Huntington chorea is not associated with hyperactivity of nigrostriatal dopaminergic neurons: studies in postmortem tissues and in rats with kainic acid lesions.

We estimated dopamine release postmortem in the neostriatum of patients with Huntington disease (HD) and in controls. In HD, dopamine levels were unchanged in caudate and elevated in putamen, but homovanillic acid (HVA) and the ratio HVA:dopamine were unaltered in both nuclei. When rats were injected with kainic acid (an experimental model of HD), dopamine levels in striatum remained unchanged 2 to 30 days postoperatively; HVA and 3,4-dihydroxyphenylacetic acid (DOPAC) increased significantly from 2 to 18 days after injections but returned to normal levels later. These findings suggest that the nigrostriatal projection adapts to loss of striatal neurons that normally influence dopamine release and is not hyperactive in HD chorea.