COCAINE INCREASES EXTRANEURONAL LEVELS OF ASPARTATE AND GLUTAMATE IN THE NUCLEUS-ACCUMBENS

Intracerebral microdialysis was used to assess the effects of cocaine- HCl on extracellular concentrations of the excitatory amino acids aspa rtate and glutamate in the nucleus accumbens of awake, freely moving r ats. After an initial equilibration period, cocaine (7.5, 15 or 30 mg/ kg) or saline was injected i.p., and samples were collected for an add itional 2 h. The highest dose of cocaine (30 mg/kg, i.p.) caused a 4-f old increase in glutamate levels and an 18-fold increase in aspartate levels over baseline. To verify that the source of the extracellular a spartate and glutamate was neuronal, additional experiments were condu cted using Ca2+-free microdialysis buffer, and buffer containing 10 mu M tetrodotoxin. Local perfusion with Ca2+-free buffer reduced the inc rease of extracellular aspartate and glutamate in rats injected with 3 0 mg/kg cocaine. Tetrodotoxin significantly decreased the cocaine-indu ced increase in excitatory amino acids, but not the behavioral respons e.