| Spinal cord injury (SCI), a common severe trauma in the central nervous system (CNS), often results in an irreversible loss of sensory and motor function, with manifestations mainly including the total loss of sensory and motor function below the injuried segmental spinal cord, and the urinary and fecal incontinence. The paraplegia following spinal cord injury not only brings great pain for patients both physically and mentally, but also gives the families and society a heavy economic burden and causes a severe social problem. With the development of modern society, SCI presents new characteristics of"three high and one low (high incidence rate, high disability rate, high expense and low mortality )", therefore, it has been a hot spot and a troublesome task for the neurologic scientists to put more emphasis on the research to repair of SCI and rehabilitation of paraplegia. The previous treatments mainly focused on the rehabilitative care and the symptomatic treatments, which including the reposition fixing after spinal fracture and dislocation, spinal decompression, and the absorbing of edema and improvement of microcirculation and so on, with no perfect therapeutic effect. Recently, cellular transplantation especially the transplantation of neural stem cells (NSCs) brings new development for the treatment of SCI, which aims at the promoting effect on regeneration and repair of the injuried spinal cord. The main mechanisms of SCI treatment with cellular transplantation are as follows: (1) The spinal cord defect was filled with transplanted cells, which offers a place and clues for the growth and adherence of neurons and axonal elongation; (2) Regenerative neurons were transplanted to replace the injuried or necrotic neurons to reconstruct the neural pathways; (3) The transplanted cells will provide various of neurotrophic factors (NTFs) promoting the axonal regeneration, including brain-dedrived neurotrophic factor (BDNF), neurotrophins (NTs), nerve growth factor( NGF), and so on, with wide application in the future. Neural stem cells (NSCs) are a kind of stem cells with self-renewal and multi-directional differentiation potentials in the mammal embryonic neural tissue (including cerebral cortex, lateral cerebral ventricle, subependymal layer, hippocampus, corpora striata, mesencephalon and spinal cord) and the adult animal CNS (including cerebral cortex, subependymal region, lateral cerebral ventricle, dentate fascia, smell gyrus and ependyma of the central canal of the spinal cord). As the seed cells for the repair of injury in the nervous system, NSCs are not only enough for the requirement of transplantation, but also have a potential to differentiate into three different neural cell lines including neurons. It is easy to obtain NSCs, so does the culture and identification, meanwhile, with a characteristic of great proliferation and differentiation potential in vitro, and so on, NSCs can be used as the donator in the transplantation. Although the function of NSCs is theoretically perfect, however, recently, researches have found out that there are problems as follows in the single application of NSCs for the treatment of adult SCI: it has an limited potential in the management of the development of neurons, and a common lack of the conditions for the NSCs induced to be neurons; there is no solution for the disadvantageous fact that there are only a few differentiated neurons after NSCs transplantation, and great proliferation of glial cells; Insufficient neurons were offered for the functional connections among the large amounts of axons; what was more, the formation of large amounts of glial scar not only occupied the space required for the growth of intact axon but also secreted some inhibitory factors of the axonal growth,so the regeneration of axons was retardarce. Therefore, it has become a major concern that how to promote the differentiation of transplanted NSCs in the injuried spinal cord into neurons and inhibit the proliferation of glial scar during the repair of SCI.As a first-line antiepileptic and anticonvulsion drug, valproic acid (VPA) has been widely applied clinically for 40 years with the reliable security. Recent studies have demonstrated that VPA can raise the ratio of NSCs differentiation towards neurons in vitro as high as about 80%, meanwhile, it can protect the neurons, and reduce the inflammatory reaction and the proliferation of glial cells, etc. However, there are few reports on whether VPA can greatly promote the differentiation of NSCs towards neurons, and inhibit the formation of glial scar in vivo, which will facilitate the repair of SCI. So we observed whether VPA could promote the differentiation of NSCs towards neurons and inhibit their differentiation into glial cells in vivo. NSCs transplantation Combined with the treatment of VPA was taken to observe their repair on the adult rats with SCI.Experiments were designed with six groups as follows: group of rats with hemi-section of spinal cord T10 (group A); group of rats with an absorbable gelatin sponge at the hemi-section of spinal cord T10 (group B); group of rats with an absorbable gelatin sponge at the hemi-section of spinal cord T10 and introperitoneal injection twice daily of VPA at a dose of 300mg/kg/d (group C); group of rats with an NSCs adsorbed gelatin sponge at the hemi-section of spinal cord T10 (group D); group of rats with an NSCs adsorbed gelatin sponge at the hemi-section of spinal cord T10 and introperitoneal injection twice daily of VPA at a dose of 300mg/kg/d at the same time(group E); group of rats with an absorbable gelatin sponge which had adsorbed NSCs and 1.0 mmol /L VPA (15μl) at the hemi-section of spinal cord T10 and introperitoneal injection twice daily of VPA at a dose of 300mg/kg/d simultaneously(group F). The effect of VPA on the proliferation, migration and differentiation of transplanted NSCs was observed by immunohistochemistry and pathomorphology technology, while the connections of the regenerated fibers with host and their axon-plasma transporting function was evaluated by the nuclear yellow , DIL tracing, finally, Basso-Beattie-Bresnahan locomotor rating scale (BBB scale) and electrophysiology examination were carried on posttreatment. The main results and conclusions were as follows:(1) VPA can promote the proliferation of NSCs in vitro with some degree of dose- effect and time-effect relationship, and the 1.0 mmol /L level is the best dose as well as 3-7 day of culture is the duration.(2) VPA can play an important role in the regulation of differentiation of NSCs in vitro, inhibiting the differentiation of NSCs towards glial cells and promoting towards neurons with a ratio as high as 80%.(3) With the research on samples in vivo, we find out that the transplanted NSCs can not only survive, but also migrate to the neighbor area of injuried spinal cord.(4) In 2 weeks after spinal cord injury, VPA can partly keep the NSCs transplanted into injuried spinal cord in a proliferation state, and after 2 weeks, it can also promote the differentiation of transplanted NSCs into neurons in vivo.(5) With the neuropathological examination, following the transplantation NSCs into injuried spinal cord combined with VPA treatment in adult rats, it was observed that the transplanted NSCs can fill up the defection of injuried tissue, a large amount of regenerated nerve fibers are regular, and the proliferation of astrocyte cells inhibited, and the formation of glial scar not tested. Meanwhile, the differentiated neurons in transplanted area can construct an ordered fiber connection with the host spinal cord around the injury area, which results in good effect on the structural repair of injuried spinal cord.(6) With the nuclear yellow, DIL retrograde and anterograde tracing research, it was found that axoplasmic transportion of injuried spinal cord can be well recovered after NSCs transplantation combined with treatment of VPA in adult rats.(7) With the studying of BBB scale and evoked potential detection, it was tested that the recovery both hind-limb movement and sensory as well as motor conductance function of injuried spinal cord can be promoted obviously following the transplantation of NSCs combined with the VPA therapy in adult rats.
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