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Antinociceptive effect of morphine microinjections into the spinal trigeminal subnucleus oralis
P Luccarini1, R Cadet, M Saade
1Laboratoire de Physiologie Oro-Faciale, Faculté Chirurgie Dentaire, Clermont-Ferrand, France.
Abstract:
We analysed the effects of morphine microinjections (0.2 microliter) into the subnucleus oralis (SNO), i.e. the rostral division of the spinal trigeminal nucleus, on the formalin test adapted for orofacial pain. Duration of rubbing following an injection (50 microliters) of formalin solution (1.5%) in the right upper lip of the rat was measured. Compared to microinjections of saline (NaCl, 0.9%) used as control, 90 and 180 nmol microliter-1 of morphine solution in the SNO significantly curtailed rubbing. This effect was dose-dependent, reversed by naloxone, and also site-specific to the SNO since no effect was observed after microinjection of morphine into areas adjacent to the SNO. These results are further evidence for the involvement of the SNO in perioral nociceptive mechanisms.
Insights
Morphine microinjections into the subnucleus oralis (SNO) significantly reduced orofacial pain in rats. This pain relief was dose-dependent and reversed by naloxone, indicating the SNO
Area of Science:
- Neuroscience
- Pain Research
- Pharmacology
Background:
- Orofacial pain is a significant clinical challenge.
- The spinal trigeminal nucleus plays a crucial role in processing facial pain signals.
- The subnucleus oralis (SNO), a rostral division, is implicated in nociceptive mechanisms.
Purpose of the Study:
- To investigate the analgesic effects of morphine microinjections into the SNO.
- To determine the role of the SNO in orofacial pain modulation.
Main Methods:
- The formalin test was adapted for orofacial pain in rats.
- Morphine or saline was microinjected into the SNO.
- Rubbing behavior, indicative of pain, was measured after formalin injection.
Main Results:
- Morphine microinjections into the SNO significantly reduced rubbing behavior in a dose-dependent manner.
- The analgesic effect of morphine was reversed by naloxone, confirming opioid receptor involvement.
- Morphine microinjections into adjacent areas did not produce similar analgesic effects, indicating SNO site-specificity.
Conclusions:
- The subnucleus oralis (SNO) is involved in the central processing of orofacial nociception.
- Microinjections of morphine into the SNO exert significant analgesic effects on orofacial pain.
- These findings support the SNO as a potential target for managing orofacial pain.