Catecholamine uptake inhibitors elevate 6-hydroxydopamine in brain after administration of 6-hydroxydopa

Desipramine and nomifensine, two norepinephrine uptake blockers, elevated by 63-248% the levels of 6-hydroxydopamine found in the frontal cortex at 1-4 h after administration of 6-OH-DOPA. Nomifensine also elevated 6-hydroxydopamine by 83% in the striatum at 4 h. These results nullify prior suggestions in the literature that 6-OH-DOPA is decarboxylated to 6-hydroxydopamine mainly outside of catecholamine nerve terminals and that 6-hydroxydopamine subsequently gains access to nerve terminals via the axonal membrane transport system for catecholamines.