American Journal of Physiology. Regulatory, Integrative and Comparative Physiology

INTRODUCTION: Breath-holding preceded by either an overnight fast or hyperventilation have been shown to potentiate the risk of a hypoxic blackout. However, no study has explored the combined effects of fasting and hyperventilation on apneic performance and associated physiological responses. METHODS: Nine, non-divers (8 males) attended the laboratory on two separate occasions (≥48-h apart), both after a 12-h overnight fast. During each visit a hyperoxic rebreathing trial was performed followed by three repeated maximal static apneas preceded by either normal breathing (NORM) or a 30s hyperventilation (HYPER)...

The estrous cycle is known to modify food, fluid, and electrolyte intake behaviors and energy homeostasis in various species, in part through fluctuations in estrogen levels. Simultaneously, commonly commercially available rodent dietary formulations greatly vary in soy protein content, and thereby the delivery of biologically active phytoestrogens. To explore the interactions among the estrous cycle, sodium, fluid, and caloric seeking behaviors, and energy homeostasis, young adult C57BL/6J female mice were maintained on soy protein-free 2920x diet and provided water, or a choice between water and 0...

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No abstract text is available yet for this article.

Divers are at enhanced risk of suffering from acute cognitive deterioration because of the low ambient temperatures and the narcotic action of inert gases inspired at high pressures. Yet, the behavioral effects of cold and inert gas narcosis have commonly been assessed in isolation and during short-term provocations. We therefore evaluated the interactive influence of mild hypothermia and narcosis engendered by a subanesthetic dose of nitrous oxide (N2 O; a normobaric intervention analog of hyperbaric nitrogen) on cognitive function during prolonged iterative exposure...

INTRODUCTION: Cachexia is a muscle wasting syndrome commonly observed in patients with cancer, which can significantly worsen clinical outcomes. Due to a global rise in obesity, the coexistence of cachexia in obese individuals poses unique challenges, with the impact of excessive adiposity on cachexia severity and underlying pathophysiology not well-defined. Understanding the interplay between cachexia and obesity is crucial for improving diagnosis and treatment strategies for these patients; therefore, the present study examined differences in cachexia between lean and obese mice bearing Lewis-Lung Carcinoma (LLC) tumors...

Adipose biopsy techniques are relatively undefined for exercise physiology research in individuals at or near normal weight. The purpose of this study was to compare the influence of two adipose biopsy techniques on tissue quality through measurements of adipocyte cell size, as well as mRNA and protein levels of select pro- and anti-inflammatory cytokines and adipokines. Thirteen participants (9M, 4W; 28±4 y; 27±3 kg•m-2 ; VO2 max: 3.3±0.7 L•min-1 ) underwent subcutaneous adipose biopsies on either side of the umbilicus (incision: ~8 cm lateral, sampling area: ~5 cm lateral) using 1) a 6 mm Bergström biopsy needle and 2) a mini-liposuction approach with a 4 mm Mercedes biopsy needle that employed pre-biopsy tumescent delivery (~30 mL 0...

Although body fluid volume control by the kidneys may be classified as a long-term arterial pressure (AP) control system, it does not necessarily follow that the urine flow (UF) response to changes in AP is slow. We quantified the dynamic characteristics of the UF response to short-term AP changes by changing mean AP between 60 mmHg and 100 mmHg every 10 s according to a binary white noise sequence in anesthetized rats ( n = 8). In a baro-on trial (the carotid sinus baroreflex was enabled), the UF response represented the combined synergistic effects of pressure diuresis (PD) and neurally mediated antidiuresis (NMA)...

The impacts of carbohydrate (CHO) availability on time to task failure (TTF) and physiological responses to exercise at the maximal lactate steady state (MLSS) have not been studied. Ten participants (3 females, 7 males) completed this double blinded, placebo-controlled study that involved a ramp incremental test, MLSS determination, and four TTF trials at MLSS, all performed on a cycle ergometer. Using a combination of nutritional (CHO [7g/kg] and placebo [PLA; 0g/kg] drinks) and exercise interventions (no exercise [REST] and glycogen reducing exercise [EX]), the four conditions were expected to differ in pre-exercise CHO availability (RESTCHO > RESTPLA > EXCHO > EXPLA )...

The inner ear of teleost fish regulates the ionic and acid-base chemistry and secretes the protein matrix of the endolymph to facilitate otolith biomineralization, which are used to maintain vestibular and auditory functions. The otolith is biomineralized in a concentric ring pattern corresponding to seasonal growth, and this CaCO3 polycrystal has become a vital aging and life-history tool for fishery managers, ecologists, and conservation biologists. Moreover, biomineralization patterns are sensitive to environmental variability including climate change, thereby threatening the accuracy and relevance of otolith-reliant toolkits...

The hypoxia-inducible factor (HIF) is considered key in the transcriptional response to low oxygen. Yet, HIF's role in absence of oxygen (anoxia) and in preparation for reoxygenation remains unclear. Recent studies suggest that mounting a HIF response may be counterproductive for anoxia survival. We here studied the champion of anoxia survival, the crucian carp ( Carassius carassius ), and hypothesized that expression of prolyl hydroxylase domains, PHDs (the upstream regulators of HIF), are upregulated to circumvent an energy-costly activation of HIF in anoxia and to prepare for reoxygenation...

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We investigated whether reducing face skin temperature alters arterial blood pressure control and lower body negative pressure (LBNP) tolerance after exercise heat stress. Eight subjects (1 female; age, 27 ± 9 years) exercised at ~63% VO2max until core temperature had increased ~1.5°C before undergoing LBNP to pre syncope either with fanning to return face skin temperature to baseline (∆-5°C, Fan trial) or without (No Fan trial). LBNP tolerance was quantified as cumulative stress index (CSI; mmHg*min)...

Hagfishes are characterized by omo- and iono-conforming nature similar to marine invertebrates. Conventionally, hagfishes had been recognized as the most primitive living vertebrate that retains plesiomorphic features. However, some of the "ancestral" features of hagfishes, such as rudimentary eyes and the lack of vertebrae, have been proven to be deceptive. Similarly, by the principle of maximum parsimony, the unique body fluid regulatory strategy of hagfishes seems to be apomorphic, since the lamprey, another cyclostome, adopts osmo- and iono-regulatory mechanisms as in jawed vertebrates...

The hormone leptin reduces food intake through actions in the peripheral and central nervous system, including in the hindbrain nucleus of the solitary tract (NTS). The NTS receives viscerosensory information via vagal afferents, including information from the gastrointestinal tract, which is then relayed to other CNS sites critical for control of food intake. Leptin receptors (lepRs) are expressed by a subpopulation of NTS neurons, and knockdown of these receptors increases both food intake and body weight...

Down syndrome (Ds) is associated with congenital heart defects at birth, but cardiac function has not been assessed at older ages. We used the Ts65Dn mouse, a model of Ds, to quantify heart structure and function with echocardiography in 18-month male Ts65Dn and WT mice. Heart weight, nicotinamide adenine dinucleotide (NAD) signaling, and mitochondrial (citrate synthase) activity were investigated, as these pathways may be implicated in the cardiac pathology of Ds. The left ventricle was smaller in Ts65Dn vs WT, as well as the anterior wall thickness of the left ventricle during both diastole (LVAW_d; mm) and systole (LVAW_s; mm) as assessed by echocardiography...

The effect of exertional heat stroke (EHS) exposure on skeletal muscles is incompletely understood. Muscle weakness is an early symptom of EHS but is not considered a major target of multiorgan injury. Previously, in a preclinical mouse model of EHS, we observed vulnerability of limb muscles to a second EHS exposure, suggesting hidden processes contributing to declines in muscle resilience. Here, we evaluated possible molecular origins of EHS-induced declines in muscle resilience. Female C57BL/6 mice [total n =56; 28/condition, i...

This single-blind, crossover study aimed to measure and evaluate the short-term metabolic responses to continuous and intermittent hypoxic patterns in individuals with obesity. Indirect calorimetry was used to quantify changes in resting metabolic rate (RMR), carbohydrate (CHOox , %CHO) and fat oxidation (FATox , %FAT) in nine individuals with obesity pre- and post-: (i) breathing normoxic air [normoxic sham control (NS-control)]; (ii) breathing continuous hypoxia (CH); or (iii) breathing intermittent hypoxia (IH)...

Although Gaussian white noise (GWN) inputs offer a theoretical framework for identifying higher-order nonlinearity, an actual application to the data of the neural arc of the carotid sinus baroreflex did not succeed in fully predicting the well-known sigmoidal nonlinearity. In the present study, we assumed that the neural arc can be approximated by a cascade of a linear dynamic (LD) component and a nonlinear static (NS) component. We analyzed the data obtained using GWN inputs with a mean of 120 mmHg and standard deviations (SDs) of 10, 20, and 30 mmHg for 15 min each in anesthetized rats (n = 7)...

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