Transcriptional Alterations in the Trigeminal Ganglia, Nucleus and Peripheral Blood Mononuclear Cells in a Rat Orofacial Pain Model

Abstract

Orofacial pain and headache disorders are among the most debilitating pain conditions. While the pathophysiological basis of these disorders may be diverse, it is generally accepted that a common mechanism behind the arising pain is the sensitization of extra- and intracranial trigeminal primary afferents. In the present study we investigated gene expression changes in the trigeminal ganglia (TRG), trigeminal nucleus caudalis (TNC) and peripheral blood mononuclear cells (PBMC) evoked by Complete Freund's Adjuvant (CFA)-induced orofacial inflammation in rats, as a model of trigeminal sensitization. Microarray analysis revealed 512 differentially expressed genes between the ipsi- and contralateral TRG samples 7 days after CFA injection. Time-dependent expression changes of G-protein coupled receptor 39 (Gpr39), kisspeptin-1 receptor (Kiss1r), kisspeptin (Kiss1), as well as synaptic plasticity-associated Lkaaear1 (Lkr) and Neurod2 mRNA were described on the basis of qPCR results. The greatest alterations were observed on day 3 ipsilaterally, when orofacial mechanical allodynia reached its maximum. This corresponded well with patterns of neuronal (Fosb), microglia (Iba1), and astrocyte (Gfap) activation markers in both TRG and TNC, and interestingly also in PBMCs. This is the first description of up- and downregulated genes both in primary and secondary sensory neurones of the trigeminovascular system that might play important roles in neuroinflammatory activation mechanisms. We are the first to show transcriptomic alterations in the PBMCs that are similar to the neuronal changes. These results open new perspectives and initiate further investigations in the research of trigeminal pain disorders.

Dolor orofacial en la clínica odontológica

“…El manejo de las cefaleas experimentó una evidente mejoría con la creación en 1988 de la Clasificación Internacional del Dolor de cabeza (International Headache Classification), con la cual, no solo el diagnóstico, sino también el conocimiento de las frecuencias de los distintos tipos de dolor en la sociedad y sus respectivos tratamientos han evolucionado ampliamente (97). Aunque la base fisiopatológica de los diferentes tipos de cefaleas puede ser muy diversa, en todos ellos existe una sensibilización de las aferencias del nervio trigémino (a nivel intra o extracraneal) (98).…”

Neurotransmitter and tryptophan metabolite concentration changes in the complete Freund’s adjuvant model of orofacial pain

“…The pathomechanism of these disorders may be further investigated by using animal models with the activation of nociceptive pathways of the TS [1,3,5]. The administration of inflammation-inducing substances to the orofacial area can evoke the above-described activation/sensitization of the primary and secondary trigeminal neurons during pain processing [6,7]. For the induction of this peripheral inflammation, the application of Complete Freund's adjuvant (CFA) into the whisker pad or the dural parietal surface is a widely used method [6,8,9] as it is able to enhance local reaction at the injection site and then to evoke the release of inflammatory cytokines, alongside with hyperalgesia/allodynia on the face via the activation/sensitization of the TS [7].…”

“…The administration of inflammation-inducing substances to the orofacial area can evoke the above-described activation/sensitization of the primary and secondary trigeminal neurons during pain processing [6,7]. For the induction of this peripheral inflammation, the application of Complete Freund's adjuvant (CFA) into the whisker pad or the dural parietal surface is a widely used method [6,8,9] as it is able to enhance local reaction at the injection site and then to evoke the release of inflammatory cytokines, alongside with hyperalgesia/allodynia on the face via the activation/sensitization of the TS [7]. Regarding the delay of the development of peripheral and central sensitization, indirect data from studies with CFA injection to the paw demonstrated that pain hypersensitivities were observed 24 h after the injection [9][10][11][12][13], whereas data from studies with orofacial CFA model, more precisely from the temporomandibular joint induced inflammation model, suggest that both thermal and mechanical allodynia peak at 24 h as well [14].…”

“…Regarding the delay of the development of peripheral and central sensitization, indirect data from studies with CFA injection to the paw demonstrated that pain hypersensitivities were observed 24 h after the injection [9][10][11][12][13], whereas data from studies with orofacial CFA model, more precisely from the temporomandibular joint induced inflammation model, suggest that both thermal and mechanical allodynia peak at 24 h as well [14]. The orofacial CFA model has been thoroughly studied regarding gene expression characteristics [6,[15][16][17][18][19][20]. Recently, in relation to two migraine-related biomarkers, the pituitary adenylate cyclase-activating peptide (PACAP) and calcitonin gene-related peptide (CGRP), their increasing levels were detected starting even 24 h after the administration of CFA in the trigeminal nucleus caudalis (TNC) [9].…”

Neurotransmitter and tryptophan metabolite concentration changes in the Complete Freund’s adjuvant model of orofacial pain

“…The pathomechanism of these disorders may be further investigated by using animal models with the activation of nociceptive pathways of the TS [1,3,5]. The administration of inflammation-inducing substances to the orofacial area can evoke the above-described activation/sensitization of the primary and secondary trigeminal neurons during pain processing [6,7]. For the induction of this peripheral inflammation, the application of Complete Freund's adjuvant (CFA) into the whisker pad or the dural parietal surface is a widely used method [6,8,9] as it is able to enhance local reaction at the injection site and then to evoke the release of inflammatory cytokines, alongside with hyperalgesia/allodynia on the face via the activation/sensitization of the TS [7].…”