Objective To investigate the effects of acute and chronic administration of the non-competitive NMDA receptor antagonists MK-801 on c-Fos protein expression in different brain regions of mice and an-tagonistic action of clozapine.Methods Immunohistochemistry was used to detect the expression of c-Fos protein.Results MK-801(0.6 mg·kg-1)acute administration produced a significant increase in the expression of c-Fos protein in the layers Ⅲ-Ⅳ of posterior cingulate and retrosplenial(PC/RS)cortex,which was consistent with the previous reports.Moreover,we presented a new finding that MK-801(0.6 mg·kg-1)chronic administration for 8 days produced a significant increase of c-Fos protein expression in the PC/RS cortex,prefrontal cortex(PFC)and hypothalamus of mice.Among that,c-Fos protein expression in the PC/RS cortex of mice was most significant.Compared acute administration with chronic administration,we found that MK-801 chronic administration significantly increased the expression of c-Fos protein in the PC/RS cortex,PFC and hypothalamus.Furthermore,pretreatment of mice with clozapine significantly decreased the expression of c-Fos protein induced by MK-801 acute and chronic administration.Conclusions Marked expression of c-Fos protein induced by MK-801 is associated with neurotransmitters’ change noted in our previous studies,and c-Fos protein,the marker of neuronal activation,might play an important role in the chronic pathophysiological process of schizophrenic model induced by NMDA receptor antagonist. Objective To investigate the effects of acute and chronic administration of the non-competitive NMDA receptor antagonists MK-801 on c-Fos protein expression in different brain regions of mice and an-tagonistic action of clozapine. Methods Immunohistochemistry was used to detect the expression of acute administration produced a significant increase in the expression of c-Fos protein in the layers III-IV of posterior cingulate and retrosplenial (PC / RS) cortex, which c-Fos protein.Results MK-801 (0.6 mg · kg -1) was consistent with the previous reports. Moreover, we presented a new finding that chronic-administration of MK-801 (0.6 mg · kg-1) produced a significant increase of c-Fos protein expression in the PC / RS cortex, prefrontal cortex (PFC) and hypothalamus of mice. Among that, c-Fos protein expression in the PC / RS cortex of mice was the most significant. Compared acute administration with chronic administration, we found that MK-801 chronic administration significantly increased the expression of c-Fos protein in the PC / RS cortex, PFC and hypothalamus. Frther and pretreatment of mice with clozapine significantly decreased the expression of c-Fos protein induced by MK-801 acute and chronic administration. Conclusions Marked expression of c-Fos protein induced by MK-801 is associated with neurotransmitters’ change noted in our previous studies, and c-Fos protein, the marker of neuronal activation, might play an important role in the chronic pathophysiological process of schizophrenic model induced by NMDA receptor antagonist.