Incarvillea sinensis is a Bignoniaceae plant used to treat rheumatism and relieve pain in traditional Chinese medicine. As a major component of I. sinensis, incarvillateine has shown analgesic activity in mice formalin tests. Using a series of animal models, this study further evaluated the effects of incarvillateine against acute, inflammatory, and neuropathic pain. Incarvillateine (10 or 20 mg/kg, i.p.) dose-dependently attenuated acetic acid-induced writhing, but did not affect thermal threshold in the hot plate test. In a Complete Freund’s Adjuvant model, incarvillateine inhibited both thermal hyperalgesia and paw edema, and increased interleukin-1β levels. Additionally, incarvillateine attenuated mechanical allodynia induced by spared nerve injury or paclitaxel, whereas normal mechanical sensation was not affected. Incarvillateine did not affect locomotor activity and time on the rotarod at analgesic doses, and no tolerance was observed after 7 consecutive daily doses. Moreover, incarvillateine-induced antinociception was attenuated by theophylline, 1,3-dipropyl-8-cyclopentylxanthine, and 3,7-dimethyl-1-propargylxanthine, but not naloxone, indicating that the effects of incarvillateine on chronic pain were related to the adenosine system, but not opioid system. These results indicate that incarvillateine is a novel analgesic compound that is effective against inflammatory and neuropathic pain, and that its effects are associated with activation of the adenosine system.
Accumulating evidence suggests that vesicular glutamate transporters (VGLUTs), which control the storage and release of glutamate, may play a role in pain processing. Chicago sky blue 6B (CSB6B), which is structurally related to glutamate, is a competitive VGLUT inhibitor without affecting plasma membrane transporters. The present study was designed to investigate the antinociceptive effects of CSB6B in a number of pain models. The hot-plate test was used as an acute thermal pain test. Inflammatory pain was evaluated using acetic acid writhing, formalin, and complete Freund's adjuvant tests. Intracerebroventricular administration of CSB6B did not affect acute thermal pain responses in 50 or 55°C hot plate tests. However, CSB6B attenuated acetic acid-induced writhing in a dose-dependent and time-dependent manner. In addition, CSB6B reduced licking/biting behavior during the second phase, but not during the first phase, following an intraplantar injection of formalin. In the complete Freund's adjuvant test, a significant attenuation of thermal hyperalgesia was also observed in CSB6B-treated mice. At antinociceptive doses, CSB6B did not affect mice spontaneous locomotor activity. The present study shows that pharmacological inhibition of VGLUT activity was sufficient to attenuate experimental inflammatory pain and suggests that regulation of VGLUTs might be a novel therapeutic strategy for the treatment of pain.
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