INCREASED DOPAMINE CLEARANCE IN THE NON-LESIONED STRIATUM OF RHESUS-MONKEYS WITH UNILATERAL 1-METHYL-4-PHENYL-1,2,3,6-TETRAHYDROPYRIDINE (MPTP) STRIATAL LESIONS

In vivo electrochemistry was used to examine the clearance of locally applied dopamine in the caudate nuclei of normal, control monkeys and in the non-lesioned and lesioned caudate nuclei of unilateral 1-methyl-6-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys. Chronoamperometric recordings were continuously made using Nafion-coated carbon fiber electrodes in anesthetized animals while a calibrated amount of dopamine was pressure ejected from a micropipette adjacent (250-300 mu m) to the electrode. The dopamine signals recorded from the MPTP-lesioned caudate nuclei had a greater amplitude and time course than those recorded from both the controls and from the non-lesioned side of the treated animals, indicating a loss of high-affinity uptake in the lesioned caudate. However, the time course was faster, and the clearance rate greater, in signals recorded from the contralateral side of the treated animals when compared to control caudate nuclei. This suggests that there is an up-regulation in high-affinity dopamine uptake in the non-lesioned side of the MPTP-treated animals. This change may represent a compensatory mechanism that is attempting to maintain a balance in extracellular dopamine levels between the lesioned and non-lesioned sides.