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Chin J Physiol. 2015 Feb 28;58(1):72-8. doi: 10.4077/CJP.2015.BAD307.

Tonic modulation of nociceptive behavior and allodynia by cannabinoid receptors in formalin test in rats.

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Department of Neurology, the First Affiliated Hospital of Chongqing Medical University, Chongqing 400016, People's Republic of China.
Key Laboratory of Orthopaedics, Disease of Gansu Province, Department of Orthopaedics, the Second Hospital of Lanzhou University, Lanzhou 730030, Gansu, People's Republic of China.


Cannabinoids produce anti-nociceptive and anti-hyperalgesic effects in acute, inflammatory and neuropathic pain models. The current study investigated the role of cannabinoid (CB1 and CB2) receptors in modulating formalin-induced nociceptive behavior and mechanical allodynia in the rat. Rats received subcutaneous plantar injections of 5% formalin in the hind paws. Licking, biting and paw flinching nociceptive behaviors were measured 0-60 min after formalin injection. Allodynia was measured at 3 and 6 h, and 1, 3, 5 and 7 days post-injection using the mechanical paw withdrawal threshold. Animals in the experimental group were given i.p. injections of CB1 and CB2 receptor antagonists AM281 and AM630 at a dose of 1 mg/kg concomitant with formalin, and then twice daily for the following 7 days. AM281 and AM630 enhanced nociceptive behaviors, and attenuated the bilateral mechanical paw withdrawal threshold, compared with the vehicle. The results indicate that CB1 and CB2 receptors mediate a tonically inhibitory action on formalin-induced inflammatory pain, especially long-term allodynia, in bilateral hind paws.

[Indexed for MEDLINE]

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