Tools for analysis and conditional deletion of subsets of sensory neurons

Background: Somatosensation depends on primary sensory neurons of the trigeminal and dorsal root ganglia (DRG). Transcriptional profiling of mouse DRG sensory neurons has defined at least 18 distinct neuronal cell types. Using an advillin promoter, we have generated a transgenic mouse line that only expresses diphtheria toxin A (DTA) in sensory neurons in the presence of Cre recombinase. This has allowed us to ablate specific neuronal subsets within the DRG using a range of established and novel Cre lines that encompass all sets of sensory neurons. Methods: A floxed-tdTomato-stop-DTA bacterial artificial chromosome (BAC) transgenic reporter line (AdvDTA) under the control of the mouse advillin DRG promoter was generated. The line was first validated using a Nav1.8Cre and then crossed to CGRPCreER (Calca), ThCreERT2, Tmem45bCre, Tmem233Cre, Ntng1Cre and TrkBCreER (Ntrk2) lines. Pain behavioural assays included Hargreaves’, hot plate, Randall-Selitto, cold plantar, partial sciatic nerve ligation and formalin tests. Results: Motor activity, as assessed by the rotarod test, was normal for all lines tested. Noxious mechanosensation was significantly reduced when either Nav1.8 positive neurons or Tmem45b positive neurons were ablated whilst acute heat pain was unaffected. In contrast, noxious mechanosensation was normal following ablation of CGRP-positive neurons but acute heat pain thresholds were significantly elevated and a reduction in nocifensive responses was observed in the second phase of the formalin test. Ablation of TrkB-positive neurons led to significant deficits in mechanical hypersensitivity in the partial sciatic nerve ligation neuropathic pain model. Conclusions: Ablation of specific DRG neuronal subsets using the AdvDTA line will be a useful resource for further functional characterization of somatosensory processing, neuro-immune interactions and chronic pain disorders.

Conditioned medium from the stem cells of human exfoliated deciduous teeth ameliorates neuropathic pain in a partial sciatic nerve ligation model

BackgroundAlthough recent studies have revealed the powerful antinociceptive effect of human dental pulp stem cells in an animal model for diabetes and osteoarthritis, its analgesic mechanisms are still largely elusive. We have previously reported that conditioned medium (CM) from dental pulp stem cells of deciduous teeth (SHED-CM) or its components, monocyte chemoattractant protein-1 (MCP-1) and the secreted ectodomain of sialic acid-binding Ig-like lectin-9 (sSiglec-9), directly induces anti-inflammatory M2 macrophages, however the antinociceptive activity of induced M2 is unknown. In this study, we investigated the antinociceptive effect of SHED-CM, MCP-1, and sSiglec-9 or secretome from M2-induced by SHED-CM (M2-CM) against neuropathic pain (NP) using a partial sciatic nerve ligation (PSL) mouse model and analyzed the mechanical bases of their antinociceptive effects. MethodsPSL mice were treated using SHED-CM with or without mannosylated-Clodrosome, specifically depleting M2 macrophages, recombinant MCP-1 and sSiglec-9 protein, M2-CM, or fibroblast-CM. Human Schwann cells activated by TNF-α in vitro were treated with M2-CM. The expression of pro-inflammatory mediators, neuroprotective factors, the nociceptive receptor, and markers for M1, M2, and activated glial cells in injured sciatic nerve (SCN), dorsal root ganglion, or spinal cord were evaluated by RT-PCR and immunohistochemistry. Mechanical allodynia of PSL mice was analyzed via von Frey test. ResultsIn the behavioral test, intravenous administration of SHED-CM greatly improved the PSL-induced hypersensitivity. SHED-CM treatment recruited M2 macrophages in the injured SCN and ipsilateral L4/L5 dorsal root ganglion and suppressed microglial activation in the spinal cord. Specific depletion of the M2 by mannosylated-Clodrosome markedly reduced the antinociceptive effect of SHED-CM. Intravenous administration of both MCP-1/sSiglec-9 and M2-CM ameliorated the PSL-induced hypersensitivity. We found that M2-CM directly suppressed the expression of nociceptive receptors as well as proinflammatory mediators in Schwann cells. ConclusionTaken together, our data suggest that SHED-CM ameliorates NP through the induction of the analgesic anti-inflammatory M2 macrophages. Thus, SHED-CM may present as a potential novel therapeutic candidate for NP.

Controlled activation of cortical astrocytes can reverse neuropathic chronic pain

Chronic pain is a major public health problem that currently lacks effective treatment options. Here, we report a novel combination therapy that can effectively reverse chronic pain induced by nerve injury in mice. By combing transient nerve block to inhibit noxious afferent input from injured peripheral nerves, with transient concurrent activation of astrocytes in the somatosensory cortex (S1) by either transcranial direct current stimulation (tDCS) or via the chemogenetic DREADD system, we could reverse allodynia previously established by partial sciatic nerve ligation (PSL). Activation of astrocytes initiated spine plasticity to reduce synapses formed shortly after PSL. The cure from allodynia persisted long after ceasing active treatment. Thus, our study represents the first report of a robust, readily translatable approach for treating chronic pain that capitalizes on the causative interplay between noxious afferents, sensitized central neuronal circuits and astrocytic-activation induced plasticity.

Gallic Acid improved Amytryptiline effect in neuropathic pain induced by Partial Sciatic Nerve Ligation (PSNL) in Rats

Aim and Backround: Amytriptiline (AMY) a antidepressant used in the treatment of neuropathic pain. However with limited therapeutic benefits and side effects of AMY is not helpful to majority of the neuropathic pain patients. Gallic acid (GA) is a polyphenolic product with potential antioxidant effects and useful in neuropathic pain. Objective: The purpose of the study was to investigate the improved neuropathic pain relief with GA in combination with AMY in rats. Methods: Partial sciatic nerve ligation (PSNL) method is used for neuropathic pain induction in rats. The rats were randomly divided into 6 groups (n = 8), and treated with drugs or vehicle once daily for 15 days after the pain induction. The first group was served as Normal control and received normal saline (p.o), second group was served as Sham Control and received Normal Saline (p.o), third group served as Surgery Control, received normal saline (p.o), fourth group was received with AMY (25mg/kg, p.o), fifth group was received with GA (100mg/kg,p.o), sixth group was received with both AMY and GA. Further behavioural studies for pain were carried out on days 1,4,7,10,13,16,19 and 22. Histological studies of sciatic nerves carried out on days 1, 15 and 22 and on 22nd day all the remaining animals were sacrificed for sciatic nerve tissues biochemical estimations. Results: GA attenuates neuropathic pain better in combination with AMY by ameliorating the behavioral, biochemical and histopathological signs and symptoms. This effect resulting due to its antioxidant, antinociceptive and anti-inflammatory actions. It also potentiates AMY antinociceptive and antioxidant effects when given in combination in a continuous treatment. Conclusion: The results suggest that GA in combination with AMYattenuated the neuropathic pain. Hence, the use of GA as an adjunctive with AMY in the neuropathic pain will be more therapeutically beneficial and further studies in patients to confirm the results is warranted.