The cannabinoid CB₁ receptor antagonist, SR141716A, selectively facilitates nociceptive responses of dorsal horn neurones in the rat

The effect of spinal administration of the selective cannabinoid CB₁ receptor antagonist, SR141716A, and the selective CB₂ receptor antagonist, SR144528, on innocuous versus noxious evoked responses of dorsal horn neurones in the spinal cord of the anaesthetized rat was investigated. SR141716A (0.001–1 ng 50 μl⁻¹) dose‐relatedly facilitated the non‐potentiated component of the electrical C‐fibre mediated neuronal response (120±6, 156±13, 192±33 and 192±31% of control respectively; n=6). In contrast, SR144528 (0.001–1 ng 50 μl⁻¹) did not influence the non‐potentiated component of the C‐fibre evoked neuronal response (n=5). The electrical evoked Aβ‐fibre mediated neuronal responses were not influenced by SR141716A or SR144528. The results of this study provide evidence that tonic cannabinoid CB₁ receptor activation, but not CB₂ receptor activation, attenuates acute nociceptive transmission, at the level of the spinal cord. These results suggest a selective antinociceptive role of the endogenous cannabinoids at spinal CB₁ receptors.

British Journal of Pharmacology (1999) 127, 1765–1767; doi:10.1038/sj.bjp.0702758

DOI: 10.1038/sj.bjp.0702758

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