Neuroscience Institute, Georgia State University, Atlanta, Georgia, 30302-5030.
J Comp Neurol. 2014 Mar;522(4):794-810. doi: 10.1002/cne.23446.
The relative simplicity of certain invertebrate nervous systems, such as those of gastropod molluscs, allows behaviors to be dissected at the level of small neural circuits composed of individually identifiable neurons. Elucidating the neurotransmitter phenotype of neurons in neural circuits is important for understanding how those neural circuits function. In this study, we examined the distribution of γ-aminobutyric-acid;-immunoreactive (GABA-ir) neurons in four species of sea slugs (Mollusca, Gastropoda, Opisthobranchia, Nudibranchia): Tritonia diomedea, Melibe leonina, Dendronotus iris, and Hermissenda crassicornis. We found consistent patterns of GABA immunoreactivity in the pedal and cerebral-pleural ganglia across species. In particular, there were bilateral clusters in the lateral and medial regions of the dorsal surface of the cerebral ganglia as well as a cluster on the ventral surface of the pedal ganglia. There were also individual GABA-ir neurons that were recognizable across species. The invariant presence of these individual neurons and clusters suggests that they are homologous, although there were interspecies differences in the numbers of neurons in the clusters. The GABAergic system was largely restricted to the central nervous system, with the majority of axons confined to ganglionic connectives and commissures, suggesting a central, integrative role for GABA. GABA was a candidate inhibitory neurotransmitter for neurons in central pattern generator (CPG) circuits underlying swimming behaviors in these species, however none of the known swim CPG neurons were GABA-ir. Although the functions of these GABA-ir neurons are not known, it is clear that their presence has been strongly conserved across nudibranchs.
某些无脊椎动物神经系统相对简单，例如腹足纲软体动物的神经系统，这使得行为能够在由可单独识别的神经元组成的小神经回路水平上进行剖析。阐明神经回路中神经元的神经递质表型对于理解这些神经回路的功能很重要。在这项研究中，我们检查了 4 种海蛞蝓（软体动物门，腹足纲，后鳃亚纲，裸鳃目）中的γ-氨基丁酸免疫阳性（GABA-ir）神经元的分布：Tritonia diomedea、Melibe leonina、Dendronotus iris 和 Hermissenda crassicornis。我们发现 GABA 免疫反应在足神经节和脑-脏神经节中的分布在物种间具有一致性。特别是，在脑神经节背表面的侧部和中部区域以及足神经节腹表面存在双侧簇。还有一些在各个物种中均可识别的 GABA-ir 神经元。这些单个神经元和簇的不变存在表明它们是同源的，尽管在簇中的神经元数量上存在种间差异。GABA 能系统主要局限于中枢神经系统，大多数轴突局限于神经节连接和神经连合，表明 GABA 具有中枢整合作用。GABA 是这些物种游泳行为中中央模式发生器（CPG）回路中神经元的候选抑制性神经递质，然而，已知的游泳 CPG 神经元均不是 GABA-ir。尽管这些 GABA-ir 神经元的功能尚不清楚，但它们在裸鳃目动物中的存在显然已经得到了强烈的保守。
