Failure of a peripheral dopaminergic marker in Parkinson's disease.

[3H]-spiperone binding on human lymphocytes did not reveal the occurrence of dopamine receptors. However, lower values were observed in Parkinsonism and the displaceable binding was increased after levodopa treatment although this was not specific only for levodopa and, furthermore, was not correlated with the clinical symptomatology. This non-specific binding in lymphocytes corresponds to trapping, presumably in lysosomes and thus does not reflect the dopaminergic receptors state in Parkinson's disease.