In vivo properties of neural stem cells after transplantation into the rat brain-Studies of phenotypic differentiation and functional integration using cell-specific labelling and electrophysiological techniques

Abstract: In the present thesis, we have examined the in vivo properties of in vitro expanded human and rat neural stem-and progenitor cells after transplantation into the neonatal and adult rat brain. The survival and differentiation of the grafted cells were assessed using species-specific antisera, and pre-labelling with the reporter gene green fluorescent protein (GFP). Long-term growth factor-expanded human progenitors successfully survived after grafting into the neonatal and adult striatum, subventricular zone (SVZ) and hippocampus. Target-directed migration, and region-specific neuronal differentiation of grafted cells were observed after transplantation into the neurogenic SVZ and hippocampus. Extensive migration of implanted cells identified as glial progenitors, occured within white matter. In the striatum and hippocampus, neuronal and glial differentiation were most pronounced at the graft core, with both neuronal and glial processes extending over long distances. A fraction of non-migratory undifferentiated cells remained at the implantation site. Neurogenic properties of the neural cell line RN33B, carrying the GFP reporter gene, were studied after grafting to the neonatal brain. Large numbers of RN33B cells differentiated into pyramidal neurons in the cortex and hippocampus, with projections to normal target regions, such as the thalamus and contralateral hippocampus, respectively, as revealed by retrograde tracing. Whole-cell patch clamp recordings of grafted cortical pyramidal neurons showed that RN33B cells develop physiological properties of mature neurons and become functionally integrated within host neural circuitry. Our data demonstrate a remarkable capacity of expandable neural precursors for different types of migration, and multipotential differentiation, along neuronal and glial lineages. Along with region-specific neuronal differentiation we observed establishment of appropriate anatomical projections, and functional integration into host circuitry. These results suggest that these cell types are highly useful for further research into the mechanisms responsible for cellular migration, differentiation and integration in the mature central nervous system.