Thyroxine and Seasonality in American Tree Sparrows

甲状腺切除会阻碍从繁殖季节到非繁殖季节的过渡，这一普遍观察导致了一种概念，即甲状腺激素在终止季节性繁殖方面发挥了关键作用。威尔逊博士的概念模型基于对专性光周期的美国树雀(Spizella Arborea)的广泛研究，设想了甲状腺激素在季节性中更普遍的作用，包括对性腺生长和婚后蜕皮的甲状腺激素依赖性控制性，以及性腺退化的甲状腺激素依赖性控制性腺退化。来自他实验室的最新数据支持这样的假设，即甲状腺素(一种具有组织活性的甲状腺激素)在大脑中起作用，为季节性的光刺激美国树雀编程。甲状腺激素依赖的编程在光刺激早期发生，类似于一个类似组织的过程，因为随后季节性的表达不需要甲状腺激素。了解甲状腺激素在大脑中的作用对于促进对季节性生理基础的理解至关重要。他使用急性模型系统，在光刺激的第一天注射一次甲状腺素，就能根据季节性对雄性美洲树雀进行甲状腺摘除，再加上免疫细胞化学和放射自显影技术，他希望能揭示潜在的“可编程”细胞。这些细胞的发现将为探索神经网络和/或神经胶质连接提供一个起点，这些神经网络和/或神经胶质连接促进了甲状腺激素依赖的季节性编程，并为研究甲状腺激素作用的细胞机制提供了起点。

The common observation that thyroidectomy blocks the transition from the breeding season to the nonbreeding season has led to the concept that thyroid hormone plays a key role in the termination of seasonal reproduction. Dr. Wilson's conceptual model, based on extensive studies on the obligately photoperiodic American tree sparrow (Spizella arborea), envisions a more pervasive role of thyroid hormone in seasonality and includes thyroid hormone-dependent control of gonadal growth and postnuptial molt as well as thyroid hormone-dependent control of gonadal regression. Recent data from his laboratory support the hypothesis that thyroxine (is the tissue-active thyroid hormone that) acts in the brain to program photostimulated American tree sparrows for seasonality. Thyroxine-dependent programming occurs early during photostimulation and resembles an organizational-like process in that thyroxine is not later required for expression of seasonality. Knowing where thyroxine acts in the brain is essential for advancing understanding of the physiological basis of seasonality. Using an acute model system, wherein a single injection of thyroxine on the first day of photostimulation programs thyrodectomized male American tree sparrows for seasonality, coupled with immunocytochemical and autoradiographic techniques, he expects to reveal potential "programmable" cells. Revealing such cells will provide a starting point for exploring the neural networks and/or glial connections that facilitate thyroxine-dependent programming of seasonality and for studying the cellular mechanism of thyroid hormone action.