Antinociception and sedation following intracerebroventricular administration of Δ9-tetrahydrocannabinol in female vs. male rats

Systemically administered cannabinoids produce greater antinociceptive and sedative effects in female compared to male rats. Sex differences in the brain endocannabinoid system have also been reported. The aim of this study was to determine whether sex differences in antinociceptive and motoric effects of a cannabinoid can be attributed to supraspinal mechanisms. Vehicle or Delta(9)-tetrahydrocannabinol (THC, 100 mu g) was administered i.c.v., and behavioral effects were compared between gonadally intact male and female rats, and among females in different estrous stages (early proestrus, late proestrus, estrus and diestrus). Antinociception on the tail withdrawal and paw pressure tests after icy. THC was slightly but not significantly greater in females (pooled across estrous stages) compared to males. THC suppressed locomotor activity similarly in all groups, with the exception that only males showed hyperlocomotion. at 4 h post-injection. When females in the four estrous stages were compared, females in late proestrus showed significantly greater THC-induced antinociception than females in estrus (and males). These results suggest that supraspinal mechanisms may contribute to greater systemic THC effects in females compared to males, and to estrous stage-dependent differences in THC effects among females. (C) 2010 Elsevier B.V. All rights reserved.