Many seasonally-breeding species use daylength to time reproduction. Light-induced release of progonadal hormones involves a complex cascade of responses both inside and outside the brain. In this study, we used induction of early growth response 1 (Egr-1), the protein product of an immediate early gene, to evaluate the time course of such responses in male white-throated sparrows (Zonotrichia albicollis) exposed to a single long day. Induction of Egr-1 in the pars tuberalis began ∼11 h after dawn. This response was followed ∼6 h hours later by dramatic induction in the tuberal hypothalamus, including in the ependymal cells lining the third ventricle. At approximately the same time, Egr-1 was induced in dopaminergic and vasoactive intestinal peptide neurons in the tuberal hypothalamus and in dopaminergic neurons of the premammillary nucleus. We noted no induction in gonadotropin-releasing hormone (GnRH) neurons until 2 h after dawn the following morning. Overall, our results indicate that Egr-1 responses in GnRH neurons occur rather late during photostimulation, compared with responses in other cell populations, and that such induction may reflect new synthesis related to GnRH depletion rather than stimulation by light cues.

中文翻译：

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在季节性繁殖的鸣禽的下丘脑中光诱导的Egr-1表达的时程。

许多季节育种利用白天来进行时间繁殖。光诱导的性腺激素释放涉及大脑内部和外部的复杂级联反应。在这项研究中，我们使用了诱导早期生长反应1（Egr-1）（即立即早期基因的蛋白质产物）的方法，来评估暴露于单个长的雄性白喉麻雀（Zonotrichia albicollis）中这种反应的时间过程天。黎明后约11 h开始在球茎杆中诱导Egr-1。约6小时后，在下丘脑的下部，包括在第三脑室的室管膜细胞中，引起了明显的诱导反应。大约在同一时间，在下丘脑下丘脑和乳头前核的多巴胺能神经元中的多巴胺能和血管活性肠肽神经元中诱导出Egr-1。我们注意到直到第二天早晨黎明后2小时才诱导促性腺激素释放激素（GnRH）神经元。总体而言，我们的结果表明，与其他细胞群体中的应答相比，GnRH神经元中的Egr-1应答在光刺激过程中发生得较晚，并且这种诱导可能反映了与GnRH耗竭有关的新合成，而不是光信号刺激。