Printed in Great Britain A SIMPLE METHOD FOR STUDYING THE INNERVATION OF A COMPLEX MUSCLE

The innervation of an insect muscle can be studied by correlating the evoked spikes in neuronal cell bodies with extracellular or intracellularly recorded events in various parts of the muscle (Burrows & Hoyle, 1973; Hoyle & Burrows, 1973; Phillips, 1980). However, when a muscle is innervated by a large number of neurones, difficulties may occur: first, in the reliable identification of the neurones (especially when their cell bodies are closely clustered) and secondly, in maintaining stable records from the cell bodies for a sufficient period of time to permit reliable investi-gation of the muscle. To eliminate these difficulties, a new method of identifying the neurones was developed, mainly based on the distribution of the axons on the muscle surface, the size of the EPSP or IPSP which they produce on the muscle fibres, and the size of the action potential recorded from the motor nerves of the muscle. The method was first applied to study the innervation of the mesothoracic flexor tibiae muscle of the locust. Not only is this muscle innervated by a large number of neurones with their cell bodies lying very close together (Theophilidis, 1979; Wilso