Opioid receptors in skeletal muscle of normal and dystrophic mice

Autoradiography was used to investigate the presence of opioid receptors in soleus, extensor digitorum longus (EDL) and diaphragm muscles in two strains (C57BL/6J and C57BL/10) of mice which can inherit muscular dystrophy. Binding sites for two radiolabelled opioid ligands [125I]beta-endorphin and [3H]naloxone, were seen in a few muscle fibres in the normal mice. However, a significantly greater number of fibres exhibited the binding sites in the dystrophic individuals of both strains. The binding sites were not restricted to the endplate regions but were present over the entire surface in these fibres.