CRITICAL INTERVAL FOR RESCUE OF AXOTOMIZED NEURONS BY TRANSPLANTS

To determine whether embryonic spinal cord transplants retained the ab ility to prevent retrograde death of Clarke's nucleus (CN) neurons if supplied after a delay, we hemisected adult rats at the T8 spinal cord segment and placed transplants of fetal tissue into the hemisection c avity immediately or up to 14 days later. Transplants provided in the first 7 days after injury prevented virtually all of the 30% loss of C N neurons at L1 ipsilateral to hemisection that occurs without a trans plant. Transplants supplied at 14 days post-hemisection were ineffecti ve. Because prevention of retrograde neuron death is one mechanism by which transplants may contribute to locomotor recovery after spinal co rd injury, this window of effectiveness should be considered in the de sign of clinical trials.