bluuebunny/crossref_metadata_2025 huggingface dataset:
Single‐vs. double‐leg cycling: lower cardiorespiratory demands and perceived effort for a greater relative power output
Authors: MacInnis Martin J , Morris Nathaniel , Sonne Michael W , Zuniga Amanda Farias , Keir Peter J , Potvin Jim R , Gibala Martin J
Published: November 2023

Single‐leg cycling is an insightful model of unilateral exercise. It affords a unique comparison of exercise interventions in a within‐subject manner, as the addition of a counterweight to the contralateral pedal facilitates the ‘feel’ of normal double‐leg cycling. The present study characterized physiological responses to single‐ and double‐leg cycling performed at the same relative intensities in twelve men (age: 21 ± 2 years; BMI: 24 ± 3 kg/m2). Graded‐exercise tests initially established that peak oxygen uptake (VO2 peak; +31%), ventilation (VE peak; +33%), heart rate (HRpeak; +9%), and power output (PPO; +78%) were higher (main effect of mode; p < 0.05) during double‐compared to single‐leg cycling. On separate days, subjects subsequently performed four experimental trials, which involved 30‐min bouts of either moderate‐intensity continuous training (MICT) or high‐intensity interval training (HIIT) in a single‐ or double‐leg manner. Although performed at the same percentage of the respective PPO, single‐leg exercise elicited a greater average power output per leg than double‐leg exercise (+13%; p < 0.001). In contrast, average EMG responses from the vastus lateralis and vastus medialis were similar for single‐ and double‐leg cycling (p > 0.05), although the semitendinosus was activated to a greater extent for single‐leg cycling relative to double‐leg cycling (p < 0.001). Single‐leg cycling elicited markedly lower VE, VO2, and HR responses and ratings of perceived exertion compared to double‐leg cycling (p < 0.05). In summary, single‐leg cycling allows for a greater power output (per leg) than double‐leg cycling, while eliciting lower cardiorespiratory and perceptual responses.

Support or Funding Information

Natural Sciences and Engineering Research Council of Canada (NSERC)
Muscle Sympathetic Nerve Responses to Passive and Active One‐legged Cycling: Insight into the Contributions of Central Command
Authors: Doherty Connor J. , Incognito Anthony V. , Notay Karambir , Burns Matthew J. , Nardone Massimo , Seed Jeremy D. , Millar Philip J.
Published: November 2023

Prior studies using neuromuscular blockade to increase perception of effort during mild or moderate intensity handgrip exercise have demonstrated that activation of higher brain regions, termed central command, contribute importantly to cardiac parasympathetic withdrawal but have limited influence on muscle sympathetic activation. The purpose of the present study was to investigate the contribution of central command to the control of muscle sympathetic nerve activity (MSNA) during dynamic one‐legged cycling. Heart rate (HR), mean arterial pressure (MAP), stroke volume, and MSNA (contralateral leg microneurography) were measured in 18 healthy participants (9 men; 22±3 yr of age) at baseline and during two minutes of upright passive cycling movement and active unloaded cycling, each separated by 10 minutes of rest. The increases in HR were greater during the first (Δ3±3 vs. Δ11±7 bpm, p<0.0001) and second (Δ3±4 vs. Δ9±6 bpm, p<0.0001) minute, and MAP during the second minute (Δ4±3 vs. Δ7±5 mmHg, p<0.01), of active unloaded cycling compared to passive cycling movement. Stroke volume increased over time (p<0.001) but was not different between passive and active unloaded cycling (p>0.05). MSNA burst frequency decreased similarly during the first (Δ−4±5 vs. Δ−3±5 bursts/min, p>0.05) and second (Δ−6±4 vs. Δ−4±4 bursts/min, p>0.05) minute of passive and active unloaded cycling. In contrast, total MSNA demonstrated attenuated reductions during the first (Δ−3.2±3.0 vs. Δ−0.6±3.3 arbitrary units/min, p<0.05 [Δ−18±16% vs. Δ0±31%, p<0.05]) and second (Δ−4.5±3.3 vs. Δ−1.5±3.5 arbitrary units/min, p<0.01 [Δ−28±17% vs. Δ−11±24%, p<0.05]) minute of active unloaded cycling. These results support the concept that muscle sympathetic burst occurrence and strength can be regulated independently and suggest that during dynamic leg exercise central command primarily alters vasoconstrictor outflow through modulations in muscle sympathetic burst strength.

Support or Funding Information

This research was supported by a Natural Science and Engineering Research Council (NSERC) of Canada Discovery Grant (P.J.M), the Canada Foundation for Innovation (P.J.M.), and a Canadian Institutes of Health Research Fredrick Banting and Charles Best Canada Graduate Scholarship (A.V.I.).
Poincare Analysis of Spontaneous Respiratory Sinus Arrhythmia during High Altitude Ascent: Effects on oxygenation
Authors: Saran Gurkarn , Lavoie Lauren , Linares Andrea , Pfoh Jamie , Bruce Christina , Borle Kennedy , Brandt Rachelle , Tjandra Kartika , Day Trevor A
Published: November 2023

Respiratory sinus arrhythmia (RSA) is the transient fluctuation in heart rate (HR) in phase with the respiratory cycle. Poincare spectral analysis is used to (a) quantify heart rate variability (HRV) through short term (SD1; i.e., RSA) and long term (SD2) fluctuations in heart rate and (b) determine components of autonomic nervous system activity (low and high frequency; LF and HF; sympathetic and parasympathetic, respectively). Although RSA likely represents the dominance of the parasympathetic nervous system at rest, there is controversy regarding the mechanisms underlying RSA, as well as the possible physiological utility. RSA may improve ventilation and perfusion (V/Q) matching in the lungs, and may protect against oxygen desaturation in the context of hypoxic exposure. We aimed to investigate the relationship between RSA magnitude and peripheral oxygen saturation (SpO2) during incremental ascent to high altitude (4370m). We hypothesized that (a) RSA magnitude (SD1/SD2) ratio would decrease during ascent to high altitude as a result of sympathetic nervous system activation and (b) individuals with a larger SD1/SD2 ratio during ascent would have increased SpO2 through improved V/Q matching. Measurements were conducted over eleven days at 1045m (baseline, day 1), 3440m (day 7), 3860m (day 9), and 4370m (day 11) during a trek to altitude in the Nepal Himalaya. Participants (26±2.1 years; BMI 23.8±1.1 kg/m2; 9 females, n=12) were instrumented with an ECG and finger pulse oximeter (SpO2 %) and tested on rest days after one night at each altitude. Spontaneous RSA was measured from the ECG periods during the last 7‐min of a 10‐min baseline and evaluated using Poincare plots. There was no significant difference between the SD1/SD2 ratio during incremental ascent to 4370m (P=0.65). There was also no significant difference observed in the LF/HF ratios during ascent to 4370m (P=0.66), suggesting that the sympathetic/parasympathetic ratio remained unchanged with ascent. Additionally, we correlated SD1/SD2 ratio and SpO2 at 4370m when individuals were most hypoxic at rest (SpO2 87.2±0.8%) and found no significant correlation (r=0.32, P=0.31). Our data suggests that during slow incremental ascent to high altitude, there is no difference in spontaneous RSA or the balance between sympathetic and parasympathetic nervous system activity. Individuals with larger SD1/SD2 ratios do not have improved SpO2, suggesting that RSA magnitude does not improve V/Q matching during high altitude ascent.

Support or Funding Information

Natural Sciences and Engineering Research Council of Canada, Student Temporary Employment Program of Alberta, Alberta Innovates Health Solutions Summer Studentship,
Imposed expiratory resistance, hyperinflation, and dyspnea are dissociated from locomotor fatigue during moderate exercise
Authors: Wickman Brooke E , Sasaki Katelynn G , Torrecillas‐Sanchez Eduardo , Cannon Daniel T
Published: November 2023

Expiratory flow resistance (e.g. asthma, chronic obstructive pulmonary disease) results in dyspnea, dynamic hyperinflation, and premature exercise intolerance during heavy intensity exercise. This cascade seems to be primarily precipitated by abnormal lung mechanics that result in exacerbated symptoms and reduced maximal evocable limb motor activity. We do not know whether this cascade behaves in the same way during moderate exercise where only modest locomotor fatigue is expected to develop.

We hypothesized that expiratory flow resistance would result in dynamic hyperinflation, dyspnea, and exacerbated locomotor fatigue during moderate intensity exercise in a similar manner to that during heavy intensity exercise.

Volunteers (N=10, 27±6 yr) completed constant power moderate exercise (50% peak ramp power) with 3 levels of imposed expiratory flow resistance (7, 9, 11 cm H2O·L·s−1) or control (no imposed flow resistance). We measured operating lung volumes during exercise with inspiratory capacity maneuvers. Participants reported dyspnea and leg effort using a Borg 10‐point scale. At the termination of exercise we used a rapid switch from hyperbolic to isokinetic cycling to measure the decline in peak isokinetic power (Piso).

Decline in Piso was not different when expiratory flow resistance was imposed (p>0.05). Inspiratory capacity was smaller at the end of exercise in the most severe resistance (11 cm H2O·L·s−1) as compared to control (2.31±1.52 vs. 3.15±0.71 L; p<0.05). Similarly, inspiratory reserve volume was smaller at the end of exercise in the most severe resistance as compared to control (−0.07±1.28 vs. 0.82±0.43 L; p<0.05). Dyspnea was greater at the end of exercise in both mild and severe resistance (7 and 11 cm H2O·L·s−1) as compared to control (5.7±2.5 and 5.2±1.9 vs. 3.7±1.6; p<0.05). Piso was not related to inspiratory reserve volume, inspiratory capacity, or dyspnea (p>0.05).

Imposed severe expiratory flow resistance results in hyperinflation and exacerbated dyspnea in healthy volunteers. Unlike what we have found during heavy exercise, however, abnormal lung mechanics and dyspnea were not related to maximal locomotor power during moderate exercise.
Muscle Inflammatory Signaling's Contribution to Cancer Cachexia‐induced Decrements in Muscle Function
Authors: VanderVeen Brandon , Hardee Justin , Fix Dennis , Carson James
Published: November 2023

Although skeletal muscle mass loss defines cachexia, changes in muscle function related to strength loss and increased fatigue can further impact life quality and health status. However, there are gaps in our understanding of the cachectic environment that regulates muscle function. While cancer‐induced inflammatory signaling can disrupt skeletal muscle protein turnover regulation, inflammatory signaling's contribution to altered cachectic muscle function remains to be determined. Therefore, the purpose of this study was to determine cancer cachexia‐induced inflammatory signaling's contribution to decrements in the functional properties of skeletal muscle. Two preclinical models of cancer cachexia were examined; the ApcMin/+ (MIN) and Lewis lung carcinoma (LLC) implanted mice. The MIN mouse has a nonsense mutation on the Apc gene and develop intestinal tumors by 12 weeks of age resulting in a cachectic phenotype by 20 weeks of age. 106 LLC tumor cells were injected into the flank and mice develop severe cachexia within 5 weeks. Skeletal muscle function and inflammatory signaling was examined in male, MIN (20‐wk, >5% BW loss) and LLC (13‐wk, 30 days' post injection) mice. Tibialis anterior (TA) twitch properties, tetanic force and fatigue were examined in‐situ to maintain intact nerve and blood supply. LLC and MIN decreased TA mass and twitch characteristics compared to their respective controls. LLC and MIN increased 1/2 relaxation time (½ RT), and this change was independent to altered twitch tension. LLC (−33%) and MIN (−41%) decreased tetanic force. Interestingly, only MIN decreased specific tetanic force (−13%). TA fatigability was increased in both MIN (−22%) and LLC (−11%). MIN and LLC increased muscle STAT3 and p65 phosphorylation. The induction of STAT3 and p65 phosphorylation was inversely related to absolute force (R=−0.76, p<0.0001), but only p65 phosphorylation was inversely related to specific tension (R=−0.71, p=0.002). Inflammation was not associated with increased fatigue. There was a trend for STAT3 phosphorylation to be related too increased ½ RT (R=0.46, p=0.07). Cachexia progression altered several skeletal muscle functional properties in 2 distinct cancer cachexia models. While decrements in force production were associated with muscle inflammatory signaling, fatigue susceptibility was not.

Support or Funding Information

R01CA121249‐07
Passive Heating Impairs Cardiac Autonomic Regulation during Exercise and Post‐Exercise Recovery
Authors: Peçanha Tiago , Forjaz Cláudia , Low David
Published: November 2023

AIM

The aim of this study was to assess the effects of passive heating on exercise and post‐exercise cardiac autonomic regulation.

METHODS

Twelve healthy young men (25±5 yrs, 23.8±1.9 kg/m2, 47.3±7.9 ml.kg−1.min−1) randomly underwent two experimental sessions: heat stress (HEAT) and control (CON). Each session composed of: a heat stress or normothermic control intervention; 7 min of cycling at 40% HRreserve (EX1); 7 min of cycling at 60% HRreserve (EX2); and 10 min of recovery in the seated position (REC). HEAT consisted of 60 min whole‐body passive heating by perfusing hot water (48°C) in a tube‐lined suit to increase core temperature (Tc) by ~1°C. CON consisted of normothermia exposure for a similar timeframe. Heart rate (HR) and finger blood pressure were continuously assessed. HR variability (HRV) was assessed using the vagal‐related RMSSD index, baroreflex sensitivity (BRS) was assessed using the sequence technique and HR recovery (HRR) was assessed through the absolute decrease of HR at 60 (HRR60s) and 300 s (HRR300s) after exercise. Tc, skin temperature (Tsk), forearm skin blood flow (SKBF) and cutaneous vascular conductance (CVC) were also continuously measured throughout.

RESULTS

Tc, Tsk, SKBF and CVC were significantly increased in HEAT compared with CON (Tc: 38.0±0.3 vs. 37.1±0.3 °C; Tsk: 36.8±0.6 vs. 33.2±0.8 °C; SKBF: 160±96 vs. 50±34 A.U.; CVC: 2.3±1.3 vs. 0.6±0.3 A.U/mmHg; all p<0.05). During exercise, HRV and BRS were not different between trials during EX1 and EX2. However, when comparing EX1 of CON with EX2 of HS (i.e. similar absolute workloads), HRV (0.8 ± 0.4 vs. 1.9 ± 0.7 ms; p<0.01) and BRS (0.6 vs. 0.3 vs. 1.5 ± 1.0 ms/mmHg; p<0.01) were significantly reduced in HS. During recovery, HRV (1.7 ± 0.6 vs. 2.6 ± 0.9 ms, p<0.01) and BRS (6 ± 3 vs. 4 ± 3 ms/mmHg; p<0.01) were significantly reduced in HS. Furthermore, HRR60s and HRR300s were significantly reduced in HS (HRR60s = 27±9 vs. 46±10 bpm; HRR300s = 39 ± 12 vs. 61 ± 13 bpm; p<0.01).

CONCLUSION

Passive heating impairs cardiac autonomic regulation during exercise at the same absolute workload and during recovery.

Support or Funding Information

FAPESP 2013/04997‐0; 2013/05519‐4; 2015/15466‐0
Dietary Nitrate and Skeletal Muscle Recovery after Injury in Young and Old Mice
Authors: Hahn Dongwoo , Patel Ravi , Kelley Rachel C , Coblentz Philip D , Ferreira Leonardo F
Published: November 2023

Nitric oxide availability has been shown to modulate skeletal muscle hypertrophy and regeneration post‐injury. Aging decreases nitric oxide availability and delays skeletal muscle recovery from injury. Dietary nitrate increases nitric oxide availability in skeletal muscle vessels and fibers. However, it is unclear whether dietary nitrate can accelerate aged skeletal muscle regeneration post‐injury. Therefore, our goal was to investigate the effect of dietary nitrate on skeletal muscle recovery from injury in aging. Young (n=36, 6 months old) and old (n=20, 24 months old) mice received sodium nitrate (NaNO3, 1mM) in drinking water or vehicle (deionized H2O) ad libitum for a total of 14 days. Seven days after the start of treatment, we injected cardiotoxin (CTX, 10 μM) into the tibialis anterior (TA) and extensor digitorum longus (EDL) from one limb, and saline into muscles of the contralateral limb. Seven days post‐injection, we collected the TA and EDL for measurements of muscle force, morphology, protein and mRNA. CTX decreased TA and EDL weights by ~30% each (p < 0.05), and the effects were independent of age or treatment. CTX decreased EDL maximal tetanic absolute (mN) and specific force (N/cm2) by 65% and 50% (P < 0.05 vs. non‐injected controls), respectively, and the effects were independent of age or treatment. CTX increased protein abundance of myogenin in the TA, an effect that was independent of age or treatment. Dietary NaNO3 decreased protein levels of embryonic myosin heavy chain (eMHC) in saline‐injected TA of old animals, whereas eMHC protein abundance increased after CTX injection. Protein levels of eMHC in CTX‐injected TA of animals receiving NaNO3 were similar to those from CTX‐ and saline‐injected muscles of old mice drinking vehicle. Overall, our data heretofore suggest that dietary NaNO3 did not accelerate the recovery of skeletal muscle force and weight, or markers of myogenesis in young and old animals. An interesting observation was that dietary NaNO3 decreased the levels of eMHC in saline‐injected muscle from old animals.

Support or Funding Information

NIA R03 AG040400‐02
The Effects of Low‐Intensity Exercise during Bed Rest in Healthy Older Adults
Authors: Galvan Fego , Arentson‐Lantz Emily , Nagamma Sneha , Deer Rachel R. , Fry Christopher S. , Wacher Adam , Paddon‐Jones Douglas
Published: November 2023

Aging results in the involuntary loss of muscle mass and strength. These rates of decline are exacerbated with hospitalization, illness, and injury (i.e., catabolic stressors). Acutely ill, hospitalized adults have significantly reduced daily activity (~740 steps/day) compared to their healthy counterparts (~6250 steps/day). While intense exercise is clearly not practical for older, hospitalized individuals, low‐intensity exercise may be a more practical alternative. 60 minutes of daily longitudinal loading (1G artificial gravity/centrifugation) has been shown to maintain muscle protein synthesis during bed rest in a young adult population. Thus, we hypothesized that low‐intensity exercise (2,000 steps/day) would mitigate the loss of muscle mass and function during 7‐days of bed rest in healthy older adults.

We employed a 7‐day bed rest protocol as a model of the physical inactivity associated with hospitalization. Dietary intake and daily steps were strictly controlled. Volunteers were randomized into two experimental groups: bed rest alone (CON: N=10, 68±5 y) or bed rest + 2,000 daily steps (STEP: N=7, 68±6 y). Isometric strength, leg lean mass (LLM) and blood glucose area under the curve (AUC) were assessed at baseline and after 7‐days of bed rest. Changes in isokinetic extension (60°/s) (CON: −13.3±3.3 N·m vs STEP: −14.4±3.8 N·m), LLM (CON: −932.3±181.8 g vs STEP: −700.4±149.2 g), and blood glucose AUC (CON: 456.4±1016.5 mg/dl/120 min vs STEP: −901.4±986.4 mg/dl/120 min) were similar between groups.

Data from this ongoing clinical trial suggests that a single bout of 2,000 steps/day is not sufficient to counter the catabolic effects of 7‐days bed rest in healthy older adults. Future exploration of the effects of a greater number of steps/day, the combined effects of nutritional support plus exercise or distributing activity across the day may be needed to have clinically translatable benefits.

Support or Funding Information

Supported by RO1 NR012973, P30 AG024832.
Aberrant Light‐Induced Depression is Associated with Decreased Adult Hippocampal Neurogenesis in Mice
Authors: Massman Logan Joseph , Engeland William C , Kofuji Paulo
Published: November 2023

In today's world of constant activity, people are frequently exposed to light outside of the natural daytime hours. This leads to a disruption in the endogenous circadian rhythm resulting in various mood disorders in humans (Bedrosian and Nelson 2013). In mice, it has been shown that aberrant light is sufficient to induce a depressive‐like phenotype; however, there is no clear explanation of the neurological basis for this phenomenon except light input is transmitted by intrinsically photosensitive retinal ganglion cells (Legates et al 2012). In other mouse models of depression, adult hippocampal neurogenesis (AHN) has been shown to be decreased (Mahar et al 2014). This study tested whether aberrant light‐induced depression was associated with decreased AHN in mice. Adult male C57B/6 mice were housed in standard light conditions (12:12 hours (T24) LD) or aberrant light conditions (3.5:3.5 hours (T7) LD) for at least three weeks prior to testing. Mice were assayed for a depressive‐like phenotype using a two‐bottle sucrose preference test over four days. Mice exposed to T7 LD showed significant reductions in sucrose preference compared to mice on T24 LD. Immunohistochemical fluorescent labeling for the cell proliferation marker Ki‐67 was then used to quantify AHN in the dentate gyrus. Mice under T7 LD had significant reduction of AHN compared to mice on T24 LD. These parallel observations of decreased sucrose preference and decreased AHN resulting from chronic exposure to aberrant light (T7 LD) suggest that AHN may provide the neurological basis for aberrant light‐induced depression.

Support or Funding Information

APS Undergraduate Summer Research Fellowship and NIH RO3NS094419
Copeptin: More than Just a Surrogate Biomarker
Authors: Haddock Christopher J. , Wille Hannah M. , Yosten Gina L.C. , Samson Willis K.
Published: November 2023

Copeptin is a 39 amino acid peptide derived from the vasopressin preprohormone. The function of vasopression is well characterized; however, the receptor and physiological function of copeptin remain unknown. These peptides are secreted at a 1:1 ratio, indicating that the actions of vasopression could “mask” the effects of copeptin. Thus, the physiologic effects of copeptin have been difficult to ascertain. Currently, copeptin is used as a surrogate biomarker for vasopression secretion due to the short half‐life of and difficulty measuring vasopression, but the biological activity of copeptin has not been confirmed. To evaluate the potential biological effects of copeptin, we exposed three cell types (HEK293, KATOIII, and ARPE19) to increasing concentrations of copeptin. Using real time quantitative PCR we have discovered that incubation with 100nM copeptin leads to increases in mRNA expression of the early transcriptional activation marker c‐FOS in all three cell types. Transcriptional activation indicates that copeptin is working through a receptor, and because the effects of vasopressin are mediated through G protein‐coupled receptors (GPCRs) V1, V2, and V3, we hypothesize that copeptin also signals through a GPCR. We are testing this hypothesis using a “deductive ligand‐receptor matching strategy” developed in our lab. Candidates for a potential receptor fall into a class of GPCRs with no known ligand, Orphan GPCRs. To narrow the pool of candidate receptors for copeptin, we have compared expression profiles of all orphan GPCRs in the copeptin‐responsive cell lines. This strategy generated a short list of orphan GPCRs expressed by all three cell types. One of the candidate receptors expressed in all responding cell types is likely responsible for mediating the transcriptional effects of copeptin. We are using knockdown/rescue experiments to determine which receptor copeptin is signaling through. We also are developing an animal model to determine the physiologic effects of copeptin, leading to a better understanding of the function of this peptide.

Support or Funding Information

NIH HL121456
Determining the Role of CEBP/α in Functional β‐cell Mass
Authors: Kener Kyle B , Ray Jason D. , Ballard Matthew , Utsch Will , Tessem Jeffery Sivert
Published: November 2023

Type 1 and type 2 diabetes both result in decreased functional β‐cell mass. Increasing functional β‐cell mass could be used as a cure for diabetes, either through the ex vivo expansion of β‐cells for transplantation or through in vivo expansion of endogenous β‐cells. We have shown that Nkx6.1 is necessary and sufficient to increase functional β‐cell mass by increasing proliferation, enhancing β‐cell function, and improving β‐cell survival. Furthermore, we have shown that c‐Fos is a critical early‐activated Nkx6.1 target gene that is essential to implement this molecular pathway. Here we demonstrate that CEBP/α is necessary for Nkx6.1 mediated upregulation of c‐Fos. We show that Nkx6.1 induces expression of CEBP/α, and that CEBP/α induces expression of c‐Fos. We show that CEBP/α is sufficient to induce β‐cell proliferation. We show that overexpression of CEBP/α protects β‐cells from apoptotic stimuli. We demonstrate the effect of CEBP/α overexpression on glucose stimulated insulin secretion. These data support the hypothesis that CEBP/α is part of the Nkx6.1 pathway for maintaining and increasing functional β‐cell mass and suggest that CEBP/α could be used as a potential target for enhancing functional β‐cell mass.

Support or Funding Information

BYU MEG Grant to JST, BYU ORCA Grant to JDR and KBK
Free Fatty Acid Receptor 3 Plays a Role in High Fat Diet Induced β Cell Dysfunction and β Cell Stress
Authors: Priyadarshini Medha , Ludvik Anton E , Cole Connor , Newman Marsha , Layden Brian T
Published: November 2023

A role of the gut microbiota in the development of both type 1 and type 2 diabetes has been suggested. The free fatty acid receptor 3 (FFA3) is considered to be a nutrient sensor that may be mediating the gut microbiota actions via the gut microbial metabolites, short chain fatty acids. As this receptor is expressed in β cells, a suggested metabolic interface may be occurring between β cells and the gut microbiota. We have previously shown that FFA3 inhibits β cell function in islets ex vivo. Exploring the physiological relevance of this observation in vivo, male mice with genetic knockout (KO) of FFA3 and their wildtype (WT) littermates were characterized with regard to glucose homeostasis. It was found that FFA3‐KO mice exhibit significantly higher insulin secretion and glucose infusion rates in hyperglycemic clamps consistent with enhanced insulin secretion by FFA3‐KO islets ex vivo. No differences were observed in energy expenditure, glycemic status and insulin sensitivity in FFA3‐KO and WT mice. With the exception of significantly enhanced insulin secretion in FFA3‐KO as compared to the WT mice upon intraperitoneal glucose challenge, no overt metabolic phenotype was observed under normal physiologic conditions. To investigate if FFA3 contributes to the β cell response to stress, two different models were utilized. First, under metabolic stress induced by high fat diet feeding, the WT mice developed impaired glucose tolerance as compared to the FFA3‐KO mice, owing mainly to enhanced insulin secretion with FFA3‐KO mice. Despite less insulin secretion (50–70% lower as compared to FFA3‐KO mice), WT mice had similar islet architecture and islet mass as FFA3‐KO mice. Surprisingly, challenge with single high dose of streptozotocin (STZ, agent inducing β cell damage), led to accelerated incidence of diabetes development in FFA3‐KO mice compared to the WT mice. Additionally, greater insulin deficiency and decreased β cell mass was observed in FFA3‐KO mice following STZ treatment, as compared to WT mice. Taken together, FFA3 mediates insulin secretion and the β cell response to high fat diet feeding without alteration in the islet mass. FFA3 also regulates the β cell responses to STZ treatment. Thus, these data demonstrate that FFA3 plays an important role in insulin secretion and β cell response to stressors.

Support or Funding Information

Support for the project has been from the Department of Veterans Affairs, Veterans Health Administration, Office of Research and Development, Career Development Grant No.1IK2BX001587‐01 (to B. T. Layden). M. Priyadarshini is supported by an American Heart Association postdoctoral fellowship (no. 15POST22410016).
Fibroblast Growth Factor 1 Ameliorates Diabetic Nephropathy Through an Anti‐inflammatory Mechanism
Authors: Lin Qian , Cai Lu , Tan Yi
Published: November 2023

A recent study demonstrated metabolic roles for fibroblast growth factor 1 (FGF1) in glucose homeostasis (Nature. 2014; 513:436). But its strong mitogenic activity hampers its wide use in diabetes. We have recently engineered a FGF1 partial agonist carrying triple mutations (FGF1Δ HS) that diminish the ability of FGF1 to induce heparan sulfate (HS)‐assisted FGF receptor (FGFR) dimerization and activation. FGF1Δ HS exhibited a major loss in proliferative potential, while preserving the full metabolic activity of wild‐type FGF1 (FGF1WT). In the present study, we further tested the potential of FGF1Δ HS in treatment of diabetic nephropathy (DN). Treatment of db/db type 2 diabetes (T2D) with FGFWT and FGF1Δ HS (0.5 mg/kg) every other day for 2 months, both FGF1WT and FGF1Δ HS significantly reduced blood glucose, urinary albumin, and prevented glomerular hypertrophy, mesangial matrix expansion and renal fibrosis. Similarly, treatment of streptozotocin (STZ)‐induced type 1 diabetes (TID) with FGF1WT and FGF1Δ HS also significantly prevented diabetes‐induced renal morphological and functional changes, but without significant effects on blood glucose levels. These results imply that the renal protection of FGF1WT and FGF1Δ HS is independent of their insulin sensitizing activity. Since renal inflammation is a critical cause of DN, and FGF1 exhibits a potent anti‐inflammatory property (Nature. 2014; 513:436), we hypothesized that the protection of FGF1 against DN is associated with its anti‐inflammatory capability. As expected, both FGF1WTand FGF1 HStreatments significantly reduced the inflammatory cytokines (TNF‐α and IL‐6) expression and CD68+ macrophage infiltration in renal tissues in both T1D and T2D, which were accompanied by an inhibition of inflammatory signal (JNK/NF‐κB) activation. Direct exposure of renal mesangial cell to high glucose or TNF‐α induced similar inflammatory and fibrotic responses as observed in diabetes, which could be prevented by FGF1WTand FGF1Δ HSpre‐treatment. More importantly, administration of FGF1Δ HSto 9‐month‐old db/db mice completely prevented the further development of DN with remarkable amelioration of renal inflammation and fibrosis. These results demonstrate that FGF1 prevents DN largely via inhibiting renal inflammation. FGF1Δ HSmight be a therapeutic approach for the treatment of DN without promoting undesired tissue proliferation.
Chronic Hypertension Switches Irritant‐Induced Pulmonary‐Cardiac Reflexes to Sympathoexcitation
Authors: Taylor‐Clark Tom , Hooper J Shane
Published: November 2023

Inhalation of pollutants acutely increases morbidity and mortality in individuals with pre‐existing cardiovascular disease. In these individuals, pollutants cause hazardous tachyarrhythmia and decreased heart rate variability consistent with sympathoexcitation. Nevertheless, in healthy animals and humans, inhalation of pollutants and irritants evokes parasympathetic‐mediated bradycardia. Here, we have compared the changes in blood pressure and the cardiac cycle in normotensive Wistar‐Kyoto rats (WK) and Spontaneously Hypertensive rats (SH) upon inhalation of allyl isothiocyanate (AITC), a selective agonist of TRPA1, the major pollutant‐sensor expressed on airway nociceptive nerves. Studies were performed in conscious, unrestrained 15‐week old rats using radiotelemetry. Resting mean arterial blood pressure were 188 mmHg and 120 mmHg for SH and WK, respectively. Resting heart rates were not different between the strains (~360 bpm). Inhalation of AITC caused substantial bradycardia and AV nodal block in WK, which was prevented by the muscarinic inhibitor atropine. In SH, inhalation of AITC caused bouts of brady‐tachycardia accompanied by both AV block and premature ventricular contractions (PVCs). Atropine prevented the evoked bradycardia and AV block in SH, exposing greater reflex tachycardia. The beta1‐adrenoceptor antagonist atenolol prevented AITC‐evoked tachycardia and PVCs in SH. AITC caused much greater hypertension in SH compared to WK. 24 hour treatment of captopril, the angiotensin converting enzyme inhibitor, normalized blood pressure in SH. Nevertheless, captopril had no effect on AITC‐evoked reflexes in SH. These data indicate that pre‐existing chronic hypertension remodels pollution‐sensitive pulmonary‐cardiac reflexes from parasympathetic towards sympathoexcitation. The remodeled reflex is not dependent on preservation of the hypertension.

Support or Funding Information

American Heart Association Grant‐in‐Aid (16GRNT31460004)
Inflammation and Impaired α2‐Adrenergic Receptor‐Mediated Inhibition of Ca2+ Channels Contribute to Hypertension in DOCA‐Salt but not Obese Dahl SS Rats
Authors: Mui Ryan K , Fernandes Roxanne N , Garver Hannah G , Fink Gregory D , Xu Hui , Galligan James J
Published: November 2023

Introduction

Inflammation is associated with increased sympathetic nerve activity in hypertension. Inhibition of norepinephrine (NE) release from nerve terminals occurs through prejunctional α2‐adrenergic receptor (α2AR)‐mediated inhibition of N‐type voltage‐gated Ca2+ channels. Inflammation has been implicated in adrenergic receptor desensitization. Desensitization of α2AR occurs through G‐protein receptor kinases (GRKs) that uncouple receptors from G‐proteins. We tested the hypothesis that DOCA‐salt and a high fat diet (HFD) causes inflammation and impaired inhibition of Ca2+ channels through desensitization of prejunctional α2ARs.

Methods

Uniphrectomized rats were given water (SHAM) or 200mg/kg DOCA (sc) and 1% NaCl/0.2% KCl water (DOCA) for 4 weeks. Dahl salt‐sensitive (Dahl SS) rats were given a high fat diet (HFD, 60% kcal from fat) or normal fat diet (NFD, 10% kcal from fat) for 26 weeks. Inflammation was assessed by macrophage staining (CD163) in mesenteric arteries and qRT‐PCR of celiac/splanchnic ganglia for MCP‐1, TNFα, and IL‐6. Whole cell patch clamp was used to measure α2AR‐mediated inhibition of Ca2+ channels using NE and UK1430 (agonists) and yohimbine (antagonist). mRNA levels of α2AR (2A, 2B, 2C) and GRK (2,3,5) in celiac/splanchnic ganglia were measured by qRT‐PCR. Paroxetine was used to inhibit GRK2 vs. fluoxetine (control). Clodronate‐embedded liposomes were used to deplete macrophages.

Results

DOCA‐salt and HFD treatment caused hypertension vs. controls. Vascular macrophage infiltration and mRNA levels of MCP‐1, TNFα, and IL‐6 mRNA were significantly higher in DOCA‐salt vs. SHAM rats, but not in HFD vs. NFD Dahl SS rats. DOCA‐salt and HFD treatment impaired α2AR‐mediated inhibition of Ca2+ channels by NE and UK14304 treatment in celiac ganglion neurons. Yohimbine blocked the effects of NE in all neurons. There were no differences in α2AR (2A,2B,2C) mRNA levels in DOCA‐salt and HFD vs. controls. GRK2 mRNA levels were higher in DOCA‐salt vs. SHAM rats, but lower in HFD vs. NFD Dahl SS rats. Paroxetine did not increase α2AR‐mediated inhibition of Ca2+ channels in neurons from DOCA‐salt rats vs. fluoxetine treatment. Macrophage depletion preserved α2AR function and lowered blood pressure in DOCA‐salt rats.

Conclusions

Inflammation and macrophage‐associated impairment of α2AR‐mediated inhibition of Ca2+ channels occur in DOCA‐salt but not HFD‐Dahl SS rats. DOCA‐salt and HFD treatment does not affect α2AR mRNA expression. In DOCA‐salt rats, α2AR dysfunction does not occur via GRK‐dependent desensitization. In HFD‐Dahl SS rats, equivalent α2AR function to NFD rats may be attributed to decreased GRK2 expression.

Support or Funding Information

Supported by NIH 2P01HL070687 and American Heart Association (15PRE25090218)
Noisy Timing Of Nicotinic Synaptic Activity Promotes Amplification In Sympathetic Ganglia
Authors: Horn John P , Kullmann Paul H.M.
Published: November 2023

Hypertension and heart failure can be driven and exacerbated by sympathetic hyperactivity. We hypothesize that remodeling of synaptic integration in sympathetic ganglia may contribute to such hyperactivity. Here we describe normal physiological properties of cholinergic nicotinic synapses using high resolution patch‐clamp recordings from the isolated, intact rat superior cervical ganglion. Synaptic currents were recorded under voltage‐clamp from individual synapses using minimal presynaptic stimulation of the cervical sympathetic trunk. Using dynamic‐clamp, the excitability of each cell was then measured in terms of the threshold‐synaptic conductance required to stimulate an action potential. Synaptic strength was then calibrated by calculating the synaptic conductance (gsyn) and expressing it as fraction of thresh‐gsyn. This revealed that synaptic strength ranges from 10 to 1000% thresh‐gsyn. The effect of timing was analyzed by comparing EPSC amplitudes evoked by 1Hz stimulation at regular 1 second intervals with those evoked using exponentially distributed intervals. Interestingly, noisy 1 Hz stimulation increased the variability (sd) of EPSCs, but had no effect on their average amplitude. This effect was seen across the full range of synaptic strengths observed. To explore the consequences of this finding, we simulated how regular and noisy trains of synaptic events modeled on our data evoked spikes in a conductance‐based model neuron. The results showed that when noisy stimulation increased the variability of EPSCs, the spike output of the system increased. We conclude that noisy synaptic activity, like that seen in intracellular recordings from sympathetic neurons in living animals, creates a form of stochastic resonance. In other words, the noise introduced by timing in conjunction with quantal fluctuations observed with regular stimulation has the effect of increasing the output signal (spikes) from this system.
GABA and Glycine: Fine Tuning for Inhibitory Control of Brainstem RVLM Neurons
Authors: Gao Hong , Derbenev Andrei
Published: November 2023

Presympathetic neurons in the rostral ventrolateral medulla (RVLM) are best known for their contribution to the control of sympathetic nervous system and homeostatic functions of the body. Both glycine and GABA were identified as fast inhibitory neurotransmitters in the RVLM. GABA is essential for the control of the excitability of neurons, while glycine also inhibits neurons in the RVLM, and thus control sympathetic output. Despite the critical role of GABA and glycine as inhibitory neurotransmitters, surprisingly little is known about the mechanisms of GABA and glycine release and/or co‐release. Using whole‐cell patch‐clamp recordings from presympathetic neurons identified with PRV‐152, we examined GABAergic and glycinergic inhibitory mechanisms in rat brainstem slices containing RVLM neurons. We tested the hypothesis that the release of glycine is associated with the activity of neuronal network. We found that inhibitory postsynaptic currents (IPSCs) recorded from RVLM neurons composed from both GABAergic and glycinergic events. In steady state conditions, GABA is the predominant inhibitory neurotransmitter in the RVLM. Interestingly, after activation of the inhibitory network, we found that GABAergic and glycinergic neurotransmission were reversed. Under resting condition, the proportion of glycinergic IPSCs was less than 10% of the total IPSCs. Activation of the inhibitory network produced saturation of inhibitory events mediated by GABA and increased the average frequency of glycine‐mediated IPSCs. After network activation, glycinergic IPSCs represent more than half of the total IPSCs in the RVLM. Our data suggest that after saturation of GABA, glycinergic inhibition provides a secondary synaptic inhibition in presympathetic RVLM neurons. This novel mechanism has the potential for fine tuning of the sympathetic output controlling homeostatic functions.

Support or Funding Information

Supported by NHLBI R01HL122829
Neuromuscular inactivity of the respiratory control system during overwintering in bullfrogs, Lithobates catesbeianus
Authors: Santin Joseph M. , Hartzler Lynn
Published: November 2023

In clinical disorders, inactivity typically results in loss of normal neuromuscular function. In contrast, hibernating, estivating, and overwintering animals use compensatory mechanisms and/or avoidance strategies to preserve motor function in the face of inevitable dormancy. Semiaquatic frogs typically overwinter in ponds that may be covered by ice and, therefore, do not regulate lung breathing for weeks to months. Despite a lack of lung breathing, motor function of the respiratory system in American bullfrogs, Lithobates catesbeianus, remains fully competent during the winter and operates adequately to match ventilation to metabolism in early spring. Unlike overwintering hibernators with unloaded limb muscles and putatively inactive locomotor systems, frogs may continue producing respiratory motor activity during cold‐submergence to maintain a functional respiratory motor system. Inactivity avoidance could occur because anuran amphibians have respiratory mechanics that, counterintuitively, can produce ventilatory motor patterns under water. Therefore, we hypothesized that bullfrogs generate respiratory motor patterns during cold‐submergence as a mechanism to avoid disuse and preserve motor performance. To test this hypothesis, we measured activity of respiratory muscles (buccal floor compressor, posterior m. intermandibularis and glottal dilator, m. dilator laryngis) via chronic electromyography (EMG) in freely behaving bullfrogs at 20°C and while submerged at 2°C (n=8). As expected, activation of the glottal dilators coincided with large amplitude activity of the buccal floor compressors to produce lung ventilation. In contrast, small amplitude oscillatory activity of the buccal floor compressors occurred without activation of glottal dilators, indicative of buccal ventilation. We found that bullfrogs took 5.5±1.4 breaths per minute when surfacing at 20°C, and we confirmed that underwater “ventilation cycles” occur at a rate of 1.7±0.2 events per minute at 20°C. At 2°C, bullfrogs neither surfaced to ventilate their lungs (2°C vs. 20°C; p<0.0001; one‐way ANOVA), nor did they activate either group of respiratory muscles when submerged at 2°C for 10 days (2°C vs. 20°C; p<0.0001; one‐way ANOVA). Tonic activity characteristic of resting muscle tone did not change after submergence at 2°C in buccal floor compressors or the glottal dilators, for at least 10 days (buccal floor, p=0.4, one‐way ANOVA; glottal dilator, p=0.55, one‐way ANOVA). In conclusion, bullfrogs experience bona fide respiratory motor inactivity during cold‐submergence associated with overwintering. Underwater neuromuscular activation is, therefore, an unlikely mechanism to preserve respiratory motor function after overwintering, but normal function may be maintained through compensation at the level of the motor network.

Support or Funding Information

National Science Foundation grant IOS‐1257338

Wright State Research Council

Wright State Biomedical Science PhD Program
FishResp: an R‐package for Filtering and Analyzing Raw Data in Aquatic Respirometry
Authors: Morozov Sergey , McCairns Scott R.J. , Merilä Juha
Published: November 2023

One of the most common approaches for measuring metabolic rate of aquatic animals is whole‐body respirometry. Respirometry systems that are currently available on the market allow researchers to get raw respirometry data of high accuracy. However, further data processing, including quality‐control tests, is left to researchers' discretion. There is currently no universal tool for filtering raw data and extraction of key parameters from the massive datasets consisting point observations. This methodological disunity affects further comparability of research findings, and published studies contain contradictory estimations of metabolic rates in different fish species. For example, background respiration of microorganisms present inside chambers and tubing is one of the most significant factors that influence the quality and reliability of raw respirometry data. Different methodologies are known to correct for microbial oxygen consumption, but a lack of such correction appears to be common in many published studies. The problem is especially relevant when respirometry measurements are performed in conditions favorable for microbial growth, e.g. at high water temperatures. Consequently, without proper quality controls and data filtering, oxygen consumption in aquatic animals may be significantly overestimated.

To overcome problems associated with raw respirometry data processing, we have developed an R‐package ‘FishResp’. This package is freely available, versatile and easy‐to‐use. Being compatible with raw data from various commercial respirometry systems, it allows users to perform quality control checks for chamber leaking and microbial oxygen consumption. We demonstrate the virtues of FishResp and its applicability in correcting for background respiration, using raw data obtained from metabolic rate measurements of the Trinidadian guppy (Poecilia reticulata). This example is peculiar as the species' reported mean standard metabolic rate measured at 25–26°C temperature varies substantially in different studies (100–500 mgO2/kg/h). Using FishResp software, we show that background respiration in chambers may make up to 75% of the total oxygen consumption during a long‐term experiment with a regular cleaning protocol.

We wish to promote FishResp as a common tool for raw data processing in metabolic rate estimation in aquatic animals. A user‐friendly GUI version and a simple user manual are under development and will be available at the official website fishresp.org in 2017.

Support or Funding Information

SM: LUOVA doctoral programme, Alfred Kordelin Foundation, Oskar Öflund Foundation; RJSM, JM: Academy of Finland
Expression of skeletal muscle miRNA are unaltered during 14 days of bed rest but decrease following 7 days of reloading in middle‐aged adults
Authors: Arentson‐Lantz Emily J , Lamon Séverine , Fry Christopher S , English Kirk L , Paddon‐Jones Doug
Published: November 2023

microRNA (miRNA) play an important role in mitigating expression of molecular pathways that govern skeletal muscle health. Bed rest accelerates the loss of muscle mass and function; however, little is known about the role that miRNA play in muscle health during inactivity and subsequent recovery. We examined the effect of 14 days of bed rest and 7 days of rehabilitation on miRNA expression, muscle atrophy and function in middle‐aged adults. Muscle biopsies were obtained from the vastus lateralis of healthy middle‐aged (average age 51.7±1 y) male and female adults (n=19) before (PreBR) and after (PostBR) 14 days of bed rest and after (Rehab) 7 days of rehabilitation for miRNA and immunohistochemical analysis. Body composition, muscle strength and aerobic capacity were assessed using iDEXA, dynamometry, and VO‐2‐ max testing, respectively. Collective miRNA expression was screened using Firefly Bioworks multiplex assay with a custom panel of 65 candidate species. Based on prelimnary statistical analysis of multiplex assay, individual miRNA expression was confirmed using miRNA‐specific stem‐loop primers (TaqMan® microRNA assay kit) and qPCR. Expression of miR206 (1.07, 1.22, and 0.94 ± 0.16 for PreBR, PostBR, and Rehab), mir133a (1.10, 1.18, and 0.95 ± 0.05 for PreBR, PostBR, and Rehab), mir378 (1.46, 1.47, and 1.20 ± 0.05 for PreBR, PostBR, and Rehab) and let7b (0.89, 0.97 and 0.87 ± 0.05 for PreBR, PostBR, and Rehab) did not change with bed rest, but were significantly decreased following 7 days of rehabilitation. Muscle quality, relative VO2 max (ml/min/kg), fiber cross sectional area and satellite cell number decreased during bed rest and did not return to baseline values. The precise role of miRNAs in muscle regrowth is not well understood. However, the overall pattern of response of miRNAs 206, 133a, 378 and let7‐b to rehabilitation indicate they may involved in the coordinated process to restore muscle mass and function following disuse.

Support or Funding Information

This research was supported by: NSBRI‐NNJ08ZSA002N, RO1 NR012973, P30 AG024832.