DOPA RESISTANCE IN MULTIPLE-SYSTEM ATROPHY - LOSS OF POSTSYNAPTIC D2 RECEPTORS

Postmortem autoradiography was used to explore the mechanisms underlyi ng L-dopa resistance in 2 patients with multiple-system atrophy. Indic es of striatal presynaptic dopamine terminal loss and dopamine (D1 and D2) receptors were provided by H-3-mazindol, H-3-SCH 23390, and I-125 -sulpiride binding. Neuronal loss, gliosis, and loss of postsynaptic D 2 receptors preferentially involved the middle and posterior of the pu tamen, that region of the striatum most intimately involved in motor f unction. Loss of D1 receptors in the same area occurred in only 1 pati ent. These findings suggest that in multiple-system atrophy, resistanc e to L-dopa is due to a loss of putamental D2 receptors. The different ial effects on D1 and D2 receptors in 1 patient implies that different subpopulations of striatal neurons were selectively involved.