NON-EXOCYTOTIC GABA OVERFLOW IN RAT STRIATUM INHIBITS GNAWING

The present study tested the hypotheses that spontaneous gamma-aminobu tyric acid (GABA) efflux in anterior rat striatum is 1) independent of intra- and extracellular calcium; and 2) is physiologically relevant. Extracellular dopamine (DA) and GABA were sampled from striatum of aw ake, freely moving rats using in vivo microdialysis. Although dialysat e concentrations of DA were 2 to 3 times greater than GABA and were de creased by at least 70% by removal of calcium, GABA was unaffected eve n in the presence of EGTA or the intracellular calcium chelator APTRA- AM. Functional significance of this non-exocytotic pool of GABA was te sted by injecting 3-mercaptopropionic acid (3-MPA), an inhibitor of GA BA synthesis, into the striatum via a guide cannula sidled alongside a microdialysis probe and measuring subsequent effects on behavior and perfusate concentrations of GABA. Results show that 3-MPA increases gn awing behavior suggesting that basal, non-exocytotic GABA overflow nor mally functions to suppress gnawing.