Three-day-old neonatal rats had their common peroneal nerve crushed 3 mm from the extensor digitorum longus (EDL) muscle. At periodic intervals of 7, 10, 14, 21 and 28 days following nerve injury the EDL muscles were removed, weighed, stained using the silver cholinesterase method and their muscle fibres counted. In these rats during the re-innervation process, the bands of Biingner were absent, some endplates disintegrated and a large proportion of the muscle fibres were lost. This study has shown that interruption of the normal nerve-muscle interaction during the neonatal period is highly detrimental to the subsequent growth and development of the muscle.
The motoneurones with axons in the common peroneal nerve (CPN) of the rat and monkey were examined using retrograde labelling with horseradish peroxidase (HRP). In both species, the CPN motoneurone pool was localized in the dorsolateral part of the ventral horn of the spinal cord. In the rat, the labelled motoneurones were located between the L3 and L6 spinal segments whereas in the monkey, they extended from the caudal end of L4 to the L6 spinal segments. In both species the majority of the labelled neurones were located within the L5 segment. The mean number of the CPN motoneurones in the rat and monkey was 458 and 1148, respectively. A bimodal size distribution of motoneurones was found in both species.