bluuebunny/crossref_metadata_2025 huggingface dataset:
Local skin temperature alters cutaneous vasoconstrictor responses to a simulated hemorrhagic challenge while heat stressed
Authors: Pearson James , AI Lucas Rebekah , Crandall Craig G
Published: June 2021

Tolerance to simulated hemorrhage is reduced with hyperthermia, due in part to inadequate cutaneous vasoconstriction. It is unclear how elevated skin temperatures, as experienced by soldiers on active duty, influence cutaneous vasoconstriction during simulated hemorrhage. 8 healthy males (34 ± 9 yr, 80.2 ± 4.2 kg) underwent a simulated hemorrhagic challenge via lower body negative pressure (LBNP) to pre‐syncope while heat stressed sufficient to increase core (Tcore Δ1.2 ± 0.2°C) and mean skin temperatures (Tsk mean 38.2 ± 0.7°C). Local skin temperatures at three forearm sites were held at 35.2±0.6°C, 38.2±0.2°C and 41.3± 0.7°C throughout heat stress and LBNP. At pre‐syncope mean arterial pressure declined (74±6 to 53 ± 8 mmHg P < 0.0001) while mean Tsk (38.2±0.7°C; P = 0.92) and local Tsk (35.1±0.8; 38.3±0.3 and 41.5±0.6°C; P > 0.05) were unchanged relative to heat stress baseline (i.e., pre‐LBNP). The magnitude of reduction in cutaneous vascular conductance during the final 90 seconds of LBNP from heat stress baseline was influenced by local Tsk (8% at ~35°C; 3% at ~38°C and 2% at ~42°C; P < 0.0001). In hyperthermic individuals the extent of cutaneous vasoconstriction during a simulated hemorrhage is dependent on skin temperature. In situations where a soldier's skin temperature exceeds 38°C, cutaneous vasoconstriction to a hemorrhagic challenge is likely negligible.

NIH HL61388 and HL84072
Tolerance to a hemorrhagic challenge during heat stress is improved with inspiratory resistance breathing
Authors: Brothers R. Matthew , Ganio Matthew S. , Lucas Rebekah A. I. , Crandall Craig G
Published: June 2021

The mechanism(s) by which heat stress alters blood pressure control and tolerance to a simulated hemorrhagic challenge is multifaceted; however, heat‐induced reductions in central blood volume play a key role. Inspiratory resistance breathing improves blood pressure control and tolerance during simulated hemorrhage in normothermic individuals. It is unknown if similar improvements occur with this maneuver in heat stress conditions. This study tested the hypothesis that inspiratory resistance breathing improves tolerance to simulated hemorrhage in individuals with elevated internal temperatures. On 2 separate days, 8 subjects performed a simulated hemorrhage challenge (lower body negative pressure, LBNP) to pre‐syncope following an increase in internal temperature of 1.5 °C. During one trial subjects breathed through an inspiratory impedance device set at 0 cmH20 of resistance (Sham) while on the other day the device was set at −7 cmH20 of resistance (Experimental). Tolerance was quantified as cumulative stress index (CSI). Subjects were more tolerant to the LBNP challenge during the Experimental protocol as indexed by a larger CSI (Sham: 520±306 mmHg × min; Experimental: 682±324 mmHg × min, P<0.01). These data indicate that inspiratory resistance breathing modestly improves tolerance to a simulated hemorrhagic challenge during heat stress.

Support NIH‐HL61388 & HL84072
Simulation of expired nitrogen (N2) after inhaling argon (Ar) at 1 atmosphere
Authors: Cruz Julio Cesar
Published: June 2021

Expired Ar and N2, after inhaling Ar, were obtained in 1965 and published in 1991 (Cruz. Respir. Physiol. 86:1,1991). However, only Ar data was used to develop a model of inhaled inert gases. Because expired N2 behaved differently than Ar, especially, after holding the breath at 10s and 20s, at the end of inspiration, N2 was ignored. After introducing a new equation where FAr is a function of lung volume and time (unpublished), I was able to understand how Ar was inhaled and distributed in the alveoli. I learned that the expired Ar was generated by uneven flows from parallel regions of the lung. Now, I'm presenting the simulated expirogram of N2 (Figure, heavy line) after inhaling in 2s, 1.9L of 21% O2, 79% Ar from FRC (4L) and exhaling in 3s to RV (1.4L). New concepts were introduced in mixing the inhaled gas with the expiratory reserve volume (ERV), by the mechanism of convection‐diffusion during inspiration (Caucha et al. Am. J. Respir. Crit. Care Med. 183: A5180, 2011). These concepts are here applied. At FRC, the amount of alveolar N2 (3.245L) was distributed from apex‐to‐base of the lung following West lung model. The amount of N2 in the ERV was 2.114L, which was mixed with the amount of Ar that reached the alveoli (1.165L). The simulated expired N2 (thin line) was insufficient to reach experimental N2 (symbols) because of the assumptions of the expired Ar used: VD=425ml and k value (50L−1) of the exponential equation, the latter produced a progressive decline of Ar from VD to ERV. In order to fit the experimental N2 data, it was necessary to reduce the VD to 370ml and k to 40L−1. In addition, it was added 101ml of alveolar N2 present in the RV that diffused to ERV during Ar inhalation. It is concluded that the N2 expirogram is not the mirror image of the Ar expirogram.

Supported in part by the Centro de Enseñanza, Investigación y Servicios (CEIS).
Hyperthermia potentiates the IL‐6 mRNA response to LPS in C2C12 muscle cells
Authors: Welc Steven S , Chen Dan L. , Clanton Thomas L.
Published: June 2021

In heat stroke and bacterial infection, skeletal muscles (SM) can be exposed simultaneously to hyperthermia (HT) and endotoxin. Both are potent stimuli of IL‐6 in SM. We hypothesized that when these stimuli act together they potentiate SM IL‐6 production, which could implicate a role for SM in whole body innate immune responses.

Aims

1) to treat C2C12 cells with LPS or LPS+HT (42°C) and compare IL‐6 mRNA at 1, 2, 3, and 6 h, 2) to compare IL‐6 protein between treatments, and 3) to compare the response of myoblasts (MYOB) and myotubes (MYOT) to these co‐stimuli. Cells were supplemented with LPS (1 ug/ml) and simultaneously exposed to 37°C or 42°C for 1 h, then harvested or allowed to recover at 37°C for 1, 2, or 5 h. In a separate experiment, MYOT were treated with LPS (1000, 100, 10, and 1 ng/ml) and the supernatant was sampled at 6 h and analyzed for IL‐6 protein. Significant up regulation of IL‐6 mRNA was seen in MYOB and MYOT in response to LPS (P<0.05). Furthermore, the addition of HT potentiated the increase of IL‐6 mRNA compared to LPS alone (P<0.05); the amplification spanned 3h (MYOB) and 6 h (MYOT). Interestingly, IL‐6 protein was either not different or attenuated in HT+LPS vs. LPS. Results further demonstrate that HT is a functional stimulus for IL‐6 mRNA, possibly part of the HSF‐initiated heat shock response. We speculate variations in IL‐6 protein are a consequence of translational inhibition associated with mild heat shock.

Supported by: AHA #11GRNT7990119
Hypothalamic mechanisms relating to improvement of thermal tolerance in heat‐and‐exercise‐acclimated mice
Authors: Tokizawa Ken , Lin Chen-Hsien , Uchida Yuki , Sakakibara Shin-ichi , Nagashima Kei
Published: June 2021

Repeated exposure to moderate heat improves heat tolerance and acclimation. Exercise induces the improvement more effectively than just being at rest. The underlying central mechanisms of those phenomena have remained unclear.

Male mice were individually housed at 32°C (HE) or 25°C (NE). The mice in two groups had two‐different exercise conditions: with (EXE) and without (CON) access to running wheels. After eight weeks, the mice had a 2‐h exposure at 36°C.

Core temperature and oxygen consumption were lower in HE groups than in NE groups. In the heat exposure of 36°C, core temperature was lower in EXE groups than in CON groups during the first 1 h of the exposure. Ki67‐immunoreactive cell, a marker of cell proliferation, was not observed in the hypothalamus in NE‐CON mice. However, the cells were found in medial preoptic nucleus and dorsomedial hypothalamus in NE‐EXE, HE‐CON, and HE‐EXE mice. cFos immunoreactive cell in the median and medial preoptic nucleus was greater in EXE groups than in CON groups.

These results may indicate that daily exercise and long‐term exposure to mild heat, separately, are sufficient to improve heat tolerance and acclimation respectively, and their combined effect induces both improvements. Neurogenesis and neuronal reactivity in the hypothalamus may be responsible for these thermal adaptations.
Evaluation of Uosm:Posm ratio and Posm as Hydration Biomarkers in Healthy Young Women During Daily Activities
Authors: Armstrong Lawrence E , Johnson Evan C , Munoz Colleen X , LeBellego Laurent , Klein Alexis , Casa Douglas J , Maresh Carl M.
Published: June 2021

The urine‐to‐plasma osmolality ratio (Uosm:Posm) is used clinically to diagnose renal and metabolic disorders. Uosm:Posm<1 also represents a state of relative water excess. Diet records of 120 college women were analyzed [beverage water + food water = total fluid intake (TFI)] for 5d to identify 14 high volume (HIGH) and 14 low volume (LOW) drinkers (age, 20.3±1.7 y). Experimental protocol: 2 baseline days verified ad libitum TFI status of HIGH (3.21 L/d) and LOW (1.64 L/d). During a controlled intervention (days 3–6) with mineral water (Volvic™), HIGH consumed less than baseline (TFI, 2.00 L/d; H↔L) and LOW consumed more than baseline (TFI, 3.50 L/d; L↔H). On ad libitum recovery day 7, TFI were: HIGH, 3.17, LOW, 1.71 L/d. Duplicate Uosm (24h collection) and Posm (morning) samples were analyzed via freezing point depression osmometry. Mean (± SD) Uosm:Posm were H↔L: d1, 1.3±0.4; d2, 1.4±0.5; d3, 2.0±0.8; d4, 2.1±0.9; d5, 2.1±0.8; d6, 2.0±0.8; d7, 1.2±0.6. L↔H: d1, 2.7±0.7; d2, 2.6±0.6; d3, 0.9±0.2; d4, 0.9±0.3; d5, 0.9±0.1; d6, 1.0±0.4; d7, 1.9±0.7. 11/13 of Uosm:Posm<1 values occurred for H↔L on d1, d2 and d7, and 32/33 occurred for L↔H on d3 to d6. Mean daily Posm values were similar (7d range: H↔L, 292 – 295; L↔H, 293 – 296 mOsm/kg), reflecting neuroendocrine regulation. These data indicate that Uosm:Posm warrants further investigation as an index of human hydration status across days. Funded by Danone Research, France.
Head cooling improves orthostatic tolerance during passive whole‐body heating
Authors: Davis Scott L , Rola Kelyn S , Fjortoft Silje , Korra Monika , Murphy Megan N , Wilson Thad E
Published: June 2021

Whole‐body heating (WBH) reduces middle cerebral artery blood velocity (MCAVmean) and orthostatic tolerance in humans. To identify if focal head cooling is an effective orthostatic tolerance counter measure during WBH, MCAVmean and orthostatic tolerance were determined in five subjects during a progressive lower body negative pressure (LBNP) tolerance test during: 1) normothermia (34 °C water perfused through a tube‐lined suit and hood), 2) WBH‐head heating (48 °C suit and hood), and 3) WBH‐head cooling (48 °C suit and 20 °C hood). Tolerance tests during WBH were performed following an increase in internal temperature ~1.0 °C. Orthostatic tolerance was not different between WBH‐head cooling (481±15 cumulative stress index, CSI) and normothermia (775±42 CSI) but was significantly reduced during WBH‐head heating (328±167 CSI) compared to normothermia (P=0.02). LBNP‐induced changes in MCAVmean from baseline were similar between WBH‐head cooling (−16±5 cm•s−1) and normothermia (−17±7 cm•s−1) and trended lower compared to WBH‐head heating (−25±5 cm•s−1; P=0.09). These data indicated that focal head cooling, via better maintenance of brain blood flow, may be able to serve as a counter measure during heat stress conditions.
Modeling Intracranial Pressure in Microgravity during Parabolic Flight
Authors: Bachman Larry Lee , Patterson Kevin G. , Hegstad Thomas M. , Grigoryan Edward A. , Sayad-Shah Mehria , Hargens Alan R.
Published: June 2021

Some astronauts return from spaceflight with papilledema probably due to intracranial hypertension secondary to head‐ward fluid shifts.

Study objectives were to determine (1) the feasibility of venous congestion as a mechanism contributing to elevated intracranial pressure (ICP), and (2) the angle of head‐down tilt (HDT) that best represents ICP measured in microgravity.

Our student team constructed a physical model of neck and cranial circulations in accordance with average adult human proportions to produce pressures and flows equivalent to physiological norms while upright, supine and at various tilt angles. The model flew aboard two NASA parabolic flights in July 2011.

Jugular venous pressure and ICP changed in parallel and linearly during partial gravities, but rose disproportionately in microgravity to the same magnitude regardless of arterial pressure, central venous pressure or flow rate, corresponding to values measured at 11±5º HDT. Venous flow resistance increased 300% in microgravity, possibly due to unique flow properties through collapsible vessels. Results suggest that venous pressures elevate ICP, and future crewmember studies should examine cervical venous pressures, flows and valve incompetence. Moreover, countermeasures should focus on lowering cranial venous pressures by facilitating cephalic venous return.

Supported by NASA RGSFOP, CA Space Grant, and UCSD Dept of Ortho. Surg.
Pan‐omic Approaches to Study the Effects of Microgravity on Host Responses to Toxins
Authors: Waddy Edward , Chakraborty Nabarun , Gautam Aarti , Santos William , Hoke Allison , Jett Marti , Hammamieh Rasha
Published: June 2021

Microgravity, as indicated by previous studies, enhances bacterial virulence but depresses a host's immunity cascade. Presumably, pathogenic insults occurring in space may trigger altered immunological pathways in host cells. Understanding this paradigm is essential to establishing proper wound care management. A host toxin model was designed to address this research hypothesis and was executed aboard the Space Transportation System (STS)‐135. Preparatory ground work focused on designing a bioreactor‐based experimental model that could be integrated with the Cell Culture Module (CCM); which is semi‐automated equipment that was previously operated in space.

Human microvascular endothelial cells were inoculated in 6 bioreactors on the ground, and the CCM supported these cells for the first 10 d of flight. Four bioreactors batched in 2 were exposed to lipopolysaccharide (LPS), an endotoxin commonly found in gram‐negative bacteria, for two different time periods (4 h and 8 h). At the end of each time point the cells were fixed and maintained in a fixed state until after the STS‐135 landed.

Molecular samples extracted from the retrieved cells were found to have good integrity. A high throughput pan‐omics study, followed by in silico data analysis, is underway to identify the genomic signatures and pathways, and disease footprints corresponding to microgravity induced immunity cascades.
Redox Regulation of nNOS Translocation and Muscle Atrophy During Short‐term Mechanical Unloading
Authors: Lawler John M , Kunst Mary , Joshi Kumar , Hord Jeff M , Lee Yang , Martinez Daniel A
Published: June 2021

Reduced mechanical loading causes substantial atrophy of skeletal muscle. An emerging signaling event during mechanical unloading is the translocation of nNOS from the sarcolemmal dystrophin‐glycoprotein complex (DGC). Clues from Duchenne muscular dystrophy papers implicate NAD(P)H oxidase and caveolin‐3 as accomplices in eliciting DGC perturbations. EUK‐134, a mimetic of superoxide dismutase and catalase, was used to test the causal role of redox signaling in nNOS translocation and muscle atrophy as a result of short‐term (54 hours) hindlimb unloading (HU). Fischer‐344 rats were divided into loaded controls (CON), hindlimb unloaded, and HU + EUK‐134. We found that translocation of nNOS from the sarcolemma occurred with HU, and removal was virtually abolished by EUK‐134. Elevation of caveolin‐3 localization with HU was also attenuated by EUK‐134. In addition, mechanical unloading increased localization of NAD(P)H oxidase subunits gp91phox(Nox2) and p47phox and increased oxidative stress (4‐hydroxynonenal), effects also abrogated by EUK‐134. Further, unloading‐induced muscle fiber atrophy and fiber‐type shift from slow to fast were also mitigated by EUK‐134. Our findings indicate that nNOS translocation from the sarcolemma is an early event during mechanical unloading, redox‐dependent, and linked to morphological changes in skeletal muscle. Supported by NIH (AR054084).
Markers of autophagy are elevated in cardiac tissue following doxorubicin administration
Authors: Kavazis Andreas N , Smuder Ashley J , Min Kisuk , Powers Scott K
Published: June 2021

Doxorubicin is an antitumor agent used in cancer treatment, but its clinical use is limited due to cardiotoxicity. Although, numerous studies have investigated the signaling pathways responsible for doxorubicin‐induced cardiotoxicity, the role that the autophagy/lysosomal system plays in doxorubicin‐induced cardiac damage remains unknown. We hypothesized that systemic doxorubicin administration would result in increased activation of the autophagy system in the heart. To test this postulate, adult, male Sprague‐Dawley rats were randomly assigned to placebo or doxorubicin groups. Doxorubicin animals received doxorubicin hydrochloride (20 mg/kg body weight IP) 24 hours prior to sacrifice, whereas placebo groups received saline injections. Following treatment, hearts were excised and used for biochemical analyses. Doxorubicin administration resulted in increased cardiac levels of mRNA and protein abundance of key autophagy markers. Specifically, mRNA levels of beclin (+58%), ATG12 (+41%), and LC3 (+46%) were significantly (p<0.05) increased in the heart following doxorubicin administration. Also, protein levels of beclin (+32%), ATG12 (+47%), and ATG7 (+28%) were significantly (p<0.05) increased in heart muscle isolated from animals treated with doxorubicin. These findings suggest that increased autophagy is a contributing factor of doxorubicin‐induced cardiotoxicity.
Differential myogenic and cell cycle gene translation following unaccustomed resistance loading may contribute to disparate myofiber hypertrophy potential during resistance training
Authors: Stec Michael John , Thalacker-Mercer Anna , Cui Xiangqin , Merritt Ed , Bamman Marcas
Published: June 2021

Mechanisms underlying disparate skeletal muscle hypertrophic responses to resistance training (RT) among individuals are largely unknown. 66 adults were clustered as non‐ (Non), modest (Mod), or extreme (Xtr) responders based on change in myofiber area after 16 wk RT. Via genomic microarray we identified large differences in the muscle transcriptome among response clusters prior to RT. We therefore analyzed muscle protein levels of select targets (HES6, annexin A2, ER‐alpha, myogenin, MyoD, cyclin D1, p21, p27, NFkB) before and 24 h after the first (unaccustomed) resistance exercise (RE) bout to determine if cluster differences in basal mRNA expression affected translational responses to RE. MyoD and p27 decreased in all clusters (P<0.05) while cluster x time intrxns (P<0.05) were found for HES6, myogenin, and cyclin D1. Compared to Mod and Xtr, basal HES6 and cyclin D1 tended to be lower in Non (P=0.10) and increased after RE only in Non (HES6 55%, cyclin D1 34%). These findings suggest the unique basal gene expression profile among Non may lead to differential translational responses to RE as compared to subjects who proficiently achieve RT‐induced myofiber hypertrophy (Mod and Xtr). Future research should determine whether unique translational patterns following unaccustomed RE play a role in the failed hypertrophy among Non. Support: 5R01AG017896, VA Merit, 5UL1 RR025777.
Satellite cell expression of myogenic regulatory factors is altered when co‐cultured with preadipocytes
Authors: Thornton Kara Jean , Chapalamadugu Kalyan C. , Doumit Matthew E. , Murdoch Gordon K.
Published: June 2021

Postnatal skeletal muscle hypertrophy requires activation, proliferation, and differentiation of muscle satellite cells (SCs) driven by expression of several myogenic regulatory factors (MRFs). The interaction between SCs and non‐myogenic cells within the unique microenvironment of the muscle is poorly characterized. SCs induced to differentiate in either a mono‐culture (MC) or co‐culture (CC) with preadipocytes, were isolated using laser‐assisted cell catapulting. Temporal expression of paired box transcription factor 7 (Pax7) and four MRFs; myogenic differentiation factor (MyoD), myogenin (Myf4), myogenic factor 5 and myocyte enhancement factor 2a were compared in SCs. MRF expression using TaqMan™ qRT‐PCR was performed at 0, 4, 8, 16, 24, 32, 40 and 48 hours post‐differentiation (PD). As compared to MC, differentiation of SCs in CC resulted in i) an increased Pax7 expression at 32 (p=0.05) and 48 (p=0.02) hrs PD ii) an elevated MyoD expression at 16 (p=0.05) and 48 (p=0.06), hrs PD and iii) a reduced Myf4 expression at 32 (p=0.04) and 40 (p=0.06) hrs PD. Altered MRF expression in SCs grown in CC, as compared to MC, indicates that preadipocytes can influence activation and differentiation of SCs. Furthermore, this CC is an improved model of the in vivo satellite cell niche and may aid in elucidating the complex mediation of postnatal SC activation.
Angiopoietins regulate capillary network in non‐obese type 2 diabetic muscle, but VEGF is not necessary for the angiogenic response to exercise
Authors: Fujino Hidemi , Kondo Hiroyo , Murakami Shinichiro , Fujita Naoto , Nagatomo Fumiko , Ishihara Akihiko
Published: June 2021

PURPOSE

To gain insight into the regulation of angiogenic process, we visualized the capillary network and evaluated the angiogenic and metabolic factors over the course of exercise training in non‐obese type 2 diabetes.

METHODS

The Goto‐Kakizaki (GK) rats were randomly divided into an exercise training (T2DM+Ex) and a sedentary (T2DM), while the Wistar rats were used as a control (Con). T2DM+Ex rats were trained at a low‐intensity for 60 min on a treadmill 6 times a week for 3 weeks. The 3‐D capillary network in soleus muscle was visualized using confocal laser microscopy. The expression of angiogenic factors (VEGF, KDR, Flt‐1, Ang‐1, Ang‐2, and Tie‐2), HIF‐1 alpha, AMPK and GLUT4 in the soleus muscle were determined by TaqMan probe‐based real‐time PCR.

RESULTS

The capillary volume of the soleus muscle was lower in T2DM than in Con rats, whereas that in T2DM+Ex was higher. Angiopoietin pathway and metabolic factors in the T2DM+Ex were significantly increased compared with those in Con and T2DM although VEGF was not changes among three groups.

CONCLUSION

These findings suggest that exercise training improves the regression of capillary network in diabetic muscle without the change of VEGF, and that the angiopoietin pathway in diabetic muscle could be upregulated by exercise training. Supported by Grants‐in‐Aid for Science Research from the Japanese Ministry of Education, Culture, Sports, Science and Technology.
Fast‐To‐Slow: Myosin Heavy Chain Alterations in Response to Altered Six1 Gene Expression
Authors: Collins Brittany C , Gordon Bradley S , Kostek Matthew C
Published: June 2021

Muscle activation patterns (e.g. exercise) affect muscle fiber‐type proportions in skeletal muscle. The developmental gene, Six1's, expression is altered by exercise, and altering its expression affects fiber‐type proportions in mice, though how is unclear.

PURPOSE

Examine the effect of Six1 expression on the myosin heavy chain (MyHC) genes during muscle fiber formation.

METHODS

C2C12 mouse myoblasts were grown in standard conditions. When cells reached 80% confluence, they were transfected with Six1 over‐expression vectors or empty vector control. 24 hours later, cells were switched to differentiation medium. After four days, cells were harvested. Six1, MyHC, and Myogenin gene expression was analyzed by qRT‐PCR.

RESULTS

When compared to empty vector control, Six1 expression increased 700 ± 243.4 fold (p = 0.02), MyHC‐IIb expression decreased 2 ± 0.12 fold (p = 0.01), MyHC‐IIx decreased 1.5 ± 0.09 fold (p = 0.05), MyHC‐I increased 2 ± 0.24 fold (p = 0.03), and MyHC‐IIa expression did not change. Six1 over‐expression caused a Myogenin increase 2.7 ± 0.34 fold (p = 0.02). A second Six1 expression vector confirmed these results.

CONCLUSION

Six1 over‐expression differentially affects the muscle fiber‐type gene program during the formation of a muscle fiber. Together with our previous in‐vivo data, this suggests that Six1 expression affects the fiber‐type shift induced by muscle activation patterns.
Differential adaptation of glycolytic and oxidative muscles to hypoxia
Authors: De Theye Chiel Charles , Koehler S. Eleonore , Schols Annemie M.W.J. , Lamers Wouter H. , Langen Ramon J.C.
Published: June 2021

Background

COPD‐associated skeletal muscle atrophy is found in glycolytic rather than oxidative muscle fibers. We hypothesize that hypoxia is a trigger for this fiber type‐specific atrophy.

Methods

Mice were kept under normoxia or hypoxia. Oxygen levels were reduced stepwise to 8% during 48h, and maintained for 21 days. Food intake was monitored and mice were sacrificed at days 4 and 21.

Results

Reduction of oxidative (Soleus) muscle weight was due to hypoxia‐induced hypophagia. Glycolytic (EDL) muscle weight reduction involved additional hypophagia‐independent effects. Cross sectional area (CSA) of individual fibers was reduced in glycolytic but not oxidative muscle. Expression of genes involved in proteasomal and lysosomal protein degradation, ER stress and glucocorticoid receptor (GR) signaling were increased in both muscles. In glycolytic muscle, upregulation could not be explained by hypophagia alone. Capillary contacts per fiber CSA increased in both muscles. In oxidative muscle, this was due to a reduction of the interstitial space, whereas in glycolytic muscle fiber CSA decreased.

Conclusions

Muscle mass, muscle fiber CSA, proteolysis, ER‐stress and GR signaling are more affected by hypoxia in glycolytic than oxidative muscle. In oxidative, but not glycolytic muscle, these alterations are accounted for by hypophagia.

Supported by the Dutch Top Institute Pharma (project # T1‐201).
Attenuated Muscle Regrowth with Age is Not Associated with Differences in Anabolic and Catabolic Pathways
Authors: Dupont-Versteegden Esther E , Ferry Amy L , Hoch Johanna M , White Jena L
Published: June 2021

The ability to recover muscle size after disuse is attenuated at old age. We hypothesized that anabolic and catabolic pathways were altered with aging thereby inhibiting the regrowth response. Male Fisher344/Brown Norway rats at 6 (young) and 32 (old) months of age were divided into 3 groups: ambulatory controls, hindlimb suspended (HS) for 2 weeks and HS followed by two weeks reloading (RE). Soleus muscle weight and muscle fiber cross sectional area decreased with HS and recovered to control in young, but not old rats. mRNA abundance of protein degradation marker MAFbx and autophagy markers Atg5 and Atg7 increased with HS and were restored to control with RE in soleus muscle of young and old rats. Similarly, phosphorylated GSK3β was decreased with atrophy induced by HS and returned to control upon reloading in both ages. In contrast, no changes in phsophorylated p70s6kinase were observed at either age. We conclude that changes in anabolic and catabolic pathways associated with alterations in muscle size are similar in soleus muscles of young and old rats, suggesting that factors external to muscle may play a role in the attenuated muscle regrowth response in the aged. Funding NIH AG28925
Effects of twice‐daily ingestion of essential amino acids on amino acid transporter transcript and protein expression in older adults prior to total knee arthroplasty
Authors: Hocker Austin Dean , Bailey Ashley N. , Senesac Hilary A. , Ratchford Stephen M. , Jewett Brian A. , Lantz Brick A. , Shah Steven N. , Dreyer Hans C.
Published: June 2021

Following total knee arthroplasty (TKA) surgery, persistent muscle atrophy and weakness are the greatest clinical barriers to functional recovery. Essential amino acid (EAA) ingestion has been shown to be a potent stimulator of muscle anabolism and to acutely stimulate amino acid transporter mRNA and protein levels in muscle. We examined the effect of twice‐daily EAA supplementation on amino acid transporter gene expression and total protein levels. In this placebo controlled study muscle biopsies were obtained after an overnight fast, under anesthesia immediately prior to TKA surgery following seven days of twice‐daily ingestion of 20g EAA (n=9) or placebo (n=7). Biopsies were analyzed for transcript and protein expression of amino acid transporters using quantitative PCR and Western blotting and compared to placebo. Preliminary results indicate significantly higher mRNA levels for SNAT2 (p<0.01), SNAT4 (p<0.05), and LAT3 (p<0.01) and suggest trends toward increased mRNA for LAT1 (p<0.10) and PAT2 (p<0.10) and decreased mRNA for CAT2 (p<0.10). Total protein levels for CD98 and LAT1 were unchanged between groups. Total protein levels for CD98 and LAT1 were unchanged between groups. These preliminary data suggest EAA supplementation may up‐regulate amino acid transporters at the transcriptional level and regulation of these transporters may involve independent pathways. Support: NICHD K01HD057332
Sympathetic overactivation explains the exaggerated exercise pressor response in chronic kidney disease
Authors: Park Jeanie , Quyyumi Arshed A. , Middlekauff Holly R.
Published: June 2021

Our previous work has shown that chronic kidney disease (CKD) patients have an exaggerated exercise blood pressure (BP) response. We hypothesized that the exaggerated BP response is mediated by overactivation of the sympathetic nervous system (SNS). We measured BP and muscle sympathetic nerve activity (MSNA) in 5 hypertensive CKD patients and 10 hypertensive controls during rhythmic handgrip (RHG 20%), and static handgrip (SHG 30%) followed by forearm posthandgrip circulatory arrest (PHGCA), during D5W infusion, and repeated in CKD patients during nitroprusside (NTP) infusion to equalize exercise‐induced BP responses. CKD patients had exaggerated increases in systolic BP during RHG 20%, SHG 30%, and PHGCA. During D5W infusion, there was no difference in MSNA responses during exercise between the groups. However, ameliorating the exaggerated BP response with NTP, and thereby eliminating baroreflex‐mediated suppression of SNS, revealed that CKD patients had significantly augmented increases in MSNA during RHG 20% and SHG 30%, but not during PHGCA. These findings suggest that the SNS overactivation is due to increased mechanoreceptor or central command activation, but not increased metaboreceptor activation. In conclusion, CKD patients have an exaggerated exercise pressor response mediated by SNS overactivation that may be due to heightened mechanoreceptor sensitivity. Supported by K grant HL098744.
Spinal Cord GABA Receptors Inhibit the Exercise Pressor Reflex in Decerebrate Rats
Authors: Wang Han-Jun , Patel Kaushik P. , Zucker Irving H. , Wang Wei
Published: June 2021

Neurotransmitters and neuromodulators released by contraction‐activated skeletal muscle afferents into the dorsal horn of the spinal cord initiate the central component of the exercise pressor reflex (EPR). Evidence suggests that transmission at this synapse is mainly mediated by excitatory amino acids (i.e., glutamate). However, whether GABA, a major inhibitory neurotransmitter within the mammalian central nervous system, is involved in the modulation of the EPR at the level of the dorsal horn remains to be determined. To test this hypothesis, we performed local microinjection of either the GABA(A) antagonist bicuculline or the GABA(B) antagonist CGP 52432 into the ipisilateral L4/L5 dorsal horns to determine the effect of these GABA receptor antagonists on the pressor response to either static contraction induced by stimulation of the peripheral end of L4/L5 ventral roots or passive stretch in decerebrate rats. We found that microinjection of either bicuculline (1 mM, 100 nl) or CGP 52432 (10 mM, 100 nl) into the L4/5 dorsal horns significantly increased the pressor and cardioaccelerator responses to either static contraction or passive stretch in decerebrate rats. Data are presented in the table. In addition, microinjection of these two antagonists also caused a temporary increase in the baseline blood pressure and heart rate which returned to normal level in 2–3 min. These data suggest that GABA evokes a tonic inhibition of the EPR at the level of dorsal horn in spinal cord.
Gestational stress promotes apneas in newborn rats
Authors: Kinkead Richard , Fournier Stephanie , Steele Shelby , Dolbec Cecile , Bairam Aida
Published: June 2021

Because gestational stress (GS) compromises brain development, we hypothesized that it promotes apneas in newborn rats. Dams assigned to the stress group were subjected to cage displacement and exposure to predator odour extract from the 9th to 19th day of gestation. Controls were undisturbed. Plethysmographic measurements of respiratory activity in newborn (P0 to P4) showed that the frequency of apneic events were greater in pups born to stressed dams. At P4, pulse oxymetry monitoring showed that GS augments the proportion of apneas with O2 desaturation in males but not females. During acute hypoxia (12% O2), the reflexive increase in breathing frequency augmented with age, but this response was consistently lower in GS pups. Variability of the phrenic burst interval recorded from in vitro “en bloc” medullary preparations decreased with age but was higher in GS pups than controls. At birth, medullary serotonin (5‐HT) and noradrenalin levels of GS pups were lower than controls. Bath application of 5‐HT (in vitro) and injection of 8‐OH DPAT (5‐HT1A agonist; in vivo) reduced instability and apneas of GS pups to control levels. We conclude that disruption of the endocrine milieu during foetal life interferes with respiratory control development of the offspring. Deficit in medullary 5‐HT contributes to the deleterious effects of GS on respiratory activity at birth.
Effects of postnatal development, temperature and the pons on respiratory rhythm and pattern generation in rat pups
Authors: FONG ANGELINA Y , Zimmer M Beth , Milsom William K
Published: June 2021

Episodic breathing is common in premature infants and is found in fetal rats but rarely reported in postnatal (P) in vitro preparations. We discovered that episodic breathing patterns were common (>60%) in in vitro pontomedullary‐spinal cord preparations at 27°C from rat pups on the day of birth (P0), but the occurrence of this breathing pattern declined with postnatal development. Chemical inhibition and physical removal of the pons eliminated the episodic breathing pattern at P0. Interestingly, episodic breathing patterns could be restored in older preparations (P2 – P4) by decreasing temperature (23°C), with or without the pons. In preparations held at 27°C, with a continuous rhythm, an episodic rhythm could be produced by activating GABA receptors (100μM GABA). In preparations with an episodic pattern, antagonism of opioid receptors by naloxone (1–5μm) did not affect the episodic rhythm while blockade of GABAA receptors by bicuculline (BIC, 10μM) converted the episodic rhythm to a continuous rhythm. However, in preparations held at 23°C, BIC (10μM) had the opposite effect, promoting episodicity. Together, these data suggest the mechanisms required for episodic rhythm generation are intrinsic to the medulla, and are modulated by postnatal development, temperature sensitive mechanisms (such as TRP channels) and pontine factors. Funded by NSERC (Canada).
Brain insulin modulates the cardiovascular response to central command and exercise pressor reflex stimulation in rats
Authors: Mizuno Masaki , Downey Ryan , Mitchell Jere H , Smith Scott A
Published: June 2021

Evidence demonstrates that insulin not only regulates glucose metabolism but also neural activity within the brain. Neural input from central command (CC) and the skeletal muscle exercise pressor reflex (EPR) to cardiovascular regulatory centers within the brain contribute importantly to the control of the circulation during exercise. However, whether brain insulin modulates CC and EPR activity remains undetermined. Brain insulin inhibits hypothalamic neural activity and decreases the blood pressure response to brain stem stimulation. Thus, we hypothesized that brain insulin attenuates the circulatory response to activation of CC and the EPR. To test this hypothesis, the cardiovascular responses to stimulation of the mesencephalic locomotor region (CC activation) and contraction of hindlimb skeletal muscle (EPR activation) were measured in decerebrate Sprague‐Dawley rats before and 60 min after intracerebroventricular injection of insulin (0.25 U/kg). Insulin administration reduced the mean arterial pressure and heart rate responses to stimulation of the mesencephalic locomotor region (change from baseline: 71 ± 20 vs. 25 ± 19 mmHg; 8 ± 3 vs. 3 ± 1 bpm, respectively) as well as skeletal muscle contraction (change from baseline: 56 ± 13 vs. 25 ± 9 mmHg; 17 ± 5 vs. 6 ± 4 bpm, respectively). The results suggest that both CC and EPR activity can be attenuated by insulin within the brain. Supported by NIH HL‐088422
Fos expression in the FoxP2 and Lmx1b neurons of the parabrachial nucleus following cardiovascular changes
Authors: Miller Rebecca , Knuepfer Mark , Loewy Arthur
Published: June 2021

The parabrachial nucleus (PB) is a key brainstem site that receives visceral afferent inputs from the nucleus tractus solitarius, and sends efferent projections to the forebrain. Since the chemical identity of the cardiovascular‐receptive PB neurons remains largely unknown, we used a new approach to define the PB neurons on the basis of their neural lineage. Discrete subpopulations of the PB neurons in adult rats constitutively express the transcription factors Forkhead box protein2 (FoxP2), LIM homeodomain transcription factor 1 beta (Lmx1b), and in some cases, both. Fos‐activation in the PB was analyzed after sustained hypotension or hypertension in conscious rats. Hypotension and hypertension produced similar Fos‐expression patterns. Fos‐activated FoxP2 neurons were found in the dorsal lateral and external lateral PB subgroups and Fos‐activated Lmx1b neurons were concentrated in the medial and external lateral PB regions. Lmx1b activated neurons were present in the dorsomedial PB. Kölliker‐Fuse neurons express both FoxP2 and Lmx1b, and only a few were Fos‐activated after cardiovascular changes. In conclusion, five PB subdivisions (dorsal lateral, dorsal medial, external lateral, and medial, Kölliker‐Fuse) receive cardiovascular information. These data clearly implicate specific PB populations in cardiovascular regulation. Supported by NIH Grants HL‐25449, NS057105, and DA0017371.
Hemodynamic responses to electrical stimulation of the aortic depressor nerve, in conscious rats, after α2 adrenergic receptor blockade
Authors: Durand Marina Toledo , Dias Leila Oliveira , Castania Jaci Airton , Salgado Helio Cesar
Published: June 2021

We evaluated the attendant of postjunctional α2 adrenergic receptors in the hemodynamic response to electrical stimulation of the aortic depressor nerve (ADN) in conscious rats. The efficacy of MK‐467, a selective α2 adrenergic receptor antagonist, in attenuating the hypertensive and bradycardic response to clonidine, an α2 adrenergic receptor agonist, was also evaluated. The animals were anesthetized (sodium pentobarbital) for catheterization of femoral artery and vein, and placement of electrodes for ADN stimulation. Three sets of electrical stimulation (20s, 1mA, 2ms and 60 Hz) was applied before and after (10, 20 and 30 min) the administration of MK‐467 (3mg/kg iv). ADN stimulation (n=7) elicited a hypotensive response which was not affected by MK‐467 (−36±4, −41±2, −32±4 vs −37±3, −32±5, −31±5 mmHg before). Nevertheless, the bradycardic response after MK‐467 was enhanced (−123±25, −85±16, −60±14 vs −46±8, −41±7, −45±8 bpm before). MK‐467 (n=7) remarkably attenuated the hypertensive (5±4 vs 40±3 mmHg before) and the bradycardic (−10±5 vs −58±9 bpm before) response to clonidine (1.5 mg/kg iv). The results demonstrate that MK‐467 promoted a remarkable blockade of the peripheral α2 adrenergic receptor, but did not affect the hypotensive response produced by electrical ADN stimulation, precluding a role played by the deactivation of postjunctional α2 adrenergic receptors in this hypotensive response.
Selective innervation of upper and lower thoracic spinal segments by medullary raphe neurons in felines
Authors: Carlino Laura , Weber Sarah A , Gowen Michael F , Yates Bill J
Published: June 2021

The medullary raphe nuclei mediate a variety of physiological responses, including the regulation of blood pressure. We have demonstrated that vestibular stimulation results in distinct changes in blood flow in the upper and lower body, indicating that the nervous system has the capacity to elicit regionally‐specific changes in blood flow. Prior physiological studies have shown that neurons in the rostral ventrolateral medulla (RVLM) are not responsible for this response patterning. In the present study, we ascertained whether neurons in the medullary raphe nuclei have the capacity to independently regulate sympathetic outflow to different body regions. For this purpose, multiple injections of the fluorescent dye Fast Blue were made into the vicinity of the intermediolateral cell column (IML) in T4, whereas multiple injections of Fluoro‐Ruby were made near the IML in T10. Retrogradely labeled neurons were mapped in the medullary raphe nuclei. Neurons that were single‐labeled for each of the dyes and those that were double‐labeled were noted in approximately equal numbers. These findings show that although some medullary raphe neurons regulate sympathetic outflow from multiple spinal segments, others have the capacity to control activity in specific segments.
PGE2 facilitates the activation of renal sensory nerves by a positive feedback mechanism involving activation of PLC and COX‐2
Authors: Kopp Ulla C , Cicha Michael Z
Published: June 2021

PGE2 facilitates the activation of sensory nerves. In the kidney, norepinephrine (NE)‐mediated activation of α1‐adrenoceptors activates PLC and increases PGE2 synthesis. PGE2 activates adenylyl cyclase(AC)/cAMP/PKA leading to release of substance P and stimulation of renal sensory nerves. NE‐mediated activation of renal α2‐adrenoceptors suppresses the activation of renal sensory nerves by decreasing the activation of AC and PG synthesis. Activation of AC by forskolin enhanced NE‐induced PGE2 synthesis and substance P release. Because these studies suggest that PGE2 may increase PGE2 synthesis by activating AC, we studied if inhibition of PG‐synthesis would reduce the release of substance P produced by PGE2. In isolated rat renal pelvises, PGE2, 0.03 μM, increased substance P release from 4.5±0.3 to 11.5±0.6 pg/min. Indomethacin or the COX‐2 inhibitors etodolac or DFU reduced the PGE2‐induced release of substance P by 34±5% and 29±3%, the effects of etodolac and DFU being similar. The PGE2‐induced release of substance P was reduced by the PLC inhibitor U73122 by 62±13% and the PKC inhibitor calphostine by 49±7%. In indomethacin‐treated pelvises, U73122 failed to reduce the PGE2‐induced release of substance P. We conclude that PGE2 facilitates the activation of renal sensory nerves by a positive feedback mechanism involving activation of AC activating PLC leading to induction of COX‐2 and PGE2 release.
The influence of breathing on hemodynamic oscillations at presyncope
Authors: Rickards Caroline , Hinojosa-Laborde Carmen , Ryan Kathy L , Convertino Victor A
Published: June 2021

We hypothesized that oscillations in muscle sympathetic nerve activity (MSNA), arterial pressure (AP), and middle cerebral artery blood velocity (MCAv) transition from the Mayer wave frequency (~0.1 Hz) to the prevailing breathing frequency immediately prior to presyncope during progressive central hypovolemia. Ten subjects were instrumented for ECG, end‐tidal CO2 (surrogate for respiration), AP, MCAv, and MSNA, then completed a lower body negative pressure (LBNP) test to presyncope. The 6‐min immediately prior to presyncope were divided into two discrete 3‐min periods, “sub‐max” and “max”. High frequency (HF) and low frequency (LF) powers were calculated for mean AP (MAP), mean MCAv, and MSNA at each time period. The LF/HF ratio for each metric was also calculated as an index of balance between HF oscillations (predominantly influenced by respiration) and LF oscillations (predominantly influenced by sympathetic activity). Peak respiratory frequency remained in the HF range (0.15–0.4 Hz), and did not change (P=0.90) from sub‐max to max. The LF/HF ratio decreased (P≤0.08) from sub‐max to max for MAP (8.7±2.4 to 6.1±1.4), mean MCAv (4.1±0.8 to 2.2±0.4), and MSNA (0.74±0.15 to 0.51±0.09), indicative of a shift from LF oscillations to HF oscillations. In support of our hypothesis, hemodynamic oscillations transitioned from sympathetically‐mediated to respiratory‐mediated as subjects reached presyncope.
GABA‐A receptors mediating sympathoinhibition elicited by moxonidine in rats
Authors: Alves Thales Biffe , Totola Leonardo T , Takakura Ana C , Colombari Eduardo , Moreira Thiago S
Published: June 2021

The sympathoinhibition elicited by moxonidine has been attributed to activation of α2‐adrenergic/imidazoline receptors in the rostral ventrolateral medulla (RVLM) and, more recently, in the nucleus of the solitary tract (NTS). In the present study, we aimed to determine the role of the γ‐aminobutyric acid (GABA) mechanisms in the commissural NTS (cNTS) in mediating anti‐hypertensive effects of moxonidine in anesthetized normotensive rats. Mean arterial pressure (MAP) and splanchnic sympathetic nerve activity (sSNA) were recorded in urethane anaesthetized and artificially ventilated male Wistar rats (280–320 g, n = 5–7). Injections of moxonidine (2.5 and 5 nmol/50 nl) into the cNTS reduced resting MAP (105 ± 3 and 95 ± 5 mmHg, vs. pre‐injection: 117 ± 4 mmHg) and resting sSNA (92 ± 1 and 82 ± 3% of the control). The pre‐treatment with the GABA‐A antagonist bicuculline (25 pmol/50 nl) in the cNTS blocked the hypotension (Δ = −2 ± 3 mmHg, vs. moxonidine: Δ = −22 ± 4 mmHg) and sympathoinhibition (Δ = −1 ± 2%, vs. moxonidine: Δ = −18 ± 3%; p<0.05) elicited by moxonidine‐injected (5 nmol/50 nl) in the cNTS. These current data suggest that GABAergic mechanisms in the cNTS are essential for the sympathoinhibition and hypotension of moxonidine.

Financial support: FAPESP; CNPq; CAPES.
Aldosterone Acts in the Nucleus of the Solitary Tract to Alter Stress Responsiveness
Authors: cho namjik , McCowan Michael , Scheuer Deborah A
Published: June 2021

Aldosterone (aldo) acts at brain mineralocorticoid receptors (MR) to increase arterial pressure. We hypothesized that activation of MR selectively within the Nucleus Tractus Solitarius (NTS), a key circulatory control center, would enhance the cardiovascular response restraint stress. Mean arterial pressure (MAP) was measured by radiotelemetry in adult male Sprague–Dawley rats. Chronic elevations in aldo levels within the NTS were achieved by implanting pellets of 1% aldo over the NTS (n=4). Sham pellets were made of silastic (n=4). All rats were subjected to 60 min of restraint stress daily for 11 days. On day 12 they were exposed to a novel stress by placing them in 1 cm of room temp water for 15 min. Aldo did not alter baseline MAP. Aldo attenuated the integrated MAP response to restraint stress on the first day (990±50 mmHg/60 min vs 1510± 82 mmHg/60 min, aldo vs sham, P=0.002). The MAP response to the final restraint stress was not significantly affected by aldo. With water stress, the integrated MAP response was enhanced in the aldo‐ vs. the sham‐treated rats (416±14 mmHg/15 min vs. 332±32 mmHg/15 min, P=0.054). Compared with the sham rats, the aldo‐treated rats gained less weight during the period of chronic stress (2±5 gm, n=4 vs. 24±7 gm, n=3, P=0.04). We conclude that aldosterone acts in the NTS to influence stress responsiveness. Support: NIH#HL 076807, AHA#GRNT 4460047.