THE DIFFERENTIATION OF DENTATE GRANULE CELLS FOLLOWING TRANSPLANTATION

Immature cells transplanted into an adult host must adapt to their new environment. In the present study we have shown the dendritic develop ment of dentate granule cells following transplantation. The adult hos t granule cells were lesioned by a fluid injection into the infragranu lar cleavage plane of the dentate gyrus. Few, if any, granule cells su rvived the lesion and the molecular layer (ML) shrank. When allogeneic neonatal granule cells were included in the fluid, the host granule c ells were simultaneously killed and replaced. In order to visualize th e dendrites, the granule cells were filled with Lucifer yellow (LY) in fixed sections and subsequently immunoreacted with an antibody to LY. The granule cell dendrites in the transplant were shorter in length, had a greater cross-sectional area, had more spines, and were more coi led and bent than control granule cell dendrites. The dendrites in the transplant formed functional synapses as indicated by cytochrome oxid ase histochemistry and the transplant prevented xc03some of the ML shr inkage. Acetylcholinesterase (ACHE) xkreaction product increased both in lesioned and in transplant groups. The laminar pattern of ACHE in t he control ML was not seen after the lesion and did not return in anim als with successful transplants. We conclude that (i) the dendrites of neurons in the transplant adapted to the adult host environment and a shrinking ML with remarkable structural plasticity; (ii) the transpla nt prevented some of the shrinkage of the ML; (iii) the transplant cou ld not reverse some of the lesion- induced changes in host organizatio n, such as the organization of ACHE inputs to the ML; and (iv) a pheno typically specific population of transplanted neurons can replace trau matically lesioned neurons of the same type even if the host condition s continue to change. (C) 1994 Academic Press,Inc.