ROLE OF SPINAL NMDA AND AMPA RECEPTORS IN EPISODIC HYPERTENSION IN CONSCIOUS SPINAL RATS

The neurotransmitters mediating the spinal sympathetic reflexes that i nitiate episodic hypertension after spinal cord injury are unknown. We examined the role of glutamatergic transmission in these reflexes by testing effects of the N-methyl-D-aspartate (NMDA)-receptor antagonist 2-amino-5-phosphonopentanoic acid (AP-5) and of the lpha-amino-3-hydr oxy-5-methyl-4-isoxazolepropionic acid (AMPA)-receptor antagonist 2,3- dihydroxy-6-nitro-7-sulfamoylbenzoquinone (NBQX) on the reflex hyperte nsion caused by colon distension. Antagonists were administered intrat hecally in conscious rats 1-2 days (acute, n = 10) or 15-16 days (chro nic, n = 14) after cord transection at the fifth thoracic segment unde r barbiturate anesthesia. AP-5 blocked presser responses to intratheca l NMDA but had no effect on responses to AMPA; similarly, NBQX blocked responses to AMPA but had no effect on responses to NMDA. Before anta gonist injection, colon distension increased mean arterial pressure by 24 +/- 1 mmHg (from 100 +/- 3 mmHg) and by 37 +/- 2 mmHg (from 116 +/ - 3 mmHg) in the acute and chronic groups, respectively. Pretreatment with AP-5 attenuated the presser responses by 36 and 37% in these resp ective groups; pretreatment with NBQX attenuated them by 34 and 31%. T hese data suggest that both NMDA and AMPA receptors contribute to spin al viscerosympathetic transmission and initiation of episodic hyperten sion in conscious spinal rats.