Effect of a limited target area on regeneration of specific neuromuscular connections in the crayfish.

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Abstract
The axons innervating the superficial flexor muscles of the crayfish P. clarkii can regenerate their connections with the same degree of precision observed in control animals. The effect of removing part of the target area of these axons on their capacity to regenerate specific connections was examined. In one set of experiments the nerve was cut between the 1st medial muscle fibers and allowed to regenerate in the absence of the lateral muscle fibers. The regenerated connectivity maps of four axons were compared to the pattern of connections observed in the medial fibers of animals in which the nerve had not been cut. Axons 2 and 3 regenerated their control pattern of connections and junction-potential sizes. Axon 1 innervated below control values, while axon 4 innervated above control values in terms of both the presence of a connection and amplitude of the junction potential. In another set of experiments the nerve was cut and transplanted to the most medial of the lateral muscle fibers, while all the medial muscle fibers were removed. Comparisons were made in this case between the regenerated connectivity maps and the pattern of connections observed in the lateral muscle fibers of animals in which the nerve had not been cut. Axons 3 and 4 regenerated their control pattern of connections and junction-potential sizes. Axons 1 and 2 innervated more fibers than controls and showed a tendency to have higher-than-normal junction-potential sizes. These individual neurons differ in their sensitivity to changes in the number of muscle fibers available for innervation.

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