Involvement of transtient receptor potential channels in the sexual dimorphism of a mouse model of chronic migraine

Abstract

Chronic pain strongly deteriorates quality of life and lacks adequate treatment, the impact of chronic pain is especially crude in women originating inequality in pain assessment and treatment. We chose a model of chronic migraine to study the effect of sex in pain chronification, as migraine is considered a chronic sensitization that presents a strong sexual dimorphism. We used in vitro and murine models to investigate the role of TRP channels and neuropeptide CGRP in the sexual dimorphism of this chronic pain model. The model of chronic migraine was established by repeated intraperitoneal injections of nitroglycerin in male and female C57BL/6J adult mice. We used mechanical sensitivity measurements by Von Frey filaments to monitor sensory hypersensitivity of mice under chronical nitroglycerin administration. To study of the role of TRPA1, TRPM8 and CGRP in model, we used knockout mice and pharmacological tools. We further studied the activity of these genes by calcium imaging and their expression by qPCR in trigeminal neurons and cell lines expressing the murine and human receptors. Finally, CGRP release was assessed by immunocytochemistry. The chronic migraine model was characterized by a stronger chronification process in females. Furthermore, CGRP knockout mice or treated with a CGRP exocytosis inhibitor did not develop chronic pain. We found out that TRPA1 is essential for nitroglycerin sensitization of the animals as it functions as a nitroglycerin receptor, and this activation produced the CGRP release from trigeminal neurons. TRPM8 did present differential activity in-vivo attending to the sex, playing a protective role in male mice that was testosterone-dependent. In-vitro experiments could corroborate the agonistic activity of testosterone over TRPM8. In summary, we present a migraine model based on nitroglycerin administration that shares characteristics with migraine in humans, as it presents stronger effect in female animals and is CGRP dependent. We described TRPA1 as the main trigger of hypersensitivity through CGRP release, while TRPM8 had a protective effect that was sex dependent, counterbalancing hypersensitivity exclusively in males. Finally, we propose that TRPM8 activation in males by testosterone overrides chronic sensitization produced by nitroglycerin administration.