Permanent alterations of spinal cord reflexes following nerve lesion in newborn rats

Sciatic nerve lesion in newborn rats is known to cause degeneration of a la rge number of axotomized motoneurones and spinal ganglion cells. Some of th e surviving motoneurones exhibit abnormal firing properties and the project ion pattern of central terminals of sensory neurones is altered. We report here on long-term changes in spinal cord reflexes in adult rats following n eonatal nerve crush. In acutely spinalized and anaesthetized adult rats 4-6 months old in which the sciatic nerve had been crushed on one side at birt h, the tibial nerve, common peroneal nerve or sural nerve were stimulated o n the reinnervated and control side and reflex responses were recorded from the L5 ventral spinal roots. Ventral root responses (VRRs) to tibial and p eroneal nerve stimulation on the side of the nerve lesion were significantl y smaller in amplitude representing only about 15 % of the mean amplitude o f VRRs on the control side. The calculated central delay of the first, pres umably monosynaptic component of the VRR potential was 1.6 ms on the contro l side while the earliest VRR wave on the side of the nerve lesion appeared after a mean central latency of 4.0 ms that seems too long to be of monosy naptic origin. These results suggest that neonatal sciatic nerve injury mar kedly alters the physiological properties and synaptic connectivity in spin al cord neurones and causes a marked depression of spinal cord responses to peripheral nerve stimulation.