Transplantation of neuronal precursors and immature neurons (neuroblasts) is one of highly potential approaches towards regeneration of injured and degenerating neuronal circuits in the central nervous system. Appropriate interaction of donor cells with existing network is a critical factor for successful repopulation therapy. The aim of the study was to investigate whether newly introduced neuronal precursors and neuroblasts may survive, differentiate, and form proper neuronal projections and dendritic network to target areas within the barrel cortex of postnatal mice. Additionally, we extended our evaluation to systemic spatial comparison in reference to the barrel cortex cytoarchitecture. We isolated immature neuroblasts from late-stage embryonic somatosensory cortex (>E16) from mice expressing green fluorescent protein (eGFP) in order to unambiguously track developing population of reconstituted neurons. To determine a real specificity of transplanted neuroblasts to survival and neuronal arborization, cells were injected into different compartments of the barrel cortex, such as barrel hollow and interbarrel septae. Each mouse received a single injection of 1000-3000 cells throughout the cortical depth. After three to eight weeks of survival time (and additional group with 6-month-survival), brains were processed for immunohistochemistry for detection of eGFP-expressing cells and neuron-specific markers. A delicate neuronal network extending from transplanted cells within the recipient cortex was evaluated in reference to the barrel field cytoarchitecture visualized by the cytochrome oxidase staining in selected alternative sections. Transplanted GFP-expressing neurons were mostly observed in interbarrel regions. The cells expressed mature neuronal markers MAP2, NeuN and presented morphology of typical neurons. The local fiber outhgrowth was highly anisotropic throughout cortical layers—in layer IV it was mostly limited to interbarrel septa while was almost symmetrically radiating in supragranular and subgranular layers. Our results provide evidence that limiting cues exists in the barrel cortex, and that they are layerspecific. We confirmed that such anisotropy has a long-lasting effect. Our studies allow investigation of survival, differentiation, and integration of transplanted neurons in the mouse cortex in the area- and layer-specific manner. Supported by NINDS and the Foundation for Polish Sciences.
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