Abstract: Objective To investigate the effects of (+)-5-methyl-10,11-dihydro-5H-dibenzoa,dcyclohepten-5,10-imine maleate(MK-801)on the changes of dopamine(DA)content and Fos protein expression in anterior cingulate cortex(ACC)of rats induced by noxious electrical stimulation of saphenous nerve(SN).Methods Seventy-two male Wistar rats were randomly divided into control group,sham stimulation group,electrical stimulation group,low-(0.5 mg/kg body weight)and high-dose(1.0 mg/kg body weight)MK-801 group,and NS control group.The rats were sacrificed after the treatments and then the right side ACC were collected and homogenized.After spinning at 10 000 rpm at 4 ℃ for 20 min,20 μL of the supernatant was harvested from each sample.High performance liquid chromatography electrochemical detection was used to measure DA content in ACC.ACC brain tissues of the different groups were cut to continuous coronal frozen sections.Then immunohistochemistry method was used to measure the Fos protein expression of ACC.Results Compared with those of the sham stimulation group,DA content(24.89±2.50 ng/g),Fos protein expression(8.481 1±1.243 2),and the percentage of positive cells(3.133 8±0.824 2%) in the rats ACC of electrical stimulation group were significantly increased.Compared with those of the electrical stimulation group,DA content(15.07±3.75 and 14.84±2.92 ng/g),Fos protein expression (7.107 8±0.610 7 and 7.037 5±0.411 8),and the percentage of positive cells(2.173 9±0.4668%and 2.047 6±0.361 3%)in the rats ACC of low- and high-dose MK-801 group were significantly decreased,indicating that MK-801 antagonized the increases in DA content and Fos protein expression in ACC caused by noxious electrical stimulation of SN.Conclusion The results suggest that N-methyl-D-aspartate receptor may be involved in the increases in DA content and Fos protein expression of rats ACC induced by nociceptive afferent singnal from SN.