Morphology and synaptic physiology of the main closer muscle in regenerating claws ofAlpheus

Abstract

1. The present paper examines the changes that take place in the synaptic physiology and morphology of the main closer (Cl1) muscle during simultaneous regeneration of pincer and snapper claws. 2. Regenerating chelipeds appear one moult cycle after removal of the original claws. Both chelipeds are small but exhibit discrete differences in skeletal structure, Cl1 muscle morphology, and synaptic physiology. 3. After the first moult cycle excitatory and inhibitory synaptic terminals on Cl1 muscle fibers are formed at about the same time. Synaptic contacts are initially made on fibers in the proximal portion of the main closer muscle, and only later during the second moult cycle are synaptic connections made on more distally located Cl1 fibers. 4. After two moult cycles, the pincer main closer muscle is composed of fibers of different diameters and sarcomeres that exhibit a bimodal length distribution. The thicker fibers are located centrally in the muscle and have sarcomeres 2 and 3 μm long, while intermediate length sarcomeres are characteristic of thinner Cl1 fibers on the lateral and medial margins. 5. Prior to the third moult cycle, snapper Cl1 sarcomeres exhibit a unimodal distribution, whereas after 3 moults the sarcomeres show a bimodal distribution. Data from a series of snapper claws in different stages of regeneration revealed that there is a close matching between the synaptic physiology and the morphology of the main closer muscle fibers.