Lynn Sharon E, Perfito Nicole, Guardado Daisy, Bentley George E
Department of Biology, The College of Wooster, 931 College Mall, Wooster, OH 44619, United States.
Department of Integrative Biology, The University of California, Berkeley, 3060 Valley Life Sciences Building, Berkeley, CA 94720, United States.
Gen Comp Endocrinol. 2015 May 1;215:1-9. doi: 10.1016/j.ygcen.2015.03.010. Epub 2015 Apr 4.
Food abundance is closely associated with reproductive readiness in vertebrates. Food scarcity can activate the hypothalamo-pituitary-adrenal axis, decrease sex steroid secretion, and dampen reproductive behavior. However, the mechanisms underlying these transient effects are unclear. Gonadotropin inhibitory hormone (GnIH), a neuropeptide present in the brain and gonads, is also influenced by glucocorticoids and fasting in some species. We investigated whether fasting stress activated the GnIH system in zebra finches (Taeniopygia guttata), with the potential for downstream effects on reproductive physiology and behavior. We fasted or fed males ad libitum for 10h. Fasting increased corticosterone and decreased testosterone in circulation. To assess whether the decrease in testosterone was mediated by changes in the hypothalamus and/or the gonads, we (1) quantified GnRH- and GnIH-positive neurons in the hypothalamus, (2) assessed hypothalamic gene expression for GnRH and GnIH, and (3) examined gene expression for proteins involved in testosterone synthesis in fasted and control birds. No measure of hypothalamic neuropeptides was related to treatment or circulating steroids. However, birds with higher corticosterone had higher testicular GnIH expression and lower testosterone. StAR and LHR expression were lower in the testes of fasted birds than controls. Thus, the decrease in testosterone was not likely mediated by hypothalamic GnIH, but rather by direct actions of fasting and/or corticosterone on the testes, indicating that the testes can integrate and respond to cues of stress directly. Such local inhibition of testosterone synthesis may allow for rapid and reversible changes in physiology and behavior when conditions are inappropriate for breeding.
食物丰富程度与脊椎动物的繁殖准备密切相关。食物短缺会激活下丘脑 - 垂体 - 肾上腺轴，减少性类固醇分泌，并抑制繁殖行为。然而，这些短暂效应背后的机制尚不清楚。促性腺激素抑制激素（GnIH）是一种存在于大脑和性腺中的神经肽，在某些物种中也受糖皮质激素和禁食的影响。我们研究了禁食应激是否会激活斑胸草雀（Taeniopygia guttata）的GnIH系统，以及其对繁殖生理和行为的潜在下游影响。我们对雄性斑胸草雀进行了10小时的禁食或随意喂食。禁食会增加循环中的皮质酮并降低睾酮水平。为了评估睾酮水平的降低是否由下丘脑和/或性腺的变化介导，我们（1）量化了下丘脑中GnRH和GnIH阳性神经元的数量，（2）评估了下丘脑GnRH和GnIH的基因表达，（3）检测了禁食组和对照组鸟类中参与睾酮合成的蛋白质的基因表达。下丘脑神经肽的任何测量指标均与处理方式或循环类固醇无关。然而，皮质酮水平较高的鸟类睾丸GnIH表达较高，睾酮水平较低。禁食鸟类睾丸中的StAR和LHR表达低于对照组。因此，睾酮水平的降低不太可能由下丘脑GnIH介导，而是由禁食和/或皮质酮对睾丸的直接作用介导，这表明睾丸可以直接整合并响应应激信号。当条件不适合繁殖时，这种对睾酮合成的局部抑制可能会使生理和行为发生快速且可逆的变化。
