ADRENALECTOMY ATTENUATES STRESS-INDUCED ELEVATIONS IN EXTRACELLULAR GLUTAMATE CONCENTRATIONS IN THE HIPPOCAMPUS

Glucocorticoids and stress have deleterious effects on hippocampal cel l morphology and survival. It has been hypothesized that these effects are mediated via an excitatory amino acid mechanism. The present stud y was designed to evaluate the effects of acute stress on the extracel lular levels of glutamate in the hippocampus and to determine if adren alectomy modifies this response. Rats were adrenalectomized or sham-ad renalectomized and implanted with microdialysis probes in the CA3 regi on of the hippocampus. Three days later rats were subjected to an acut e 1-h period of immobilization stress. Stress significantly increased extracellular glutamate levels in the sham-operated rats, which peaked at 20 min following the initiation of stress. Extracellular glutamate levels also increased immediately following the termination of stress . In the adrenalectomized rats there was a 30% decrease in basal extra cellular concentrations of glutamate and a marked attenuation (-70%) o f the stress-induced increase in extracellular glutamate levels. Extra cellular concentrations of taurine were not modified by adrenalectomy and did not change in response to stress. These results suggest that g lucocorticoid-induced elevations in extracellular glutamate concentrat ions may contribute to the deleterious effects of stress on hippocampa l neurons.