Abstract： Objective To explore the influence of recombination granulocyte colony stimulating factor (rG-CSF)on mobilization and distribution of bone marrow stem cells (BMSCs) in blood and brain tissue,and its role in protecting brain in rats with cerebral ischemia.Methods One hundred and six SpragueDawley(SD)rats were divided into sham-operated group (n=10),model group(n=48),rG-CSF group (n=48) according to the method of random digital table,and rats in model and rG-CSF groups were divided into four subgroups:i.e.2,3,7 and 14 days subgroups,with 12 rats in each subgroup.Middle cerebral artery occlusion(MCAO)model was reproduced with nylon thread.In rats of rG-CSF group rG-CSF (10 btg/kg)was administered by subcutaneous injection 3 days before and 2 days after operation respectively,once a day.Rats in sham-operated and model groups were administered with normal saline in the same volume,once a day.At the corresponding time after operation,general neural function score(GNFS)of rats was measured.Blood was collected through abdominal aorta,then white blood cell (WBC) and CD34+ cells in peripheral blood were counted.Brain pathologic changes were observed,and expression of CD34+ cells in rats brain tissue was determined by using immunohistochemical method.Results ①GNFS was lower obviously in 2-day model group compared with that in sham-operated group,and then increased gradually.At 7 days and 14 days after operation,GNFS in rG-CSF group was higher significantly than that in model group (7 days:11.86±0.69 vs.10.53±0.76,14 days:13.38±0.52 vs.12.38±0.52,both P<0.01).②WBC and CD34+ cells in peripheral blood in model group increased obviously,with the highest level appeared at 3 days and lowered at 7 days and 14 days.Increase of WBC and CD34+ cells in rats of rG-CSF group was more obvious than that of model group at each time point except CD34+ in 14 days group [WBC (×109/L)2 days:11.75±1.76 vs.8.07±1.27,3 days:13.07±1.70 vs.10.88±1.78,7 days:8.63±1.36 vs.5.58士1.57,14 days:6.98士0.98 vs.4.87士0.92;CD34'(cells/t~1)2 days:8.83±2.14 vs.3.17±0.75,3 days:13.50±1.87 vs.5.00±1.55,7 days:5.33±1.21 vs.2.33±1.21,P<0.05 or P<0.01].③Expression of CD34+ cells in the brain of rats in 2-day model group increased significantly,and the highest level appeared at 7 days and decreased at 14 days.Absorbance (A) value of CD34+ cells expression in rat brains of each rG-CSF group was more significant than that in model group(2 days:43.21±4.41 vs.22.04±2.95,3 days:45.79±1.76 vs.25.69±2.44,7 days:52.09±2.86 vs.33.04±2.62,14 days:29.73±1.99 vs.16.91±2.95,all P<0.01).④ The signs of injury to brain in pathological examination were less obvious in 14 days rG-CSF group.Conclusion BMSCs could be induced to enter peripheral blood and "home" to brain tissue after cerebral ischemia.It was showed that BMSCs increased in number at first and then decreased in peripheral blood and brain,the peak number was found on 3rd day in peripheral blood and 7th day in brain.Mobilization with rG-CSF could increase the number of BMSCs in peripheral blood and brain tissue.The effect of mobilization of BMSCs on protecting brain was significant after cerebral ischemia,and effect appeared to be more pronounced with prolongation of mobilization.