Animal Studies

Prolonged postoperative pain is a major concern and occurs more frequently in women, but mechanisms remain elusive. NR2B-containging N-methyl-d-aspartate (NMDA) receptor is a key component of nociception transduction. Divalent metal transporter 1 (DMT1)-mediated iron overload involves NMDA-induced neurotoxicity in males. Kalirin-7 is vital in synaptic plasticity underlying pathological pain in males. Herein, the requirement for kalirin-7 in NR2B phosphorylation-dependent iron accumulation and spine plasticity in postoperative pain after tibial fracture in female mice has been examined.

The nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are trophic factors required by distinct population of sensory neurons during development of the nervous system. Neurons that fail to receive appropriate trophic support are lost during this period of naturally occurring cell death. In the last decade, our understanding of the signalling pathways regulating neuronal death following NGF deprivation has advanced substantially. However, the signaling mechanisms promoting BDNF-deprivation induced sensory neuron degeneration are largely unknown. Using a well-established culture model of dorsal root ganglion (DRG), we have examined degeneration mechanisms triggered upon BDNF withdrawal in sensory neurons. Our results indicate differences and similarities between the molecular signalling pathways behind NGF and BDNF deprivation-induced death. For instance, we observed that the inhibition of Trk receptors (K252a), PKC (Gö6976), protein translation (cycloheximide) or caspases (zVAD-fmk) provides protection from NGF deprivation-induced death but not from degeneration evoked by BDNF-withdrawal. Interestingly, degeneration of BDNF-dependent sensory neurons requires BAX and appears to rely on reactive oxygen species generation rather than caspases to induce degeneration. These results highlight the complexity and divergence of mechanisms regulating developmental sensory neuron death. The elimination of neuronal cells generated in excess during embryonic stages characterizes the maturation of the nervous system. Here we address the developmental cell death mechanisms of BDNF-dependent dorsal root ganglion neurons , comparing and contrast them with those deployed in NGF-dependent sensory neurons. We observe several important differences between the molecular signalling pathways behind NGF and BDNF deprivation-induced death. Significantly, degeneration of BDNF-dependent sensory neurons requires BAX but not caspase activation, instead reactive oxygen species generation appears to play a key role in degeneration. This work highlights the complexity of cell death mechanisms in distinct embryonic sensory neuron populations.

The aim of the present study was to investigate the effects of microRNA (miR)‑142‑3p on neuropathic pain caused by sciatic nerve injury in chronic compression injury (CCI) rats, and further investigate its mechanism. Rat experiments were divided into four parts in the study. In the first part, the rats were divided into the Sham and CCI groups. The expression of miR‑142‑3p, AC9 and cAMP were detected. In the second part, the rats were divided into the Sham, CCI, miR‑142‑3p mimic, mimic‑negative control (NC), miR‑142‑3p small interfering RNA (siRNA) and siRNA‑NC groups. The expression of cAMP and the levels of AMPK pathway‑related proteins were detected. In the third part, the rats were randomly divided into Sham, CCI, AC9 mimic, mi‑NC, AC9 siRNA and si‑NC groups. Double luciferase reporter assay was used to analyse the targeting relationship between miR‑142‑3p and AC9. In the fourth part, the rats were divided into the Sham, CCI, miR‑142‑3p siRNA, AC9 mimic, miR‑142‑3p siRNA + AC9 siRNA, cAMP activator (Forskolin) and miR‑142‑3p siRNA + cAMP inhibitor groups. The expression of miR‑142‑3p was significantly increased while AC9 and cAMP expression significantly decreased in CCI rats. However, AC9 overexpression significantly increased the levels of cAMP protein. Luciferase reporter assay also proved that AC9 is the target gene of miR‑142‑3p. Moreover, miR‑142‑3p silencing was found to reduce neuropathic pain in CCI rats by upregulating the expression of AC9. It was also found that cAMP activation can relieve neuropathic pain and promote the expression of AMPK‑related proteins in CCI rats. Silencing miR‑142‑3p can target AC9 to reduce the expression of inflammatory factors and neuropathic pain in CCI rats by increasing the expression of cAMP/AMPK pathway‑related proteins.

Oxytocin receptor (OXTR), a G protein-coupled receptor, has been demonstrated to play a significant role in analgesia after activation by its canonical agonist, oxytocin (OXT) in the dorsal root ganglion (DRG). However, the role of OXTR in the trigeminal nervous system on the orofacial neuropathic pain is still little known. In the present study, we aimed to investigate the regulation effect and mechanism of OXTR in the trigeminal ganglion (TG) and spinal trigeminal nucleus caudalis (SpVc) on orofacial ectopic pain induced by trigeminal nerve injury. Inferior alveolar nerve (IAN) was transected to establish trigeminal ectopic pain model. Von Frey filaments behavioral test demonstrated IAN transection (IANX) evoked mechanical hypersensitivity in the whisker pad since from day 1 to at least day 14 after surgery. In addition, administration of OXT (50 μM and 100 μM) into the TG attenuated the mechanical hypersensitivity induced by IANX, which was reversed by pre-treatment with L-368,899 (a selective antagonist of OXTR) into the TG. In addition, immunofluorescence (IF) showed the expression of OXTR in neurons in the TG and SpVc. Furthermore, western blot (WB) analysis indicated that the upregulated expression of OXTR, calcitonin gene-related peptide (CGRP), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) in the TG and SpVc after IANX was inhibited by the administration of OXT into the TG. And the inhibition effect of OXT on the expression of CGRP, IL-1β, and TNF-α was abolished by pre-application of L-368,899 into the TG.

There has been a long-standing debate regarding the role of peripheral afferents in mediating rapid-onset anorexia among other responses elicited by peripheral inflammatory insults. Thus, the current study assessed the sufficiency of peripheral afferents expressing toll-like receptor 4 (TLR4) to the initiation of the anorexia caused by peripheral bacterial lipopolysaccharide (LPS). We generated a Tlr4 null (Tlr4) mouse in which Tlr4 expression is globally disrupted by a loxP-flanked transcription blocking cassette. This novel mouse model allowed us to restore the endogenous TLR4 expression in specific cell types. Using Zp3-Cre and Na1.8-Cre mice, we produced mice that express TLR4 in all cells (Tlr4 X Zp3-Cre) and in peripheral afferents (Tlr4 X Na1.8-Cre), respectively. We validated the Tlr4 mice, which were phenotypically identical to previously reported global TLR4 knock-out mice. Contrary to our expectations, the administration of LPS did not cause rapid-onset anorexia in mice with Na1.8-restricted TLR4. The later result prompted us to identify Tlr4-expressing vagal afferents using hybridization. , we found that Tlr4 mRNA was primarily enriched in vagal Na1.8 afferents located in the jugular ganglion that co-expressed Calcitonin gene-related peptide (CGRP). , the application of LPS to cultured Na1.8-restricted TLR4 afferents was sufficient to stimulate the release and expression of CGRP. In summary, we demonstrated using a new mouse model that vagally-expressed TLR4 is selectively involved in stimulating the release of CGRP, but not in causing anorexia. Using a new transgenic mouse model, our data establish that TLR4 is both sufficient and required for the release of CGRP from a subset of vagal afferents. This finding may be relevant to the understanding of how bacterial infections modulate nerves.