Abstract: AIM: To explore the effects in different dosage of ketamine on the expression of nitric oxide syn-thase (NOS)in medial septal nuclei (MS)and vertical diagonal band (VDB)of rats.METHODS: 40 SD rats were randomized into normal control group, normal saline (NS)group, low, middle and high dosage of ketamine (25,50, 100 mg·kg^-1, ip)group.Each group was main-tained intraperitoneally by given daily dosage once a day for a period up to 7 days.That was done at 21∶00 hour each night, and by 2 h of the last administration, poured, fixed and slicedwere carried out.Method of nic-otinamide adenosine dinucleotide phosphate diaphorase (NADPH-d)was used to show the expression of NOS in MS andVDB parsdorsalis and ventro.RESULTS: Com-pared with normal control and NS group, the number of NOS positive neurons were decreased inMS andVDB pars dorsalis and ventro in ketamine groups.There were statis-tical meaing in different-dosage groups of ketamine(P<0.05 or P<0.01).Cell-dyeing became lighten, and cel-luar average optical density value wasincreased inMS and VDB pars dorsalis and ventro in each administered ket-amine groups, There were statistical meaing in high and low dosage of ketamine(P<0.01).CONCLUSION: Ketamine can reduce the expression of NOS in MS and VDB by dosage dependence, which suggests that anesthe-sia effect of ketamine has possible correlation with neuro-pathic side effect.

Key words: ketamine, medial septal nuclei, diago-nal band, nitric oxide synthasdyeing, rats