Direct comparison of cervical and high thoracic spinal cord injury reveals distinct autonomic and cardiovascular consequences

Abstract

A wide range of spinal cord levels (cervical 8–thoracic 6) project to the stellate ganglia (which provides >90% of sympathetic supply to the heart), with a peak at the thoracic 2 (T2) level. We hypothesize that despite the proximity of the lesions, high thoracic spinal cord injuries (i.e., T2–3 SCI) do not closely mimic the hemodynamic responses recorded with cervical SCI (i.e., C6–7 SCI). To test this hypothesis, rats were instrumented with an intra-arterial telemetry device (Data Sciences International PA-C40) for recording arterial pressure, heart rate, and locomotor activity as well as a catheter within the intraperitoneal space. After recovery, rats were subjected to complete C6–7 spinal cord transection ( n = 8), sham transection ( n = 4), or T2–3 spinal cord transection ( n = 7). After the spinal cord transection or sham transection, arterial pressure, heart rate, and activity counts were recorded in conscious animals, in a thermoneutral environment, for 20 s every minute, 24 h/day for 12 consecutive weeks. After 12 wk, chronic reflex- and stress-induced cardiovascular and hormonal responses were compared in all groups. C6–7 rats had hypotension, bradycardia, and reduced physical activity. In contrast, T2–3 rats were tachycardic. C6–7 rats compared with T2–3 and spinal intact rats also had reduced cardiac sympathetic tonus, reduced reflex- and stress induced cardiovascular responses, and reduced sympathetic support of blood pressure as well as enhanced reliance on angiotensin to maintain arterial blood pressure. Thus injuries above and below the peak level (T2) of spinal cord projections to the stellate ganglia have remarkably different outcomes. NEW & NOTEWORTHY Twelve consecutive weeks of resting hemodynamic data as well as chronic reflex- and stress-induced cardiovascular, autonomic, and hormonal responses were compared in spinal intact and C6–7 and T2–3 spinal cord-transected rats. C6–7 rats compared with T2–3 and spinal intact rats had reduced cardiac sympathetic tonus, reduced reflex- and stress-induced cardiovascular responses, and reduced sympathetic support of blood pressure as well as enhanced reliance on angiotensin to maintain arterial blood pressure. Thus injuries above and below the peak level (T2) of spinal cord projections to the stellate ganglia have remarkably different outcomes.