Background Olfactory ensheathing cells(OECs)can promote many kinds of neuron growth and axonal extension.Theaim of the study was to investigate the effects of co-culturing with OECs on neuron apoptosis in vitro.Methods Apoptosis was induced by treatment of cultured dorsal root ganglion neurons with 1 mmol/L hydrogenperoxide(H_2O_2).Cells were randomly arranged into the following treatment groups.In group 1,OECs at different density(10~4/ml to 8×10~5/ml)were added immediately after H_2O_2 treatment and cells were co-cultured for 24 hours.In group 2,OECs were added at different time points(0,4,8,12 and 24 hours)after H_2O_2 treatment.Apoptotic cell death wasdetermined by Hoechst 33258 staining and flow cytometry(FCM).Cell viability was determined by using methylthiazoleterazolium(MTT)assays.Results The results showed in the Hoechest 33258 staining,FCM and MTT that OECs have both thedensity-dependent protection and time-dependent protection on neuron apoptosis.The apoptosis decreased and thedorsal root ganglion neuron viability increased,when the density of OECs was increased in co-culture groups.But furtherincreasing OEC density above 2×10~5/ml(i.e.8×10~5/ml)failed to exert additional protection.As the interval betweenadding H_2O_2 and adding OECs was increased,the amounts of apoptosis cells were also increased.When OECs wereadded 24 hours after H_2O_2,no significant protection was observed.Conclusion These results indicated that OECs could protect dorsal root ganglion neurons from apoptosis induced byH_2O_2 in a density- and time-dependent manner.Chin Med J 2007:120(16):1438-1443 Background Olfactory ensheathing cells (OECs) can promote many kinds of neuron growth and axonal extension. Aim of the study was to investigate the effects of co-culturing with OECs on neuron apoptosis in vitro. Methods Apoptosis was induced by treatment of cultured dorsal root ganglion neurons with 1 mmol / L hydrogenperoxide (H 2 O 2) .Cells were randomly arranged into the following treatment groups.In group 1, OECs at different density (10 ~ 4 / ml to 8 × 10 ~ 5 / ml) were added immediately after H_2O_2 treatment and cells were co-cultured for 24 hours.In group 2, OECs were added at different time points (0,4,8,12 and 24 hours) after H 2 O 2 treatment. Apoptotic cell death was determined by Hoechst 33258 staining and flow cytometry .Cell viability was determined by using methylthiazoleterazolium (MTT) assays. Results The results showed in the Hoechest 33258 staining, FCM and MTT that OECs have both the density-dependent protection and time-dependent protection on neuron apoptosis. The apoptosis decreased and thedorsal root ganglion neuron viability increased, when the density of OECs was increased in co-culture groups. further increasing oEC density above 2 × 10-5 / ml (ie8 × 10-5 / ml) failed to exert additional protection. As the interval betweenadding H_2O_2 and adding OECs was increased, the amounts of apoptosis cells were also increased. Who OECs wereadded 24 hours after H_2O_2, no significant protection was observed. Confc these these results indicated that OECs could protect dorsal root ganglion neurons from apoptosis induced by H_2O_2 in a density- and time-dependent manner. Chin Med J 2007: 120 (16): 1438-1443