Grafted neural stem cells migrate to substantia nigra and improve behavior in Parkinsonian rats

Neural stem cell (NSC) transplantation has the potential to treat neurodegenerative diseases such as Parkinson's disease (PD). In this study, we investigated the effect of transplanted NSCs in a PD animal model. NSCs isolated from the subventricular zone (SVZ) of E14 rats were cultured in vitro to produce neurospheres, which were subsequently infected with recombinant adeno-associated virus (rAAV₂) expressing enhanced green fluorescent protein (EGFP). The PD animal model was established by unilateral injection of 6-hydroxydopamine (6-OHDA) into the medial forebrain bundle (MFB) of Sprague–Dawley rats. Once the model was established, EGFP-expressing NSCs were transplanted into the substantia nigra pars compacta (SNc) or striatum of PD rats. We found that NSCs transplanted into either site significantly reduced apomorphine-induced circling behavior of PD rats. Pathological analysis revealed that the EGFP-expressing NSCs could be detected at both injection sites at 1, 2 and 4 months after transplantation. SNc transplanted cells dispersed within the SNc with a significant portion differentiated into tyrosine hydroxylase-positive neurons. Whereas cells transplanted into the striatum migrated ventrally and posteriorly towards the SNc. These results suggest that the 6-OHDA damaged brain area attracts grafted NSCs, which migrated from the striatum and survived for a long time in SNc, resulting in behavioral improvement of PD rats.