INDUCTION OF MATURE NEURONAL PROPERTIES IN IMMORTALIZED NEURONAL PRECURSOR CELLS FOLLOWING GRAFTING INTO THE NEONATAL CNS

RN33B, a conditionally-immortalized neuronal cell line, survives and d ifferentiates following grafting into the neocortex and hippocampus of adult and neonatal rat hosts. We have previously shown that these cel ls assume shapes characteristic of endogenous neurons at the integrati on site and persist up to 24 weeks post-grafting. In the present study we use electron microscopy and immunohistochemistry to characterize s uch cells. Differentiated RN33B cells were identical in size to endoge nous neurons and their sizes depended on the specific location of inte gration. RN33B cells in the granule cell layer of the dentate gyrus an d CA3 and CA1 pyramidal layers were 9.0, 15.3, and 12.6 mu m in diamet er, respectively. Grafted RN33B cells received synapses from fibres of host origin. Differentiated cells expressed neuronal markers, but not glial markers. Some differentiated cells expressed glutamate both in vitro and in vivo whereas undifferentiated cells did not. Grafted RN33 B cells that differentiated with morphologies similar to CA3 pyramidal neurons and pyramidal cortical neurons expressed Py antigen, a neuron al marker that is differentially expressed in endogenous large pyramid al neurons of the cerebral cortex and large pyramids of hippocampal fi eld CA3. This Py immunoreactivity was region-specific and corresponded to the endogenous pattern of Py immunostaining. Collectively, these d ata indicate that RN33B cells are capable of region-specific different iation and have the potential to integrate functionally into the host CNS.