Farries M A, Perkel D J
Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
J Neurophysiol. 2000 Nov;84(5):2502-13. doi: 10.1152/jn.2000.84.5.2502.
The forebrains of mammals and birds appear quite different in their gross morphology, making it difficult to identify homologies between them and to assess how far they have diverged in organization. Nevertheless one set of forebrain structures, the basal ganglia, has been successfully compared in mammals and birds. Anatomical, histochemical, and molecular data have identified the avian homologues of the mammalian basal ganglia and indicate that they are very similar in organization, suggesting that they perform similar functions in the two classes. However, the physiological properties of the avian basal ganglia have not been studied, and these properties are critical for inferring functional similarity. We have used a zebra finch brain slice preparation to characterize the intrinsic physiological properties of neurons in the avian basal ganglia, particularly in the input structure of the basal ganglia, the striatum. We found that avian striatum contains a cell type that closely resembles the medium spiny neuron, the principal cell type of mammalian striatum. Avian striatum also contains a rare cell type that is very similar to an interneuron class found in mammalian striatum, the low-threshold spike cell. On the other hand, we found an aspiny, fast-firing cell type in avian striatum that is distinct from all known classes of mammalian striatal neuron. These neurons usually fired spontaneously at 10 Hz or more and were capable of sustained firing at very high rates when injected with depolarizing current. The existence of this cell type represents an important difference between avian striatum and mammalian dorsal striatum. Our data support the general idea that the organization and functional properties of the basal ganglia have been largely conserved in mammals and birds, but they imply that avian striatum is not identical to mammalian dorsal striatum.
哺乳动物和鸟类的前脑在总体形态上看起来截然不同，这使得难以确定它们之间的同源性，也难以评估它们在组织结构上的差异程度。然而，有一组前脑结构，即基底神经节，已在哺乳动物和鸟类中成功进行了比较。解剖学、组织化学和分子数据已经确定了哺乳动物基底神经节的鸟类同源物，并表明它们在组织结构上非常相似，这表明它们在这两类动物中执行相似的功能。然而，鸟类基底神经节的生理特性尚未得到研究，而这些特性对于推断功能相似性至关重要。我们使用斑胸草雀脑片制备来表征鸟类基底神经节中神经元的内在生理特性，特别是在基底神经节的输入结构纹状体中。我们发现鸟类纹状体包含一种细胞类型，它与中等棘状神经元非常相似，中等棘状神经元是哺乳动物纹状体的主要细胞类型。鸟类纹状体还包含一种罕见的细胞类型，它与在哺乳动物纹状体中发现的一种中间神经元类型非常相似，即低阈值棘突细胞。另一方面，我们在鸟类纹状体中发现了一种无棘、快速放电的细胞类型，它与所有已知的哺乳动物纹状体神经元类别都不同。这些神经元通常以10赫兹或更高的频率自发放电，并且在注入去极化电流时能够以非常高的频率持续放电。这种细胞类型的存在代表了鸟类纹状体和哺乳动物背侧纹状体之间的一个重要差异。我们的数据支持这样一个总体观点，即基底神经节的组织结构和功能特性在哺乳动物和鸟类中在很大程度上是保守的，但它们意味着鸟类纹状体与哺乳动物背侧纹状体并不相同。
