Inhibition of neuroleptic binding by human brain extracts--an effect of endogenous dopamine?

Extracts of autopsied human brain tissue exhibited a specific inhibition of [3H]spiroperidol binding, in support of previous reports. The extent of binding inhibition varied depending upon the brain region from which the tissue was taken. We observed two peaks of inhibition binding from extracts of caudate or putamen placed on a Sephadex G10 column. Results of experiments to characterize the extract in the second peak indicate a correlation between inhibition of spiroperidol binding and dopamine content of the tissue. The content of the first peak could not be definitively identified but indirect evidence indicates that it may be a high molecular weight conjugate of dopamine that is formed at low concentrations. No evidence was obtained to suggest the existence of previously undetected neuroleptic-like material in human brain.