Activation Of Nerve Fibers Research Articles

Functional roles of bladder α1-adrenoceptors in the activation of single-unit primary bladder afferent activity in rats.

To clarify the involvement of bladder α1-adrenoceptors (α1-ARs) in afferent pathways by investigating the effects of silodosin and BMY7378, selective α1A- or α1D-AR antagonists, respectively, on single-unit afferent nerve fibre activity (SAA) of the primary bladder afferent nerves and their relationship with bladder microcontractions in rats. A total of 63 female Sprague-Dawley rats were anaesthetized with urethane. The SAA of Aδ and C fibres generated from the left L6 dorsal roots was determined using electrical stimulation of the left pelvic nerve and bladder distension. After measuring baseline SAA during constant filling cystometry, the procedure was repeated with i.v. (0.3-30 μg/kg) or intravesical (10 μm) administration of each antagonist. In separate rats, the bladder was filled with saline until the intravesical pressure reached 30 cmH2 O, and was kept under isovolumetric conditions, then the recording was performed with i.v.-administered vehicle and silodosin (0.3 μg/kg). A total of Aδ fibres and 33 C fibres were isolated from 63 rats. The SAA of Aδ fibres, but not C fibres, were dose-dependently decreased after both i.v. and intravesical administrations of each of the antagonists. In the experiments under bladder isovolumetric conditions, silodosin administration significantly decreased the SAA of Aδ fibres, but not C fibres, compared with vehicle administration. There were no significant effects on either the mean basal bladder pressure or microcontractions. The present study suggests that both α1A- or α1D-ARs in the rat bladder are involved in the activation of the bladder mechanosensory Aδ fibres during bladder filling, and that this activation may not be related to bladder microcontractions.

Cholinergic activation of the murine trachealis muscle via non-vesicular acetylcholine release involving low-affinity choline transporters

In addition to quantal, vesicular release of acetylcholine (ACh), there is also non-quantal release at the motor endplate which is insufficient to evoke postsynaptic responses unless acetylcholinesterase (AChE) is inhibited. We here addressed potential non-quantal release in the mouse trachea by organ bath experiments and (immuno)histochemical methods. Electrical field stimulation (EFS) of nerve terminals elicited tracheal constriction that is largely due to ACh release. Classical enzyme histochemistry demonstrated acetylcholinesterase (AChE) activity in nerve fibers in the muscle and butyrylcholinesterase (BChE) activity in the smooth muscle cells. Acute inhibition of both esterases by eserine significantly raised tracheal tone which was fully sensitive to atropine. This effect was reduced, but not abolished, in AChE, but not in BChE gene-deficient mice. The eserine-induced increase in tracheal tone was unaffected by vesamicol (10−5M), an inhibitor of the vesicular acetylcholine transporter, and by corticosterone (10−4M), an inhibitor of organic cation transporters. Hemicholinium-3, in low concentrations an inhibitor of the high-affinity choline transporter-1 (CHT1), completely abrogated the eserine effects when applied in high concentrations (10−4M) pointing towards an involvement of low-affinity choline transporters. To evaluate the cellular sources of non-quantal ACh release in the trachea, expression of low-affinity choline transporter-like family (CTL1-5) was evaluated by RT-PCR analysis. Even though these transporters were largely abundant in the epithelium, denudation of airway epithelial cells had no effect on eserine-induced tracheal contraction, indicating a non-quantal release of ACh from non-epithelial sources in the airways. These data provide evidence for an epithelium-independent non-vesicular, non-quantal ACh release in the mouse trachea involving low-affinity choline transporters.

Brain imaging signatures of the relationship between epidermal nerve fibers and heat pain perception

Although the small-diameter primary afferent fibers in the skin promptly respond to nociceptive stimuli and convey sensory inputs to the central nervous system, the neural signatures that underpin the relationship between cutaneous afferent fibers and pain perception remain elusive. We combined skin biopsy at the lateral aspect of the distal leg, which is used to quantify cutaneous afferent fibers, with fMRI, which is used to assess brain responses and functional connectivity, to investigate the relationship between cutaneous sensory nerves and the corresponding pain perception in the brain after applying heat pain stimulation to the dorsum of the right foot in healthy subjects. During painful stimulation, the degree of cutaneous innervation, as measured by epidermal nerve fiber density, was correlated with individual blood oxygen level-dependent (BOLD) signals of the posterior insular cortex and of the thalamus, periaqueductal gray, and rostral ventromedial medulla. Pain perception was associated with the activation of the anterior insular cortex and with the functional connectivity from the anterior insular cortex to the primary somatosensory cortex during painful stimulation. Most importantly, both epidermal nerve fiber density and activity in the posterior insular cortex showed a positive correlation with the strength of coupling under pain between the anterior insular cortex and the primary somatosensory cortex. Thus, our findings support the notion that the neural circuitry subserving pain perception interacts with the cerebral correlates of peripheral nociceptive fibers, which implicates an indirect role for skin nerves in human pain perception.

Modeling the impact of spinal cord stimulation paddle lead position on impedance, stimulation threshold, and activation region.

The effectiveness of spinal cord stimulation (SCS) for chronic pain treatment depends on selection of appropriate stimulation settings, which can be especially challenging following posture change or SCS lead migration. The objective of this work was to investigate the feasibility of using SCS lead impedance for determining the location of a SCS lead and for detecting lead migration, as well as the impact of axial movement and rotation of the St. Jude Medical PENTA™ paddle in the dorsal-ventral or medial-lateral directions on dorsal column (DC) stimulation thresholds and neural activation regions. We used a two-stage computational model, including a finite element method model of field potentials in the spinal cord during stimulation, coupled to a biophysical cable model of mammalian, myelinated nerve fibers to calculate tissue impedance and nerve fiber activation within the DC. We found that SCS lead impedance was highly sensitive to the distance between the lead and cerebrospinal fluid (CSF) layer. In addition, among all the lead positions studied, medial-lateral movement resulted in the most substantial changes to SC activation regions. These results suggest that impedance can be used for detecting paddle position and lead migration, and therefore for guiding SCS programming.

Abnormal Auditory Gain in Hyperacusis: Investigation with a Computational Model.

Hyperacusis is a frequent auditory disorder that is characterized by abnormal loudness perception where sounds of relatively normal volume are perceived as too loud or even painfully loud. As hyperacusis patients show decreased loudness discomfort levels (LDLs) and steeper loudness growth functions, it has been hypothesized that hyperacusis might be caused by an increase in neuronal response gain in the auditory system. Moreover, since about 85% of hyperacusis patients also experience tinnitus, the conditions might be caused by a common mechanism. However, the mechanisms that give rise to hyperacusis have remained unclear. Here, we have used a computational model of the auditory system to investigate candidate mechanisms for hyperacusis. Assuming that perceived loudness is proportional to the summed activity of all auditory nerve (AN) fibers, the model was tuned to reproduce normal loudness perception. We then evaluated a variety of potential hyperacusis gain mechanisms by determining their effects on model equal-loudness contours and comparing the results to the LDLs of hyperacusis patients with normal hearing thresholds. Hyperacusis was best accounted for by an increase in non-linear gain in the central auditory system. Good fits to the average patient LDLs were obtained for a general increase in gain that affected all frequency channels to the same degree, and also for a frequency-specific gain increase in the high-frequency range. Moreover, the gain needed to be applied after subtraction of spontaneous activity of the AN, which is in contrast to current theories of tinnitus generation based on amplification of spontaneous activity. Hyperacusis and tinnitus might therefore be caused by different changes in neuronal processing in the central auditory system.

Clinical comparison of botulinum toxin in motor and autonomic disorders: Similarities and differences

Botulinum toxin is a well established, highly effective and safe treatment option for movement disorders and autonomic diseases with excellent long term results. There is increasing evidence that the beneficial effect in both motor and autonomic indication is based on a complex mode of botulinum toxin action modulating efferent as well as afferent nerve fiber activity. In particular, this has been shown for the treatment of dystonia, spasticity and overactive bladder. A unique observation is that botulinum toxin has a markedly longer duration of action in autonomic than in motor disorders for which the reason remains unclear. Although botulinum toxin type B seems to have an initially higher affinity to autonomic nerve endings there is currently no clear evidence that type B is superior to type A in autonomic disorders. The risk of antibody formation probably does not depend on the target tissue injected and seems to be similar for movement disorders and autonomic indications. More research is needed to better understand similarities and differences of treatment outcome in motor and autonomic disorders.

Animal models of spontaneous activity in the healthy and impaired auditory system.

Spontaneous neural activity in the auditory nerve fibers and in auditory cortex in healthy animals is discussed with respect to the question: Is spontaneous activity noise or information carrier? The studies reviewed suggest strongly that spontaneous activity is a carrier of information. Subsequently, I review the numerous findings in the impaired auditory system, particularly with reference to noise trauma and tinnitus. Here the common assumption is that tinnitus reflects increased noise in the auditory system that among others affects temporal processing and interferes with the gap-startle reflex, which is frequently used as a behavioral assay for tinnitus. It is, however, more likely that the increased spontaneous activity in tinnitus, firing rate as well as neural synchrony, carries information that shapes the activity of downstream structures, including non-auditory ones, and leading to the tinnitus percept. The main drivers of that process are bursting and synchronous firing, which facilitates transfer of activity across synapses, and allows formation of auditory objects, such as tinnitus.

Rebuttal from John H. Coote and Michael J. White.

The study by D'Souza et al. (2015) provides evidence that endurance exercise training results in down-regulation of the pacemaker channel protein HCN4, with a consequent decrease in the funny current, so lengthening hyperpolarization between action potentials. We do not dispute this. However, training bradycardia does not occur without a functioning autonomic nervous system and is dependent on an increase in cardiac parasympathetic activity (Haykowsky & Tymchak, 2007; Coote & White, 2015). Part of our evidence is based on power spectral analysis of oscillations in the heart rhythm. These variations at the lower end of the frequency range (respiration, blood pressure and endocrine influenced) dominate the cardiac rhythm. Many studies have associated the degree of heart rate variability at the respiratory frequency with cardiac vagal tone. This has been criticized as having no substantial experimental basis (Stein et al. 2002; Monfredi et al. 2014; D'Souza et al. 2015). However, this is unfounded since experimental manoeuvres shown to change activity in cardiac parasympathetic nerve fibres (Davidson et al. 1976) also relate to similar changes in the respiratory-dependent peak in the power spectrum and these effects on the spectral peak are absent after cholinergic blockade (Akselrod et al. 1981; Pomeranz et al. 1985). The changes are too short term to involve down-regulation of the pacemaker channel protein HCN4. Thus an increase in the power of the respiratory peak of the spectrum of variations in heart rate following a period of endurance training would suggest an increase in cardiac parasympathetic activity. Monfredi et al. (2014), on the contrary, argue that the increase of variability is due primarily to a lower intrinsic pacemaker rate because the longer cycle lengths result in a non-linear (exponential) increase in variability of the interspike intervals. Therefore they contend that if intrinsic heart rate is lower, then a priori the heart rate variability will be greater. However, this does not accord with other evidence (Buch et al. 2002; Coote & White, 2015). In particular a comprehensive study in a group of healthy volunteers showed that inhibiting the funny current If with ivabradine did not reduce the respiratory-related peak in the spectrogram despite a significant fall in heart rate of 11 beats min–1 (Joannides et al. 2005). In conclusion, the bradycardia of endurance exercise not only depends on a decrease in intrinsic rate but also on an increase in cardiac parasympathetic activity.

REGIONAL ANESTHESIA CONTINUOUS BRACHIAL PLEXUS BLOCK WITH ULTRASONOGRAPHY GUIDANCE

Background: Regional anesthesia has an anti-inflammatory effect that blockade the C-fiber hence reduced cytokine production and blocked the activity of the sympathetic nerve fibers. Postoperative pain caused primarily by tissue inflammation and activity of the C-fibers in the manner of reduced the production of cytokines, regional anesthesia may limit the inflammatory response after surgery and severity of postoperative pain. Methods: This study is a clinical experimental study with randomized pre and post test control group design. A total of 24 samples were recruited in this study divided into two groups each consisting of 12 samples. The first group was given regional anesthesia method of continuous brachial plexus block with ultrasound guidance and the second group with general anesthesia method. T-test or Mann Whitney continued multivariate linear regression analysis was performed to analyze the differences in treatment and not because of differences in the initial values with significance level of p<0.05. Results: This study reports that the mean decreased levels of IL-6 postoperatively in 1stgroup is 29.8 lower than in 2ndgroup and it is statistically significant p< 0.05. There was an increase of IL-10 mean levels from preoperative to postoperatively with significance level of p<0.05 in both groups. Declined in the mean levels of PAF postoperatively in 1st group 1.3 lower than 2nd group and it was statistically significant p<0.05. The declined of postoperative VAS in 1st group is 3.1 lower than 2nd group and it is statistically significant p< 0.05, and it also contained the pure effect of PAF levels against value of VAS that any increased 1ng/ml levels of PAF then an increase in the value of 0.18 cm VAS and this was statistically significant p<0.05. Selection of this anesthesia technique in orthopedic antebrachii surgery provides better inflammatory response and improved clinical outcomes.

OPA1-related auditory neuropathy: site of lesion and outcome of cochlear implantation.

Hearing impairment is the second most prevalent clinical feature after optic atrophy in dominant optic atrophy associated with mutations in the OPA1 gene. In this study we characterized the hearing dysfunction in OPA1-linked disorders and provided effective rehabilitative options to improve speech perception. We studied two groups of OPA1 subjects, one comprising 11 patients (seven males; age range 13-79 years) carrying OPA1 mutations inducing haploinsufficiency, the other, 10 subjects (three males; age range 5-58 years) carrying OPA1 missense mutations. Both groups underwent audiometric assessment with pure tone and speech perception evaluation, and otoacoustic emissions and auditory brainstem response recording. Cochlear potentials were recorded through transtympanic electrocochleography from the group of patients harbouring OPA1 missense mutations and were compared to recordings obtained from 20 control subjects with normal hearing and from 19 subjects with cochlear hearing loss. Eight patients carrying OPA1 missense mutations underwent cochlear implantation. Speech perception measures and electrically-evoked auditory nerve and brainstem responses were obtained after 1 year of cochlear implant use. Nine of 11 patients carrying OPA1 mutations inducing haploinsufficiency had normal hearing function. In contrast, all but one subject harbouring OPA1 missense mutations displayed impaired speech perception, abnormal brainstem responses and presence of otoacoustic emissions consistent with auditory neuropathy. In electrocochleography recordings, cochlear microphonic had enhanced amplitudes while summating potential showed normal latency and peak amplitude consistent with preservation of both outer and inner hair cell activities. After cancelling the cochlear microphonic, the synchronized neural response seen in both normally-hearing controls and subjects with cochlear hearing loss was replaced by a prolonged, low-amplitude negative potential that decreased in both amplitude and duration during rapid stimulation consistent with neural generation. The use of cochlear implant improved speech perception in all but one patient. Brainstem potentials were recorded in response to electrical stimulation in five of six subjects, whereas no compound action potential was evoked from the auditory nerve through the cochlear implant. These findings indicate that underlying the hearing impairment in patients carrying OPA1 missense mutations is a disordered synchrony in auditory nerve fibre activity resulting from neural degeneration affecting the terminal dendrites. Cochlear implantation improves speech perception and synchronous activation of auditory pathways by bypassing the site of lesion.

Экспериментальное обоснование ретрактильного механизма формирования диастаза пересеченных нервов и дополнение к методам его лечения

Relevance Mechanisms of formation and treatment of the interval space between stumps of sectioned nerve remain one of actual and poorly studied factors of formation of hypercollagen scar of nerve and nevroma. The purpose of the study The goal of the work is study of possibility of retraction of nerve fibers in formation of interval between stumps of sectioned nerve and an attempt at its inhibition. Materials and methods Signs of retraction of nerve fibers on human amputated extremities are studied with aid of silver impregnation of fixed preparations by Bielschowsky-Gros. For experimental study of regularities of contraction of myelinated and myelinles nerve fibers at their section there are used models of living preparations of vertebrate and invertebrate animals. With aid of phase-contrast computerized videomicroscopy, a possibility of participation of contraction of nerve fibers in an increase of space between stumps of sectioned nerve is studied. A possibility of medicament inhibition of this retraction with aid of blockers of cytoplasmic mobility is shown. Electrophysiological methods are used for study of effect of these substances on neuromembranes and a possibility of use of the tested blockers is checked in experiments of treatment of the whole animals. Results and their discussion On fixed histological preparations of nerves of damaged and amputated human extremities there are detected signs of contractile activities of nerve fibers. In experiments on isolated living fibers for the first time demonstrated is dynamics of the bidirectional retraction of myelinated nerve fibers, which accepts their participation in enlargement of diastasis of cross-sectioned nerves. On myelinles axons with preserved neuronal bodies there is studied action of blockers of contractile activity of the cytoplasm: nimodipine, cytochalasin, blebbistatin, and colchicine. There is proved participation in retraction of axons of the main protein polymers of the axoplasmic cytoskeleton and a possibility of use of these blockers for inhibition of posttraumatic retraction of nerve fibers. Electrophysiological experiments have shown a low toxicity of these agents and a possibility of their use for treatment of the traumatic diastasis of nerves in experiments on the whole animals. Conclusion 1. There is shown the capability for retraction in myelin nerve fibers of human and other vertebrates after transaction of nerves. 2. Based on experiments on living single neurons with preserved processes, a hypothesis is formulated about participation of active contraction of axons in mechanism of formation of diastasis. 3. There is analyzed the ability of several main blockers of the axoplasm motility: cytochalasin B, blebbistatin, colchicine, and nimodipine to stop traumatic retraction of neurites. 4. The absence is shown of pathological influences of the studied inhibitors on electrophysiological properties of the neuromembrane, which admits their use for treatment of diastasis at transaction of nerves in the whole experimental animals. Key words Nerve diastase, nervous fibres retraction, mechanism axoplasm retraction, axon retraction inhibitors

An Auxiliary Educational Tool for Propagating Single and Compound Nerve Action Potential

Objective: The use of simulation in medical education has become an important and successfully implemented auxiliary method, recently. In this study, we aimed to present a compact screen-based computer simulation for second year medical students so that they may experience various aspects of peripheral nerve electrophysiology by themselves. Methods: The model used in the calculations combines both the passive and active membrane properties which were described in passive cable theory and in the classical study of Hodgkin and Huxley on membrane potential generation, respectively. Results: The simulation provides numerical and visual demonstration for various electrophysiological features of nerve cell such as membrane potential development, threshold stimulus, refractoriness, conduction in myelinated fiber, myelin and temperature effect on conduction etc. Besides, users may also have experience on propagation of compound nerve action potential that is the combined activation of nerve fibers. Conclusion: We suggest that this simulation may be considered as an auxiliary tool for classical physiology laboratory sessions. It is our intent to share and to make the simulation freely available to all interested readers.

Mast Cell Activation in Sickle Mice Stimulates Endothelial Dysfunction

We showed that mast cell activation/degranulation contributes to pain and neurogenic inflammation characterized by increased vascular permeability in sickle mice (Vincent et al., Blood 2013). Mast cells are tissue resident inflammatory cells, which are located in the vicinity of vasculature and nerve fibers. Neurogenic inflammation is mediated by activation of peripheral nerve fibers via the release of vasoactive and neurinflammatory peptide, substance P. However, the products of mast cell activation may have direct effects on the vasculature. Sickle pathobiology is characterized by endothelial dysfunction, inflammation and oxidative stress. We hypothesized that the neuropeptides, proteases, and cytokines released from activated mast cells lead to endothelial dysfunction by stimulating endoplasmic reticulum (ER) stress, and mitochondrial dysfunction, leading to oxidative stress. We examined the direct effect of mast cell activation on endothelium. Since morphine is used to treat pain in sickle cell disease (SCD) and also influences endothelial signaling (Gupta et al., Cancer Res 2002), we investigated if morphine contributes to endothelial dysfunction.Methods. We isolated mast cells from the skin of HbSS-BERK sickle mice, which demonstrate severe mast cell activation and hyperalgesia (pain) and HbAA-BERK control mice. Mast cells from sickle mouse skin continue to degranulate in culture, but the mast cells from control mice do not. We collected the supernatant from mast cell cultures and used it to treat primary mouse brain microvascular endothelial cells (MBMEC) in vitro. ER stress was assayed using ER-Tracker Green (Glibenclamide BODIPY FL) dye (Molecular Probes) on live cells followed by laser scanning confocal microscopy (LSCM). ER stress markers, E74-like factor 2a (ELF2a), X-box binding protein 1 (XBP1), and glucose regulated protein 78 (GRP78), were analyzed with Western Immunoblotting. Mitochondrial function was analyzed by estimating mitochondrial membrane potential with MitoProbe JC-1 (Molecular Probes), which exhibits potential-dependent accumulation in mitochondria, causing a fluorescence emission shift from green (~529 nm) to red (~590 nm). Mitochondrial depolarization (dysfunction) was analyzed by a decrease in red/green ratio using LSCM. ROS was assayed using 2’7’-dichlorofluorescein diacetate and quantifying the fluorescence at the max excitation and emission spectra of 495 nm and 529 nm, respectively.Results. Supernatant from sickle mast cells led to significant ER stress in MBMEC, as compared to the supernatant from control mast cells (p<0.05). Western blotting demonstrated an increase in ER stress markers, phosphor-elF2a, sXBP1 and GRP78, in MBMEC incubated with sickle mast cell supernatant as compared to control mast cell supernatant. Complementary to the sickle mast cell-induced ER stress, mitochondria potential decreased in MBMEC treated with sickle mast cell supernatant as compared to control mast cell supernatant (p < 0.05). We observed that supernatant from activated cutaneous mast cells stimulated a 10-fold increase in reactive oxygen species (ROS) in MBMEC (p < 0.05). This effect was further exacerbated in MBMEC treated with both sickle mast cell supernatant and morphine (p < 0.01). Morphine alone increased ROS production 4-fold in MBMEC. ER stress inhibitor, Salubrinal, inhibited ROS production in MBMEC induced by sickle mast cells. Together, these data suggest that mast cell activation stimulates ER stress in MBMEC, which may lead to mitochondrial dysfunction and generation of ROS. Thus, mast cell degranulation alone/and in addition to morphine, may contribute to endothelial dysfunction in SCD. DisclosuresNo relevant conflicts of interest to declare.

Effects of Diet and Mating on Sickle Cell Disease Murine

Patients experiencing chronic and/or recurrent pain show a correlative decline in health and lifespan. In turn, declining health and sensory effects may contribute to persistent pain and poor response to analgesia. We therefore hypothesized that dietary alterations to improve health and stress reduction by mating may reduce chronic pain in male sickle mice.Methods. We used male HbSS-BERK (sickle) mice, which show hyperalgesia as compared to and HbAA-BERK (control) mice (Kohli et al., Blood 2010). Breeders and pups up to 12 wks of age were fed Sickle Mouse Diet (59M3, TestDiet) and 18% Protein Rodent Diet (2018, Harlan), thereafter, called ‘sickle’ and ‘rodent’ diet. Sickle diet contained 26.4% Protein, 11.1% fat and 27.5% and 26% kcal/g of each, respectively. Rodent diet contained 18.6% protein and 6.2% fat, and 24% and 18% kcal/g of each, respectively. Vitamins were about 2-fold higher in sickle as compared to rodent diet. Sickle mice showing hyperalgesia were recruited and treated as follows: [A] Rodent diet without mating (RD/M-); [B] Sickle diet with mating (SD/M+); [C] Rodent diet with mating (RD/M+); [D] Sickle diet without mating (SD/M-) and [E] mice on SD and mating for 4 weeks, were deprived of SD and mating and fed RD. Control mice which do not show hyperalgesia were fed RD without mating. Sensory testing was performed at baseline (BL) at recruitment and weekly, to evaluate mechanical hyperalgesia with von Frey filaments, thermal hyperalgesia in response to heat/cold and grip force for musculoskeletal/deep tissue hyperalgesia. Following the treatments, release of cytokines from skin biopsies was analyzed by cytokine arrays as described by us earlier (Vincent et al., Blood 2013), and spinal cords were analyzed for nociceptive signaling.Results. We did not observe difference in the body weight of mice between different groups at any time. White blood cell counts and spleen weight were significantly increased in group E following the withdrawal of SD and mating as compared to group C on SD/M+ (p<0.05), but the liver and kidney did not show any difference amongst groups. Groups B and C involving mating with SD/M+ or RD/M+, respectively, showed maximum decrease in mechanical, and thermal hyperalgesia following 3 weeks of treatment as compared to baseline (p<0.05 and 0.0001 for mechanical, p<0.001 and 0.0001 for thermal, respectively for B and C), suggesting that mating decreases sensitivity to noxious stimuli including touch and temperature. In group E (mice were in mating and with SD for 4 wks), withdrawal of sickle diet and mating for 4 weeks, led to a significant increase in thermal hyperalgesia as compared to the start of the withdrawal (p<0.05 for mechanical and heat). Group D (SD/M-) showed a significant decline thermal hyperalgesia one week after starting the sickle diet as compared to BL (p<0.0001 for cold and <0.005 for heat). Thus sickle diet in the absence of mating reduced hyperalgesia, but the reduction with sickle diet only (SD/M-) was significantly less than the reduction caused by mating (RD/M+) or by sickle diet with mating (SD/M+), suggesting that mating is more effective than diet in ameliorating pain. None of the groups demonstrated a decrease in grip force, suggesting that deep tissue pain was not influenced or that the strength of mice was not influenced and the influence is perhaps restricted to the periphery (skin). Cytokine profile of the skin showed a significant decrease in IL6, MIP-1a, RANTES, MCP-1 and GM-CSF in group B, (SD/M+) as compared to group A, (RD/M-), indicating that the diet and mating decrease inflammation in the periphery, thus reducing the activation of peripheral nerve fibers, resulting in reduced hyperalgesia. Consistent with reduced inflammation, spinal cords of group B (SD/M+) showed a significant decrease in nociceptive signaling of phosphorylation of Stat3 pathway as compared to group A (RD/M-). Since, Stat3 is associated with transcription of inflammatory cytokines, it likely reduces the inflammatory response in the spinal cord and inflammatory pain. These data suggest that high protein/high fat diet and mating reduce inflammation and hyperalgesia in sickle mice. Stress appears to be a critical factor in the perception of pain, because mating attenuated hyperalgesia. Thus, improving general health and happiness and stress reduction may reduce pain in SCD. DisclosuresNo relevant conflicts of interest to declare.

Structure, function, and signaling of taste G-protein-coupled receptors.

Detection of tastes is critical for animals. Sweet, umami and bitter taste are mediated by G-protein-coupled receptors that are expressed in the taste receptor cells. TAS1Rs which belong to class C G-protein-coupled receptors form heterodimeric complexes to function as sweet (TAS1R2 + TAS1R3) or umami (TAS1R1 + TAS1R3) taste receptors. Umami taste is also considered to be mediated by mGluRs. TAS2Rs belong to class A G-protein-coupled receptors and are responsible for bitter taste. After activation of these receptors, their second messenger pathways lead to depolarization and intracellular calcium increase in taste receptor cells. Then, transmitter is released from taste receptor cells leading to activation of taste nerve fibers and taste information is sent to the central nervous system. Recent studies on heterologous expression system and molecular modeling lead to better understanding of binding site of TAS1Rs and TAS2Rs and molecular mechanisms for interaction between taste substances and these receptors. TAS1Rs and TAS2Rs have multiple and single binding sites for structurally diverse ligands, respectively. Sensitivities of these receptors are known to differ among individuals, strains, and species. In addition, some species abolish these receptors and signaling molecules. Here we focus on structure, function, signaling, polymorphism, and molecular evolution of the taste G-protein-coupled receptors.

CRPS-Related Neurogenic Edema Responsive to Dextromethorphan/Quinidine

Dear Editor, Complex regional pain syndrome (CRPS) generally follows trauma to soft tissue (CRPS type I) or a major peripheral nerve (CRPS type II), and is characterized by severe pain disproportionate to the inciting injury, which may migrate to regions anatomically removed from the site of trauma. Apart from pain, patients with CRPS demonstrate sensory (e.g., hyperesthesia or allodynia), vasomotor (e.g., temperature or skin color asymmetry), sudomotor (e.g., edema or sweating changes), or motor/trophic changes (tremor, dystonia, thinning of nails) [1]. The pathophysiology of CRPS remains unknown, but potential mechanisms include injury to C- and A-delta sensory nerve fibers resulting in neurogenic inflammation and central sensitization [2]. According to this model, nerve fiber activation causes release substance P and calcitonin gene-related peptides resulting in protein extravasation, edema, and accumulation of inflammatory cytokines. N-methyl-D-aspartate (NMDA) receptor-mediated central sensitization ensues, and inflammation (e.g., microglial activation) spreads up the neuraxis, correlating with spread of pain beyond the site of injury. …

Selective Inhibitory Effect of Imidafenacin and 5-Hydroxymethyl Tolterodine on Capsaicin Sensitive C Fibers of the Primary Bladder Mechanosensitive Afferent Nerves in the Rat

Imidafenacin and fesoterodine are used to treat overactive bladder. Imidafenacin, fesoterodine and its active metabolite 5-hydroxymethyl tolterodine are muscarinic receptor antagonists. It is believed that these agents act on afferent nerves in addition to smooth muscle. We investigated the effects of imidafenacin and 5-hydroxymethyl tolterodine on single unit afferent activity of mechanosensitive capsaicin sensitive and insensitive primary bladder afferent nerve fibers in rats. Female Sprague Dawley® rats were anesthetized. Single unit afferent activity was recorded from the L6 dorsal roots and classified by conduction velocity as that of Aδ or C fibers. After measuring control single afferent activity during constant filling cystometry the procedure was repeated with intravenous administration of imidafenacin (0.3 to 30 μg/kg) or 5-hydroxymethyl tolterodine (0.01 to 1 mg/kg) at cumulative doses with or without intravesical capsaicin or oxotremorine-M instillation. A total of 139 single unit afferent fibers were isolated from 111 rats, including 19 Aδ and 120 C fibers. Neither imidafenacin nor 5-hydroxymethyl tolterodine significantly affected the overall single unit afferent activity of Aδ or C fibers. Based on capsaicin sensitivity C fibers were divided into capsaicin sensitive and insensitive groups. Each antimuscarinic inhibited the single unit afferent activity of capsaicin sensitive C fibers but not of capsaicin insensitive C fibers at the highest dose. Moreover, oxotremorine-M facilitated single unit afferent activity in a proportion of C fibers. The facilitated single unit afferent activity was significantly attenuated by the highest dose of imidafenacin. These findings demonstrate that imidafenacin and 5-hydroxymethyl tolterodine can selectively inhibit capsaicin sensitive C fibers among mechanosensitive bladder afferents by antagonizing bladder muscarinic receptors.

Enhanced insulin sensitivity and acute regulation of metabolic genes and signaling pathways after a single electrical or manual acupuncture session in female insulin-resistant rats.

To compare the effect of a single session of acupuncture with either low-frequency electrical or manual stimulation on insulin sensitivity and molecular pathways in the insulin-resistant dihydrotestosterone-induced rat polycystic ovary syndrome (PCOS) model. Both stimulations cause activation of afferent nerve fibers. In addition, electrical stimulation causes muscle contractions, enabling us to differentiate changes induced by activation of sensory afferents from contraction-induced changes. Control and PCOS rats were divided into no-stimulation, manual-, and electrical stimulation groups and insulin sensitivity was measured by euglycemic hyperinsulinemic clamp. Manually stimulated needles were rotated 180° ten times every 5 min, or low-frequency electrical stimulation was applied to evoke muscle twitches for 45 min. Gene and protein expression were analyzed by real-time PCR and Western blot. The glucose infusion rate (GIR) was lower in PCOS rats than in controls. Electrical stimulation was superior to manual stimulation during treatment but both methods increased GIR to the same extent in the post-stimulation period. Electrical stimulation decreased mRNA expression of Adipor2, Adrb1, Fndc5, Erk2, and Tfam in soleus muscle and increased ovarian Adrb2 and Pdf. Manual stimulation decreased ovarian mRNA expression of Erk2 and Sdnd. Electrical stimulation increased phosphorylated ERK levels in soleus muscle. One acupuncture session with electrical stimulation improves insulin sensitivity and modulates skeletal muscle gene and protein expression more than manual stimulation. Although electrical stimulation is superior to manual in enhancing insulin sensitivity during stimulation, they are equally effective after stimulation indicating that it is activation of sensory afferents rather than muscle contraction per se leading to the observed changes.

Decreased basal tear in aged mice is linked to morphological and functional changes in corneal sensory nerve fibers

AbstractPurpose To determine whether the effects of aging on density, morphology and functional activity of corneal cold sensory nerve fibers are associated with changes in basal tearing rate.Methods TRPM8‐EYFP and TRPM8‐KO mice of different ages ranging from 90 to 720 postnatal days were studied. Basal tearing was measured in anesthetized animals, using phenol red threads. Corneal nerves expressing EYFP protein were identified in whole mount corneas using immunohistochemical techniques. Also, trigeminal ganglia (TG) were processed for immunofluorescence techniques against TrkA and CGRP. Extracellular electrical activity of single sensory nerve endings of the corneal surface was recorded in excised and superfused eyes.Results The number of TRPM8+ fibers and nerve terminals decreased with age. Also, fibers of p90 mice were morphologically different from those of p720 TRPM8‐EYFP mice resembling those found in TRPM8‐KO mice. Basal tearing rate decreased in parallel with the reduction in number of TRPM8+ fibers. Two different populations of sensory nerve endings responding to cold were distinguished electrophysiologically: Low and High‐threshold cold terminals. With aging, the incidence of low‐threshold cold nerve endings decreased while more high‐threshold nerve endings were found. Also, a population of non‐peptidergic and another of peptidergic TRPM8+ neurons were distinguished in the TG.Conclusion Corneal cold sensory fibers and terminals of TRPM8‐EYFP mice developed parallel changes in number and morphology, functional activity and basal tearing rate during aging, thus supporting the hypothesis that cold thermoreceptor activity and basal tearing are functionally associated.

Combined KHFAC + DC nerve block without onset or reduced nerve conductivity after block

Objective. Kilohertz frequency alternating current (KHFAC) waveforms have been shown to provide peripheral nerve conductivity block in many acute and chronic animal models. KHFAC nerve block could be used to address multiple disorders caused by neural over-activity, including blocking pain and spasticity. However, one drawback of KHFAC block is a transient activation of nerve fibers during the initiation of the nerve block, called the onset response. The objective of this study is to evaluate the feasibility of using charge balanced direct current (CBDC) waveforms to temporarily block motor nerve conductivity distally to the KHFAC electrodes to mitigate the block onset-response. Approach. A total of eight animals were used in this study. A set of four animals were used to assess feasibility and reproducibility of a combined KHFAC + CBDC block. A following randomized study, conducted on a second set of four animals, compared the onset response resulting from KHFAC alone and combined KHFAC + CBDC waveforms. To quantify the onset, peak forces and the force-time integral were measured during KHFAC block initiation. Nerve conductivity was monitored throughout the study by comparing muscle twitch forces evoked by supra-maximal stimulation proximal and distal to the block electrodes. Each animal of the randomized study received at least 300 s (range: 318–1563 s) of cumulative dc to investigate the impact of combined KHFAC + CBDC on nerve viability. Main results. The peak onset force was reduced significantly from 20.73 N (range: 18.6–26.5 N) with KHFAC alone to 0.45 N (range: 0.2–0.7 N) with the combined CBDC and KHFAC block waveform (p < 0.001). The area under the force curve was reduced from 6.8 Ns (range: 3.5–21.9 Ns) to 0.54 Ns (range: 0.18–0.86 Ns) (p < 0.01). No change in nerve conductivity was observed after application of the combined KHFAC + CBDC block relative to KHFAC waveforms. Significance. The distal application of CBDC can significantly reduce or even completely prevent the KHFAC onset response without a change in nerve conductivity.