Expression of c-fos mRNA and c-fos protein in neocortical transplants placed into excitotoxin-induced lesions in adult rats.

Using anatomical and electrophysiological methods, previous studies from this laboratory demonstrated that fetal neocortical block transplants placed into the excitotoxically ablated cortex of adult rats can establish functional connections with the host central nervous system. In order to further examine functional integration at the level of genomic activation/molecular signaling systems, transplants were analyzed for the presence of c-fos mRNA and Fos protein-labeled cells following a 20-min exposure of the animal to a novel open-field environment. This behavioral testing paradigm, which previously was shown to induce expression of c-fos mRNA in several brain regions including the sensorimotor cortex, was administered at 3 months after grafting. The transplants were found to express c-fos mRNA as well as c-fos protein following novelty exposure. These labeled cells were distributed primarily along the peripheral margin of the grafts. This study therefore suggests that at least some neurons within transplants become integrated with the host pathways at the level of molecular signal transduction.