The role of CNS NMDA receptors and nitric oxide in visceral hyperalgesia.
The studies summarized here document the role of NMDA receptors and nitric oxide in the lumbosacral spinal cord and rostral ventromedial medulla in the maintenance of visceral hyperalgesia. Experiments were conducted in rats in which drugs were administered into either the lumbosacral intrathecal space or directly into the rostral ventromedial medulla. The visceral stimulus was noxious colorectal distension, administered before and 3 h after intracolonic instillation of either saline or 25% zymosan. The visceromotor response to colonic distension was quantified and found to be significantly enhanced in rats in which the colon had previously been treated with zymosan. Enhanced responses to distension were attenuated dose-dependently by intrathecal administration of the NMDA receptor channel blocker MK-801 and by inhibition of the neuronal isoform of nitric oxide synthase (nNOS). In corresponding studies wherein drugs were administered directly into the rostral ventromedial medulla, NMDA receptor antagonism and NOS inhibition dose-dependently attenuated exaggerated responses to colonic distension. Taken together, these data suggest that zymosan-produced visceral hyperalgesia is influenced both at the level of the spinal cord and rostral ventromedial medulla, and that descending facilitatory influences from the rostral ventromedial medulla are important to the maintenance of visceral hyperalgesia.
Coutinho
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SV
Department of Pharmacology, College of Medicine, The University of Iowa, 2-471 Bowen Science Building, Iowa City, IA 52242-1109, USA.
Urban
M O
MO
Gebhart
G F
GF
D000818:Animals; D002490:Central Nervous System / Q000187:drug effects / Q000378:metabolism*; D003106:Colon / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006930:Hyperalgesia / Q000139:chemically induced / Q000378:metabolism*; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000378:metabolism; D009569:Nitric Oxide / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000502:physiology*; D012007:Rectum / Q000187:drug effects / Q000378:metabolism; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism; D014110:Touch; D014781:Viscera / Q000187:drug effects / Q000378:metabolism; D015054:Zymosan / Q000494:pharmacology
D004791:Enzyme Inhibitors; D016194:Receptors, N-Methyl-D-Aspartate; D009569:Nitric Oxide; D015054:Zymosan