Sensitivity of sympathetically correlated spinal interneurons, renal sympathetic nerve activity, and arterial pressure to somatic and visceral stimuli after chronic spinal injury

Abstract

In the chronic stage of spinal cord injury in humans, both innocuous and noxious somatic and vis-ceral stimuli can elicit severe autonomic dysreflexia characterized by potentially dangerous, sym-pathetically mediated, increases in arterial pressure. We hypothesized that a similar sympathetic hyperexcitability would be manifested in spinal sympathetic networks of chronically spinally tran-sected rats. To test this hypothesis, we compared the responses of sympathetically correlated spinal interneurons and arterial pressure to both innocuous and noxious stimuli in acutely and chronically spinally transected rats. Experiments were conducted in anesthetized female rats, either within hours of T3 spinal transection (rats with acute spinal transection) or one month after T3 spinal transec-tion (rats with chronic spinal transection). Sympathetically correlated spinal interneurons were iden-tified by cross correlating their ongoing activity with simultaneously recorded renal sympathetic nerve activity. Cutaneous stimuli (either light brushing or noxious pinch) were delivered to a wide area of the ipsilateral side of the rat. Colorectal distension was used as a noxious visceral stimulus. The activity of sympathetically correlated interneurons was increased by stimulation of more of the body surface and decreased by stimulation of less of the body surface in rats with chronic spina