Abstract: Objective Many experiment results have confirmed that neural stem cells(NSCs) exist in adult central nervous system(CNS).These NSCs will be activated to proliferate,migrate and differentiate by some factors such as growth factors,neurotrophic factors,injury,glucocorticosteroids,exercises,and so on.Intermittent hypoxia is a lesion factor suffered with frequently.Some experiments in vitro have showed that intermittent hypoxia increased the proliferation capacity of NSCs.In present study,the effect of intermittent hypoxia on the proliferation and differentiation of in situ adult NSCs in 6-hydroxydopamine(6-OHDA) lesioned rat brains was investigated.Moreover,the behavioral change was also observed.Methods 6-OHDA was injected into one-side medial forebrain bundle(MFB) of adult rats to establish a model of Parkinson's disease(PD).Before treated with hypoxia exposure,successful parkinsonian model rats were intraperitoneally injected with 5-bromodeoxyuridine(BrdU,100 mg/kg weight) and then treated with 3000 meters high altitude 4 h/d for consecutively 2 weeks.After that,these animals were placed back into normoxia environment for another 2 weeks.Animal behavior test and histology experiments were carried out after two-weeks hypoxia and two-weeks normoxia exposure.The mRNA expression of hypoxia induction factor(HIF)-1α in striatum near to subventricular zone(SVZ) and hippocampus was examined by RT-PCR array.Results Hypoxia did not affect the behavioral disorders of parkinsonian rats.Immunostaining results showed that under hypoxia condition,the number of newborn cells increased greatly,especially in SVZ.Neonatal cells were not found in substantia nigra and possessed the very low differentiation capacity,and they were not found to give rise to neurons and astrocytes.In striatum lesioned by 6-OHDA injection,the neonatal cells did not undergo committed differentiation procedure to become tyrosine hydroxylase(TH)-immunoreative dopaminergic neurons.Contrary to control,the expression of HIF-1α in striatum and hippocampus was not influenced by hypoxia exposure.Conclusion The results showed that intermittent hypoxia could activate the proliferation of adult NSCs in situ,however,it could not induce these neonatal cells to differentiate into specific dopaminergic neurons which was the target neurons in the therapy for PD.These primary results indicated that simple injury factor such as 6-OHDA or hypoxia,could not contribute to thecommitted differentiation,and proliferating NSCs could not restore the function lesion of nervous system.Combination with other inductionfactors,for example,neurotrophic factors,may help the certain differentiation of adult NSCs in situ,thereby benefit the therapy of neurodegenerative diseases.

Key words: hypoxia, neural stem cells, proliferation, differentiation