American Journal of Physiology-Regulatory, Integrative and Comparative Physiology

When exposed to low temperature, homeothermic vertebrates maintain internal body temperature by activating thermogenesis and by altered metabolism, synchronized by neuroendocrine responses. Although such physiological responses also occur in poikilothermic vertebrates, the prevailing notion is that their reactions are passive. Here, we explored molecular hypothalamic and physiological responses to cold stress in the tropical poikilotherm Nile tilapia (Oreochromis niloticus). We show that cold exposed tilapia exhibit complex homeostatic responses, including increased hypothalamic oxytocin, plasma glucose and cortisol concomitant with reduced plasma lactate and metabolic rate. Pharmacological or genetic blockage of oxytocin signaling further affected metabolic rate in two cold-exposed poikilothermic models. This indicates that oxytocin, a known thermoregulator in homeotherms, actively regulates temperature-related homeostasis in poikilotherms. Overall, our findings show that the brain of poikilotherms actively responds to cold temperature by regulating metabolic physiology. Moreover, we identify oxytocin signaling as an adaptive and evolutionarily conserved metabolic regulator of temperature-related homeostasis.

Respiratory chemosensitivity is an important mechanism by which the brain senses changes in blood partial pressure of CO2 (PCO2). It is proposed that special neurons (and astrocytes) in various brainstem regions play key roles as CO2 central respiratory chemosensors in rodents. Although common marmosets (Callithrix jacchus), New-World non-human primates, show similar respiratory responses to elevated inspired CO2 as rodents, the chemosensitive regions in marmoset brain have not been defined yet. Here, we used c-fos immunostainings to identify brain-wide CO2-activated brain regions in common marmosets. In addition, we mapped the location of the retrotrapezoid nucleus (RTN) and raphe nuclei in the marmoset brainstem based on colocalization of CO2-induced c-fos immunoreactivity with Phox2b, and TPH immunostaining, respectively. Our data also indicated that, similar to rodents, marmoset RTN astrocytes express Phox2b and have complex processes that create a meshwork structure at the ventral surface of medulla. Our data highlight some cellular and structural regional similarities in brainstem of the common marmosets and rodents.

The human diving reflex (DR), an innate defensive reflex triggered during periods of apnea, concurrently activates both the sympathetic and parasympathetic branches of the autonomic nervous system to regulate physiology against challenging demands. Despite pupil dilation and constriction being antagonistically controlled by the two autonomic branches, the effect of the diving reflex on pupil diameter fluctuations is still unknown. Thus, we compared participants pupil diameter fluctuations while breathing or performing apnea either with (Wet) or without (Dry) face immersion in cold water. We found that pupil diameter fluctuations in both apneic conditions are associated with lower power in the low-frequency band (< 0.25 Hz) while in the Wet condition, a reallocation of power towards higher frequencies (> 0.25 Hz) occurs, together with an increased entropy, contrary to the remaining conditions. This indicates a shift in autonomic balance and an increased complexity of pupil fluctuations during the diving reflex. Our findings present pupil dynamics as a valuable entry point to the exploration of autonomic adjustments for this reflex.

Blood gas disturbances caused by exposure to low oxygen (hypoxia) or high carbon dioxide levels (hypercapnia) lead to a compensatory increase in pulmonary ventilation. Among the motor changes supporting these reflex respiratory responses is the recruitment of abdominal muscles (ABD) during the expiratory phase, which can enhance expiratory airflow or alter the duration of the expiratory phase. In this study, we assessed the functional impact of ABD recruitment on metabolic, motor, and ventilatory parameters in unanesthetized, freely behaving animals. Sprague-Dawley Holtzman male adult rats (n=7) were instrumented to perform simultaneous recordings of pulmonary ventilation, body temperature, diaphragmatic and ABD activities, and O2 consumption during exposure to various levels of hypoxia (12-8% O2) and hypercapnia (3-7% CO2). We observed that hypoxia or hypercapnia conditions evoked AE; however, ABD recruitment did not occur during the entire exposure period, displaying an intermittent profile. The occurrence of AE during hypoxia and hypercapnia conditions was linked to additional increases in tidal volume when compared to periods without ABD activity (P<0.05) and showed no associations with changes in diaphragmatic burst amplitude. Analyses of flow-like patterns suggested that AE during hypoxia recruited expiratory reserve volume during late expiration, while under hypercapnia, it accelerated lung emptying and increased the expiratory flow peak during post-inspiration. We also observed that AE was associated with an increase in oxygen consumption and did not improve air convection requirement, suggesting that this motor behavior may influence other aspects of respiration that potentially improve alveolar ventilation and gas exchange. Key points summaryO_LIAbdominal recruitment during the expiratory phase, known as active expiration (AE), emerges during blood gas disturbances to enhance pulmonary ventilation; however, the effect of AE on metabolic, motor, and ventilatory parameters in freely behaving animals exposed to hypoxia or hypercapnia remains uncertain. C_LIO_LIBy simultaneously recording pulmonary ventilation, diaphragmatic and abdominal activities, and O2 consumption, we found that the occurrence of AE during hypoxia or hypercapnia exposure resulted in an additional increase in tidal volume. C_LIO_LIAE was not evident during all periods of exposure to hypoxia or hypercapnia, and its expression increased O2 consumption. C_LIO_LIAnalysis of flow-like signals suggested that AE during hypoxia recruits expiratory reserve volume in late expiration, while under hypercapnia, it facilitates lung emptying and increases the peak expiratory flow post-inspiration. C_LIO_LIDespite being similar from a motor perspective, the impact of AE on lung ventilation differs between hypoxia and hypercapnia in unanesthetized rats. C_LI

Carotid bodies are the sensory organs for detecting hypoxemia (decreased arterial blood oxygen levels) and ensuing chemo reflex is a major regulator of breathing and blood pressure. Chang et al (2015) proposed that olfactory receptor 78 (Olfr78) plays a major role in hypoxic sensing by the carotid body. However, such a possibility was questioned by a subsequent study ((Torres-Torrelo et al. 2018). The discrepancy between the two reports prompted the present study to re-examine the role of Olfr78 in hypoxic sensing by the carotid body (CB). Studies were performed on age and gender matched Olfr78 knock out mice generated on BL6 and JAX backgrounds and corresponding wild type mice. Breathing was monitored by plethysmography in un-sedated and efferent phrenic nerve activity in anesthetized mice. Carotid body sensory nerve activity was determined ex vivo and [Ca2+]i responses were monitored in isolated glomus cells, the primary O2 sensing cells of the carotid body. Olfr78 null mice on both BL6 and JAX backgrounds exhibited attenuated hypoxic ventilatory response, whereas breathing responses to CO2 were unaffected. The magnitude of hyperoxia-induced depression of breathing (Dejours test), which is an indirect measure of carotid body hypoxic sensing, was markedly reduced in Olfr78 mutant mice on both background strains. Furthermore, carotid body sensory nerve and glomus cell [Ca2+]i responses to hypoxia were attenuated in BL6 and JAX Olfr78 null mice. These results suggest that Olfr78 plays an important role in hypoxic sensing by the carotid body.

The transcriptome of nutrient sensing and the regulation of gut motility by nutrients in a stomachless fish with a short digestive tract; the ballan wrasse (Labrus berggylta) were investigated. Using an in vitro model, we differentiate how signals initiated by physical stretch and nutrients modulate the gut evacuation rate and motility patterns, and transcriptomic changes. Stretch on the intestine by inert cellulose initiated fast evacuation out of the anterior intestine compared to the digestible protein and lipid. Stretch on the intestine upregulated genes associated with increased muscle activity, whereas nutrients stimulated pathways related to ribosomal activity and the increase in the expression of several neuropeptides which are directly involved in gut motility regulation. Our findings show that physical pressure in the intestine initiate contractions propelling the matter towards the exit, whereas the sensing of nutrients modulates the motility to prolong the residence of digesta in the digestive tract for optimal digestion. Summary statementPressure by food speed up peristalsis in the intestine, but the intestines ability to sense nutrients slow down peristalsis for better digestion. This is partly controlled by genetic regulation.

This research provides an in-depth exploration into the triggers and corresponding autonomic responses of piloerection, a phenomenon prevalent across various species. In non-human species, piloerection occurs in reaction to a variety of environmental changes, including social interactions and temperature shifts. However, its understanding in humans has been confined to emotional contexts. This is problematic because it reflects solely upon subjective experience rather than an objective response to the environment, and because, given our shared evolutionary paths, piloerection should function similarly in humans and other animals. We observed 1,198 piloerection episodes from eight participants while simultaneously recording multiple autonomic and body temperature indices, finding that piloerection in humans can indeed be elicited by thermal, tactile, and audio-visual stimuli. The data also revealed variations in cardiac reactivity measures: audio-visual piloerection was associated with greater sympathetic arousal, while tactile piloerection was linked to greater parasympathetic arousal. Despite prevailing notions of piloerection as a vestigial response in humans, it does respond to decreases in skin temperature and induces a rise in skin temperature during episodes. This research underscores that piloerection in humans is not solely an affective response to emotional stimuli. Rather, it is best understood as a reflexive response to environmental changes, suggesting a shared functional similarity with other species.

Nausea is a common disease symptom, yet there is no consensus regarding its physiological markers. In contrast, the process of vomiting is well documented as sequential muscular contractions of the diaphragm and abdominal muscles and esophageal shortening. Nausea, like other self-reported perceptions, is difficult to distinguish in preclinical models, but based on human experience emesis is usually preceded by nausea. Here we focused on measuring gastrointestinal and cardiorespiratory changes prior to emesis to provide additional insights into markers for nausea. Felines were instrumented to chronically record heart rate, respiration, and electromyographic (EMG) activity from the stomach and duodenum before and after intragastric delivery of saline or copper sulfate (CuSO4, from 83 to 322 mg). CuSO4 is a prototypical emetic test agent that triggers vomiting primarily by action on GI vagal afferent fibers when administered intragastrically. CuSO4 infusion elicited a significant increase in heart rate, decrease in respiratory rate, and a disruption of gastric and intestinal EMG activity several minutes prior to emesis. The change in EMG activity was most consistent in the duodenum. Administration of saline did not induce these effects. Increasing the dose of CuSO4 did not alter the physiologic changes induced by the treatment. It is postulated that the intestinal EMG activity was related to a retrograde movement of chyme from the intestine to the stomach. These findings suggest that monitoring of intestinal EMG activity, perhaps in combination with heart rate, may provide the best indicator of the onset of nausea following treatments and in disease conditions, including GI disease, associated with emesis.

The heart of ascidians, marine invertebrate chordates, exhibits a tubular structure, and heartbeats propagate from one end to the other. The direction of pulsation waves intermittently reverses in the heart of ascidians and their relatives; however, the underlying mechanisms remain unclear. We herein performed a series of experiments to characterize the pacemaker systems in isolated hearts and their fragments and applied a mathematical model to examine the conditions leading to heart reversals. The isolated heart of Ciona sufficiently performed heart reversals, and experimental bisections of isolated hearts revealed that independent pacemakers resided on each side and also that their beating frequencies periodically changed as they expressed bimodal rhythms. Only fragments including 5% or shorter terminal regions of the heart tube maintained autonomous pulsation rhythms, whereas other regions did not. Our mathematical model, based on FitzHugh-Nagumo equations applied to a one-dimensional alignment of cells, demonstrated that the difference between frequencies expressed by the two independent terminal pacemakers determined the direction of propagated waves. Changes in the statuses of the terminal pacemakers between the excitatory and oscillatory modes as well as in their endogenous oscillation frequencies were sufficient to lead to heart reversals. These results suggest that the directions of pulsation waves in the Ciona heart reverse according to the changing rhythms independently expressed by remotely coupled terminal pacemakers. Summary statementPulsation waves traveling along the heart tube of the ascidian Ciona intermittently reverse because of autonomous and periodical changes in beating frequencies at a pair of terminal pacemakers.

Female Aedes aegypti secrete urine rapidly post-bloodmeal ingestion, with diuresis beginning immediately for removal of excess salts and water. This post-prandial diuresis includes a peak, post-peak, and late phase, involving the combined actions of multiple hormones, including diuretic and anti-diuretic factors. Calcitonin-like diuretic hormone 31 (DH31) and kinin peptides stimulate diuresis through actions on their cognate receptors localized in the Malpighian renal tubules (MTs). In contrast, the anti-diuretic neurohormone, CAPA, inhibits secretion by MTs stimulated by select diuretic hormones, including DH31. While DH31 and kinin are critical in achieving post-prandial diuresis, and CAPA functions as an important anti-diuretic hormone, the kinetics of their release and haemolymph levels remain unknown. Herein, using heterologously expressed A. aegypti DH31, CAPA, and kinin receptors, we investigated the titres of these hormones in the haemolymph of female mosquitoes at different time points after blood feeding. Haemolymph extracts from female mosquitoes contained levels of diuretic peptides, specifically kinin and DH31, that increased immediately post-bloodmeal, with levels peaking at 2 and 5 min, respectively, while DH31 levels remained elevated for 15 min. Comparatively, levels of CAPA peptides in the haemolymph steadily increase 15 min post-blood feeding, with levels peaking at 30 min. Synergistic actions were observed between DH31 and a kinin-like peptides on the MTs, providing a physiological context for the rapid release of these peptides into the female haemolymph. Altogether, these results demonstrate that DH31 and kinin are released immediately post-bloodmeal and, along with CAPA peptides, have a coordinative action on the MTs to maintain haemolymph homeostasis through regulation of primary urine secretion. Summary statementThis study characterizes neuropeptidergic regulators of the Malpighian renal tubules by quantifying their circulating titres and release post-blood feeding in the female mosquito, A. aegypti.

Patients with obstructive sleep apnea (OSA) experience chronic intermittent hypoxia (CIH). OSA patients and CIH-treated rodents exhibit autonomic dysfunction, characterized by overactive sympathetic nervous system and hypertension, mediated through hyperactive carotid body (CB) chemoreflex. Activation of olfactory receptor 78 (Olfr78) by hydrogen sulfide (H2S) is implicated in CB activation and autonomic responses to CIH, but the downstream signaling pathways remain unknown. Given that odorant receptor signaling is coupled to adenylyl cyclase 3 (Adcy3), we hypothesized that Adcy3-dependent cAMP contributes to CB and autonomic responses to CIH. Our findings show that CIH increases cAMP levels in the CB, a response absent in Adcy3, Cth, and Olfr78 null mice. CBs from Cth and Olfr78 mutant mice lacked persulfidation response to CIH, indicating that Adcy3 activation by CIH requires Olfr78 activation by H2S. CIH also enhanced glomus cell Ca2+ influx, an effect absent in Cnga2 and Adcy3 mutants, suggesting that CIH-induced cAMP mediates enhanced Ca2+ responses through cyclic nucleotide-gated channels. Furthermore, Adcy3 null mice did not exhibit neither CB activation nor autonomic dysfunction by CIH. These results demonstrate that Adcy3-dependent cAMP is a downstream signaling pathway to H2S/Olfr78, mediating CIH-induced CB activation and autonomic dysfunction.

Obstructive sleep apnea (OSA) is characterized by recurrent respiratory events that trigger autonomic arousals and blood pressure (BP) surges, contributing to elevated cardiovascular risk. Photoplethysmography (PPG)-derived timing markers such as pulse arrival time (PAT) are frequently used as noninvasive surrogates of BP dynamics, yet their interpretation is confounded by the pre-ejection period and peripheral vascular effects. Here, we used detrended fluctuation analysis (DFA) to quantify short- and long-term scaling exponents of continuous blood pressure (Portapres), PPG-, and PAT-derived signals across sleep stages in healthy individuals and patients with OSA. Directly measured systolic and diastolic BP exhibited a robust short- to long-term crossover across all sleep stages, with elevated short-range exponents (1 > 1) and lower long-range exponents (2 < 1), reflecting well-organized autonomic and vascular control. In OSA, this crossover persisted but was visibly attenuated, consistent with reduced short-term adaptability of cardiovascular regulation. In contrast, PAT-based indices showed substantially weaker short-range correlations and minimal crossover structure. Systolic PAT displayed almost no separation between 1 and 2, and PPG-derived measures exhibited scaling patterns that differed fundamentally from BP. Across modalities, PAT (whether derived from BP or PPG) failed to reproduce the multiscale organization characteristic of beat-to-beat BP dynamics. Group comparisons further identified systolic BP scaling, particularly the short-range exponent 1, as the most sensitive marker of cardiovascular dysregulation in OSA, whereas PAT and PPG provided complementary but physiologically distinct information related to peripheral vascular and autonomic modulation. These findings demonstrate that PAT and PPG timing measures should not be used as surrogates for BP in fractal or scaling analyses and underscore the unique diagnostic value of BP-derived scaling behavior for assessing cardiovascular regulation during sleep.

In humans the skin is a primary thermoregulatory organ, with vasodilation leading to rapid body cooling, whereas in Rodentia the tail performs an analogous function. Many thermodetection mechanisms are likely to be involved including transient receptor potential vanilloid-type 4 (TRPV4), a widely distributed ion channel with both mechanical and thermosensitive properties. Previous studies have shown that TRPV4 can act as a vasodilator by local action in blood vessels, and in this study, we investigated whether TRPV4 activity effects mus muscularis tail vascular tone and thermoregulation. We measured tail blood flow by pressure plethysmography in lightly sedated mus muscularis (CD1 strain) at a range of ambient temperatures, with and without intraperitoneal administration of the blood brain barrier crossing TRPV4 antagonist GSK2193874. We also measured heart rate and blood pressure with and without GSK2193874. As expected for a thermoregulatory organ, we found that tail blood flow increased with temperature. However, unexpectedly we found that the TRPV4 antagonist GSK2193874 increased tail blood flow at all temperatures, and we observed changes in heart rate variability. Since TRPV4 activation stimulates the relaxation of peripheral resistance arteries (vasodilation) that would increase tail blood flow, these data suggest that increases in tail blood flow resulting from the TRPV4 antagonist may arise from a site other than the blood vessels themselves, perhaps in central cardiovascular control centres such as the hypothalamus.

Current models of colon motility are largely based on studies of distal regions where distension-induced neural peristalsis predominates, but the proximal colon significantly differs in terms of cellular organization and its rhythmic motor activity that continues without external sensory input, emphasizing the need to define the unique mechanisms utilized by the proximal colon. With the long-term goal of developing a new model for the rhythmic initiation of proximal colon motor complexes (CMCs), we used in situ calcium imaging to define activity patterns in key players for colon motility [i.e., submucosal interstitial cells of Cajal (ICC-SM) and myenteric neurons of the enteric nervous system (ENS)], while simultaneously monitoring motor output in the proximal mouse colon. We observed repeated patterns of activity in ICC-SM and ENS myenteric neurons during the intervals between CMCs that could be used to predict the timing of subsequent CMC events. Based on our findings, we propose a novel hypothesis that cyclical interactions between the ENS and ICC-SM act as an intrinsic pattern generator for the rhythmic initiation of proximal CMCs.

The Acute Respiratory Distress Syndrome (ARDS) describes a heterogenous population of patients with acute severe respiratory failure. However, contemporary advances have begun to identify distinct sub-phenotypes that exist within its broader envelope. These sub-phenotypes have varied outcomes and respond differently to several previously studied interventions. A more precise understanding of their pathobiology and an ability to prospectively identify them, may allow for the development of precision therapies in ARDS. Historically, animal models have played a key role in translational research, although few studies have so far assessed either the ability of animal models to replicate these sub-phenotypes or investigated the presence of sub-phenotypes within animal models. Here, in three ovine models of ARDS, using combinations of oleic acid and intravenous, or intratracheal lipopolysaccharide, we demonstrate the presence of sub-phenotypes which qualitatively resemble those found in clinical cohorts. Principal Components Analysis and partitional clustering reveal two clusters, differentiated by markers of shock, inflammation, and lung injury. This study provides the first preliminary evidence of ARDS phenotypes in pre-clinical models and develops a methodology for investigating this phenomenon in future studies.

Once a year, penguins undergo a catastrophic moult replacing their entire plumage during a fasting period on land or on sea-ice during which time individuals can lose 45% of their body mass. In penguins, new feather synthesis precedes the loss of old feathers leading to an accumulation of two feathers layers (double coat) before the old plumage is shed. We hypothesize that the combination of the high metabolism required for new feathers synthesis and the potentially high thermal insulation linked to the double coat could lead to a thermal challenge requiring additional peripheral circulation to thermal windows to dissipate extra-heat. To test this hypothesis, we measured the surface temperature of different body regions of captive Gentoo penguins (Pygoscelis papua) throughout the moult under constant environmental conditions. The surface temperature of the main body trunk decreased during the initial stages of the moult, therefore suggesting a higher thermal insulation. On the opposite, the periorbital region, a potential proxy of core temperature in birds, increased during these same early moulting stages. The surface temperature of bill, flipper and foot (thermal windows) tended to initially increase during the moult period, highlighting the likely need for extra heat dissipation in moulting penguins. These results raise questions regarding the thermoregulatory capacities of wild penguins during the challenging period of moulting on land in the current context of global warming.

Thermoregulation is essential for survival in homeothermic animals. Vagal sensory nerves are well known to detect visceral signals and regulate physiological functions, including feeding, metabolism and immunity. However, their role in thermoregulation remains poorly understood. Cholecystokinin (CCK), a gut hormone released postprandially, activates vagal sensory nerves via CCK-A receptors (CCK-AR). Exogenous CCK has been reported to induce thermogenesis in the intrascapular brown adipose tissue (iBAT), but the involvement of vagal sensory nerves and the central neural mechanisms that mediate this effect are not fully understood. In this study, we assessed the thermogenic effect of intraperitoneally (I.P.) administered CCK-8 and investigated the underlying autonomic reflex pathways. I.P. CCK-8 transiently and dose-dependently increased rectal temperature. This response was significantly attenuated by pharmacological blockade of CCK-AR, subdiaphragmatic vagotomy, or knockdown of CCK-AR primarily targeting in vagal sensory neurons. In addition, CCK-8 activated sympathetic nerve activity via vagal afferents. CCK-8-induced thermogenesis was blunted by iBAT sympathectomy or {beta}3-adrenergic receptor blockade. Furthermore, I.P. CCK-8 activated oxytocin neurons in the paraventricular nucleus of the hypothalamus (PVHOXT). Chemogenetic inhibition of PVHOXT neurons or intracerebroventricular administration of an oxytocin receptor (OXTR) antagonist attenuated the thermogenic response. These findings demonstrate, for the first time, the full neural circuitry underlying CCK-induced thermogenesis by delineating its afferent input (CCK-AR-expressing vagal sensory neurons), central integrative hub (PVHOXT neurons and OXTR signaling), and efferent output (iBAT sympathetic nerves). This study further suggests that CCK-AR -expressing vagal sensory neurons may contribute to thermoregulation under physiological conditions in which CCK is endogenously released. Key points summaryO_LIVagal sensory nerves, which connect the gut and the brain, play a key role in regulating meal-related physiology, however their role in thermoregulation remains incompletely understood. C_LIO_LIThis study reveals for the first time the full autonomic reflex pathways underlying thermogenic effect of the gut hormone cholecystokinin (CCK), comprising afferent input (CCK-A receptor-expressing vagal afferents), a central integrative hub (oxytocin neurons in the hypothalamic paraventricular nucleus; PVHOXT neurons), and efferent output (intrascapular brown adipose tissue via sympathetic nerves). C_LIO_LIBoth CCK-A receptors-expressing vagal afferents and sympathetic nerves innervating brown adipose tissue are required for thermogenesis induced by exogenous CCK-8. C_LIO_LIActivation of PVHOXT neurons by CCK-8 is critically involved in mediating this thermogenic effect. C_LIO_LIThis newly identified gut-brain-fat axis may contribute to part of diet-induced thermogenesis, and its impairment could be involved in the development of metabolic disorders such as obesity. C_LI

Respiration and blood pressure (BP) are regulated to maintain optimal delivery of O2 to every cell in the body. Arterial hypoxemia is sensed by the carotid body (CB), which initiates sympathetic reflex arcs to the diaphragm to increase ventilation, and to the adrenal medulla (AM) to increase catecholamine secretion and thereby increase BP. However, the underlying molecular mechanisms have not been fully delineated. Here, we report that the relative activities of hypoxia-inducible factor-1 (HIF-1) and HIF-2 determine the set point for the CB and AM, with respect to their maintenance of BP and respiration. In Hif2a+/- mice, which are heterozygous for a knockout allele at the locus encoding HIF-2, expression of HIF-1 and NADPH oxidase 2 was increased in the CB and AM, resulting in an oxidized intracellular redox state with augmented sensitivity to hypoxia, increased BP, and respiratory abnormalities, which were all normalized by treatment with a HIF-1 inhibitor or a superoxide anion scavenger. By contrast, in Hif1a+/- mice, which are heterozygous for a knockout allele at the locus encoding HIF-1, the expression of HIF-2 and superoxide dismutase 2 was increased in the CB and AM, resulting in a reduced intracellular redox state with impaired CB and ventilatory responses to chronic hypoxia, which were normalized by treatment with a HIF-2 inhibitor. None of the abnormalities that were observed in Hif1a+/- or Hif2a+/- mice were observed in Hif1a+/-; Hif2a+/- double- heterozygous mice. Our results demonstrate that redox balance in the CB and AM, which is determined by mutual antagonism between HIF- isoforms, establishes the set point for responses of the CB and AM to hypoxia, and is required for the maintenance of normal BP and respiration.

During exposure to extreme stress, the CNS of mammals and insects fails through a phenomenon known as spreading depolarization (SD). SD is characterized by an abrupt disruption of ion gradients across neural and glial membranes that spreads through the CNS, silencing neural activity. In humans, SD is associated with neuropathological conditions like migraine and stroke. In insects, it is coincident with critical thermal limits for activity and can be conveniently monitored by observing the transperineurial potential (TPP). We used the TPP to explore the temperature-dependence and plasticity of SD thresholds and SD-induced changes to the TPP in fruit flies (Drosophila melanogaster) acclimated to different temperatures. Specifically, we characterized the effects of thermal acclimation on the TPP characteristics of cold-induced SD, after which we induced SD via anoxia at different temperatures in both acclimation groups to examine the interactive effects of temperature and acclimation status. Lastly, we investigated these effects on the rate of SD propagation across the fruit fly CNS. Cold acclimation enhanced resistance to both cold- and anoxic SD and our TPP measurements revealed independent and interactive effects of temperature and acclimation on the TPP and SD propagation. This suggests thermodynamic processes and physiological mechanisms interact to modulate the threshold for activity through SD and its electrophysiological phenomenology. These findings are discussed in relation to conceptual models for SD and established mechanisms for variation in the thermal threshold for SD.

Food restriction (FR) enhances the sensitivity to cardiopulmonary reflexes and 1- adrenoreceptors in the female, despite hypotension. The effect of male FR on cardiopulmonary and systemic vascular function is not well understood. This study examines the effects of FR on cardiopulmonary, isolated mesenteric arterial function and potential underlying mechanisms. We hypothesized that FR decreased eNOS activity in mesenteric arteries. Male Sprague Dawley (SD) rats were randomly divided into three groups: (1) control (n=30), (2) 20 percent of food reduction (FR20, n=30), and (3) 40 percent of food reduction (FR40, n=30) for five weeks. Non-invasive blood pressure was measured twice a week. Pulmonary arterial pressure (PAP) was measured using isolated/perfused lungs in rats. The isolated vascular reactivity was assessed in double-wire myograph. After five weeks, food restricted rats exhibited a lower mean arterial pressure and heart rate, however, only FR40 groups exhibited statistically significant differences. The basal tone of PAP and various vasoconstrictors did not show significant differences in pulmonary circulation between each group. We observed that food restriction were enhanced the sensitivity (EC50) in response to 1-adrenoreceptors (phenylephrine, PhE)-induced vasoconstriction, but not to serotonin, U46619, and high K+ in the mesenteric arteries. FR reduced endothelium-dependent relaxation via decreased function of endothelial nitric oxide synthase (eNOS)-nitric oxide (NO) pathway in the mesenteric arteries. PhE-mediated vasoconstriction in mesenteric arteries was eliminated in the presence of eNOS inhibitor (L-NAME). In addition, incubation with NOX2/4 inhibitors (apocynin, GKT137831, VAS2870) and reactive oxygen species (ROS) scavenger inhibitor (Tiron) were eliminated the differences of PhE-mediated vasoconstriction but not to cyclooxygenase inhibitor (indomethacin) in the mesenteric artery. Augmentation of 1-adrenergic mediated contraction via inhibition of eNOS-NO pathway by increased activation of ROS through NOX2/4 in response to FR. Reduced eNOS-NO signaling might be a pathophysiological counterbalance to prevent hypovolemic shock in response to FR.