Increased expression of TRPV1 in the central nucleus of the amygdala is involved in orthodontic pain during experimental tooth movement in rats

Abstract

Abstract Pain is one of the most common adverse reactions during orthodontic treatment, which troubles patients a lot. Transient receptor potential vanilloid 1 (TRPV1) plays a crucial role in pain transmission and is expressed in the peripheral nervous system, but there is a paucity of literature on the roles of TRPV1 in the central nervous system. The central amygdala (CeA) integrates multiple sensory signals including nociceptive sensory information. However, how the involvement of TRPV1 in the CeA in orthodontic pain has not been investigated. To explore this, we constructed an experimental tooth movement (ETM) model using precision springs and evaluated pain behaviour based on face-grooming and the rat grimace scale (RGS). TRPV1 expression in the CeA was evaluated using immunofluorescence and western blotting. Face-grooming and RGS score peaked on day 1 then decreased gradually to baseline levels on day 7. Immunofluorescence and western blotting analysis revealed that TRPV1 expression in the CeA increased after ETM. Furthermore, changes in TRPV1 expression in the CeA were positively associated with RGS behaviour. Our findings suggest that TRPV1 in the CeA is modulated by ETM and is involved in tooth-movement pain, providing a new understanding of central regulation on orthodontic pain.