Brain enkephalin receptors in Parkinson's disease.

Brain enkephalin receptors were studied in post-mortem brain samples of 27 patients with Parkinson's disease and of 26 control subjects without extrapyramidal disorders by the radioligand-binding technique using 3H-leu-enkephalin, 3H-met-enkephalin and 3H-naloxone. The specific binding of both 3H-leu- and 3H-met-enkephalins was significantly increased in the caudate nucleus, putamen, nucleus accumbens, limbic cortex and hippocampus. Scatchard analysis showed that there was an increase in the receptor number, but no significant changes in the mean dissociation constant. Levodopa treatment did not have any significant effect on the enkephalin bindings. A significantly decreased binding of 3H-naloxone was found in the parkinsonian caudate nucleus. Thus there is a supersensitivity of a population of enkephalin receptors in the striatum and limbic system, as well as a loss of other opiate receptors in the striatum, suggesting the involvement of certain brain enkephalin neurons in the pathophysiological process of Parkinson's disease.