CHARACTERIZATION OF EXTRACELLULAR AMINO-ACIDS IN STRIATUM OF FREELY MOVING RATS BY IN-VIVO MICRODIALYSIS

To investigate the characteristics of extracellular amino acids releas ed from the striatum, we performed in vivo microdialysis in non-anaest hetised, freely moving rats. Amino acids were determined after precolu mn derivatisation with o-phthalaldehyde by high-performance liquid chr omatography and fluorescence detection. The omission of Ca2+ in the pe rfusion medium partially decreased the basal concentration of aspartat e and glutamate. This shows that a small fraction of basal concentrati on of aspartate and glutamate is of neuronal origin. The effect of hig h K+ and veratrine stimulation was evaluated in the presence or absenc e of Ca2+ or tetrodotoxin (1 mu M). High K+ and veratrine caused a rem arkable increase in the aspartate and glutamate efflux. The omission o f Ca2+ only partially decreased K+-stimulated aspartate and glutamate efflux. Tetrodotoxin completely antagonised veratrine-stimulated aspar tate and glutamate efflux. Although glycine and taurine releases were stimulated by high K+ and veratrine, their release was not always anta gonised with Ca2+ omission or tetrodotoxin inclusion. Thus, the neuron al origin of stimulated release of glycine and taurine is unclear. Alt hough tetrodotoxin sensitivity and Ca2+-dependency are regarded as a b asic criterion for classical neurotransmitters in microdialysis experi ments, they should not be adapted to the physiological characteristics of the release of amino acids.