Cassone V M, Brooks D S, Kelm T A
Department of Biology, Texas A & M University, College Station 77843-3528, USA.
Brain Behav Evol. 1995;45(5):241-56. doi: 10.1159/000113553.
The roles that the pineal gland and its hormone melatonin play in the regulation of circadian rhythmicity and photoperiodism vary among vertebrate species. Recently, putative sites of melatonin action have been elucidated in several avian and mammalian species by application of in vitro binding of a radioiodinated melatonin agonist, 2[125I]iodomelatonin (IMEL) and autoradioradiography. These studies in mammals, birds and reptiles have indicated profound differences in the distribution of IMEL binding between these diverse groups, suggesting that these large differences in binding may reflect differences in melatonin function. The present study was performed to determine systematically whether the variance in IMEL binding among avian species corresponds to changes in circadian organization and/or phylogenetic relationships. The distribution of specific IMEL binding was determined in the brains from birds belonging to 14 different species in 5 Orders (Psittaciformes, Passeriformes, Columbiformes, Galliformes and Anseriformes) using in vitro binding, autoradiography and computer-assisted image analysis. The distribution was compared to a similar study in 3 species of turtles as an outgroup. The data indicated IMEL binding in retinorecipient structures of the circadian, tectofugal, thalamofugal and accessory optic visual pathways in all avian species. Relay nuclei and integrative structures of the tectofugal, thalamofugal, accessory optic, and limbic systems, however, bound the hormone to varying degrees. In turtles, binding was observed in retinorecipient structures of the thalamofugal visual pathway and in retinorecipient and integrative areas of the tectofugal visual pathway. No binding was observed in the pineal gland, tuberal hypothalamus or adenohypophysis in any avian or testudine species. This distribution is drastically different from that observed in mammals, where binding predominates in the pars tuberalis of the adenohypophysis and in the suprachiasmatic nucleus, suggesting that the circadian system may influence a wide array of sensory and integrative functions in birds and reptiles through the circadian secretion of melatonin, but that this capacity has been lost in mammals.
松果体及其激素褪黑素在昼夜节律和光周期调节中所起的作用在脊椎动物物种间存在差异。最近，通过应用放射性碘化褪黑素激动剂2[¹²⁵I]碘褪黑素（IMEL）的体外结合及放射自显影技术，在几种鸟类和哺乳动物物种中阐明了褪黑素的假定作用位点。这些在哺乳动物、鸟类和爬行动物中的研究表明，不同类群之间IMEL结合的分布存在显著差异，这表明这些结合上的巨大差异可能反映了褪黑素功能的差异。本研究旨在系统地确定鸟类物种间IMEL结合的差异是否与昼夜节律组织和/或系统发育关系的变化相对应。使用体外结合、放射自显影和计算机辅助图像分析技术，测定了属于5个目（鹦形目、雀形目、鸽形目、鸡形目和雁形目）的14个不同物种鸟类大脑中特异性IMEL结合的分布情况。将该分布与作为外类群的3种龟类的类似研究进行了比较。数据表明，所有鸟类物种的昼夜节律、顶盖传出、丘脑传出和副视视觉通路的视网膜接受结构中均存在IMEL结合。然而，顶盖传出、丘脑传出、副视和边缘系统的中继核和整合结构对该激素的结合程度各不相同。在龟类中，在丘脑传出视觉通路的视网膜接受结构以及顶盖传出视觉通路的视网膜接受和整合区域观察到了结合。在任何鸟类或龟类物种的松果体、结节下丘脑或腺垂体中均未观察到结合。这种分布与在哺乳动物中观察到的情况截然不同，在哺乳动物中，结合主要发生在下丘脑腺垂体的结节部和视交叉上核，这表明昼夜节律系统可能通过褪黑素的昼夜分泌影响鸟类和爬行动物广泛的感觉和整合功能，但这种能力在哺乳动物中已经丧失。
