GABA-A receptor (GAR) mediated presynaptic inhibition of afferent input to the spinal cord is critical for the establishment of nociceptive threshold. In the absence of injury, spinal administration of GAR antagonists produce hyperalgesia and allodynia whereas GAR agonists are analgesic. We recently demonstrated, however, that in the presence of persistent inflammation, there is a shift in GAR signaling such that activation of spinal GARs actually contributes to inflammatory hyperalgesia: spinal administration GAR antagonists reverse inflammatory hyperalgesia while GAR agonists exacerbate it. Our preliminary data suggest this shift reflects a presynaptic change in GAR signaling which includes the emergence of distinct GAR receptor subunits and a depolarizing shift in the anion equilibrium potential (Eanion). A depolarizing shift in Eanion may enable GAR activation to become excitatory. However, our recent data also indicate that midazolam, a benzodiazepine receptor agonist, retains analgesic efficacy in the presence of inflammation, indicating that a depolarizing shift in Eanion alone is insufficient to account for the inflammation-induced shift in GAR signaling. The apparent shift in spinal GAR signaling has profound implications for 1) our understanding of the underlying mechanisms of persistent pain, 2) the clinical use of an array of general anesthetics such a isoflurane, propofol and etomidate, and 3) the development of novel therapeutic interventions for the treatment of pain. Therefore, we have proposed a series of experiments described under 4 specific aims, designed to identify mechanisms underlying spinal GAR signaling in the presence and absence of inflammation.
In Specific Aim 1, we will characterize inflammation-induced changes in the biophysical properties and pharmacology of GAR mediated currents and the regulation of anion homeostasis in cutaneous sensory neurons.
In Specific Aim 2, we will characterize inflammation-induced changes in the expression and distribution of GAR subunits in cutaneous sensory neurons.
In Specific Aim 3, we will assess the functional consequences of inflammation-induced changes in GAR subunit expression and intracellular anion homeostasis. And in Specific Aim 4, we will determine the extent to which specific GAR subunits in cutaneous sensory neurons mediate the emergence of pronociceptive actions of GAR signaling in the presence of inflammation. The experiments described under these 4 aims, involving an array of approaches ranging from behavioral pharmacology to viral vector mediated manipulation of gene expression, are designed to test the central hypothesis that persistent inflammation results in changes in GAR signaling that reflect a combination of changes in Eanion and GAR subunit expression in primary afferent neurons.

Public Health Relevance

3-aminobutyric acid-A (GABA-A) receptors on the central terminals of primary afferent neurons appear to play critical role both in the inhibition of acute pain and the maintenance of persistent pain in the presence of injury. The mechanisms underlying this shift in GABA-A receptor signaling remain to be identified, but it has profound implications for 1) our understanding of the underlying mechanisms of persistent pain, 2) the clinical use of an array of general anesthetics such a isoflurane, propofol and etomidate, and 3) the development of novel therapeutic interventions for the treatment of pain. Therefore, with the ultimate goals of both minimizing deleterious consequences of general anesthetics and identifying novel targets for therapeutic interventions, we have proposed a series of experiments designed to identify mechanisms underlying the shift in spinal GABA-A receptor signaling in the presence of inflammation.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS063010-02
Application #
7791308
Study Section
Special Emphasis Panel (ZRG1-IFCN-E (04))
Program Officer
Porter, Linda L
Project Start
2009-04-01
Project End
2012-03-31
Budget Start
2010-04-01
Budget End
2011-03-31
Support Year
2
Fiscal Year
2010
Total Cost
$353,575
Indirect Cost
Name
University of Pittsburgh
Department
Anesthesiology
Type
Schools of Medicine
DUNS #
004514360
City
Pittsburgh
State
PA
Country
United States
Zip Code
15213
Zhang, X-L; Lee, K-Y; Priest, B T et al. (2015) Inflammatory mediator-induced modulation of GABAA currents in human sensory neurons. Neuroscience 310:401-9
Zhu, Y; Zhang, X-L; Gold, M S (2014) Activity-dependent hyperpolarization of EGABA is absent in cutaneous DRG neurons from inflamed rats. Neuroscience 256:1-9
Zhu, Y; Lu, S G; Gold, M S (2012) Persistent inflammation increases GABA-induced depolarization of rat cutaneous dorsal root ganglion neurons in vitro. Neuroscience 220:330-40
Gold, Michael S (2012) Whole-cell recording in isolated primary sensory neurons. Methods Mol Biol 851:73-97
Lee, Kwan Yeop; Gold, Michael S (2012) Inflammatory mediators potentiate high affinity GABA(A) currents in rat dorsal root ganglion neurons. Neurosci Lett 518:128-32
Zhu, Yi; Dua, Shiv; Gold, Michael S (2012) Inflammation-induced shift in spinal GABA(A) signaling is associated with a tyrosine kinase-dependent increase in GABA(A) current density in nociceptive afferents. J Neurophysiol 108:2581-93
Lee, K Y; Charbonnet, M; Gold, M S (2012) Upregulation of high-affinity GABA(A) receptors in cultured rat dorsal root ganglion neurons. Neuroscience 208:133-42
Doyon, Nicolas; Prescott, Steven A; Castonguay, Annie et al. (2011) Efficacy of synaptic inhibition depends on multiple, dynamically interacting mechanisms implicated in chloride homeostasis. PLoS Comput Biol 7:e1002149
Mao, Jianren; Gold, Michael S; Backonja, Miroslav Misha (2011) Combination drug therapy for chronic pain: a call for more clinical studies. J Pain 12:157-66
Williams, Brian A; Hough, Karen A; Tsui, Becky Y K et al. (2011) Neurotoxicity of adjuvants used in perineural anesthesia and analgesia in comparison with ropivacaine. Reg Anesth Pain Med 36:225-30

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