IN-VIVO BLOCKADE OF THALAMIC GABA(B) RECEPTORS INCREASES EXCITATORY AMINO-ACID LEVELS

The effect of intrathalamic application of GABA(B) receptor antagonist s on the basal excitatory amino-acid levels was studied using microdia lysis probes implanted in the dorsal lateral geniculate nucleus and in the ventrobasal complex. In both nuclei, continuous perfusion of the GABA(B) receptor antagonist 3-aminopropyl-(diethoxymethyl)-phosphinic acid (CGP 35348) produced an increase in the extracellular concentrati on of aspartate and (to a lesser extent) glutamate, but no change was observed in the level of taurine, the main amino acid involved in the regulation of brain osmolarity processes. In contrast, mino-2-hydroxy- 2-(4-chlorophenyl)-propanesulphonic acid (2-hydroxy-saclofen), another GABA(B) receptor antagonist, failed to affect the extracellular conce ntration of aspartate, glutamate and taurine. Thus, the basal level of excitatory amino acids in the thalamus in vivo is under the control o f CGP 35348-sensitive GABA(B) receptors.