REFLEX AND MORPHOLOGICAL-CHANGES IN SPINAL PREGANGLIONIC NEURONS AFTER CORD INJURY IN RATS

Autonomic dysreflexia manifested as episodic hypertension after spinal cord injury may occur because of changes in sympathetic preganglionic neurons (SPNs) in response to loss of bulbospinal inputs. We studied dysreflexia in rats one week after midthoracic spinal cord hemisection or complete transection. After cord hemisection at the fifth thoracic segment all rats had hemiparaplegia and after complete transection th ey were paraplegic and exhibited dysreflexia characterized by presser responses to distension of the urinary bladder. Changes in morphology of SPNs retrogradely labelled by cholera toxin and Fluoro Gold were ex amined and changes also were assessed in expression of the synaptic ve sicular protein synaptophysin. A comparison of SPNs rostral and caudal to the lesion revealed significant dendritic degeneration and decreas ed soma size after the loss of supraspinal input. Expression of synapt ophysin was normally observed rostral to a cord hemisection but this i mmunoreactivity was increased caudal to the lesion. In conclusion sign ificant structural changes in SPNs occur within a week after cord inju ry. The abnormal cardiovascular control and exaggerated reflex reactio ns may be due to new synapse formation on these SPNs.