MEASUREMENT AND PHARMACOLOGICAL MANIPULATION OF EXTRACELLULAR GABA LEVELS IN THE NUCLEUS-ACCUMBENS OF THE RAT

Extracellular endogenous gamma-aminobutyric acid (GABA) in the nucleus accumbens of conscious rats was measured using in vivo microdialysis combined with high performance liquid chromatography and fluorometric detection. The perfusion of high potassium (50 mu M, 20 min) dialysis solution significantly increased GABA levels. GABA levels were decreas ed in the dialysate, when tetrodotoxin (1 mu M) was added in the perfu sion or when a calcium-free solution was perfused. Thee perfusion of n ipecotic acid (100 mu M, an uptake inhibitor of GABA) or aminooxy acet ic acid (100 mu M, a GABA transaminase inhibitor) significantly increa sed GABA levels. Local perfusion of sulpiride (10 mu M, 120 min), a do pamine D-2 receptor antagonist, also significantly increased extracell ular GABA levels in the nucleus accumbens. These findings suggest that the detected GABA in the dialysate is the neurotransmitter which orig inated from GABA-containing neurons. The inhibition of D-2 dopamine re ceptors caused increases in GABA release in rat nucleus accumbens in r ats.