Sex differences in antinociceptive response to Δ-9-tetrahydrocannabinol and CP 55,940 in the mouse formalin test

Cannabinoids have shown promise for the treatment of intractable pain states and may represent an alternative pharmacotherapy for pain management. A growing body of clinical evidence suggests a role for sex in pain perception and in cannabinoid response. We examined cannabinoid sensitivity and tolerance in male and female mice expressing a desensitization-resistant form (S426A/S430A) of the cannabinoid type 1 receptor (CB1R). Mice were assessed for acute and inflammatory nociceptive behaviors in the formalin test following pretreatment with either vehicle or mixed CB1R/CB2R agonists, Δ-9-tetrahydrocannabinol ([INCREMENT]-THC) (1-6 mg/kg) or CP 55,940 (0.06-0.2 mg/kg). Tolerance to the effects of 6 mg/kg [INCREMENT]-THC or 0.1 mg/kg CP 55,940 was examined by the formalin test following chronic daily dosing. Female mice showed decreased sensitivity to the effects of [INCREMENT]-THC and CP 55,940 compared with male mice. The S426A/S430A mutation increased the attenuation of nociceptive behaviors for both agonists in both sexes. Female mice displayed delayed tolerance to [INCREMENT]-THC compared with male mice, whereas the S426A/S430A mutation conferred a delay in tolerance to [INCREMENT]-THC in both sexes. Male S426A/S430A mutant mice also display resistance to tolerance to CP 55,940 compared with wild-type controls. This study demonstrates sex and genotype differences in response for two different cannabinoid agonists. The results underscore the importance of including both male and female mice in preclinical studies of pain and cannabinoid pharmacology.