Distinct synaptic mechanisms underlying the analgesic effects of GABA transporter subtypes 1 and 3 inhibitors in the spinal dorsal horn

Abstract Background The widely used analgesic acetaminophen is metabolized to N-acylphenolamine, which induces analgesia by acting directly on transient receptor potential vanilloid 1 or cannabinoid 1 receptors in the brain. Although these receptors are also abundant in the spinal cord, no previous studies have reported analgesic effects of acetaminophen or N-acylphenolamine mediated by the spinal cord dorsal horn. We hypothesized that clinical doses of acetaminophen induce analgesia via these spinal mechanisms. Methods We assessed our hypothesis in a rat model using behavioral measures. We also used in vivo and in vitro whole cell patch-clamp recordings of dorsal horn neurons to assess excitatory synaptic transmission. Results Intravenous acetaminophen decreased peripheral pinch-induced excitatory responses in the dorsal horn (53.1 ± 20.7% of control; n = 10; P < 0.01), while direct application of acetaminophen to the dorsal horn did not reduce these responses. Direct application of N-acylphenolamine decreased the amplitudes of monosynaptic excitatory postsynaptic currents evoked by C-fiber stimulation (control, 462.5 ± 197.5 pA; N-acylphenolamine, 272.5 ± 134.5 pA; n = 10; P = 0.022) but not those evoked by stimulation of Aδ-fibers. These phenomena were mediated by transient receptor potential vanilloid 1 receptors, but not cannabinoid 1 receptors. The analgesic effects of acetaminophen and N-acylphenolamine were stronger in rats experiencing an inflammatory pain model compared to naïve rats. Conclusions Our results suggest that the acetaminophen metabolite N-acylphenolamine induces analgesia directly via transient receptor potential vanilloid 1 receptors expressed on central terminals of C-fibers in the spinal dorsal horn and leads to conduction block, shunt currents, and desensitization of these fibers.

Download Full-text

Single Intraperitoneal Injection of Low-Dose Ketamine Pretreatment Alleviates Mechanical Hyperalgesia and Downregulates the Expression of Inflammatory Cytokines in Spinal Dorsal Horn of Rats

Journal of Anesthesia and Perioperative Medicine ◽

10.24015/japm.2015.0032 ◽

2015 ◽

Vol 2 (5) ◽

pp. 236-243

Author(s):

Li Xu ◽

Yu Shen ◽

Lin Liu ◽

Yin Cui ◽

Xiao-Ping Gu ◽

...

Keyword(s):

Dorsal Horn ◽

Inflammatory Cytokines ◽

Intraperitoneal Injection ◽

Spinal Dorsal Horn ◽

Low Dose ◽

Mechanical Hyperalgesia ◽

Spinal Dorsal ◽

Single Intraperitoneal Injection

Download Full-text

Faculty Opinions recommendation of Spread of excitation across modality borders in spinal dorsal horn of neuropathic rats.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1105023.561186 ◽

2008 ◽

Author(s):

Nanna Finnerup

Keyword(s):

Dorsal Horn ◽

Spinal Dorsal Horn ◽

Spinal Dorsal ◽

Spread Of Excitation

Download Full-text

Faculty Opinions recommendation of Innocuous, not noxious, input activates PKCgamma interneurons of the spinal dorsal horn via myelinated afferent fibers.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1120062.576194 ◽

2008 ◽

Author(s):

Nanna Finnerup

Keyword(s):

Dorsal Horn ◽

Spinal Dorsal Horn ◽

Spinal Dorsal ◽

Afferent Fibers

Download Full-text

Calcitonin gene-related peptide regulates spinal microglial activation through the histone H3 lysine 27 trimethylation via enhancer of zeste homolog-2 in rats with neuropathic pain

Journal of Neuroinflammation ◽

10.1186/s12974-021-02168-1 ◽

2021 ◽

Vol 18 (1) ◽

Author(s):

Qi An ◽

Chenyan Sun ◽

Ruidi Li ◽

Shuhui Chen ◽

Xinpei Gu ◽

...

Keyword(s):

Neuropathic Pain ◽

Dorsal Horn ◽

Nerve Injury ◽

Spinal Dorsal Horn ◽

Microglial Activation ◽

Microglial Cells ◽

Gene Promoters ◽

Spinal Dorsal ◽

Related Peptide ◽

Calcitonin Gene

Abstract Background Calcitonin gene-related peptide (CGRP) as a mediator of microglial activation at the transcriptional level may facilitate nociceptive signaling. Trimethylation of H3 lysine 27 (H3K27me3) by enhancer of zeste homolog 2 (EZH2) is an epigenetic mark that regulates inflammatory-related gene expression after peripheral nerve injury. In this study, we explored the relationship between CGRP and H3K27me3 in microglial activation after nerve injury, and elucidated the underlying mechanisms in the pathogenesis of chronic neuropathic pain. Methods Microglial cells (BV2) were treated with CGRP and differentially enrichments of H3K27me3 on gene promoters were examined using ChIP-seq. A chronic constriction injury (CCI) rat model was used to evaluate the role of CGRP on microglial activation and EZH2/H3K27me3 signaling in CCI-induced neuropathic pain. Results Overexpressions of EZH2 and H3K27me3 were confirmed in spinal microglia of CCI rats by immunofluorescence. CGRP treatment induced the increased of H3K27me3 expression in the spinal dorsal horn and cultured microglial cells (BV2) through EZH2. ChIP-seq data indicated that CGRP significantly altered H3K27me3 enrichments on gene promoters in microglia following CGRP treatment, including 173 gaining H3K27me3 and 75 losing this mark, which mostly enriched in regulation of cell growth, phagosome, and inflammation. qRT-PCR verified expressions of representative candidate genes (TRAF3IP2, BCL2L11, ITGAM, DAB2, NLRP12, WNT3, ADAM10) and real-time cell analysis (RTCA) verified microglial proliferation. Additionally, CGRP treatment and CCI increased expressions of ITGAM, ADAM10, MCP-1, and CX3CR1, key mediators of microglial activation in spinal dorsal horn and cultured microglial cells. Such increased effects induced by CCI were suppressed by CGRP antagonist and EZH2 inhibitor, which were concurrently associated with the attenuated mechanical and thermal hyperalgesia in CCI rats. Conclusion Our findings highly indicate that CGRP is implicated in the genesis of neuropathic pain through regulating microglial activation via EZH2-mediated H3K27me3 in the spinal dorsal horn.

Download Full-text