Department of Biology, Hofstra University, Hempstead, New York, USA.
Department of Biology, East Carolina University, Greenville, North Carolina, USA.
Genes Brain Behav. 2020 Sep;19(7):e12653. doi: 10.1111/gbb.12653. Epub 2020 Apr 1.
Prolactin is often referred to as the "parental hormone" but there are examples in which prolactin and parental behavior are disconnected. One intriguing example is in avian obligate brood parasites; species exhibiting high circulating prolactin but no parental care. To understand this disconnect, we examined transcriptional and behavioral responses to prolactin in brown-headed (Molothrus ater) and bronzed (M aeneus) brood parasitic cowbirds. We first examine prolactin-dependent regulation of transcriptome wide gene expression in the preoptic area (POA), a brain region associated with parental care across vertebrates. We next examined prolactin-dependent abundance of seven parental care-related candidate genes in hypothalamic regions that are prolactin-responsive in other avian species. We found no evidence of prolactin sensitivity in cowbirds in either case. To understand this prolactin insensitivity, we compared prolactin receptor transcript abundance between parasitic and nonparasitic species and between prolactin treated and untreated cowbirds. We observed significantly lower prolactin receptor transcript abundance in brown-headed but not bronzed cowbird POA compared with a nonparasite and no prolactin-dependent changes in either parasitic species. Finally, estrogen-primed female brown-headed cowbirds with or without prolactin treatment exhibited significantly greater avoidance of nestling begging stimuli compared with untreated birds. Taken together, our results suggest that modified prolactin receptor distributions in the POA and surrounding hypothalamic regions disconnect prolactin from parental care in brood parasitic cowbirds.
催乳素通常被称为“亲代激素”，但也有一些例子表明催乳素和亲代行为是脱节的。鸟类专性巢寄生的一个有趣的例子是，物种表现出高循环催乳素，但没有亲代照顾。为了理解这种脱节，我们研究了棕色（Molothrus ater）和青铜色（M aeneus）巢寄生牛鹂对催乳素的转录和行为反应。我们首先检查了催乳素依赖的转录组广泛基因表达的调节，在视前区（POA），一个与脊椎动物亲代照顾相关的大脑区域。接下来，我们研究了下丘脑区域中与亲代照顾相关的七个候选基因的催乳素依赖性丰度，这些区域在其他鸟类物种中对催乳素有反应。在这两种情况下，我们都没有发现牛鹂对催乳素敏感的证据。为了理解这种催乳素不敏感，我们比较了寄生和非寄生物种以及接受和未接受催乳素处理的牛鹂之间的催乳素受体转录丰度。我们观察到，与非寄生虫相比，棕色头牛鹂的视前区催乳素受体转录丰度显著降低，但青铜色牛鹂没有，两种寄生物种都没有催乳素依赖性变化。最后，用雌激素预处理的棕色头雌性牛鹂，无论是否接受催乳素处理，对雏鸟乞食刺激的回避程度明显高于未处理的鸟类。总之，我们的研究结果表明，POA 及其周围下丘脑区域中催乳素受体分布的改变使催乳素与巢寄生牛鹂的亲代照顾脱节。
