gms | German Medical Science

Objective: After spinal cord injury (SCI), primary and secondary damage occur due to several endogenous processes including inflammation and development of a glial scar. So far many different approaches have been tried to boost regeneration, axonal regrowth and sprouting. We have tried a new technique with implantation of a graft extracted from the subventricular zone (SVZ), an almost unique region within the central nervous system known for developing stem cells throughout adult life. In addition a SVZ graft has the ability of growing in a specific direction.

Methods: Mice expressing GFP under the β-actin promoter were used to obtain the SVZ graft. For SCI in C57 black6 mice a hemitransectomy of the spinal cord at the Th7 level was performed. Immediately afterwards the 0,5 mm³ GFP SVZ graft was implanted. Control mice received GFP motor cortex or olfactory bulb grafts. In addition corticospinal tracts were traced with BDA. Motor impairment and functional regeneration were measured using BMS and behavioral tests. Mice were sacrificed after 3, 7, 14, 28 and 56 days. Due to GFP homologous and grafted cells and axons could easily be distinguished. Using immunohistochemical techniques the survival of the grafted cells, axonal regrowth, newly established connections and the size of the glial scar was counted and measured by two blinded researchers.

Results: In all our studied mice the graft survived the observation period. Using histological analyses we are perfectly able to distinguish host cells from implanted cells, because the later ones firmly express GFP. GFP expressing neurons, blood vessels and astrocytes could be found and were identified with immunocytochemistry. Motor impairment and functional regeneration tests showed a slightly better outcome of the experimental group. Regrowing axons were monitored via BDA tracing.

Conclusions: We present a new technique monitoring a GFP SVZ graft over a long period. This approach allows to stable monitor the ingrowth of transplanted cells at the SCI site, as well as to study their role in the regulation of endogenous regenerative processes. By interposing the disrupted nerve fibers with a graft we are able to help regrowing axons to find their way, thus establishing reconnections and resulting in lesser motor impairment. We think our method will help to develop a new way to overcome some of the detrimental effects of SCI. In humans SVZ grafts could be obtained with an endoscopic approach to the lateral ventricle and afterwards transplanted.