ABSTRACT
OBJECTIVE Previous studies showed that over activation of NMDA receptors may be a crucial cause of long-term potentiation (LTP) and cognitive impairment induced by stress or corticosterone. However, other studies showed that the function of NMDA receptors is insufficient since the NMDA receptors co-agonist D-serine could improve stress-induced cognitive impairment. The purpose of this study is to clarify whether over activation of NMDA receptors or hypofunction of NMDA receptors is involved in hippocampal impairment of LTP by corticosterone and the underlying mechanisms. METHODS Cort was injected subcutaneously 1 h before the high-frequency stimulation (HFS) to induce LTP impairment. NMDA receptor antagonists and agonists were administrated by icv. RESULTS Hippocampal LTP and object location recognition memory were impaired in corticosterone-treated mice. Corticosterone increased the gluta?mate level in hippocampal tissues, neither NMDA receptors antagonist nor its subtype antagonists alleviated impairment of LTP, while enhancing the function of NMDA receptors by D-serine did alleviate impairment of LTP by corticosterone, suggesting that hypofunction of NMDA receptors might be one of the main reasons for impairment of LTP by corticoste?rone. Further results showed that the level of D-serine and its precursor L-serine did not change. D-serine release-related protein Na+-independent alanine-serine-cysteine transporter-1 (ASC-1) in the cell membrane was decreased and increas?ing D-serine release by the selective activator of ASC-1 antiporter activity alleviated impairment of LTP by corticoste?rone. CONCLUSION Taken together, this study demonstrates that hypofunction of NMDA receptors may be involved in impairment of LTP by corticosterone and reduced D-serine release may be an important reason for its hypofunction, which is an important complement to existing mechanisms of corticosterone-induced LTP and cognitive impairment.