Storozhuk M V, Castellucci V F
Laboratoire de Neurobiologie et Comportement, Institut de Recherches Département de Physiologie, Pavillon Paul-G. -Desmarais, Université de Montréal, Quebec, Canada.
J Exp Biol. 1999 Jan;202(Pt 2):115-20. doi: 10.1242/jeb.202.2.115.
The monosynaptic component of withdrawal reflexes in Aplysia californica, from sensory neurones to motor neurones, is a critical site of the synaptic modulation occurring during short-term and long-term behavioural changes. There are four clusters of sensory neurones (LE, rLE, RE, RF) innervating the receptive field for the gill and siphon withdrawal reflex. The receptive fields of these cells are located on the siphon, the mantle, the branchial cavity and the gill itself. In most studies, the synapses made by the sensory neurones of the LE cluster of the abdominal ganglion or the VC cluster of the pleural ganglion have been investigated and shown to be facilitated by the neuromodulator serotonin (5-hydroxytryptamine, 5-HT). In this report, we have examined the effect of 5-HT on the synaptic junctions of the RF cluster neurones. The duration of action potentials in these cells, unlike those of the other clusters, is barely affected by serotonin. We found that while the LE synapses are facilitated by 5-HT (10 micromol l-1), the RF synapses are not. In fact, the RF-L14 connections are actually depressed by 5-HT; this effect is not due to shunting in the postsynaptic neurone. The RF-L7 connections are also depressed by 5-HT, although the effect is smaller. The RF-L14 connections are blocked by the non-NMDA receptor agonist CNQX (100 micromol l-1), suggesting that the transmitter and the postsynaptic receptors involved are similar to those present on the LE or VC cluster cells. The absence of serotonin-induced facilitation of the RF cluster cells may provide the animal with a means of reducing the nonspecific effects of aversive sensitization and therefore of allowing a greater specificity and more flexibility in plastic behavioural changes.
加州海兔缩鳃反射中的单突触成分，即从感觉神经元到运动神经元的部分，是短期和长期行为变化过程中发生突触调制的关键部位。有四组感觉神经元（LE、rLE、RE、RF）支配鳃和虹吸管缩鳃反射的感受野。这些细胞的感受野位于虹吸管、外套膜、鳃腔和鳃本身。在大多数研究中，已经对腹神经节LE簇或胸膜神经节VC簇的感觉神经元形成的突触进行了研究，并表明这些突触受到神经调质5-羟色胺（5- HT）的易化作用。在本报告中，我们研究了5- HT对RF簇神经元突触连接的影响。与其他簇的细胞不同，这些细胞动作电位的持续时间几乎不受5- HT的影响。我们发现，虽然LE突触受到5- HT（10 μmol/L）的易化作用，但RF突触却没有。事实上，RF-L14连接实际上受到5- HT的抑制；这种效应并非由于突触后神经元的分流所致。RF-L7连接也受到5- HT的抑制，尽管作用较小。RF-L14连接被非NMDA受体激动剂CNQX（100 μmol/L）阻断，这表明所涉及的递质和突触后受体与LE或VC簇细胞上的相似。RF簇细胞缺乏5- HT诱导的易化作用，可能为动物提供了一种减少厌恶致敏非特异性效应的方式，从而在可塑性行为变化中允许更高的特异性和更大的灵活性。
