The effect of fetal neocortical transplants on lesion-induced cerebral cortex plasticity

Sensorimotor cortical lesions in newborn rats lead to the formation of abnormal projections from the opposite intact sensorimotor cortex. In the present study the influence of fetal neocortical transplants on this lesion-induced plasticity was examined. Newborn rats received unilateral frontal neocortical lesions. One experimental group received grafts of fetal neocortical tissue (E14-E16) into the lesion cavities. Another group served as lesion-only animals, while a third group was left unlesioned and without grafts as normal controls. At 3 mo of age, the animals received injections of the anterograde tracer biotinylated dextran amine (BDA) into the sensorimotor cortex contralateral to the lesion/transplantation area. After sacrifice 2 wk later, the brains were processed histochemically for detection of BDA-labeled cells and fibers. As a measure of the lesion-induced axonal sprouting response, corticothalamic and corticopontine fibers crossing the midline were counted. Significantly fewer cortical efferent fibers crossed the thalamic midline in the transplanted rats compared to the lesion-only controls. In contrast, the presence of transplants did not reduce the corticopontine sprouting response. These results therefore indicate that fetal neocortical grafts have a modulatory, yet variable effect on the lesion-induced axonal sprouting of contralateral sensorimotor cortical neurons.