Central opioid receptors mediate morphine-induced itch and chronic itch

AbstractOpioids, such as morphine are mainstay treatments for clinical pain conditions. Itch is a common side effect of opioids, particularly as a result of epidural or intrathecal (i.t.) administration. Recent progress has advanced our understanding of itch circuits in the spinal cord. However, the mechanisms underlying opioid-induced itch are not fully understood, although an interaction between µ-opioid receptor (MOR) and gastrin-releasing peptide receptor (GRPR) in spinal GRPR-expressing neurons has been implicated. In this study we investigated the cellular mechanisms of intrathecal (i.t.) opioid-induced itch by conditional deletion of MOR-encoding Oprm1 in distinct populations of interneurons and sensory neurons. We found that i.t. injection of the MOR agonists morphine or DAMGO elicited dose-dependent scratching, but this pruritus was totally abolished in mice with a specific Oprm1 deletion in Vgat+ neurons (Oprm1-Vgat). Loss of MOR in somatostatin+ interneurons and TRPV1+ sensory neurons did not affect morphine-induced itch but impaired morphine-induced antinociception. In situ hybridization revealed Oprm1 expression in 30% of inhibitory and 20% of excitatory interneurons in the spinal dorsal horn. Whole-cell recordings from spinal cord slices showed that DAMGO induced outward currents in 9 out of 19 Vgat+ interneurons examined. Morphine also inhibited action potentials in Vgat+ interneurons and suppressed evoked IPSCs in postsynaptic Vgat- excitatory neurons, suggesting a mechanism of disinhibition by MOR agonists. Notably, morphine-elicited itch was suppressed by i.t. administration of NPY and abolished by spinal ablation of GRPR+ neurons, whereas i.t. GRP-induced itch response remained intact in mice lacking Oprm1-Vgat. Additionally, chronic itch from DNFB-induced allergic contact dermatitis was decreased by Oprm1-Vgat deletion. Finally, naloxone, but not peripherally restricted naloxone methiodide, inhibited chronic itch in the DNFB model and the cutaneous T-cell lymphoma (CTCL) model, indicating a contribution of central MOR signaling to chronic itch. Our findings demonstrate that i.t. morphine elicits itch via acting on MOR on spinal inhibitory interneurons, leading to disinhibition of the spinal itch circuit. Our data also suggest that chronic itch could be effectively treated with CNS-targeted naloxone.

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Central opioid receptors mediate morphine-induced itch and chronic itch via disinhibition

Brain ◽

10.1093/brain/awaa430 ◽

2020 ◽

Author(s):

Zilong Wang ◽

Changyu Jiang ◽

Hongyu Yao ◽

Ouyang Chen ◽

Sreya Rahman ◽

...

Keyword(s):

Spinal Cord ◽

Opioid Receptor ◽

Sensory Neurons ◽

Cervical Spinal Cord ◽

Intrathecal Morphine ◽

Intrathecal Injection ◽

Intrathecal Administration ◽

Common Side Effect ◽

Cellular Mechanisms ◽

Chronic Itch

Abstract Opioids such as morphine are mainstay treatments for clinical pain conditions. Itch is a common side effect of opioids, particularly as a result of epidural or intrathecal administration. Recent progress has advanced our understanding of itch circuits in the spinal cord. However, the mechanisms underlying opioid-induced itch are not fully understood, although an interaction between µ-opioid receptor (MOR) and gastrin-releasing peptide receptor (GRPR) in spinal GRPR-expressing neurons has been implicated. In this study we investigated the cellular mechanisms of intrathecal opioid-induced itch by conditional deletion of MOR-encoding Oprm1 in distinct populations of interneurons and sensory neurons. We found that intrathecal injection of the MOR agonists morphine or DAMGO elicited dose-dependent scratching as well as licking and biting, but this pruritus was totally abolished in mice with a specific Oprm1 deletion in Vgat+ neurons [Oprm1-Vgat (Slc32a1)]. Loss of MOR in somatostatin+ interneurons and TRPV1+ sensory neurons did not affect morphine-induced itch but impaired morphine-induced antinociception. In situ hybridization revealed Oprm1 expression in 30% of inhibitory and 20% of excitatory interneurons in the spinal dorsal horn. Whole-cell recordings from spinal cord slices showed that DAMGO induced outward currents in 9 of 19 Vgat+ interneurons examined. Morphine also inhibited action potentials in Vgat+ interneurons. Furthermore, morphine suppressed evoked inhibitory postsynaptic currents in postsynaptic Vgat− excitatory neurons, suggesting a mechanism of disinhibition by MOR agonists. Notably, morphine-elicited itch was suppressed by intrathecal administration of NPY and abolished by spinal ablation of GRPR+ neurons with intrathecal injection of bombesin-saporin, whereas intrathecal GRP-induced itch response remained intact in mice lacking Oprm1-Vgat. Intrathecal bombesin-saporin treatment reduced the number of GRPR+ neurons by 97% in the lumber spinal cord and 91% in the cervical spinal cord, without changing the number of Oprm1+ neurons. Additionally, chronic itch from DNFB-induced allergic contact dermatitis was decreased by Oprm1-Vgat deletion. Finally, naloxone, but not peripherally restricted naloxone methiodide, inhibited chronic itch in the DNFB model and the CTCL model, indicating a contribution of central MOR signalling to chronic itch. Our findings demonstrate that intrathecal morphine elicits itch via acting on MOR on spinal inhibitory interneurons, leading to disinhibition of the spinal itch circuit. Our data have also provided mechanistic insights into the current treatment of chronic itch with opioid receptor antagonist such as naloxone.

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Molecular signature of pruriceptive MrgprA3+ neurons

10.1101/727396 ◽

2019 ◽

Author(s):

Yanyan Xing ◽

Junyu Chen ◽

Henry Hilley ◽

Haley Steele ◽

Jingjing Yang ◽

...

Keyword(s):

Sensory Neurons ◽

Molecular Mechanisms ◽

Molecular Signature ◽

Neuronal Populations ◽

Pathological Conditions ◽

Chronic Itch ◽

Itch Sensation ◽

Profile Changes ◽

Allergic Contact

ABSTRACTItch, initiated by the activation of sensory neurons, is frequently associated with dermatological or systemic diseases and significantly affects patient quality of life. MrgprA3+ sensory neurons have been identified as one of the major itch-sensing neuronal populations. Mounting evidence has demonstrated that peripheral pathological conditions induce physiological regulations of sensory neurons, which is critical for the maintenance of chronic itch sensation. However, the underlying molecular mechanisms are not clear. Here we performed RNA sequencing of genetically labeled MrgprA3+ neurons under both naïve and allergic contact dermatitis condition. Our results revealed the unique molecular signature of itch-sensing neurons and the distinct transcriptional profile changes that result in response to dermatitis. We found enrichment of nine Mrgpr family members and two histamine receptors in MrgprA3+ neurons, suggesting that MrgprA3+ neurons are the main, direct neuronal target for histamine and Mrgprs agonists. In addition, Ptpn6 and Pcdh12 were identified as novel and highly selective markers of MrgprA3+ neurons. We also discovered that MrgprA3+ neurons respond to skin dermatitis in a way that is unique from other sensory neurons by regulating a combination of transcriptional factors, ion channels, and key molecules involved in synaptic transmission. These results significantly increase our knowledge of itch transmission and uncover potentially novel targets for combating itch.

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Peptide plasticity in primary sensory neurons and spinal cord during adjuvant-induced arthritis in the rat: an immunocytochemical and in situ hybridization study

Neuroscience ◽

10.1016/s0306-4522(97)00272-8 ◽

1997 ◽

Vol 82 (2) ◽

pp. 575-589 ◽

Cited By ~ 99

Author(s):

L Calzà ◽

M Pozza ◽

M Zanni ◽

C.U Manzini ◽

E Manzini ◽

...

Keyword(s):

Spinal Cord ◽

In Situ Hybridization ◽

Sensory Neurons ◽

Primary Sensory Neurons ◽

Hybridization Study ◽

Adjuvant Induced Arthritis

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Involvement of sensory neuron-TRPV4 in acute and chronic itch behaviors

10.1101/2021.07.06.451366 ◽

2021 ◽

Author(s):

Quan Fang ◽

Zilong Wang ◽

Abbie Suttle ◽

Yong Chen

Keyword(s):

Sensory Neuron ◽

Sensory Neurons ◽

Well Being ◽

Conditional Knockout ◽

Nonselective Cation Channel ◽

Dry Skin ◽

Skin Cells ◽

Chronic Itch ◽

Allergic Contact

Itch, particularly chronic itch, negatively impacts patients' physical, social, and psychological well-being, leading to deterioration in their quality of life. Limited understanding of itch mechanisms hinders the development of effective antipruritic treatments.TRPV4, a multimodally activated nonselective cation channel, has been detected in sensory neurons of dorsal root and trigeminal ganglion (DRG, TG) and skin cells (e.g. keratinocytes, mast cells, and macrophages). Recent evidence from experimental and clinical relevant studies has implicated that TRPV4 in skin cells plays an important role in both acute and chronic itch. In contrast, little is known whether TRPV4 in sensory neurons directly contributes to scratching behaviors. Here we used sensory neuron-Trpv4 conditional knockout (cKO) mice to address this question. Our results showed that TRPV4 in sensory neurons contributes to scratching behavior evoked by histaminergic (histamine and 48/80) and partial histaminergic (5-HT), but not non-histaminergic (SLIGRL and CQ) pruritogens. Moreover, we observed that TRPV4 in sensory neurons is required for dry skin, but not allergic contact dermatitis, -associated chronic itch. These findings suggest that neuronal-TRPV4 might be specific for some forms of acute and chronic itch.

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Immunoprecipitation (IP) of Homer 1a, injection of virions and in situ hybridization in the spinal cord

Protocol Exchange ◽

10.1038/nprot.2006.154 ◽

2006 ◽

Author(s):

Rohini Kuner

Keyword(s):

Spinal Cord ◽

In Situ Hybridization

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PATH-23. ADULT SPINAL CORD ASTROBLASTOMA WITH EWSR1-BEND2 FUSION

Neuro-Oncology ◽

10.1093/neuonc/noaa222.658 ◽

2020 ◽

Vol 22 (Supplement_3) ◽

pp. iii429-iii429

Author(s):

Takeyoshi Tsutsui ◽

Yoshiki Arakawa ◽

Yasuhide Makino ◽

Hiroharu Kataoka ◽

Sachiko Minamiguti ◽

...

Keyword(s):

Spinal Cord ◽

Residual Tumor ◽

Intramedullary Tumor ◽

Partial Removal ◽

Weighted Image ◽

Eosinophilic Cytoplasm ◽

S 100 ◽

High Cellularity ◽

Adult Spinal Cord

Abstract The most recurrent fusion of CNS high-grade neuroepithelial tumor with MN1alteration(HGNET-MN1) is MN1- BEN Domain Containing 2(BEND2) fusion. Recently, there was a report of a 3-month-old boy with spinal astroblastoma, classified as CNS HGNET-MN1 by DKFZ methylation classification but positive for EWSR1-BEND2 fusion(Yamasaki, 2019). Here, we report a 36-year old man with a spinal cord astroblastoma with EWSR1 alternation. The patient presented with back pain, gait disorder and dysesthesia in lower extremities and trunk was referred to our hospital. MRI showed intramedullary tumor in Th3-5 level, displaying low-intensity on T1 weighted image, high-intensity on T2 weighted image, and homogeneous gadolinium enhancement. Partial removal was performed with the laminectomy. The tumor extended to extramedullary and its boundary was unclear. Histological examinations showed the epithelium-like tumor cells with eosinophilic cytoplasm with high cellularity palisade, intracellar fibrosis, and mitosis. Immunohistochemical staining showed positive for Olig2, GFAP, EMA, SSTR2, S-100, but negative for p53, PgRAE1/AE3. The tumor was diagnosed as astroblastoma, and was classified as HGNET-MN1 by the DKFZ methylation classifier. However, the MN1 alternation was not detected by fluorescence in situ hybridization, instead EWSR1 and BEND2 alternations which suggested EWSR1-BEND2 fusion were detected. After radiation therapy of 54Gy/30fr with bevacizumab and temozolomide, the residual tumor reduced the size and his symptoms improved. This case provides evidence that EWSR1-BEND2 fusion is recurrent in HGNET-MN1 and, as previously reported, suggests the importance of BEND2 in this entity. These two cases suggested that it may be the BEND2 alteration that biologically defines the HGNET-MN1 subclass rather than MN1.

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In situ imaging reveals disparity between prostaglandin localization and abundance of prostaglandin synthases

Communications Biology ◽

10.1038/s42003-021-02488-1 ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Kyle D. Duncan ◽

Xiaofei Sun ◽

Erin S. Baker ◽

Sudhansu K. Dey ◽

Ingela Lanekoff

Keyword(s):

Mass Spectrometry Imaging ◽

Rna Localization ◽

Imaging Method ◽

Related Protein ◽

Uterine Tissue ◽

Tissue Localization ◽

Physiological Processes ◽

Conditional Deletion ◽

Regional Abundance

AbstractProstaglandins are important lipids involved in mediating many physiological processes, such as allergic responses, inflammation, and pregnancy. However, technical limitations of in-situ prostaglandin detection in tissue have led researchers to infer prostaglandin tissue distributions from localization of regulatory synthases, such as COX1 and COX2. Herein, we apply a novel mass spectrometry imaging method for direct in situ tissue localization of prostaglandins, and combine it with techniques for protein expression and RNA localization. We report that prostaglandin D2, its precursors, and downstream synthases co-localize with the highest expression of COX1, and not COX2. Further, we study tissue with a conditional deletion of transformation-related protein 53 where pregnancy success is low and confirm that PG levels are altered, although localization is conserved. Our studies reveal that the abundance of COX and prostaglandin D2 synthases in cellular regions does not mirror the regional abundance of prostaglandins. Thus, we deduce that prostaglandins tissue localization and abundance may not be inferred by COX or prostaglandin synthases in uterine tissue, and must be resolved by an in situ prostaglandin imaging.

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