SEROTONERGIC MODULATION OF SPINAL-CORD SYMPATHETIC PREGANGLIONIC NEURON ACTIVITY IN CARDIOVASCULAR REGULATION

The present study demonstrates the effect of activation of spinal serotonergic receptors on heart rate, blood pressure and cardiac arrhythmia induced by coronary artery ligation in cervical spinal cord transected and bilaterally vagotomized dogs. Intrathecal injection of serotonin (5-HT) evoked a fall in blood pressure (mean decrease, 16 +/- 3) and a decrease in heart rate (mean change, 24 +/- 6) and these effects were blocked by intrathecal pretreatment with methysergide. The magnitude of ventricular ectopics evoked by coronary artery ligation was decreased by serotonin (mean decrease, 31 +/- 5%), and this effect of serotonin was blocked by methysergide pretreatment intrathecally (mean change, 7 +/- 5%). Methysergide per se, increased the magnitude of ventricular ectopics (mean increase, 24 +/- 5%). The serotonergic receptors of the spinal cord appear to have an inhibitory influence on the cardiovascular functions.