Radiolabeled drugs as probes of central nervous system neurons.

Methylspiperone, carfentanil, and suriclone, labeled with 11C, can be used in assessment of dopamine, mu-type opiate receptors, and benzodiazapine receptors in the brains of living human beings. These relatively specific neuronal probes permit measurement of the number and state of occupancy of receptors in the brain in health and disease, and may be useful to assess endogenous neurotransmitter secretion by decreasing competitive binding of the labeled ligand. To date, the most striking finding has been a decrease in the indices of dopamine and serotonin receptor densities as a function of age in normal men and women. A possible relationship between this decrease and vitamin B6 deficiency is currently under study.