼠，并定时注射MEL（M）或生理盐水对其进行处理，并在3、6和9周后测量侵略。此外，为了评估MEL是否介导了性腺和肾上腺雄激素合成的季节性变化，在侵略性接触之前和之后的36 h，对血清睾酮（T）和DHEA浓度进行定量。LD-M和SD男性对治疗表现出相似的生理和行为反应。具体而言，LD-M和SD雄性都表现出比LD雄性更高的侵略性，并且由于有攻击性遭遇，循环DHEA和T降低，而LD雄性则升高了循环雄激素。有趣的是，LD和SD男性表现出循环雄激素与攻击行为之间的独特关系，其中攻击性相互作用（∆T）后血清T的变化与LD男性的攻击性呈负相关，而∆DHEA与SD男性的攻击性呈正相关。 。总的来说，