Electrophysiological Analysis of Peripheral Neurones and Their Possible Role in the Local Reflexes of A Mollusc

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Abstract
1. It has been shown by behavioural and electromyographic studies that local reflexes exist in the siphon wall musculature of Spisula. In contrast, the responsiveness of the siphon retractor muscles is centrally mediated. 2. Clusters of neurone somata occur at the peripheral branching points of the siphonal nerves. Intracellular records obtained from these peripheral cluster cells indicate they are efferents to the siphon wall musculature. These cells receive synaptic input from a population of touch-sensitive afferents from the siphons and mantle. None of the peripheral cells from which records have been obtained provided any indication of being sensory in function. 3. ‘Central delay’ measurements indicate the presence of only one synaptic transfer between the afferent input to a peripheral nerve junction and the output of cluster cells. 4. The synaptic input to the cluster cells is shown to be subject to short-term modification (antifacilitation). This coupled with the direct evidence that the peripheral cells are functional neurones supports the possibility that molluscan peripheral neurones could mediate habituated responses.