Transneuronal Degeneration Due to Peripheral Nerve Injury in the Rats

Kwak, Hyun Ho; Yoo, Byung Ki; Kim, Myoung Hee; Park, Hyung Woo

Abstract

When an axon is severed, degenerative changes occur in the injured neuron as well as in those with which it has synaptic connections through transneuronal degeneration. Transneuronal degeneration includes all atrophic or degenerative changes that occur in nerve cells following the disappearance of their efferent (retrograde transneuronal degeneration) or afferent (anterograde transneuronal degeneration) connections. Previous studies have shown that transneuronal degeneration may occur in the neurons of various central nervous system following injury to their peripheral nerve. However, the effect of transneuronal degeneration on the neurons which are related with damaged neurons functionally and structurally is not elucidated yet. Denervation due to axonal degeneration or dysfunction of nerve cell bodies leads to physiological and biochemical changes in the skeletal muscles, and the extent of neuronal degeneration can be assessed through the muscle atrophy and the changes in muscle fiber type density. In order to identify the effect of transneuronal degeneration on the adjacent peripheral nerves as well as muscles, the left femoral nerve of Sprague -Dawley rats was transected, and changes in their spinal cords and hindlimb muscles were analysed morphologically and histochemically. The results obtained are as follows : 1. the motor neurons of ipsilateral anterior horn of femoral nerve transected rats showed reduction in size and degenerative features such as shriven shape and nucleus moved to periphery of the cell body. 2. All three muscle fiber types of rectus femoris and adductor longus were reduced in muscle fiber size, but no such changes were observed in semitendinosus. 3. In rectus femoris and adductor longus, type IIa muscle fiber was increased in number and the number of type IIb fiber was reduced, whereas no change was observed in all three muscle fiber types of semitendinosus. These findings indicate that damaged neurons following peripheral nerve injury can affect other adjacent neurons through transneuronal degeneration and cause the denervative changes in the muscles innervated by those adjacent neurons concomitantly, and such effects are only observed in the same spinal cord level.