INHIBITION OF GLUTAMATE UPTAKE INDUCES PROGRESSIVE ACCUMULATION OF EXTRACELLULAR GLUTAMATE AND NEURONAL DAMAGE IN RAT CORTICAL CULTURES

It is known that neurons exposed to high concentrations of glutamate d egenerate and die, The clearance of this amino acid from the extracell ular space depends on their active transport by Na+-dependent high-aff inity carriers, In the present study we tested whether inhibition of g lutamate transport in mixed glial/neuronal cortical cultures induces a ccumulation of extracellular glutamate and whether such increase resul ts in cell damage, Three inhibitors of glutamate transport were used: L-trans-pyrrolidine-2,4-dicarboxylate (PDC), DL-threo-beta-hydroxyaspa rtate (THA), and dihydrokainate (DHK). Cell damage was assessed by lig ht microscopy observations, reduction of (4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide, and leakage of lactate dehydrogenase, P DC induced a significant concentration- and time-dependent neuronal da mage, whereas pure glial cultures were not affected, A good correlatio n was found between this damage and elevations of glutamate concentrat ion in the medium, These effects of PDC were similar in glutamine-free medium and in medium supplemented with glutamine, THA induced identic al cell damage and elevations of extracellular glutamate to those prod uced by PDC, while DHK did not affect at all any of these parameters, PDC- and THA-induced toxicity was protected by the N-methyl-D-aspartat e receptor antagonist ethyl-10,11-dihydro-5H-dibenzo-(a,d)cyclohepten- 5, 10-imine maleate but not by the non-N-methyl-D-aspartate receptor a ntagonist -dihydroxy-6-nitro-7-sulfamoylbenzo(f)quinoxaline. (C) 1996 Wiley-Liss, Inc.