Kramer Kristin M, Simmons Jennifer L, Freeman David A
Department of Biology, University of Memphis, Memphis, TN 38152, USA.
Horm Behav. 2008 Feb;53(2):358-65. doi: 10.1016/j.yhbeh.2007.11.002. Epub 2007 Nov 19.
Testosterone or its metabolite, estrogen, regulates aggression in males of many mammalian species. Because plasma testosterone levels are typically positively correlated with both aggression and reproduction, aggression is expected to be higher when males are in reproductive condition. However, in some photoperiodic species such as Siberian hamsters (Phodopus sungorus), males are significantly more aggressive in short day lengths when the testes are regressed and circulating testosterone concentrations are reduced. These results led to the formation of the hypothesis that aggression is modulated independently of circulating steroids in Siberian hamsters. Thus, recent studies have been designed to characterize the role of other neuroendocrine factors in modulating aggression. However, aggression may be mediated by testosterone or estrogen despite basal concentrations of these steroids by increasing sensitivity to steroids in specific brain regions. Consistent with this hypothesis, we found that males housed under short days have increased expression of estrogen receptor alpha in the bed nucleus of the stria terminalis, medial amygdala, and central amygdala. Neural activation in response to an aggressive encounter was also examined across photoperiod.
睾酮或其代谢产物雌激素调节着许多哺乳动物雄性个体的攻击性。由于血浆睾酮水平通常与攻击性和繁殖都呈正相关，所以当雄性处于繁殖状态时，预计其攻击性会更高。然而，在一些光周期物种，如西伯利亚仓鼠（Phodopus sungorus）中，当睾丸退化且循环睾酮浓度降低时，雄性在短日照条件下的攻击性会显著增强。这些结果导致了这样一种假说的形成，即西伯利亚仓鼠的攻击性是独立于循环类固醇进行调节的。因此，最近的研究旨在确定其他神经内分泌因素在调节攻击性方面的作用。然而，尽管这些类固醇的基础浓度较低，但攻击性可能通过增加特定脑区对类固醇的敏感性而由睾酮或雌激素介导。与这一假说一致，我们发现处于短日照条件下饲养的雄性个体，其终纹床核、内侧杏仁核和中央杏仁核中的雌激素受体α表达增加。我们还研究了在不同光周期下，雄性个体对攻击性遭遇的神经激活情况。
