Potential antipruritic neuronal targets of nalfurafine in the murine spinal dorsal horn : Itch

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Potential antipruritic neuronal targets of nalfurafine in the murine spinal dorsal horn

Honda, Kotaro PhDa; Tominaga, Mitsutoshi PhDa; Kusube, Fumiya MSa,b; Takamori, Kenji MD, PhDa,c,*

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Itch 8(1):p e66, January-March 2023. | DOI: 10.1097/itx.0000000000000066


Chronic pruritus is associated with various skin diseases, such as xerosis, atopic dermatitis, and psoriasis, and it interferes with our healthy life1. The mechanisms of the itch-scratch cycle remain unknown in patients suffering from chronic pruritus because the scratching behavior often relieves itch in the skin of healthy humans. Intractable pruritus is also a severe problem because it becomes resistant to existing therapies and often relates the internal diseases, such as liver and renal diseases without any apparent skin diseases2,3.

Opioids are widely known as modulators of pain and itch in the central nervous system (CNS)4–6, and an imbalance of mu and kappa opioids in the CNS is thought to be one of the causes of intractable pruritus7. Interneurons in the dorsal horn of the spinal cord secrete inhibitory neuropeptides, including dynorphin, which are induced by heat, cold, and pain stimulation to the skin, and attenuate pruritus8. These findings suggest that pruritic disease may be attenuated via suppression of the spinal itch-dedicated neurons with kappa opioid receptor (KOR) agonists. In fact, nalfurafine, a drug for intractable pruritus named as Remitch coined after “remove itch,” is an agonist of KOR which is used in clinical settings3. However, the sites of action of the antipruritic effect remain unknown.

Gastrin-releasing peptide (GRP) is a neuropeptide specific for itch transmission in the dorsal horn of the spinal cord9. The dorsal horn neurons expressing GRP receptors (GRPRs) play a role as interneurons of itch10. It was reported that KOR and GRPR-expressing neurons seemed to be the sites of action of nalfurafine. However, it remains controversial whether nalfurafine targets GRPR-expressing neurons or other targets of nalfurafine exist8. KOR is one of G protein-coupled receptors, including Gi/o unit. Activation of KOR interferes with the occurrence of neuronal spikes by regulating the potassium and calcium ion channels. It is likely that nalfurafine suppresses the spikes of neurons in the spinal dorsal horn, which is caused by intradermal injection of nonhistaminergic pruritogens11.

Electrophysiological changes are useful to analyze neuronal properties. The present study analyzed the targets of nalfurafine in the spinal dorsal horn by in vivo electrophysiological recordings. Chloroquine (CQ), a ligand of MrgprA3 in dorsal root ganglion neurons, was used as a model of intractable histamine-resistant itch in the present study. To confirm the results of in vivo electrophysiological tests, gene expressions of GRP, GRPR, and KOR were detected by RNAscope method, a high-sensitive in situ hybridization (ISH). Based on the results of behavioral, electrophysiological, and histological experiments, the influence of apoptosis on KOR-expressing cells was estimated using dynorphin-saporin to eliminate KOR-expressing cells. Here, we describe the antipruritic target dorsal horn neurons of nalfurafine.

Materials and methods


Male C57BL/6J mice, aged 6–8 weeks and weighing 19–28 g, were obtained from Japan SLC Inc. (Hamamatsu, Japan). The mice were housed in a room maintained under a 12-hour light and 12-hour dark cycle, with food and tap water provided ad libitum. The study protocol was approved (No. 2022-1) by the Institutional Animal Care and Use Committee at Juntendo University Graduate School of Medicine and Graduate School of Sports and Health Science.

In vivo electrophysiological recordings

In vivo electrophysiological experiments on the murine spinal cord were performed as described previously12. Anesthesia was induced by intraperitoneal injection of 60 mg/kg sodium somnopentyl (Kyoritsu Seiyaku Corp., Tokyo, Japan) and maintained by supplemental injections of 10–20 mg/kg/h sodium somnopentyl. After laminectomy, a tungsten microelectrode (FHC Inc., Bowdoin, ME) was inserted into the spinal cord using a micromanipulator (Scientifica, East Sussex, UK). Extracellular single-unit activity was recorded, amplified, digitized (Powerlab; ADInstruments Inc., Colorado Springs, CO), and displayed online using Chart5 software (AD Instruments Inc.)13. The exposed lumbosacral spinal cord was bathed continuously with an artificial cerebrospinal fluid (117 mM NaCl, 3.6 mM KCl, 2.5 mM CaCl2, 1.2 mM MgCl2, 1.2 mM NaH2PO4, 25 mM NaHCO3, and 11 mM glucose), equilibrated with 95% O2 and 5% CO2 at 37 °C.

A chemical search strategy13 was used to identify and isolate CQ-responsive units. To maximize the chance of isolating a CQ-responsive dorsal horn neuron, the search strategy assumed these neurons gave rise to ascending projections or served as interneurons in segmental scratch-reflex circuitry, with no attempt made to distinguish between these possibilities. Briefly, ~0.25 µL CQ (Sigma-Aldrich, St. Louis, MO, 100 µg/µL) was injected intradermally into the ventral hind paw through a 30-G needle (Nipro Corp., Osaka, Japan), and a spontaneously active unit in the superficial lumbar dorsal horn (depth <300 µm) was isolated. All units isolated in this study were located in the superficial dorsal horn 0–160 µm below the surface. After the spontaneous activity had waned, 1 µL CQ (100 µg/µL) was injected into the same site through the same 30-G needle. Only units showing a >30% increase in firing in response to the second microinjection of CQ were selected for further study. Responses were usually recorded for at least 30 minutes, although in many units, firing declined over a shorter period.

Spinal perfusion of nalfurafine hydrochloride and GRP was performed as previously described with slight modifications13. After CQ-responsive firing was recorded for 30 minutes, nalfurafine, at a final concentration of 2.5 µg/mL, was applied directly through the bath system to the spinal cord for 3 minutes. Responses were recorded for at least 30 minutes. Following spinal superfusion, GRP, at a final concentration of 150 µM (R&D Systems Inc.), was applied. The units showing a >30% increase in firing in response to GRP were regarded as GRP+ units. The criterion for a decrease in the ongoing firing was >70% decrease below the ongoing activity elicited by CQ over a 20-second period after 40 seconds of application of nalfurafine.

Itch-related scratching behavioral analyses

The back of male mice was shaved two days before the behavioral analysis. Saline, 1 nM GRP or 1 nM GRP, and 100 ng nalfurafine were intrathecally (i.t.) injected into the mice under antisera of sevofrane (Maruishi Pharmaceutical Co. Ltd, Osaka, Japan). The mice were put in the translucent box on SCLABA-Real system (Noveltec Inc., Kobe, Japan) and their scratching behavior was automatically counted for 90 minutes.

To estimate the itch transmission via KOR-non-expressing cells, apoptosis of KOR-expressing cells was induced in advance in the spinal cord. Dynorphin-saporin (Advanced Targeting Systems, Carlsbad) diluted with saline into 200 ng or 400 ng/5 µL was i.t. injected. Over 7 days after, the mice were used for the scratching behavioral analysis. To investigate the effects on the itch caused by histaminergic and nonhistaminergic pruritogens, histamine (500 mg/mL) and CQ (200 mg/mL) were intradermally injected and the evoked scratching bouts were recorded by SCLABA-Real system for 90 minutes.

ISH using RNAscope method

For the preparation of spinal cord samples for RNAscope analysis, male C57BL/6J mice, aged 10 weeks, were injected with 60 mg/kg sodium somnopentyl, and then perfusion-fixed with 4% paraformaldehyde in 0.1 M phosphate buffer (pH 7.4). Lumbar spinal cords were harvested and fixed by immersion in 10% neutral buffered formalin for 24 hours at room temperature. The tissues were dehydrated, replaced with xylene, and embedded in paraffin. The paraffin-embedded tissues were sectioned at 5 μm, and the sections were mounted on superfrost plus slide glasses (12-550-15, Fisher Scientific, Pittsburgh, PA), and analyzed using RNAscope standard protocol. The spinal cords of mice with i.t. injection of dynorphin-saporin were used for the analysis by the same procedures.

For analyses of GRP, GRPR, and KOR-expressing cells in the spinal dorsal horn, 4–6 sections were used for quantification of GRP, GRPR, and KOR-expressing cells. Spinal dorsal horn areas on the sections were assessed to a depth of 300 μm. Dots indicating targeted mRNA molecules were counted manually.

Statistical analysis

All values were expressed as the mean±SEM. Statistical analyses were performed using Prism 7 software (GraphPad Software). A P-value of <0.05 was considered statistically significant.


We examined whether an exogenous KOR agonist, nalfurafine, inhibit scratching bouts evoked by i.t. injection of GRP (Fig. 1). GRP-evoked scratching bouts were reduced by ~56.7% (Fig. 1 A) with no sedation (Fig. 1 B). We next examined the itch-dedicated pathway in the spinal dorsal horn by using in vivo electrophysiology (Fig. 2). In this experiment, CQ was selected as a pruritogen causing nonhistaminergic itch, because nalfurafine also targets nonhistaminergic itch. A few of the CQ-responsive neurons showed reduced firings in a duration of nalfurafine (a blue box in Fig. 2 A). Almost all of the CQ-responsive neurons showed no effect on their firings after spinal application of nalfurafine (a blue box in Fig. 2 B). Furthermore, 1 of the 3 nalfurafine-suppressed neurons responded to additional administration of GRP to the spinal cord (a yellow box in Fig. 2 C). Summarizing these results in a Venn diagram, 15.8% (3/19) of CQ+ units were inhibited by spinal application of nalfurafine, while 84.2% (16/19) of CQ+ units were not (Fig. 2 D). Moreover, 33.3% (1/3) of the nalfurafine-suppressed units responded to GRP, while the rest did not (a sector form in Fig. 2 D).

Figure 1:
Effects of intrathecal injection of nalfurafine on locomotion activity and gastrin-releasing peptide (GRP)-evoked scratching behavior (A) Intrathecal injection of 25–100 ng nalfurafine did not affect locomotory activities for 90 minutes in mice (n=8). (B) Scratching bouts induced by intrathecal injection of 1 nmol GRP were suppressed by co-injection of 100 ng nalfurafine (n=7). **P<0.01.
Figure 2:
Representative responses of spinal chloroquine (CQ)-responsive cells to nalfurafine and gastrin-releasing peptide (GRP). A, Firing of a superficial dorsal horn unit in response to intradermal injection of CQ was suppressed by nalfurafine administration. B, Nalfurafine did not suppress the firing of the unit excited by intradermal CQ injection. C, Response of the unit to subsequent GRP administration. Note that the unit began to gradually fire after perfusion restarted. D, Summary of the responses of spinal CQ+ units to nalfurafine and GRP. (Left) Nalfurafine reduced the firing rate of only 3 of 19 CQ+ units. (Right) Of 3 nalfurafine-suppressed units, only 1 fired in response to GRP. Arrows indicate each application time. Blue (A, B) and yellow (C) boxes, reaction times to nalfurafine and GRP, respectively.

We further examined the ratio of GRP-expressing or GRPR-expressing neurons in KOR-expressing neurons because nalfurafine might target GRP-expressing neurons mainly (Fig. 3). Expression of these genes was visualized by ISH (Figs. 3 A–D) and cells both or either expressing GRP or GRPR and KOR were counted manually (Figs. 3 E, F). 24.8% or 13.6% of KOR-expressing cells were found to co-express GRP or GRPR, suggesting that ~40% (ie, 24.8% + 13.6%) of KOR-expressing cells involved itch-dedicated pathways in the spinal cord (red circles in Figs. 3 E, F). Notably, there were GRP-expressing or GRPR-expressing cells without KOR expression and they were the majority of all GRP-expressing or GRPR-expressing cells (green circles in Figs. 3 E, F).

Figure 3:
Expression of GRP, GRP receptor (GRPR), and kappa opioid receptor (KOR) mRNAs in the dorsal horn of the spinal cord. A, Expressions of KOR (red) and GRP (green) mRNAs. B, Magnified image of the boxed area in (A). C, Expressions of KOR (red) and GRPR (green) mRNAs. D, Magnified image of the boxed area in (C). E and F, Venn diagram showing the numbers of cells in the lumbar dorsal horn expressing (E) GRP and KOR and (F) GRPR and KOR. The percentages indicate the rate of doubly-positive cells. The arrowheads indicate representative GRP+ KOR+ and GRPR+ KOR+ cells.

Subsequently, we examined the function of GRPR-expressing neurons without KOR expression in itch transmission using target toxin of dynorphin-saporin to eliminate KOR-expressing cells (Fig. 4). Elimination of KOR-expressing cells by i.t. injection of dynorphin-saporin did not affect the spontaneous scratching behaviors (Fig. 4 A). Using these mice, scratching bouts evoked by i.t. injection of 1 nmol GRP and the combination of GRP and nalfurafine were counted, but the differences in the number of scratching bouts were not significant in these cases (Figs. 4 B, C). The percentage of the targeted neurons expressing both GRPR and KOR in dynorphin–saporin-treated mice decreased from 16.4% to 3.8% (Fig. 4 D).

Figure 4:
Behavioral analysis of dynorphin-saporin injected mice. Mice with intrathecal injection of blank-saporin or dynorphin-saporin were used in this experiment. A, Spontaneous scratching bouts of mice injected with blank-saporin or dynorphin-saporin were analyzed. B and C, Scratching bouts evoked by GRP (1 nmol) or GRP (1 nmol) and nalfurafine (100 ng) intrathecal (i.t.) injection were analyzed. D, The ratio of cells with both KOR and GRPR-expressing in GRPR-expressing cells decreased from 16.4% to 3.8%.

We also analyzed the difference in apoptosis efficiency in the laminal layers of the spinal dorsal horn in dynorphin-saporin-treated mice. DRG sensory neurons were grouped into peptidergic neurons that terminate the lamina 1 and 2 outer layers or non-peptidergic neurons that terminate the lamina 2 inner layer. The dorsal horn of the spinal cord obtained from mice treated with blank-saporin or dynorphin-saporin injection was divided into superficial (0–50 μm from the surface of the spinal dorsal horn) and deeper (50–100 μm from the surface) areas on the sections. The distribution of GRPR-single, KOR-single-positive, and double-positive cells and the results of the analysis of apoptosis efficiency are shown in Table 1 (Supplemental Digital Content, https://links.lww.com/ITX/A13). The number of cells was expressed as the ratio of the number of target cells to the number of GRPR-single positive cells, and this ratio was used to calculate apoptosis efficiency.

In the 0–50-μm area from the surface of the spinal dorsal horn, the ratio of the number of GRPR-single-positive and KOR-single-positive cells decreased from 1:0.25 to 1:0.12 before/after dynorphin-saporin injection; the rate difference was 0.13, and the apoptosis rate was 52.3%. The ratio of the number of GRPR-single-positive and double-positive cells decreased from 1:0.197 to 1:0.026; the rate difference was 0.171, and the apoptosis rate was 86.8%. Meanwhile, in the 50- to 100-μm area from the surface of the spinal dorsal horn, the ratio of the number of GRPR-single-positive and KOR-single-positive cells decreased from 1:1.036 to 0.571 with dynorphin-saporin injection; the rate difference was 0.465, and the apoptosis rate was 44.9%. The ratio of the number of GRPR-single-positive and double-positive cells decreased from 0.290 to 0.048 with dynorphin-saporin injection; the rate difference was 0.243, and the apoptosis rate was 83.6%. These results suggested that dynorphin-saporin exerts a stronger effect on double-positive cells than on KOR-single-positive cells within 0–100 μm from the surface. Because the rate of apoptosis depends on the expression level of targeted receptors, the expression level of KOR might be higher in double-positive cells than in KOR-single-positive cells.

We further hypothesized that the mice with a reduction in KOR-expressing neurons in the spinal cord would have less responsiveness to CQ. The responses to CQ and histamine administrated by intradermal injection were evaluated in mice that had a reduction in KOR-expressing neurons (Fig. 5). Our data revealed that the number of scratching bouts decreased significantly (P=0.0105) in CQ-injected mice (Fig. 5 A), but not in histamine-injected mice (Fig. 5 B).

Figure 5:
Response to pruritogens in dynorphin-saporin injected mice. A, Chloroquine-evoked scratching bouts in blank-saporin or dynorphin-saporin injected mice were analyzed. B, Histamine-evoked scratching bouts in the same mice group were analyzed.


The results of the present study revealed that a few neurons in the spinal dorsal horn were candidate sites of action for nalfurafine, and the actual responsiveness was confirmed by electrophysiological recordings. ISH using the spinal cord sample suggested that KOR-expressing neurons were a minor group in the itch neuronal pathways. Behavioral analysis with ablation of KOR-expressing neurons indicated that KOR-expressing neurons were available when CQ was intradermally injected. These results indicates that the role of the itch-dedicated pathway in KOR-expressing neurons of the spinal cord was limited to the response to CQ-evoked itch in mice. Based on these results, we described a schematic summary of the sites of action of nalfurafine in the spinal cord (Fig. 6).

Figure 6:
Schematic diagram of the sites of action of nalfurafine in the spinal cord. Nalfurafine targets chloroquine-evoked itch via kappa opioid receptor (KOR)-expressing and gastrin-releasing peptide (GRP)-expressing or GRPR-expressing neurons, but not histamine-evoked itch which is thought to be unrelated to KOR-expressing neurons in the spinal cord. The ratios between GRP-expressing, and GRP-expressing and KOR-expressing neurons along with GRPR-expressing, and KOR-expressing and GRPR-expressing neurons were showed as the number described at the side of circles indicating these neurons.

Sites of action of nalfurafine in the spinal cord

A few of the sites of action of nalfurafine was electrophysiologically and histologically detected in Figures 2 and 3, suggesting that nalfurafine targets both GRP+ KOR+ and GRPR+ KOR+ cells which are present in a 2:1 ratio, in the spinal dorsal horn. However, GRP+ KOR+ and GRPR+ KOR+ cells formed a minor group in the GRP–GRPR axis, suggesting that GRP+ KOR- or GRPR+ KOR- cells function as interneurons in the spinal neuronal pathway of itch. Because the roles of GRP are through not only synaptic transmission, but also its receptors on the cell membrane have been reported, nalfurafine may reduce the density of GRP secreted into surroundings of target cells and recover the severe itch14. Nalfurafine reduced scratching bouts by i.t. injection of GRP (Fig. 1) and mice with ablation of KOR-expressing cells exhibited no significant change and tended to increase scratching bouts by GRP i.t. injection (Fig. 4 B). The administration of the mixture of GRP and nalfurafine also tended to increase scratching bouts in mice with ablation of KOR-expressing neurons (Fig. 4 C). These results indicate that both excitatory and inhibitory neurons express KOR in the spinal cord. Understanding of phenotypic characteristics may become difficult when GRP and the mixture of GRP and nalfurafine were i.t. injected. However, this is yet unclear.

Antipruritic roles of KOR agonists

Morphine, an opioid analgesic, is a mu-receptor agonist and induces itch as a side effect. Since itch caused by MOR activation is not ameliorated by antihistamines, but is inhibited by KOR activation, KOR agonists are expected as a treatment for intractable pruritus. Since nalfurafine has been shown to exhibit an antipruritic effect when taken orally, the KOR-mediated antipruritic effect may consist of a combination of effects on the central and peripheral nervous systems, including the dorsal root ganglia and immune cells15. Results of the present study showed that transduction of itch by CQ of nonhistaminergic pruritogens was involved in only part of KOR-expressing neurons in the spinal cord. It was suggested that antipruritic mechanism by peroral administration of nalfurafine may be collectively responsible with brain and immune cells. IL-6 is an essential factor in itching triggered by calcium phosphate associated with kidney disease and sensitizes the DRG neurons16,17. LPS-stimulated macrophages secrete IL-6, which is inhibited by KOR agonists18. Furthermore, the infiltration of M1 macrophages has been reported in kidney disease19. Since nalfurafine is indicated for the treatment of pruritus in patients with chronic renal failure, it may attenuate the pruritus triggered by calcium phosphate, via the inhibition of activated M1 macrophages that secrete IL-6.

The suppressive effect of KOR agonist on histaminergic itch is controversial because some previous studies showed the suppression of scratching bouts evoked by histamine and compound 48/80 intradermal injection6,11, while others showed no effect on that by histamine and neuromedin B20 in mice. Our result, that histaminergic itch was not transmitted via KOR-expressing neuronal pathway in the spinal cord, supporting the latter perspective. Considering that the GRP-expressing neurons in the spinal cord are dispensable for itch transmission, the primary afferent of dorsal root ganglia transmitting histaminergic itch may select KOR nonexpressing GRPR neurons in the spinal cord21. Alternatively, histamine-evoked scratching bouts were decreased by i.t. injection of the glutamate receptor antagonist, but not the GRPR antagonist, suggesting less contribution of spinal GRP/GRPR system in histaminergic itch13. Because histamine-responsive neurons of dorsal root ganglia express vglut2 and substance P, glutamate receptors-expressing, and/or NK1R-expressing, but KOR-nonexpressing neurons may be the main pathway of histaminergic itch transmission in the spinal cord. Peripheral administration of KOR agonist inhibited the effect of capsaicin, that is, Trpv1 activation, suggesting that systemic administration of KOR agonist may inhibit itch peripherally, including histaminergic itch, in humans22.

Termination of DRG sensory neurons of itch to the spinal dorsal horn

The expression of the histamine receptor Hrh1 and the CQ receptor MrgprA3 had been investigated in DRG sensory neurons, but the characteristics were uncertain. These receptors were considered to be expressed on CGRP-positive peptidergic neurons because the induction of apoptosis in CGRP-positive neurons decreases histamine-evoked and CQ-evoked scratching bouts, but not of those evoked by β-alanine23. However, Hrh1 and MrgprA3 were found in both IB4-positive (suggesting non-peptidergic) and IB4-negative (peptidergic) sensory neurons, but the expression level correlated negatively or positively, respectively24. Another study reported the expression of Hrh1 only in non-peptidergic neurons25. Screening of DRG neurons by Ret-eGFP suggested that Ret-eGFPlow: IB4-negative (peptidergic) cells expressed Hrh126. CGRP-coexpressing and P2X3-coexpressing sensory neurons were identified in mice and humans, suggesting that the grouping of sensory neurons into peptidergic or nonpeptidergic must be performed carefully27. Tracing the expression of GFP derived from pruritogenic c-fos expression in DRG sensory neurons in the dorsal horn of the spinal cord is needed in the future to reveal the termination of sensory Hrh1 receptors and MrgprA3-expressing neurons. The characteristics of the neuronal pathways of itch sensation evoked by CQ or histamine were not revealed in our study because the differences in apoptosis rates between the superficial and deeper areas were <10%.

Limitations of in vivo electrophysiological experiments by the extracellular single-unit recording

The extracellular single-unit recording is a well-established electrophysiological experimental technique for analyzing neural responses12. In this study, we analyzed the effects of nalfurafine on CQ-responsive spinal neurons. The selection of CQ-responsive neurons is based on a well-established strategy, but this does not exclude the possibility that the selected neurons are unknown inhibitory neurons, such as those involved in the gate control theory of itch28. In addition, it does not exclude the possibility that minor pain from physical stimulation when the needle was inserted and when the administered solution was injected may excite the pain nerve. However, the spinal neurons that are continuously excited for several minutes immediately after intradermal CQ administration are likely to be afferent itch nerves, because it has been confirmed that intradermal administration of CQ does not cause pain-related wiping behavior. GRP was administered after the administration of nalfurafine to confirm the possibility that the recorded neurons were GRPR-expressing, but this did not exclude the possibility that they were NK1R-expressing neurons, which are predicted to belong to the itch neural pathway upstream of GRPR-expressing cells in the spinal cord29,30. Albeit, these assumptions do not change our conclusion that the spinal neurons inhibited by nalfurafine is a minor group.

Conclusion and perspective

In this study, we revealed that few sites of action of nalfurafine were detected in the spinal dorsal horn, but they were important for the itch neuronal transmission evoked by CQ. This suggested that the neuronal pathway grouped by the expression of receptors inhibiting neuronal firing is a promising target for itch relief by injecting low doses in case of different pruritogens. In the future, it is necessary to perform selective KOR knock out in GRPR and KOR double-positive neurons to obtain a thorough understanding of the role of KOR in itch neuronal transmission.

Sources of funding

This work was supported by Grant for Cross-disciplinary Collaboration, Juntendo University (30-25) and a JSPS KAKENHI Grand Number JP18K07396 and JP20H03568.

Conflicts of interest disclosure

The authors declare that they have no financial conflict of interest with regard to the content of this report.


The authors thank Prof Hisashi Naito and Prof Fumiyuki Yamakura for permission to use the animal experimental facility in the Sakura Campus and laboratory animal care janitors in Juntendo University. They also thank Enago (http://www.enago.jp) for the English language review.


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Itch neural pathway; Spinal cord; Kappa opioid receptor

Supplemental Digital Content

Copyright © 2023 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of The International Forum for the Study of Itch.