Sexual dimorphisms in structure and physiology are widespread in the animal kingdom, including humans. Extreme examples of dimorphic secondary sexual characteristics arise from sexual selection where they are used as indicators of fitness of potential mates (e.g. tail feathers in peacocks and birds of paradise). Some sexual dimorphisms arise from intrasexual competition for resources, such as territory and mates, and include increased body size and weaponry (e.g. antlers) in males of many species. Other sexual dimorphisms are necessitated by sex differences in reproductive physiology, including genitalia, and mammary glands. Accompanying these obvious sexually dimorphic features, sex differences in the brain ensure the expression of maleor female-typical behaviors to maximize the fitness of each sex. The vast majority of sex differences in neuroanatomy, neurochemistry and neuronal structure and connectivity are established by the organizational influences of gonadal sex steroids or genes found on sex chromosomes. Sex differences in adult steroid hormone secretion also contribute to sex differences in the brain. Sex differences in the brain are likely more pervasive than many appreciate. A recent study reported that up to 2.5% of genes are differentially expressed or spliced in the brains of men and women (Trabzuni et al., 2013). Despite these sex differences, most biomedical research is carried out in only one sex, typically males, and therefore fails to identify many of the consequences of sex differences in brain in relation to disease (Beery and Zucker, 2011; McCarthy et al., 2012). Unfortunately there has been resistance in some circles to accept that sex differences in the human brain exist or have any biological relevance (Fine, 2010). This stance is somewhat puzzling given the vast documentation of brain sexual dimorphisms in animal models. It is highly unlikely that sexual dimorphisms in the brain disappeared in early hominids or more recent ancestors. Indeed there is a remarkable conservation in the genes that are differentially expressed between the sexes in humans and rhesus macaques (Reinius et al., 2008). Sex differences in several aspects of human behavior and cognition are commonly reported, but the extent that these differences arise from biology versus societal influences is rarely clear. Unfortunately the debate about sex differences in the human brain often takes on a political nature, as some believe that these differences may be used to imply superiority or inferiority of either gender for cognitive abilities, or to be an excuse for sex differences in less than complimentary behavior (Fine, 2010). However, we feel that sex differences in the brain should be embraced for enriching humanity, rather than being ignored for denigrating one sex or the other. Sex differences in the brain, where they exist, they are rarely absolute. They imply differences in means, often with considerable overlap between males and females. Nevertheless, it is critical to explore sexual dimorphisms in the brain for their impact and therapeutic implications for disease. This is particularly the case for many neurological and psychiatric diseases. As noted by one of the contributors of this issue, Thomas Insel, Director of the National Institute of Mental Health was quoted as saying ‘‘It’s pretty difficult to find any single factor that’s more predictive for (psychiatric) disorders than gender’’ (Davies, 2014). With that knowledge it is irresponsible to ignore sexual dimorphisms in the human brain, as insights from these differences may help us better understand the etiology of sex biased diseases and ultimately may lead to better therapeutic approaches. In this special issue we explore the sexually dimorphic nature of several psychiatric and neurological disorders with reviews of both preclinical animal studies and clinical data.

中文翻译：

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神经和精神疾病的性别差异

结构和生理上的性别二态性在动物界很普遍，包括人类。双态第二性征的极端例子来自性选择，它们被用作潜在配偶适合度的指标（例如孔雀和天堂鸟的尾羽）。一些性别二态性源于性内对资源（例如领土和配偶）的竞争，包括许多物种雄性的体型和武器（例如鹿角）的增加。其他性别二态性是生殖生理的性别差异所必需的，包括生殖器和乳腺。伴随着这些明显的性别二态性特征，大脑中的性别差异确保了男性或女性典型行为的表达，以最大限度地提高每个性别的适应度。神经解剖学、神经化学和神经元结构和连接方面的绝大多数性别差异是由性腺性类固醇或性染色体上发现的基因的组织影响建立的。成人类固醇激素分泌的性别差异也会导致大脑的性别差异。大脑中的性别差异可能比许多人想象的更普遍。最近的一项研究报告称，高达 2.5% 的基因在男性和女性的大脑中差异表达或剪接（Trabzuni 等，2013）。尽管存在这些性别差异，但大多数生物医学研究仅针对一种性别进行，通常是男性，因此无法确定大脑中性别差异与疾病相关的许多后果（Beery 和 Zucker，2011 年；McCarthy 等人，2012 年） ）。不幸的是，某些圈子一直拒绝接受人类大脑中存在性别差异或具有任何生物学相关性（Fine，2010）。鉴于动物模型中大脑性别二态性的大量文献，这种立场有些令人费解。在早期人类或更近代的祖先中，大脑中的性别二态性极不可能消失。事实上，人类和恒河猴性别差异表达的基因存在显着的保守性（Reinius 等，2008）。人类行为和认知的几个方面的性别差异通常被报道，但这些差异产生于生物学与社会影响的程度很少清楚。不幸的是，关于人脑性别差异的争论往往带有政治性质，因为有些人认为，这些差异可能被用来暗示任一性别在认知能力方面的优势或劣势，或者成为在不太互补的行为中性别差异的借口（Fine，2010）。然而，我们认为大脑中的性别差异应该被接受来丰富人类，而不是因为贬低一种性别而被忽视。大脑中存在的性别差异很少是绝对的。它们意味着手段上的差异，通常男性和女性之间有相当大的重叠。然而，探索大脑中的性别二态性对疾病的影响和治疗意义至关重要。许多神经和精神疾病尤其如此。正如本期撰稿人之一 Thomas Insel 所指出的，引用美国国家心理健康研究所所长的话说：“很难找到比性别更能预测（精神）疾病的单一因素”（戴维斯，2014 年）。有了这些知识，忽视人类大脑中的性别二态性是不负责任的，因为从这些差异中获得的见解可以帮助我们更好地了解性别偏见疾病的病因，并最终可能导致更好的治疗方法。在本期特刊中，我们通过对临床前动物研究和临床数据的回顾，探讨了几种精神和神经疾病的性别二态性。有了这些知识，忽视人类大脑中的性别二态性是不负责任的，因为从这些差异中获得的见解可以帮助我们更好地了解性别偏见疾病的病因，并最终可能导致更好的治疗方法。在本期特刊中，我们通过对临床前动物研究和临床数据的回顾，探讨了几种精神和神经疾病的性别二态性。有了这些知识，忽视人类大脑中的性别二态性是不负责任的，因为从这些差异中获得的见解可以帮助我们更好地了解性别偏见疾病的病因，并最终可能导致更好的治疗方法。在本期特刊中，我们通过对临床前动物研究和临床数据的回顾，探讨了几种精神和神经疾病的性别二态性。