Publications (2)3.69 Total impact
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ABSTRACT: The present study investigated the role of the peripheral NR2 subunits of N-methyl-d-aspartatic acid (NMDA) receptors in inflammatory orofacial pain. Experiments were carried out using adult male Sprague-Dawley rats weighing 220 to 280 g. Formalin (5%, 50 μl) was applied subcutaneously to the vibrissa pad. For each animal, the number of noxious behavioral responses, including rubbing or scratching of the facial region proximal to the injection site, was recorded for 9 sequential 5 min intervals. NR2 subunit antagonists were injected subcutaneously at 20 min prior to formalin injection. The subcutaneous injection of 100 or 200 μg of memantine significantly suppressed the number of scratches in the second phase of the behavioral responses to formalin. The subcutaneous injection of 0.25, 2.5, or 25 μg of 5,7-dichlorokynurenic acid also produced significant antinociceptive effects in the second phase. The subcutaneous injection of AP-5 at high dose produced significant antinociceptive effects in the second phase. The subcutaneous injection of PPPA and Ro 25-6981 both significantly suppressed the number of scratches in the second phase. The antinociceptive doses of memantine (200 μg), 5,7-dichlorokynurenic acid (25 μg), AP-5 (20 μg), PPPA (2.5 μg), or Ro 25-6981 (50 μg) injected into the contralateral hind paw did not affect the number of scratches in both the first and second phases. Moreover, the peripheral administration of NR2 subunit antagonists, including other NMDA receptor blockers, did not produce any motor dysfunction. These results indicate that a targeted blockade of peripheral NR2 receptors is a potentially important new method of treating inflammatory pain in the orofacial area.
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ABSTRACT: It has been well known that excitatory amino acids, primarily glutamate, are involved in the transmission of nociception in pathological and physiological conditions in the spinal and brainstem level. Recently, peripheral glutamate also play a critical role in the peripheral nociceptive transmissions. The present study investigated the role of N-methyl-D-aspartic acid (NMDA) or non-NMDA ionotropic glutamate receptors in formalin-induced TMJ pain. Experi-ments were carried out on male Sprague-Dawley rats weighing 220-280 g. Intra-articular injection was performed under halothane anesthesia. Under anesthesia, AP-7 (10, 100 µM, 1 mM/20 µL), a NMDA receptor antagonist, or CNQX disodium salt (0.5, 5, 50, 500 µM/20 µL), a non-NMDA receptor antagonist, were administered intra-articularly 10 min prior to the application of 5% formalin. For each animal, the number of behavioral responses, such as rubbing and/or scratching the TMJ region, was recorded for nine successive 5-min intervals. Intra-articular pretreatment with 1 mM of AP-7 or 50 µM CNQX significantly decreased the formalin-induced scratching behavioral responses during the second phase. Intra-articular pretreatment with 500 µM of CNQX significantly decreased the formalin-induced scratching behavior during both the first and the second phase. These results indicate that the intra-articular administration of NMDA or non-NMDA receptor antagonists inhibit formalin-induced TMJ nociception, and peripheral ionotropic glutamate receptors may play an important role in the TMJ nociception.
Kyungpook National University
Daikyū, Daegu, South Korea
- Department of Oral Physiology