Laboratory of Reproductive Neuroendocrinology, Department of Integrative Biology , University of California at Berkeley , USA.
PeerJ. 2013 Aug 15;1:e139. doi: 10.7717/peerj.139. eCollection 2013.
The gonadotropin releasing hormone (GnRH) system in the hypothalamus is often considered the final point in integration of environmental cues as they pertain to the reproductive axis. However, cues such as stress and food availability are detectable in the plasma (as glucocorticoid and metabolic fuel fluctuations). Vertebrate gonads express glucocorticoid receptor, therefore we hypothesized that the gonads can detect and respond directly to cues of stress. We provide evidence here that, in addition to regulation by the brain, the gonads of European starlings (Sturnus vulgaris) respond directly to fluctuations in corticosterone and metabolic fuels by modulating sex steroid secretion. Using a 4-h gonad culture, we show that physiologically-relevant concentrations of corticosterone and metabolic stress (via use of the glucose utilization inhibitor 2-deoxy-D-glucose and the fatty acid oxidation inhibitor ethyl 2-mercaptoacetate (2DG/MA)) can directly decrease testosterone and estradiol secretion from luteinizing hormone and follicle-stimulating hormone (LH/FSH)-stimulated testes and ovaries. This effect is regulated seasonally. Prior to the breeding season, testes and ovaries respond to corticosterone and 2DG/MA by significantly decreasing gonadal steroid release. Within the breeding season, the testes do not respond to these cues of stress, while the ovaries respond only to corticosterone. This seasonal difference in response may be due in part to the influence of these cues of stress on gonadal neuropeptide expression: corticosterone upregulates GnIH expression in the testes while metabolic stress upregulates GnIH in the ovaries. Thus the gonads can directly respond to fluctuations in corticosterone and metabolic fuels during a time of critical importance to the onset of breeding.
下丘脑的促性腺激素释放激素 (GnRH) 系统通常被认为是整合与生殖轴相关的环境线索的最终点。然而，压力和食物供应等线索可以在血浆中检测到（如糖皮质激素和代谢燃料波动）。脊椎动物性腺表达糖皮质激素受体，因此我们假设性腺可以直接检测到压力线索并做出反应。我们在这里提供的证据表明，除了受大脑调节外，欧洲椋鸟（Sturnus vulgaris）的性腺还可以通过调节性激素分泌来直接响应皮质酮和代谢燃料的波动。使用 4 小时性腺培养，我们表明，生理相关浓度的皮质酮和代谢应激（通过使用葡萄糖利用抑制剂 2-脱氧-D-葡萄糖和脂肪酸氧化抑制剂乙基 2-巯基乙酸酯（2DG/MA））可以直接降低黄体生成素和促卵泡激素（LH/FSH）刺激的睾丸和卵巢中睾酮和雌二醇的分泌。这种作用具有季节性。在繁殖季节之前，睾丸和卵巢通过显着降低性腺类固醇释放来响应皮质酮和 2DG/MA。在繁殖季节内，睾丸对这些应激线索没有反应，而卵巢仅对皮质酮有反应。这种反应的季节性差异部分可能是由于这些应激线索对性腺神经肽表达的影响：皮质酮上调睾丸中的 GnIH 表达，而代谢应激上调卵巢中的 GnIH。因此，在繁殖开始的关键时期，性腺可以直接响应皮质酮和代谢燃料的波动。
