Induction of nitric oxide synthase and motoneuron death in newborn and early postnatal rats following spinal root avulsion.

It is well established that immature motoneurons are more vulnerable to axonal injury than the adult ones. Many previous studies used distal axonal injury, such as sciatic nerve transection, to examine the response of immature motoneurons to injury. In the present study, a more severe injury, spinal root avulsion, was performed in newborn and early postnatal rats, and the response of immature spinal motoneurons to the injury was observed. In newborn rats, root avulsion causes motoneuron loss which is similar to that of previous studies by distal axonal injury. During the early postnatal development, motoneuron loss in immature rats is greater following root avulsion when compared to cell loss following distal axonal injury at any given age. Following root avulsion, nitric oxide synthase (NOS) is induced in injured immature motoneurons. The induction and accumulation of NOS in injured motoneurons is much more rapid in the immature animals than in the adult, which is coincident with the more rapid motoneuron loss in the immature animals. Results of the present study indicate an involvement of NOS in neuronal degeneration. However, the precise role of NOS in the response of motoneurons to axonal injury is not clear and needs to be further studied.