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Brain Struct Funct. 2018 Apr;223(3):1149-1164. doi: 10.1007/s00429-017-1543-7. Epub 2017 Nov 1.

Noradrenergic fiber sprouting and altered transduction in neuropathic prefrontal cortex.

Author information

1
Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, 3801 University, Montreal, QC, H3A 2B4, Canada.
2
Alan Edwards Centre for Research on Pain, McGill University, Montreal, QC, H3A 0G1, Canada.
3
Department of Pharmacology and Therapeutics, McGill University, Montreal, QC, H3G 1Y6, Canada.
4
Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, 3801 University, Montreal, QC, H3A 2B4, Canada. philippe.seguela@mcgill.ca.
5
Alan Edwards Centre for Research on Pain, McGill University, Montreal, QC, H3A 0G1, Canada. philippe.seguela@mcgill.ca.

Abstract

Functional changes in hyperpolarization-activated and cyclic nucleotide-gated (HCN) channels have been shown to contribute to medial prefrontal (mPFC) hyperexcitability after peripheral nerve injury. A reduction in the open probability of these neuronal channels might be relevant since this can enhance membrane input resistance and synaptic summation. However, the molecular mechanisms underlying neuropathy-associated alterations in HCN channel activity remain elusive. Using the spared nerve injury model of neuropathic pain in Long-Evans rats, we first discovered a significant increase in noradrenergic innervation within the mPFC of nerve-injured compared to control animals. Patch-clamp recordings in layer II/III pyramidal neurons of the mPFC revealed that adrenoceptors, primarily the α2 subtype, can modulate the voltage-dependent activation of HCN channels and the abnormal prefrontal excitability following peripheral neuropathy. Additionally, microinfusions of the α2 adrenoceptor agonist clonidine in the mPFC of neuropathic rats provided analgesic effects, indicating the behavioral significance for this noradrenergic pathway in manifestations of the chronic pain state. Taken together, our results provide insights into the role of cortical catecholaminergic neuromodulation in neuropathic pain and suggest that altered noradrenergic transduction may play a major role in the HCN channel dysfunction and pyramidal hyperactivity observed in several chronic pain conditions.

KEYWORDS:

Clonidine; HCN channels; Monoamines; Neuromodulation; Neuropathic pain

PMID:
29094305
DOI:
10.1007/s00429-017-1543-7

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