Spinal Nmur2-positive Neurons Play a Crucial Role in Mechanical Itch.

The dorsal spinal cord is crucial for the transmission and modulation of multiple somatosensory modalities, such as itch, pain, and touch. Despite being essential for the well-being and survival of an individual, itch and pain, in their chronic forms, have increasingly been recognized as clinical problems. Although considerable progress has been made in our understanding of the neurochemical processing of nociceptive and chemical itch sensations, the neural substrate that is crucial for mechanical itch processing is still unclear. Here, using genetic and functional manipulation, we identified a population of spinal neurons expressing neuromedin U receptor 2 (Nmur2+) as critical elements for mechanical itch. We found that spinal Nmur2+ neurons are predominantly excitatory neurons, and are enriched in the superficial laminae of the dorsal horn. Pharmacogenetic activation of cervical spinal Nmur2+ neurons evoked scratching behavior. Conversely, the ablation of these neurons using a caspase-3-based method decreased von Frey filament-induced scratching behavior without affecting responses to other somatosensory modalities. Similarly, suppressing the excitability of cervical spinal Nmur2+ neurons via the overexpression of functional Kir2.1 potassium channels reduced scratching in response to innocuous mechanical stimuli, but not to pruritogen application. At the lumbar level, pharmacogenetic activation of these neurons evoked licking and lifting behaviors. However, ablating these neurons did not affect the behavior associated with acute pain. Thus, these results revealed the crucial role of spinal Nmur2+ neurons in mechanical itch. Our study provides important insights into the neural basis of mechanical itch, paving the way for developing novel therapies for chronic itch. PERSPECTIVE: Excitatory Nmur2+ neurons in the superficial dorsal spinal cord are essential for mechanical but not chemical itch information processing. These spinal Nmur2+ neurons represent a potential cellular target for future therapeutic interventions against chronic itch. Spinal and supraspinal Nmur2+ neurons may play different roles in pain signal processing.

Different neuronal populations mediate inflammatory pain analgesia by exogenous and endogenous opioids.

Mu-opioid receptors (MORs) are crucial for analgesia by both exogenous and endogenous opioids. However, the distinct mechanisms underlying these two types of opioid analgesia remain largely unknown. Here, we demonstrate that analgesic effects of exogenous and endogenous opioids on inflammatory pain are mediated by MORs expressed in distinct subpopulations of neurons in mice. We found that the exogenous opioid-induced analgesia of inflammatory pain is mediated by MORs in Vglut2+ glutamatergic but not GABAergic neurons. In contrast, analgesia by endogenous opioids is mediated by MORs in GABAergic rather than Vglut2+ glutamatergic neurons. Furthermore, MORs expressed at the spinal level is mainly involved in the analgesic effect of morphine in acute pain, but not in endogenous opioid analgesia during chronic inflammatory pain. Thus, our study revealed distinct mechanisms underlying analgesia by exogenous and endogenous opioids, and laid the foundation for further dissecting the circuit mechanism underlying opioid analgesia.

Topography of Reward and Aversion Encoding in the Mesolimbic Dopaminergic System.

Dopamine (DA) neurons in the VTA play essential roles in adaptive motivated behavior, which requires rapid discrimination between positive and negative motivational signature. However, the precise functional DA circuitry processing reward and aversive information remain elusive. Here, we report that the encoding of reward and aversion by the DA system in the NAc is tightly associated with its anatomical location. By recording the dynamics of DA release with genetically encoded fluorescent DA sensor using in vivo fiber photometry in freely moving male mice, we found that the DA-sensor signal in the dorsomedial NAc shell and dorsolateral NAc shell were increased during rewarding events and decreased during aversive noxious events. In contrast, the release of DA in the ventromedial NAc shell was increased by both rewarding and aversive stimuli, whereas the DA-sensor signal in the central ventromedial NAc shell and ventrolateral NAc shell showed complex dynamics. Furthermore, the activity of DA fibers in different subregions of NAc measured with calcium sensor largely recapitulated the changes of DA-sensor signal in response to rewarding and aversive stimuli. In addition, correlation analysis showed that the response magnitude of DA-sensor or fibers significantly changed along the DV axis of the NAc. These results revealed the distinct role of the mesolimbic DA system in different subregions of NAc in encoding value and salience.SIGNIFICANCE STATEMENT Adaptive motivated behavior requires rapid discrimination between favorable and harmful events and is dynamically modulated by dopamine (DA) neurons in the VTA. However, the precise relationship between distinct DA circuitry and reward/aversion signal encoding is not well understood. Here, by recording the dynamics of DA release and the activity of DA fibers in each subregion of the NAc using in vivo fiber photometry in freely moving animals, we found that the DA system in the dorsomedial/dorsolateral, ventromedial, and ventrolateral NAc shell plays different roles in encoding value and salience. These results extend our knowledge about how the mesolimbic DA system process motivational information at the circuitry level.

Paeoniflorin suppresses TGF-ß mediated epithelial-mesenchymal transition in pulmonary fibrosis through a Smad-dependent pathway.

AIM: Paeoniflorin has shown to attenuate bleomycin-induced pulmonary fibrosis (PF) in mice. Because the epithelial-mesenchymal transition (EMT) in type 2 lung endothelial cells contributes to excessive fibroblasts and myofibroblasts during multiple fibrosis of tissues, we investigated the effects of paeoniflorin on TGF-ß mediated pulmonary EMT in bleomycin-induced PF mice. METHODS: PF was induced in mice by intratracheal instillation of bleomycin (5 mg/kg). The mice were orally treated with paeoniflorin or prednisone for 21 d. After the mice were sacrificed, lung tissues were collected for analysis. An in vitro EMT model was established in alveolar epithelial cells (A549 cells) incubated with TGF-ß1 (2 ng/mL). EMT identification and the expression of related proteins were performed using immunohistochemistry, transwell assay, ELISA, Western blot and RT-qPCR. RESULTS: In PF mice, paeoniflorin (50, 100 mg·kg(-1)·d(-1)) or prednisone (6 mg·kg(-1)·d(-1)) significantly decreased the expression of FSP-1 and α-SMA, and increased the expression of E-cadherin in lung tissues. In A549 cells, TGF-ß1 stimulation induced EMT, as shown by the changes in cell morphology, the increased cell migration, and the increased vimentin and α-SMA expression as well as type I and type III collagen levels, and by the decreased E-cadherin expression. In contrast, effects of paeoniflorin on EMT disappeared when the A549 cells were pretreated with TGF-ß1 for 24 h. TGF-ß1 stimulation markedly increased the expression of Snail and activated Smad2/3, Akt, ERK, JNK and p38 MAPK in A549 cells. Co-incubation with paeoniflorin (1-30 µmol/L) dose-dependently attenuated TGF-ß1-induced expression of Snail and activation of Smad2/3, but slightly affected TGF-ß1-induced activation of Akt, ERK, JNK and p38 MAPK. Moreover, paeoniflorin markedly increased Smad7 level, and decreased ALK5 level in A549 cells. CONCLUSION: Paeoniflorin suppresses the early stages of TGF-ß mediated EMT in alveolar epithelial cells, likely by decreasing the expression of the transcription factors Snail via a Smad-dependent pathway involving the up-regulation of Smad7.

[Effect of Madecassoside on Intestinal Mucosal Immunity in Collagen-Induced Arthritis Rats].

OBJECTIVE: To explore the changes of intestinal mucosal immunity in collagen-induced arthritis rats and the impact of madecassoside on these changes. METHODS: Collagen-induced arthritis was established in female Wistar rats. Treatment group was orally administrated madecassoside once daily for consecutive 21 days, while blank control and model groups were orally administered saline at the same volume. The concentrations of sIgA in small intestine content and IFN-γ in small intestinal tissue homogenate were determined by ELISA. The proportions of CD4+ T and CD8+ T in the epithelium and laminar propria of small intestine were detected by flow cytometry, and the ratios of CD4+/CD8+ were calculated. The relative expressions of CD80, CD86, IL-6, IL-12 and Foxp3 mRNA in the small intestine were determined by real-time PCR. RESULTS: Compared with blank control rats, the concentrations of sIgA in small intestine content and IFN-γ in small intestinal tissue homogenate from model rats were increased, the ratios of CD4+/CD8+ in the epithelium and laminar propria of small intestine were higher and the relative expressions of CD80, CD86, IL-6 and IL-12 mRNA in the small intestine were increased. Madecassoside treatment decreased the concentrations of sIgA in small intestine content and IFN-γ in small intestinal tissue, downregulated the ratios of CD4+/CD8+ in the epithelium and laminar propria and decreased the relative expressions of CD80, CD86, IL-6 and IL-12 mRNA, while upregulated the relative expression of Foxp3 mRNA in the small intestine. CONCLUSION: The intestinal mucosal immune response is enhanced in collagen-induced arthritis rats, the antigen presenting cells are activated abnormally and the immune tolerance is disturbed. Madecassoside treatment can downregulate the intestinal mucosal immune response and benefit for the induction and maintenance of intestinal immune tolerance.