Reduced expression of regeneration associated genes in chronically axotomized facial motoneurons

Nerve Wrap for Local Delivery of FK506/Tacrolimus Accelerates Nerve Regeneration

Peripheral nerve injuries (PNIs) occur frequently and can lead to devastating and permanent sensory and motor function disabilities. Systemic tacrolimus (FK506) administration has been shown to hasten recovery and improve functional outcomes after PNI repair. Unfortunately, high systemic levels of FK506 can result in adverse side effects. The localized administration of FK506 could provide the neuroregenerative benefits of FK506 while avoiding systemic, off-target side effects. This study investigates the utility of a novel FK506-impregnated polyester urethane urea (PEUU) nerve wrap to treat PNI in a previously validated rat infraorbital nerve (ION) transection and repair model. ION function was assessed by microelectrode recordings of trigeminal ganglion cells responding to controlled vibrissae deflections in ION-transected and -repaired animals, with and without the nerve wrap. Peristimulus time histograms (PSTHs) having 1 ms bins were constructed from spike times of individual single units. Responses to stimulus onsets (ON responses) were calculated during a 20 ms period beginning 1 ms after deflection onset; this epoch captures the initial, transient phase of the whisker-evoked response. Compared to no-wrap controls, rats with PEUU-FK506 wraps functionally recovered earlier, displaying larger response magnitudes. With nerve wrap treatment, FK506 blood levels up to six weeks were measured nearly at the limit of quantification (LOQ ≥ 2.0 ng/mL); whereas the drug concentrations within the ION and muscle were much higher, demonstrating the local delivery of FK506 to treat PNI. An immunohistological assessment of ION showed increased myelin expression for animals assigned to neurorrhaphy with PEUU-FK506 treatment compared to untreated or systemic-FK506-treated animals, suggesting that improved PNI outcomes using PEUU-FK506 is mediated by the modulation of Schwann cell activity.

Brief Electrical Stimulation Promotes Recovery after Surgical Repair of Injured Peripheral Nerves

Injured peripheral nerves regenerate their axons in contrast to those in the central nervous system. Yet, functional recovery after surgical repair is often disappointing. The basis for poor recovery is progressive deterioration with time and distance of the growth capacity of the neurons that lose their contact with targets (chronic axotomy) and the growth support of the chronically denervated Schwann cells (SC) in the distal nerve stumps. Nonetheless, chronically denervated atrophic muscle retains the capacity for reinnervation. Declining electrical activity of motoneurons accompanies the progressive fall in axotomized neuronal and denervated SC expression of regeneration-associated-genes and declining regenerative success. Reduced motoneuronal activity is due to the withdrawal of synaptic contacts from the soma. Exogenous neurotrophic factors that promote nerve regeneration can replace the endogenous factors whose expression declines with time. But the profuse axonal outgrowth they provoke and the difficulties in their delivery hinder their efficacy. Brief (1 h) low-frequency (20 Hz) electrical stimulation (ES) proximal to the injury site promotes the expression of endogenous growth factors and, in turn, dramatically accelerates axon outgrowth and target reinnervation. The latter ES effect has been demonstrated in both rats and humans. A conditioning ES of intact nerve days prior to nerve injury increases axonal outgrowth and regeneration rate. Thereby, this form of ES is amenable for nerve transfer surgeries and end-to-side neurorrhaphies. However, additional surgery for applying the required electrodes may be a hurdle. ES is applicable in all surgeries with excellent outcomes.

The Dynamics of Nerve Degeneration and Regeneration in a Healthy Milieu and in Diabetes

Appropriate animal models, mimicking conditions of both health and disease, are needed to understand not only the biology and the physiology of neurons and other cells under normal conditions but also under stress conditions, like nerve injuries and neuropathy. In such conditions, understanding how genes and different factors are activated through the well-orchestrated programs in neurons and other related cells is crucial. Knowledge about key players associated with nerve regeneration intended for axonal outgrowth, migration of Schwann cells with respect to suitable substrates, invasion of macrophages, appropriate conditioning of extracellular matrix, activation of fibroblasts, formation of endothelial cells and blood vessels, and activation of other players in healthy and diabetic conditions is relevant. Appropriate physical and chemical attractions and repulsions are needed for an optimal and directed regeneration and are investigated in various nerve injury and repair/reconstruction models using healthy and diabetic rat models with relevant blood glucose levels. Understanding dynamic processes constantly occurring in neuropathies, like diabetic neuropathy, with concomitant degeneration and regeneration, requires advanced technology and bioinformatics for an integrated view of the behavior of different cell types based on genomics, transcriptomics, proteomics, and imaging at different visualization levels. Single-cell-transcriptional profile analysis of different cells may reveal any heterogeneity among key players in peripheral nerves in health and disease.

The Effect of Electrical Stimulation on Nerve Regeneration Following Peripheral Nerve Injury

Peripheral nerve injuries (PNI) are common and often result in lifelong disability. The peripheral nervous system has an inherent ability to regenerate following injury, yet complete functional recovery is rare. Despite advances in the diagnosis and repair of PNIs, many patients suffer from chronic pain, and sensory and motor dysfunction. One promising surgical adjunct is the application of intraoperative electrical stimulation (ES) to peripheral nerves. ES acts through second messenger cyclic AMP to augment the intrinsic molecular pathways of regeneration. Decades of animal studies have demonstrated that 20 Hz ES delivered post-surgically accelerates axonal outgrowth and end organ reinnervation. This work has been translated clinically in a series of randomized clinical trials, which suggest that ES can be used as an efficacious therapy to improve patient outcomes following PNIs. The aim of this review is to discuss the cellular physiology and the limitations of regeneration after peripheral nerve injuries. The proposed mechanisms of ES protocols and how they facilitate nerve regeneration depending on timing of administration are outlined. Finally, future directions of research that may provide new perspectives on the optimal delivery of ES following PNI are discussed.

The Effects of Exercise on Cerebellar Growth-Associated Protein 43 and Adenylyl Cyclase- Associated Protein 1 Gene Expression and Proteins in Diabetic-Induced Neuropathy and Healthy Male Wistar Rats

BACKGROUND

The effect of exercise on the cerebellum cells in diabetic-induced neuropathy and healthy situations is not clear yet. Growth-associated protein 43 (GAP-43) and adenylyl cyclase-associated protein 1 (CAP-1) proteins can restore nerve cells. This study aimed to investigate the effect of aerobic exercise on GAP-43 and CAP-1 and their mRNA in the cerebellar tissue of diabetic-induced neuropathy and healthy Wistar rats.

METHODS

Around 40 healthy male Wistar rats with a mean weight of 271 ± 11.2 g were divided randomly into four groups; healthy aerobic exercise, diabetic-aerobic exercise, healthy-control, and diabetic-control. The exercise group performed aerobic exercise 5 days per week for 6 weeks.

RESULTS

Exercise increased CAP1 protein in the cerebellum tissue of healthy (P = 0.002) and diabetic (P = 0.002) groups compared with matched control groups. The effect of exercise on CAP1 was greater in diabetic compared with the healthy group (P = 0.002). The expression of CAP1 mRNA in the cerebellum was higher in the healthy exercise compared with the healthy control group (P = 0.002) and in the healthy exercise compared with the diabetic exercise group (P = 0.026). GAP43 protein was lower in the healthy exercise compared with the healthy control group (P = 0.002) while it was higher in diabetic exercise compared to the healthy exercise group (P = 0.002). Expression of GAP43 mRNA in the cerebellum was higher in the healthy (P = 0.002) and diabetic (P = 0.002) exercise groups compared to non-exercise matched groups and in the diabetic control group compared with the healthy control group (P = 0.002). Exercise improved latency in diabetic (P = 0.001) and healthy exercise groups (P = 0.02). No significant difference was found in blood glucose between exercise and control groups (P > 0.05).

CONCLUSION

Exercise improved cerebellar functions in healthy and diabetic rats, probably mediating by CAP1 protein, even without changing blood glucose.

The Regenerative Potential of Facial Nerve Motoneurons following Chronic Axotomy in Rats

Background

The precise mechanisms of nerve regeneration remain unclear. The potential of facial nerve regeneration and probable mechanisms involved following chronic facial nerve injury should be further studied.

Methods

Adult male Wistar rats were used to model either (i) facial nerve injury (axotomy) or (ii) reinjury (chronic axotomy followed by a second axotomy within 5 months). The rats were housed in the animal facility of the Eye and ENT Hospital of Shanghai Medical School, Fudan University (Shanghai, China). Expression of Shh (sonic hedgehog) and growth-associated protein 43 (GAP43, a neuronal marker) was detected in bilateral facial nuclei using reverse transcriptase PCR, western blotting analysis, and immunohistochemistry. The number of surviving motoneurons was quantified, and facial nerve regeneration was examined using transmission electron microscopy.

Results

Reinjury of the facial nerve 12 weeks after the first axotomy resulted in upregulation of GAP43 mRNA and protein expression in neurons ipsilateral to the axotomy; immunohistochemistry revealed that Shh expression was higher compared with control side facial nuclei at the same time point. GAP43 expression subsequently decreased.

Conclusion

The greatest regeneration potential of the facial nerve occurred within 5 months following chronic axotomy in rats, and regeneration may involve the Shh signaling pathway.

The experimental research on neuroplasticity in rats' hippocampus subjected to chronic cerebral hypoperfusion and interfered by Modified Dioscorea Pills

Background

Chronic Cerebral Hypoperfusion (CCH) is a common, crucial and tough problem for old people. It easily leads to Lacunar Infarction and even Vascular Dementia (VD). Western medicine has the advantage to relieve some VD symptoms but fails to cure it. Some classic Chinese medicines have good efficacies to treat and delay the cerebral functional decline resulted from CCH. Among them Modified Dioscorea Pills (MDP) has been proven to have a convincing effect in curing VD. So far the knowledge about neuroplasticity in CCH is little known and the underlying interfered mechanism by MDP on neuroplasticity has not yet been explored. This study explores the changes of neuroplasticity involving neurogenesis, angiogenesis and synaptogenesis in CCH and interfered by MDP.

Methods

40 male SD rats were divided into the Sham operated Group, the Model Group and the MDP Group according to a Random Number Table. Bilateral Common Carotid Arteries Occlusion (BCCAO) was adopted to prepare CCH models. MDP condense decoction had been administered by gavage to rats in the MDP Group (10g·Kg-1·d-1) for 45 days; Rats in the other two groups were accepted normal salts as substitution with same dosage and course. Through Morris Water Maze (MWM) test, pathological observation of hippocampus, ultrastructural study on synapse, Real Time Polymerase Chain Reaction (RT-PCR) and immunohistochemistry detection, the capacities of intelligence of rats, the morphological character of hippocampus CA1 zone and the synapse associated protein and gene such as Growth Associated Protein (GAP-43) mRNA, Vascular Endothelial Growth Factor (VEGF) mRNA, Microtubule-associated Protein (MAP)-2, Synaptophysin (SYP), Postsynaptic Density protein (PSD)-95 and Micro Vessel Density (MVD) were determined. Through one-way ANOVA the data was analyzed and when P＜0.05 the result was considered significant.

Results

Compared to the Model Group, rats in the MDP Group achieved much better behavioral performance (P＜0.05); more neurons and more synapses regenerated; the expression of SYP, PSD-95and MAP-2 up-regulated (P＜0.05); The expressions of GAP-43 mRNA and VEGF mRNA in the Model Group were higher than those in the Sham operated Group (P＜0.05), but they reached the highest in the MDP Group (P＜0.05); The count of MVD in the Sham operated Group is the lowest, it is higher in the MDP Group and it reaches highest in the Model Group (P＜0.05).

Conclusions

Some key genes promoting neuroplasticity such as GAP-43 mRNA and VEGF mRNA remarkably up-regulated in CCH, they only boost angiogenesis but fail to facilitate neurogenesis and synaptogenesis in CCH. However, accompanied by furtherly up-regulation of these two key genes, MDP obviously improves neurogenesis, synaptogenesis and temperate angiogenesis in CCH which may be underlying its good efficacy.

Various exercise intensities differentially regulate GAP-43 and CAP-1 expression in the rat hippocampus

Exercise intensity is known to affect neuroplasticity. Although corticosterone and lactate levels have been linked to neuroplasticity, the effect of different endurance exercise intensity-dependent production of these biochemicals on the behaviour of hippocampal growth cone markers remains incompletely explored. Here, we investigated the effects of three different endurance treadmill training episodes for six weeks on GAP-43 and CAP-1 expression in the hippocampus of adult male Wistar rats. Our findings showed that mild exercise intensity (MEI) with a lactate production slightly higher than the lactate threshold (LT) is the optimal form of physical activity for elevating GAP-43 without changing CAP-1 expression. It was further observed that high exercise intensity (HEI) with the highest level of corticosterone and lactate production, reduced GAP-43 expression, yet increased CAP-1 expression in the hippocampus. Like HEI, we further identified similar expression patterns for these markers in low exercise intensity (LEI) with blood lactate production below LT and corticosterone level similar to MEI. The findings suggested that in high-intensity exercise, the negative pattern of hippocampal neuroplasticity depends on both corticosterone and lactate levels, whereas in low-intensity exercise, the most important factor determining this negative pattern is the lactate level. Generally, MEI with a lactate production of slightly higher than LT is the most optimal intensity for improving hippocampal neuroplasticity.

Resveratrol inhibits paclitaxel-induced neuropathic pain by the activation of PI3K/Akt and SIRT1/PGC1α pathway

Background

Phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) is one of the essential signaling pathways for the development and maintenance of neuropathic pain.

Objective

To investigate the effect of resveratrol (RES) on paclitaxel-induced neuropathic pain in rats and elucidate the underlying molecular mechanisms.

Method

Male Sprague Dawley rats were randomly divided into seven groups (n=10/group): Group C, Group P, Group R, Group R+P, Group LY + R+P, Group LY (the specific inhibitor of PI3K), Group E (the specific inhibitor of sirtuin 1 [SIRT1]). Paw withdrawal mechanical threshold (PWT) and thermal withdrawal latency (TWL) were recorded. Mitochondrial histomorphology was performed by transmission electron microscope. PI3K, p-Akt, and t-Akt expressions were tested using immunohistochemistry. Western blot was used to detect p-Akt, t-Akt, SIRT1, and PGC1α expressions. The apoptosis in the striatum, spinal dorsal horns (SDH), and dorsal root ganglions (DRG) tissues was assayed by TUNEL. ELISA was used to detect the contents of IL-β, IL-10, malondialdehyde (MDA), and superoxide dismutase (SOD) in striatum, SDH, and DRG tissues.

Results

Compared to the control group, PWT and TWL in the P and LY +R+P groups were significantly decreased on 8th and 14th day after paclitaxel administration (P<0.05). The expressions of p-Akt, SIRT1, and PGC1α were decreased in paclitaxel-induced neuropathic rats; however, the expressions of p-Akt, SIRT1, and PGC1α were significantly increased after RES treatment (P<0.05). Furthermore, the expression of p-Akt was decreased by LY294002 (P<0.05), and amount of SIRT1 and PGC1α expression was inhibited by EX-527 (P<0.05). The t-Akt level was not significantly changed in all groups. RES prevented paclitaxel-induced mitochondrial damage by PI3K/Akt. RES improves the pain symptoms of paclitaxel neuralgia rats by increasing the IL-10 and decreasing the expression of IL-1β. RES increases the SOD and reduces the MDA. RES reduces apoptosis by SIRT1/PGC1α signal pathway.

Conclusion

Our results suggest that RES may inhibit paclitaxel-induced neuropathic pain via PI3K/Akt and SIRT1/PGC1α pathways.

Adsorptive properties of graphene oxide on vitamin B12 and their effect on the promotion of peripheral nerve regeneration

OBJECTIVES

To observe whether Graphene oxide (GO) can absorb vitamin B12 (VB12) and Decellularized scaffold - acellular nerve allograft (ANA) modified GO-VB12 promote the repair of ischiadic nervus defects in a rat model.

METHODS

The adsorption of GO on vitamin and the optimum adsorption conditions were investigated by single factor experiment. The adsorption properties of the material were observed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) to determine the success of adsorption on VB12. GO-VB12-ANA was prepared by vibration mixing method and bridged to injured ischiadic nervus. The nerve action potential, wet weight ratio of gastrocnemius muscle and the expression of GAP-43 were investigated by contrast test to detect its effect on nerve regeneration.

RESULTS

The optimized adsorption conditions for GO on VB12 solution were listed as follows: adsorbent dosage was 6 mg, shaking time was 70 min, the pH value was 6, the optimum concentration of VB12 was 50 mg/L and the theoretical saturated adsorption capacity was 21.51 mg/g. The nerve action potential, wet weight ratio of gastrocnemius muscle and the expression of GAP-43 in nerve fiber of GO-VB12-ANA group were close to the normal values and significantly higher than those of ANA and rotation group.

CONCLUSIONS

Based on the adsorption function of GO on VB12, GO-VB12-ANA can promote regeneration of injured ischiadic nervus, providing the experimental basis for the clinical application of nanomaterials.

Selected gene profiles of stressed NSC-34 cells and rat spinal cord following peripheral nerve reconstruction and minocycline treatment

The present study was conducted to investigate the effects of minocycline on the expression of selected transcriptional and translational profiles in the rat spinal cord following sciatic nerve (SNR) transection and microsurgical coaptation. The mRNA and protein expression levels of B cell lymphoma-2 (Bcl-2), Bcl-2-associated X protein (Bax), caspase-3, major histocompatibility complex I (MHC I), tumor necrosis factor-α (TNF-α), activating transcription factor 3 (ATF3), vascular endothelial growth factor (VEGF), matrix metalloproteinase 9 (MMP9), and growth associated protein-43 (GAP-43) were monitored in the rat lumbar spinal cord following microsurgical reconstruction of the sciatic nerves and minocycline treatment. The present study used semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. As a PCR analysis of spinal cord tissue enabled the examination of the expression patterns of all cell types including glia, the motorneuron-like NSC-34 cell line was used to investigate expression level changes in motorneurons. As stressors, oxygen glucose deprivation (OGD) and lipopolysaccharide (LPS) treatment were performed. SNR did not induce significant degeneration of ventral horn motorneurons, whereas microglia activation and synaptic terminal retraction were detectable. All genes were constitutively expressed at the mRNA and protein levels in untreated spinal cord and control cells. SNR significantly increased the mRNA expression levels of all genes, albeit only temporarily. In all genes except MMP9 and GAP-43, the induction was seen ipsilaterally and contralaterally. The effects of minocycline were moderate. The expression levels of MMP9, TNF-α, MHC I, VEGF, and GAP-43 were reduced, whereas those of Bax and Bcl-2 were unaffected. OGD, but not LPS, was toxic for NSC-34 cells. No changes in the expression levels of Bax, caspase-3, MHC I or ATF3 were observed. These results indicated that motorneurons were not preferentially or solely responsible for SNR-mediated upregulation of these genes. MMP9, TNF-α, VEGF and Bcl-2 were stress-activated. These results suggest that a substantial participation of motorneurons in gene expression levels in vivo. Minocycline was also shown to have inhibitory effects. The nuclear factor-κB signalling pathway may be a possible target of minocycline.

Nerve Regeneration: Understanding Biology and Its Influence on Return of Function After Nerve Transfers

Poor functional outcomes are frequent after peripheral nerve injuries despite the regenerative support of Schwann cells. Motoneurons and, to a lesser extent, sensory neurons survive the injuries but outgrowth of axons across the injury site is slow. The neuronal regenerative capacity and the support of regenerating axons by the chronically denervated Schwann cells progressively declines with time and distance of the injury from the denervated targets. Strategies, including brief low-frequency electrical stimulation that accelerates target reinnervation and functional recovery, and the insertion of cross-bridges between a donor nerve and a recipient denervated nerve stump, are effective in promoting functional outcomes after complete and incomplete injuries.

Electrical Stimulation to Enhance Axon Regeneration After Peripheral Nerve Injuries in Animal Models and Humans

Injured peripheral nerves regenerate their lost axons but functional recovery in humans is frequently disappointing. This is so particularly when injuries require regeneration over long distances and/or over long time periods. Fat replacement of chronically denervated muscles, a commonly accepted explanation, does not account for poor functional recovery. Rather, the basis for the poor nerve regeneration is the transient expression of growth-associated genes that accounts for declining regenerative capacity of neurons and the regenerative support of Schwann cells over time. Brief low-frequency electrical stimulation accelerates motor and sensory axon outgrowth across injury sites that, even after delayed surgical repair of injured nerves in animal models and patients, enhances nerve regeneration and target reinnervation. The stimulation elevates neuronal cyclic adenosine monophosphate and, in turn, the expression of neurotrophic factors and other growth-associated genes, including cytoskeletal proteins. Electrical stimulation of denervated muscles immediately after nerve transection and surgical repair also accelerates muscle reinnervation but, at this time, how the daily requirement of long-duration electrical pulses can be delivered to muscles remains a practical issue prior to translation to patients. Finally, the technique of inserting autologous nerve grafts that bridge between a donor nerve and an adjacent recipient denervated nerve stump significantly improves nerve regeneration after delayed nerve repair, the donor nerves sustaining the capacity of the denervated Schwann cells to support nerve regeneration. These reviewed methods to promote nerve regeneration and, in turn, to enhance functional recovery after nerve injury and surgical repair are sufficiently promising for early translation to the clinic.

Modulation of Matrix Metalloproteinases Activity in the Ventral Horn of the Spinal Cord Re-stores Neuroglial Synaptic Homeostasis and Neurotrophic Support following Peripheral Nerve Injury

Modulation of extracellular matrix (ECM) remodeling after peripheral nerve injury (PNI) could represent a valid therapeutic strategy to prevent maladaptive synaptic plasticity in central nervous system (CNS). Inhibition of matrix metalloproteinases (MMPs) and maintaining a neurotrophic support could represent two approaches to prevent or reduce the maladaptive plastic changes in the ventral horn of spinal cord following PNI. The purpose of our study was to analyze changes in the ventral horn produced by gliopathy determined by the suffering of motor neurons following spared nerve injury (SNI) of the sciatic nerve and how the intrathecal (i.t.) administration of GM6001 (a MMPs inhibitor) or the NGF mimetic peptide BB14 modulate these events. Immunohistochemical analysis of spinal cord sections revealed that motor neuron disease following SNI was associated with increased microglial (Iba1) and astrocytic (GFAP) response in the ventral horn of the spinal cord, indicative of reactive gliosis. These changes were paralleled by decreased glial aminoacid transporters (glutamate GLT1 and glycine GlyT1), increased levels of the neuronal glutamate transporter EAAC1, and a net increase of the Glutamate/GABA ratio, as measured by HPLC analysis. These molecular changes correlated to a significant reduction of mature NGF levels in the ventral horn. Continuous i.t. infusion of both GM6001 and BB14 reduced reactive astrogliosis, recovered the expression of neuronal and glial transporters, lowering the Glutamate/GABA ratio. Inhibition of MMPs by GM6001 significantly increased mature NGF levels, but it was absolutely ineffective in modifying the reactivity of microglia cells. Therefore, MMPs inhibition, although supplies neurotrophic support to ECM components and restores neuro-glial transporters expression, differently modulates astrocytic and microglial response after PNI.

Strategies to promote peripheral nerve regeneration: electrical stimulation and/or exercise

Enhancing the regeneration of axons is often considered to be a therapeutic target for improving functional recovery after peripheral nerve injury. In this review, the evidence for the efficacy of electrical stimulation (ES), daily exercise and their combination in promoting nerve regeneration after peripheral nerve injuries in both animal models and in human patients is explored. The rationale, effectiveness and molecular basis of ES and exercise in accelerating axon outgrowth are reviewed. In comparing the effects of ES and exercise in enhancing axon regeneration, increased neural activity, neurotrophins and androgens are considered to be common requirements. Similarly, there are sex-specific requirements for exercise to enhance axon regeneration in the periphery and for sustaining synaptic inputs onto injured motoneurons. ES promotes nerve regeneration after delayed nerve repair in humans and rats. The effectiveness of exercise is less clear. Although ES, but not exercise, results in a significant misdirection of regenerating motor axons to reinnervate different muscle targets, the loss of neuromuscular specificity encountered has only a very small impact on resulting functional recovery. Both ES and exercise are promising experimental treatments for peripheral nerve injury that seem to be ready to be translated to clinical use.

Astrocytes and Microglia-Mediated Immune Response in Maladaptive Plasticity is Differently Modulated by NGF in the Ventral Horn of the Spinal Cord Following Peripheral Nerve Injury

Reactive astrocytes and activated microglia are the key players in several pathophysiologic modifications of the central nervous system. We used the spared nerve injury (SNI) of the sciatic nerve to induce glial maladaptive response in the ventral horn of lumbar spinal cord and examine its role in the remodeling of the tripartite synapse plasticity. Imaging the ventral horn revealed that SNI was associated with both an early microglial and astrocytic activation, assessed, respectively, by analysis of Iba1 and GFAP expression. Microglia, in particular, localized peculiarly surrounding the motor neurons somata. Perineuronal astrocytes, which play a key role in maintaining the homeostasis of neuronal circuitry, underwent a substantial phenotypic change following peripheral axotomy, producing reactive gliosis. The gliosis was associated with the reduction of glial aminoacid transporters (GLT1 and GlyT1) and increase of neuronal glutamate transporter EAAC1. Although the expression of GABAergic neuronal marker GAD65/67 showed no change, glutamate increase, as demonstrated by HPLC analysis, shifted the excitatory/inhibitory balance as showed by the net increase of the glutamate/GABA ratio. Moreover, endogenous NGF levels were altered in SNI animals and not restored by the intrathecal NGF administration. This treatment reverted phenotypic changes associated with reactive astrocytosis, but failed to modify microglia activation. These findings on one hand confirm the correlation between gliopathy and maladaptive plasticity of the spinal synaptic circuitry, on the other hand add new data concerning the complex peculiar behavior of different glial cells in neuronal degenerative processes, defining a special role of microglia in sustaining the inflammatory response.

Brief electrical stimulation improves nerve regeneration after delayed repair in Sprague Dawley rats

Functional recovery after peripheral nerve injury and surgical repair declines with time and distance because the injured neurons without target contacts (chronic axotomy) progressively lose their regenerative capacity and chronically denervated Schwann cells (SCs) atrophy and fail to support axon regeneration. Findings that brief low frequency electrical stimulation (ES) accelerates axon outgrowth and muscle reinnervation after immediate nerve surgery in rats and human patients suggest that ES might improve regeneration after delayed nerve repair. To test this hypothesis, common peroneal (CP) neurons were chronically axotomized and/or tibial (TIB) SCs and ankle extensor muscles were chronically denervated by transection and ligation in rats. The CP and TIB nerves were cross-sutured after three months and subjected to either sham or one hour 20Hz ES. Using retrograde tracing, we found that ES significantly increased the numbers of both motor and sensory neurons that regenerated their axons after a three month period of chronic CP axotomy and/or chronic TIB SC denervation. Muscle and motor unit forces recorded to determine the numbers of neurons that reinnervated gastrocnemius muscle demonstrated that ES significantly increased the numbers of motoneurons that reinnervated chronically denervated muscles. We conclude that electrical stimulation of chronically axotomized motor and sensory neurons is effective in accelerating axon outgrowth into chronically denervated nerve stumps and improving target reinnervation after delayed nerve repair. Possible mechanisms for the efficacy of ES in promoting axon regeneration and target reinnervation after delayed nerve repair include the upregulation of neurotrophic factors.