Increased transport of 3,4-dihydroxyphenylacetic acid from brain during performance of operant behavior in the rat

Although the performance of positively reinforced operant behavior is accompanied by increased turnover of brain dopamine in the rat, the accumulation of 3,4-dihydroxyphenylacetic acid (DOPAC), the major metabolic product of dopamine in brain, is not increased during operant performance. The hypothesis that the lack of increased DOPAC accumulation stems from an increase in the rate at which DOPAC is eliminated from the brain was tested by measuring the relative rate of DOPAC transport from brain in rats performing operant behavior and in control rats. The transport of DOPAC was estimated following inhibition of monoamine oxidase with pargyline. The pargyline-induced depletions of DOPAC in the caudate putamen and amygdala were significantly greater in rats that performed operant behavior than in control rats. In the caudate putamen, the concentrations of homovanillic acid and 5-hydroxyindoleacetic acid were also depleted by pargyline to a greater extent in operant performing rats than in controls. These results suggest that in addition to the increased turnover of dopamine in central neurons during operant behavior, the rate of elimination of acidic amine metabolites from brain is also accelerated.