Abstract
One of the possible sites of action of the analgesic effect of morphine is the Nucleus Raphe Magnus, as morphine injected into this structure induces analgesia in transient pain models. In order to test if morphine in the Nucleus Raphe Magnus is also analgesic in a tonic pain model, 5 μg of morphine or saline (control) were microinjected into the Nucleus Raphe Magnus of the rat. Analgesic effects were assessed following nociceptive stimulation using transient heating of the tail (phasic pain) and subcutaneous orofacial injection of 1.5 % formalin (tonic pain). While morphine was strongly analgesic for the tail-flick response (p < 0.0001 compared to control), analgesia on the response to formalin was also observed for both early (p = 0.007) and late responses (p = 0.02). However, the response to formalin was not completely blunted. These results suggest that the Nucleus Raphe Magnus is not the exclusive site of action of morphineinduced analgesia in clinical conditions.
Keywords: Opioid, analgesia, trigeminal, tail-flick test, formalin test
Current Drug Delivery
Title: Analgesia Induced by Morphine Microinjected into the Nucleus Raphe Magnus: Effects on Tonic Pain
Volume: 4 Issue: 3
Author(s): Christian Duale, Fernando Sierralta and Radhouane Dallel
Affiliation:
Keywords: Opioid, analgesia, trigeminal, tail-flick test, formalin test
Abstract: One of the possible sites of action of the analgesic effect of morphine is the Nucleus Raphe Magnus, as morphine injected into this structure induces analgesia in transient pain models. In order to test if morphine in the Nucleus Raphe Magnus is also analgesic in a tonic pain model, 5 μg of morphine or saline (control) were microinjected into the Nucleus Raphe Magnus of the rat. Analgesic effects were assessed following nociceptive stimulation using transient heating of the tail (phasic pain) and subcutaneous orofacial injection of 1.5 % formalin (tonic pain). While morphine was strongly analgesic for the tail-flick response (p < 0.0001 compared to control), analgesia on the response to formalin was also observed for both early (p = 0.007) and late responses (p = 0.02). However, the response to formalin was not completely blunted. These results suggest that the Nucleus Raphe Magnus is not the exclusive site of action of morphineinduced analgesia in clinical conditions.
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Cite this article as:
Christian Duale , Fernando Sierralta and Radhouane Dallel , Analgesia Induced by Morphine Microinjected into the Nucleus Raphe Magnus: Effects on Tonic Pain, Current Drug Delivery 2007; 4 (3) . https://dx.doi.org/10.2174/156720107781023884
DOI https://dx.doi.org/10.2174/156720107781023884 |
Print ISSN 1567-2018 |
Publisher Name Bentham Science Publisher |
Online ISSN 1875-5704 |
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