Trudeau L E, Castellucci V F
Laboratoire de Neurobiologie et Comportement, Institut de Recherches Cliniques de Montréal, Québec, Canada.
J Neurosci. 1992 Oct;12(10):3838-48. doi: 10.1523/JNEUROSCI.12-10-03838.1992.
The gill and siphon withdrawal (GSW) reflex of Aplysia is centrally mediated by a monosynaptic and a polysynaptic pathway between sensory and motor neurons. The first objective of this article was to evaluate quantitatively the relative importance of these two components in the mediation of the GSW reflex. We have used an artificial sea water (ASW) solution containing a high concentration of divalent cations to raise the action potential threshold of the interneurons without affecting the monosynaptic component of the reflex (2:1 ASW). Compound EPSPs induced in gill or siphon motor neurons by direct stimulation of the siphon nerve or by tactile stimulation of the siphon skin were reduced by more than 75% in 2:1 ASW. These results indicate that interneurons intercalated between sensory and motor neurons are responsible for a considerable proportion of the afferent input to the motor neurons of the reflex. The second objective of this article was to compare the modulation of the monosynaptic and polysynaptic pathways. We have evaluated their respective contribution in sensitization of the GSW reflex by testing the effects of two neuromodulators of the reflex, 5-HT and small cardioactive peptide B (SCPB). We found that these two neuromodulators have a differential action on the two components of the GSW neuronal network. The polysynaptic pathway was more facilitated than the monosynaptic pathway by the neuropeptide SCPB. By contrast, 5-HT displayed an opposite selectivity. These results suggest that the polysynaptic component of the neuronal network underlying the GSW reflex is very important for its mediation. The data also indicate that the monosynaptic and polysynaptic components of the reflex can be differentially modulated. The diversity of modulatory actions at various sites of the GSW network should be relevant for learning-associated modifications in the intact animal.
海兔的鳃与虹吸管退缩（GSW）反射由感觉神经元和运动神经元之间的单突触和多突触通路在中枢介导。本文的首要目标是定量评估这两个组成部分在介导GSW反射中的相对重要性。我们使用了一种含有高浓度二价阳离子的人工海水（ASW）溶液来提高中间神经元的动作电位阈值，同时不影响反射的单突触成分（2:1 ASW）。在2:1 ASW中，直接刺激虹吸管神经或通过触觉刺激虹吸管皮肤在鳃或虹吸管运动神经元中诱发的复合兴奋性突触后电位（Compound EPSPs）降低了75%以上。这些结果表明，插入在感觉神经元和运动神经元之间的中间神经元对反射运动神经元的相当一部分传入输入负责。本文的第二个目标是比较单突触和多突触通路的调制。我们通过测试反射的两种神经调节剂5-羟色胺（5-HT）和小的心脏活性肽B（SCPB）的作用，评估了它们在GSW反射敏化中的各自贡献。我们发现这两种神经调节剂对GSW神经元网络的两个组成部分有不同的作用。神经肽SCPB对多突触通路的促进作用比对单突触通路的促进作用更大。相比之下，5-HT表现出相反的选择性。这些结果表明，GSW反射基础的神经元网络的多突触成分对其介导非常重要。数据还表明，反射的单突触和多突触成分可以受到不同的调制。GSW网络各个部位调制作用的多样性应该与完整动物中与学习相关的修饰有关。
