Dendritic outgrowth from neural cells transplanted to the hippocampal fissure.

Transplants of cell suspensions that were either selective for granule cells or contained all hippocampal cell types were placed in the hippocampal fissure or in the infragranular cleavage plane (IGCP) of the dentate gyrus. Several transplants were found in both areas in the same dentate gyrus. After a variety of post-transplant survival times, neurons of both the donor and the host were filled with lucifer yellow in fixed sections. Sections were also immunoreacted with antibodies to glial fibrillary acidic protein (GFAP), vimentin, neural cell adhesion molecule (NCAM and HNK-I/NCAM) and were histochemically reacted for ACHE. Dendrites of neurons from transplants of cells of the whole hippocampus usually stayed within the transplant. If a dendrite from such transplants did grow out of the transplant, it grew into the molecular layer (ML) of the host dentate gyrus and not into the hilus of the host. Dendrites from granule cell selective transplants grew into the ML of 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. Transplants of cells from the whole hippocampus placed in the IGCP showed the greatest ingrowth of acetylcholinesterase (ACHE) fibers. In granule cell transplants made concurrently into the fissure and the IGCP, donor granule cell dendrites grew into the host ML from both sites, demonstrating 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 would work against the dendrites growing in the opposite direction.