Delayed manipulation of regeneration within injured peripheral axons.

While several new translational strategies to enhance regrowth of peripheral axons have been identified, combined approaches with different targets are rare. Moreover, few have been studied after a significant delay when growth programs are already well established and regeneration-related protein expression has waned. Here we study two approaches, Rb1 (Retinoblastoma 1) knockdown that targets overall neuron plasticity, and near nerve insulin acting as a growth factor. Both are validated to boost regrowth only at the outset of regeneration. We show that local delivery of Rb1 siRNA alone, with electroporation to an area of prior sciatic nerve injury generated knockdown of Rb1 mRNA in ipsilateral lumbar dorsal root ganglia. While mice treated with Rb1-targeted siRNA, compared with scrambled control siRNA, starting 2 weeks after the onset of regeneration, had only limited behavioural or electrophysiological benefits, they had enhanced reinnervation of epidermal axons. We next confirmed that intrinsic Rb1 knockdown combined with exogenous insulin had dramatic synergistic impacts on the growth patterns of adult sensory neurons studied in vitro, prompting analysis of a combined approach in vivo. Using an identical delayed post-injury protocol, we noted that added insulin not only augmented epidermal reinnervation rendered by Rb1 knockdown alone but also improved indices of mechanical sensation and motor axon recovery. The findings illustrate that peripheral neurons that are well into attempted regrowth retain their responsiveness to both intrinsic and exogenous approaches that improve their recovery. We also identify a novel local approach to manipulate gene expression and outcome in regrowing axons.

Regenerative plasticity of intact human skin axons.

The evaluation of human epidermal innervation and its impact by disease has largely focused on rigorous immunohistochemical counts of PGP 9.5 labelled axons. In this brief and preliminary report, we expand the repertoire of epidermal axon markers to include those with an influence on their regenerative plasticity. We studied human lower limb punch skin samples with tandem analyses of their mRNA content using qRT-PCR. Normal human subjects (n = 11) and two patients with newly diagnosed CIDP were sampled with the latter undergoing serial tandem biopsies before and after 3 months of immunotherapy. Controls expressed regeneration proteins within dermal and epidermal axons: GAP43 (growth associated protein 43), Shh (sonic hedgehog) and SCG (superior cervical ganglion-10; stathmin 2). Moreover, this expression accompanied intraepidermal nerve fiber density (IENF) within normal established values. CIDP patients had lower IENF but also expressed GAP43, Shh, and SCG. Tandem qRT-PCR identified confirmed the presence not only of these plasticity markers but of additional regeneration related mRNAs. CIDP patients had marked elevation of several mRNAs, with improvement following treatment. The findings support the concept of dynamic skin axon plasticity in humans is relevant toward consideration of newer therapeutic approaches.

Caspase-6 is a Dispensable Enabler of Adult Mammalian Axonal Degeneration.

The progress of axonal degeneration (AxD) following injury or insult impacts both recovery from axonal transection and protection of axons from diverse insults, or axonopathy. Here we provide evidence that increases in capase-6 (Casp6) expression and action contribute to the progression of AxD. The expression of Casp6 protein and mRNA in distal branches of sensory axons undergoing AxD was confirmed. We developed and utilized a new model of axonopathy in live mice by serially visualizing the viability of cutaneous axons in the ear pinna that expressed an axonal YFP transgene, in response to capasaicin-induced AxD. Both specific pharmacological inhibition of caspase-6 and local knockdown offered early but subtle and mild attenuation of axonopathy. To evaluate an axon autonomous role of Casp6, we examined axon integrity following transection ex vivo, and analyzed the serial morphological fragmentation of neurofilament expression as a structural index of AxD. Adding a specific Casp6 inhibitor to the preparation delayed neurofilament fragmentation. Intact motor axons of Casp6 null mice had normal electrophysiological properties but, as tested serially during AxD, there was attenuated loss of excitability. Following transection, morphological features of AxD were evident in both wild type and Casp6-/- mice but the latter had evidence of slowed progression. Taken together, our findings suggest a subtle but dispensable enabling role of local Casp6 expression in axons undergoing AxD. Serial analysis of cutaneous ear pinna axons in live mice provides a useful and novel model of axonal integrity.

Sensory Neurodegeneration in Diabetes: Beyond Glucotoxicity.

Diabetic polyneuropathy in humans is of gradual, sometimes insidious onset, and is more likely to occur if glucose control is poor. Arguments that the disorder arises chiefly from glucose toxicity however ignore the greater complexity of a unique neurodegenerative disorder. For example, sensory neurons regularly thrive in media with levels of glucose at or exceeding those of poorly controlled diabetic persons. Also, all of the linkages between hyperglycemia and neuropathy develop in the setting of altered insulin availability or sensitivity. Insulin itself is recognized as a potent growth, or trophic factor for adult sensory neurons. Low doses of insulin, insufficient to alter blood glucose levels, reverse features of diabetic neurodegeneration in animal models. Insulin resistance, as occurs in diabetic adipose tissue, liver, and muscle, also develops in sensory neurons, offering a mechanism for neurodegeneration in the setting of normal or elevated insulin levels. Other interventions that "shore up" sensory neurons prevent features of diabetic polyneuropathy from developing despite persistent hyperglycemia. More recently evidence has emerged that a series of subtle molecular changes in sensory neurons can be linked to neurodegeneration including epigenetic changes in the control of gene expression. Understanding the new complexity of sensory neuron degeneration may give rise to therapeutic strategies that have a higher chance of success in the clinical trial arena.

Peripheral neuron plasticity is enhanced by brief electrical stimulation and overrides attenuated regrowth in experimental diabetes.

Peripheral nerve regrowth is less robust than commonly assumed, particularly when it accompanies common clinical scenarios such as diabetes mellitus. Brief extracellular electrical stimulation (ES) facilitates the regeneration of peripheral nerves in part through early activation of the conditioning injury response and BDNF. Here, we explored intrinsic neuronal responses to ES to identify whether ES might impact experimental diabetes, where regeneration is attenuated. ES altered several regeneration related molecules including rises in tubulin, Shh (Sonic hedgehog) and GAP43 mRNAs. ES was associated with rises in neuronal intracellular calcium but its strict linkage to regrowth was not confirmed. In contrast, we identified PI3K-PTEN involvement, an association previously linked to diabetic regenerative impairment. Following ES there were declines in PTEN protein and mRNA both in vitro and in vivo and a PI3K inhibitor blocked its action. In vitro, isolated diabetic neurons were capable of mounting robust responsiveness to ES. In vivo, ES improved electrophysiological and behavioral indices of nerve regrowth in a chronic diabetic model of mice with pre-existing neuropathy. Regrowth of myelinated axons and reinnervation of the epidermis were greater following ES than sham stimulation. Taken together, these findings identify a role for ES in supporting regeneration during the challenges of diabetes mellitus.

An official American Thoracic Society Clinical Practice guideline: the diagnosis of intensive care unit-acquired weakness in adults

RATIONALE: Profound muscle weakness during and after critical illness is termed intensive care unit-acquired weakness (ICUAW). OBJECTIVES: To develop diagnostic recommendations for ICUAW. METHODS: A multidisciplinary expert committee generated diagnostic questions. A systematic review was performed, and recommendations were developed using the Grading, Recommendations, Assessment, Development, and Evaluation (GRADE) approach. MEASUREMENT AND MAIN RESULTS: Severe sepsis, difficult ventilator liberation, and prolonged mechanical ventilation are associated with ICUAW. Physical rehabilitation improves outcomes in heterogeneous populations of ICU patients. Because it may not be feasible to provide universal physical rehabilitation, an alternative approach is to identify patients most likely to benefit. Patients with ICUAW may be such a group. Our review identified only one case series of patients with ICUAW who received physical therapy. When compared with a case series of patients with ICUAW who did not receive structured physical therapy, evidence suggested those who receive physical rehabilitation were more frequently discharged home rather than to a rehabilitative facility, although confidence intervals included no difference. Other interventions show promise, but fewer data proving patient benefit existed, thus precluding specific comment. Additionally, prior comorbidity was insufficiently defined to determine its influence on outcome, treatment response, or patient preferences for diagnostic efforts. We recommend controlled clinical trials in patients with ICUAW that compare physical rehabilitation with usual care and further research in understanding risk and patient preferences. CONCLUSIONS: Research that identifies treatments that benefit patients with ICUAW is necessary to determine whether the benefits of diagnostic testing for ICUAW outweigh its burdens.(AU)

Phenotyping animal models of diabetic neuropathy: a consensus statement of the diabetic neuropathy study group of the EASD (Neurodiab).

NIDDK, JDRF, and the Diabetic Neuropathy Study Group of EASD sponsored a meeting to explore the current status of animal models of diabetic peripheral neuropathy. The goal of the workshop was to develop a set of consensus criteria for the phenotyping of rodent models of diabetic neuropathy. The discussion was divided into five areas: (1) status of commonly used rodent models of diabetes, (2) nerve structure, (3) electrophysiological assessments of nerve function, (4) behavioral assessments of nerve function, and (5) the role of biomarkers in disease phenotyping. Participants discussed the current understanding of each area, gold standards (if applicable) for assessments of function, improvements of existing techniques, and utility of known and exploratory biomarkers. The research opportunities in each area were outlined, providing a possible roadmap for future studies. The meeting concluded with a discussion on the merits and limitations of a unified approach to phenotyping rodent models of diabetic neuropathy and a consensus formed on the definition of the minimum criteria required for establishing the presence of the disease. A neuropathy phenotype in rodents was defined as the presence of statistically different values between diabetic and control animals in 2 of 3 assessments (nocifensive behavior, nerve conduction velocities, or nerve structure). The participants propose that this framework would allow different research groups to compare and share data, with an emphasis on data targeted toward the therapeutic efficacy of drug interventions.

Nerve growth factor acts through the TrkA receptor to protect sensory neurons from the damaging effects of the HIV-1 viral protein, Vpr.

Distal sensory polyneuropathy (DSP) with associated neuropathic pain is the most common neurological disorder affecting patients with human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS). Viral protein R (Vpr) is a neurotoxic protein encoded by HIV-1 and secreted by infected macrophages. Vpr reduces neuronal viability, increases cytosolic calcium and membrane excitability of cultured dorsal root ganglion (DRG) sensory neurons, and is associated with mechanical allodynia in vivo. A clinical trial with HIV/AIDS patients demonstrated that nerve growth factor (NGF) reduced the severity of DSP-associated neuropathic pain, a problem linked to damage to small diameter, potentially NGF-responsive fibers. Herein, the actions of NGF were investigated in our Vpr model of DSP and we demonstrated that NGF significantly protected sensory neurons from the effects of Vpr. Footpads of immunodeficient Vpr transgenic (vpr/RAG1(-/-)) mice displayed allodynia (p<0.05), diminished epidermalinnervation (p<0.01) and reduced NGF mRNA expression (p<0.001) compared to immunodeficient (wildtype/RAG1(-/-)) littermate control mice. Compartmented cultures confirmed recombinant Vpr exposure to the DRG neuronal perikarya decreased distal neurite extension (p<0.01), whereas NGF exposure at these distal axons protected the DRG neurons from the Vpr-induced effect on their cell bodies. NGF prevented Vpr-induced attenuation of the phosphorylated glycogen synthase-3 axon extension pathway and tropomyosin-related kinase A (TrkA) receptor expression in DRG neurons (p<0.05) and it directly counteracted the cytosolic calcium burst caused by Vpr exposure to DRG neurons (p<0.01). TrkA receptor agonist indicated that NGFacted through the TrkA receptor to block the Vpr-mediated decrease in axon outgrowth in neonatal and adult rat and fetal human DRG neurons (p<0.05). Similarly, inhibiting the lower affinity NGF receptor, p75, blocked Vpr's effect on DRG neurons. Overall, NGF/TrkA signaling or p75 receptor inhibition protects somatic sensory neurons exposed to Vpr, thus laying the groundwork for potential therapeutic options for HIV/AIDS patients suffering from DSP.

Overexpression of human HSP27 protects sensory neurons from diabetes.

OBJECTIVES: To evaluate whether augmenting neuronal protective mechanisms might slow or arrest experimental diabetic peripheral neuropathy (DPN). DPN is one of the most common neurodegenerative disorders and is rising in prevalence. How it targets sensory neurons is uncertain; the disorder is irreversible and untreatable. We explored the intrinsic protective properties of overexpressed human HSP27 on experimental DPN. HSP27 is a small pro-survival heat shock protein that also increases axonal regeneration. METHODS: Experimental diabetes was superimposed on mice overexpressing a human HSP27 transgene and its impact was evaluated on epidermal innervation, behavioral tests of sensation and electrophysiological indices of DPN. RESULTS: Mice that overexpress human HSP27 in their sensory and motor neurons and that were made diabetic for 6 months by streptozotocin treatment were protected from a range of neuropathic abnormalities, including loss of footpad thermal sensation, mechanical allodynia, loss of epidermal innervation, and slowing of sensory conduction velocity. The protection was selective for sensory neurons in comparison to motor neurons and at 6 months provided better protection in female than male mice. Markers of RAGE-NFκB activation were attenuated by the transgene. CONCLUSIONS: The findings support the idea that diabetic polyneuropathy involves a unique, sensory-centric neurodegenerative process which can be reduced by overexpressing a single gene, an important starting point for new disease-modifying therapeutic approaches.

RGD-mediated adhesive interactions are important for peripheral axon outgrowth in vivo.

We identify an essential role for the RGD (Arg-Gly-Asp tripeptide) moiety in vivo during adult peripheral neuron regenerative growth. Beyond a peripheral nerve transection there were rises in the fibronectin extracellular matrix, and striking rises in the mRNA and protein expression of integrin subunits sensitive to RGD/fibronectin signalling. Neuron perikarya, axons and Schwann cells all expressed RGD/fibronectin sensitive integrins after injury. To evaluate the significance of RGD/fibronectin-integrin interactions, we infused solutions of a pentapeptide including the RGD motif (sRGD) serially and directly within the milieu of early axon growth across rat sciatic transection injuries. While low dose infusions of sRGD facilitated early axon ingrowth, we encountered inhibition of ingrowth and bridge formation with higher doses of sRGD indicating competitive disruption of RGD/fibronectin-integrin signalling. Fibronectin RGD moieties serve a critical and important role during peripheral axon outgrowth.

Neuronal targeting in diabetes mellitus: a story of sensory neurons and motor neurons.

Diabetes mellitus targets the peripheral nervous system in unique but disabling ways. Although several mechanisms may target peripheral neurons, they render a degenerative pattern of damage that begins in distal terminals. Moreover, sensory neurons are involved early, motor neurons later. By studying a variety of diabetic neuropathy models in rats, mice, and other species, an overall appreciation of its neurodegeneration emerges. Understanding how mechanisms of diabetes complications target peripheral neurons selectively may offer opportunities to intervene before irretrievable neuron loss develops.

Activated RHOA and peripheral axon regeneration.

The regeneration of adult peripheral neurons after transection is slow, incomplete and encumbered by severe barriers to proper regrowth. The role of RHOA GTPase has not been examined in this context. We examined the expression, activity and functional role of RHOA GTPase and its ROK effector, inhibitors of regeneration, during peripheral axon outgrowth. We used qRT-PCR, quantitative immunohistochemistry, and assays of RHOA activation to examine expression in sensory neurons of rats with sciatic transection injuries. In vitro, we exposed dissociated adult sensory neurons, not grown on inhibitory substrates, to a RHOA-ROK inhibitor HA-1077 and measured neurite initiation and outgrowth. In vivo, we exposed early regenerating axons and Schwann cells directly to HA-1077 in a conduit connecting the proximal and distal stumps of transected sciatic nerves. Intact adult dorsal root ganglia sensory neurons expressed RHOA and ROK 1 mRNAs and protein and there were rises in RHOA after injury. Activated GTP-bound RHOA, undetectable in intact ganglia, was dramatically upregulated in both neurons and axons after injury. Adult rat sensory neurons in vitro demonstrated a dose-related increase in the initiation of neurite outgrowth, and in the proportion with long neurites when they were exposed to a ROK antagonist. Regenerative bridges that were directly exposed to the ROK inhibitor had a dose-related rise in the extent and distance of in vivo axon and partnered Schwann cell regrowth within them. RHOA activation and signaling are features of adult peripheral axon regeneration within its own milieu, independent of myelin. Inhibition of its activation may benefit peripheral axon lesions.

Local erythropoietin signaling enhances regeneration in peripheral axons.

Erythropoietin (EPO) and its receptor (EPO-R), mediate neuroprotection from axonopathy and apoptosis in the peripheral nervous system (PNS). We examined the impact and potential mechanisms of local EPO signaling on regenerating PNS axons in vivo and in vitro. As a consequence of injury, peripheral nerve axons and DRG neurons have a marked increase in the expression of EPO and EPO-R. Local delivery of EPO via conduit over 2 weeks to rat sciatic nerve following crush injury increased the density and maturity of regenerating myelinated axons growing distally from the crush site. In addition, EPO also rescued retrograde degeneration and atrophy of axons. EPO substantially increased the density and intensity of calcitonin gene-related peptide (CGRP) expression within outgrowing axons. Behavioral improvements in sensorimotor function also occurred in rats exposed to near nerve EPO delivery. EPO delivery led to decreased nuclear factor kappaB (NFkB) activation but increased phosphorylation of Akt and STAT3 within nerve and dorsal root ganglia neurons indicating rescue from an injury phenotype. Spinal cord explant studies also demonstrated a similar dose-dependent effect of EPO upon motor axonal outgrowth. Local EPO signaling enhances regenerating peripheral nervous system axons in addition to its known neuroprotection. Exogenous EPO may have a therapeutic role in a large number of peripheral nerve diseases through its impact on regeneration.

Facilitated sprouting in a peripheral nerve injury.

During regeneration of injured peripheral nerves, local conditions may influence how regenerative axon sprouts emerge from parent axons. More extensive lesions might be expected to disrupt such growth. In this work, we discovered instead that long segmental crush injuries facilitate the growth and maturation of substantially more axon sprouts than do classical short crush injuries (20 mm length vs. 2 mm). At identical distances from the proximal site of axon interruption there was a 45% rise in the numbers of neurofilament labeled axons extending through a long segmental crush zone by 1 week. By 2 weeks, there was a 35% greater density of regenerating myelinated axons in long compared with short crush injuries just beyond (5 mm) the proximal injury site. Moreover, despite the larger numbers of axons, their maturity was identical and they were regular, parallel, associated with Schwann cells (SCs) and essentially indistinguishable between the injuries. Backlabeling with Fluorogold indicated that despite these differences, the axons arose from similar numbers of parent motor and sensory neurons. Neither injury was associated with ischemia. Both injuries were associated with rises in GFAP (glial acidic fibrillary protein) and p75 mRNAs, markers of SC plasticity but p75, GFAP and brain-derived neurotrophic factor mRNAs did not differ between the injuries. There was a higher local mRNA level of GAP43/B50 at 7 days following injury and a higher sonic hedgehog protein (Shh) mRNA at 24 h in long crush zones. GAP43/B50 protein and SHH protein both had prominent localization within regenerating axons. Long segmental nerve trunk crush injuries do not impair regeneration but instead generate greater axon plasticity that results in larger numbers of mature myelinated axons. The changes occur without apparent change in SC activation, overall nerve architecture or nerve blood flow. While the mechanism is uncertain, the findings indicate that manipulation of the nerve microenvironment can induce substantial changes in regenerative sprouting.

Incidence of Guillain-Barré syndrome in Alberta, Canada: an administrative data study.

BACKGROUND: To examine the epidemiology of Guillain-Barré syndrome (GBS) in Alberta between 1994 and 2004 with data derived from hospital administration procedures. METHODS: Data from 3,959,857 individuals (1,956,841 females and 2,003,016 males) aged 1-110 years and residing in Alberta, Canada, were included in the analysis. A Poisson regression analysis was performed to determine the predictors of GBS events. RESULTS: After age and sex standardisation to the 2001 Canadian census population, incidence rates ranged from 0.97 to 2.32 per 100,000 over the course of the 11-year period, with a mean incidence of 1.6 per 100,000. Significant effects of gender, age group and year were found. Males were found to be 1.5 times more likely to acquire GBS than females. Relative to those in their first decade, the risk of acquiring GBS increased with advancing age, whereby the incidence in males peaked in the 7th decade of life and in females in the 8th decade of life. The incidence fluctuated over the 11-year period, with a minimum in 1998 and a maximum in 2004. CONCLUSIONS: The incidence of GBS in Alberta between 1994 and 2004 fluctuated within a narrow range, was similar to that previously reported worldwide, demonstrated a male preponderance and increased in elderly patients.

Remote neurotrophic support of epidermal nerve fibres in experimental diabetes.

AIMS/HYPOTHESIS: The support of distal regenerating axons and epidermal nerve fibres through growth factor delivery may depend on the site of delivery. While low-dose systemic insulin provides trophic support for regenerating axons or axons from diabetic animals, its potential action upon the most distal neurites within the epidermis is unknown. In diabetic neuropathy, distal loss of axons is an important clinical and pathological feature. We hypothesised that insulin and IGF-1 delivered intrathecally could support the most distal epidermal nerve fibres. MATERIALS AND METHODS: As insulin and IGF-1 receptors are present upon sensory ganglion perikarya, we studied the impact of intrathecal delivery of low-dose insulin and equimolar IGF-1 on the density of epidermal axons expressing protein gene product 9.5 in experimental diabetic rats. After 2 months of diabetes induced by streptozotocin injection, intrathecal delivery of low-dose insulin or IGF-1 or saline was provided for 1 month, with comparison to compatible doses of subcutaneous insulin delivery. RESULTS: Diabetes, in itself, was associated with a decline in epidermal nerve fibre density. Delivery of both intrathecal IGF-1 and insulin was associated with significant improvement in epidermal fibre density (greatest with IGF-1) and length relative to placebo. CONCLUSIONS/INTERPRETATION: Central intrathecal delivery of IGF-1 and insulin offers remote support for epidermal nerve fibres, subjected to 'dying-back' in early diabetic polyneuropathy.

Rescue and regeneration of injured peripheral nerve axons by intrathecal insulin.

Insulin peptide, acting through tyrosine kinase receptor pathways, contributes to nerve development or repair. In this work, we examined the direction, impact and repertoire of insulin signaling in vivo during peripheral nerve regeneration in rats. First, we demonstrated that insulin receptor is expressed on lumbar dorsal root ganglia neuronal perikarya using immunohistochemistry. Immunoblots and polymerase chain reactions confirmed the presence of both alpha and beta insulin receptor subunits in dorsal root ganglia. In vivo and in vitro assessment of dorsal root ganglion neurons showed preferential localization of insulin receptor to perikaryal sites. In vivo, intrathecal delivery of fluorescein isothiocyanate-labeled insulin identified localization around dorsal root ganglia neurons. The direction and impact of potential insulin signaling was evaluated by concurrently delivering insulin or carrier over a 2 week period using mini-osmotic pumps, either intrathecally, near nerve, or with both deliveries, following a selective sural nerve crush injury. Only intrathecal insulin increased the number and maturity of regenerating sensory sural nerve axons distal to the crush site. As well, only intrathecal insulin rescued retrograde loss of sural axons after crush. In a separate experiment, insulin also rescued retrograde loss and atrophy of deep peroneal, largely motor, axons post-injury. Intrathecal insulin increased the expression of calcitonin-gene-related peptide in regenerating sprouts, increased the number of visualized regenerating fiber clusters, and reduced downregulation of calcitonin-gene-related peptide in dorsal root ganglia neurons. Insulin delivered intrathecally does not appear to influence expression of insulin-like growth factor-1 at dorsal root ganglion neurons or near peripheral nerve injury, but was associated with upregulation of insulin receptor alpha subunit in dorsal root ganglia. Intrathecal insulin delivery was associated with greater recovery of thermal sensation and longer distances to stimulus response with the pinch test following sural nerve crush. Insulin signaling at neuron perikarya can drive distal sensory axon regrowth, rescue retrograde alterations of axons and alter axon peptide expression. Moreover, such actions are associated with upregulation of its own receptor.

Nitric oxide in damage, disease and repair of the peripheral nervous system.

Peripheral nerves provide essential connections between the central nervous system and muscles, autonomic structures and sensory organs. Nitric oxide (NO) participates in critical actions involving several aspects of peripheral nerve function and disease. It offers important roles in "normal" afferent signaling of pain through the dorsal horn of the spinal cord and in autonomic control through nitrergic innervation. NO is generated during the fundamental processes of Wallerian degeneration of peripheral nerves following injury that bear on subsequent regenerative events. Through its actions on vasa nervorum, the blood supply to nerves, NO participates in microvascular changes following injury but also has direct roles in axon and myelin breakdown and "clearance" prior to regeneration. During such processes, NO contributes to the development of neuropathic pain. Excessive local levels of NO during inflammation may damage axons and growth cones. Low-grade chronic rises in NO may also contribute toward peripheral nerve damage, or neuropathy in diabetes. In this review, we consider the evidence for these roles and their potential importance in disease and repair of peripheral nerves.