FURTHER INVESTIGATIONS INTO THE PATHOPHYSIOLOGY OF MPTP-INDUCED PARKINSONISM IN THE PRIMATE - AN INTRACEREBRAL MICRODIALYSIS STUDY OF GAMMA-AMINOBUTYRIC-ACID IN THE LATERAL SEGMENT OF THE GLOBUS-PALLIDUS

The technique of intracerebral microdialysis has been employed to examine the extracellular level of gamma-aminobutyric acid (GABA) within the lateral segment of the globus pallidus of two cynomolgus monkeys, before and after the induction of parkinsonism with N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Microdialysis probes were acutely implanted through indwelling cannulae positioned at several sites above the lentiform nuclei in the conscious primates, and the basal and potassium (100 mM) evoked amino acid levels were monitored for 3 h. These procedures were repeated at fresh sites within the lateral globus pallidus following the induction of parkinsonism with MPTP. The levels of a number of amino acids, including Asn, Ala, Gln, Ser, and Tau were unchanged following MPTP treatment, whereas both the basal and K+-evoked release of GABA was consistently increased. This observation represents further corroboration of the evidence for increased GABAergic input to the lateral globus pallidus in MPTP-induced parkinsonism.