DENDRITIC OUTGROWTH FROM NEURAL CELLS TRANSPLANTED TO THE HIPPOCAMPALFISSURE

Transplants of cell suspensions that were either selective for granule cells or contained all hippocampal cell types were placed in the hipp ocampal fissure or in the infragranular cleavage plane (IGCP) of the d entate gyrus. Several transplants were found in both areas in the same dentate gyrus. After a variety of post-transplant survival times, neu rons of both the donor and the host were filled with lucifer yellow in fixed sections. Sections were also immunoreacted with antibodies to g lial fibrillary acidic protein (GFAP), vimentin, neural cell adhesion molecule (NCAM and HNK-1/NCAM) and were histochemically reacted for AC HE. Dendrites of neurons from transplants of cells of the whole hippoc ampus usually stayed within the transplant. If a dendrite from such tr ansplants did grow out of the transplant, it grew into the molecular l ayer (ML) of the host dentate gyrus and not into the hilus of the host . Dendrites from granule cell selective transplants grew into the ML o f the host and those that grew from fissure transplants were inverted from the normal orientation of host granule cell dendrites. Dendrites also grew out of the transplant in the absence of reactive gliosis. Tr ansplants of cells from the whole hippocampus placed in the IGCP showe d the greatest ingrowth of acetylcholinesterase (ACHE) fibers. In gran ule cell transplants made concurrently into the fissure and the IGCP, donor granule cell dendrites grew into the host ML from both sites, de monstrating that a gradient of tropic factors across the ML could not account for the direction and orientation of the dendritic outgrowth, since a gradient that directed the growth of one set of dendrites woul d work against the dendrites growing in the opposite direction.