Abstract: Besides maintaining the female secondary sexual characteristics, estrogen also plays important roles in the nervous system, especially in the brain: it can protect tissue from cerebral ischemia reperfusion injury and reduce infarct area by suppressing free radical formation, and can also regulate the release of excitatory amino acids. As an antioxidant, estrogen can protect the nervous system by regulating the body’s redox homeostasis. In addition, estrogen can play its neuroprotective role through estrogen receptors (ER). ER-α and ER-β, two typical ER subtypes that are mainly located in the nucleus, are both expressed in the cerebral cortex and hippocampus. It has been found that ER-α level in the cortex and hippocampus of ovariotomy rats is decreased accompanying decreased learning and memory. LTP, synaptic density and learning and memory are all affected in ER-β gene knock-out mice. NMDA receptor is critical in learning and memory and is coexpressed in hippocampus with estrogen receptors. Estrogen may activate ERK1/2 signal transduction pathway through membrane estrogen receptors, thus inducing the phosphorylation of the NR2B subunit of NMDA receptor to activate NMDA receptor. In addition, the synaptic plasticity can be affected by estrogen and its receptors, as well as by NMDA receptor.

Key words: estrogen, estrogen receptor, glutamic acid, N-methyl-D-aspartic acid receptor(NMDA receptor), learning and memory