Chronic itch is a presenting sign in numerous diseases associated with the skin, the immune, and the nervous systems. Chronic itch is largely resistant to conventional antihistamines, and few effective therapies are available. We have previously uncovered a small subset of itch- specific neurons which express gastrin-releasing peptide receptor (GRPR), an itch receptor, in the spinal cord. GRPR+ neurons are required for pruritoceptive but not for nociceptive transmission. We have also begun to elucidate the function of neuromedin B receptor (NMBR), another itch receptor in the spinal cord. Our goal is to investigate fundamental mechanisms of itch transmission. We will take advantage of several unique mouse lines to examine the dorsal horn itch circuitry at the single cell level.
Aim 1 will determine neurochemical, anatomic and electrophysiological properties of GRPR neurons. We will examine the neurotransmitter phenotype of GRPR neurons and whether GRPR neurons are projection or interneurons by retrograde labeling. We will also examine electrophysiological properties of GRPR neurons using whole cell patch-clamp recording.
Aim 2 will determine the synaptic mechanisms underlying GRP-mediated itch transmission. We will test the hypothesis that GRP-evoked excitation of GRPR neurons is mediated by modulation of ionotropic glutamate receptors (iGluRs) and GRP-dependent mechanism is differentially involved in pruritogens-induced pruriceptive transmission. We will also determine the role of glutamatergic input in this process and examine whether nonhistaminergic and histaminergic pruritogen act through GRP and iGluRs.
Aim 3 will determine molecular properties and function of itch-sensing neurons in chronic itch condition. We will determine whether ectopic GRPR expression induced in chronic itch condition is dependent on primary GRPR neurons by cell ablation approach. Moreover, we will characterize the electric properties of GRPR neurons in chronic itch condition. Finally, we will examine the role of NMBR neurons in itch sensation using NMB-saporin approach.

Public Health Relevance

Chronic itch is a major unmet medical problem which remains poorly understood. We will study the signaling mechanism in the spinal cord using a wide range of approaches. Our proposed studies will lead to a better understanding of central neural mechanism that underlies the modulation of itch transmission, and may provide a basis for designing a better strategy for chronic itch management.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Research Project (R01)
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Somatosensory and Chemosensory Systems Study Section (SCS)
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Tseng, Hung H
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Washington University
Schools of Medicine
Saint Louis
United States
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Zhao, Zhong-Qiu; Liu, Xian-Yu; Jeffry, Joseph et al. (2014) Descending control of itch transmission by the serotonergic system via 5-HT1A-facilitated GRP-GRPR signaling. Neuron 84:821-34
Zhao, Zhong-Qiu; Wan, Li; Liu, Xian-Yu et al. (2014) Cross-inhibition of NMBR and GRPR signaling maintains normal histaminergic itch transmission. J Neurosci 34:12402-14
Liu, Zhixiang; Zhou, Jingfeng; Li, Yi et al. (2014) Dorsal raphe neurons signal reward through 5-HT and glutamate. Neuron 81:1360-74
Liu, Xian-Yu; Wan, Li; Huo, Fu-Quan et al. (2014) B-type natriuretic peptide is neither itch-specific nor functions upstream of the GRP-GRPR signaling pathway. Mol Pain 10:4
Jeffry, Joseph; Kim, Seungil; Chen, Zhou-Feng (2011) Itch signaling in the nervous system. Physiology (Bethesda) 26:286-92
Liu, Qin; Tang, Zongxiang; Surdenikova, Lenka et al. (2009) Sensory neuron-specific GPCR Mrgprs are itch receptors mediating chloroquine-induced pruritus. Cell 139:1353-65
Sun, Yan-Gang; Zhao, Zhong-Qiu; Meng, Xiu-Li et al. (2009) Cellular basis of itch sensation. Science 325:1531-4