N-methyl-D-aspartate receptor involvement in dexamethasone and stress-induced hypothalamic somatostatin release in rats

The median eminence (ME) push-pull perfusion technique was used in this work and the results clearly showed that ip. administration of MK-801 (4 mg/kg), a specific N-methyl-D-aspartate (NMDA) receptor antagonist, totally abolished dexamethasone (Dex) (300 mu g/100g i.p. injected) and immobilization stress-induced hypothalamic somatostatin release in adult male rats. We also observed that glutamate from median eminence-hypothalamic medio basal (ME-MBH) complex, measured by high performance Liquid chromatography (HPLC), exhibited a conspicuous secretory pattern, with the total amount released not modified by Dex administration. This indicates that Dex and stress-induced somatostatin (SS) secretion is not mediated by endogenous glutamate variations but likely by activation of NMDA receptors.