Time course of segmental reflex changes after chronic spinal cord hemisection in the rat

In a companion paper (Hultborn & Malmsten 1983 a) it was described that, in the cat, direct excitatory reflexes became larger on the side of a chronic spinal hemisection than on the other side. In this paper the time course for change of the size of excitatory reflexes after spinal cord hemisection in the rat is described. Ipsilateral reflexes obtained by stimulation of cut dorsal roots L 4 and L 5 were recorded in the corresponding cut ventral roots. It was found that reflexes became larger on the lesioned (left) side than on the opposite side. For both mono- and polysynaptic reflexes there was a marked peak in left/right ratio on reflex size at 2 to 6 days post lesion. The ratio then returned to normal but increased again from about 21 days until at least 135 days. In control rats reflexes were larger on the right side, in agreement with findings in the cat.