Cardinali D P
Arch Biol Med Exp. 1984 Dec;17(3-4):239-47.
Daylength is the major environmental variable governing seasonal breeding, and the pineal gland is needed for this response to occur in many photosensitive species. Although dependent upon the integrity of its peripheral sympathetic innervation, the pineal has no efferent projections, and therefore it affects neuroendocrine function by humoral means. Melatonin has been proposed as the pineal hormone; its timed administration replicate the effect of daylength on seasonal breeding in several mammals, including long-day, like the hamster, and short-day breeders, like the sheep. The pineal is regulated primarily by photo-periodic information attaining the gland through a polysynaptic pathway initiated in the retinohypothalamic tract. Secondary regulators of pineal secretory activity are several steroid and polypeptide hormones. Melatonin synthesis is maximal during nighttime while during daylight it is suppressed. Melatonin acts on specific receptor sites at hypothalamic and perhaps extrahypothalamic sites to affect LHRH release. Changes in calcium fluxes, cyclic nucleotide and prostaglandin synthesis may underlie the neuroendocrine activity of melatonin at hypothalamic sites.
日照长度是控制季节性繁殖的主要环境变量，许多光敏物种发生这种反应需要松果体。尽管松果体依赖于其外周交感神经支配的完整性，但它没有传出投射，因此它通过体液方式影响神经内分泌功能。褪黑素被认为是松果体激素；在几种哺乳动物中，包括长日照繁殖动物（如仓鼠）和短日照繁殖动物（如绵羊），定时给予褪黑素可复制日照长度对季节性繁殖的影响。松果体主要受通过视网膜下丘脑束起始的多突触途径到达该腺体的光周期信息调节。松果体分泌活动的次要调节因子是几种类固醇和多肽激素。褪黑素合成在夜间达到最大值，而在白天则受到抑制。褪黑素作用于下丘脑以及可能的下丘脑外部位的特定受体位点，以影响促性腺激素释放激素（LHRH）的释放。钙通量、环核苷酸和前列腺素合成的变化可能是褪黑素在下丘脑部位神经内分泌活动的基础。
