Optogenetic stimulation of the motor cortex alleviates neuropathic pain in rats of infraorbital nerve injury with/withou

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(2020) 21:106

The Journal of Headache and Pain

RESEARCH ARTICLE

Open Access

Optogenetic stimulation of the motor cortex alleviates neuropathic pain in rats of infraorbital nerve injury with/without CGRP knock-down Jaisan Islam1, Elina KC1, Byeong Ho Oh2, Soochong Kim3, Sang-hwan Hyun3 and Young Seok Park1,2,3,4*

Abstract Background: Previous studies have reported that electrical stimulation of the motor cortex is effective in reducing trigeminal neuropathic pain; however, the effects of optical motor cortex stimulation remain unclear. Objective: The present study aimed to investigate whether optical stimulation of the primary motor cortex can modulate chronic neuropathic pain in rats with infraorbital nerve constriction injury. Methods: Animals were randomly divided into a trigeminal neuralgia group, a sham group, and a control group. Trigeminal neuropathic pain was generated via constriction of the infraorbital nerve and animals were treated via selective inhibition of calcitonin gene-related peptide in the trigeminal ganglion. We assessed alterations in behavioral responses in the pre-stimulation, stimulation, and post-stimulation conditions. In vivo extracellular recordings were obtained from the ventral posteromedial nucleus of the thalamus, and viral and α-CGRP expression were investigated in the primary motor cortex and trigeminal ganglion, respectively. Results: We found that optogenetic stimulation significantly improved pain behaviors in the trigeminal neuralgia animals and it provided more significant improvement with inhibited α-CGRP state than active α-CGRP state. Electrophysiological recordings revealed decreases in abnormal thalamic firing during the stimulation-on condition. Conclusion: Our findings suggest that optical motor cortex stimulation can alleviate pain behaviors in a rat model of trigeminal neuropathic pain. Transmission of trigeminal pain signals can be modulated via knock-down of αCGRP and optical motor cortex stimulation. Keywords: Optogenetics, Neuropathic pain, Trigeminal ganglion, α-CGRP, Thalamus, Motor cortex

* Correspondence: [email protected]; [email protected] 1 Department of Neuroscience, College of Medicine, Chungbuk National University, Cheongju, South Korea 2 Department of Neurosurgery, Chungbuk National University Hospital, Cheongju, South Korea Full list of author information is available at the end of the article © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended