FRINK Linked Data Fragments server

Matches in SemOpenAlex for { <https://semopenalex.org/work/W2171563789> ?p ?o ?g. }

• W2171563789 endingPage "834" @default.
• W2171563789 startingPage "821" @default.
• W2171563789 abstract "•Central 5-HT signaling facilitates itch transmission•5-HT1A potentiates GRPR-mediated itch signaling•5-HT1A and GRPR are present in close proximity•Blockade of 5-HT1A function reduces chronic itch Central serotonin (5-hydroxytryptophan, 5-HT) modulates somatosensory transduction, but how it achieves sensory modality-specific modulation remains unclear. Here we report that enhancing serotonergic tone via administration of 5-HT potentiates itch sensation, whereas mice lacking 5-HT or serotonergic neurons in the brainstem exhibit markedly reduced scratching behavior. Through pharmacological and behavioral screening, we identified 5-HT1A as a key receptor in facilitating gastrin-releasing peptide (GRP)-dependent scratching behavior. Coactivation of 5-HT1A and GRP receptors (GRPR) greatly potentiates subthreshold, GRP-induced Ca2+ transients, and action potential firing of GRPR+ neurons. Immunostaining, biochemical, and biophysical studies suggest that 5-HT1A and GRPR may function as receptor heteromeric complexes. Furthermore, 5-HT1A blockade significantly attenuates, whereas its activation contributes to, long-lasting itch transmission. Thus, our studies demonstrate that the descending 5-HT system facilitates GRP-GRPR signaling via 5-HT1A to augment itch-specific outputs, and a disruption of crosstalk between 5-HT1A and GRPR may be a useful antipruritic strategy.Video AbstracteyJraWQiOiI4ZjUxYWNhY2IzYjhiNjNlNzFlYmIzYWFmYTU5NmZmYyIsImFsZyI6IlJTMjU2In0.eyJzdWIiOiJiYmMwNmYxMGRhMDQ0OWQ2NjMyYjI2NmUyNTk2YWQ0ZiIsImtpZCI6IjhmNTFhY2FjYjNiOGI2M2U3MWViYjNhYWZhNTk2ZmZjIiwiZXhwIjoxNjc4OTQzNjk0fQ.bhmcm89Rts8NHpWqZd8AIVkl3_KMI8hOySSU__hGVt2OaVfC_eYGSxGrq0Wix5Q20W_TjYuLv0-kp_dLVH5M_Z5WZimm-z2lQPrmY5s-7FXUGPxnYQ5K_aqVzJqtasT40CHJBFfu-zNUtV_YE-sdY8NNNYkTbOJQFy2WGB9Ahz05d-_7VVpjuQyABh-zsefjnMlZgdhe5Hlxia9qpY8sf-kgmufogCusO5gmxLc9QiU-W7JDhwkAa0W7H9Sc7UVpaoGprBLygnSmtNBFamZA6rhxQUvF6gK_7fp8Tmn2cAmJnub_ZlMrVrPtmuFsSZieLrN34ALuDKyX0zHTFmEDwA(mp4, (11.59 MB) Download video Central serotonin (5-hydroxytryptophan, 5-HT) modulates somatosensory transduction, but how it achieves sensory modality-specific modulation remains unclear. Here we report that enhancing serotonergic tone via administration of 5-HT potentiates itch sensation, whereas mice lacking 5-HT or serotonergic neurons in the brainstem exhibit markedly reduced scratching behavior. Through pharmacological and behavioral screening, we identified 5-HT1A as a key receptor in facilitating gastrin-releasing peptide (GRP)-dependent scratching behavior. Coactivation of 5-HT1A and GRP receptors (GRPR) greatly potentiates subthreshold, GRP-induced Ca2+ transients, and action potential firing of GRPR+ neurons. Immunostaining, biochemical, and biophysical studies suggest that 5-HT1A and GRPR may function as receptor heteromeric complexes. Furthermore, 5-HT1A blockade significantly attenuates, whereas its activation contributes to, long-lasting itch transmission. Thus, our studies demonstrate that the descending 5-HT system facilitates GRP-GRPR signaling via 5-HT1A to augment itch-specific outputs, and a disruption of crosstalk between 5-HT1A and GRPR may be a useful antipruritic strategy. Somatosensory integration and transduction in the spinal cord and the trigeminal brainstem are subject to monoaminergic modulation. As an integral part of an animal’s adaptive response to an ever-changing environment, facilitatory and inhibitory modulation of somatosensory neural circuits is crucial for the maintenance of homeostasis. Monoaminergic modulation of neural circuits serves an important role in regulating behavioral responses to somatosensory inputs. One notable example is that an array of monoamine neuromodulators produced by supraspinal regions is important for the modulation of nociceptive transmission (Basbaum and Fields, 1984Basbaum A.I. Fields H.L. Endogenous pain control systems: brainstem spinal pathways and endorphin circuitry.Annu. Rev. Neurosci. 1984; 7: 309-338Crossref PubMed Scopus (2237) Google Scholar, Suzuki et al., 2004Suzuki R. Rygh L.J. Dickenson A.H. Bad news from the brain: descending 5-HT pathways that control spinal pain processing.Trends Pharmacol. Sci. 2004; 25: 613-617Abstract Full Text Full Text PDF PubMed Scopus (397) Google Scholar). Given the fundamental role of central modulation in sensory transduction, one can presume that itch sensation is similarly modulated at several levels. Imaging studies in human subjects indicated that pain-mediated inhibition of itch is associated with an activity level of the midbrain regions such as periaqueductal gray matter (PAG), an area known for pain modulation (Mochizuki et al., 2003Mochizuki H. Tashiro M. Kano M. Sakurada Y. Itoh M. Yanai K. Imaging of central itch modulation in the human brain using positron emission tomography.Pain. 2003; 105: 339-346Abstract Full Text Full Text PDF PubMed Scopus (187) Google Scholar). Experiments in humans also indicated that noxious counterirritants reduce itch sensation (Murray and Weaver, 1975Murray F.S. Weaver M.M. Effects of ipsilateral and contralateral counterirritation on experimentally produced itch in human beings.J. Comp. Physiol. Psychol. 1975; 89: 819-826Crossref PubMed Scopus (32) Google Scholar, Ward et al., 1996Ward L. Wright E. McMahon S.B. A comparison of the effects of noxious and innocuous counterstimuli on experimentally induced itch and pain.Pain. 1996; 64: 129-138Abstract Full Text PDF PubMed Scopus (127) Google Scholar, Yosipovitch et al., 2007Yosipovitch G. Duque M.I. Fast K. Dawn A.G. Coghill R.C. Scratching and noxious heat stimuli inhibit itch in humans: a psychophysical study.Br. J. Dermatol. 2007; 156: 629-634Crossref PubMed Scopus (80) Google Scholar). Interruption of the upper cervical spinal cord of rodents attenuated dry skin-induced itch, suggesting an involvement of the descending spinal pathway in itch responses (Akiyama et al., 2011Akiyama T. Iodi Carstens M. Carstens E. Transmitters and pathways mediating inhibition of spinal itch-signaling neurons by scratching and other counterstimuli.PLoS ONE. 2011; 6: e22665Crossref PubMed Scopus (89) Google Scholar). G protein-coupled receptors (GPCRs), or seven trans-membrane proteins, constitute a large repertoire of cellular sensors required for transducing sensory signals from the skin to the brain (Jeffry et al., 2011Jeffry J. Kim S. Chen Z.F. Itch signaling in the nervous system.Physiology (Bethesda). 2011; 26: 286-292Crossref PubMed Scopus (78) Google Scholar, Julius and Nathans, 2012Julius D. Nathans J. Signaling by sensory receptors.Cold Spring Harb. Perspect. Biol. 2012; 4: a005991Crossref Scopus (50) Google Scholar). Gastrin-releasing peptide receptor (GRPR) is a Gq protein-coupled receptor that belongs to the mammalian bombesin receptor family (Jensen et al., 2008Jensen R.T. Battey J.F. Spindel E.R. Benya R.V. International Union of Pharmacology. LXVIII. Mammalian bombesin receptors: nomenclature, distribution, pharmacology, signaling, and functions in normal and disease states.Pharmacol. Rev. 2008; 60: 1-42Crossref PubMed Scopus (411) Google Scholar, Kroog et al., 1995Kroog G.S. Jensen R.T. Battey J.F. Mammalian bombesin receptors.Med. Res. Rev. 1995; 15: 389-417Crossref PubMed Scopus (146) Google Scholar). GRPR is expressed in laminae I–II of spinal cord neurons and has an important role in the transmission of pruritogenic information (Liu et al., 2011Liu X.Y. Liu Z.C. Sun Y.G. Ross M. Kim S. Tsai F.F. Li Q.F. Jeffry J. Kim J.Y. Loh H.H. Chen Z.F. Unidirectional cross-activation of GRPR by MOR1D uncouples itch and analgesia induced by opioids.Cell. 2011; 147: 447-458Abstract Full Text Full Text PDF PubMed Scopus (218) Google Scholar, O’Donohue et al., 1984O’Donohue T.L. Massari V.J. Pazoles C.J. Chronwall B.M. Shults C.W. Quirion R. Chase T.N. Moody T.W. A role for bombesin in sensory processing in the spinal cord.J. Neurosci. 1984; 4: 2956-2962PubMed Google Scholar, Sun and Chen, 2007Sun Y.G. Chen Z.F. A gastrin-releasing peptide receptor mediates the itch sensation in the spinal cord.Nature. 2007; 448: 700-703Crossref PubMed Scopus (571) Google Scholar, Sun et al., 2009Sun Y.G. Zhao Z.Q. Meng X.L. Yin J. Liu X.Y. Chen Z.F. Cellular basis of itch sensation.Science. 2009; 325: 1531-1534Crossref PubMed Scopus (449) Google Scholar). Gastrin-releasing peptide (GRP), an endogenous neuropeptide for itch, is expressed in a subset of dorsal root ganglion (DRG) and trigeminal ganglion (TG) cells and mediates GRPR activation in the spinal cord (Sun and Chen, 2007Sun Y.G. Chen Z.F. A gastrin-releasing peptide receptor mediates the itch sensation in the spinal cord.Nature. 2007; 448: 700-703Crossref PubMed Scopus (571) Google Scholar, Takanami et al., 2014Takanami K. Sakamoto H. Matsuda K.I. Satoh K. Tanida T. Yamada S. Inoue K. Oti T. Sakamoto T. Kawata M. Distribution of gastrin-releasing peptide in the rat trigeminal and spinal somatosensory systems.J. Comp. Neurol. 2014; 522: 1858-1873Crossref PubMed Scopus (34) Google Scholar, Zhao et al., 2013Zhao Z.-Q. Huo F.-Q. Jeffry J. Hampton L. Demehri S. Kim S. Liu X.-Y. Barry D.M. Wan L. Liu Z.-C. et al.Chronic itch development in sensory neurons requires BRAF signaling pathways.J. Clin. Invest. 2013; 123: 4769-4780Crossref PubMed Scopus (80) Google Scholar). While confusion has arisen about GRP expression in DRG neurons, the issue has recently been clarified (Liu et al., 2014Liu X.Y. Wan L. Huo F.Q. Barry D.M. Li H. Zhao Z.Q. Chen Z.F. B-type natriuretic peptide is neither itch-specific nor functions upstream of the GRP-GRPR signaling pathway.Mol. Pain. 2014; 10: 4Crossref PubMed Scopus (57) Google Scholar, Takanami et al., 2014Takanami K. Sakamoto H. Matsuda K.I. Satoh K. Tanida T. Yamada S. Inoue K. Oti T. Sakamoto T. Kawata M. Distribution of gastrin-releasing peptide in the rat trigeminal and spinal somatosensory systems.J. Comp. Neurol. 2014; 522: 1858-1873Crossref PubMed Scopus (34) Google Scholar, Zhao et al., 2013Zhao Z.-Q. Huo F.-Q. Jeffry J. Hampton L. Demehri S. Kim S. Liu X.-Y. Barry D.M. Wan L. Liu Z.-C. et al.Chronic itch development in sensory neurons requires BRAF signaling pathways.J. Clin. Invest. 2013; 123: 4769-4780Crossref PubMed Scopus (80) Google Scholar, Zhao et al., 2014Zhao Z.Q. Wan L. Liu X.Y. Huo F.Q. Li H. Barry D.M. Krieger S. Kim S. Liu Z.C. Xu J. et al.Cross-Inhibition of NMBR and GRPR Signaling Maintains Normal Histaminergic Itch Transmission.J. Neurosci. 2014; 34: 12402-12414Crossref PubMed Scopus (40) Google Scholar). The GRP-GRPR pathway is primarily engaged in transducing nonhistaminergic acute itch sensation and may play a relatively minor role in histaminergic itch (Akiyama et al., 2014Akiyama T. Tominaga M. Takamori K. Carstens M.I. Carstens E. Roles of glutamate, substance P, and gastrin-releasing peptide as spinal neurotransmitters of histaminergic and nonhistaminergic itch.Pain. 2014; 155: 80-92Abstract Full Text Full Text PDF PubMed Scopus (74) Google Scholar, Sun et al., 2009Sun Y.G. Zhao Z.Q. Meng X.L. Yin J. Liu X.Y. Chen Z.F. Cellular basis of itch sensation.Science. 2009; 325: 1531-1534Crossref PubMed Scopus (449) Google Scholar, Zhao et al., 2014Zhao Z.Q. Wan L. Liu X.Y. Huo F.Q. Li H. Barry D.M. Krieger S. Kim S. Liu Z.C. Xu J. et al.Cross-Inhibition of NMBR and GRPR Signaling Maintains Normal Histaminergic Itch Transmission.J. Neurosci. 2014; 34: 12402-12414Crossref PubMed Scopus (40) Google Scholar). Enhanced GRP and GRPR expression is positively correlated with the intensity of chronic itch manifested by increased scratching bouts of animals (Nattkemper et al., 2013Nattkemper L.A. Zhao Z.Q. Nichols A.J. Papoiu A.D. Shively C.A. Chen Z.F. Yosipovitch G. Overexpression of the gastrin-releasing peptide in cutaneous nerve fibers and its receptor in the spinal cord in primates with chronic itch.J. Invest. Dermatol. 2013; 133: 2489-2492Crossref PubMed Scopus (41) Google Scholar, Tominaga et al., 2009Tominaga M. Ogawa H. Takamori K. Histological characterization of cutaneous nerve fibers containing gastrin-releasing peptide in NC/Nga mice: an atopic dermatitis model.J. Invest. Dermatol. 2009; 129: 2901-2905Crossref PubMed Scopus (60) Google Scholar, Zhao et al., 2013Zhao Z.-Q. Huo F.-Q. Jeffry J. Hampton L. Demehri S. Kim S. Liu X.-Y. Barry D.M. Wan L. Liu Z.-C. et al.Chronic itch development in sensory neurons requires BRAF signaling pathways.J. Clin. Invest. 2013; 123: 4769-4780Crossref PubMed Scopus (80) Google Scholar). Conversely, loss of GRPR or GRP markedly reduces chronic itch (Lagerström et al., 2010Lagerström M.C. Rogoz K. Abrahamsen B. Persson E. Reinius B. Nordenankar K. Olund C. Smith C. Mendez J.A. Chen Z.F. et al.VGLUT2-dependent sensory neurons in the TRPV1 population regulate pain and itch.Neuron. 2010; 68: 529-542Abstract Full Text Full Text PDF PubMed Scopus (171) Google Scholar, Zhao et al., 2013Zhao Z.-Q. Huo F.-Q. Jeffry J. Hampton L. Demehri S. Kim S. Liu X.-Y. Barry D.M. Wan L. Liu Z.-C. et al.Chronic itch development in sensory neurons requires BRAF signaling pathways.J. Clin. Invest. 2013; 123: 4769-4780Crossref PubMed Scopus (80) Google Scholar), demonstrating the importance of GRPR in the development and maintenance of chronic itch. Despite these studies, molecular mechanisms by which the function of GRPR is modulated remain elusive. Serotonergic neurons reside principally in the brainstem raphe nuclei and modulate a myriad of behavioral and physiological functions through descending and ascending pathways (Barnes and Sharp, 1999Barnes N.M. Sharp T. A review of central 5-HT receptors and their function.Neuropharmacology. 1999; 38: 1083-1152Crossref PubMed Scopus (2721) Google Scholar, Dillon et al., 2004Dillon S.R. Sprecher C. Hammond A. Bilsborough J. Rosenfeld-Franklin M. Presnell S.R. Haugen H.S. Maurer M. Harder B. Johnston J. et al.Interleukin 31, a cytokine produced by activated T cells, induces dermatitis in mice.Nat. Immunol. 2004; 5: 752-760Crossref PubMed Scopus (744) Google Scholar). Serotonergic neurons in the rostral ventromedial medulla (RVM), including nucleus raphe magnus (NRM) and surrounding reticular formation, project to both the trigeminal nucleus caudalis (SpVc) and the dorsal horn of the spinal cord and modulate nociceptive transmission in a bidirectional fashion (Basbaum and Fields, 1984Basbaum A.I. Fields H.L. Endogenous pain control systems: brainstem spinal pathways and endorphin circuitry.Annu. Rev. Neurosci. 1984; 7: 309-338Crossref PubMed Scopus (2237) Google Scholar, Millan, 2002Millan M.J. Descending control of pain.Prog. Neurobiol. 2002; 66: 355-474Crossref PubMed Scopus (2345) Google Scholar, Ossipov et al., 2010Ossipov M.H. Dussor G.O. Porreca F. Central modulation of pain.J. Clin. Invest. 2010; 120: 3779-3787Crossref PubMed Scopus (707) Google Scholar, Suzuki et al., 2004Suzuki R. Rygh L.J. Dickenson A.H. Bad news from the brain: descending 5-HT pathways that control spinal pain processing.Trends Pharmacol. Sci. 2004; 25: 613-617Abstract Full Text Full Text PDF PubMed Scopus (397) Google Scholar). In contrast to numerous studies of serotonergic modulation of pain, little is known about the involvement of central 5-HT and receptor mechanisms in itch modulation. In this study, we tested the hypothesis that 5-HT signaling has a pivotal role in itch modulation. To evaluate the involvement of the central serotonergic system in modulation of itch transmission, we first examined the scratching behavior of Lmx1bf/f/p mice to intradermal injection (i.d.) of chloroquine (CQ), a representative nonhistaminergic pruritogen that acts, in part, via a Mas-related GPCR (MrgprA3) in sensory neurons and GRPR in the spinal cord (Liu et al., 2009Liu Q. Tang Z. Surdenikova L. Kim S. Patel K.N. Kim A. Ru F. Guan Y. Weng H.J. Geng Y. et al.Sensory neuron-specific GPCR Mrgprs are itch receptors mediating chloroquine-induced pruritus.Cell. 2009; 139: 1353-1365Abstract Full Text Full Text PDF PubMed Scopus (563) Google Scholar, Sun and Chen, 2007Sun Y.G. Chen Z.F. A gastrin-releasing peptide receptor mediates the itch sensation in the spinal cord.Nature. 2007; 448: 700-703Crossref PubMed Scopus (571) Google Scholar). LMX1B is a LIM homeodomain-containing transcription factor that is required for the development of all central 5-HT neurons (Ding et al., 2003Ding Y.Q. Marklund U. Yuan W. Yin J. Wegman L. Ericson J. Deneris E. Johnson R.L. Chen Z.F. Lmx1b is essential for the development of serotonergic neurons.Nat. Neurosci. 2003; 6: 933-938Crossref PubMed Scopus (223) Google Scholar). We previously generated conditional Lmx1bf/f/p mice in which Lmx1b is conditionally ablated in Pet1-expressing serotonergic neurons in the raphe nuclei. As a result, all central 5-HT neurons of Lmx1bf/f/p mice were ablated due to lack of Lmx1b (Zhao et al., 2006Zhao Z.Q. Scott M. Chiechio S. Wang J.S. Renner K.J. Gereau 4th, R.W. Johnson R.L. Deneris E.S. Chen Z.F. Lmx1b is required for maintenance of central serotonergic neurons and mice lacking central serotonergic system exhibit normal locomotor activity.J. Neurosci. 2006; 26: 12781-12788Crossref PubMed Scopus (177) Google Scholar). However, these mice survive and exhibit normal motor function and thus represent a unique genetic model for investigating the role of central 5-HT neurons in diverse physiological functions (Zhao et al., 2007aZhao Z.Q. Chiechio S. Sun Y.G. Zhang K.H. Zhao C.S. Scott M. Johnson R.L. Deneris E.S. Renner K.J. Gereau 4th, R.W. Chen Z.F. Mice lacking central serotonergic neurons show enhanced inflammatory pain and an impaired analgesic response to antidepressant drugs.J. Neurosci. 2007; 27: 6045-6053Crossref PubMed Scopus (113) Google Scholar, Zhao et al., 2007bZhao Z.Q. Gao Y.J. Sun Y.G. Zhao C.S. Gereau 4th, R.W. Chen Z.F. Central serotonergic neurons are differentially required for opioid analgesia but not for morphine tolerance or morphine reward.Proc. Natl. Acad. Sci. USA. 2007; 104: 14519-14524Crossref PubMed Scopus (58) Google Scholar). Compared with wild-type (WT) mice, CQ-evoked scratching responses were significantly reduced in Lmx1bf/f/p mice (Figure 1A), demonstrating that central 5-HT neurons exert a constitutive tone for positively modulating itch transmission. To determine whether the decrease was specifically due to a loss of 5-HT or whether other factors originating in central 5-HT neurons were involved, we generated mice lacking tryptophan hydroxylase 2 (Tph2), which encodes the rate-limiting enzyme for 5-HT synthesis in the brain (Walther et al., 2003Walther D.J. Peter J.U. Bashammakh S. Hörtnagl H. Voits M. Fink H. Bader M. Synthesis of serotonin by a second tryptophan hydroxylase isoform.Science. 2003; 299: 76Crossref PubMed Scopus (1213) Google Scholar) using gene targeting strategy (Figure 1B). Tph2−/− mice showed no expression of Tph2 and 5-HT in the central nervous system but maintained normal presumptive 5-HT neurons (Figure 1B) (Kim et al., 2014Kim J.Y. Kim A. Zhao Z.Q. Liu X.Y. Chen Z.F. Postnatal maintenance of the 5-Ht1a-Pet1 autoregulatory loop by serotonin in the raphe nuclei of the brainstem.Mol. Brain. 2014; 7: 48Crossref PubMed Scopus (17) Google Scholar, Liu et al., 2011Liu X.Y. Liu Z.C. Sun Y.G. Ross M. Kim S. Tsai F.F. Li Q.F. Jeffry J. Kim J.Y. Loh H.H. Chen Z.F. Unidirectional cross-activation of GRPR by MOR1D uncouples itch and analgesia induced by opioids.Cell. 2011; 147: 447-458Abstract Full Text Full Text PDF PubMed Scopus (218) Google Scholar). Tph2−/− mice displayed a significant reduction in scratching response after i.d. injection of CQ in nape models (Figure 1C), recapitulating the phenotype of Lmx1bf/f/p mice. Since 5-HT signaling in the brain and the spinal cord may contribute differentially to the modulation of itch sensation, next we asked whether impaired itch sensation observed in Lmx1bf/f/p mice and Tph2−/− mice may be ascribed to a blockage of the descending 5-HT pathway. We selectively degenerated spinal 5-HT+ terminals in the spinal cord by an intrathecal injection (i.t.) of 5,7-dihydroxytryptamine (5,7-DHT) following pretreatment with desipramine to prevent the transport of 5,7-DHT into noradrenergic and dopaminergic terminals (Björklund et al., 1975Björklund A. Baumgarten H.G. Rensch A. 5,7-Dihydroxytryptamine: improvement of its selectivity for serotonin neurons in the CNS by pretreatment with desipramine.J. Neurochem. 1975; 24: 833-835Crossref PubMed Scopus (277) Google Scholar). At 2 weeks after 5,7-DHT injection, when spinal 5-HT+ fibers were depleted (Figure S1A, available online), mice exhibited an attenuated scratching response to CQ (Figure 1D), mimicking the phenotype of Lmx1bf/f/p mice and Tph2−/− mice. These loss-of-function studies confirm the contribution of descending 5-HT signaling to the modulation of itch sensation. To complement the loss-of-function approaches, we next determined whether we could rescue the attenuated itch transmission of Tph2−/− mice and Lmx1bf/f/p mice using an intraperitoneal (i.p.) injection of the 5-HT precursor, 5-hydroxytryptophan (5-HTP), to boost 5-HT tone. Exogenous 5-HTP can be decarboxylated to 5-HT by aromatic L-amino acid decarboxylase (AADC), thereby bypassing the need for TPH2 for 5-HT synthesis (Figure 1B) (Birdsall, 1998Birdsall T.C. 5-Hydroxytryptophan: a clinically-effective serotonin precursor.Altern. Med. Rev. 1998; 3: 271-280PubMed Google Scholar). Indeed, immunohistochemical staining (IHC) revealed abundant 5-HT staining in the spinal cord of Tph2−/− mice after 5-HTP injection (Figure 1E, top panel). In contrast, Lmx1bf/f/p mice treated with 5-HTP failed to produce 5-HT in the brain (Figure 1E, lower row). High-performance liquid chromatography (HPLC) analysis also revealed a significant increase in 5-HT concentrations and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA), in the brain and spinal cord of Tph2−/− and wild-type mice treated with 5-HTP (Figures S1B–S1E). These studies demonstrate a successful conversion of 5-HT from 5-HTP in the absence of TPH2 and that 5-HT synthesis is critically dependent on 5-HT neurons that express AADC. We next examined scratching responses of Tph2−/− mice after 5-HTP injection and found that 5-HTP injection indeed restored normal scratching responses of Tph2−/− mice to CQ (Figure 1F). However, the same treatment failed to enhance CQ-elicited scratching in Lmx1bf/f/p mice (Figure 1G). This finding complements the results from the 5,7-DHT lesion study suggesting that 5-HT is important in the facilitation of CQ-induced itch and supports the notion that AADC in 5-HT neurons is required for catalyzing the conversion of 5-HTP into 5-HT. These results also demonstrate that peripheral 5-HT is not involved in modulation of itch transmission. Consistently, WT mice treated with 5-HTP showed a dramatic increase of CQ-elicited scratching (Figure 1H). Since CQ-elicited itch is dependent on GRP-GRPR signaling (Sun and Chen, 2007Sun Y.G. Chen Z.F. A gastrin-releasing peptide receptor mediates the itch sensation in the spinal cord.Nature. 2007; 448: 700-703Crossref PubMed Scopus (571) Google Scholar), we reasoned that 5-HT might synergistically act with GRP to enhance the function of GRPR. We tested this possibility by examining the GRP-induced scratching (GIS) with an intracisternal injection in mice treated with 5-HTP. Indeed, GIS was markedly potentiated by 5-HTP (Figure 1I), revealing a positive correlation between the activity of GRPR and central 5-HT tone. Importantly, 5-HTP injection did not affect the scratching response induced by CQ in Grpr KO mice (Figure 1J). Taken together, we conclude that spinal 5-HT signaling facilitates itch transmission through GRPR. To identify the 5-HT receptor subtype that mediates the facilitating effect of descending 5-HT on itch transmission, we carried out pharmacological and behavioral screening by injecting a variety of 5-HT receptor agonists and GRP into the spinal cord of WT mice. GRP at 0.01 nmol was used because this dose was insufficient to elicit scratching behavior greater than vehicle (Figure 2A). The use of a minimal concentration of GRP serves to enhance the sensitivity of screening for identifying 5-HT receptor agonists that may potentiate GRP action. Of all the agonists tested for the 5-HT receptor subtypes, only R-(+)-8-OH-DPAT (DPAT), a 5-HT1A agonist, showed a robust facilitating effect on GIS (Figure 2A), and the effect of DPAT is dose dependent (Figure 2B). Notably, i.t. DPAT alone failed to induce scratch behavior (Figure 2A). Although DPAT is also a partial agonist for 5-HT7 receptor, it is unlikely that 5-HT7 is involved since AS-19, an agonist for 5-HT7, did not enhance GIS significantly (Figure 2A). Furthermore, agonists for other 5-HT receptor subtypes failed to increase GIS (Figure 2A). We next employed WAY100635 (WAY), a highly specific 5-HT1A antagonist, to verify whether the robust scratching response elicited by DPAT/GRP is mediated by 5-HT1A. Pretreatment of mice with WAY (10 μg, i.t.) for 5 min nearly abolished scratching behavior evoked by DPAT/GRP coinjection (Figure 2C). Importantly, DPAT failed to enhance scratching behavior in Htr1a−/− mice and Grpr KO mice (Figure 2D). These data demonstrate that activation of spinal 5-HT1A is required for the facilitation of GRPR function in itch transmission. Since an elevated 5-HT level facilitates itch elicited by CQ, it is likely that 5-HT1A activation may facilitate CQ-elicited itch as well. Indeed, CQ-induced scratching behavior was greatly enhanced by i.t. DPAT (Figure 2E), mimicking the effect of 5-HTP (Figure 1H). Conversely, preinjection of WAY markedly attenuated CQ-induced scratching behavior (Figure 2F). Furthermore, CQ-induced scratching behavior was significantly attenuated after spinal siRNA knockdown of Htr1a (Figure 2G), which was functionally confirmed by reduced facilitatory effect of DPAT on GIS (Figure 2H). These results suggest that activation of spinal 5-HT1A is important for mediating descending 5-HT signaling to facilitate the function of GRPR in pruriceptive transmission. 5-HT terminals mainly originated from the NRM are densely distributed in the superficial part (laminae I and IIo) of the dorsal spinal cord and SpVc of the brainstem (Li et al., 1997Li J.L. Kaneko T. Shigemoto R. Mizuno N. Distribution of trigeminohypothalamic and spinohypothalamic tract neurons displaying substance P receptor-like immunoreactivity in the rat.J. Comp. Neurol. 1997; 378: 508-521Crossref PubMed Scopus (54) Google Scholar). To examine whether 5-HT+ terminals make connections with GRPR+ neurons in the dorsal spinal cord, we performed double immunohistochemistry IHC for 5-HT and eGFP in GRPR-eGFP mice. Indeed, numerous 5-HT+ fibers and GRPR+ neurons were detected in the superficial laminae of the dorsal spinal cord, and 5-HT+ fibers overlap with all GRPR+ neurons (Figures 3A–3F). Synaptic connections between 5-HT+ terminals and GRPR+ neurons were further examined by electron microscopy using a double-immunolabeling method (Li et al., 1997Li J.L. Kaneko T. Shigemoto R. Mizuno N. Distribution of trigeminohypothalamic and spinohypothalamic tract neurons displaying substance P receptor-like immunoreactivity in the rat.J. Comp. Neurol. 1997; 378: 508-521Crossref PubMed Scopus (54) Google Scholar) for 5-HT and eGFP. In the lumbar cord, both 5-HT+ terminals identified by the nanogold-silver enhancement and eGFP (GRPR)+ neurons revealed by the immunoperoxidase products were observed to distribute in the same pattern as found by our double IHC (Figures 3A–3F). 5-HT+ terminals form synapses with GRPR+ dendritic profiles (Figures 3G and 3H). Of the synaptic types characterized (Uchizono, 1965Uchizono K. Characteristics of excitatory and inhibitory synapses in the central nervous system of the cat.Nature. 1965; 207: 642-643Crossref PubMed Scopus (710) Google Scholar), 85.5% (71/83) were symmetric synapses (Figure 3G), while 14.5% (12/83) were asymmetric ones (Figure 3H). Therefore, serotoninergic descending terminals predominantly make symmetrical synapses with GRPR+ neurons in the dorsal spinal cord. One prerequisite for 5-HT1A and GRPR crosstalk is the coexpression of two partner receptors in the same neurons (Pin et al., 2007Pin J.P. Neubig R. Bouvier M. Devi L. Filizola M. Javitch J.A. Lohse M.J. Milligan G. Palczewski K. Parmentier M. Spedding M. International Union of Basic and Clinical Pharmacology. LXVII. Recommendations for the recognition and nomenclature of G protein-coupled receptor heteromultimers.Pharmacol. Rev. 2007; 59: 5-13Crossref PubMed Scopus (243) Google Scholar). The expression of 5-HT1A is heavily concentrated in the dorsal horn of the spinal cord (Zhang et al., 2002Zhang Y.Q. Gao X. Ji G.C. Huang Y.L. Wu G.C. Zhao Z.Q. Expression of 5-HT1A receptor mRNA in rat lumbar spinal dorsal horn neurons after peripheral inflammation.Pain. 2002; 98: 287-295Abstract Full Text Full Text PDF PubMed Scopus (55) Google Scholar). To examine whether 5-HT1A is also expressed in GRPR+ neurons, we performed double IHC of 5-HT1A and GFP in the spinal cord of GRPR-eGFP mice using anti-GFP antibody and anti-5-HT1A antibody (Figure S2). 5-HT1A is broadly expressed in the dorsal horn (Figures 3I–3N). Double IHC revealed that the overwhelming majority (91%) of GFP-expressing cells in the dorsal spinal cord were costained with 5-HT1A (Figure 3N). Moreover, we examined the coexpression of Htr1a and Grpr in GRPR-eGFP neurons using single-cell RT-PCR (Figure S3B) and found Htr1a mRNA signals in 78% (7/9) of eGFP+ neurons (Table S1). Furthermore, all eGFP+ neurons expressed Grpr mRNA (Table S1), validating the usage of eGFP as a marker for GRPR expression in GRPR-eGFP mice. GRPR mediates itch sensation through the PLCβ/IP3 pathway and intracellular Ca2+ release (Liu et al., 2011Liu X.Y. Liu Z.C. Sun Y.G. Ross M. Kim S. Tsai F.F. Li Q.F. Jeffry J. Kim J.Y. Loh H.H. Chen Z.F. Unidirectional cross-activation of GRPR by MOR1" @default.
• W2171563789 created "2016-06-24" @default.
• W2171563789 creator A5004738900 @default.
• W2171563789 creator A5005316378 @default.
• W2171563789 creator A5006735523 @default.
• W2171563789 creator A5009297589 @default.
• W2171563789 creator A5013970170 @default.
• W2171563789 creator A5017664426 @default.
• W2171563789 creator A5024081826 @default.
• W2171563789 creator A5025554163 @default.
• W2171563789 creator A5025792713 @default.
• W2171563789 creator A5028344363 @default.
• W2171563789 creator A5029984161 @default.
• W2171563789 creator A5041277456 @default.
• W2171563789 creator A5041792310 @default.
• W2171563789 creator A5049970884 @default.
• W2171563789 creator A5061276758 @default.
• W2171563789 creator A5065859286 @default.
• W2171563789 creator A5066236832 @default.
• W2171563789 creator A5068831165 @default.
• W2171563789 creator A5073323794 @default.
• W2171563789 creator A5075572452 @default.
• W2171563789 creator A5078979775 @default.
• W2171563789 date "2014-11-01" @default.
• W2171563789 modified "2023-10-01" @default.
• W2171563789 title "Descending Control of Itch Transmission by the Serotonergic System via 5-HT1A-Facilitated GRP-GRPR Signaling" @default.
• W2171563789 cites W1502907908 @default.
• W2171563789 cites W1584563661 @default.
• W2171563789 cites W1595449036 @default.
• W2171563789 cites W1963655114 @default.
• W2171563789 cites W1969225757 @default.
• W2171563789 cites W1976114760 @default.
• W2171563789 cites W1977163272 @default.
• W2171563789 cites W1980310343 @default.
• W2171563789 cites W1981291046 @default.
• W2171563789 cites W1981811701 @default.
• W2171563789 cites W1982134608 @default.
• W2171563789 cites W1983111827 @default.
• W2171563789 cites W1997444760 @default.
• W2171563789 cites W2005134040 @default.
• W2171563789 cites W2006689459 @default.
• W2171563789 cites W2010704106 @default.
• W2171563789 cites W2011468607 @default.
• W2171563789 cites W2011562671 @default.
• W2171563789 cites W2014001501 @default.
• W2171563789 cites W2016780116 @default.
• W2171563789 cites W2017013284 @default.
• W2171563789 cites W2028536961 @default.
• W2171563789 cites W2032062642 @default.
• W2171563789 cites W2035221267 @default.
• W2171563789 cites W2035895112 @default.
• W2171563789 cites W2038467323 @default.
• W2171563789 cites W2054124635 @default.
• W2171563789 cites W2059827330 @default.
• W2171563789 cites W2061947800 @default.
• W2171563789 cites W2062700118 @default.
• W2171563789 cites W2065094796 @default.
• W2171563789 cites W2068512721 @default.
• W2171563789 cites W2070290419 @default.
• W2171563789 cites W2072653944 @default.
• W2171563789 cites W2081252796 @default.
• W2171563789 cites W2085472738 @default.
• W2171563789 cites W2085514543 @default.
• W2171563789 cites W2089147575 @default.
• W2171563789 cites W2090486787 @default.
• W2171563789 cites W2098799628 @default.
• W2171563789 cites W2101459312 @default.
• W2171563789 cites W2103889073 @default.
• W2171563789 cites W2108089366 @default.
• W2171563789 cites W2116326600 @default.
• W2171563789 cites W2121105777 @default.
• W2171563789 cites W2124140084 @default.
• W2171563789 cites W2132367206 @default.
• W2171563789 cites W2133300173 @default.
• W2171563789 cites W2133696258 @default.
• W2171563789 cites W2135733191 @default.
• W2171563789 cites W2135906456 @default.
• W2171563789 cites W2136547072 @default.
• W2171563789 cites W2138512124 @default.
• W2171563789 cites W2140849424 @default.
• W2171563789 cites W2145661651 @default.
• W2171563789 cites W2145906584 @default.
• W2171563789 cites W2157856809 @default.
• W2171563789 cites W2158271326 @default.
• W2171563789 cites W2159370695 @default.
• W2171563789 cites W2162047613 @default.
• W2171563789 cites W2167244529 @default.
• W2171563789 cites W2169965375 @default.
• W2171563789 cites W2186554153 @default.
• W2171563789 cites W2331665880 @default.
• W2171563789 cites W2470961608 @default.
• W2171563789 doi "https://doi.org/10.1016/j.neuron.2014.10.003" @default.
• W2171563789 hasPubMedCentralId "https://www.ncbi.nlm.nih.gov/pmc/articles/4254557" @default.
• W2171563789 hasPubMedId "https://pubmed.ncbi.nlm.nih.gov/25453842" @default.
• W2171563789 hasPublicationYear "2014" @default.
• W2171563789 type Work @default.
• W2171563789 sameAs 2171563789 @default.
• W2171563789 citedByCount "100" @default.

• next