Objective   To explore the effects of erythropoietin (EPO) on the proliferation and differentiation of neural stem cells and on the cognition function of vascular dementia (VD) rats.    Methods   Totally 45 Sprague-Dawlev (SD) rats were randomly and equally divided into the sham control group

the VD group

and the treatment group. The VD rat model was established by performing cerebral ischemia/reperfusion repeatedly and given an intraperitoneal injection sodium nitroprusside.  The rats from the treatment group received an introperitoneal injection of EPO after the establish of VD model

and the animals from the others were treated with normal saline. The learning-memory abilities were measured by using computerized shuttle-training case and the proliferation and differentiation of neural stem cells were detected by immunofluorescence staining.    Results   The active avoidance reaction (AAR) ratio in the VD group was significantly decreased compared with the sham control group (P0.01)

but that in the treatment group was higher than the VD group (P0.01) though still lower than the sham group (P0.01). During  the 4 weeks we observed

BrdU labeled cells were migrated from the subgranular zone to granule cell layer. In  1 week after the model established

the number of BrdU labeled cells in the VD group was significantly larger than in the sham control group

but lower than that in the treatment group (P0.01). Immunofluorescence staining showed that the number of BrdU and DCX double  labeled cells in the treatment group was significantly larger than that in the VD group. In 4 weeks

the number of BrdU labeled cell was decreased in each group

especially in the VD group

and the number of BrdU and NSE double labeled cells in the treatment group was significantly larger than that in the VD group. But the percentage of BrdU-labeled cells co-labeled with DCX/NSE had no significant difference.    Conclusion   EPO treatment enhances the proliferation of neural stem cells and improves the ability of learning and memory in VD rats，but has no obvious influence on the differentiation of the neural stem cells.