The neural basis of Itch is poorly understood despite its importance as a primary quality of cutaneous sensation and as a clinical symptom of many neurological and other disorders. During our previous funding period we discovered that itch is mediated by subpopulations of nociceptive primary neurons and nociceptive spinothalamic tract (STT) neurons, some responsive to histamine, and others to the spicules of cowhage that evoked a histamine independent itch via a novel cysteine protease that we identified. We devised a precise method of eliciting pruritic and nociceptive chemically evoked sensations (dysesthesias) by using chemically inert (heat inactivated) spicules soaked in an endogenous cysteine protease, histamine, or capsaicin. We propose to continue our combined, psychophysical and neurophysiological study of itch requiring the integrated efforts of three different projects each using a different experimental approach. Project 1 will measure psychophysically the itch, nociceptive sensations and dysesthesias evoked by heat-inactivated cowhage spicules containing histamine, capsaicin or an endogenous cysteine protease. The effects of mechanical, thermal or chemical stimuli in enhancing or suppressing itch and the effects of blocking conduction in myelinated nerve fibers will be examined to reveal underlying neural mechanisms controlling itch. Project 2 will electrophysiologically record the responses, to the same stimuli used in project 1, of peripheral nerve fibers in monkey to determine the separate contributions of nociceptive neurons with myelinated vs. non-myelinated axons to itch and nociceptive sensations and to the enhancement and inhibition of itch. Project 3 will electrophysiologically record the responses of STT- and thalamic neurons to the same stimuli used in projects 1 &2. In addition, the effects of iontophoretic application of morphine, a GABA inhibitor, and the blocking of descending pathways from suprasegmental areas on STT neuronal responses will reveal spinal mechanisms of the enhancement and inhibition of itch, nociception and pruritic dysesthesias. A core providing administration, instrumentation, statistics and informatics will facilitate the collection, analysis and evaluation of the data obtained from each project. By increasing our understanding of the peripheral and central neural mechanisms that code and modulate itch and nociceptive sensations, our combined studies will provide new targets for novel therapies to relieve itch and pain.
The proposed psychophysical and neurophysiological studies of experimentally produced itch and pain will advance our understanding of how these sensations are mediated by sensory neurons in the peripheral and central nervous system. Identification of these neurons and their properties will provide targets for pharmacological therapies to relieve chronic itch and pain in humans.
|Moser, H R; Giesler Jr, G J (2014) Itch elicited by intradermal injection of serotonin, intracisternal injection of morphine, and their synergistic interactions in rats. Neuroscience 274:119-27|
|Qu, Lintao; Fan, Ni; Ma, Chao et al. (2014) Enhanced excitability of MRGPRA3- and MRGPRD-positive nociceptors in a model of inflammatory itch and pain. Brain 137:1039-50|
|LaMotte, Robert H; Dong, Xinzhong; Ringkamp, Matthias (2014) Sensory neurons and circuits mediating itch. Nat Rev Neurosci 15:19-31|
|Ringkamp, Matthias; Raja, Srinivasa N (2014) A sore spot: central or peripheral generation of chronic neuropathic spontaneous pain? Pain 155:1189-91|
|Moser, Hannah R; Giesler Jr, Glenn J (2014) Characterization of pruriceptive trigeminothalamic tract neurons in rats. J Neurophysiol 111:1574-89|
|Wooten, Matthew; Weng, Hao-Jui; Hartke, Timothy V et al. (2014) Three functionally distinct classes of C-fibre nociceptors in primates. Nat Commun 5:4122|
|Moser, Hannah R; Giesler Jr, Glenn J (2013) Itch and analgesia resulting from intrathecal application of morphine: contrasting effects on different populations of trigeminothalamic tract neurons. J Neurosci 33:6093-101|
|Han, Liang; Ma, Chao; Liu, Qin et al. (2013) A subpopulation of nociceptors specifically linked to itch. Nat Neurosci 16:174-82|
|Sikand, Parul; Dong, Xinzhong; LaMotte, Robert H (2011) BAM8-22 peptide produces itch and nociceptive sensations in humans independent of histamine release. J Neurosci 31:7563-7|
|LaMotte, Robert H; Shimada, Steven G; Sikand, Parul (2011) Mouse models of acute, chemical itch and pain in humans. Exp Dermatol 20:778-82|
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