Strain differences in autotomy in mice after peripheral nerve transection or repair

Adiponectin receptor 1-mediated stimulation of Cav3.2 channels in trigeminal ganglion neurons induces nociceptive behaviors in mice

BACKGROUND

Adipokines, including adiponectin, are implicated in nociceptive pain; however, the underlying cellular and molecular mechanisms remain unknown.

METHODS

Using electrophysiological recording, immunostaining, molecular biological approaches and animal behaviour tests, we elucidated a pivotal role of adiponectin in regulating membrane excitability and pain sensitivity by manipulating Cav3.2 channels in trigeminal ganglion (TG) neurons.

RESULTS

Adiponectin enhanced T-type Ca2+ channel currents (IT) in TG neurons through the activation of adiponectin receptor 1 (adipoR1) but independently of heterotrimeric G protein-mediated signaling. Coimmunoprecipitation revealed a physical association between AdipoR1 and casein kinase II alpha-subunits (CK2α) in the TG, and inhibiting CK2 activity by chemical inhibitor or siRNA targeting CK2α prevented the adiponectin-induced IT response. Adiponectin significantly activated protein kinase C (PKC), and this effect was abrogated by CK2α knockdown. Adiponectin increased the membrane abundance of PKC beta1 (PKCβ1). Blocking PKCβ1 pharmacologically or genetically abrogated the adiponectin-induced IT increase. In heterologous expression systems, activation of adipoR1 induced a selective enhancement of Cav3.2 channel currents, dependent on PKCβ1 signaling. Functionally, adiponectin increased TG neuronal excitability and induced mechanical pain hypersensitivity, both attenuated by T-type channel blockade. In a trigeminal neuralgia model induced by chronic constriction injury of infraorbital nerve, blockade of adipoR1 signaling suppressed mechanical allodynia, which was prevented by silencing Cav3.2.

CONCLUSION

Our study elucidates a novel signaling cascade wherein adiponectin stimulates TG Cav3.2 channels via adipoR1 coupled to a novel CK2α-dependent PKCβ1. This process induces neuronal hyperexcitability and pain hypersensitivity. Insight into adipoR-Cav3.2 signaling in sensory neurons provides attractive targets for pain treatment.

Foramen lacerum impingement of trigeminal nerve root as a rodent model for trigeminal neuralgia

Trigeminal neuralgia (TN) is a classic neuralgic pain condition with distinct clinical characteristics. Modeling TN in rodents is challenging. Recently, we found that a foramen in the rodent skull base, the foramen lacerum, provides direct access to the trigeminal nerve root. Using this access, we developed a foramen lacerum impingement of trigeminal nerve root (FLIT) model and observed distinct pain-like behaviors in rodents, including paroxysmal asymmetric facial grimaces, head tilt when eating, avoidance of solid chow, and lack of wood chewing. The FLIT model recapitulated key clinical features of TN, including lancinating pain-like behavior and dental pain-like behavior. Importantly, when compared with a trigeminal neuropathic pain model (infraorbital nerve chronic constriction injury [IoN-CCI]), the FLIT model was associated with significantly higher numbers of c-Fos-positive cells in the primary somatosensory cortex (S1), unraveling robust cortical activation in the FLIT model. On intravital 2-photon calcium imaging, synchronized S1 neural dynamics were present in the FLIT but not the IoN-CCI model, revealing differential implication of cortical activation in different pain models. Taken together, our results indicate that FLIT is a clinically relevant rodent model of TN that could facilitate pain research and therapeutics development.

Evaluation of peripheral nerve regeneration in Murphy Roths Large mouse strain following transection injury

Aim: Murphy Roths Large (MRL/MpJ) mice have demonstrated the ability to heal with minimal or no scar formation in several tissue types. In order to identify a novel animal model, this study sought to evaluate whether this attribute applies to peripheral nerve regeneration. Materials & methods: This was a two-phase study. 6-week-old male mice were divided into two interventional groups: nerve repair and nerve graft. The MRL/MpJ was compared with the C57BL/6J strain for evaluation of both functional and histological outcomes. Results: MRL/MpJ strain demonstrated superior axon myelination and less scar formation, however functional outcomes did not show significant difference between strains. Conclusion: Superior histological outcomes did not translate into superior peripheral nerve regeneration in MRL/MpJ strain.

Human IL12p80 Promotes Murine Oligodendrocyte Differentiation to Repair Nerve Injury

Nerve injury of the central nervous system and the peripheral nervous system still poses a major challenge in modern clinics. Understanding the roles of neurotrophic factors and their molecular mechanisms on neuro-regeneration will not only benefit patients with neural damage but could potentially treat neurodegenerative disorders, such as amyotrophic lateral sclerosis. In this study, we showed that human IL12 p40-p40 homodimer (hIL12p80) within PLA and PLGA conduits improved sciatic nerve regeneration in mice. As such, the group of conduits with NSCs and hIL12p80 (CNI) showed the best recovery among the groups in the sciatic functional index (SFI), compound muscle action potential (CMAP), and Rotarod performance analyses. In addition, the CNI group had a faster recovery and outperformed the other groups in SFI and Rotarod performance tests beginning in the fourth week post-surgery. Immunohistochemistry showed that the CNI group increased the diameter of the newly regenerated nerve by two-fold (p < 0.01). In vitro studies showed that hIL12p80 stimulated differentiation of mouse NSCs to oligodendrocyte lineages through phosphorylation of Stat3 at Y705 and S727. Furthermore, implantation using PLGA conduits (C2.0 and C2.1) showed better recovery in the Rotarod test and CMAP than using PLA conduits in FVB mice. In B6 mice, the group with C2.1 + NSCs + hIL12p80 (C2.1NI) not only promoted sciatic functional recovery but also reduced the rate of experimental autotomy. These results suggested that hIL12p80, combined with NSCs, enhanced the functional recovery and accelerated the regeneration of damaged nerves in the sciatic nerve injury mice. Our findings could further shed light on IL12′s application not only in damaged nerves but also in rectifying the oligodendrocytes’ defects in neurodegenerative diseases, such as amyotrophic lateral sclerosis and multiple sclerosis.

Fluorescent Reporter Mice for Nerve Guidance Conduit Assessment: A High-Throughput in vivo Model

OBJECTIVE

Use of cell culture and conventional in vivo mammalian models to assess nerve regeneration across guidance conduits is resource-intensive. Herein we describe a high-throughput platform utilizing transgenic mice for stain-free axon visualization paired with rapid cryosection techniques for low-cost screening of novel bioengineered nerve guidance conduit performance.

METHODS

Interposition repair of sciatic nerve transection in mice expressing yellow fluorescent protein in peripheral neurons (Thy1.2 YFP-16) was performed with various bioengineered neural conduit compositions using a rapid sutureless entubulation technique under isoflurane anesthesia. Axonal ingrowth was assessed at 3 and 6 weeks using epifluorescent microscopy following cryosectioning.

RESULTS

Mean procedure time (incision-to-closure) was less than 2½ minutes. Direct operational costs of a 3-week experiment was calculated at $21.47 per animal. Tissue processing steps were minimized to aldehyde fixation, cryoprotection and sectioning, and rapid fluorescent dye staining for conduit visualization. Fluorescent microscopy readily resolved robust axonal sprouting at 3 weeks, with clear elucidation of ingrowth-permissive, semipermissive, or restrictive nerve guidance conduit environments.

CONCLUSION

A rapid and cost-efficient in vivo platform for screening of nerve guidance conduit performance has been described.

LEVEL OF EVIDENCE

NA. Laryngoscope, E392-E392, 2018.

Effect of nerve injury on the number of dorsal root ganglion neurons and autotomy behavior in adult Bax-deficient mice

Background

The proapoptotic molecule BAX, plays an important role in mitochondrial apoptotic pathway. Dorsal root ganglion (DRG) neurons depend on neurotrophic factors for survival at early developmental stages. Withdrawal of neurotrophic factors will induce apoptosis in DRG neurons, but this type of cell death can be delayed or prevented in neonatal Bax knockout (KO) mice. In adult animals, evidence also shows that DRG neurons are less dependent upon neurotrophic factors for survival. However, little is known about the effect of Bax deletion on the survival of normal and denervated DRG neurons in adult mice.

Methods

A unilateral sciatic nerve transection was performed in adult Bax KO mice and wild-type (WT) littermates. Stereological method was employed to quantify the number of lumbar-5 DRG neurons 1 month post-surgery. Nerve injury-induced autotomy behavior was also examined on days 1, 3, and 7 post-surgery.

Results

There were significantly more neurons in contralateral DRGs of KO mice as compared with WT mice. The number of neurons was reduced in ipsilateral DRGs in both KO and WT mice. No changes in size distributions of DRG neuron profiles were detected before or after nerve injury. Injury-induced autotomy behavior developed much earlier and was more serious in KO mice.

Conclusion

Although postnatal death or loss of DRG neurons is partially prevented by Bax deletion, this effect cannot interfere with long-term nerve injury-induced neuronal loss. The exaggerated self-amputation behavior observed in the mutant mice indicates that Bax deficiency may enhance the development of spontaneous pain following nerve injury.

The effects of picric acid (2,4,6-trinitrophenol) and a bite-deterrent chemical (denatonium benzoate) on autotomy in rats after peripheral nerve lesion

Denervation of the hind limb is a technique used to study peripheral nerve regeneration. Autotomy or autophagia is an undesirable response to denervation in such studies. Application of a commercially available lotion used to deter nail biting in humans reduced autotomy in rats after denervation but did not completely prevent it. In this study, this authors evaluated the application of picric acid to prevent autotomy in rats in peripheral nerve experiments. They carried out sciatic nerve transection in 41 adult female Wistar rats and then applied either bite-deterrent lotion (n = 26) or saturated picric acid solution (n = 15) topically to the affected hind limb immediately after surgery and every day for 1 month. Autotomy scores were lower for rats treated with picric acid than for rats treated with bite-deterrent lotion 1 week and 2 weeks after surgery but were not different between the two groups 4 weeks after surgery. The authors conclude that application of picric acid could be used as an alternative strategy to prevent autotomy in peripheral nerve studies.

Double gene therapy with granulocyte colony-stimulating factor and vascular endothelial growth factor acts synergistically to improve nerve regeneration and functional outcome after sciatic nerve injury in mice

Peripheral-nerve injuries are a common clinical problem and often result in long-term functional deficits. Reconstruction of peripheral-nerve defects is currently undertaken with nerve autografts. However, there is a limited availability of nerves that can be sacrificed and the functional recovery is never 100% satisfactory. We have previously shown that gene therapy with vascular endothelial growth factor (VEGF) significantly improved nerve regeneration, neuronal survival, and muscle activity. Our hypothesis is that granulocyte colony-stimulating factor (G-CSF) synergizes with VEGF to improve the functional outcome after sciatic nerve transection. The left sciatic nerves and the adjacent muscle groups of adult mice were exposed, and 50 or 100 μg (in 50 μl PBS) of VEGF and/or G-CSF genes was injected locally, just below the sciatic nerve, and transferred by electroporation. The sciatic nerves were transected and placed in an empty polycaprolactone (PCL) nerve guide, leaving a 3-mm gap to challenge nerve regeneration. After 6 weeks, the mice were perfused and the sciatic nerve, the dorsal root ganglion (DRG), the spinal cord and the gastrocnemius muscle were processed for light and transmission electron microscopy. Treated animals showed significant improvement in functional and histological analyses compared with the control group. However, the best results were obtained with the G-CSF+VEGF-treated animals: quantitative analysis of regenerated nerves showed a significant increase in the number of myelinated fibers and blood vessels, and the number of neurons in the DRG and motoneurons in the spinal cord was significantly higher. Motor function also showed that functional recovery occurred earlier in animals receiving G-CSF+VEGF-treatment. The gastrocnemius muscle showed an increase in weight and in the levels of creatine phosphokinase, suggesting an improvement of reinnervation and muscle activity. These results suggest that these two factors acted synergistically and optimized the nerve repair potential, improving regeneration after a transection lesion.

Comparison of Biodegradable Conduits within Aged Rat Sciatic Nerve Defects

BACKGROUND

Considering that little is known about the peripheral nerve regenerative capacity of elderly patients, the authors studied nerve regenerative capacity in aged rats and compared the effect of three synthetic nerve guides with different material characteristics and porosity. The authors hypothesized that the use of a biodegradable composite nerve guide (CultiGuides) would promote nerve regeneration and functional recovery in a manner similar to treatment with autografts or U.S. Food and Drug Administration-approved polyglycolic acid Neurotubes in an aged rat sciatic nerve defect model.

METHODS

Aged Sprague-Dawley rats (11 months old) underwent a 1-cm sciatic nerve resection in the right leg [group 1, control (contralateral leg samples), n = 10; group 2, negative (nerve gap defect), n = 6; group 3, autograft, n = 10; group 4, polycaprolactone, n = 10; group 5, CultiGuides, n = 10; and group 6, Neurotube, n = 10].

RESULTS

After 12 weeks, the negative group did not demonstrate any nerve regeneration. In the regenerated and distal nerve, all treated groups had increased myelinated areas compared with the negative control. In the regenerated nerve, there was a significant increase in myelination in the Neurotube group compared with the polycaprolactone group (p < 0.001). However, in the distal nerve, there were no differences among the treatment groups. Walking track analyses and gastrocnemius muscle weight ratios were not different among treatment groups 3 through 6.

CONCLUSIONS

The results showed differences in myelination; Neurotubes promoted the highest degree of myelination (p < 0.001) as compared with all groups. The authors found no improvement in function of the repaired nerve as measured by percentage of autotomy, the sciatic function index, and gastrocnemius muscle weight. No group was able to recover function in this aged model.

Strain-dependent recovery of spontaneous hindlimb movement in spinal cord transected mice (CD1, C57BL/6, BALB/c)

Reorganization and plasticity after spinal cord injury have been recently shown to take place in sublesional neuronal networks, but the possibility of strain-dependent changes at that level has never been explored. The authors studied the spontaneous return of hindlimb movement in low-thoracic spinal cord transected (Tx) mice from 3 commonly used strains. Without intervention, most CD1, C57BL/6, and BALB/c mice displayed some hindlimb movement recovery after Tx. Although all assessment methods unanimously reported that CD1 displayed higher recovery levels than did the C57BL/6 and BALB/c, higher scores were generally found with the Antri-Orsal-Barthe (M. Antri, D. Orsal, & J. Y. Barthe, 2002) and the Average Combined Score (P. A. Guertin, 2005a) methods. Such spontaneous recovery in low-thoracic Tx mice is likely the result of neuronal plasticity at the lumbosacral spinal cord level, suggesting that these sublesional changes are strain dependent.