GLUTAMATE UPTAKE IMPAIRMENT AND NEURONAL DAMAGE IN YOUNG AND AGED RATS IN-VIVO

The extracellular concentration of glutamate increases during hypoxia/ ischemia probably due to deficient uptake. Glutamate might contribute to neuronal damage associated with this disorder and to neurodegenerat ion during aging. In the present study, we have tested the effect of t wo inhibitors of glutamate transport, L-trans-pyrrolidine-2,4-dicarbox ylate and dihydrokainate, on the extracellular levels of glutamate and on neuronal damage, which was quantitatively studied by image analysi s of histological brain sections. Drugs were administered by microdial ysis and glutamate concentration was determined by HPLC in the striatu m and the hippocampus of 3-month-old and 22-24-month-old rats. In both regions studied, the basal concentration of extracellular glutamate w as higher in aged than in young rats. Pyrrolidine dicarboxylate induce d a substantial elevation of extracellular glutamate in both regions, and although this increase was almost twofold higher in old than in yo ung animals, no neuronal damage was observed. In contrast, dihydrokain ate had a poor effect on glutamate levels, but induced clear neuronal damage in the striatum and the hippocampus in both groups of rats. The present results suggest that age appears not to be a significant fact or in the sensitivity of neurons to the toxic effect of extracellular glutamate increase via blockade of its transport system.