Finger Thomas E
Department of Cell and Developmental Biology, University of Colorado Denver, Aurora, CO, USA.
Integr Zool. 2009 Mar;4(1):53-63. doi: 10.1111/j.1749-4877.2008.00135.x.
The great number of species of teleosts permits highly specialized forms to evolve to occupy particular niches. This diversity allows for extreme variations in brain structure according to particular sensory or motor adaptations. In the case of the taste system, goldfish (Carassius auratus L., 1758) and some carps have evolved a specialized intraoral food-sorting apparatus along with corresponding specializations of gustatory centers in the brainstem. A comparison of circuitry within the complex vagal lobe of goldfish, and of the simpler gustatory lobes in catfish (Ictalurus punctatus Rafinesque, 1818) shows numerous similarities in organization and neurotransmitters. Double labeling studies using horseradish peroxidase and biotinylated dextran amine in catfish shows a direct projection from the vagal lobe to the motoneurons of nucleus ambiguous which innervate oropharyngeal musculature. Therefore, a three neuron reflex arc connects gustatory input to motor output. In the vagal lobe of goldfish, a similar three neuron arc can be identified: from primary gustatory afferent, to vagal lobe interneuron, thence to dendrites of the vagal motoneurons that innervate the pharyngeal muscles. Therefore, despite large differences in the gross appearance of the vagal gustatory systems in the brains of catfish and goldfish, the essential connectivity and circuitry is similar. This suggests that evolutionary change in the central nervous system largely proceeds by rearrangement and elaboration of existing systems, rather than by addition of new structures or circuits.
硬骨鱼种类繁多，使得高度特化的形态得以进化，以占据特定的生态位。这种多样性使得大脑结构能够根据特定的感觉或运动适应而产生极大的变化。就味觉系统而言，金鱼（Carassius auratus L., 1758）和一些鲤鱼进化出了一种专门的口腔内食物分拣装置，以及脑干中味觉中枢的相应特化。对金鱼复杂迷走叶内的神经回路与鲶鱼（Ictalurus punctatus Rafinesque, 1818）较简单的味觉叶进行比较，结果显示在组织结构和神经递质方面有许多相似之处。在鲶鱼中使用辣根过氧化物酶和生物素化葡聚糖胺进行的双重标记研究表明，从迷走叶到支配口咽肌肉组织的疑核运动神经元有直接投射。因此，一个三神经元反射弧将味觉输入与运动输出联系起来。在金鱼的迷走叶中，可以识别出类似的三神经元弧：从初级味觉传入神经元，到迷走叶中间神经元，再到支配咽部肌肉的迷走运动神经元的树突。因此，尽管鲶鱼和金鱼大脑中迷走味觉系统的总体外观有很大差异，但基本的连接性和神经回路是相似的。这表明中枢神经系统的进化变化很大程度上是通过对现有系统的重新排列和细化来进行的，而不是通过添加新的结构或回路。
