EFFECT OF GRADED SPINAL-CORD COMPRESSION ON CARDIOVASCULAR NEURONS INTHE ROSTRO-VENTRO-LATERAL MEDULLA

In patients with spinal cord injury, cardiovascular disturbances such as hypotension, bradycardia and autonomic dysreflexia can be directly linked to abnormalities of central autonomic control. To date, the cha nges in bulbospinal innervation of sympathetic preganglionic neurons a fter compressive spinal cord injury have not been investigated. Thus, we examined the effect of varying severity of compressive spinal cord injury on neurons of the rostro-ventro-lateral medulla, a nucleus of k ey importance in cardiovascular control. Adult rats with 20 g, 35 g an d 50 g clip compression injuries (n=18) of the cord at T1 and uninjure d controls (n=13) were studied. Neurons in the rostro-ventro-lateral m edulla with preserved spinal connections eight weeks after spinal cord injury were identified by retrograde labelling with 4% FluoroGold int roduced into the cord at T6. Bulbospinal neurons in the rostro-ventro- lateral medulla were also examined immunocytochemically for the adrena line-synthesizing enzyme phenylethanolamine-N-methyltransferase. In co ntrol rats an average of 451 +/- 12 rostro-ventro-lateral medulla neur ons were phenylethanolamine-N-methyltransferase positive. Of these, 21 3 +/- 6 projected to the T6 spinal cord. The number of rostro-ventro-l ateral medulla neurons retrogradely labelled by FluoroGold decreased a s a linear function of severity of spinal cord injury (r= -0.95; P<0.0 001). After 500 spinal cord injury at T1, only 7 +/- 1 rostro-ventro-l ateral medulla neurons were labelled by FluoroGold, of which 6 +/- 1 w ere phenylethanolamine-N-methyltransferase positive. Moreover, the num ber of phenylethanolamine-N-methyltransferase positive rostro-ventro-l ateral medulla neurons decreased to 361 +/- 16 after 50 g spinal cord injury. We conclude that compressive spinal cord injury results in dis connection of rostro-ventro-lateral medulla neurons, which project to the thoracic spinal cord, and that these changes vary with the severit y of injury. The majority of these axotomized rostro-ventro-lateral me dulla neurons maintain their immunopositivity for the adrenaline-synth esizing enzyme phenylethanolamine-N-methyltransferase. (C) 1998 IBRO. Published by Elsevier Science Ltd.