Microgliosis is a common response to multiple types of damage in the CNS. However, the origin of the cells involved in this process is still controversial and the relative importance of local expansion versus recruitment of microglia progenitors from the bloodstream is unclear. Here, we investigated the origin of microglia using chimeric animals obtained by parabiosis. We found no evidence of microglia progenitor recruitment from the circulation in denervation or CNS neurodegenerative disease, suggesting that maintenance and local expansion of microglia are solely dependent on the self-renewal of CNS resident cells in these models.

The mitogenic actions of epidermal growth factor (EGF) were examined in low-density, dissociated cultures of embryonic day 14 mouse striatal primordia, under serum-free defined conditions. EGF induced the proliferation of single progenitor cells that began to divide between 5 and 7 d in vitro, and after 13 d in vitro had formed a cluster of undifferentiated cells that expressed nestin, an intermediate filament present in neuroepithelial stem cells. In the continued presence of EGF, cells migrated from the proliferating core and differentiated into neurons and astrocytes. The actions of EGF were mimicked by the homolog transforming growth factor alpha (TGF alpha), but not by NGF, basic fibroblast growth factor, platelet-derived growth factor, or TGF beta. In EGF-generated cultures, cells with neuronal morphology contained immunoreactivity for GABA, substance P, and methionine-enkephalin, three neurotransmitters of the adult striatum. Amplification of embryonic day 14 striatal mRNA by using reverse transcription/PCR revealed mRNAs for EGF, TGF alpha, and the EGF receptor. These findings suggest that EGF and/or TGF alpha may act on a multipotent progenitor cell in the striatum to generate both neurons and astrocytes.

Spinal cord injury can lead to severe motor, sensory and autonomic dysfunction. Currently, there is no effective treatment for the injured spinal cord. The transplantation of Schwann cells, neural stem cells or progenitor cells, olfactory ensheathing cells, oligodendrocyte precursor cells and mesenchymal stem cells has been investigated as potential therapies for spinal cord injury. However, little is known about the mechanisms through which these individual cell types promote repair and functional improvements. The five most commonly proposed mechanisms include neuroprotection, immunomodulation, axon regeneration, neuronal relay formation and myelin regeneration. A better understanding of the mechanisms whereby these cells promote functional improvements, as well as an appreciation of the obstacles in implementing these therapies and effectively modeling spinal cord injury, will be important to make cell transplantation a viable clinical option and may lead to the development of more targeted therapies.

Cell transplantation therapies have become a major focus in pre-clinical research as a promising strategy for the treatment of spinal cord injury (SCI). In this article, we systematically review the available pre-clinical literature on the most commonly used cell types in order to assess the body of evidence that may support their translation to human SCI patients. These cell types include Schwann cells, olfactory ensheathing glial cells, embryonic and adult neural stem=progenitor cells, fate-restricted neural=glial precursor cells, and bone-marrow stromal cells. Studies were included for review only if they described the transplantation of the cell substrate into an in-vivo model of traumatic SCI, induced either bluntly or sharply. Using these inclusion criteria, 162 studies were identified and reviewed in detail, emphasizing their behavioral effects (although not limiting the scope of the discussion to behavioral effects alone). Significant differences between cells of the same ''type'' exist based on the species and age of donor, as well as culture conditions and mode of delivery. Many of these studies used cell transplantations in combination with other strategies. The systematic review makes it very apparent that cells derived from rodent sources have been the most extensively studied, while only 19 studies reported the transplantation of human cells, nine of which utilized bone-marrow stromal cells. Similarly, the vast majority of studies have been conducted in rodent models of injury, and few studies have investigated cell transplantation in larger mammals or primates. With respect to the timing of intervention, nearly all of the studies reviewed were conducted with transplantations occurring subacutely and acutely, while chronic treatments were rare and often failed to yield functional benefits.