AN EXPERIMENTAL STUDY OF NERVE ROOTS DAMAGE UNDER STRETCH FORCE

The most considerable cause of nerve root damage are compression force and stretch force. Many researchers had reported about experimental study of the compression force, but it is difficult to find the report describing the stretch force to the nerve roots. The purpose of this study is to evaluate the physiological reaction of nerve roots of rats nuder stretch force. The nerve roots were prepared from the cauda equina of 8 Wister rats (weight: 300 – 400g). We investigated the changes in threshold and action potential of the nerve roots under stretch force and compression force. The threshold of the nerve roots increased and action potential decreased in parallel with stretch force. Also, the threshold and action potential recovered after releasing the stretch force. On the other hand, by compression force, the action potential decreased parallel with compression force, but the threshold did not change with compression force. Ten minutes after releasing compression force, the action potential did not recover as much as before, and the threshold increased rather than control. The different physiological reactions that occurred between compression force and stretch force are hard to explain by circulation insufficiency, as previously reported (hypoxemia and lack of nutrition). We considered that the etiology of the stretch force might be a change in internal pressure of nerve roots and a structural change in nerve cells. The physiological reaction of the nerve root under stretch force differed from that under compression force and recovered from the damage after release from stretch force.