Depletion of brain noradrenaline and dopamine by 6‐hydroxydopamine

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Abstract
1 After intracisternal administration, 6-hydroxydopamine had a greater effect on brain noradrenaline than on dopamine. 2 Administration of two doses of 6-hydroxydopamine increased the depletion of noradrenaline but not of dopamine. 3 Small doses of 6-hydroxydopamine decreased the concentration of noradrenaline with little or no effect on dopamine. Tyrosine hydroxylase activity was not reduced with these treatments. 4 While pargyline pretreatment offered no advantage in the depletion of brain noradrenaline after 6-hydroxydopamine, depletion of brain dopamine was greatly potentiated by this treatment. The reduction of striatal tyrosine hydroxylase activity observed after 6-hydroxydopamine was also potentiated by pargyline pretreatment. 5 The amounts of labelled noradrenaline and dopamine formed from 3H-tyrosine were greatly reduced by 6-hydroxydopamine treatment. After 3H-DOPA, formation of noradrenaline was greatly reduced while formation of labelled dopamine was only moderately reduced suggesting that decarboxylation of DOPA can occur in other than catecholamine containing neurones. 6 Desmethylimipramine and imipramine inhibited depletion of noradrenaline produced by 6-hydroxydopamine but did not alter depletion of dopamine. Reserpine did not inhibit depletion of catecholamines produced by 6-hydroxydopamine. 7 Administration of 6-hydroxydopamine to developing rats lowered both noradrenaline and dopamine concentrations as well as the tyrosine hydroxylase activity in the brains of these animals.

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