Department of Biology and Center for the Integrative Study of Animal Behavior, Indiana University, Bloomington, IN, USA.
Department of Neuroscience, University of Minnesota Twin Cities, Minneapolis, MN, USA.
J Neuroendocrinol. 2020 Aug;32(8):e12894. doi: 10.1111/jne.12894. Epub 2020 Aug 18.
Many animal species exhibit year-round aggression, a behaviour that allows individuals to compete for limited resources in their environment (eg, food and mates). Interestingly, this high degree of territoriality persists during the non-breeding season, despite low levels of circulating gonadal steroids (ie, testosterone [T] and oestradiol [E ]). Our previous work suggests that the pineal hormone melatonin mediates a 'seasonal switch' from gonadal to adrenal regulation of aggression in Siberian hamsters (Phodopus sungorus); solitary, seasonally breeding mammals that display increased aggression during the short, 'winter-like' days (SDs) of the non-breeding season. To test the hypothesis that melatonin elevates non-breeding aggression by increasing circulating and neural steroid metabolism, we housed female hamsters in long days (LDs) or SDs, administered them timed or mis-timed melatonin injections (mimic or do not mimic a SD-like signal, respectively), and measured aggression, circulating hormone profiles and aromatase (ARO) immunoreactivity in brain regions associated with aggressive or reproductive behaviours (paraventricular hypothalamic nucleus [PVN], periaqueductal gray [PAG] and ventral tegmental area [VTA]). Females that were responsive to SD photoperiods (SD-R) and LD females given timed melatonin injections (Mel-T) exhibited gonadal regression and reduced circulating E , but increased aggression and circulating dehydroepiandrosterone (DHEA). Furthermore, aggressive challenges differentially altered circulating hormone profiles across seasonal phenotypes; reproductively inactive females (ie, SD-R and Mel-T females) reduced circulating DHEA and T, but increased E after an aggressive interaction, whereas reproductively active females (ie, LD females, SD non-responder females and LD females given mis-timed melatonin injections) solely increased circulating E . Although no differences in neural ARO abundance were observed, LD and SD-R females showed distinct associations between ARO cell density and aggressive behaviour in the PVN, PAG and VTA. Taken together, these results suggest that melatonin increases non-breeding aggression by elevating circulating steroid metabolism after an aggressive encounter and by regulating behaviourally relevant neural circuits in a region-specific manner.
许多动物物种表现出全年的攻击性，这种行为使个体能够在其环境中竞争有限的资源（例如食物和伴侣）。有趣的是，尽管循环性腺类固醇（即睾酮[T]和雌二醇[E]）水平较低，但这种高度的领地性在非繁殖季节仍然存在。我们之前的工作表明，松果腺激素褪黑素介导了从性腺到肾上腺调节西伯利亚仓鼠（Phodopus sungorus）攻击性的“季节性转变”；这些是独居的、季节性繁殖的哺乳动物，在非繁殖季节的短“冬季样”日子（SD）中表现出更高的攻击性。为了检验褪黑素通过增加循环和神经类固醇代谢来提高非繁殖季节攻击性的假设，我们将雌性仓鼠饲养在长日（LDs）或 SD 中，给予它们定时或错误定时的褪黑素注射（分别模拟或不模拟 SD 样信号），并测量攻击性、循环激素谱和与攻击性或生殖行为相关的脑区中的芳香酶（ARO）免疫反应性（室旁下丘脑核[PVN]、导水管周围灰质[PAG]和腹侧被盖区[VTA]）。对 SD 光周期有反应的雌性（SD-R）和接受定时褪黑素注射的 LD 雌性（Mel-T）表现出性腺退化和循环 E 减少，但攻击性和循环脱氢表雄酮（DHEA）增加。此外，攻击性挑战在季节性表型中以不同的方式改变了循环激素谱；生殖不活跃的雌性（即 SD-R 和 Mel-T 雌性）在攻击性相互作用后减少了循环 DHEA 和 T，但增加了 E，而生殖活跃的雌性（即 LD 雌性、SD 无反应的雌性和接受错误定时褪黑素注射的 LD 雌性）仅增加了循环 E 。虽然没有观察到神经 ARO 丰度的差异，但 LD 和 SD-R 雌性在 PVN、PAG 和 VTA 中显示出 ARO 细胞密度与攻击性行为之间的独特关联。总的来说，这些结果表明，褪黑素通过在攻击性遭遇后提高循环类固醇代谢，以及通过特定区域的方式调节与行为相关的神经回路，来增加非繁殖季节的攻击性。
