Sex differences in the expression of the endocannabinoid system within V1M cortex and PAG of Sprague Dawley rats

Abstract

Background Several chronic pain disorders, such as migraine and fibromyalgia, have an increased prevalence in the female population. The underlying mechanisms of this sex-biased prevalence have yet to be thoroughly documented, but could be related to endogenous differences in neuromodulators in pain networks, including the endocannabinoid system. The cellular endocannabinoid system comprises the endogenous lipid signals 2-AG (2-arachidonoylglycerol) and AEA (anandamide); the enzymes that synthesize and degrade them; and the cannabinoid receptors. The relative prevalence of different components of the endocannabinoid system in specific brain regions may alter responses to endogenous and exogenous ligands. Methods Brain tissue from naïve male and estrous staged female Sprague Dawley rats was harvested from V1M cortex, periaqueductal gray, trigeminal nerve, and trigeminal nucleus caudalis. Tissue was analyzed for relative levels of endocannabinoid enzymes, ligands, and receptors via mass spectrometry, unlabeled quantitative proteomic analysis, and immunohistochemistry. Results Mass spectrometry revealed significant differences in 2-AG and AEA concentrations between males and females, as well as between female estrous cycle stages. Specifically, 2-AG concentration was lower within female PAG as compared to male PAG (*p = 0.0077); female 2-AG concentration within the PAG did not demonstrate estrous stage dependence. Immunohistochemistry followed by proteomics confirmed the prevalence of 2-AG-endocannabinoid system enzymes in the female PAG. Conclusions Our results suggest that sex differences exist in the endocannabinoid system in two CNS regions relevant to cortical spreading depression (V1M cortex) and descending modulatory networks in pain/anxiety (PAG). These basal differences in endogenous endocannabinoid mechanisms may facilitate the development of chronic pain conditions and may also underlie sex differences in response to therapeutic intervention.

Sex‐specific cannabinoid 1 receptors on GABAergic neurons in the ventrolateral periaqueductal gray mediate analgesia in mice

“…Our finding that female mice had higher expression of CB 1 Rs on GABAergic neurons than male mice was strongly supported by previous work (Levine et al., 2021). Levine revealed that CB 1 R staining on neurons in the vlPAG was much greater for females than males.…”

“…In addition, Levine et al. (2021) also found that 2‐AG, the most important retrograde signaling molecular, was lower in the female PAG compared to the male PAG (Levine et al., 2021). They also utilized immunohistochemical analysis to confirm that female mice had higher 2‐AG synthetic enzymes (DAGL), and 2‐AG hydrolyzing enzymes (MAGL and ABHD6), which may contribute to the decreased 2‐AG in female mice.…”

Use of Cannabis and Cannabinoids for Treatment of Cancer

“…The 2-AG concentration was lower within the female PAG compared with the male PAG; this was confirmed using immunohistochemistry and proteomics. The observed sex differences in endogenous endocannabinoid mechanisms may in turn underlie the development of chronic pain conditions, as well as variations seen in therapy responses [ 366 ]. Sex differences in tolerance to THC were shown in mice with cisplatin-evoked chronic neuropathic pain [ 367 ].…”

Salivary Endocannabinoid Profiles in Chronic Orofacial Pain and Headache Disorders: An Observational Study Using a Novel Tool for Diagnosis and Management

“…These findings are consistent with Cupini et al [ 37 ], who detected a higher activity of FAAH and the AEA transporter in the platelets of female migraine patients than in males. In rodents, the ECS within pain modulatory pathways demonstrated sexual dimorphism, with significant differences between males and females in 2-AG and AEA concentrations [ 38 ]. Furthermore, it was suggested that sex differences in eCB ‘tone’ develop early, with growing pre-clinical evidence that gonadal hormones influence the expression of cannabinoid receptors and ligands, as well as their affinity and efficacy at receptors in various brain regions [ 39 ].…”