Selective hippocampal lesions differentially affect the phenotypic fate of transplanted neuronal precursor cells.

RN33B cells, a CNS-derived neuronal precursor cell line, transplanted into normal adult rat hippocampus can survive and morphologically differentiate with their ultimate morphology dependent on the integration site. This study examined the differentiation and structural integration of RN33B cells transplanted into the lesioned adult hippocampus. Pyramidal neurons of the CA1-3 regions or granular neurons in the dentate gyrus were preferentially destroyed by unilateral intraventricular kainic-acid or intradentate colchicine injections, respectively. One week after the lesion, a suspension of undifferentiated beta-galactosidase (beta-gal)-labeled RN33B cells was stereotaxically transplanted into the lesioned or the contralateral hippocampus. After 5-7 weeks, sections of the recipient brains were analyzed by toluidine blue staining and immunohistochemistry for beta-gal, GFAP, and OX-42. A reactive gliosis was observed on the lesioned side which persisted up to 7 weeks postlesion (the latest time point examined). RN33b cells survived in the lesioned hippocampus and assumed variable morphologies depending on the hippocampal layer into which they integrated. Only RN33B cells located in intact or partially damaged cell layers or in the unlesioned contralateral hippocampus differentiated with morphologies similar to those of endogenous neurons characteristic of those layers. Cells located in layers completely depleted of endogenous neurons assumed bipolar morphologies or sent out multiple processes with no structural polarity, unlike the neuronal morphologies characteristically seen in intact hippocampal cell layers. These data suggest that the presence of some endogenous neurons and partially conserved cytoarchitectural organization are essential for immortalized neuroepithelial precursor cells to differentiate into region-specific neuronal cell types.