Unilateral facial injection of Botulinum neurotoxin A attenuates bilateral trigeminal neuropathic pain and anxiety-like behaviors through inhibition of TLR2-mediated neuroinflammation in mice

Abstract

Objectives In this study, we investigated the possible analgesic effects of Botulinum toxin type A (BoNT/A) on trigeminal neuralgia (TN). A modified TN mouse model was established by chronic constriction injury of the distal infraorbital nerve (dIoN-CCI) in mice, and the possible roles of microglia toll-like receptor 2 (TLR2) and neuroinflammation was investigated. Methods Male C57BL/6 mice were divided into 3 groups, including sham group, vehicle-treated TN group and BoNT/A-treated TN group. Bilateral mechanical pain hypersensitivity, anxiety-like and depressive-like behaviors were evaluated by using von Frey test, open field, elevated plus-maze testing, and forced swimming test in mice, respectively. The mRNA or protein expression levels of toll-like receptors (TLRs), glia activation markers and proinflammatory factors in the trigeminal nucleus caudalis (TNC) were tested by RT-qPCR, immunofluorescence and Western blotting. We also tested the pain behaviors of TN in Tlr2−/− mice. Results We found that unilateral subcutaneous injection of BoNT/A into the whisker pad on the ipsilateral side of dIoN-CCI mice significantly attenuated bilateral mechanical pain hypersensitivity and anxiety-like behaviors induced by dIoN-CCI surgery in mice. The dIoN-CCI surgery significantly up-regulated the expression of TLR2, MyD88, CD11b (a microglia marker), IL-1β, TNF-α and IL-6 in the ipsilateral TNC in mice, and BoNT/A injection significantly inhibited the expression of these factors. Immunostaining results confirmed that BoNT/A injection significantly inhibited the microglia activation in the ipsilateral TNC in dIoN-CCI mice. TLR2 deficiency also alleviated bilateral mechanical pain hypersensitivity and the up-regulation of MyD88 expression in the TNC of dIoN-CCI mice. Conclusion These results indicate that unilateral injection of BoNT/A attenuated bilateral mechanical pain hypersensitivity and anxiety-like behaviors in dIoN-CCI mice, and the analgesic effects of BoNT/A may be associated with the inhibition of TLR2-mediated neuroinflammation in the TNC.

Toll-like receptors and their role in neuropathic pain and migraine

“…Previous studies have suggested that TLR2 is involved in the pathogenesis of neuropathic pain and trigeminal neuralgia. However, the mechanism of TLR2 pathway during migraine attacks remains unclear [ 40 ].…”

“…TLRs are normally expressed in immune and glial cells of the CNS [39,40]. In addition to pathogen recognition, TLRs also function to recognize the molecular patterns of ligands associated with cellular stress, tissue damage, or cell death [41][42][43].…”

N-Methyl D-aspartate receptor subtype 2B/Ca2+/calmodulin-dependent protein kinase II signaling in the lateral habenula regulates orofacial allodynia and anxiety-like behaviors in a mouse model of trigeminal neuralgia

“…The activation of CaMKII + neurons in the bilateral LHb may induce pain and anxiety via LHb regulation of the 5-HT, dopaminergic (Li et al, 2017;Metzger et al, 2021), and overall reward systems (Wang et al, 2017) given its complex network of nerve projections (Hetu et al, 2016;Browne et al, 2018). Although adult male C57BL/6 mice are frequently used in the study of TN and related emotions (Trevisan et al, 2016;Chen et al, 2021) and we also provided preliminary evidence demonstrating that the LHb plays an important role in the regulation of TN and related anxiety-like behaviors using these mice (Cui et al, 2020b), whether our findings differs according to species and sex requires further validation. This is an important topic that we are currently working on.…”

Therapeutic Efficacy of Botulinum Toxin in Trigeminal Neuralgia

“…A study assessing the efficacy of BTX-A through inhibition of microglia toll-like receptor 2 (TLR2)-mediated neuroinflammation in mice demonstrated that BTX-A significantly inhibited microglia activation, thus demonstrating the mechanism behind the efficacy of BTX-A in TN. Subcutaneous unilateral injection of BTX-A in whisker pad attenuated the bilateral mechanical pain hypersensitivity and anxiety-like behaviors [ 32 ]. Another study involving rats showed that BTX-A when administered peripherally localized bilaterally in the trigeminal ganglia and demonstrated a role of axonal and hematogenous transport in the therapeutic role of BTX-A.…”