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 t his lesion-induced plasticity was examined, Newborn rats received unil ateral frontal neocortical lesions, One experimental group received gr afts of fetal neocortical tissue (E14-E16) into the lesion cavities, A nother group served as lesion-only animals, while a third group was le ft unlesioned and without grafts as normal controls, At 3 mo of age, t he 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 we re processed histochemically for detection of BDA-labeled cells and fi bers, As a measure of the lesion-induced axonal sprouting response, co rticothalamic and corticopontine fibers crossing the midline were coun ted. 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 corticop ontine sprouting response, These results therefore indicate that fetal neocortical grafts have a modulatory, yet variable effect on the lesi on-induced axonal sprouting of contralateral sensorimotor cortical neu rons.