Respiratory Adjustments Research Articles

Modulation by Astrocytes of AMPA Currents in the NTS Neurons of Mice Is Reduced by Short Term-Sustained Hypoxia

Hypoxia due to reduction in the partial pressure of oxygen in the arterial blood (PaO2) activates the afferents of peripheral chemoreflex to produce cardiovascular and respiratory adjustments to bring PaO2 back to the normal range. Herein we evaluated the possible changes of astrocytic modulation on glutamatergic transmission in NTS neurons of mice submitted to short term-sustained hypoxia (SH). To reach this goal, we used Male C57Bl/6J mice (18-20g), which were submitted to SH (FiO2 0.1) or normoxia for 24 hours. Brainstem slices and whole-cell patch clamp technique were used to evaluate the synaptic transmission in NTS neurons. The intracellular calcium concentration in NTS astrocytes was evaluated by multiphoton microscopy and transgenic Aldh-CRE-GCAMP6f mice (Institutional Ethical Committee Approvals: #016/2018 and #1109/2022R1). SH increased the amplitude of TS-evoked AMPA currents [control: -72.8 ± 13.3 pA ( n = 12) vs SH: -120 ± 14.4 pA ( n = 21)] in NTS neurons with no changes on the rise- or decay-time. SH also increased the amplitude [control: 35.88 ± 7.9 pA ( n = 12) vs SH: 72.74 ± 15.47 pA ( n = 10)] and decay time [control: 61.8 ± 15.2 ms ( n = 9) vs SH: 286 ± 86.7 ms ( n = 10)] of TS evoked-NMDA currents in neurons, while the amplitude of extrasynaptic NMDA currents [control: 28.7 ± 7.4 pA ( n = 10) vs SH: 24.7 ± 3.2 pA ( n = 7)] was not affected. Perfusion with fluoracetate (FAC), a glial metabolism inhibitor, decreased the amplitude of TS-evoked AMPA currents in control group [aCSF: -54.29 ± 16.1 pA vs aCSF + FAC: -24.43 ± 6.82 pA ( n =9)] without affecting AMPA currents in SH neurons [aCSF: -124.5 ± 35.27 pA vs aCSF + FAC: -130.5 ± 50.16 pA ( n =8)]. The passive properties of astrocytes did not change after SH [RMP: -83.73 ± 11.85 mV ( n =10) vs −83.63 ± 11.86 mV ( n =10); Rinput: 123 ± 127.5 MΩ ( n =9) vs 208 ± 212.7 MΩ ( n =10)]. The increase in intracellular calcium concentration induced by AMPA in the astrocytes of control and SH mice was similar [Control: 112.8 ± 15.41 ΔF/F0 (n=68 ROIs) vs SH: 56.38 ± 18.31 ΔF/F0 (n=13 ROIs)]. The data shows that SH increased the evoked glutamatergic currents in NTS neurons of mice, probably due to a reduction in the astrocytic modulation of excitatory transmission by mechanisms apparently independent of astrocytic intracellular calcium. FAPESP (2018/15957-2, 2018/02336-0 and 2022/05237-8), CNPq (309338/2020-4) and CAPES-PROEX (23038.006922/2021-31). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Comparative transcriptome analysis of respiration-related genes in nodules of phosphate-deficient soybean (Glycine max cv. Williams 82)

A transcriptome analysis was used to compare the nodule transcriptomes of the model soybean ‘Williams 82’ inoculated with two Bradyrhizobium diazoefficiens strains (USDA110 vs. CB1809) under phosphate (Pi) deficiency. The entire dataset revealed a core set of low-Pi-responsive genes and recognized enormous differential transcriptional changes between the Pi-deprived USDA110-nodules and CB1809-nodules. The lower symbiotic efficiency of the Pi-starved USDA110 nodules was ascribed to the downregulation of an F1-ATPase gene engaged in oxidative phosphorylation, more likely contributing to diminished ATP production. To cope with energy shortage caused by Pi stress, the Pi-deprived USDA110-nodules preferentially upregulated the expression of a large number of genes encoding enzymes implicated in specialized energy-demanding pathways, such as the mitochondrial respiratory chain (i.e., cytochrome c oxidase), alcoholic fermentation (i.e., pyruvate decarboxylase and alcohol dehydrogenase) and glycolysis (e.g., hexokinase, phosphofructokinase, glyceraldehyde‐3‐phosphate dehydrogenase and pyruvate kinase). These respiratory adjustments were likely associated with higher metabolic cost and redox imbalance, thereby, negatively affecting nodule symbiosis under Pi deprivation. In contrast, the Pi-starved CB1809-nodules reduced the metabolic cost by regulating a lower number of genes and increasing the expression of genes encoding proteins implicated in non-phosphorylating bypasses (e.g., flavoprotein alpha and flavoprotein:ubiqionone oxidoreductase), which could promote the carbohydrate utilization efficiency and energy metabolism. Notably, the upregulation of a transcript encoding a malate dehydrogenase could boost the CB1809-nodules under Pi stress. The dynamic shifts in energy metabolism in the Pi-deprived USDA110-nodules and CB1809-nodules could be transformative to upgrade the mechanistic/conceptual understandings of soybean adaptation to Pi deficiency at the transcriptional level.

Monitoring laryngeal and respiratory adjustments during voice production using a simulation-based voice production inversion neural network

Previously we reported a simulation-based neural network for estimating vocal fold properties and subglottal pressure from the produced voice. In this study, we evaluate the feasibility of using this neural network to monitor laryngeal and respiratory adjustments during speech production in individual speakers. Acoustic and aerodynamic data were collected in human subjects while producing utterances of five repetitions of the syllable /pa/ at different loudness levels. Voice features were then extracted and used as input to the neural network to estimate changes in vocal physiology and subglottal pressure. The results showed all subjects increased the subglottal pressure and vocal fold adduction when producing a louder voice, although the degrees of laryngeal and respiratory adjustments were speaker-specific. The neural network also estimated on average shorter and thinner vocal folds in female subjects than male subjects. These results demonstrate the potential of this neural network toward monitoring and identifying potentially unhealthy vocal behaviors.

Respiratory Responses to Two Voice Interventions for Parkinson's Disease.

The purpose of this study was to examine the respiratory strategies used by persons with Parkinson's disease (PD) to support louder speech in response to two voice interventions. Contrasting interventions were selected to investigate the role of internal and external cue strategies on treatment outcomes. LSVT LOUD, which uses an internal cueing framework, and the SpeechVive prosthesis, which employs an external noise cue to elicit louder speech, were studied. Thirty-four persons with hypophonia secondary to idiopathic PD were assigned to one of three groups: LSVT LOUD (n = 12), SpeechVive (n = 12), or a nontreatment clinical control (n = 10). The LSVT LOUD and SpeechVive participants received 8 weeks of voice intervention. Acoustic and respiratory kinematic data were simultaneously collected at pre-, mid- and posttreatment during a monologue speech sample. Intervention outcomes included sound pressure level (SPL), utterance length, lung volume initiation, lung volume termination, and lung volume excursion. As compared to controls, the LSVT LOUD and SpeechVive participants significantly increased SPL at mid- and posttreatment, thus confirming a positive intervention effect. Treatment-related changes in speech breathing were further identified, including significantly longer utterance lengths (syllables per breath group) at mid- and posttreatment, as compared to pretreatment. The respiratory strategies used to support louder speech varied by group. The LSVT LOUD participants terminated lung volume at significantly lower levels at mid- and posttreatment, as compared to pretreatment. This finding suggests the use of greater expiratory muscle effort by the LSVT LOUD participants to support louder speech. Participants in the SpeechVive group did not significantly alter their respiratory strategies across the intervention period. Single-subject effect sizes highlight the variability in respiratory strategies used across speakers to support louder speech. This study provides emerging evidence to suggest that the LSVT LOUD and SpeechVive therapies elicit different respiratory adjustments in persons with PD. The study highlights the need to consider respiratory function when addressing voice targets in persons with PD.

Settleable atmospheric particulate matter affects cardiorespiratory responses to hypoxia in Nile tilapia (Oreochromis niloticus)

Atmospheric particulate matter (APM) emitted by iron ore processing industries has a complex composition, including diverse metallic particles and nanoparticles. Settleable APM (SePM) causes air to water cross-contamination and has recently been demonstrated to have harmful sublethal impacts on fish, eliciting stress responses, affecting the immune system, and reducing blood oxygen-carrying capacity. These findings imply potential consequences for fish aerobic performance and energy allocation, particularly in their ability to tolerate respiratory challenges such as aquatic hypoxia. To assess that potential limitation, we analyzed metabolic, cardiorespiratory, and morphological alterations after exposing tilapia, Oreochromis niloticus, to an environmentally relevant concentration of SePM (96 h) and progressive hypoxia. The contamination initiated detectable gill damage, reducing respiratory efficiency, increasing ventilatory effort, and compromising fish capacity to deal with hypoxia. Even in normoxia, the resting respiratory frequency was elevated and limited respiratory adjustments during hypoxia. SePM increased O2crit from 26 to 34% of O2 (1.84 to 2.76 mg O2·L−1). Such ventilatory inefficacy implies higher ventilatory cost with relevant alterations in energy allocation. Progression in gill damage might be problematic and cause: infection, blood loss, ion imbalance, and limited cardiorespiratory performance. The contamination did not cause immediate lethality but may threaten fish populations due to limitations in physiological performance. This was the first investigation to evaluate the physiological responses of fish to hypoxia after SePM contamination. We suggest that the present level of environmental SePM deserves attention. The present results demonstrate the need for comprehensive studies on SePM effects in aquatic fauna.

Influence of High Hemoglobin-Oxygen Affinity on Humans During Hypoxia.

Humans elicit a robust series of physiological responses to maintain adequate oxygen delivery during hypoxia, including a transient reduction in hemoglobin-oxygen (Hb-O2) affinity. However, high Hb-O2 affinity has been identified as a beneficial adaptation in several species that have been exposed to high altitude for generations. The observed differences in Hb-O2 affinity between humans and species adapted to high altitude pose a central question: is higher or lower Hb-O2 affinity in humans more advantageous when O2 availability is limited? Humans with genetic mutations in hemoglobin structure resulting in high Hb-O2 affinity have shown attenuated cardiorespiratory adjustments during hypoxia both at rest and during exercise, providing unique insight into this central question. Therefore, the purpose of this review is to examine the influence of high Hb-O2 affinity during hypoxia through comparison of cardiovascular and respiratory adjustments elicited by humans with high Hb-O2 affinity compared to those with normal Hb-O2 affinity.

5-HT neurons of the medullary raphe contribute to respiratory control in toads

Air-breathing vertebrates undergo respiratory adjustments when faced with disturbances in the gas composition of the environment. In mammals, the medullary raphe nuclei are involved in the neuronal pathway that mediates the ventilatory responses to hypoxia and hypercarbia. We investigate whether the serotoninergic neurons of the medullary raphe nuclei of toads (Rhinella diptycha) play a functional role in respiratory control during resting conditions (room air), hypercarbia (5% CO2), and hypoxia (5% O2). The raphe nuclei were located and identified based on the location of the serotoninergic neurons in the brainstem. We then lesioned the medullary raphe (raphe pallidus, obscurus and magnus) with anti-SERT-SAP and measured ventilation in both control and lesioned groups and we observed that serotonin (5-HT) specific chemical lesions of the medullary raphe caused reduced respiratory responses to both hypercarbia and hypoxia. In summary, we report that the serotoninergic neurons of the medullary raphe of the cururu toad Rhinella diptycha participate in the chemoreflex responses during hypercarbia and hypoxia, but not during resting conditions. This current evidence in anurans, together with the available data in mammals, brings insights to the evolution of brain sites, such as the medullary raphe, involved in the ventilatory chemoreflex in vertebrates.

Breaking Silos: The Team-Based Approach to Coronavirus Disease 2019 Pandemic Staffing.

Breaking Silos: The Team-Based Approach to Coronavirus Disease 2019 Pandemic Staffing.

Acclimation capability inferred by metabolic performance in two sea cucumber species from different latitudes.

The notion that thermal specialists from tropical regions live closer to their temperature limits than temperate eurytherms, seems too generalized. Species specific differences in physiological and biochemical stress reactions are linked to key components of organism fitness, like metabolic capacity, which indicates that acclimation potential across latitudes might be highly diverse rather than simplistic. In this study the exposure of a tropical (Holothuria scabra) and a temperate (Holothuria forskali) sea cucumber species to identical cold- and warm-acclimation stress was compared using the key metabolic parameters, respiration rate, enzyme activity (ETS, LDH, IDH), and energy reserve fractions (lipid, carbohydrate and protein). Results show much broader respiratory adjustments, as response to temperature change, in H. scabra (2-30 μgO2*gww-1*h-1) compared to H. forskali (1.5-6.6 μgO2*gww-1*h-1). Moreover, the tropical species showed clearly pronounced up and down regulation of metabolic enzymes and shifts in energy reserves, due to thermal acclimation, while the same metabolic indicators remained consistent in the temperate species. In summary, these findings indicate enhanced metabolic plasticity in H. scabra at the cost of elevated energy expenditures, which seems to favor the tropical stenotherm in terms of thermal acclimation capacity. The comparison of such holistic metabolic analyses between conspecifics and congeners, may help to predict the heterogeneous effects of global temperature changes across latitudinal gradients.

Enhancement of excitatory transmission in NTS neurons projecting to ventral medulla of rats exposed to sustained hypoxia is blunted by minocycline.

Rats subjected to sustained hypoxia (SH) present increases in arterial pressure (AP) and in glutamatergic transmission in the nucleus tractus solitarius (NTS) neurons sending projections to ventrolateral medulla (VLM). Treatment with minocycline, a microglial inhibitor, attenuated the increase in AP in response to SH. The increase in the amplitude of glutamatergic postsynaptic currents in the NTS-VLM neurons, induced by postsynaptic mechanisms, was blunted by minocycline treatment. The number of microglial cells was increased in the NTS of vehicle-treated SH rats but not in the NTS of minocycline-treated rats. The data show that microglial recruitment/proliferation induced by SH is associated with the enhancement of excitatory neurotransmission in NTS-VLM neurons, which may contribute to the observed increase in AP. Short-term sustained hypoxia (SH) produces significant autonomic and respiratory adjustments and triggers activation of microglia, the resident immune cells in the brain. SH also enhances glutamatergic neurotransmission in the NTS. Here we evaluated the role of microglial activation induced by SH on the cardiovascular changes and mainly on glutamatergic neurotransmission in NTS neurons sending projections to the ventrolateral medulla (NTS-VLM), using a microglia inhibitor (minocycline). Direct measurement of arterial pressure (AP) in freely moving rats showed that SH (24h, fraction of inspired oxygen ( ) 0.1) in vehicle and minocycline (30mg/kg i.p. for 3days)-treated groups produced a significant increase in AP in relation to control groups under normoxic conditions, but this increase was significantly lower in minocycline-treated rats. Whole-cell patch-clamp recordings revealed that the active properties of the membrane were comparable among the groups. Nevertheless, the amplitudes of glutamatergic postsynaptic currents, evoked by tractus solitarius stimulation, were increased in NTS-VLM neurons of SH rats. Changes in asynchronous glutamatergic currents indicated that the observed increase in amplitude was due to postsynaptic mechanisms. These changes were blunted in the SH group previously treated with minocycline. Using immunofluorescence, we found that the number of microglial cells was increased in the NTS of vehicle-treated SH rats but not in the NTS neurons of minocycline-treated rats. Our data support the concept that microglial activation induced by SH is associated with the enhancement of excitatory neurotransmission in NTS-VLM neurons, which may contribute to the increase in AP observed in this experimental model.

Tasks and means of therapeutic exercises in patients with breast cancer in pre- and postoperative periods

The mainstay of radical treatment for patients with breast cancer (BC) is a surgical intervention: radical mastectomy (RME) of different modifications or organ-sparing operations. In the preoperative period, the tasks of therapeutic exercises (TEs) are psychological preparation of a patient for active participation in his / her treatment, as well as complete breath training. Classes are done in a group of convalescents, by applying dynamic and static breathing exercises. In the early postoperative period, the tasks of TEs are to prevent hypostatic pneumonia, surgical-site shoulder joint stiffness and to improve systemic and regional blood and lymph circulation. Analysis of 1235 patients who had undergone RME and 212 patients who had radical resection showed that restricted shoulder joint motion due to hand immobilization in an adducted position and late initiation of TEs occurred in 44.6 and 33.5 % of the patients, respectively. Individual TEs classes include breathing exercises, position treatment, and special exercises to restore shoulder joint function and to control posture. Lymphadenectomy and failure to ligate intersected lymphatic vessels lead to inevitable lymphorrhea and seroma. Analysis of 1447 patents indicated that early initiation of TEs failed to affect seroma duration and extent and wound dehiscence. In the latter (that, according to the author»s data, occurs in 3.7 % of cases after RME and in 9.2 % after preoperative radiotherapy), TEs are limited by position treatment until the wound heals or secondary sutures are applied. The tasks of the late postoperative period are recovery of the full range of shoulder joint motion, normal posture, cardiovascular and respiratory adjustments to increased physical exercises, and general tonic exposure. The paper gives TEs sets developed for each period.

PO-0733 Minimal Invasive Surfactant Therapy: Cui Bono?

Background Minimal invasive surfactant therapy (MIST) is associated with a diminished need for mechanical ventilation. Insufficient insight exists in predictive success factors. Aim Defining success factors for MIST. Methods From 2011–2013 preterm infants admitted to the NICU with respiratory distress and radiographically established IRDS with FiO2 Results 40 neonates (GA 24 +2 –37 +1 weeks [30 weeks], birth weight 600–3330 gram [1375 gram], IRDS grade I-III) were eligible. In 38 patients MIST was performed (2/40 were nonetheless intubated due to unrest). Tube insertion caused bradycardia with spontaneous recovery in one patient. Surfactant administration caused desaturation with spontaneous recovery in all patients and apnea in one patient. There were no complications. Therapeutic success was reached in 24/38 (63,2%) patients. In 6/24 (25%) respiratory adjustments were necessary; increasing PEEP in 2/24, starting nIPPV in 4/24. Causes for intubation 14/38 (27,8%) were rebound IRDS (6/14), sepsis (5/14) and insufficient drive to breath 2/14. Gestational age, birth weight, FiO2/IRDS degree, timing of MIST and gastric tube route (nasal/oral) were not correlated with success. Conclusion Success factors for MIST are a calm patient, an adequate drive to breathe and the absence of sepsis.

Different respiratory behaviors disclosed by induced bronchoconstriction in mild asthma patients

Respiratory responses to bronchoconstriction in asthma have been partially assessed and their significance is unclear. In 44 mild asthma patients we investigated respiratory responses during increasing levels of methacholine-induced bronchoconstriction. Inspiratory muscle activity, tidal volume, inspiratory and expiratory times were continuously monitored; breathing discomfort was rated. Mean inspiratory flow, respiratory frequency and ventilation were calculated. Lung function was assessed prior to and at maximum bronchoconstriction. Bronchoconstriction “dose-dependently” increased inspiratory muscle activity and breathing discomfort (P<0.01). In 37 patients (84.1%), the increase in inspiratory muscle activity was associated with increases in mean inspiratory flow and ventilation (P<0.01) because of selective rises in breathing depth (volume responders), or rate (frequency responders) or both (dual responders). In seven patients (15.9%) ventilation was unchanged. Individual respiratory responses were reproducible. With bronchoconstriction, frequency responders displayed greater hyperinflation and stronger breathing discomfort than volume responders (P<0.01). Analysis of the responses to induced bronchoconstriction disclosed distinctive and reproducible respiratory adjustments that may identify functionally different asthma subpopulations.

Acid-base status of ammonia-poisoned steers

Although several studies on ammonia poisoning have been carried out, there is a lack of information on acid-base balance status in ammonia-poisoned cattle. Twelve crossbred steers received intraruminally 0.5 g of urea per kg of body weight in order to induce a clinical picture of ammonia poisoning. Blood samples were collected throughout the trials in order to determine the blood ammonia, lactate, and perform blood gas analysis. All cattle presented aclassical clinical picture of ammonia poisoning, with a blood ammonia concentration rising progressively from the beginning until reaching higher values at 180 min (27 ± 3 to 1719 ± 101 µmol L-1), with a similar pattern occurring with blood L-lactate levels (1.7 ± 0.3 to 26.0 ± 1.7 mmol L-1). The higher the blood ammonia concentration the higher the blood L-lactate levels (r = 0.86). All animals developed metabolic acidosis, as blood pH lowered to 7.24 ± 0.03. The steers tried to compensate the metabolic acidosis mainly through the use of blood buffers and respiratory adjustments by lowering the pCO2 levels in the blood to 32.8 ± 2.0 mm Hg.

HIGHLIGHTS FROM THE LITERATURE

HIGHLIGHTS FROM THE LITERATURE

Confrontation with blood and disgust stimuli precipitates respiratory dysregulation in blood–injection–injury phobia

Blood–injection–injury (BII) phobia patients sometimes faint during exposure to relevant stimuli. However, mechanisms and timing of physiological adjustments in BII phobia remain poorly understood. In a larger sample of 60 patients and 20 controls, we sought to replicate findings of a prior study demonstrating the role of hyperventilation in the phobic response. We also investigated the timing of respiratory adjustment across an extended exposure recovery period. In addition, because intense disgust is commonly reported by patients, responses to surgery films were compared to a pure disgust film. End-tidal PCO 2 dropped significantly while volume and flow increased during the surgery film in patients compared to controls and to other emotional films except disgust. Patients recovered quickly following the disgust film but not the surgery film. PCO 2, volume, and flow parameters showed robust associations with anxiety, disgust, and physical symptoms. Findings suggest that respiratory adjustments during and after phobic exposure may provide a critical missing link in the understanding of the psychophysiology of this singular disorder, including why fainting often occurs after the stimulus is removed.

Catecholamines and the Effects of Exercise, Training and Gender

Stress hormones, adrenaline (epinephrine) and noradrenaline (norepinephrine), are responsible for many adaptations both at rest and during exercise. Since their discovery, thousands of studies have focused on these two catecholamines and their importance in many adaptive processes to different stressors such as exercise, hypoglycaemia, hypoxia and heat exposure, and these studies are now well acknowledged. In fact, since adrenaline and noradrenaline are the main hormones whose concentrations increase markedly during exercise, many researchers have worked on the effect of exercise on these amines and reported 1.5 to >20 times basal concentrations depending on exercise characteristics (e.g. duration and intensity). Similarly, several studies have shown that adrenaline and noradrenaline are involved in cardiovascular and respiratory adjustments and in substrate mobilization and utilization. Thus, many studies have focused on physical training and gender effects on catecholamine response to exercise in an effort to verify if significant differences in catecholamine responses to exercise could be partly responsible for the different performances observed between trained and untrained subjects and/or men and women. In fact, previous studies conducted in men have used different types of exercise to compare trained and untrained subjects in response to exercise at the same absolute or relative intensity. Their results were conflicting for a while. As research progressed, parameters such as age, nutritional and emotional state have been found to influence catecholamine concentrations. As a result, most of the recent studies have taken into account all these parameters. Those studies also used very well trained subjects and/or more intense exercise, which is known to have a greater effect on catecholamine response so that differences between trained and untrained subjects are more likely to appear. Most findings then reported a higher adrenaline response to exercise in endurance-trained compared with untrained subjects in response to intense exercise at the same relative intensity as all-out exercise. This phenomenon is referred to as the 'sports adrenal medulla'. This higher capacity to secrete adrenaline was observed both in response to physical exercise and to other stimuli such as hypoglycaemia and hypoxia. For some authors, this phenomenon can partly explain the higher physical performance observed in trained compared with untrained subjects. More recently, these findings have also been reported in anaerobic-trained subjects in response to supramaximal exercise. In women, studies remain scarce; the results are more conflicting than in men and the physical training type (aerobic or anaerobic) effects on catecholamine response remain to be specified. Conversely, the works undertaken in animals are more unanimous and suggest that physical training can increase the capacity to secrete adrenaline via an increase of the adrenal gland volume and adrenaline content.

Respiratory and cardiovascular responses evoked by tibialis anterior muscle afferent fibers in rats

The muscle metaboreflex is thought to be one of the neural mechanisms involved in the cardiovascular and respiratory adjustments to muscular activity. The afferent arm of the reflex is composed of thinly myelinated group III and unmyelinated group IV sensitive fibers. Such reflex arc had been extensively described in cats, dogs, rabbits and humans. However, results obtained in rats are controversial and the role of the afferent fibers from the tibialis anterior skeletal muscle has never been shown. The purpose of the present experiments was to study the responses of both respiratory and cardiovascular systems following activation of the metabosensitive fibers originating from tibialis anterior muscle in non decerebrated and non vagotomized barbituric anesthetized adult rats. Mean arterial blood pressure, mean arterial blood flow, heart rate and phrenic nerve activity (frequency and amplitude) were monitored during electrically induced fatigue or after intramuscular injection of potassium chloride or lactic acid (specific stimuli of the group III and IV afferent fibers). The experiments were performed under normal condition, then after regional circulatory occlusion, which isolated and maintained the neural drive and abolished humoral communication and after section of the peroneal nerve innervating the tibialis anterior muscle. We showed that cardiorespiratory parameters were increased significantly in response to stimuli under normal conditions and after venous outflow occlusion excluding any participation of central chemoception. No change was observed after nerve section. Our data indicate that changes occurring in rat hindlimb muscle such as the tibialis anterior are sufficient to regulate the cardiorespiratory function via metabosensitive fiber activation.

Ventilatory roll off during sustained hypercapnia is gender specific in pekin ducks

The objective of the present study was to examine the relative roles of peripheral versus central mechanisms in producing ventilatory adjustments in pekin ducks during prolonged (5 h) hypercapnia (5% inspired CO2), and to determine whether these adjustments differed between male and female ducks. After 20 min of CO2 exposure, intact ducks increased total ventilation (VE) 2.5-3-fold above control values, due to large increases (approximately 200%) in tidal volume (VT) and slightly smaller increases (approximately 140%) in breathing frequency (fR). This response was accompanied by respiratory acidosis (pHa fell from approximately 7.46 to approximately 7.41) and hypercapnia (PaCO2 increased from approximately 35 to approximately 40 Torr). In males, VE fell progressively thereafter due exclusively to a fall in fR, in parallel with a rapid partial recovery of pH (to 7.44) while PaCO2 continued to climb (to approximately 42 Torr). In females, VE remained elevated during hypercapnia, and no pH recovery occurred. This suggests that a respiratory decline resulting from acid-base compensation (probably due to HCO3- mobilization) occurred in males but not in females. Bicarbonate mobilization, and thus pH compensation, may have been reduced in females due to the CaCO3 requirements of eggshell formation. In males, the acute ventilatory response was reduced slightly by denervation of the carotid bodies or intrapulmonary chemoreceptors, but there was no effect of denervation of either receptor group on the responses to prolonged CO2. We conclude that pH compensation triggered by constant or increasing PaCO2, acting at central chemoreceptors, likely mediates the respiratory adjustments seen in male pekin ducks during hypercapnia. Furthermore, we suggest that this ventilatory response be considered a gender-specific hypercapnic ventilatory roll off, in the context of the various time domains of the hypercapnic ventilatory response.

Cerebellar fastigial nuclei activity during blood pressure challenges

The cerebellar fastigial nuclei (FN) assist in regulating compensatory responses to large blood pressure changes and show structural injury and functional impairment to cardiovascular challenges in syndromes with sleep-disordered breathing. The patterned time course of FN responses to elevation or lowering of blood pressure and location of responsive regions within the nuclei are unclear. We evaluated FN neural activity in six anesthetized rats using optical imaging procedures during elevation and lowering of arterial pressure by phenylephrine and nitroprusside, respectively. Hypertension diminished optical correlates of FN neural activity, while measures of activity increased to hypotension, with peak neural responses occurring 5-10 s later than peak blood pressure changes. Blood pressure responses were followed by heart rate changes, and peak respiratory rates developed even later, in close temporal proximity to FN activity patterns. Although overall topographical response trends were similar, regional patterns of altered neural activity appeared to both hypertension and hypotension. The extent of neural change was greater during recovery from hypertension than for hypotension at high-dose levels. Blood pressure levels saturated with increasing phenylephrine doses, while FN activity continued to decline. No saturation appeared in heart or respiratory rate trends. The findings suggest that the FN compensate for large blood pressure changes by sympathoexcitatory and inhibitory processes, which accompany late-developing somatic or respiratory adjustments.