MK-801 Protects against Intracellular Ca2+ Overloading and Improves N-methyl-d-aspartate Receptor Expression in Cerebral Cortex of Methylmercury-Poisoned Rats

Overexposure to methylmercury (MeHg) has been known to induce neurotoxicity. The objective of this study is to explore mechanisms that contribute to MeHg-induced nerve cell apoptosis focusing on the alteration of intracellular Ca²⁺ homeostasis and expression of N-methyl-d-aspartate receptors (NMDARs) subunits in rat cerebral cortex and whether MK801, a non-competitive NMDAR antagonist, could attenuate MeHg-induced neurotoxicity. Fifty rats were randomly divided into five groups of 10 animals in each group: control group, MK801 control group, MeHg-treated group (4 and 12 μmol/kg) and MK801 pre-treated group. Administration of MeHg at a dose of 12 μmol/kg for 4 weeks significantly increased in intracellular Ca²⁺]_i and total Hg levels and that enhanced neurocyte apoptosis rate in cerebral cortex. In addition, the inhibitory effect of MeHg on Na⁺-K⁺-ATPase and Ca²⁺-ATPases might be one of the reasons that cause a significant increase of Ca²⁺]_i in neurocyte. Over activated by increased cytosolic Ca²⁺ loading, calpains degraded NMDAR subunits leading ultimately to nerve cell damage. However, pretreatment with MK801 at a dose of 0.3 μmol/kg could prevent Ca²⁺ homeostasis dysregulation and alleviate the neurocyte apoptosis. In conclusion, the neuroprotective effects of MK801 appeared to be mediated not only via its NMDA receptor binding properties but also by maintaining intracellular calcium homeostasis.