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J Neurosci. 2015 Apr 15;35(15):6057-67. doi: 10.1523/JNEUROSCI.4495-14.2015.

Engagement of the GABA to KCC2 signaling pathway contributes to the analgesic effects of A3AR agonists in neuropathic pain.

Author information

1
Department of Pharmacological and Physiological Science, St. Louis University School of Medicine, St. Louis, Missouri 63104.
2
Institut Universitaire en Santé Mentale de Québec, Québec City, Quebec G1J 2G3, Canada, Department of Psychiatry & Neuroscience, Université Laval, Québec City, Quebec G1K 7P4, Canada.
3
Department of Surgery, Center for Anatomical Science and Education, St. Louis University School of Medicine, St. Louis, Missouri 63104.
4
Department of Pharmacology, College of Medicine, University of Arizona, Tucson, Arizona 85724-5050, and.
5
Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0810.
6
Department of Pharmacological and Physiological Science, St. Louis University School of Medicine, St. Louis, Missouri 63104, salvemd@slu.edu.

Erratum in

  • J Neurosci. 2015 Jun 10;35(23):8971.

Abstract

More than 1.5 billion people worldwide suffer from chronic pain, yet current treatment strategies often lack efficacy or have deleterious side effects in patients. Adenosine is an inhibitory neuromodulator that was previously thought to mediate antinociception through the A1 and A2A receptor subtypes. We have since demonstrated that A3AR agonists have potent analgesic actions in preclinical rodent models of neuropathic pain and that A3AR analgesia is independent of adenosine A1 or A2A unwanted effects. Herein, we explored the contribution of the GABA inhibitory system to A3AR-mediated analgesia using well-characterized mouse and rat models of chronic constriction injury (CCI)-induced neuropathic pain. The deregulation of GABA signaling in pathophysiological pain states is well established: GABA signaling can be hampered by a reduction in extracellular GABA synthesis by GAD65 and enhanced extracellular GABA reuptake via the GABA transporter, GAT-1. In neuropathic pain, GABAAR-mediated signaling can be further disrupted by the loss of the KCC2 chloride anion gradient. Here, we demonstrate that A3AR agonists (IB-MECA and MRS5698) reverse neuropathic pain via a spinal mechanism of action that modulates GABA activity. Spinal administration of the GABAA antagonist, bicuculline, disrupted A3AR-mediated analgesia. Furthermore, A3AR-mediated analgesia was associated with reductions in CCI-related GAD65 and GAT-1 serine dephosphorylation as well as an enhancement of KCC2 serine phosphorylation and activity. Our results suggest that A3AR-mediated reversal of neuropathic pain increases modulation of GABA inhibitory neurotransmission both directly and indirectly through protection of KCC2 function, underscoring the unique utility of A3AR agonists in chronic pain.

KEYWORDS:

GABA; KCC2; adenosine; adenosine receptors; neuropathic pain

PMID:
25878279
PMCID:
PMC4397603
DOI:
10.1523/JNEUROSCI.4495-14.2015
[Indexed for MEDLINE]
Free PMC Article

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