MORPHOLOGICAL ASSESSMENT OF GRAFTED RAT AND MOUSE CORTICAL-NEURONS - A LIGHT AND ELECTRON-MICROSCOPIC STUDY

The morphology of cortical neurons grafted into (or near) the rat stri atum was studied by means of intracellular Lucifer yellow injections i n fixed slices. Rat donor syngeneic cortical tissue (from postnatal da y 1 old rats; AO strain) as well as mouse donor xenogeneic cortical ti ssue (prenatal day 19; C3H/HE strain) were grafted as solid pieces int o 8-12 week-old rats (AO strain). Recipients of mouse xenografts were immunosuppressed with a monoclonal antibody against the interleukin-2 receptor. After perfusion and sectioning of the graft-containing areas , individual slices were incubated in the DNA stain 4.6-diamidino-2-ph enyl-indole (DAPI) to visualize the cell nuclei. Grafts could be easil y identified by a surrounding rim of astrocytes which outline the bord er between grafted and host tissue. Grafted cortical neurons were intr acellularly filled with Lucifer yellow, DAB-photoconverted, and furthe r processed for light and electron microscopy. In general, no cortical lamination could be observed in the grafted rat and mouse cortical ti ssue, but neurons were loosely packed throughout the graft. Two major cell types could be identified in all grafts investigated so far. The majority resembled those described as spiny neurons (85%), which could be further classified into pyramid-like, spiny stellate-like or fusif orm spiny neurons, with somata ranging between 15 and 25 mu m in diame ter. The remaining 15% resembled non-spiny neurons with either a multi polar basket-like or fusiform morphology. Dendrites of spiny and non-s piny neurons, which could extend to distances up to 400 mu m, were nev er seen to cross the astrocytic border, but some main axon and axonal collaterals of spiny neurons were found to leave the graft. On the bas is of light microscopic observations no difference was found between m ouse and rat grafted cortical neurons. The results of this study show that grafted cortical neurons retain some of the characteristic featur es of neurons in the intact adult cerebral cortex, although there appe ars to be a greater preponderance of spiny neurons in grafted tissue. This may reflect an immaturity of the grafted tissue or a response to the striatal environment. (C) 1994 Wiley-Liss, Inc.