A Pilot Study of the Efficacy of Heart Rate Variability (HRV) Biofeedback in Patients with Fibromyalgia

Fibromyalgia (FM) is a non-inflammatory rheumatologic disorder characterized by musculoskeletal pain, fatigue, depression, cognitive dysfunction and sleep disturbance. Research suggests that autonomic dysfunction may account for some of the symptomatology of FM. An open label trial of biofeedback training was conducted to manipulate suboptimal heart rate variability (HRV), a key marker of autonomic dysfunction. Methods: Twelve women ages 18–60 with FM completed 10 weekly sessions of HRV biofeedback. They were taught to breathe at their resonant frequency (RF) and asked to practice twice daily. At sessions 1, 10 and 3-month follow-up, physiological and questionnaire data were collected. Results: There were clinically significant decreases in depression and pain and improvement in functioning from Session 1 to a 3-month follow-up. For depression, the improvement occurred by Session 10. HRV and blood pressure variability (BPV) increased during biofeedback tasks. HRV increased from Sessions 1–10, while BPV decreased from Session 1 to the 3 month follow-up. Conclusions: These data suggest that HRV biofeedback may be a useful treatment for FM, perhaps mediated by autonomic changes. While HRV effects were immediate, blood pressure, baroreflex, and therapeutic effects were delayed. This is consistent with data on the relationship among stress, HPA axis activity, and brain function.     

Elevated excitatory neurotransmitter levels in the fibromyalgia brain

Consistent brain imaging findings demonstrate that neurobiological factors may contribute to the pathology of 'central' pain states such as fibromyalgia (FM). Studies using proton magnetic resonance spectroscopy suggest that glutamate (Glu), a key excitatory neurotransmitter, may be present in higher concentrations within the brains of FM patients. This neurotransmitter imbalance is present in multiple brain regions that have been implicated in processing pain information. However, it is unknown if elevated Glu is acting at the synapse. New investigations are needed to investigate the molecular action of Glu in FM and to investigate these findings during treatment that modulates glutamatergic neurotransmission.     

Altered near‐infrared spectroscopy response to breath‐holding in patients with fibromyalgia

Fibromyalgia (FM) is a complex syndrome characterized by chronic widespread pain and a heightened response to pressure. Most medical researches pointed out that FM patients with endothelial dysfunction and arterial stiffness. A continuous‐wave near‐infrared spectroscopy (NIRS) system is used in present study to measure the hemodynamic changes elicited by breath‐holding task in patients with FM. Each patient completed a questionnaire survey including demographics, characteristics of body pain, associated symptoms, headache profiles and Hospital Anxiety and Depression Scale. A total of 27 FM patients and 26 health controls were enrolled. In comparison with healthy controls, patients with FM showed lower maximal and averaged change of oxyhemoglobin concentration in both the left (1.634 ±0.890 and 0.810 ±0.525 μM) and the right (1.576 ±0.897 and 0.811 ±0.601 μM) prefrontal cortex than healthy controls (P < .05 for both sides) during the breath‐holding task. In conclusion, FM is associated with altered cerebrovascular reactivity measured by NIRS and breath‐holding task, which may reflect endothelial dysfunction or arterial stiffness. Oxygenated hemoglobin concentration changes of healthy controls and FM patients.      

Fibromyalgia--a clinical entity?

Fibromyalgia (FM) is a syndrome characterized by widespread musculoskeletal pain and tenderness at specified sites, fatigue, and unrefreshing sleep. The American College of Rheumatology (ACR) has recently accepted diagnostic criteria for FM. The ACR criteria have high diagnostic specificity, sensitivity, and accuracy. Laboratory investigations show a disturbed microcirculation in painful muscles, a decrease in adenosine triphosphate and phosphocreatine, and a reduced relaxation rate. Pain analyses indicate that the pain is nociceptive. A characteristic physiological sleep disturbance has been described that is correlated to the symptoms. The etiology of FM is not known. The etiology may be different in different patients. FM is a clinical entity, but should be regarded as a syndrome rather than a disease.     

Catechol-O-methyltransferase gene haplotypes in Mexican and Spanish patients with fibromyalgia

Autonomic dysfunction is frequent in patients with fibromyalgia (FM). Heart rate variability analyses have demonstrated signs of ongoing sympathetic hyperactivity. Catecholamines are sympathetic neurotransmitters. Catechol-O-methyltransferase (COMT), an enzyme, is the major catecholamine-clearing pathway. There are several single-nucleotide polymorphisms (SNPs) in the COMT gene associated with the different catecholamine-clearing abilities of the COMT enzyme. These SNPs are in linkage disequilibrium and segregate as 'haplotypes'. Healthy females with a particular COMT gene haplotype (ACCG) producing a defective enzyme are more sensitive to painful stimuli. The objective of our study was to define whether women with FM, from two different countries (Mexico and Spain), have the COMT gene haplotypes that have been previously associated with greater sensitivity to pain. All the individuals in the study were female. Fifty-seven Mexican patients and 78 Spanish patients were compared with their respective healthy control groups. All participants filled out the Fibromyalgia Impact Questionnaire (FIQ). Six COMT SNPs (rs2097903, rs6269, rs4633, rs4818, rs4680, and rs165599) were genotyped from peripheral blood DNA. In Spanish patients, there was a significant association between three SNPs (rs6269, rs4818, and rs4680) and the presence of FM when compared with healthy controls. Moreover, in Spanish patients with the 'high pain sensitivity' haplotype (ACCG), the disease, as assessed by the FIQ, was more severe. By contrast, Mexican patients displayed only a weak association between rs6269 and rs165599, and some FIQ subscales. In our group of Spanish patients, there was an association between FM and the COMT haplotype previously associated with high pain sensitivity. This association was not observed in Mexican patients. Studies with a larger sample size are needed in order to verify or amend these preliminary results.     

Effects of lifestyle physical activity on perceived symptoms and physical function in adults with fibromyalgia: results of a randomized trial

Introduction  

Although exercise is therapeutic for adults with fibromyalgia (FM), its symptoms often create obstacles that discourage exercise. We evaluated the effects of accumulating at least 30 minutes of self-selected lifestyle physical activity (LPA) on perceived physical function, pain, fatigue, body mass index, depression, tenderness, and the six-minute walk test in adults with FM.     

Biology and therapy of fibromyalgia: pain in fibromyalgia syndrome

Fibromyalgia (FM) pain is frequent in the general population but its pathogenesis is only poorly understood. Many recent studies have emphasized the role of central nervous system pain processing abnormalities in FM, including central sensitization and inadequate pain inhibition. However, increasing evidence points towards peripheral tissues as relevant contributors of painful impulse input that might either initiate or maintain central sensitization, or both. It is well known that persistent or intense nociception can lead to neuroplastic changes in the spinal cord and brain, resulting in central sensitization and pain. This mechanism represents a hallmark of FM and many other chronic pain syndromes, including irritable bowel syndrome, temporomandibular disorder, migraine, and low back pain. Importantly, after central sensitization has been established only minimal nociceptive input is required for the maintenance of the chronic pain state. Additional factors, including pain related negative affect and poor sleep have been shown to significantly contribute to clinical FM pain. Better understanding of these mechanisms and their relationship to central sensitization and clinical pain will provide new approaches for the prevention and treatment of FM and other chronic pain syndromes.     

Resistance exercise improves muscle strength,health status and pain intensity in fibromyalgia—a randomized controlled trial

IntroductionFibromyalgia (FM) is characterized by persistent widespread pain, increased pain sensitivity and tenderness. Muscle strength in women with FM is reduced compared to healthy women. The aim of this study was to examine the effects of a progressive resistance exercise program on muscle strength, health status, and current pain intensity in women with FM.MethodsA total of 130 women with FM (age 22–64 years, symptom duration 0–35 years) were included in this assessor-blinded randomized controlled multi-center trial examining the effects of progressive resistance group exercise compared with an active control group. A person-centred model of exercise was used to support the participants’ self-confidence for management of exercise because of known risks of activity-induced pain in FM. The intervention was performed twice a week for 15 weeks and was supervised by experienced physiotherapists. Primary outcome measure was isometric knee-extension force (Steve Strong®), secondary outcome measures were health status (FIQ total score), current pain intensity (VAS), 6MWT, isometric elbow-flexion force, hand-grip force, health related quality of life, pain disability, pain acceptance, fear avoidance beliefs, and patient global impression of change (PGIC). Outcomes were assessed at baseline and immediately after the intervention. Long-term follow up comprised the self-reported questionnaires only and was conducted after 13–18 months. Between-group and within-group differences were calculated using non-parametric statistics.ResultsSignificant improvements were found for isometric knee-extension force (p = 0.010), health status (p = 0.038), current pain intensity (p = 0.033), 6MWT (p = 0.003), isometric elbow flexion force (p = 0.02), pain disability (p = 0.005), and pain acceptance (p = 0.043) in the resistance exercise group (n = 56) when compared to the control group (n = 49). PGIC differed significantly (p = 0.001) in favor of the resistance exercise group at post-treatment examinations. No significant differences between the resistance exercise group and the active control group were found regarding change in self-reported questionnaires from baseline to 13–18 months.ConclusionsPerson-centered progressive resistance exercise was found to be a feasible mode of exercise for women with FM, improving muscle strength, health status, and current pain intensity when assessed immediately after the intervention.

Trial registration

ClinicalTrials.gov identification number: {"type":"clinical-trial","attrs":{"text":"NCT01226784","term_id":"NCT01226784"}}NCT01226784, Oct 21, 2010.     

Nitrite and nitric oxide metabolism in peripheral artery disease

Peripheral artery disease (PAD) represents a burgeoning form of cardiovascular disease associated with significant clinical morbidity and increased 5 year cardiovascular disease mortality. It is characterized by impaired blood flow to the lower extremities, claudication pain and severe exercise intolerance. Pathophysiological factors contributing to PAD include atherosclerosis, endothelial cell dysfunction, and defective nitric oxide metabolite physiology and biochemistry that collectively lead to intermittent or chronic tissue ischemia. Recent work from our laboratories is revealing that nitrite/nitrate anion and nitric oxide metabolism plays an important role in modulating functional and pathophysiological responses during this disease. In this review, we discuss experimental and clinical findings demonstrating that nitrite anion acts to ameliorate numerous pathophysiological events associated with PAD and chronic tissue ischemia. We also highlight future directions for this promising line of therapy.     

Is Metabolic Flexibility Altered in Multiple Sclerosis Patients?

Objectives

Metabolic flexibility is defined as ability to adjust fuel oxidation to fuel availability. Multiple sclerosis (MS) results in reduced muscle strength and exercise intolerance. We tested the hypothesis that altered metabolic flexibility contributes to exercise intolerance in MS patients.

Methods

We studied 16 patients (all on glatiramer) and 16 matched healthy controls. Energy expenditure (EE), and carbohydrate (COX) and lipid oxidation (LOX) rates were determined by calorimetry, before and after an oral glucose load. We made measurements either at rest (canopy device) or during 40 min low-grade (0.5 W/kg) exercise (metabolic chamber). We also obtained plasma, and adipose tissue and skeletal muscle dialysate samples by microdialysis to study tissue-level metabolism under resting conditions.

Results

At rest, fasting and postprandial plasma glucose, insulin, and free fatty acid levels did not differ between patients and controls. Fasting and postprandial COX was higher and LOX lower in patients. In adipose, fasting and postprandial dialysate glucose, lactate, and glycerol levels were higher in patients vs. controls. In muscle, fasting and postprandial dialysate metabolite levels did not differ significantly between the groups. During exercise, EE did not differ between the groups. However, COX increased sharply over 20 min in patients, without reaching a steady state, followed by an immediate decrease within the next 20 min and fell even below basal levels after exercise in patients, compared to controls.

Conclusions

Glucose tolerance is not impaired in MS patients. At rest, there is no indication for metabolic inflexibility or mitochondrial dysfunction in skeletal muscle. The increased adipose tissue lipolytic activity might result from glatiramer treatment. Autonomic dysfunction might cause dysregulation of postprandial thermogenesis at rest and lipid mobilization during exercise.     

Can alcohol consumption be an alternative treatment for fibromyalgia?

Treatment of chronic pain conditions such as fibromyalgia is challenging due to limitations of drug therapies. An initial exploration into the relationships between self-reported alcohol consumption, symptom severity, and quality of life for individuals with fibromyalgia sheds new light on plausible hypotheses and potential mechanisms of action for future research. Evidence suggests that alcohol consumption may improve social and psychological factors because of activity in the ascending and descending pain pathways in modulating gamma-aminobutyric acid neurotransmission. Further methodologically rigorous studies in this field to improve well-being of individuals with fibromyalgia are warranted.In a previous issue of Arthritis Research & Therapy, Kim and colleagues [1] reported the first study to examine the association between alcohol consumption, symptom severity, and quality of life of individuals with fibromyalgia (FM). Treatment of chronic pain conditions such as FM is challenging because the drug therapies currently available are expensive and associated with numerous limitations such as undesirable side effects and addiction or tolerance issues. Despite undergoing drug treatment, patients are often left with unrelieved pain, restricted mobility, and reduced physical function. Lifestyle interventions, including dietary modifications such as alcohol consumption, have gained popularity as explorations in symptom management.Several observational studies have examined the association between alcohol consumption and chronic pain conditions. In a prospective study, Bergman and colleagues [2] found that regular weekly or daily alcohol consumption is a significant protective factor for the development of chronic pain. Two case–control studies have also shown that moderate alcohol consumption correlates with a reduced risk of rheumatoid arthritis [3,4]. However, a systematic review of nine epidemiological studies has concluded that alcohol consumption is not associated with low back pain [5]. Kim and colleagues are the first to examine the association between alcohol consumption and FM symptom severity and quality of life. Among the 946 adult FM patients (94 % women, mean age of 49 years old) reporting low or moderate alcohol consumption (≤3 or >3 to 7 drinks per week), there was lower FM symptom severity and better quality-of-life scores compared with those who reported no alcohol consumption (non-drinkers). However, these associations were not observed in patients who were heavy drinkers (>7 drinks per week) compared with non-drinkers. Drinkers had higher education, less unemployment, lower body mass index, and lower frequency of opioid use than non-drinkers. Thus, their analyses were adjusted for these potential confounders.Because alcohol consumption consists of complex behaviors that intersect with many social, economic, psychological, and demographic factors, disentangling this complex web of relationships is a challenge. Interestingly, after exploring possible mechanisms for their findings, Kim and colleagues speculated that alcohol consumption may attenuate FM symptoms and improve quality of life by mediating psychological benefits and stress relief or by promoting factors associated with social integration. Another possible mechanism proposed is central nervous mediation via the modulating gamma-aminobutyric acid (GABA) system. Several neurotransmitters (including GABA) in the ascending and descending pain pathways have been implicated in FM [6]. Thus, behavioral and pharmacological therapies that modulate or mimic the effects of GABA production can be promising for FM treatment.This initial exploration into the relationships between alcohol consumption, symptom severity, and quality of life for FM has posed a number of questions that need to be answered by future studies with stronger study designs. Kim and colleagues discussed limitations associated with cross-sectional study design, and we would like to underscore additional concerns relating to the potential for non-random misclassifications of alcohol consumption among FM patients with different levels of symptom severity or quality of life. Such information bias is not uncommon in cross-sectional studies providing data on both exposure and outcome variables from questionnaires. Because the questionnaires are administered at the same time in a cross-sectional study and relied on respondent recall, the measurement errors of exposure (that is, alcohol consumption) may be dependent on the measurement errors of the outcomes (that is, quality of life or FM symptoms). If such dependent bias occurs, the observed association between exposure and outcome is likely to be inflated [7]. Owing to lack of prior data demonstrating that such bias exists in cross-sectional studies of alcohol consumption and FM symptom severity, we provide a possible scenario to examine the potential impacts of dependent bias on this relationship. FM patients who on one occasion had more severe symptoms may in fact have consumed more alcohol to ameliorate symptoms and thus may have felt better (fewer symptoms) at the time of the survey, or FM patients with more severe symptoms at the time of the survey may have stopped drinking alcohol (thus no symptom relief) because of their symptoms. The impact of such dependent bias would result in an inflation of the ‘true’ association. Owing to cross-sectional design, this potential bias cannot be evaluated. In addition to the potential for dependent bias, patients with FM may be too embarrassed to reveal their ‘true’ alcohol intake level because of social desirability biases [8]. Such reporting bias [9], however, is likely to be random and independent of symptom severity. There is still great uncertainty in the study results; therefore, we agree with Kim and colleagues that these preliminary results should not be used as grounds for advising patients to drink alcohol.In sum, the study by Kim and colleagues sheds new light on plausible hypotheses and mechanisms to consider in future methodologically rigorous studies to improve the well-being of individuals with FM. Because it may not be feasible to randomize alcohol consumption in human subject research, methodologically rigorous prospective longitudinal studies are needed. Measuring alcohol consumption at different time points is essential in order to minimize dependent biases from patient-reported exposure and outcome measures.     

Endothelial dysfunction and exercise performance in lone atrial fibrillation or associated with hypertension or diabetes: different results with cardioversion

Endothelial dysfunction and underperfusion of exercising muscle contribute to exercise intolerance, hyperventilation, and breathlessness in atrial fibrillation (AF). Cardioversion (CV) improves endothelial function and exercise performance. We examined whether CV is equally beneficial in diabetes and hypertension, diseases that cause endothelial dysfunction and are often associated with AF. Cardiopulmonary exercise and pulmonary and endothelial (brachial artery flow-mediated dilation) function were tested before and after CV in patients with AF alone (n = 18, group 1) or AF with hypertension (n = 19, group 2) or diabetes (n = 19, group 3). Compared with group 1, peak exercise workload, O2 consumption (Vo2), O2 pulse, aerobic efficiency (Delta Vo2/Delta WR), and ratio of brachial diameter changes to flow changes (Delta D/Delta F) were reduced in group 2 and, to a greater extent, in group 3; exercise ventilation efficiency (Ve/Vco2 slope) and dead space-to-tidal volume ratio (Vd/Vt) were similar among groups. CV had less effect on peak workload (+7% vs. +18%), peak Vo2 (+12% vs. +17%), O2 pulse (+33% vs. +50%), Delta Vo2/Delta WR (+7% vs. +12%), Ve/Vco2 slope (-6% vs. -12%), Delta D/Delta F (+7% vs. +10%), and breathlessness (Borg scale) in group 2 than in group 1 and was ineffective in group 3. The antioxidant vitamin C, tested in eight additional patients in each cohort, improved flow-mediated dilation in groups 1 and 2 before, but not after, CV and was ineffective in group 3, suggesting that the oxidative injury is least in lone AF, greater in hypertension with AF, and greater still in diabetes with AF. Comorbidities that impair endothelial activity worsen endothelial dysfunction and exercise intolerance in AF. The advantages of CV appear to be inversely related to the extent of the underlying oxidative injury.     

Analgesic Effect of Electroacupuncture in a Mouse Fibromyalgia Model: Roles of TRPV1, TRPV4, and pERK

Fibromyalgia (FM) is among the most common chronic pain syndromes encountered in clinical practice, but there is limited understanding of FM pathogenesis. We examined the contribution of transient receptor potential vanilloid 1 (TRPV1) and TRPV4 channels to chronic pain in the repeated acid injection mouse model of FM and the potential therapeutic efficacy of electroacupuncture. Electroacupuncture (EA) at the bilateral Zusanli (ST36) acupoint reduced the long-lasting mechanical hyperalgesia induced by repeated acid saline (pH 4) injection in mouse hindpaw. Isolated L5 dorsal root ganglion (DRG) neurons from FM model mice (FM group) were hyperexcitable, an effect reversed by EA pretreatment (FM + EA group). The increase in mechanical hyperalgesia was also accompanied by upregulation of TRPV1 expression and phosphoactivation of extracellular signal regulated kinase (pERK) in the DRG, whereas DRG expression levels of TRPV4, p-p38, and p-JNK were unaltered. Blockade of TRPV1, which was achieved using TRPV1 knockout mice or via antagonist injection, and pERK suppressed development of FM-like pain. Both TRPV1 and TRPV4 protein expression levels were increased in the spinal cord (SC) of model mice, and EA at the ST36 acupoint decreased overexpression. This study strongly suggests that DRG TRPV1 overexpression and pERK signaling, as well as SC TRPV1 and TRPV4 overexpression, mediate hyperalgesia in a mouse FM pain model. The therapeutic efficacy of EA may result from the reversal of these changes in pain transmission pathways.     

Changes in pain and insulin-like growth factor 1 in fibromyalgia during exercise: the involvement of cerebrospinal inflammatory factors and neuropeptides

Introduction

Fibromyalgia (FM) is characterized by chronic pain. Impaired growth hormone responses and reduced serum insulin-like growth factor 1 (IGF-1) are common in FM. The aim was to examine changes in serum IGF-1, cerebrospinal fluid (CSF), neuropeptides, and cytokines during aerobic exercise in FM patients.

Methods

In total, 49 patients (median age, 52 years) with FM were included in the study. They were randomized to either the moderate- to high-intensity Nordic Walking (NW) program (n = 26) or the supervised low-intensity walking (LIW) program (n = 23). Patients participated in blood tests before and after 15 weeks of aerobic exercise. Changes in serum levels of free IGF-1, pain rating on a 0- to 100-mm scale, pain threshold, and 6-minute walk test (6MWT) were examined. CSF, neuropeptides, matrix metalloproteinase 3 (MMP-3), and inflammatory cytokines were determined. Nonparametric tests were used for group comparisons and correlation analyses.

Results

Serum free IGF-1 levels did not change during 15 weeks of exercise between the two groups, although the 6MWT significantly improved in the NW group (p = 0.033) when compared with LIW. Pain did not significantly change in any of the groups, but tended to decrease (p = 0.052) over time in the total group. A tendency toward a correlation was noted between baseline IGF-1 and a decrease of pain in response to exercise (r = 0.278; p = 0.059). When adjusted for age, this tendency disappeared. The change in serum free IGF-1 correlated positively with an alteration in CSF substance P (SP) levels (r^s = 0.495; p = 0.072), neuropeptide Y (NPY) (r^s = 0.802; p = 0.001), and pain threshold (r^s = 0.276; p = 0.058). Differing CSF SP levels correlated positively to a change in pain threshold (r^s = 0.600; p = 0.023), whereas the shift in CSF MMP-3 inversely correlated with an altered pain threshold (r^s = -0.569; p = 0.034).

Conclusions

The baseline level of serum free IGF-1 did not change during high or low intensity of aerobic exercise. Changes in IGF-1 correlated positively with a variation in CSF SP, NPY, and pain threshold. These data indicate a beneficial role of IGF-1 during exercise in FM.Trial registration: ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00643006","term_id":"NCT00643006"}}NCT00643006.     

Mechanisms of post-flight orthostatic intolerance

Post-flight orthostatic intolerance is a dramatic physiological consequence of human adaptation to microgravity made inappropriate by a sudden return to 1-G. The immediate mechanism is almost always a failure to maintain adequate tissue perfusion, specifically perfusion of the central nervous system, but vestibular dysfunction may occasionally be the primary cause. Orthostatic intolerance is present in a wide range of clinical disorders of the nervous and cardiovascular systems. The intolerance that is produced by spaceflight and 1-G analogs (bed rest, head-down tilt at a moderate angle, water immersion) is different from its clinical counterparts by being only transiently present in subjects who otherwise have normal cardiovascular and regulatory systems. However, the same set of basic pathophysiological elements should be considered in the analysis of any form of orthostatic intolerance.     

Islet neuronal abnormalities associated with impaired insulin secretion in type 2 diabetes in the Chinese hamster.

This study examined the relationship between islet neurohormonal characteristics and the defective glucose-stimulated insulin secretion in genetic type 2 diabetic Chinese hamsters. Two different sublines were studied: diabetes-prone CHIG hamsters and control CHIA hamsters. The CHIG hamsters were divided into three subgroups, depending on severity of hyperglycemia. Compared to normoglycemic CHIG hamsters and control CHIA hamsters, severely hyperglycemic CHIG hamsters (glucose > 15 mmol/l) showed marked glucose intolerance during i.p. glucose tolerance test and 75% impairment of glucose-stimulated insulin secretion from isolated islets. Mildly hyperglycemic CHIG animals (glucose 7.2-15 mmol/l) showed only moderate glucose intolerance and a 60% impairment of glucose-stimulated insulin secretion from the islets. Immunostaining for neuropeptide Y and tyrosine hydroxylase (markers for adrenergic nerves) and for vasoactive intestinal peptide (marker for cholinergic nerves) revealed significant reduction in immunostaining of islets in the severely but not in the mildly hyperglycemic animals, compared to control CHIA hamsters. The study therefore provides evidence that in this model of type 2 diabetes in Chinese hamsters, severe hyperglycemia is accompanied not only by marked glucose intolerance and islet dysfunction but also by reduced islet innervation. This suggests that islet neuronal alterations may contribute to islet dysfunction in severe but not in mild diabetes.