Next-generation RNA sequencing elucidates transcriptomic signatures of pathophysiologic nerve regeneration.

The cellular and molecular underpinnings of Wallerian degeneration have been robustly explored in laboratory models of successful nerve regeneration. In contrast, there is limited interrogation of failed regeneration, which is the challenge facing clinical practice. Specifically, we lack insight on the pathophysiologic mechanisms that lead to the formation of neuromas-in-continuity (NIC). To address this knowledge gap, we have developed and validated a novel basic science model of rapid-stretch nerve injury, which provides a biofidelic injury with NIC development and incomplete neurologic recovery. In this study, we applied next-generation RNA sequencing to elucidate the temporal transcriptional landscape of pathophysiologic nerve regeneration. To corroborate genetic analysis, nerves were subject to immunofluorescent staining for transcripts representative of the prominent biological pathways identified. Pathophysiologic nerve regeneration produces substantially altered genetic profiles both temporally and in the mature neuroma microenvironment, in contrast to the coordinated genetic signatures of Wallerian degeneration and successful regeneration. To our knowledge, this study presents as the first transcriptional study of NIC pathophysiology and has identified cellular death, fibrosis, neurodegeneration, metabolism, and unresolved inflammatory signatures that diverge from pathways elaborated by traditional models of successful nerve regeneration.

Development of a computerized 2D rating scale for continuous and simultaneous evaluation of two dimensions of a sensory stimulus.

Introduction: One-dimensional rating scales are widely used in research and in the clinic to assess individuals' perceptions of sensory stimuli. Although these scales provide essential knowledge of stimulus perception, their limitation to one dimension hinders our understanding of complex stimuli. Methods: To allow improved investigation of complex stimuli, a two-dimensional scale based on the one-dimensional Gracely Box Scale was developed and tested in healthy participants on a visual and an auditory task (rating changes in brightness and size of circles and rating changes in frequency and sound pressure of sounds, which was compared to ratings on one-dimensional scales). Before performing these tasks, participants were familiarized with the intensity descriptors of the two-dimensional scale by completing two tasks. First, participants sorted the descriptors based on their judgment of the intensity of the descriptors. Second, participants evaluated the intensity of the descriptors by pressing a button for the duration they considered matching the intensity of the descriptors or squeezing a hand grip dynamometer as strong as they considered matching the intensity of the descriptors. Results: Results from these tasks confirmed the order of the descriptors as displayed on the original rating scale. Results from the visual and auditory tasks showed that participants were able to rate changes in the physical attributes of visual or auditory stimuli on the two-dimensional scale as accurately as on one-dimensional scales. Discussion: These results support the use of a two-dimensional scale to simultaneously report multiple dimensions of complex stimuli.

CYP1B1-derived epoxides modulate the TRPA1 channel in chronic pain.

Pain is often debilitating, and current treatments are neither universally efficacious nor without risks. Transient receptor potential (TRP) ion channels offer alternative targets for pain relief, but little is known about the regulation or identities of endogenous TRP ligands that affect inflammation and pain. Here, transcriptomic and targeted lipidomic analysis of damaged tissue from the mouse spinal nerve ligation (SNL)-induced chronic pain model revealed a time-dependent increase in Cyp1b1 mRNA and a concurrent accumulation of 8,9-epoxyeicosatrienoic acid (EET) and 19,20-EpDPA post injury. Production of 8,9-EET and 19,20-EpDPA by human/mouse CYP1B1 was confirmed in vitro, and 8,9-EET and 19,20-EpDPA selectively and dose-dependently sensitized and activated TRPA1 in overexpressing HEK-293 cells and Trpa1-expressing/AITC-responsive cultured mouse peptidergic dorsal root ganglia (DRG) neurons. TRPA1 activation by 8,9-EET and 19,20-EpDPA was attenuated by the antagonist A967079, and mouse TRPA1 was more responsive to 8,9-EET and 19,20-EpDPA than human TRPA1. This latter effect mapped to residues Y933, G939, and S921 of TRPA1. Intra-plantar injection of 19,20-EpDPA induced acute mechanical, but not thermal hypersensitivity in mice, which was also blocked by A967079. Similarly, Cyp1b1-knockout mice displayed a reduced chronic pain phenotype following SNL injury. These data suggest that manipulation of the CYP1B1-oxylipin-TRPA1 axis might have therapeutic benefit.

Gene and protein expression of dorsal root ganglion sensory receptors in normotensive and hypertensive male rats.

The exercise pressor reflex (EPR), a neurocirculatory control mechanism, is exaggerated in hypertensive humans and rats. Disease-related abnormalities within the afferent arm of the reflex loop, including mechano- and metabosensitive receptors located at the terminal end of group III/IV muscle afferents, may contribute to the dysfunctional EPR in hypertension. Using control (WKY) and spontaneous hypertensive (SHR) rats, we examined dorsal root ganglion (DRG) gene and protein expression of molecular receptors recognized as significant determinants of the EPR. Twelve lumbar DRGs (6 left, 6 right) were harvested from each of 10 WKY [arterial blood pressure (MAP): 96 ± 9 mmHg] and 10 SHR (MAP: 144 ± 9 mmHg). DRGs from the left side were used for protein expression (Western blotting; normalized to GAPDH), whereas right-side DRGs (i.e., parallel structure) were used to determine mRNA levels (RNA-sequencing, normalized to TPM). Analyses focused on metabosensitive (ASIC3, Bradykinin receptor B2, EP4, P2X3, TRPv1) and mechanosensitive (Piezo1/2) receptors. Although Piezo1 was similar in both groups (P = 0.75), protein expression for all other receptors was significantly higher in SHR compared with WKY. With the exception of a greater Bradykinin-receptor B2 in SHR (P < 0.05), mRNA expression of all other receptors was not different between groups (P > 0.18). The higher protein content of these sensory receptors in SHR indirectly supports the previously proposed hypothesis that the exaggerated EPR in hypertension is, in part, due to disease-related abnormalities within the afferent arm of the reflex loop. The upregulated receptor content, combined with normal mRNA levels, insinuates that posttranscriptional regulation of sensory receptor protein expression might be impaired in hypertension.

Nicotinic Acetylcholine Receptor Partial Antagonist Polyamides from Tunicates and Their Predatory Sea Slugs.

In our efforts to discover new drugs to treat pain, we identified molleamines A-E (1-5) as major neuroactive components of the sea slug, Pleurobranchus forskalii, and their prey, Didemnum molle, tunicates. The chemical structures of molleamines were elucidated by spectroscopy and confirmed by the total synthesis of molleamines A (1) and C (3). Synthetic 3 completely blocked acetylcholine-induced calcium flux in peptidergic nociceptors (PNs) in the somatosensory nervous system. Compound 3 affected neither the α7 nAChR nor the muscarinic acetylcholine receptors in calcium flux assays. In addition to nociceptors, 3 partially blocked the acetylcholine-induced calcium flux in the sympathetic nervous system, including neurons from the superior cervical ganglion. Electrophysiology revealed a block of α3ß4 (mouse) and α6/α3ß4 (rat) nicotinic acetylcholine receptors (nAChRs), with IC50 values of 1.4 and 3.1 µM, respectively. Molleamine C (3) is a partial antagonist, reaching a maximum block of 76-82% of the acetylcholine signal and showing no partial agonist response. Molleamine C (3) may thus provide a lead compound for the development of neuroactive compounds with unique biological properties.

Neuroactive Type-A γ-Aminobutyric Acid Receptor Allosteric Modulator Steroids from the Hypobranchial Gland of Marine Mollusk, Conus geographus.

In a program to identify pain treatments with low addiction potential, we isolated five steroids, conosteroids A-E (1-5), from the hypobranchial gland of the mollusk Conus geographus. Compounds 1-5 were active in a mouse dorsal root ganglion (DRG) assay that suggested that they might be analgesic. A synthetic analogue 6 was used for a detailed pharmacological study. Compound 6 significantly increased the pain threshold in mice in the hot-plate test at 2 and 50 mg/kg. Compound 6 at 500 nM antagonizes type-A γ-aminobutyric acid receptors (GABAARs). In a patch-clamp experiment, out of the six subunit combinations tested, 6 exhibited subtype selectivity, most strongly antagonizing α1ß1γ2 and α4ß3γ2 receptors (IC50 1.5 and 1.0 µM, respectively). Although the structures of 1-6 differ from those of known neuroactive steroids, they are cell-type-selective modulators of GABAARs, expanding the known chemical space of neuroactive steroids.

Observation of Complement Protein Gene Expression Before and After Surgery in Opioid-Consuming and Opioid-Naive Patients.

Opioids may influence inflammation. We compared genes associated with pain and inflammation in patients who consumed opioids (3-120 mg of oral morphine equivalents per day) with those who did not for differential expression. White blood cells were assayed in 20 patients presenting for total lower extremity joint replacement. We focused on messenger ribonucleic acid expression of complement proteins. We report that the expression of a complement inhibitor, complement 4 binding protein A, was reduced, and the expression of a complement activator, complement factor D, was increased in opioid-consuming patients. We conclude that opioid consumption may influence expression of complement activators and inhibitors.

Gene Variants in Hepatic Metabolism, Gamma-Aminobutyric Acid-ergic Reward, and Prostaglandin Pathways in Opioid-Consuming and Opioid-Naïve Patients Presenting for Lower Extremity Total Joint Replacement.

Gene variants may contribute to individual differences in the experience of pain and the efficacy and reward of treatments. We explored gene variation in opioid-naïve and opioid-consuming patients undergoing elective lower extremity total joint replacement. We focused on 3 gene pathways including prostaglandin, gamma-aminobutyric acid (GABA)-ergic reward, and hepatic metabolism pathways. We report that for genes with possible or probable deleterious impact in these 3 pathways, opioid consumers had more gene variants than opioid-naïve patients (median 3 vs 1, P = .0092). We conclude that chronic opiate users may have genetic susceptibility to altered responses in reward/dependency and pain/inflammation pathways.

Skeletal muscle interstitial fluid metabolomics at rest and associated with an exercise bout: application in rats and humans.

Blood or biopsies are often used to characterize metabolites that are modulated by exercising muscle. However, blood has inputs derived from multiple tissues, biopsies cannot discriminate between secreted and intracellular metabolites, and their invasive nature is challenging for frequent collections in sensitive populations (e.g., children and pregnant women). Thus, minimally invasive approaches to interstitial fluid (IF) metabolomics would be valuable. A catheter was designed to collect IF from the gastrocnemius muscle of acutely anesthetized adult male rats at rest or immediately following 20 min of exercise (~60% of maximal O2 uptake). Nontargeted, gas chromatography-time-of-flight mass spectrometry analysis was used to detect 299 metabolites, including nonannotated metabolites, sugars, fatty acids, amino acids, and purine metabolites and derivatives. Just 43% of all detected metabolites were common to IF and blood plasma, and only 20% of exercise-modified metabolites were shared in both pools, highlighting that the blood does not fully reflect the metabolic outcomes in muscle. Notable exercise patterns included increased IF amino acids (except leucine and isoleucine), increased α-ketoglutarate and citrate (which may reflect tricarboxylic acid cataplerosis or shifts in nonmitochondrial pathways), and higher concentration of the signaling lipid oleamide. A preliminary study of human muscle IF was conducted using a 20-kDa microdialysis catheter placed in the vastus lateralis of five healthy adults at rest and during exercise (65% of estimated maximal heart rate). Approximately 70% of commonly detected metabolites discriminating rest vs. exercise in rats were also changed in exercising humans. Interstitium metabolomics may aid in the identification of molecules that signal muscle work (e.g., exertion and fatigue) and muscle health.

Propofol for Treatment-Resistant Depression: A Pilot Study.

Background: We hypothesized that propofol, a unique general anesthetic that engages N-methyl-D-aspartate and gamma-aminobutyric acid receptors, has antidepressant properties. This open-label trial was designed to collect preliminary data regarding the feasibility, tolerability, and efficacy of deep propofol anesthesia for treatment-resistant depression. Methods: Ten participants with moderate-to-severe medication-resistant depression (age 18-45 years and otherwise healthy) each received a series of 10 propofol infusions. Propofol was dosed to strongly suppress electroencephalographic activity for 15 minutes. The primary depression outcome was the 24-item Hamilton Depression Rating Scale. Self-rated depression scores were compared with a group of 20 patients who received electroconvulsive therapy. Results: Propofol treatments were well tolerated by all subjects. No serious adverse events occurred. Montreal Cognitive Assessment scores remained stable. Hamilton scores decreased by a mean of 20 points (range 0-45 points), corresponding to a mean 58% improvement from baseline (range 0-100%). Six of the 10 subjects met the criteria for response (>50% improvement). Self-rated depression improved similarly in the propofol group and electroconvulsive therapy group. Five of the 6 propofol responders remained well for at least 3 months. In posthoc analyses, electroencephalographic measures predicted clinical response to propofol. Conclusions: These findings demonstrate that high-dose propofol treatment is feasible and well tolerated by individuals with treatment-resistant depression who are otherwise healthy. Propofol may trigger rapid, durable antidepressant effects similar to electroconvulsive therapy but with fewer side effects. Controlled studies are warranted to further evaluate propofol's antidepressant efficacy and mechanisms of action. ClinicalTrials.gov: NCT02935647.

Correction: Antidepressant and Neurocognitive Effects of Isoflurane Anesthesia versus Electroconvulsive Therapy in Refractory Depression.

[This corrects the article DOI: 10.1371/journal.pone.0069809.].

Neural consequences of post-exertion malaise in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome.

Post exertion malaise is one of the most debilitating aspects of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome, yet the neurobiological consequences are largely unexplored. The objective of the study was to determine the neural consequences of acute exercise using functional brain imaging. Fifteen female Myalgic Encephalomyelitis/Chronic Fatigue Syndrome patients and 15 healthy female controls completed 30min of submaximal exercise (70% of peak heart rate) on a cycle ergometer. Symptom assessments (e.g. fatigue, pain, mood) and brain imaging data were collected one week prior to and 24h following exercise. Functional brain images were obtained during performance of: 1) a fatiguing cognitive task - the Paced Auditory Serial Addition Task, 2) a non-fatiguing cognitive task - simple number recognition, and 3) a non-fatiguing motor task - finger tapping. Symptom and exercise data were analyzed using independent samples t-tests. Cognitive performance data were analyzed using mixed-model analysis of variance with repeated measures. Brain responses to fatiguing and non-fatiguing tasks were analyzed using linear mixed effects with cluster-wise (101-voxels) alpha of 0.05. Myalgic Encephalomyelitis/Chronic Fatigue Syndrome patients reported large symptom changes compared to controls (effect size ≥0.8, p<0.05). Patients and controls had similar physiological responses to exercise (p>0.05). However, patients exercised at significantly lower Watts and reported greater exertion and leg muscle pain (p<0.05). For cognitive performance, a significant Group by Time interaction (p<0.05), demonstrated pre- to post-exercise improvements for controls and worsening for patients. Brain responses to finger tapping did not differ between groups at either time point. During number recognition, controls exhibited greater brain activity (p<0.05) in the posterior cingulate cortex, but only for the pre-exercise scan. For the Paced Serial Auditory Addition Task, there was a significant Group by Time interaction (p<0.05) with patients exhibiting increased brain activity from pre- to post-exercise compared to controls bilaterally for inferior and superior parietal and cingulate cortices. Changes in brain activity were significantly related to symptoms for patients (p<0.05). Acute exercise exacerbated symptoms, impaired cognitive performance and affected brain function in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome patients. These converging results, linking symptom exacerbation with brain function, provide objective evidence of the detrimental neurophysiological effects of post-exertion malaise.

Acylcarnitines as markers of exercise-associated fuel partitioning, xenometabolism, and potential signals to muscle afferent neurons.

NEW FINDINGS: What is the central question of this study? Does improved metabolic health and insulin sensitivity following a weight-loss and fitness intervention in sedentary, obese women alter exercise-associated fuel metabolism and incomplete mitochondrial fatty acid oxidation (FAO), as tracked by blood acylcarnitine patterns? What is the main finding and its importance? Despite improved fitness and blood sugar control, indices of incomplete mitochondrial FAO increased in a similar manner in response to a fixed load acute exercise bout; this indicates that intramitochondrial muscle FAO is inherently inefficient and is tethered directly to ATP turnover. With insulin resistance or type 2 diabetes mellitus, mismatches between mitochondrial fatty acid fuel delivery and oxidative phosphorylation/tricarboxylic acid cycle activity may contribute to inordinate accumulation of short- or medium-chain acylcarnitine fatty acid derivatives [markers of incomplete long-chain fatty acid oxidation (FAO)]. We reasoned that incomplete FAO in muscle would be ameliorated concurrent with improved insulin sensitivity and fitness following a ∼14 week training and weight-loss intervention in obese, sedentary, insulin-resistant women. Contrary to this hypothesis, overnight-fasted and exercise-induced plasma C4-C14 acylcarnitines did not differ between pre- and postintervention phases. These metabolites all increased robustly with exercise (∼45% of pre-intervention peak oxygen consumption) and decreased during a 20 min cool-down. This supports the idea that, regardless of insulin sensitivity and fitness, intramitochondrial muscle ß-oxidation and attendant incomplete FAO are closely tethered to absolute ATP turnover rate. Acute exercise also led to branched-chain amino acid acylcarnitine derivative patterns suggestive of rapid and transient diminution of branched-chain amino acid flux through the mitochondrial branched-chain ketoacid dehydrogenase complex. We confirmed our prior novel observation that a weight-loss/fitness intervention alters plasma xenometabolites [i.e. cis-3,4-methylene-heptanoylcarnitine and γ-butyrobetaine (a co-metabolite possibly derived in part from gut bacteria)], suggesting that host metabolic health regulated gut microbe metabolism. Finally, we considered whether acylcarnitine metabolites signal to muscle-innervating afferents; palmitoylcarnitine at concentrations as low as 1-10 µm activated a subset (∼2.5-5%) of these neurons ex vivo. This supports the hypothesis that in addition to tracking exercise-associated shifts in fuel metabolism, muscle acylcarnitines act as signals of exertion to short-loop somatosensory-motor circuits or to the brain.

Alendronate Attenuates Spinal Microglial Activation and Neuropathic Pain.

UNLABELLED: Many derivatives of bisphosphonates, which are inhibitors of bone resorption, have been developed as promising agents for painful pathologies in patients with bone resorption-related diseases. The mechanism for pain relief by bisphosphonates remains uncertain. Studies have reported that bisphosphonates could reduce central neurochemical changes involved in the generation and maintenance of bone cancer pain. In this study, we hypothesized that bisphosphonates would inhibit spinal microglial activation and prevent the development of hyperalgesia caused by peripheral tissue injury. We investigated the effects of alendronate (a nitrogen-containing bisphosphonate) on the development of neuropathic pain and its role in modulating microglial activation in vivo and in vitro. Intrathecal and intraperitoneal administration of alendronate relieved neuropathic pain behaviors induced by chronic constriction sciatic nerve injury. Alendronate also significantly attenuated spinal microglial activation and p38 mitogen-activated protein kinase (MAPK) phosphorylation without affecting astrocytes. In vitro, alendronate downregulated phosphorylated p38 and phosphorylated extracellular signal regulated kinase expression in lipopolysaccharide-stimulated primary microglia within 1 hour, and pretreatment with alendronate for 12 and 24 hours decreased the expression of inflammatory cytokines (tumor necrosis factor α, and interleukins 1ß and 6). These findings indicate that alendronate could effectively relieve chronic constriction sciatic nerve injury-induced neuropathic pain by at least partially inhibiting the activation of spinal microglia and the p38 MAPK signaling pathway. PERSPECTIVE: Alendronate could relieve neuropathic pain behaviors in animals by inhibiting the activation of spinal cord microglia and the p38 MAPK cell signaling pathway. Therapeutic applications of alendronate may be extended beyond bone metabolism-related disease.

Gene Expression Factor Analysis to Differentiate Pathways Linked to Fibromyalgia, Chronic Fatigue Syndrome, and Depression in a Diverse Patient Sample.

OBJECTIVE: To determine if independent candidate genes can be grouped into meaningful biologic factors, and whether these factors are associated with the diagnosis of chronic fatigue syndrome (CFS) and fibromyalgia syndrome (FMS), while controlling for comorbid depression, sex, and age. METHODS: We included leukocyte messenger RNA gene expression from a total of 261 individuals, including healthy controls (n = 61), patients with FMS only (n = 15), with CFS only (n = 33), with comorbid CFS and FMS (n = 79), and with medication-resistant (n = 42) or medication-responsive (n = 31) depression. We used exploratory factor analysis (EFA) on 34 candidate genes to determine factor scores and regression analysis to examine whether these factors were associated with specific diagnoses. RESULTS: EFA resulted in 4 independent factors with minimal overlap of genes between factors, explaining 51% of the variance. We labeled these factors by function as 1) purinergic and cellular modulators, 2) neuronal growth and immune function, 3) nociception and stress mediators, and 4) energy and mitochondrial function. Regression analysis predicting these biologic factors using FMS, CFS, depression severity, age, and sex revealed that greater expression in factors 1 and 3 was positively associated with CFS and negatively associated with depression severity (Quick Inventory for Depression Symptomatology score), but not associated with FMS. CONCLUSION: Expression of candidate genes can be grouped into meaningful clusters, and CFS and depression are associated with the same 2 clusters, but in opposite directions, when controlling for comorbid FMS. Given high comorbid disease and interrelationships between biomarkers, EFA may help determine patient subgroups in this population based on gene expression.

Fatigue sensation and gene expression in trained cyclists following a 40 km time trial in the heat.

PURPOSE: We examined the effect of race-effort cycling exercise with and without heat stress on post-exercise perceptions of fatigue and pain, as well as mRNA expression in genes related to exercise responses. METHODS: Trained cyclists (n = 20) completed 40 km time trials during temperate (TC, 21 °C) and hot (HC, 35 °C) conditions. Blood lactates were measured 1 and 5 min post-exercise. Venous blood samples and ratings of fatigue and pain perceptions were obtained at baseline and at 0.5, 8, 24, and 48 h post-exercise. Leukocyte mRNA expression was performed for metabolite detecting, adrenergic, monoamine, and immune receptors using qPCR. RESULTS: Significantly lower mean power (157 ± 32.3 vs 187 ± 40 W) and lactates (6.4 ± 1.7 vs 8.8 ± 3.2 and 4.2 ± 1.5 vs 6.6 ± 2.7 mmol L(-1) at 1- and 5-min post-exercise) were observed for HC versus TC, respectively (p < 0.05). Increases (p < 0.05) in physical fatigue and pain perception during TTs did not differ between TC and HC (p > 0.30). Both trials resulted in significant post-exercise decreases in metabolite detecting receptors ASIC3, P2X4, TRPV1, and TRPV4; increases in adrenergic receptors α2a, α2c, and ß1; decreases in adrenergic ß2, the immune receptor TLR4, and dopamine (DRD4); and increases in serotonin (HTR1D) and IL-10 (p < 0.05). Post-exercise IL-6 differed between TC and HC, with significantly greater increases observed following HC (p < 0.05). CONCLUSIONS: Both TT performances appeared to be regulated around a specific sensory perception of fatigue and pain. Heat stress may have compensated for lower lactate during HC, thereby matching changes in metabolite detecting and other mRNAs across conditions.

CaMKII Controls Whether Touch Is Painful.

The sensation of touch is initiated when fast conducting low-threshold mechanoreceptors (Aß-LTMRs) generate impulses at their terminals in the skin. Plasticity in this system is evident in the process of adaption, in which a period of diminished sensitivity follows prior stimulation. CaMKII is an ideal candidate for mediating activity-dependent plasticity in touch because it shifts into an enhanced activation state after neuronal depolarizations and can thereby reflect past firing history. Here we show that sensory neuron CaMKII autophosphorylation encodes the level of Aß-LTMR activity in rat models of sensory deprivation (whisker clipping, tail suspension, casting). Blockade of CaMKII signaling limits normal adaptation of action potential generation in Aß-LTMRs in excised skin. CaMKII activity is also required for natural filtering of impulse trains as they travel through the sensory neuron T-junction in the DRG. Blockade of CaMKII selectively in presynaptic Aß-LTMRs removes dorsal horn inhibition that otherwise prevents Aß-LTMR input from activating nociceptive lamina I neurons. Together, these consequences of reduced CaMKII function in Aß-LTMRs cause low-intensity mechanical stimulation to produce pain behavior. We conclude that, without normal sensory activity to maintain adequate levels of CaMKII function, the touch pathway shifts into a pain system. In the clinical setting, sensory disuse may be a critical factor that enhances and prolongs chronic pain initiated by other conditions. SIGNIFICANCE STATEMENT: The sensation of touch is served by specialized sensory neurons termed low-threshold mechanoreceptors (LTMRs). We examined the role of CaMKII in regulating the function of these neurons. Loss of CaMKII function, such as occurred in rats during sensory deprivation, elevated the generation and propagation of impulses by LTMRs, and altered the spinal cord circuitry in such a way that low-threshold mechanical stimuli produced pain behavior. Because limbs are protected from use during a painful condition, this sensitization of LTMRs may perpetuate pain and prevent functional rehabilitation.

Effect of Pregabalin on Cardiovascular Responses to Exercise and Postexercise Pain and Fatigue in Fibromyalgia: A Randomized, Double-Blind, Crossover Pilot Study.

Pregabalin, an approved treatment for fibromyalgia (FM), has been shown to decrease sympathetic nervous system (SNS) activity and inhibit sympathetically maintained pain, but its effects on exercise responses have not been reported. Methods. Using a randomized double-blind crossover design, we assessed the effect of 5 weeks of pregabalin (versus placebo) on acute cardiovascular and subjective responses to moderate exercise in 19 FM patients. Blood pressure (BP), heart rate (HR), and ratings of perceived exertion (RPE) during exercise and ratings of pain, physical fatigue, and mental fatigue before, during, and for 48 hours after exercise were compared in patients on pregabalin versus placebo and also versus 18 healthy controls. Results. On placebo, exercise RPE and BP were significantly higher in FM patients than controls (p < 0.04). Pregabalin responders (n = 12, defined by patient satisfaction and symptom changes) had significantly lower exercise BP, HR, and RPE on pregabalin versus placebo (p < 0.03) and no longer differed from controls (p > 0.26). Cardiovascular responses of nonresponders (n = 7) were not altered by pregabalin. In responders, pregabalin improved ratings of fatigue and pain (p < 0.04), but negative effects on pain and fatigue were seen in nonresponders. Conclusions. These preliminary findings suggest that pregabalin may normalize cardiovascular and subjective responses to exercise in many FM patients.