Detection of homovanillic acid in vivo using microcomputer-controlled voltammetry: simultaneous monitoring of rat motor activity and striatal dopamine release.

Linear sweep voltammograms recorded with carbon paste electrodes in the striatum of the unanaesthetised, unrestrained rat show three separate peaks. The effect on peak 3 of either unilateral 6-hydroxydopamine lesion of the substantia nigra or intraperitoneal administration of alpha-methyl-paratyrosine, supports our earlier conclusion that peak 3 is due to the dopamine metabolite homovanillic acid. Administration of gamma-butyrolactone, which inhibits firing of dopaminergic nigrostriatal neurones, produces an immediate decrease in striatal homovanillic acid, followed by a prolonged increase. Dopamine-receptor agonists and antagonists produce changes in the extracellular concentration of homovanillic acid which are predicted by their effects on dopamine release. Simultaneous monitoring of total motor activity and homovanillic acid show significant correlation between these two parameters. The usefulness of this technique for monitoring dopamine release is critically evaluated in the light of these results.