POMC neuropeptides and their receptors in the neuromuscular system of wobbler mice.

The pro-opiomelanocortin-derived peptides, beta-endorphin (beta-EP), ACTH and alpha-MSH act in concert to promote synaptogenesis and nerve growth in the neuromuscular system. Immunocytochemistry was used to detect the peptides in triceps muscles of normal developing and adult mice and in adult wobbler mice with motor neurone disease. Immunoreactivity for beta-EP and alpha-MSH/ACTH was present in some intramuscular motor nerves. There was a significantly higher proportion of immunoreactive nerves in the muscles of the developing and the diseased mice than in the normal adults. ACTH and beta-EP receptors were revealed using autoradiography. Specific binding sites for 125I-labelled ACTH and 125I-labelled beta-EP were present in some fibres in all muscles examined. There were significantly higher proportions of fibres exhibiting specific beta-EP and specific ACTH binding sites in the muscles of the developing and the diseased mice compared to the muscles of normal adults. It seems likely that the high incidence of immunoreactive nerves and of muscle fibres with the peptide receptors in the developing and diseased mice reflects the trophic actions of the peptides in the neuromuscular system.