Propofol Alleviates Neuropathic Pain Induced by Chronic Contractile Injury by Regulating the Spinal glun2b-p38mapkepac1 Pathway

Background. Propofol acts as an intravenous anesthetic cure which is widely used as a therapy for the craniocerebral injury that comprised surgical anesthesia as well as the sedation done in the intensive care units. Propofol is one of the most commonly used and efficient anesthetics where the painful effects are followed by an injection of propofol. In many cases, patients experience pain followed by anxiety, boredom, fear, and even myocardial ischemia. Objective. This study was performed to investigate the underlying mechanism of propofol and its effect on regulating spinal glun2b-p38mapkepac1 pathways in chronic contractile injury. Material and Methods. Contractile injury was performed by ligation around the nerve of the thigh region postanesthesia. Rats were divided into three groups to analyze the changes like mechanical allodynia by the paw withdrawal threshold and histopathological analysis for assessing cellular degradation. L4-L6 from the spinal dorsal horns were isolated and harvested for studying protein expression, by the method of western blotting and immunofluorescence analysis. Results. The pain caused due to mechanical allodynia in the paw region was highest at 1 hour postinduction and lasted for three days postinjury. Pain was significantly less in the group receiving propofol when compared with the isoflurane group for the first two hours of injury. In the propofol group, EPAC1, GluN2B, and p38 MAP K were significantly lower. Conclusion. In the rat model of induced chronic contractile injury, postsurgery there was a suppression of the GluN2B-p38MAPK/EPAC1 signaling pathway in the propofol group. As the p38MAPK/EPAC pathway has a significant role in the postoperative hyperalgesia, thus our experiment suggests that propofol has analgesic effects.

Voluntary Exercise Ameliorates Neuropathic Pain by Suppressing Calcitonin Gene-Related Peptide and Ionized Calcium-Binding Adapter Molecule 1 Overexpression in the Lumbar Dorsal Horns in Response to Injury to the Cervical Spinal Cord

Background Neuropathic pain (NP) is a frequent finding in patients diagnosed with spinal cord injuries (SCIs). We aimed to investigate the effects of voluntary exercise on NP after SCI and to elucidate its potential mechanisms. MethodsA rat model of post-SCI NP induced by compression of the posterior or lateral cervical spinal cord was used to evaluate the effects of voluntary exercise by measuring the bilateral withdrawal of the hind paws using the Von Frey filament and Hargreaves tests. The place escape/avoid paradigm was used to evaluate supraspinal pain processing and somatosensory evoked potentials (SEPs) were used to examine disturbances in proprioception. Locomotor function was evaluated using Basso, Beattie, and Bresnahan (BBB) scoring. Pathologic findings in hematoxylin and eosin-stained tissue and magnetic resonance imaging were used to evaluate the morphological changes after SCI. The lesion size within the cervical spinal cord was evaluated by staining with Eriochrome cyanine R. Quantitative polymerase chain reaction and immunohistochemistry were used to assess the expression of calcitonin gene-related peptide (CGRP) and ionized calcium-binding adapter molecule 1 (Iba-1) in the lumbar dorsal horns. ResultsAll injured rats developed mechanical hypersensitivity, hyposensitivity, and thermal hyperalgesia in the contralateral hind paws at one week post-injury. Rats that underwent lateral compression injury developed NP in the ipsilateral hind paws one week later than rats with a posterior compression injury. Our findings revealed that voluntary exercise ameliorated mechanical allodynia and thermal hyperalgesia, and significantly improved proprioception as measured by SEP, but had no impact on mechanical hypoalgesia or motor recovery and provided no significant neuroprotection after recovery from an acute SCI. SCI-induced NP was accompanied by increased expression of CGRP and Iba-1 in the lumbar dorsal horn. These responses were reduced in rats that underwent voluntary exercise. ConclusionsVoluntary exercise ameliorates NP that develops in rats after compression injury. Increased expression of CGRP and Iba-1 in the lumbar dorsal horns of rats exhibiting symptoms of NP suggests that microglial activation might play a crucial role in its development. Collectively, voluntary exercise may be a promising therapeutic modality to treat NP that develops clinically in response to SCI.

Downregulation of metallothionein-2 contributes to oxaliplatin-induced neuropathic pain

Background We previously reported a correlation between small doses of oxaliplatin penetrating onto the spinal cord and acute pain after chemotherapy. Here, we propose that MT2 within the spinal dorsal horns participates in the development of oxaliplatin-induced neuropathic pain and may be a pharmacological target for the prevention and treatment of chemotherapy-induced peripheral neuropathy (CIPN). Methods The rat model of CIPN was established by 5 consecutive injections of oxaliplatin (0.4 mg/100 g/day). Genetic restoration of neuron-specific metallothionein-2 was implemented 21 days before oxaliplatin treatment, and also, genetic inhibition by metallothionein-2 siRNA was performed. Mechanical allodynia and locomotor activity were assayed. Cell-specific expression of metallothionein-2, the mRNA levels of pro-inflammatory cytokines, nuclear translocation of NF-κB, the protein levels of expression of IκB-α, and interaction between IκB-α and P65 were evaluated in the spinal dorsal horns. Also, in vitro interaction of sequentially deleted IκB-α promoter with metallothionein-2 was used to assess the signal transduction mechanism. Results We found that oxaliplatin induced downregulation of metallothionein-2 in rat spinal cord neurons. By contrast, genetic restoration of metallothionein-2 in the spinal dorsal horn neuron blocked and reversed neuropathic pain in oxaliplatin-treated rats of both sexes, whereas genetic inhibition of metallothionein-2 triggered neuropathic pain in normal rats. Overall locomotor activity was not impaired after the genetic alterations of metallothionein-2. At the molecular level, metallothionein-2 modulated oxaliplatin-induced neuroinflammation, activation of NF-κB, and inactive transcriptional expression of IκB-α promoter, and these processes could be blocked by genetic restoration of metallothionein-2 in the spinal dorsal horn neurons. Conclusions Metallothionein-2 is a potential target for the prevention and treatment of CIPN. A reduction of NF-κB activation and inflammatory responses by enhancing the transcription of IκB-α promoter is proposed in the mechanism.

circDym prevents chronic neuropathic pain by competitive inhibition of Nlgn2 mRNA transport in neurites

Aims: Neuropathic pain (NP) is a chronic syndrome that is refractory to current analgesics through unknown mechanisms. Epigenetic regulation in spinal dorsal horn neurons is reported to contribute to the initiation and maintenance of NP. Circular RNAs (circRNAs) are involved in various biological processes in neurons, but molecular mechanism of how the involvement in NP are lacking. Methods: To study NP, we used a sciatic chronic constriction injury (CCI) model in C57 mice, with the level of mechanical allodynia determined using von Frey monofilaments. The injured ipsilateral spinal dorsal horns in lumbar segments (L3–L5) were collected and total RNA and protein extracted. Transcriptome sequencing, qRT-PCR, western blot analysis, and immunoprecipitation were performed. Bioinformatic analysis was conducted using R packages. The patient cohort was analysed using logistic regression analysis. Results: circDym was identified as one of the NP-related circRNA candidates and qRT-PCR showed that its expression was significantly lower in both the CCI mouse models and in the peripheral blood of patients with NP. Overexpression of circDym significantly attenuated injury induced by NP. Further examination indicated that circDym functions by inhibiting synaptic localization of Nlgn2 mRNA by competitively binding with the RNA-binding protein, Fmrp, resulting in decreased expression of GABAAR, thus leading to the inhibition of chronic pain. Single-cell sequencing results showed that Prodynorphin-positive and Cholecystokinin-positive neurons were likely responsible for this process. Conclusions: We identified circDym, which works through a coupling mechanism, as a novel biomarker and therapeutic target for NP.

Reversible Tau Phosphorylation Induced by Synthetic Torpor in the Spinal Cord of the Rat

Tau is a key protein in neurons, where it affects the dynamics of the microtubule system. The hyperphosphorylation of Tau (PP-Tau) commonly leads to the formation of neurofibrillary tangles, as it occurs in tauopathies, a group of neurodegenerative diseases, including Alzheimer's. Hypothermia-related accumulation of PP-Tau has been described in hibernators and during synthetic torpor (ST), a torpor-like condition that has been induced in rats, a non-hibernating species. Remarkably, in ST PP-Tau is reversible and Tau de-phosphorylates within a few hours following the torpor bout, apparently not evolving into pathology. These observations have been limited to the brain, but in animal models of tauopathies, PP-Tau accumulation also appears to occur in the spinal cord (SpCo). The aim of the present work was to assess whether ST leads to PP-Tau accumulation in the SpCo and whether this process is reversible. Immunofluorescence (IF) for AT8 (to assess PP-Tau) and Tau-1 (non-phosphorylated Tau) was carried out on SpCo coronal sections. AT8-IF was clearly expressed in the dorsal horns (DH) during ST, while in the ventral horns (VH) no staining was observed. The AT8-IF completely disappeared after 6 h from the return to euthermia. Tau-1-IF disappeared in both DH and VH during ST, returning to normal levels during recovery. To shed light on the cellular process underlying the PP-Tau pattern observed, the inhibited form of the glycogen-synthase kinase 3β (the main kinase acting on Tau) was assessed using IF: VH (i.e., in motor neurons) were highly stained mainly during ST, while in DH there was no staining. Since tauopathies are also related to neuroinflammation, microglia activation was also assessed through morphometric analyses, but no ST-induced microglia activation was found in the SpCo. Taken together, the present results show that, in the DH of SpCo, ST induces a reversible accumulation of PP-Tau. Since during ST there is no motor activity, the lack of AT8-IF in VH may result from an activity-related process at a cellular level. Thus, ST demonstrates a newly-described physiological mechanism that is able to resolve the accumulation of PP-Tau and apparently avoid the neurodegenerative outcome.

Downregulation of Metallothionein-2 Contributes to Oxaliplatin-induced Neuropathic Pain

Background We previously reported a correlation between small doses of oxaliplatin penetrating onto the spinal cord and acute pain after chemotherapy. Here we propose that MT2 within the spinal dorsal horns participates the development of oxaliplatin-induced neuropathic pain and may be a pharmacological target for the prevention and treatment of chemotherapy-induced peripheral neuropathy (CIPN). Methods The rat model of CIPN was established by a 5 consecutive injection of oxaliplatin (0.4 mg/ 100 g/ day). Genetic restoration or inhibition of neuron-specific metallothionein-2 was implemented 21 days before oxaliplatin treatment. Mechanical allodynia and locomotor activity were assayed. Cell-specific expression of metallothionein-2, the mRNA levels of pro-inflammatory cytokines, nuclear translocation of NF-κB, the protein levels of expression of IκB-α, and interaction between IκB-α and P65 were evaluated in the spinal dorsal horns. Also, in vitro interaction of sequentially deleted IκB-α promoter with metallothionein-2 was used to assess the signal transduction mechanism. Results We found that oxaliplatin induced downregulation of metallothionein-2 in rat spinal cord neurons. By contrast, genetic restoration of metallothionein-2 in the spinal dorsal horn neuron blocked and reversed neuropathic pain in oxaliplatin-treated rats of both sexes, whereas genetic inhibition of metallothionein-2 triggered neuropathic pain in normal rats. No locomotor impairment was observed after the genetic alterations of metallothionein-2. At the molecular level, metallothionein-2 modulated oxaliplatin-induced neuroinflammation, activation of NF-κB, and transcriptional expression of IκB-α promoter, and these processes could be blocked by genetic restoration of metallothionein-2 in the spinal dorsal horn neurons. Conclusions Metallothionein-2 is a potential target for the prevention and treatment of CIPN. A reduction of NF-κB activation and inflammatory responses by enhancing the transcription of IκB-α promoter is proposed in the mechanism.

HARDI-ZOOMit protocol improves specificity to microstructural changes in presymptomatic myelopathy

Diffusion magnetic resonance imaging (dMRI) proved promising in patients with non-myelopathic degenerative cervical cord compression (NMDCCC), i.e., without clinically manifested myelopathy. Aim of the study is to present a fast multi-shell HARDI-ZOOMit dMRI protocol and validate its usability to detect microstructural myelopathy in NMDCCC patients. In 7 young healthy volunteers, 13 age-comparable healthy controls, 18 patients with mild NMDCCC and 15 patients with severe NMDCCC, the protocol provided higher signal-to-noise ratio, enhanced visualization of white/gray matter structures in microstructural maps, improved dMRI metric reproducibility, preserved sensitivity (SE = 87.88%) and increased specificity (SP = 92.31%) of control-patient group differences when compared to DTI-RESOLVE protocol (SE = 87.88%, SP = 76.92%). Of the 56 tested microstructural parameters, HARDI-ZOOMit yielded significant patient-control differences in 19 parameters, whereas in DTI-RESOLVE data, differences were observed in 10 parameters, with mostly lower robustness. Novel marker the white-gray matter diffusivity gradient demonstrated the highest separation. HARDI-ZOOMit protocol detected larger number of crossing fibers (5–15% of voxels) with physiologically plausible orientations than DTI-RESOLVE protocol (0–8% of voxels). Crossings were detected in areas of dorsal horns and anterior white commissure. HARDI-ZOOMit protocol proved to be a sensitive and practical tool for clinical quantitative spinal cord imaging.