The Effects Of NMDA Receptor Antagonist MK-801on Hippocampal Caspase-3, Bax And Bcl-2Expression In A Mouse Model Of Intermittent Hypoxia

Objective In the present study using a mouse model of chronic intermittent hypoxia(CIH), we aimed to evaluate the CIH-induced changes in the expression of Bax,Bcl-2andcaspase-3in hippocampal neurons. The therapeutic efficacy of the NMDA receptorantagonist MK-801in attenuating CIH-induced changes of apoptotic protein expression inhippocampus was also investigated.Methods Experimental chambers were used to allow at least4-week animalinhabitancy, during which CIH was applied by cycling the nitrogen and compressed airevery60seconds for a fixed8-hour daytime(8:00AM-4:00PM). The control animals weremaintained in circulating room air. Male ICR mice (n=36) were randomly assigned tofollowing treatments for4weeks:unhandled control group(UC group), CIH group,CIH+saline group and CIH+MK-801group. MK-801, an NMDA receptor antagonist, wasadministered by intraperitoneal injection at a dose of4ug/day60minutes before theinitiation of CIH exposure. The mice in CIH+saline group received saline with subsequentexposure to intermittent hypoxia. The assessments of hippocampal expression levels ofBcl-2, Bax and caspase-3proteins were performed by Western blotting after4weeks ofCIH and compared with the time-matched control animals.In addition, the expressionlevels of Bax and caspase-3proteins in hippocampal CAl region was evaluate byimmunohistochemistry,The positive neurons in hippocampal CAl region were analysised.ResultsThe results of Western-blot assay: Compared with the UC group, the mousehippocampal expression of Bcl-2,Bax and caspase-3proteins increased significantly inCIH group and CIH+saline group (P<0.05). whereas no difference in these proteinexpression was observed between the CIH and CIH+saline animals. By contrast with CIHgroup, Pre-treatment with MK-801was shown to significantly reduce CIH-induced hippocampal expression of Bax and caspase-3proteins (P<0.05). However, there were nosignificant difference in the expression of Bcl-2protein between CIH group and andCIH+MK-801group.The results of immunohistochemistry assay: Compared with the UC group, Baximmunopositive cells and caspase-3immunopositive cells in hippocampus CA1weresignificantly increased in CIH group(P<0.05).Compared with CIH group, Baximmunopositive cells and caspase-3immunopositive cells in hippocampus CA1weresignificantly reduced in CIH+MK-801group(P<0.05).Conclusions We demonstrated that4-week CIH exposure significantly enhancedneuronal apoptotic protein expression in hippocampal CA1neurons in a mouse model ofCIH, and such changes were largely prevented by pre-treatment with NMDA receptorantagonist MK-801. These findings indicate the NMDA receptor-operated calcium channelmay play an important role in CIH-induced hippocampal neuronal damage.