THE ROLE OF GABA RECEPTORS IN THE CONTROL OF NIGROSTRIATAL DOPAMINERGIC-NEURONS - DUAL-PROBE MICRODIALYSIS STUDY IN AWAKE RATS

A microdialysis probe implanted into the substantia nigra was used to infuse gamma-aminobutyric acid-ergic (GABAergic) compounds onto cell bodies/dendrites of dopaminergic neurons, while a second microdialysis probe was used to record the extracellular concentrations of dopamine and 3,4-dihydroxy-phenylacetic acid (DOPAC) in the ipsilateral striatum. The GABA(A) receptor agonist muscimol (10-mu-mol/l) increased the release of dopamine in the ipsilateral striatum to 120% of the control values. The GABA(B) receptor agonist, (Z)-3[(aminoiminomethyl)-thiol]-prop-2-enoic acid (500-mu-mol/l), was without effect. Infusion of the GABA(A) receptor antagonists, bicuculline (50-mu-mol/l) and picrotoxin (50-mu-mol/l), stimulated the release of dopamine in the ipsilateral striatum to 160 and 130% of the controls, respectively. The GABA(B) receptor agonist, baclofen (10 and 50-mu-mol/l), strongly inhibited the release of striatal dopamine, whereas infusion of the GABA(B) receptor antagonist, 2-hydroxy-saclofen (100-mu-mol/l), was without effect. The results indicate that, in the substantia nigra, GABA(A) as well as GABA(B) receptors participate in controlling the activity of dopaminergic neurons