Modified Spared Nerve Injury Surgery Model of Neuropathic Pain in Mice.

We examined the influence of misdirection of regenerating motor axons toward the distal sensory Schwann tubes on the muscle contraction force in early nerve repair using a rat sciatic nerve model. At 0, 1, 2, 4 and 8 weeks after severing the tibial, peroneal and sural nerves, the proximal stump of the tibial nerve was anastomosed with the distal stumps of both the peroneal and sural nerves using tubulisation (n=10 in each of five groups). We intentionally used the distal stump of the sural nerve (a sensory nerve) to induce regeneration in motor axons from the proximal tibial nerve stump toward the distal sensory nerve stump. Twenty-four weeks after nerve repair, isometric contraction force and wet weight of the anterior tibial muscle were measured, and the numbers of regenerated myelinated axons (motor and sensory) in the distal sural and peroneal nerves were counted. The rates of sural nerve regeneration were significantly higher at weeks 0 and 1 than at the later repair times. However, muscle contraction force and muscle wet weight did not differ significantly between groups in which nerves were repaired within four weeks of severance. These results indicate that peripheral nerve repair within four weeks of severance does not influence the muscle contraction force of single muscle despite the misdirection of motor axons toward the distal sensory Schwann tubes.

Involuntary, Electrically Excitable Nerve Transfer for Denervation: Results From an Animal Model

Objectives Neuropathic pain is characterized by long-lasting, intractable pain. Sciatic nerve ligation is often used as an animal model of neuropathic pain, and the spared nerve injury (SNI) model, in which the common peroneal nerve (CPN) and tibial nerve (TN) are ligated, is widely used. In the present study, we evaluated the analgesic effect of a cholinergic agonist, carbachol, on a neuropathic pain model prepared by sural nerve (SN) ligation in mice. Methods The SN was tightly ligated as a branch of the sciatic nerve. Mechanical and thermal allodynia, and hyperalgesia were assessed using von Frey filaments and heat from a hot plate. The analgesic effects of intracerebroventricularly-administered morphine and carbachol were compared. Results SN ligation resulted in a significant decrease in pain threshold for mechanical stimulation 1 day after ligation. In response to thermal stimulation, allodynia was observed at 50°C and hyperalgesia at 53 and 56°C 3 days after ligation. Content of thiobarbituric acid reactive substances (TBARS) in the spinal cord increased significantly at 6 and 12 h after ligation. Acetylcholine content of the spinal cord also increased at 5 and 7 days after ligation. Intracerebroventricular administration of carbachol at 7 days after ligation produced a marked analgesic effect against mechanical and thermal stimuli, which was stronger and longer-lasting than morphine at all experimental time points. Conclusion These findings suggest that cholinergic nerves are involved in allodynia and hyperalgesia of the SN ligation neuropathic pain model.

Towards a mechanisms-based approach to pain medicine.

Whether electroacupuncture (EA) stimulation at different frequencies has a similar effect on spared nerve injury (SNI) as other neuropathic pain models, and how EA at different frequencies causes distinct analgesic effects on neuropathic pain is still not clear. Adult male Sprague-Dawley rats were randomly divided into sham SNI, SNI, 2 Hz, 100 Hz and sham EA groups. Paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) were measured. EA was performed once a day on days 1 to 14 after SNI. The expressions of transient receptor potential cation subfamily V member 1 (TRPV1) and peripheral purinergic P2X receptor 3 (P2X3) were determined by western blotting and immunofluorescence. TRPV1 siRNA and P2X3 siRNA were administered by intrathecal injection. TRPV1 or P2X3 agonists were combined with EA. There were significant decreases in PWT, but no changes in PWL in the 14 days after SNI. EA using 2- or 100-Hz stimulation similarly increased PWT at every time point. The cytosol protein expression of P2X3 in the L4-L6 dorsal root ganglia (DRG) increased, but the expression of TRPV1 decreased in the SNI model. Both these effects were ameliorated by EA, with 2-Hz stimulation having a stronger effect than 100-Hz stimulation. Blocking either TRPV1 or P2X3 specific siRNAs attenuated the decreased PWT induced by SNI. Administration of either a TRPV1 or P2X3 agonist inhibited EA analgesia. 2- and 100-Hz EA similarly induced analgesic effects in SNI. This effect was related to up-regulation and down-regulation, respectively, of cytosol protein expression of P2X3 and TRPV1 in L4-L6 DRG, with 2 Hz having a better effect than 100 Hz.

Association of statin induced reduction in serum coenzyme Q10 level and conduction deficits in motor and sensory nerves: An observational cross-sectional study

This study was designed to assess long-term reinnervation of end-to-side neurorrhaphy in the rat. The cut right peroneal nerve was repaired and sutured to the side of the intact tibial nerve. Both the extent of reinnervation and the integrity of the intact donor nerve were evaluated in 48 Sprague-Dawley rats randomly treated with fresh or delayed nerve repair with or without perineurotomy. Evaluations included nerve conduction velocity (NCV) of both the peroneal and tibial nerves, dry muscle weight, and histologic examination (neurofilament stain and morphometric assessment) at 8 and 12 months postoperatively. Although animals treated with perineurotomy tended to have better NCV and dry muscle weight recovery than those without, the difference was not statistically significant. No difference was observed between fresh and predegenerated nerve repair. The mean total (all four subgroups) NCV recovery rates were 87 percent and 94 percent for the peroneal nerve, and 93 percent and 95 percent for the tibial nerve, compared to the contralateral intact nerves, at 8 and 12 months, respectively. Tibialis anterior muscle mass measurements revealed a recovery in dry muscle weight of about 85 percent and 89 percent at 8 and 12 months, respectively, compared to the intact contralateral tibialis anterior muscles. Histologic studies with neurofilament staining revealed numerous axons at the distal end of the peroneal nerve in all groups, indicative of myelinated axonal regeneration. Morphometric analysis demonstrated that the presence of a window in the perioneurium improved the histologic picture. The mean number of myelinated fibers at 12 months postoperatively was significantly higher in animals with a perineurotomy window (compared to without) in both fresh and predegenerated nerve repair subgroups, respectively (p <0.05). These results indicated that end-to-side neurorrhaphy permits axonal regeneration from the intact donor nerve and is associated with satisfactory recovery. The effect of the procedure on the donor nerve was negligible.

Superficial peroneal and sural nerve transfer to tibial nerve for restoration of plantar sensation after complex injuries of the tibial nerve: Cadaver feasibility study

BackgroundMethyl-CpG-binding protein 2 (MeCP2), a protein with affinity for methylated cytosines, is crucial for neuronal development and function. MeCP2 regulates gene expression through activation, repression and chromatin remodeling. Mutations in MeCP2 cause Rett syndrome, and these patients display impaired nociception. We observed an increase in MeCP2 expression in mouse dorsal root ganglia (DRG) after peripheral nerve injury. The functional implication of increased MeCP2 is largely unknown. To identify regions of the genome bound by MeCP2 in the DRG and the changes induced by nerve injury, a chromatin immunoprecipitation of MeCP2 followed by sequencing (ChIP-seq) was performed 4 weeks after spared nerve injury (SNI).ResultsWhile the number of binding sites across the genome remained similar in the SNI model and sham control, SNI induced the redistribution of MeCP2 to transcriptionally relevant regions. To determine how differential binding of MeCP2 can affect gene expression in the DRG, we investigated mmu-miR-126, a microRNA locus that had enriched MeCP2 binding in the SNI model. Enriched MeCP2 binding to miR-126 locus after nerve injury repressed miR-126 expression, and this was not mediated by alterations in methylation pattern at the miR-126 locus. Downregulation of miR-126 resulted in the upregulation of its two target genes Dnmt1 and Vegfa in Neuro 2A cells and in SNI model compared to control. These target genes were significantly downregulated in Mecp2-null mice compared to wild-type littermates, indicating a regulatory role for MeCP2 in activating Dnmt1 and Vegfa expression. Intrathecal delivery of miR-126 was not sufficient to reverse nerve injury-induced mechanical and thermal hypersensitivity, but decreased Dnmt1 and Vegfa expression in the DRG.ConclusionsOur study shows a regulatory role for MeCP2 in that changes in global redistribution can result in direct and indirect modulation of gene expression in the DRG. Alterations in genome-wide binding of MeCP2 therefore provide a molecular basis for a better understanding of epigenetic regulation-induced molecular changes underlying nerve injury.Electronic supplementary materialThe online version of this article (doi:10.1186/s13072-016-0073-5) contains supplementary material, which is available to authorized users.

Ranolazine attenuates behavioral signs of neuropathic pain

After peripheral nerve lesions, some axotomized afferent neurons develop ongoing discharges that originate in the dorsal root ganglion (DRG). We investigated in vivo which functional types of afferent neurons contributed to this ectopic activity. Six to twelve days after the gastrocnemius soleus (GS) nerve supplying skeletal muscle and the sural (SU) nerve supplying skin had been transected (experimental group E1), 20.4% of afferent neurons with myelinated axons projecting into the GS nerve produced ongoing discharges of irregular or bursting pattern. In contrast, all SU neurons were silent. Additional transection of peroneal and tibial nerves (group E2) induced ongoing activity in a similar percentage of GS neurons (22.1%), but their mean discharge frequency was higher (6.0 vs 2.7 Hz), and more of them exhibited bursting discharges (63 vs 17%). When the GS nerve had been left intact while tibial, peroneal, and SU nerve had been transected (group E3), 18.8% of unlesioned GS neurons developed ongoing discharges at a mean frequency of 6.1 Hz; most of them exhibited a bursting pattern. Without a preceding nerve lesion, almost no GS neuron (1.1%) fired spontaneously. Most afferent neurons with ongoing activity had an axonal conduction velocity of 5-30 m/sec indicating that some of these neurons may have had nociceptive function. These findings provide the first evidence that after peripheral nerve injury both axotomized as well as intact afferent neurons supplying skeletal muscle but not skin afferents generate ongoing activity within the DRG, probably because of a yet unknown signal in the DRG triggered by axotomy.

One of the techniques used for treating facial paralysis is double muscle innervation using end-to-end neurorrhaphy with sectioning of healthy nerves. The aim of this study was to evaluate whether double muscle innervation by means of end-to-side neurorrhaphy could occur, with maintenance of muscle innervation. Experimental study developed at the Experimental Research Center, Faculdade de Medicina de Botucatu, Unesp. One hundred rats were allocated to five groups as follows: G1, control group; G2, the peroneal nerve was sectioned; G3, the tibial nerve was transected and the proximal stump was end-to-side sutured to the intact peroneal nerve; G4, 120 days after the G3 surgery, the peroneal nerve was sectioned proximally to the neurorrhaphy; G5, 120 days after the G3 surgery, the peroneal and tibial nerves were sectioned proximally to the neurorrhaphy. One hundred and fifty days after the surgery, G3 did not show any change in tibial muscle weight or muscle fiber diameter, but the axonal fiber diameter in the peroneal nerve distal to the neurorrhaphy had decreased. Although G4 showed atrophy of the cranial tibial muscle 30 days after sectioning the peroneal nerve, the electrophysiological test results and axonal diameter measurement confirmed that muscle reinnervation had occurred. These findings suggest that double muscle innervation did not occur through end-to-side neurorrhaphy; the tibial nerve was not able to maintain muscle innervation after the peroneal nerve had been sectioned, although muscle reinnervation was found to have occurred, 30 days after the peroneal nerve had been sectioned.

The aim of this study was to elucidate the anatomical location of tibial nerve (TN) and common peroneal nerve (CPN) in the popliteal crease for specific nerve block. Fifty fresh specimens from 27 adult Korean cadavers (16 males and 11 females, age 35-87years) were investigated. Five of the 27 cadavers were used to determine the depths of nerves in cross-section. Tibial nerve was located 50% from the most lateral point of the popliteal crease and 1.4-cm deep to the surface. In 20% of the 50 specimens, the medial sural cutaneous nerve branched out below or at the popliteal crease, whereas the CPN was located at 26% from the most lateral point of the popliteal crease and 0.7-cm deep from the surface. Furthermore, in 6% of specimens the lateral sural cutaneous nerve branched out below or at the popliteal crease. The results concerning the location of the TN and CPN at the popliteal crease offer a good guide to optimal nerve block.

Purpose: The diagnosis of Guillain-Barre syndrome (GBS) in the very early stage may be challenging. Our aim was to report the neurophysiological abnormalities in GBS within 4 days of clinical onset. We expected that GBS will be diagnosed by the assistance of neurophysiological study in the very early stage. Methods: We prospectively recruited patients with a diagnosis of GBS discharged from First Affiliated Hospital of Xi’an Jiaotong University and Xi Jing Hospital. Patients were classified into 3 groups according to the onset of symptoms to electromyography examination interval (OEI). The neurophysiological findings were carried out using standard procedures. All patients were examined by the same experienced neurophysiologist. Results: There were not significant group differences in abnormal rate, distal motor latency (DML), motor nerve conduction velocity (MNCV), F response (FR), compound muscle action potential (CMAP), conduction block (CB), sensory nerve action potential (SNAP), and sensory nerve conduction velocity among OEI ≤4 days, 4< OEI ≤10 days, and OEI > 10 days groups. Motor nerves were more affected than sensory nerves in neurophysiological presentation in very early stage patients. The difference of motor nerves and sensory nerves was statistically significant in lower limbs, but was not in upper limbs. In motor nerve conduction studies, the abnormal rate of DML, MNCV, FR, CB was more common seen in ulnar and peroneal nerve than median and tibial nerve, the abnormal rate of CMAP was the same in ulnar, median, peroneal and tibial nerve. In sensory nerve conduction studies, the abnormal rate of ulnar nerve and median nerve was higher than the superficial peroneal nerve and sural nerve. The OEI was not correlated with the SNAP decrease rate of median (r = 0.10, p = 0.23) and ulnar (r = 0.26, p = 0.06) but was statistically correlated with sural SNAP decrease rate (r = 0.29, p = 0.04). The sural-sparing pattern phenomenon was the most commonly discovered phenomenon in very early stage patients (OEI ≤4 days), followed by patients with 4< OEI ≤10 days, ultimately found in patients with OEI > 10 days. Conclusions: We suggest performing neurophysiological examination as soon as possible for suspected GBS patients, particularly focusing on multi-spots inspection of ulnar and peroneal nerves, and paying close attention to sural-sparing patterns.

Effects of the dimeric PSD-95 inhibitor UCCB01-144 in mouse models of pain, cognition and motor function