• M C Ko and J H Woods.
• Department of Pharmacology, University of Michigan, Medical School, Ann Arbor 48109-0632, USA. mko@umich.edu
• Psychopharmacology (Berl.). 1999 Apr 1; 143 (3): 322-6.

RationaleCannabinoids can reduce nociceptive responses by acting on peripheral cannabinoid receptors in rodents.ObjectivesThe study was conducted to evaluate the hypothesis that local administration of delta9-tetrahydrocannabinol (delta9-THC) can attenuate capsaicin-induced nociception in rhesus monkeys.MethodsCapsaicin (100 microg) was applied locally in the tail of rhesus monkeys to evoke a nociceptive response, thermal allodynia, in normally innocuous 46 degrees C water. delta9-THC (10-320 microg) was coadministered with capsaicin in the tail to assess local antinociceptive effects. In addition, a local antagonism study was performed to confirm the selectivity of delta9-THC action.Resultsdelta9-THC dose-dependently inhibited capsaicin-induced allodynia. This local antinociception was antagonized by small doses (10-100 microg) of the cannabinoid CB1 antagonist, SR141716A, applied in the tail. However, 100 microg SR141716A injected subcutaneously in the back did not antagonize local delta9-THC.ConclusionsThese results indicate that the site of action of locally applied delta9-THC is in the tail. It provides functional evidence that activation of peripheral cannabinoid CB1 receptors can attenuate capsaicin-induced thermal nociception in non-human primates and suggests a new approach for cannabinoids in pain management.

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