Central Dopaminergic Neurons: Effects of Alterations in Impulse Flow on the Accumulation of Dihydroxyphenylacetic Acid

Stimulation of the nigro-neostriatal or mesolimbic dopamine pathway results in a stimulus dependent increase in the accumulation of dihydroxyphenylacetic acid (DOPAC) in the neostriatum and olfactory tubercles, respectively. A block of impulse flow induced pharamacologically by administration of gamma-butyrolactone or by placement of a lesion in the dopamine pathway results in a decrease in the steady state levels of DOPAC. Drugs which have previously been shown to alter impulse flow in central dopaminergic neurons also produce a predictable change in the brain levels of DOPAC. Drugs which increase impulse flow in nigro-neostriatal or mesolimbic dopamine neurons increase DOPAC levels in the striatum and olfactory tubercles and drugs which reduce impulse flow cause a reduction in DOPAC. Pargyline, a monoamine oxidase inhibitor, causes a rapid depletion of striatal DOPAC suggesting that this metabolite is rapidly cleared from the brain. Administration of benztropine, a potent inhibitor of dopamine reuptake, causes a significant decrease in striatal DOPAC and partially prevents the stimulus-induced increase in the accumulation of DOPAC. These observations together with the finding that about 85% of the DOPAC in the striatum disappears when the dopamine neurons in the nigro-neostriatal pathway are destroyed suggests that the majority of striatal DOPAC is formed within the dopaminergic neurons and may reflect the metabolism of dopamine which has been released and recaptured. We conclude that short-term changes in brain levels of DOPAC appear to provide a useful index of alterations in the functional activity of central dopaminergic neurons.