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Copyright © 1998 by Institute of Pharmacology Polish Academy of Sciences |
Pol. J. Pharmacol., 1998, 50, 407-415 ISSN 1230-6002 |
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Differential effects of intrathecally and intracerebroventricularly administered nitric oxide donors on noxious mechanical and thermal stimulation.
H. MACHELSKA, R. PRZEWŁOCKI, M. W. RADOMSKI, B. PRZEWŁOCKA. Pol. J. Pharmacol. Pharm., 1998, 50, 407-415. Involvement of nitric oxide (NO) in nociceptive transmission is well documented. However, there is controversy concerning the exact role of NO in mediation of nociception at different levels of the nervous system. Most studies agree that NO promotes hyperalgesia at the level of the spinal cord. Conversely, at supraspinal sites exogenously applied NO has been found to be both pro- and antinociceptive. In light of this discrepancy, the aim of the present study was to compare the effects of NO donors on nociceptive transmission at spinal and supraspinal sites of the central nervous system using mechanical (paw pressure; PP) and thermal (tail-flick; TF) noxious stimulation. Four NO donors which release NO through different mechanisms were used: S-nitrosoglutathione (SNOG; 3-600 nmol), S-nitroso-N-acetylpenicillamine (SNAP; 0.18-4.5 nmol), hydroxylamine (HYD; 60-1200 nmol) and 3-morpholino-sydnonimine (SIN-1; 490-970 nmol). They were injected intrathecally (it) or intracerebroventricularly (icv) to male Wistar rats and nociceptive thresholds were evaluated in TF and PP tests. It was found that NO donors administered it or icv produced a dose-dependent hyperalgesia in the PP test. The hyperalgesia induced by mechanical stimuli was stronger after it than after icv administration of NO donors. The SIN-1-induced hyperalgesia, as evaluated by the PP test, was reversed by it pretreatment with haemoglobin (1.5-4 nmol) a NO scavenger, and methylene blue (267-1070 nmol) a guanylate cyclase and NO synthase inhibitor, suggesting that NO exerts its action by facilitating cyclic guanosine 3’,5’-monophosphate (GMP) formation. Unlike in the PP test, SNAP and SNOG had no effect on the nociceptive threshold in the TF test, and only SIN-1 administered it produced a weak hyperalgesia in that test, while HYD caused a mild but significant prolongation of the TF reflex. The above data show that NO produces hyperalgesia principally in response to noxious mechanical stimuli. This effect seems to be predominantly mediated in the spinal cord, however, it occurs at both levels of the central nervous system. Key words: hyperalgesia, mechanical stimulation, thermal stimulation |
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