Microdialysis in parkinsonian patient basal ganglia: Acute apomorphine-induced clinical and electrophysiological effects not paralleled by changes inthe release of neuroactive amino acids

During stereotaxic neurosurgery for deep brain stimulation in Parkinson's d isease (PD), we performed a microdialysis study of the extracellular amino acid (aspartate, glutamate, glycine, and GABA) concentrations. Their levels were measured in the GPe/GPi of five and in the STN of four different PD p atients, after prolonged therapy washout. The results show stable values of basal release of the examined amino acids within 1 h, The basal levels of GABA in "OFF" state were significantly higher in the GPi than in the GPe, A cute apomorphine administration, while inducing clinical amelioration and e lectrophysiological changes in the examined nuclei, did not change amino ac id concentrations. This result could be related to a limited microdialysis ability to detect subtle changes in amino acid spontaneous release. Alterna tively, it could suggest that dopaminergic receptors located in the output nuclei, possibly present also in humans, might mediate the acute apomorphin e clinical effects, not involving amino acid changes along the direct and/o r indirect pathway. (C) 2001 Academic Press.