Cross-inhibition of NMBR and GRPR signaling maintains normal histaminergic itch transmission.

We previously showed that gastrin-releasing peptide receptor (GRPR) in the spinal cord is important for mediating nonhistaminergic itch. Neuromedin B receptor (NMBR), the second member of the mammalian bombesin receptor family, is expressed in a largely nonoverlapping pattern with GRPR in the superficial spinal cord, and its role in itch transmission remains unclear. Here, we report that Nmbr knock-out (KO) mice exhibited normal scratching behavior in response to intradermal injection of pruritogens. However, mice lacking both Nmbr and Grpr (DKO mice) showed significant deficits in histaminergic itch. In contrast, the chloroquine (CQ)-evoked scratching behavior of DKO mice is not further reduced compared with Grpr KO mice. These results suggest that NMBR and GRPR could compensate for the loss of each other to maintain normal histamine-evoked itch, whereas GRPR is exclusively required for CQ-evoked scratching behavior. Interestingly, GRPR activity is enhanced in Nmbr KO mice despite the lack of upregulation of Grpr expression; so is NMBR in Grpr KO mice. We found that NMB acts exclusively through NMBR for itch transmission, whereas GRP can signal through both receptors, albeit to NMBR to a much lesser extent. Although NMBR and NMBR(+) neurons are dispensable for histaminergic itch, GRPR(+) neurons are likely to act downstream of NMBR(+) neurons to integrate NMB-NMBR-encoded histaminergic itch information in normal physiological conditions. Together, we define the respective function of NMBR and GRPR in itch transmission, and reveal an unexpected relationship not only between the two receptors but also between the two populations of interneurons in itch signaling.

B-type natriuretic peptide is neither itch-specific nor functions upstream of the GRP-GRPR signaling pathway.

BACKGROUND: A recent study by Mishra and Hoon identified B-type natriuretic peptide (BNP) as an important peptide for itch transmission and proposed that BNP activates spinal natriuretic peptide receptor-A (NPRA) expressing neurons, which release gastrin releasing peptide (GRP) to activate GRP receptor (GRPR) expressing neurons to relay itch information from the periphery to the brain (Science 340:968-971, 2013). A central premise for the validity of this novel pathway is the absence of GRP in the dorsal root ganglion (DRG) neurons. To this end, they showed that Grp mRNA in DRG neurons is either absent or barely detectable and claimed that BNP but not GRP is a major neurotransmitter for itch in pruriceptors. They showed that NPRA immunostaining is perfectly co-localized with Grp-eGFP in the spinal cord, and a few acute pain behaviors in Nppb-/- mice were tested. They claimed that BNP is an itch-selective peptide that acts as the first station of a dedicated neuronal pathway comprising a GRP-GRPR cascade for itch. However, our studies, along with the others, do not support their claims. FINDINGS: We were unable to reproduce the immunostaining of BNP and NPRA as shown by Mishra and Hoon. By contrast, we were able to detect Grp mRNA in DRGs using in situ hybridization and real time RT-PCR. We show that the expression pattern of Grp mRNA is comparable to that of GRP protein in DRGs. Pharmacological and genetic blockade of GRP-GRPR signaling does not significantly affect intrathecal BNP-induced scratching behavior. We show that BNP inhibits inflammatory pain and morphine analgesia. CONCLUSIONS: Accumulating evidence demonstrates that GRP is a key neurotransmitter in pruriceptors for mediating histamine-independent itch. BNP-NPRA signaling is involved in both itch and pain and does not function upstream of the GRP-GRPR dedicated neuronal pathway. The site of BNP action in itch and pain and its relationship with GRP remain to be clarified.

How different nitrogen fertilizers affect arsenic mobility in paddy soil after straw incorporation?

In straw return fields, nitrogen-fertilizers are added to mitigate microbial competition for nitrogen with plants. However, in arsenic (As)-contaminated paddy fields, the specific effects of different nitrogen fertilizers on As mobility after straw incorporation and the interactions among iron(Fe)/carbon(C)/nitrogen(N)/As are not well understood. In the reported microcosm experiment we monitored As-mobility as a function of different dosages of KNO3, NH4Cl and rice straw incorporation. Addition of both KNO3 and NH4Cl significantly inhibited the As mobilization induced by straw incorporation. Following the KNO3 addition, the As concentration in porewater dropped by 51-66% after 2 days of the incubation by restraining Fe reduction and enhancing Fe oxidation. High-dose NH4Cl addition reduced As in porewater by 22-43% throughout the incubation by decreasing porewater pH. High-throughput sequencing results demonstrated that KNO3 addition enriches both the denitrifying and Fe-oxidizing bacteria, while diminishing Fe-reducing bacteria; NH4Cl addition has the opposite effect on Fe-reducing bacteria. Network analysis revealed that As and Fe concentrations in porewater were positively correlated with the abundance of denitrifying and Fe-reducing bacteria. This study broadens our insight into the As biogeochemistry associated with the N/C/Fe balance in soil, which are of great significance for agronomic management and mitigation the risk of As-contaminated paddy fields.

Object Detection With Deep Learning: A Review.

Due to object detection's close relationship with video analysis and image understanding, it has attracted much research attention in recent years. Traditional object detection methods are built on handcrafted features and shallow trainable architectures. Their performance easily stagnates by constructing complex ensembles that combine multiple low-level image features with high-level context from object detectors and scene classifiers. With the rapid development in deep learning, more powerful tools, which are able to learn semantic, high-level, deeper features, are introduced to address the problems existing in traditional architectures. These models behave differently in network architecture, training strategy, and optimization function. In this paper, we provide a review of deep learning-based object detection frameworks. Our review begins with a brief introduction on the history of deep learning and its representative tool, namely, the convolutional neural network. Then, we focus on typical generic object detection architectures along with some modifications and useful tricks to improve detection performance further. As distinct specific detection tasks exhibit different characteristics, we also briefly survey several specific tasks, including salient object detection, face detection, and pedestrian detection. Experimental analyses are also provided to compare various methods and draw some meaningful conclusions. Finally, several promising directions and tasks are provided to serve as guidelines for future work in both object detection and relevant neural network-based learning systems.

Mice lacking central serotonergic neurons show enhanced inflammatory pain and an impaired analgesic response to antidepressant drugs.

A large body of literature has implicated serotonin [5-hydroxytryptamine (5-HT)] in descending modulation of nociceptive transmission. Here, we have studied the pain behavior of Lmx1b conditional knock-out mice (Lmx1b(f/f/p)), which lack 5-HT neurons in the CNS. Lmx1b(f/f/p) mutant mice showed normal thermal and visceral pain responses but were less sensitive to mechanical stimuli and exhibited enhanced inflammatory pain compared with their littermate control mice. Importantly, the analgesic effect of several antidepressant drugs, including selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), and tricyclic antidepressants, was either abolished or greatly attenuated in Lmx1b(f/f/p) mice. Moreover, in the acute versus persistent pain settings, the analgesic actions of the SNRI duloxetine and the SSRI fluoxetine were differentially affected. Together, our results provide in vivo genetic evidence demonstrating that although the predominant role of the central 5-HT system in inflammatory pain is inhibitory, its role in acute mechanical pain is facilitatory. The findings that the analgesic effects of various antidepressant drugs are differentially dependent on the central 5-HT system should help us to understand the mechanism of the analgesic action of different classes of antidepressants in the management of persistent pain.

Involvement of P311 in the affective, but not in the sensory component of pain.

Pain is comprised of the sensory and affective components. Compared to the well-investigated mechanisms of the sensory pain, much less is known about the mechanisms underlying the affective pain. In recent years, accumulating evidence suggests that the anterior cingulate cortex (ACC) is a key structure for pain affection. To identify the molecules that may be involved in the affective component of pain, we have searched the Allen Brain Atlas expression database for genes whose expression is enriched in the ACC, and found that P311, an 8-kDa peptide, showed the strong expression in the ACC. P311 is also expressed in other areas associated with pain affection including the amygdala, insular cortex and thalamus. To understand the role of P311 in pain perception, we have examined the pain behaviors of the mice lacking P311. P311-/- mice showed normal heat and mechanical sensitivity, as well as normal formalin-induced inflammatory pain. In contrast, the formalin-induced avoidance behavior, which reflects pain-related negative emotion, was significantly attenuated in P311-/- mice relative to the control mice. These results suggest that P311 is involved in the affective, but not in the sensory component of pain. Our study thus provides the first evidence suggesting that the affective and sensory pain may be regulated by distinct molecular mechanisms.

Focal adhesion kinase in netrin-1 signaling.

Netrins are a family of secreted molecules that are important for axonal outgrowth and guidance in the developing nervous system. However, the signaling mechanisms that lie immediately downstream of netrin receptors remain poorly understood. Here we report that the netrin receptor DCC (deleted in colorectal cancer) interacts with the focal adhesion kinase (FAK), a kinase implicated in regulating cell adhesion and migration. FAK was expressed in developing brains and was localized with DCC in cultured neurons. Netrin-1 induced FAK and DCC tyrosine phosphorylation. Disruption of FAK signaling abolished netrin-1-induced neurite outgrowth and attractive growth cone turning. Taken together, these results indicate a new signaling mechanism for DCC, in which FAK is activated upon netrin-1 stimulation and mediates netrin-1 function; they also identify a critical role for FAK in axon navigation.

Lmx1b is required for maintenance of central serotonergic neurons and mice lacking central serotonergic system exhibit normal locomotor activity.

Central serotonergic neurons have been implicated in numerous animal behaviors and psychiatric disorders, but the molecular mechanisms underlying their development are not well understood. Here we generated Lmx1b (LIM homeobox transcription factor 1 beta) conditional knock-out mice (Lmx1b(f/f/p)) in which Lmx1b was only deleted in Pet1 (pheochromocytoma 12 ETS factor-1)-expressing 5-HT neurons. In Lmx1b(f/f/p) mice, the initial generation of central 5-HT neurons appeared normal. However, the expression of both 5-HT-specific and non-5-HT-specific markers was lost in these neurons at later stages of development. The loss of gene expression is concomitant with downregulation of Lmx1b expression, with the exception of serotonin transporter Sert and tryptophan hydroxylase TPH2, whose expression appears to be most sensitive to Lmx1b. Interestingly, the expression of Pet1 is tightly coupled with expression of Lmx1b during later stages of embryonic development, indicating that Lmx1b maintains Pet1 expression. In Lmx1b(f/f/p) mice, almost all central 5-HT neurons failed to survive. Surprisingly, Lmx1b(f/f/p) mice survived to adulthood and exhibited normal locomotor activity. These data reveal a critical role of Lmx1b in maintaining the differentiated status of 5-HT neurons. Lmx1b(f/f/p) mice with normal locomotor function should provide a unique animal model for examining the roles of central 5-HT in a variety of animal behaviors.

[Effects of CaCO3 Application on Soil Microbial Nitrogen Cycle in an Acid Soil].

Soil nitrification and denitrification are important steps in closing the nitrogen cycle. Understanding the effects of CaCO3 application on the physicochemical properties and nitrogen cycle in acid soil would provide some theoretical and technical information for stable and sustainable utilization of this agricultural soil. In this study, a field trial was conducted in Xiangtan city, Hunan province. In this field, the soil pH was 5.54, and CaCO3 was applied at four levels: 0, 2.25, 4.5, and 7.5 t·hm-2. After one season of rice cultivation, the soil was sampled to determine dissolved organic carbon (DOC), NH4+-N, and NO3--N levels, and the potential nitrification rate (PNR) and denitrifying enzyme activity (DEA) were measured. The results showed that CaCO3 application improved the content of soil DOC (762.10-868.58 mg·kg-1) and PNR [0.59-0.82 µg·(g·h)-1]. However, excessive application of CaCO3 (7.5 t·hm-2) revealed an obvious inhibition on the activity of soil nitrification. Furthermore, the result of Pearson correlation analysis indicated that soil nitrification was positively correlated with soil DOC and negatively correlated with NH4+-N content, whereas denitrification had a significant positive correlation with NO3--N content and soil DOC, but a negative correlation with water content.

Expression of heme oxygenase-1 protein and messenger RNA in permanent cerebral ischemia in rats.

BACKGROUND: Carbon monoxide has been regarded as a gaseous molecular messenger like nitric oxide. PURPOSE: To clarify the role of heme oxygenase-1 in the permanent cerebral ischemia at the protein and mRNA level. METHODS: The expression of heme oxygenase-1 protein and messenger RNA was investigated at different time points following MCAO using immunohistochemistry, Western blotting, RT-PCR, and Northern blotting. RESULTS: Increased HO 1immunoreactivity was detected in hippocampal and cortical neurons after 1 hour of ischemia, and was also observed in astroglial cells. After 12 hours of ischemia, HO-1 was found in both neurons and glia in cerebral cortex and thalamus, and in striatal glia cells. Western blotting analysis show the expression of HO-1 protein in cortical neurons reached the peak after 12 hours of occlusion and decreased gradually, but was still detected at day 7 post-occlusion. The expression of messenger RNA was examined in the brains of rats subjected to permanent cerebral ischemia by semi-quantitative RT-PCR and Northern blotting. HO-1 mRNA transcription could be detected 1 hour after occlusion. After 1 to 6 hours of occlusion, the expression of HO-1 rose rapidly, reaching a peak at 12 hours post-occlusion, decreased gradually, and lasted until day 7 of occlusion. Although HO activity of cerebral tissue can be detected in both sham-operated group and operated groups, the HO activity in operated groups is much stronger than that in sham-operated group. CONCLUSIONS: The induction of HO-1 protein may protect cerebral tissues from ischemic damage.

Inverse-Free Extreme Learning Machine With Optimal Information Updating.

The extreme learning machine (ELM) has drawn insensitive research attentions due to its effectiveness in solving many machine learning problems. However, the matrix inversion operation involved in the algorithm is computational prohibitive and limits the wide applications of ELM in many scenarios. To overcome this problem, in this paper, we propose an inverse-free ELM to incrementally increase the number of hidden nodes, and update the connection weights progressively and optimally. Theoretical analysis proves the monotonic decrease of the training error with the proposed updating procedure and also proves the optimality in every updating step. Extensive numerical experiments show the effectiveness and accuracy of the proposed algorithm.

Facilitation of TRPV4 by TRPV1 is required for itch transmission in some sensory neuron populations.

The transient receptor potential channels (TRPs) respond to chemical irritants and temperature. TRPV1 responds to the itch-inducing endogenous signal histamine, and TRPA1 responds to the itch-inducing chemical chloroquine. We showed that, in sensory neurons, TRPV4 is important for both chloroquine- and histamine-induced itch and that TRPV1 has a role in chloroquine-induced itch. Chloroquine-induced scratching was reduced in mice in which TRPV1 was knocked down or pharmacologically inhibited. Both TRPV4 and TRPV1 were present in some sensory neurons. Pharmacological blockade of either TRPV4 or TRPV1 significantly attenuated the Ca(2+) response of sensory neurons exposed to histamine or chloroquine. Knockout of Trpv1 impaired Ca(2+) responses and reduced scratching behavior evoked by a TRPV4 agonist, whereas knockout of Trpv4 did not alter TRPV1-mediated capsaicin responses. Electrophysiological analysis of human embryonic kidney (HEK) 293 cells coexpressing TRPV4 and TRPV1 revealed that the presence of both channels enhanced the activation kinetics of TRPV4 but not of TRPV1. Biochemical and biophysical studies suggested a close proximity between TRPV4 and TRPV1 in dorsal root ganglion neurons and in cultured cells. Thus, our studies identified TRPV4 as a channel that contributes to both histamine- and chloroquine-induced itch and indicated that the function of TRPV4 in itch signaling involves TRPV1-mediated facilitation. TRP facilitation through the formation of heteromeric complexes could be a prevalent mechanism by which the vast array of somatosensory information is encoded in sensory neurons.

Effects of forms and rates of potassium fertilizers on cadmium uptake by two cultivars of spring wheat (Triticum aestivum, L.).

A greenhouse pot experiment was conducted to study the influence of potassium fertilizers in different forms and rates on cadmium (Cd) uptake by two cultivars of spring wheat (Triticum aestivum, L.): Brookton and Krichauff. Potassium fertilizers were added to soil at four levels: 0, 55, 110 and 166 mg K kg(-1) soil as KNO(3) (N), KCl (C) or K(2)SO(4) (S). CdCl(2) was added to all the treatments at a uniform rate equivalent to 15 mg Cd kg(-1) soil. Plant shoot and root dry weights (DW) of both cultivars were reduced significantly by the addition of K-fertilizer in C and S treatments but there were only marginal changes in the N treatments. The Cd concentrations in shoots and whole plants increased significantly (P<.001) with increasing K addition, from 37.5 to 81.4 mg kg(-1) and from 42.9 to 86.8 mg kg(-1) for Brookton and Krichauff, respectively. However, no obvious effect was observed in the N treatments, except for the highest K level (K3) where there was a sharp increase in Cd concentration compared to the lower additions. Forms of K-fertilizers significantly influenced the Cd concentrations in plant shoots and roots (P<.001), but there was no significant difference between C and S treatments. This experiment showed that anions Cl(-) and SO(4)(2-) increase Cd uptake by plants, which can be interpreted as Cl(-) and SO(4)(2-) complexing readily with Cd(2+) and thereby increasing the bioavailability of Cd(2+) in soils. The effect of potassium itself on plant uptake of Cd was also observed. We suggest that when applying potassium fertilizer to Cd-contaminated soils, the forms and rates should be considered.

Changes of plasma membrane AtPase activity, membrane potential and transmembrane proton gradient in Kandelia candel and Avicennia marina seedlings with various salinities.

The salt-secreting mangrove, Avicennia marina, and non-salt-secreting mangrove, Kandelia candel were cultivated in sand with various salinities(0 per thousand, 10 per thousand, 20 per thousand, 30 per thousand, 40 per thousand) for 60 d. Plasma membrane vesicles of high-purity in leaves and roots of A. marina and K. candel seedlings were obtained by two-phase partitioning. The function of the plasma membranes, the activity of ATPase, membrane potential and transmembrane proton gradient, at various salinities were investigated. The results showed that within a certain range of salinity (A. marina and roots of K. candel: 0-30 per thousand; leaves of K. candel: 0-20 per thousand), the activity of ATPase increased with increasing salinity, while high salinity (above 30 per thousand or 20 per thousand) inhibited ATPase activity. In comparison with A. marina, K. candel appeared to be more sensitive to salinity. The dynamics of membrane potential and transmembrane proton gradient in leaves and roots of A. marina and K. candel seedlings were similar to that of ATPase. When treated directly by NaCl all the indexes were inhibited markedly: there was a little increase within 0-10 per thousand (K. candel) or 0-20 per thousand (A. marina) followed by sharp declining. It indicated that the structure and function of plasma membrane was damaged severely.

Postnatal maintenance of the 5-Ht1a-Pet1 autoregulatory loop by serotonin in the raphe nuclei of the brainstem.

BACKGROUND: Despite the importance of 5-HT1A as a major target for the action of several anxiolytics/antidepressant drugs, little is known about its regulation in central serotonin (5-hydroxytryptamine, 5-HT) neurons. RESULTS: We report that expression of 5-HT1A and the transcription factor Pet1 was impaired in the rostral raphe nuclei of mice lacking tryptophan hydroxylase 2 (Tph2) after birth. The downregulation of Pet1 was recapitulated in 5-Ht1a-/- mice. Using an explant culture system, we show that reduction of Pet1 and 5-HT1A was rescued in Tph2-/- brainstem by exogenous 5-HT. In contrast, 5-HT failed to rescue reduced expression of Pet1 in 5-Ht1a-/- brainstem explant culture. CONCLUSIONS: These results suggest a causal relationship between 5-HT1A and Pet1, and reveal a potential mechanism by which 5-HT1A-Pet1 autoregulatory loop is maintained by 5-HT in a spatiotemporal-specific manner during postnatal development. Our results are relevant to understanding the pathophysiology of certain psychiatric and developmental disorders.

Descending control of itch transmission by the serotonergic system via 5-HT1A-facilitated GRP-GRPR signaling.

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 Ca(2+) 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.

Chronic itch development in sensory neurons requires BRAF signaling pathways.

Chronic itch, or pruritus, is associated with a wide range of skin abnormalities. The mechanisms responsible for chronic itch induction and persistence remain unclear. We developed a mouse model in which a constitutively active form of the serine/threonine kinase BRAF was expressed in neurons gated by the sodium channel Nav1.8 (BRAF(Nav1.8) mice). We found that constitutive BRAF pathway activation in BRAF(Nav1.8) mice results in ectopic and enhanced expression of a cohort of itch-sensing genes, including gastrin-releasing peptide (GRP) and MAS-related GPCR member A3 (MRGPRA3), in nociceptors expressing transient receptor potential vanilloid 1 (TRPV1). BRAF(Nav1.8) mice showed de novo neuronal responsiveness to pruritogens, enhanced pruriceptor excitability, and heightened evoked and spontaneous scratching behavior. GRP receptor expression was increased in the spinal cord, indicating augmented coding capacity for itch subsequent to amplified pruriceptive inputs. Enhanced GRP expression and sustained ERK phosphorylation were observed in sensory neurons of mice with allergic contact dermatitis­ or dry skin­elicited itch; however, spinal ERK activation was not required for maintaining central sensitization of itch. Inhibition of either BRAF or GRP signaling attenuated itch sensation in chronic itch mouse models. These data uncover RAF/MEK/ERK signaling as a key regulator that confers a subset of nociceptors with pruriceptive properties to initiate and maintain long-lasting itch sensation.

Cooperative sparse representation in two opposite directions for semi-supervised image annotation.

Recent studies have shown that sparse representation (SR) can deal well with many computer vision problems, and its kernel version has powerful classification capability. In this paper, we address the application of a cooperative SR in semi-supervised image annotation which can increase the amount of labeled images for further use in training image classifiers. Given a set of labeled (training) images and a set of unlabeled (test) images, the usual SR method, which we call forward SR, is used to represent each unlabeled image with several labeled ones, and then to annotate the unlabeled image according to the annotations of these labeled ones. However, to the best of our knowledge, the SR method in an opposite direction, that we call backward SR to represent each labeled image with several unlabeled images and then to annotate any unlabeled image according to the annotations of the labeled images which the unlabeled image is selected by the backward SR to represent, has not been addressed so far. In this paper, we explore how much the backward SR can contribute to image annotation, and be complementary to the forward SR. The co-training, which has been proved to be a semi-supervised method improving each other only if two classifiers are relatively independent, is then adopted to testify this complementary nature between two SRs in opposite directions. Finally, the co-training of two SRs in kernel space builds a cooperative kernel sparse representation (Co-KSR) method for image annotation. Experimental results and analyses show that two KSRs in opposite directions are complementary, and Co-KSR improves considerably over either of them with an image annotation performance better than other state-of-the-art semi-supervised classifiers such as transductive support vector machine, local and global consistency, and Gaussian fields and harmonic functions. Comparative experiments with a nonsparse solution are also performed to show that the sparsity plays an important role in the cooperation of image representations in two opposite directions. This paper extends the application of SR in image annotation and retrieval.

Cellular basis of itch sensation.

Itch and pain are two distinct sensations. Although our previous study suggested that gastrin-releasing peptide receptor (GRPR) is an itch-specific gene in the spinal cord, a long-standing question of whether there are separate neuronal pathways for itch and pain remains unsettled. We selectively ablated lamina I neurons expressing GRPR in the spinal cord of mice. These mice showed profound scratching deficits in response to all of the itching (pruritogenic) stimuli tested, irrespective of their histamine dependence. In contrast, pain behaviors were unaffected. Our data also suggest that GRPR+ neurons are different from the spinothalamic tract neurons that have been the focus of the debate. Together, the present study suggests that GRPR+ neurons constitute a long-sought labeled line for itch sensation in the spinal cord.