Nerve injury results in chronic pain following surgery, such as amputation, thoracotomy and mastectomy, as well as in cancer, degenerative conditions and metabolic diseases. The pain is typically intense, persistent and poorly responsive to currently available therapies. Significant progress has been made in understanding the pathophysiology of neuropathic pain, but there has been minimal direct examination of cell membrane and ion channel mechanisms. Increased excitability of neuronal somata of primary afferent neurons is a component of the pain generating process following nerve injury. Intracellular Ca2+ is the dominant second messenger regulating neural activity including electrogenesis, synaptic transmission, gene expression, and cell growth and death, yet no studies of membrane Ca2+ current (ICa) and intracellular Ca2+ levels following nerve injury have been reported. Using tissue from animals showing neuropathic pain behavior following nerve trauma, our novel preliminary findings from whole-cell patch clamp experiments reveal decreased membrane ICa in dorsal root ganglion (DRG) neurons with axons projecting to a sciatic nerve injury site. We have also confirmed in intact DRGs that decreased ICa substantially elevates neuronal excitability.
The aim of this proposal is to examine cellular mechanisms of neuropathic pain by determining the effects of nerve injury on ICa and intracellular Ca2+ in primary afferent neurons that may mediate hyperalgesia. We will employ a clinically relevant model of pain following nerve injury to characterize altered calcium channel function in sensory neurons, identify the channel subtype affected by injury, describe the changes in calcium channel expression with immunocytochemistry, examine intracellular Ca2+ regulation in spatial and temporal detail using Ca2+ microfluorimetry, and demonstrate the effect of decreased Ca2+ flux on membrane excitability in dissociated cells and intact tissue. The proposed studies will test the hypothesis that, in a subgroup of DRG neurons, axonal injury decreases inward Ca2+ current, which in turn decreases intracellular Ca2+ concentration both directly and through diminished Ca2+-induced Ca2+ release. The decrease in intracellular Ca2+ diminishes the Ca 2+-activated K+ current, thereby decreasing membrane afterhyperpolarization and ultimately producing elevated primary afferent excitability. Decreased ICa has not previously been explored as a mechanism of sensory change following nerve injury. This translational research will be valuable in identifying pharmacologically and anatomically specific sites for application of agents to treat neuropathic pain while preserving desired sensory and motor function.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS042150-03
Application #
6639812
Study Section
Special Emphasis Panel (ZRG1-SSS-W (37))
Program Officer
Porter, Linda L
Project Start
2001-07-15
Project End
2005-06-30
Budget Start
2003-07-01
Budget End
2004-06-30
Support Year
3
Fiscal Year
2003
Total Cost
$300,000
Indirect Cost
Name
Medical College of Wisconsin
Department
Anesthesiology
Type
Schools of Medicine
DUNS #
937639060
City
Milwaukee
State
WI
Country
United States
Zip Code
53226
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Bangaru, M L Y; Meng, J; Kaiser, D J et al. (2015) Differential expression of CaMKII isoforms and overall kinase activity in rat dorsal root ganglia after injury. Neuroscience 300:116-27
Kostic, Sandra; Pan, Bin; Guo, Yuan et al. (2014) Regulation of voltage-gated Ca(2+) currents by Ca(2+)/calmodulin-dependent protein kinase II in resting sensory neurons. Mol Cell Neurosci 62:10-8
Hogan, Quinn H; Sprick, Chelsea; Guo, Yuan et al. (2014) Divergent effects of painful nerve injury on mitochondrial Ca(2+) buffering in axotomized and adjacent sensory neurons. Brain Res 1589:112-25
Pan, Bin; Guo, Yuan; Kwok, Wai-Meng et al. (2014) Sigma-1 receptor antagonism restores injury-induced decrease of voltage-gated Ca2+ current in sensory neurons. J Pharmacol Exp Ther 350:290-300
Bangaru, Madhavi L; Weihrauch, Dorothee; Tang, Qing-Bo et al. (2013) Sigma-1 receptor expression in sensory neurons and the effect of painful peripheral nerve injury. Mol Pain 9:47
Gemes, Geza; Koopmeiners, Andrew; Rigaud, Marcel et al. (2013) Failure of action potential propagation in sensory neurons: mechanisms and loss of afferent filtering in C-type units after painful nerve injury. J Physiol 591:1111-31
Duncan, C; Mueller, S; Simon, E et al. (2013) Painful nerve injury decreases sarco-endoplasmic reticulum Caýýýýý-ATPase activity in axotomized sensory neurons. Neuroscience 231:247-57
Bangaru, Madhavi Latha Yadav; Park, Frank; Hudmon, Andy et al. (2012) Quantification of gene expression after painful nerve injury: validation of optimal reference genes. J Mol Neurosci 46:497-504
Gemes, Geza; Oyster, Katherine D; Pan, Bin et al. (2012) Painful nerve injury increases plasma membrane Ca2+-ATPase activity in axotomized sensory neurons. Mol Pain 8:46

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