LETTER


Minocycline Inhibits the Enhanced Antidromic Stimulation-induced Sensitization of C-Fibers Following Intradermal Capsaicin Injection



Kerui Gong1, 2, Qing Lin1, *
1 Department of Psychology, College of Science, University of Texas at Arlington, Arlington, Texas, USA
2 Department of Oral and Maxillofacial Surgery, University of California, San Francisco, California, USA


© 2019 Gong and Lin.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: (https://creativecommons.org/licenses/by/4.0/legalcode). This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at Department of Psychology, 501 South, University of Texas at Arlington, Arlington, TX 76019-0528, USA;
Tel: +1-817-272-0154; Fax: +1-817-272-2364; E-mail: qilin@uta.edu


Abstract

Background:

Our previous studies indicated that retrograde signaling initiating from the spinal cord was mediated by the plasticity of Dorsal Root Ganglion (DRG) neurons. Both retrograde signaling and neuronal plasticity contributed to neurogenic inflammation, which were modulated by the activity of Satellite Glial Cells (SGCs). Thus, we want to know whether retrograde signaling is involved in the hypersensitivity of nociceptive afferents, and whether this process is affected by the plasticity of DRG neurons and glia.

Objective:

The study aims to examine if retrograde signaling can induce hypersensitivity of primary afferent nociceptors and if hypersensitivity involves glial modulation.

Methods:

Antidromic Electrical Stimulation (ES) of dorsal roots was used to mimic retrograde signaling activity. C- primary nociceptive afferent activity was recorded for testing the effect of antidromic ES. In a separate group, intradermal capsaicin injection to the ipsilateral hindpaw was used to prime DRG nociceptive neurons. For the third group, a glial inhibitor, minocycline, was pre-administered to test glial modulation in this process.

Results:

Antidromic ES sensitized the responses of C-fibers to nociceptive mechanical stimuli. For rats subjected to intradermal capsaicin injection, C fibers experienced more drastic sensitization induced by antidromic ES, shown as a greater response and longer duration, implying that sensitization correlates with the activation of DRG neurons.

Minocycline pretreatment significantly blocked the priming effect of capsaicin on C-fiber sensitization induced by antidromic ES, indicating the involvement of SGCs in DRG neuronal sensitization.

Conclusion:

Retrograde signaling may be one of the important mechanisms in neurogenic inflammation-mediated nociception, and this process is subjected to satellite glial modulation.

Keywords: Neurogenic inflammation, Antidromic electrical stimulation, Single fiber recording, C fiber, Capsaicin, Minocycline, Satellite glial cell.