Changes in the number of nitric oxide-synthesizing neurones on both sides of a chronic transection of the rat spinal cord

Pain after chronic transection of the spinal cord is hypothesized to develo p because of a hyperactivity in nociceptive neurones rostral to the lesion. One of the key substances in centra I nervous nociceptive processing is ni tric oxide (NO). It has been demonstrated to tonically inhibit the backgrou nd activity of dorsal horn neurones. Here, we show that in rats with chroni c transection of the spinal cord there is a reduction of NO-synthesizing ne urones on both sides of the lesion. This reduction is likely to be associat ed with a local lack of NO which could lead to an increased background acti vity of nociceptive dorsal horn neurones. The increased background activity of nociceptive neurones just rostral to the lesion might cause spontaneous pain that is perceived in segments close to the level of the lesion. (C) 2 000 Elsevier Science Ireland Ltd. All rights reserved.