Rapid enhancement of high affinity glutamate uptake by glucocorticoids in rats cerebral cortex synaptosomes

The effects of glucocorticoids on the Na+-dependent, high affinity uptake of (3)[H]-L-glutamate in synaptosomes from cerebral cortex of rats were investigated. Glucocorticoids, including corticosterone (B), corticosterone-sulfate (Bs), hydrocortisone-hemisuccinate (F) and dexamethasone-phosphate (DEX) were found stimulating glutamate uptake in synaptosomes after 4 min incubation. The uptake was increased up to 121.4%, 125.5%, 120.8% and 113.6% of the control uptake for 10(-6) mol/L of Bs, B, F and DEX respectively. The stimulation was dose-dependent in the case of Bs, and steroid-specific while deoxycorticosterone and 17 beta-estradiol-sulfate were ineffective, and progesterone and testosterone enhanced the uptake to a lesser extent than B. The rapid stimulations of glucocorticoids on glutamate uptake in synaptsomes, detached from perikaryon, are undoubtedly attributed to the nongenomic mechanisms. The inhibitor of G-protein activation, guanosine 5-O-(2-thiodiphosphate) could at least partially block the stimulation of Bs, suggesting that the G-protein on membranes of synaptosomes might be involved in the effect of glucocorticoids.