Респираторные реакции при стимуляции и блокаде ГАМКА-рецепторов ретротрапециевидного ядра у крыс

The retrotrapezoid nucleus (RTN), located in the parafacial region, contains glutamatergic neurons that express the transcriptor factor Phox2b and that are suggested to be central respiratory chemoreceptors. Studies in anaesthetized animals or in vitro have suggested that RTN neurons are important in the control of breathing by influencing respiratory rate, inspiratory amplitude and active expiration. However, the contribution of these neurons to cardiorespiratory control in conscious rats is not clear. Male Holtzman rats (280-300 g, n = 6-8) with bilateral stainless-steel cannulae implanted into the RTN were used. In conscious rats, the microinjection of the ionotropic glutamatergic agonist NMDA (5 pmol in 50 nl) into the RTN increased respiratory frequency (by 42%), tidal volume (by 21%), ventilation (by 68%), peak expiratory flow (by 24%) and mean arterial pressure (MAP, increased by 16 ± 4, versus saline, 3 ± 2 mmHg). Bilateral inhibition of the RTN neurons with the GABA(A) agonist muscimol (100 pmol in 50 nl) reduced resting ventilation (52 ± 34, versus saline, 250 ± 56 ml min(-1) kg(-1) with absolute values) and attenuated the respiratory response to hypercapnia and hypoxia. Muscimol injected into the RTN slightly reduced resting MAP (decreased by 13 ± 7, versus saline, increased by 3 ± 2 mmHg), without changing the effects of hypercapnia or hypoxia on MAP and heart rate. The results suggest that RTN neurons activate facilitatory mechanisms important to the control of ventilation in resting, hypoxic or hypercapnic conditions in conscious rats.

The research of neurochemical mechanisms of respiratory regulation is very relevant, which is due to the need for further development of ideas about the role of various parts of the central respiratory neural network in the generation of breathing rhythm and pattern. In this aspect, the retrotrapezoid nucleus (RTN) is of interest, which is the main chemosensory structure of the medulla and provides the central chemoreflex under conditions of hypercapnia and hypoxia. Various neurotransmitters, including adenosine triphosphate (ATP), participate in the modulation of respiration at the RTN level. It is known that ATP provides purinergic signaling in the RTN during hypercapnia and hypoxia. However, under normoxia, the role of ATP in the regulation of respiration by RTN structures not been sufficiently studied. The aim of our research was to analyze the participation of ATP, as an agonist of purinergic receptors, in the mechanisms of respiratory control at the level of the RTN in rats breathing normal atmospheric air. The reasearch performed on adult rats weighing 180-220 g, anesthetized with urethane, in which the respiratory effects of microinjections of an ATP solution into the RTN were studied. Microinjections were carry out through a glass microcannula (tip diameter 30-50 μm), introduced into the brain according to stereotaxic coordinates. Control animals were injected with artificial cerebrospinal fluid into the RTN. In rats, the external respiration pattern was recorded using a spirograph connected to a tracheostomy tube, and simultaneously bioelectrical activity of the diaphragm was recorded on an electromyograph by bipolar needle electrodes Changes in frequency and volume parameters of spirogram and electromyogram (EMG) were analyzed. It has been established that microinjections of ATP into the RTN increase the respiratory activity of rats breathing atmospheric air of normal composition, as evidenced by changes in external respiration and EMG of the diaphragm. Analysis of spirogram revealed an increase in the respiratory rate (due to a decrease in the duration of inspiration and expiration), an increase in tidal volume, volumetric rate of inspiratory flow and minute lung ventilation compared to the initial level and control. Microinjections of ATP into the RTN also had a stimulating effect on the bioelectrical activity of the diaphragmatic muscle. The EMG showed an increase in the frequency of inspiratory burst discharges in combination with a decrease in the duration of both, the themselves bursts and interbursts intervals, relative to the initial values. These effects were accompanied by an increase in the amplitude of oscillations in inspiratory discharges. The observed reactions of the diaphragm statistically significantly exceeded the changes in control rats. The obtained results fit into the framework of the concept that activation of purine receptors in the medulla oblongata stimulates motor inspiratory output from the respiratory center. Taking into account the literature data, the increase in lung ventilation and bioelectrical activity of the diaphragm in response to ATP microinjections into the RTN may be explained by the activation of P2Y-type purinergic receptors. Thus, data obtained confirming the participation of the purinergic system at the level of the RTN in the respiration control in rats breathing atmospheric air of normal composition. Based on the analysis of our own and literary data, the assessment of the molecular mechanisms of action of ATP, as the most important component of the purinome, allows us to conclude that P2Y receptors play an important role in the implementation of the respiratory effects of ATP in the RTN area. The interaction of ATP with receptors of this type in the RTN region causes stimulation of external respiration and inspiratory burst activity of the diaphragmatic muscle, which indicates the contribution of purinergic signaling to the formation of inspiratory drive from the central respiratory neural network to respiratory motor neurons. It is noteworthy that the increase in respiration caused by the effect of ATP on the RTN is observed not only under conditions of altered gas homeostasis, as indicated by many publications, but also under normoxia, which is confirmed by our data. This fact allows us to consider the purinergic mechanisms of the RTN not only in the context of maintaining the body’s vital functions under hypoxic and hypercapnic conditions, but also in the aspect of regulating respiration under conditions of optimal gas balance.

Mechanical ventilation with low tidal volumes appears to provide benefit in patients having noncardiac surgery; however, whether it is beneficial in patients having cardiac surgery is unclear. We retrospectively examined patients having elective cardiac surgery requiring cardiopulmonary bypass through a median sternotomy approach who received mechanical ventilation with a single lumen endotracheal tube from January 2010 to mid-August 2016. Time-weighted average tidal volume (milliliter per kilogram predicted body weight [PBW]) during the duration of surgery excluding cardiopulmonary bypass was analyzed. The association between tidal volumes and postoperative oxygenation (measured by arterial partial pressure of oxygen (PaO2)/fraction of inspired oxygen ratio [PaO2/FIO2]), impaired oxygenation (PaO2/FIO2 <300), and clinical outcomes were examined. Of 9359 cardiac surgical patients, larger tidal volumes were associated with slightly worse postoperative oxygenation. Postoperative PaO2/FIO2 decreased an estimated 1.05% per 1 mL/kg PBW increase in tidal volume (97.5% confidence interval [CI], -1.74 to -0.37; PBon = .0005). An increase in intraoperative tidal volumes was also associated with increased odds of impaired oxygenation (odds ratio [OR; 97.5% CI]: 1.08 [1.02-1.14] per 1 mL/kg PBW increase in tidal volume; PBon = .0029), slightly longer intubation time (5% per 1 mL/kg increase in tidal volume (hazard ratio [98.33% CI], 0.95 [0.93-0.98] per 1 mL/kg PBW; PBon < .0001), and increased mortality (OR [98.33% CI], 1.34 [1.06-1.70] per 1 mL/kg PBW increase in tidal volume; PHolm = .0144). An increase in intraoperative tidal volumes was also associated with acute postoperative respiratory failure (OR [98.33% CI], 1.16 [1.03-1.32] per 1 mL/kg PBW increase in tidal volume; PHolm = .0146), but not other pulmonary complications. Lower time-weighted average intraoperative tidal volumes were associated with a very modest improvement in postoperative oxygenation in patients having cardiac surgery.

We measured oxygen consumption (VO2), carbon dioxide production (VCO2), minute volume (VE), respiratory frequency (f) and tidal volume (VT) of chickens during 15 min treadmill exercise at 0.5 ms-1 and 0.8 ms-1 at thermoneutral (23 degrees C), low (9 degrees C) and high (34 degrees C) ambient temperature (Ta); the vertebral canal was cooled to 34 degrees C during the middle 5 min of each exercise period. Temperatures of the vertebral canal (TVC) and rectum (Tre) were also measured. Exercise at 0.5 ms-1 caused increases in O2 consumption, CO2 production, minute volume and tidal volume compared to resting controls at each Ta. Minute volume and respiratory frequency were higher and tidal volume was lower in birds exercising at 34 degrees C than at 23 or 9 degrees C. Spinal cord cooling during exercise (0.5 ms-1) at 9 degrees C caused further increases in O2 consumption, tidal volume and respiratory frequency almost equivalent to those produced by an increase in the running speed to 0.8 ms-1. Spinal cord cooling during exercise (0.5 ms-1) at 23 degrees C did not significantly affect O2 consumption, CO2 production, minute volume, tidal volume or respiratory frequency. Spinal cord cooling during exercise (0.5 ms-1) at 34 degrees C did not affect O2 consumption or CO2 production, but caused decreases in minute volume and respiratory frequency and an increase in tidal volume. We conclude that the domestic fowl exhibits spinal thermosensitivity during exercise, although these responses appear to be smaller than those previously reported for the resting bird. Decreased external temperature potentiates the effects of spinal cord cooling during exercise.

Serial measurements have been made of the resting tidal and minute volumes and respiratory rates on 40 premature infants during the first 2 weeks after birth. The 40 infants were divided into three groups according to the trend of their respiratory rates. Infants whose respiratory rates were normal from birth (Group I) had the highest mean resting tidal volumes during the first 2 weeks. Mean resting tidal volumes were significantly lower throughout the first week among infants whose respiratory rates were initially high during the first hour and subsequently declined to normal (Group II) and among infants whose respiratory rates significantly increased after the first hour (Group III). Infants in Group III had the lowest tidal volumes and the most severe degrees of respiratory insufficiency. The mean resting tidal volume among infants in Group III was less at the end of the first week than that of infants in Group I at the end of the first day. Although tidal volumes in infants in Group II were in general much lower than normal the first few days after birth, exceptions to this rule may occasionally be encountered. Although all three groups showed an increase in mean tidal volumes of about 25% at the end of 24 hours over the volumes obtained during the first 3 hours after birth, the respiratory rates were different. In Group I the increase in tidal volume was accompanied by no significant change in respiratory rate; in Group II, by a significant decrease in respiratory rate; in Group III, by a significant increase in respiratory arte. During the second day Group III showed clinical improvement accompanied by a significant decrease in mean respiratory rate but not by any significant increase in mean tidal volume. Fluctuations in mean minute volumes in Groups II and III on the first 2 days were largely dependent on changes in respiratory rates.

Bicuculline dialysis in the retrotrapezoid nucleus (RTN) region stimulates breathing in the awake rat.

to the editor: Amniote vertebrates adjust the acid-base status of the blood through ventilatory alterations of PaCO2 and, to some degree, by renal modulation of bicarbonate concentration. Receptor systems for the ventilatory acid-base regulation has been studied mainly in mammals, in which the

In anesthetized animals, focal acidification of a portion of the rostral ventrolateral medulla (RVLM), the retrotrapezoid nucleus (RTN), increases respiratory output3, 6. We define the RTN region to include the RTN proper, described by retrograde tracing experiments as lying ventral to the facial nucleus19and adjacent neurons of the parapyramidal region and the juxta-facial portion of the nucleus paragigantocellularis lateralis. Focal disruption of the RTN region by cooling2 or by neurotoxin injection10,12,13 substantially reduces baseline respiratory output and the response to systemic hypercapnia. The RTN region can provide a tonic drive to breathe and is a site of central chemoreception.KeywordsRostral Ventrolateral MedullaDialysis ProbeCentral ChemoreceptorDartmouth Medical SchoolVentral Respiratory GroupThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The retrotrapezoid nucleus (RTN) drives breathing proportionally to brain PCO2 but its role during various states of vigilance needs clarification. Under normoxia, RTN lesions increased the arterial PCO2 set-point, lowered the PO2 set-point and reduced alveolar ventilation relative to CO2 production. Tidal volume was reduced and breathing frequency increased to a comparable degree during wake, slow-wave sleep and REM sleep. RTN lesions did not produce apnoeas or disordered breathing during sleep. RTN lesions in rats virtually eliminated the central respiratory chemoreflex (CRC) while preserving the cardiorespiratory responses to hypoxia; the relationship between CRC and number of surviving RTN Nmb neurons was an inverse exponential. The CRC does not function without the RTN. In the quasi-complete absence of the RTN and CRC, alveolar ventilation is reduced despite an increased drive to breathe from the carotid bodies. The retrotrapezoid nucleus (RTN) is one of several CNS nuclei that contribute, in various capacities (e.g. CO2 detection, neuronal modulation) to the central respiratory chemoreflex (CRC). Here we test how important the RTN is to PCO2 homeostasis and breathing during sleep or wake. RTN Nmb-positive neurons were killed with targeted microinjections of substance P-saporin conjugate in adult rats. Under normoxia, rats with large RTN lesions (92±4% cell loss) had normal blood pressure and arterial pH but were hypoxic (-8mmHg PaO2 ) and hypercapnic (+10mmHg ). In resting conditions, minute volume (VE ) was normal but breathing frequency (fR ) was elevated and tidal volume (VT ) reduced. Resting O2 consumption and CO2 production were normal. The hypercapnic ventilatory reflex in 65% FiO2 had an inverse exponential relationship with the number of surviving RTN neurons and was decreased by up to 92%. The hypoxic ventilatory reflex (HVR; FiO2 21-10%) persisted after RTN lesions, hypoxia-induced sighing was normal and hypoxia-induced hypotension was reduced. In rats with RTN lesions, breathing was lowest during slow-wave sleep, especially under hyperoxia, but apnoeas and sleep-disordered breathing were not observed. In conclusion, near complete RTN destruction in rats virtually eliminates the CRC but the HVR persists and sighing and the state dependence of breathing are unchanged. Under normoxia, RTN lesions cause no change in VE but alveolar ventilation is reduced by at least 21%, probably because of increased physiological dead volume. RTN lesions do not cause sleep apnoea during slow-wave sleep, even under hyperoxia.

Effect of arousal on hypercapnic ventilatory response needs to be examined

The response of breathing patterns to increased expiratory resistance is not only of physiologic interest, with respect to the control of breathing, but also of clinical interest because of its clinical relevance to obstructive diseases such as asthma and emphysema. To elucidate the response of breathing patterns to increased expiratory resistance during anesthesia, the respiratory effects of expiratory flow-resistive loading on breathing patterns were studied in 15 conscious and 10 lightly anesthetized subjects. Inspiratory time, expiratory time, respiratory frequency, inspiratory duty cycle, tidal volume, minute ventilation, and mean inspiratory flow rate were determined from a respiratory inductive plethysmograph. End-tidal CO2 was continuously recorded. In awake subjects, respiratory frequency was reduced without change in tidal volume or mean inspiratory flow rate, and minute ventilation was significantly decreased; the synchrony between rib cage and abdomen wall motion was well maintained during the loads. In contrast, in anesthetized subjects, respiratory frequency was reduced with remarkable increases in tidal volume, mean inspiratory flow rate, and minute ventilation, whereas coordination between rib cage and abdomen compartments was disturbed. End-tidal CO2 did not change in conscious subjects, but it increased in anesthetized subjects during the loads. These results indicate that there are differences between conscious and anesthetized subjects in breathing patterns during expiratory loading, and suggest that the ability to coordinate rib cage-abdomen wall motion is easily disturbed during anesthesia in patients with expiratory flow limitation.

The authors evaluated respiratory response to cholecystokinin tetrapeptide (CCK-4) in healthy volunteers. Subjects were randomly assigned to either a CCK-4 (N = 15) or placebo (N = 15) challenge under double-blind conditions. Dyspnea was reported by all of the subjects who received CCK-4 but only one subject who received placebo. CCK-4 caused a significant increase in tidal volume and minute ventilation but had no effect on breathing frequency. Placebo had no effect on any of the respiratory measures. These data indicate that the behavioral effects of CCK-4 are accompanied by changes in respiration in healthy volunteers.

Minute volume, tidal volume, and respiratory frequency were measured during hyperpnea induced by exercise, increased body temperature, and CO2 inhalation. Ventilatory characteristics were compared before and after the vagus nerve had been blocked. In normal birds exercise produced increases in both tidal volume and respiratory frequency; hyperthermia produced a typical thermal polypnea consisting of greatly increased respiratory frequency and reduced tidal volume; CO2 inhalation produced increases in tidal volume and respiratory frequency when the birds were euthermic but a slowing of respiratory rate when the birds were hyperthermic. After vagal block these pronounced differences in the pattern of ventilatory response to the various respiratory stimuli were abolished. Instead there was a uniform ventilatory response to all three stimuli consisting mainly of increases in tidal volume combined with small increases in respiratory frequency. It is concluded that in the normal animal control of the varied pattern of ventilatory response to different respiratory stimuli is dependent on vagal fiber activity.

Effects of deep breathing exercises and ambulation on pattern of Ventilation in post-operative patients

Hypoxic ventilatory response after dopamine D2 receptor blockade in unilateral rat model of Parkinson’s disease