EFFECT OF PRECIPITATED WITHDRAWAL ON EXTRACELLULAR GLUTAMATE AND ASPARTATE IN THE NUCLEUS-ACCUMBENS OF CHRONICALLY MORPHINE-TREATED RATS - AN IN-VIVO MICRODIALYSIS STUDY

Excitatory amino acids release during morphine or naloxone administrat ion was studied in rats. Microdialysis in freely moving animals and ca pillary electrophoresis with laser-induced fluorescence detection were used to measure several amino acids including glutamate and aspartate in the extracellular fluid at the nucleus accumbens. Perfusion with a calcium-free Ringer's solution decreased glutamate and aspartate in n ucleus accumbens dialysates to 35% of its baseline levels, suggesting partial synaptic origin of these amino acids. The first morphine injec tion decreased glutamate and aspartate to 50% of its baseline level. A fter repeated morphine injections this effect disappeared, suggesting tolerance. Naloxone injections to morphine-dependent rats increased 30 0% glutamate and aspartate release; these experiments suggest that exc itatory amino acid release in the nucleus accumbens might play a role in morphine withdrawal. (C) 1998 Elsevier Science Inc.