Neuropathic pain reflects a myriad of changes in the periphery, spinal cord, and supra-spinal structures. Interestingly, despite this baffling array of changes, many approved treatments for neuropathic pain recruit, augment, or mimic bulbospinal inhibition including morphine, noradrenaline (NA) re-uptake inhibitors, and clonidine. Although clinical studies suggest a baseline deficit of descending inhibition in patients with neuropathic pain, we believe that activation of this pathway is a key mechanism engaged by several effective and approved treatments. Gabapentin (GBP) is commonly used for treatment of neuropathic pain but its mechanisms for analgesia are not entirely known. We recently demonstrated GBP activates locus coeruleus (LC) neurons via glutamatergic signaling and that the anti-hypersensitivity effects of GBP in rats with peripheral nerve injury relies on this activation and subsequent spinal NA release. The goals of this proposal are to identify the mechanisms by which GBP regulates glutamate release to activate the LC and also to determine whether the mechanisms of GBP on input to LC neurons apply globally or specifically to subsets involved in analgesia and adverse effects such as somnolence, reduction of attention, and memory retention. Initially, we will examine mechanisms by which GBP modulates GABA regulation of pre-synaptic glutamate release in the LC using synaptosomes and microdialysis. Secondly, we will examine mechanisms by which GBP modulates the unique astroglial-neuronal interaction in the LC to increase extracellular glutamate, using cultured astrocytes and microdialysis. Lastly, we will administrate GBP in the LC and compare NA release in the spinal cord, prefrontal cortex, ventro-lateral preoptic area of the hypothalamus, and the dorsal hippocampus by using microdialysis to test whether GBP-induced activation in the LC is a global phenomenon or selective to projections controlling pain, attention, arousal and memory. The proposed experiments will not only provide important information for understanding analgesic mechanisms of GBP but also lead to novel hypothesis regarding the treatment of neuropathic pain.

Public Health Relevance

Gabapentin is widely used to treat chronic pain, but how it works is not well understood. In this proposal, we will study how gabapentin stimulates a natural pain-relief mechanism to reduce pain but also to cause side effects.

Agency
National Institute of Health (NIH)
Institute
National Institute on Drug Abuse (NIDA)
Type
Research Project (R01)
Project #
5R01DA027690-04
Application #
8433404
Study Section
Somatosensory and Chemosensory Systems Study Section (SCS)
Program Officer
Sorensen, Roger
Project Start
2010-03-01
Project End
2015-02-28
Budget Start
2013-03-01
Budget End
2014-02-28
Support Year
4
Fiscal Year
2013
Total Cost
$275,981
Indirect Cost
$89,507
Name
Wake Forest University Health Sciences
Department
Anesthesiology
Type
Schools of Medicine
DUNS #
937727907
City
Winston-Salem
State
NC
Country
United States
Zip Code
27157
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Suto, Takashi; Severino, Amie L; Eisenach, James C et al. (2014) Gabapentin increases extracellular glutamatergic level in the locus coeruleus via astroglial glutamate transporter-dependent mechanisms. Neuropharmacology 81:95-100
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Hayashida, Ken-ichiro (2013) Substance P-saporin for bone cancer pain in dogs: can man's best friend solve the lost in translation problem in analgesic development? Anesthesiology 119:999-1000
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