Afferent Function Research Articles

Prolonged time of after-sensation after experimental pain stimuli despite efficient conditioned pain modulation in patients with chronic neuropathic pain after traumatic nerve injuries in upper extremity.

As yet, there is limited research that can identify factors that differentiate between painful and nonpainful neuropathies after traumatic nerve injury. The aim of this study was to compare subjects with pain and without pain, all after operative nerve repair in the upper extremities. Subjects in both groups (pain, n = 69; painless, n = 62) underwent clinical assessment of sensory nerve function and psychophysical tests: quantitative sensory testing and conditioned pain modulation (CPM). Conditioned pain modulation was assessed by pain ratings to 120 seconds pressure stimuli administered before and after a 60 seconds noxious 4°C cold conditioning stimulus (CS). Time of recovery (time off) of pain intensity from peak VASmaxc after CS was recorded. Questionnaires about the quality of life (RAND-36) and disability of the extremity (QuickDash) were completed. There were no significant differences between groups for CPM (P = 0.19). Time off was 42 seconds in subjects with pain in comparison with 28 seconds in those without pain (P < 0.0001). Compared with individuals reporting no pain, participants with neuropathic pain after nerve injuries had 1.8 times the odds of recovering later after CS, gain of function findings at sensory examination (P < 0.0001), lower scores of the physical component of RAND-36 (P < 0.0001), and increase arm disability (P < 0.0001). Hyperesthesia to cold pain stimulation (P = 0.03) and lowered pain pressure threshold (P = 0.01) were found in the pain group. Recovery after the pain induced by cold CS indicates changes in central processing of pain and provides a potential measurement of endogenous pain modulation in individuals with chronic neuropathic pain.

The Mysteries of Capsaicin-Sensitive Afferents

A fundamental subdivision of nociceptive sensory neurons is named after their unique sensitivity to capsaicin, the pungent ingredient in hot chili peppers: these are the capsaicin-sensitive afferents. The initial excitation by capsaicin of these neurons manifested as burning pain sensation is followed by a lasting refractory state, traditionally referred to as “capsaicin desensitization,” during which the previously excited neurons are unresponsive not only to capsaicin but a variety of unrelated stimuli including noxious heat. The long sought-after capsaicin receptor, now known as TRPV1 (transient receptor potential cation channel, subfamily V member 1), was cloned more than two decades ago. The substantial reduction of the inflammatory phenotype of Trpv1 knockout mice has spurred extensive efforts in the pharmaceutical industry to develop small molecule TRPV1 antagonists. However, adverse effects, most importantly hyperthermia and burn injuries, have so far prevented any compounds from progressing beyond Phase 2. There is increasing evidence that these limitations can be at least partially overcome by approaches outside of the mainstream pharmaceutical development, providing novel therapeutic options through TRPV1. Although ablation of the whole TRPV1-expressing nerve population by high dose capsaicin, or more selectively by intersectional genetics, has allowed researchers to investigate the functions of capsaicin-sensitive afferents in health and disease, several “mysteries” remain unsolved to date, including the molecular underpinnings of “capsaicin desensitization,” and the exact role these nerves play in thermoregulation and heat sensation. This review tries to shed some light on these capsaicin mechanisms.

How to assess the recovery of muscular function following nerve injury: A view from surgeons and patients

Patient experience of motor recovery from denervation paralysis is complex and textured. The Medical Research Council (MRC) system of grading muscle peak volitional force is widely used as a single measure of assessment. However, it is becoming clear that current motor function assessments are not reflecting the patient lived experience of muscle reinnervation. Therefore, this study aimed to engage international expert nerve surgeons in a classical Delphi process to achieve a consensus of opinion on the ideal clinical assessment of motor function. This was compared with patient-reported impairments of reinnervated muscle. Invitations to engage in the Delphi process were extended to expert peripheral nerve surgeons across two international specialist meetings. For comparison, patients who attended a "Nerve Injury Community Day" were invited to complete a questionnaire on patient-reported impairments of reinnervated muscle. Questions were designed on the basis of a literature review and the clinical experiences of a specialist nerve injury unit. A combination of direct yes/no, multiple choice, open-ended and Likert questions were employed throughout the questionnaires. Eighteen surgeons engaged with the Delphi process; 18 and 11 responded to the first and second rounds respectively. Thirty-one patients responded to the questionnaire. It was found that clinicians were strongly biased towards efferent assessments of muscular function, while patients strongly favoured muscular fatigue, co-contraction and pain when monitoring their own recovery. The findings suggest that current clinical assessments of muscular function are inadequate and should embody measurements of afferent muscular function to better reflect the lived experience of muscle reinnervation.

Effects of Transspinal Direct Current Stimulation on Cycling Perception of Effort and Time to Exhaustion.

Ciccone, AB, Fry, AC, Emerson, DM, Gallagher, PM, Herda, TJ, and Weir, JP. Effects of transspinal direct current stimulation on cycling perception of effort and time to exhaustion. J Strength Cond Res 35(2): 347-352, 2021-In the past decade, researchers have investigated the efficacy of transspinal direct current stimulation (tsDCS) on the central nervous system and afferent neuron function in humans. Recently, data have suggested it may be possible for such tsDCS-induced changes in neuromuscular function to enhance performance. This study used noninvasive thoracic spine tsDCS to determine if cycling performance and perception of effort could be modulated by tsDCS. In 3 different stimulation conditions, anodal, cathodal, and sham, subjects cycled at 80% of their maximal aerobic capacity until exhaustion and reported their rating of perceived exertion (RPE) every minute. From this period, we compared the RPE responses over the first 3 minutes and time to exhaustion. There was no significant difference in time to exhaustion between anodal (408 ± 121 seconds), cathodal (413 ± 168 seconds), and sham (440 ± 189 seconds) conditions (p = 0.58). There was no significant difference in RPE from minutes 1-3 (collapsed across time) between anodal (12.9 ± 2.4 arbitrary units (AUs)), cathodal (13.3 ± 2.2 AUs), and sham (12.9 ± 2.1 AUs) conditions (p = 0.51). These data suggest tsDCS condition did not influence cycling performance or perception of effort during high-intensity cycling. Therefore, thoracic spine and lower abdominal montage delivering a current density of 0.071 mA·cm-2 for 20 minutes likely does not substantially improve high-intensity cycling work capacity. Therefore, more research is needed to investigate the efficacy of tsDCS and which stimulation methods may and may not enhance human performance.

The effect of α-lipoic acid treatment on plasma asymmetric dimethylarginine, a biomarker of endothelial dysfunction in diabetic neuropathy

IntroductionDiabetic neuropathy may develop on a background of hyperglycaemia and is associated with increased oxidative stress. Elevated asymmetric dimethylarginine (ADMA) levels are linked to oxidative stress reducing the synthesis of nitric oxide (NO) by uncoupling NO synthase. Oxidative stress induces considerable changes in nerve conduction velocity in diabetic patients. There is strong evidence that α-lipoic acid (ALA) as an antioxidant may improve nerve conduction and relieve neuropathic symptoms. We aimed to investigate the relationship between endothelial dysfunction and NO synthesis in type 2 diabetic patients with peripheral neuropathy after ALA treatment.Material and methodsFifty-four type 2 diabetic patients with neuropathy were included in the study. Serum ADMA concentration, ICAM-1, VCAM-1, oxidised low-density lipoprotein (oxLDL), and TNF-α levels were determined with Enzyme-Linked Immunosorbent Assay (ELISA). Nitric oxide concentration was measured by Griess reaction. Peripheral sensory nerve function was assessed by current perception threshold (CPT) testing. Autonomic function was assessed by Ewing’s five standard cardiovascular reflex tests composite autonomic score (CAS).ResultsAsymmetric dimethylarginine levels were significantly decreased (0.62 ±0.11 vs. 0.53 ±0.11 µmol/l, p &lt; 0.001), as well as TNF-α concentrations (1.21 ±0.42 pg/ml vs. 1.05 ±0.5 pg/ml, p &lt; 0.05), while NO levels were significantly increased (16.78 ±11.1 vs. 21.58 ±8.84 µmol/l, p &lt; 0.05) after six-months of 600 mg/day ALA treatment. VCAM-1, ICAM-1, and oxLDL levels did not change significantly. The CPT and CAS significantly improved after ALA treatment. The improvement of CPT values was correlated positively with the change of ADMA levels (r = 0.58, p &lt; 0.001). The change in ADMA level was more pronounced in responder patients based on both CPT and CAS.ConclusionsOur results suggest that ALA supplementation improves endothelial function characterised by serum levels of ADMA and TNF-α in patients with diabetic neuropathy. Changes in serum ADMA levels may predict the clinical response to ALA treatment.

The baroreflex afferent pathway plays a critical role in H2S-mediated autonomic control of blood pressure regulation under physiological and hypertensive conditions.

Hydrogen sulfide (H2S), which is closely related to various cardiovascular disorders, lowers blood pressure (BP), but whether this action is mediated via the modification of baroreflex afferent function has not been elucidated. Therefore, the current study aimed to investigate the role of the baroreflex afferent pathway in H2S-mediated autonomic control of BP regulation. The results showed that baroreflex sensitivity (BRS) was increased by acute intravenous NaHS (a H2S donor) administration to renovascular hypertensive (RVH) and control rats. Molecular expression data also showed that the expression levels of critical enzymes related to H2S were aberrantly downregulated in the nodose ganglion (NG) and nucleus tractus solitarius (NTS) in RVH rats. A clear reduction in BP by the microinjection of NaHS or L-cysteine into the NG was confirmed in both RVH and control rats, and a less dramatic effect was observed in model rats. Furthermore, the beneficial effects of NaHS administered by chronic intraperitoneal infusion on dysregulated systolic blood pressure (SBP), cardiac parameters, and BRS were verified in RVH rats. Moreover, the increase in BRS was attributed to activation and upregulation of the ATP-sensitive potassium (KATP) channels Kir6.2 and SUR1, which are functionally expressed in the NG and NTS. In summary, H2S plays a crucial role in the autonomic control of BP regulation by improving baroreflex afferent function due at least in part to increased KATP channel expression in the baroreflex afferent pathway under physiological and hypertensive conditions.

Brain-gut-microbiome interactions in obesity and food addiction.

Normal eating behaviour is coordinated by the tightly regulated balance between intestinal and extra-intestinal homeostatic and hedonic mechanisms. By contrast, food addiction is a complex, maladaptive eating behaviour that reflects alterations in brain-gut-microbiome (BGM) interactions and a shift of this balance towards hedonic mechanisms. Each component of the BGM axis has been implicated in the development of food addiction, with both brain to gut and gut to brain signalling playing a role. Early-life influences can prime the infant gut microbiome and brain for food addiction, which might be further reinforced by increased antibiotic usage and dietary patterns throughout adulthood. The ubiquitous availability and marketing of inexpensive, highly palatable and calorie-dense food can further shift this balance towards hedonic eating through both central (disruptions in dopaminergic signalling) and intestinal (vagal afferent function, metabolic endotoxaemia, systemic immune activation, changes to gut microbiome and metabolome) mechanisms. In this Review, we propose a systems biology model of BGM interactions, which incorporates published reports on food addiction, and provides novel insights into treatment targets aimed at each level of the BGM axis.

Estrogen-dependent MicroRNA-504 Expression and Related Baroreflex Afferent Neuroexcitation via Negative Regulation on KCNMB4 and KCa1.1 β4-subunit Expression

Large conductance of Ca2+-activated K+ channel (KCa1.1) plays an inhibitory role in neuroexcitation. However, the expression of KCNMB4/β4-subunit in the nodose ganglia (NG) and nucleus tractus solitarius (NTS), and its effect and regulation on baroreflex afferent function at post-transcriptional level of female rats remains unknown. Here, we demonstrated that the expression of β4-subunit encoded by KCNMB4 was significantly lower in females vs. males and ovariectomized (OVX) rats in the NG. Although all baroreceptor neurons (BRNs) expressed β4-subunit, altered discharge characteristics were only observed in Ah-type neurons after ovariectomy. Notably, the decreased excitability of Ah-types was restored by paxilline and further enhanced by iberiotoxin. The consistent changes were observed in excitatory post-synaptic currents. The level of miR-504 was higher in females, which was predicted to bind to the 3′UTR of KCNMB4. In consistent, an inverse expression pattern between miR-504 and KCNMB4 was observed in baroreflex afferents. The paxilline-sensitive β4-subunits is less in Ah-types and up-regulated by ovariectomy. These data indicated that KCa1.1 β4-subunit is the key regulator in neuroexcitation of Ah-types and sexual-dimorphism in baroreflex afferent function through estrogen-dependent inhibition of KCNMB4 expression via miR-504.

Increased levels of inflammatory factors are associated with severity of polyneuropathy in type 1 diabetes.

Distal symmetrical polyneuropathy (DSPN) is a severe common long-term complication of type 1 diabetes caused by impaired sensory-motor nerve function. As chronic low-grade inflammation may be involved in the pathogenesis of DSPN, we investigated the circulating levels of inflammatory markers in individuals with type 1 diabetes with and without DSPN. Furthermore, we determined to what extent these factors correlated with different peripheral sensory nerve functions. Cross-sectional study. The study included 103 individuals with type 1 diabetes with (n=50) and without DSPN (n=53) as well as a cohort of healthy controls (n=21). Circulating levels of various inflammatory markers (cytokines, chemokines and soluble adhesion molecules) were determined in serum samples by Luminex multiplexing technology. Peripheral sensory nerve testing, for example vibration, tactile and thermal perception, was assessed by standardized procedures. The cytokines IL-1α, IL-4, IL-12p70, IL-13, IL-17A and TNF-α; the chemokine MCP-1; and the adhesion molecule E-selectin were significantly increased in individuals with type 1 diabetes with DSPN compared to those without DSPN (P<.001). These observations were independent of age, sex, BMI, disease duration and blood pressure. Additionally, higher serum concentrations of cytokines and chemokines were associated with higher vibration and tactile perception thresholds, but not with heat tolerance threshold. Individuals with type 1 diabetes and concomitant DSPN display higher serum levels of several inflammatory markers. These findings support that systemic low-grade inflammation may play a role in the pathogenesis of DSPN.

Neuroinflammatory Gene Expression Pattern Is Similar between Allergic Rhinitis and Atopic Dermatitis but Distinct from Atopic Asthma.

Methods In the study, we included 86 children diagnosed with atopic asthma (n = 25), allergic rhinitis (n = 20), and atopic dermatitis (n = 20) and healthy control subjects (n = 21) of Caucasian origin from the Polish population. The blood leukocyte expression of 31 genes involved in neuroinflammatory response (neurotrophins, their receptors, neuropeptides, and histamine signaling pathway) was analysed using TaqMan low-density arrays. The relative expression of selected proteins from plasma was done using TaqMan Protein Assays. Statistical analysis was done using Statistica. Results Blood expression of 31 genes related to neuroimmune interactions showed significant increase in both allergic diseases, allergic rhinitis and atopic dermatitis, in comparison to the control group. We found 12 genes significantly increased in allergic rhinitis and 9 genes in which the expression was elevated in atopic dermatitis. Moreover, 9 genes with changed expression in atopic dermatitis overlapped with those in allergic rhinitis. Atopic asthma showed 5 genes with altered expression. The peripheral expression of neuroinflammatory genes in the human study was verified in target tissues (nasal epithelium and skin) in a rat model of allergic inflammation. Conclusions A common pattern of neuroinflammatory gene expression between allergic rhinitis and atopic dermatitis may reflect similar changes in sensory nerve function during chronic allergic inflammation.

124-OR: Progressive Loss of Corneal Nerve Fibers and Sensitivity with Duration of Obesity Type 2 Diabetes in Sprague-Dawley Rats: Valid Marker for Peripheral Neuropathy and Treatment

Purpose: Determine whether density of nerve fibers in the cornea and corneal function are valid markers for early detection and treatment of peripheral neuropathy in rat models of prediabetes and type 2 diabetes. Methods: Rat models for prediabetes and type 2 diabetes were created and longitudinally studied for loss of structure and function of sensory nerves in the cornea and skin as well as nerve conduction velocity and vascular reactivity of epineurial arterioles. Reversibility of neuro and vascular pathology was also examined in these models following chronic obesity or type 2 diabetes after dietary intervention with menhaden oil a natural source of long chain omega-3 polyunsaturated fatty acids. Results and Conclusions: Our longitudinal study demonstrated that vascular and neural dysfunction associated with obesity or type 2 diabetes occur early and are progressive. Decrease in cornea nerve fiber length and function were valid markers of disease in both the prediabetic and diabetic rat models and were more sensitive than decrease in intraepidermal nerve fiber density of the skin and thermal nociception of the hindpaw. Late intervention with menhaden oil reversed both vascular and peripheral damage induced by chronic obesity or type 2 diabetes. These studies provide support for examination of corneal structure and function as an early marker of peripheral neuropathy in prediabetes and diabetes. Furthermore, we demonstrate that omega-3 polyunsaturated fatty acids derived from fish oil as an effective treatment for peripheral neuropathy that occurs with chronic obesity or type 2 diabetes. Disclosure M.A. Yorek: Consultant; Self; Novo Nordisk Inc. Funding National Institute of Diabetes and Digestive and Kidney Diseases (DK107339); U.S. Department of Veterans Affairs (RX000889)

529-P: Insulin Replacement Therapy Does Not Fully Prevent Peripheral Neuropathy in Type 1 Diabetic Mice

Peripheral Neuropathy (PN) is one of the most common complications of diabetes worldwide, affecting up to 60% of diabetic patients. Despite strict glycemic control, the risk of PN persists in approximately 30% of type 1 diabetic (T1D) patients. Understanding the role of insulin in PN is therefore critical to designing adjunct therapies that can slow or reverse disease progression. In this study, we aimed to determine the effect of insulin replacement therapy on nerve function and identify metabolic and molecular changes in plasma and nerves of T1D mice that are not improved following euglycemia. Terminal metabolic and neuropathy phenotyping was performed in Streptozotocin (STZ)-induced T1D mice, treated with insulin for 12 weeks. Oxidative stress was quantified in plasma and sciatic nerve. DNA methylation and protein expression of key insulin signaling markers were also determined in dorsal root ganglia (DRG). T1D mice developed hyperglycemia, hypertriglyceridemia, reduced plasma insulin, PN, systemic and nerve oxidative stress. Additionally, DRG isolated from T1D mice exhibited hypermethylation and reduced insulin signaling. Insulin replacement therapy normalized glycemia and triglyceride levels, but induced hyperinsulinemia and markers of oxidative stress. While insulin treatment did not reverse large fiber neuropathy, it improved small fiber and sensory nerve function. This protective effect was accompanied with a restoration of methylation levels and insulin signaling markers in DRG. Our findings show that insulin treatment ameliorates small fiber function by correcting methylation and insulin signaling. However, we show that insulin treatment fails to rescue large fiber deficit, which is mediated at least in part by hyperinsulinemia and systemic oxidative stress. Accordingly, these results suggest that in addition to metabolic control, restoring oxidative balance may represent an adjunct therapy to fully prevent PN in T1D. Disclosure S. Eid: None. L.M. Hinder: None. J.M. Hayes: None. F. Mendelson: None. E.L. Feldman: Consultant; Self; Novartis Pharmaceuticals Corporation. Funding American Diabetes Association (7-12-BS-045 to E.L.F.); JDRF; Rose C. and Nathan L. Milstein Family Emerging Scholar Fund; A. Alfred Taubman Medical Research Institute

Vagal sensory neurons and gut-brain signaling.

Our understanding of the gut system has been revolutionized over the past decade, in particular regarding its role in immune control and psychological regulation. The vagus nerve is a crucial link between gut and brain, transmitting diverse gut-derived signals, and has been implicated in many gastrointestinal, neurological, and immunological disorders. Using state-of-the-art technologies including single-cell genomic analysis, real-time neural activity recording, trans-synaptic tracing, and electron microscopy, novel physiological functions of vagal gut afferents have been uncovered, and new gut-to-brain pathways have been revealed. Here, we review the most recent findings on vagal sensory neurons and the gut-brain signaling, focusing on the anatomical basis and the underlying molecular and cellular mechanisms. Such new discoveries explain some of the old puzzling problems and also raise new questions in this exciting and rapidly growing field.

Swallowing impairment in older adults: association with sensorimotor peripheral nerve function from the Health, Aging and Body Composition study.

The purpose of this study was to examine whether impairments in sensorimotor peripheral nerve function are associated with a higher likelihood of swallowing impairment in older adults. Health, Aging and Body Composition participants (n = 607, age = 75.8 ± 2.7years, 55.8% women, 32.3% black) underwent peripheral nerve testing at Year 4 and 11 with swallowing difficulty assessed at Year 4 and 15. Nerve conduction amplitude and velocity were measured at the peroneal motor nerve. Sensory nerve function was assessed with the vibration detection threshold and monofilament (1.4-g/10-g) testing at the big toe. Symptoms of lower extremity peripheral neuropathy and difficulty swallowing were collected by self-report. Data analysis was performed using a hierarchical approach. Odds ratios (ORs) were estimated using non-conditional logistic regression. At Year 15 108 (17.8%) participants had swallowing impairments. In fully adjusted models, the peripheral nerve impairments associated with swallowing impairment were numbness (OR 4.67; 95%CI 2.24-9.75) and poor motor nerve conduction velocity (OR 2.26; 95%CI 1.08-4.70). Other peripheral nerve impairments were not related to swallowing. The association between slow motor nerve conduction velocity and numbness and a higher likelihood of swallowing difficulties a decade later in our prospective study identifies an important area for further investigation in older adults.

Modulation of Sensory Nerve Function by Insulin: Possible Relevance to Pain, Inflammation and Axon Growth.

Insulin, besides its pivotal role in energy metabolism, may also modulate neuronal processes through acting on insulin receptors (InsRs) expressed by neurons of both the central and the peripheral nervous system. Recently, the distribution and functional significance of InsRs localized on a subset of multifunctional primary sensory neurons (PSNs) have been revealed. Systematic investigations into the cellular electrophysiology, neurochemistry and morphological traits of InsR-expressing PSNs indicated complex functional interactions among specific ion channels, proteins and neuropeptides localized in these neurons. Quantitative immunohistochemical studies have revealed disparate localization of the InsRs in somatic and visceral PSNs with a dominance of InsR-positive neurons innervating visceral organs. These findings suggested that visceral spinal PSNs involved in nociceptive and inflammatory processes are more prone to the modulatory effects of insulin than somatic PSNs. Co-localization of the InsR and transient receptor potential vanilloid 1 (TRPV1) receptor with vasoactive neuropeptides calcitonin gene-related peptide and substance P bears of crucial importance in the pathogenesis of inflammatory pathologies affecting visceral organs, such as the pancreas and the urinary bladder. Recent studies have also revealed significant novel aspects of the neurotrophic propensities of insulin with respect to axonal growth, development and regeneration.

Progressive Loss of Corneal Nerve Fibers and Sensitivity in Rats Modeling Obesity and Type 2 Diabetes Is Reversible with Omega-3 Fatty Acid Intervention: Supporting Cornea Analyses as a Marker for Peripheral Neuropathy and Treatment.

PurposeTo determine whether cornea nerve fiber density and/or corneal function are valid markers for early detection and treatment of peripheral neuropathy in rats modeling prediabetes and type 2 diabetes.MethodsHigh-fat feeding combined without or with low-dose streptozotocin was used to create rat models for prediabetes and type 2 diabetes that were longitudinally studied for loss of structure and function of sensory nerves in the cornea and skin as well as nerve conduction velocity and vascular reactivity of epineurial arterioles. There were three time points examined in each of the three conditions with 12 rats per group. The latest time point (24 weeks of high-fat diet with or without 16 weeks of hyperglycemia) was used to examine reversibility of neuro and vascular pathology following 16 weeks of treatment with menhaden oil, a natural source of long-chain omega-3 polyunsaturated fatty acids. The number of rats in the intervention study ranged from 6 to 17.ResultsOur longitudinal study demonstrated that vascular and neural dysfunction associated with obesity or type 2 diabetes occur early and are progressive. Decrease in cornea nerve fiber length and function were valid markers of disease in both the pre-diabetic and diabetic rat models and were more sensitive than decrease in intraepidermal nerve fiber density of the skin and thermal nociception of the hindpaw. Late intervention with menhaden oil significantly reversed both vascular and peripheral nerve damage induced by chronic obesity or type 2 diabetes.ConclusionThese studies provide support for examination of corneal structure and function as an early marker of peripheral neuropathy in prediabetes and type 2 diabetes. Furthermore, we demonstrate that omega-3 polyunsaturated fatty acids derived from fish oil are an effective treatment for peripheral neuropathy that occurs with chronic obesity or type 2 diabetes.

Effects of Sex and Anesthetics on Renal Sensory Nerve Responses

The anti‐hypertensive effects of renal denervation are partly attributed to denervation of renal sensory nerves, which detect changes in intrarenal pressure and nociceptive chemokines to reflexively alter sympathetic nerve activity, renal function, and blood pressure. To date, the majority of experiments have assessed renal sensory responses using either anesthesia and exclusively male animals. The purpose of the present study was to evaluate the impact of anesthesia and sex on in vivo renal afferent nerve activity (ARNA) to chemo‐ and mechano‐sensitive stimuli. Male and female Sprague‐Dawley rats (250–400g) were assessed by multifiber nerve recordings in unanesthetized decerebrate preparations, Inactin, isoflurane, or urethane anesthesia. Baseline ARNA was not different across preparations or between sexes (n=6–8/group): decerebration (M: 20±6Hz, F: 20±6Hz), Inactin (M:12±5Hz, F: 16±8 Hz), and isoflurane (M: 23±6Hz, F: 29±6Hz). However, ARNA was significantly lower in urethane‐anesthetized male rats (M: 3±1Hz, F: 29±6Hz; p&lt;0.05).To evaluate chemosensitive responses, increasing doses of capsaicin [0 – 50 μM], (50μL over 15 s) were infused into the renal artery via a suprarenal arterial catheter, which produced concentration‐dependent increase in ARNA in all groups (n=4–6/group). ARNA was most sensitive in decerebrate and Inactin vs isoflurane or urethane groups. In male rats, the threshold concentration of capsaicin to evoke a response was 1μM decerebrate (117.8±29.2Hz, p=0.02) &lt; 10μM Inactin (137.0±61.0, p=0.0002) &lt; 30μM isoflurane (102.2±37.8, p=0.02) = 30μM urethane (96.5±35.9, p=0.02). In female rats, the threshold was 1μM Inactin (117.2±37.5Hz, p=0.03) &lt; 10μM decerebrate (184.8±41.6, p=0.03) = 10μ isoflurane (93.5±10.4, p=0.02) &lt; 30μM urethane (158.8±47.6, p=0.02).To evaluate mechanosensitive responses, renal artery occlusion (30s) increased ARNA equally in all groups. However, a significant sex effect was observed using Isoflurane (M: 9±4Hz, F: 33±3Hz; p&lt;0.01). Lastly, 5‐mmHg stepwise increases in renal pelvic pressure (0–30mmHg, 30s) produced linear increases in ARNA in all groups. Using linear regression to test the magnitude (y‐intercept) and sensitivity (slope) of ARNA we found significant differences in the magnitude of males (n=6–8/group): decerebrate, 6.5±5.3Hz; Inactin, 15.7±3.4 Hz; isoflurane, 3.8±3.2Hz; urethane, 0.2±1.1Hz; p&lt;0.0001) and females (n=4–7/group): decerebrate, 8.8±10.5Hz; inactin, 9.5±6.0Hz; isoflurane, 14.2±8.6Hz; urethane, 0.2±4.5Hz; p&lt;0.0001). Between sex comparisons resulted in blunted male sensitivity to urethane (M: slope=0.1±0.1; F: slope=0.7±0.23, p&lt;0.001), and elevated female sensitivity to isoflurane (M: slope=0.1±0.2, F: slope=1.1±0.4, p&lt;0.03). Decerebrate and inactin anesthesia were similarly sensitive between sexes.In conclusion, ARNA to chemo‐ and mechano‐sensitive stimuli were similar between an unanesthetized‐decerebrate preparation vs Inactin anesthesia. Isoflurane and urethane attenuated ARNA to capsaicin and differentially altered ARNA to increased renal pelvic pressure. Sex did not consistently impact ARNA per se, but sex differences were linked to the use of isoflurane and urethane. These findings suggest decerebration or Inactin anesthesia should be employed to study renal afferent nerve function.Support or Funding InformationNIH Grants: R01 HL145875

SPARC: Topographical Organization and Morphology of Substance P‐IR Axons and Terminals in the Whole‐Mount Stomach of Rodents

Afferent fibers innervate the stomach. However, very little is known about the topographical distribution and morphological terminal structures of gastric nociceptive axons and terminals in rodents. In this study, we used Substance P (SP) as a marker to label afferent fibers in the whole‐mount dorsal and ventral stomach including longitudinal and circular muscles and the myenteric nervous system in C57BL/6J mice and SD rats. The whole‐mount dorsal and ventral stomachs were processed with the substance P (SP) primary antibody followed by the secondary antibody, and then examined using confocal microscopy. We found that: 1) SP‐IR axons and terminals extensively covered the fundus, corpus and antrum of the dorsal and ventral stomach. 2) SP‐IR varicose axons ran in parallel with the longitudinal as well as circular muscles. 3) SP‐IR varicose axons formed dense rings of terminal varicosities around individual neurons in the myenteric plexus. 4) The density of SP‐IR axons and terminals varicosities was different in the fundus, corpus and antrum. Collectively, our data showed for the first time the comprehensive topographical distribution and morphology of SP‐IR axons and terminals in different regions of the stomach. This knowledge will provide an anatomical basis for differentiated nociceptive gastric afferent functions in rodents.Support or Funding InformationNIH HEAL/SPARC Program NIH 1 U01 NS113867‐01 and NIH R15 HL137143‐01A1.

Common peroneal nerve ‘pre-release’ in total knee arthroplasty for severe valgus deformities

BackgroundCommon peroneal nerve (CPN) palsy is a devastating complication that follows total knee arthroplasty (TKA). However, there are only a few studies on concrete measures for protecting the CPN in patients. This study aimed to put forward the CPN 'pre-release' method to protect the nerve. MethodsA prospective study was conducted on 30 patients (34 knees) with severe valgus knees who underwent CPN pre-release. This was a two-incision approach, and required a separate dissection of about three centimeters from the TKA operation. Clinical measurements including pre- and postoperative motor and sensory nerve function of CPN, radiological evaluation, complications, and the revised data were analyzed and compared. ResultsThe average preoperative femorotibial angle was 31.3 ± 8.0°. All patients had completely normal motor (grade 5) and sensory nerve function of CPN postoperatively, and there was no transient or late-onset CPN palsy. Patients had a routine rehabilitation with full weight bearing after recovery from anesthesia, including the knees with unconstrained extension/flexion motion. During the last follow-up visit, the visual analog scale, Knee Society Score, Hospital for Special Surgery knee-rating scale, and range of motion were 2.06 ± 1.13, 92.18 ± 5.57, 90.18 ± 3.70, and 115.59 ± 7.76°, respectively. There were no revisions for instability and recurrent valgus deformities during follow-up. Also, the femorotibial angle, hip–knee–ankle angle, condylar–hip angle, and plateau–ankle angle were 4.9 ± 2.0°, 179.09 ± 3.21°, 89.97 ± 2.41°, and 90.53 ± 1.26°, respectively. ConclusionsThe CPN pre-release for severe valgus knees is an effective method for nerve protection, achieving an adequate and safe release of lateral soft tissue, and providing immediate and early functional rehabilitation with decreasing constrained implant.

Common peroneal nerve "pre-release" to avoid nerve palsy in total knee arthroplasty for severe valgus deformities

Objective: To investigate the clinical efficacy of common peroneal nerve "pre-release" to avoid nerve palsy in total knee arthroplasty for severe valgus deformities. Methods: Twenty patients (22 knees) with severe valgus deformities were prospectively and continuously included in Fujian Province Hospital from January 2010 to January 2016. Medial parapatellar arthrotomy, femoral distal resection using the intramedullary cutting guide with 3° to 5° of valgus and the common peroneal nerve "pre-release" was performed, the patella was routinely resurfaced. A common peroneal nerve checking was performed (LSUHSC system), then, these outcomes were collected independently using visual analogue scale (VAS) of pain, Knee Society Score (KSS), Hospital for Special Surgery Knee Score (HSS), range of motion of knees (ROM), femorotibial angle (FTA), hip-knee-ankle angle (HKA), condylar-hip angle (CHA), plateau- ankle angle (PAA). The paired t test was used to compare the data before and after the operation. Results: Patients were followed up for 18 to 55 (mean, (38±8) months). According to Krackow's classification, all cases were typed Ⅱ. All the patients had a completely normal motor (grade 5) and sensory (LSUHSC score was 5) nerve function of common peroneal nerve postoperatively. No decrease or loss in muscle strength and cutaneous sensation associated with common peroneal nerve was found. The VAS of pain, KSS, HSS, ROM, HKA, CHA, and PAA were all improved after the operation when compared with those before the operation (t=21.602, -70.238, -82.455, -20.560, 16.058, 9.682, 3.439, all P<0.05). The alignment of lower limbs was corrected basically, and the FTA decreased from 31.7°±8.0° before operation to 5.0°±2.0° at the last follow-up, the differences was statistically significant (t=16.725, P<0.05). No common peroneal nerve palsy and transient or late-onset palsy occurred, and no revision was needed for instability during the follow-up in all the patients. Conclusion: Common peroneal nerve "pre-release" for severe valgus knees may be an effective method in protecting the nerve.