Centre for Neuroendocrinology and Department of Anatomy, University of Otago, Dunedin, 9016, New Zealand.
Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI, 53210, USA.
J Chem Neuroanat. 2020 Jul;106:101786. doi: 10.1016/j.jchemneu.2020.101786. Epub 2020 Apr 9.
Seasonal reproduction is common across temperate zone avian species. In these species, physiological and behavioral adaptations have evolved to change according to day length (i.e., seasonally) in order to maximize reproductive output. The hormone prolactin regulates many aspects of parental care, a critical component of reproductive success. It's secretion in birds has been shown to be under photoperiodic control, with the highest levels measured in the spring and summer months, when birds breed and show parental care. However, to date, no study has tested whether the densities of central prolactin binding sites vary seasonally, which may also account for prolactin's effect on parental care. To test this, we collected brains from free-ranging adult male dark-eyed juncos, Junco hyemalis, a biparental songbird, in the spring, summer, and fall, and used quantitative in vitro autoradiography to compare the densities of specific prolactin binding sites across 20 different brain regions. Prolactin binding sites were found in regions that regulate parental behavior in other avian species. During the summer, several hypothalamic regions that regulate parental care, including the preoptic area and tuberal nucleus, contained lower densities of prolactin binding sites, suggesting exposure to higher endogenous prolactin levels, than at other times. This observation is consistent with the fact that circulating prolactin is highest during summer, when males would be providing care to young. Overall, these data suggest that prolactin binding sites are relatively conserved in the avian brain and that central prolactin activity supports parental care efforts in juncos and other avian species.
季节性繁殖在温带鸟类物种中很常见。在这些物种中，生理和行为适应已经进化，可以根据日照时间（即季节性）变化，以最大限度地提高繁殖产量。催乳素激素调节着许多亲代照顾的方面，这是繁殖成功的关键组成部分。已经表明，鸟类的催乳素分泌受到光周期的控制，在春季和夏季，鸟类繁殖并表现出亲代照顾时，测量到的催乳素水平最高。然而，迄今为止，没有研究测试过中央催乳素结合位点的密度是否会季节性变化，这也可能解释催乳素对亲代照顾的影响。为了测试这一点，我们从自由放养的成年雄性暗眼灯草雀（Junco hyemalis）的大脑中收集了大脑，这是一种双亲性鸣禽，分别在春季、夏季和秋季进行，并使用定量体外放射自显影技术比较了 20 个不同脑区中特定催乳素结合位点的密度。在其他鸟类中调节亲代行为的区域发现了催乳素结合位点。在夏季，调节亲代照顾的几个下丘脑区域，包括视前区和管状核，含有较低密度的催乳素结合位点，表明暴露于较高的内源性催乳素水平，而在其他时间则较低。这一观察结果与以下事实一致，即循环催乳素在夏季最高，此时雄性会为幼鸟提供照顾。总的来说，这些数据表明，催乳素结合位点在鸟类大脑中相对保守，中枢催乳素活性支持暗眼灯草雀和其他鸟类的亲代照顾努力。
