Saldanha C J, Deviche P J, Silver R
Graduate School of Arts and Sciences, Columbia University, New York, New York 10027.
Gen Comp Endocrinol. 1994 Jan;93(1):128-36. doi: 10.1006/gcen.1994.1015.
Most temperate zone birds show dramatic seasonal cycles in responsiveness to light. In the spring the hypothalamo-pituitary-gonadal axis of photosensitive birds is stimulated by long days. In the late summer birds no longer respond to long days, their gonads regress, and they are said to be photorefractory. After several weeks of refractoriness birds regain photosensitivity. During refractoriness circulating concentrations of luteinizing hormone are low and prolactin levels are high. These fluctuations in peripheral hormones result from changes in the brain rather than in the pituitary and/or the gonads. In the present study we examined seasonal changes in expression of vasoactive-intestinal polypeptide (VIP) and gonadotropin-releasing hormone (GnRH) in the brain of dark-eyed juncos (Junco hyemalis). Birds were photosensitive and exposed to long photoperiod (20:4 LD) for 1 day, 45-60 days, or not at all, or they were photorefractory (housed in 20:4 LD). The results indicate that VIP expression was similar in all photosensitive birds. However, photorefractory birds had significantly higher numbers of VIP-positive neurons in the infundibulum compared to photosensitive birds. The number of GnRH-positive neurons in the preoptic area was significantly lower in photorefractory birds and significantly higher in long-term photostimulated birds. These results indicate that the inverse relationship between circulating prolactin (released by VIP) and luteinizing hormone (released by GnRH) during refractoriness may result from neural changes in VIP and GnRH expression, respectively.
大多数温带鸟类对光的反应呈现出显著的季节性周期。在春季，光敏鸟类的下丘脑 - 垂体 - 性腺轴受到长日照的刺激。夏末时，鸟类不再对长日照产生反应，其性腺退化，此时它们被称为光不应性。经过几周的不应期后，鸟类恢复光敏性。在不应期，促黄体生成素的循环浓度较低，而催乳素水平较高。外周激素的这些波动是由大脑而非垂体和/或性腺的变化引起的。在本研究中，我们检测了暗眼灯草鹀（Junco hyemalis）大脑中血管活性肠肽（VIP）和促性腺激素释放激素（GnRH）表达的季节性变化。将鸟类分为光敏组并分别暴露于长光照周期（20:4 光暗比）1天、45 - 60天或根本不暴露，或者将它们分为光不应性组（饲养于20:4光暗比环境）。结果表明，所有光敏鸟类的VIP表达相似。然而，与光敏鸟类相比，光不应性鸟类漏斗部中VIP阳性神经元的数量显著更多。光不应性鸟类视前区中GnRH阳性神经元的数量显著更低，而长期光刺激的鸟类中该数量显著更高。这些结果表明，在不应期循环催乳素（由VIP释放）和促黄体生成素（由GnRH释放）之间的反向关系可能分别是由VIP和GnRH表达的神经变化导致的。
