Axonal transport of opiate receptors in capsaicin-sensitive neurones

Opiate receptors measured in vitro or in vivo with [3H]lofentanil in the rat vagus nerve were found to accumulate on both sides of a ligature, thus indicating a bidirectional axoplasmic transport of these receptors. When rats were treated with capsaicin, the accumulation of opiate receptors was tremendously reduced in the vagus whereas muscarinic receptors in ligated sciatic nerves were unaffected. Since capsaicin is known to affect sensory neurones, mostly those containing substance P, the present results support the idea that the opiate receptors in the vagus are associated with substance P neurones.