Abstract
Traumatic brain injuries (TBI) remain one of the leading causes of death and disability world-wide. One emerging area of TBI research is the involvement of the endocannabinoid system (ECS) in response to TBI. Endogenous cannabinoids modulate inflammation, pain, anxiety, and neurotransmitter release through the activation of the cannabinoid receptors CB1R and CB2R. CB1R and CB2R are activated by exogenous cannabinoids such as Δ9-tetrahydrocannabinol (THC) found in Cannabis sativa. As public perceptions change in the wake of Cannabis legalization, research into the potential harmful and therapeutic effects of THC following TBI deserve exploration. In this preliminary study, we investigated sex differences in behavioral effects, CB1R abundance, and cytokine profiles in a rat model of moderate TBI treated with 1 mg·kg-1 THC (i.p.). Neither TBI nor THC treatment altered catalepsy, body temperature, nociception, or spontaneous alternation as measured in the y-maze. TBI reduced male rotarod performance in both vehicle and THC-treated groups, and THC treatment decreased performance in Sham-TBI rats when compared to vehicle controls. Female rats that received a TBI and THC exhibited lower relative CB1R density when compared to the Sham-TBI+THC group. TBI was associated with reduced interleukin-4 in males; THC increased interleukin-6 in TBI males compared to Sham-TBI. These preliminary results highlight fundamental sex differences in the response of the ECS following TBI. Our results indicate the need for further investigation of the ECS and phytocannabinoids post-TBI in both acute and chronic phases.
Significance Statement The endogenous cannabinoid system is a potential target in the pathophysiology and treatment of traumatic brain injury (TBI). In this study we observed TBI reduced rotarod performance in male rats only and performance was not affected by THC. Female rats the received THC and TBI displayed lower cortical cannabinoid receptor 1 levels. These early results showcase sex differences in rodent models of TBI and the endogenous cannabinoid system.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Conflict of Interest: Authors report no conflict of interest.
Funding sources: This work was supported by a GlaxoSmithKline-Canadian Institutes of Health Research (CIHR) partnership grant (#387577) to RBL, Saskatchewan Health Research Foundation (SHRF) to JGH and RBL, as well as funding from the University of Saskatchewan College of Pharmacy and Nutrition to TB.
