Central Role of Protein Kinase A in Promoting Trigeminal Nociception in an In Vivo Model of Temporomandibular Disorders

Abstract

Aims To investigate cellular changes in the spinal trigeminal nucleus (STN) and trigeminal ganglion associated with trigeminal nociception mediated by inflammation in the temporomandibular joint (TMJ) capsule. Methods Sprague Dawley rats (n=86) were utilized to investigate cellular and behavioral responses to prolonged TMJ inflammation caused by bilateral injection of complete Freund’s adjuvant (CFA) in the capsule. To investigate the cellular effects of protein kinase A (PKA) in the STN, rats were injected intrathecally with the selective PKA inhibitor KT5720 prior to injection of CFA into both TMJ capsules. Levels of calcitonin gene-related peptide (CGRP), active PKA, and ionized calcium-binding adapter molecule 1(Iba1) in the STN and expression of phosphorylated ERK (p-ERK) in the trigeminal ganglion were determined by immunohistochemistry (n ≥ 3). Nocifensive head withdrawal responses to mechanical stimulation of the cutaneous tissue over the TMJ were monitored following CFA injection in the absence or presence of KT5720 (n = 7). Statistical analysis was performed using parametric ANOVA tests. Results Intrathecal injection of KT5720 significantly inhibited the stimulatory effect of CFA on levels of CGRP, PKA, and the microglial protein Iba1 in the STN. In addition, administration of KT5720 decreased the average number of CFA-induced nocifensive withdrawal responses to mechanical stimulation and the CFA-mediated increase in p-ERK expression in the ganglion. Conclusion These findings provide evidence that elevated PKA activity in the STN promotes cellular events temporally associated with trigeminal nociception caused by prolonged TMJ inflammation.

Secondary traumatic stress increases expression of proteins implicated in peripheral and central sensitization of trigeminal neurons

“…Immunohistochemistry and image analysis were conducted essentially as described in previous studies (Cady et al, 2011; Koop et al, 2017). Tissues were fixed in a solution of 4% paraformaldehyde overnight at 4°C, and cryoprotected by incubating tissues in 12.5% sucrose in distilled water at 4°C for one hour followed by 25% sucrose overnight at 4°C.…”

“…Statistical analysis of immunostaining data was performed essentially as described previously (Cornelison et al, 2016; Hawkins et al, 2015; Koop et al, 2017). The relative fluorescent staining intensity in spinal cord tissue was determined by measuring the grayscale intensity from four regions, in laminae I–III, of the medullary dorsal horn.…”

Glia and Orofacial Pain: Progress and Future Directions

“…upregulation) [25][26][27] −  GFAP [28][29][30][31] − Release pro-inflammatory mediators [28] −  Gap junction function [28] − Increase neuronal activity (Nav1.7 and pNR1 upregulation) [28,30] o  Iba1/CD11b [32,33] o Release pro-inflammatory mediators [34] Carrageenan injection in the TMJ ND ND ND −  Iba1 [35] Zymosan injection in the TMJ ND ND ND − Iba1 [35] Capsaicin injection in the TMJ ND − S100B [36] − Gap junction function [36,37] ND ND − Release of inflammatory mediators [21] TMD CFA injection in the TMJ ND − GFAP [22][23][24] − Release pro-inflammatory mediators [22,25,26] − Gap junction function [22] −  neuronal activity (Nav1.7 upregulation) [25][26][27] −  GFAP [28][29][30][31] − Release pro-inflammatory mediators [28] −  Gap junction function [28] − Increase neuronal activity (Nav1.7 and pNR1 upregulation) [28,30] o  Iba1/CD11b [32,33] o Release pro-inflammatory mediators [34] Carrageenan injection in the TMJ ND ND ND −  Iba1 [35] Zymosan injection in the TMJ ND ND ND − Iba1 [35] Capsaicin inje...…”

“…− Not activated [42] Dental pulp injury − Release of inflammatory mediators [21] TMD CFA injection in the TMJ ND − GFAP [22][23][24] − Release pro-inflammatory mediators [22,25,26] − Gap junction function [22] −  neuronal activity (Nav1.7 upregulation) [25][26][27] −  GFAP [28][29][30][31] − Release pro-inflammatory mediators [28] −  Gap junction function [28] − Increase neuronal activity (Nav1.7 and pNR1 upregulation) [28,30] o  Iba1/CD11b [32,33] o Release pro-inflammatory mediators [34] Carrageenan injection in the TMJ ND ND ND −  Iba1 [35] Zymosan injection in the TMJ ND ND ND − Iba1 [35] Capsaicin injection in the TMJ ND − S100B [36] − Gap junction function [36,37] ND ND…”

The Role of Nociceptive Neurons in the Pathogenesis of Psoriasis

“…TRPV1 and TRPA1 sensitization occurs through a mechanism involving multiple protein kinases, such as protein kinases C and A (PKC and PKA, respectively) and Ca 2+ /calmodulin dependent kinase II (CAMKII) ( 17 ). Elevated PKC, PKA, or CaMKII activity is associated with sensitization and activation in the nociceptive neurons ( 18 , 19 ). Numerous studies have reported that inflammation mediators can induce inconsistent activation of nociceptive neurons through G protein-coupled receptors (GPCRs) or receptor tyrosine kinases (RTKs) via cAMP/PKA, PLC/PKC, and CaMKII second messenger-signaling pathways ( 17 , 20 ).…”