Cardiac and behavioural responses to hypoxia and warming in free-swimming gilthead seabream (Sparus aurata)

Gilthead seabream were equipped with intraperitoneal biologging tags to investigate cardiac responses to hypoxia and warming, comparing when fish were either swimming freely in a tank with conspecifics or confined to individual respirometers. After tag implantation under anaesthesia, heart rate (fH) required 60 hours to recover to a stable value in a holding tank. Subsequently, when undisturbed under control conditions (normoxia, 21°C), mean fH was always significantly lower in the tank than respirometers. In progressive hypoxia (100 - 15% oxygen saturation), mean fH in the tank was significantly lower than respirometers at oxygen levels until 40%, with significant bradycardia in both holding conditions below this. Simultaneous logging of tri-axial body acceleration revealed that spontaneous activity, inferred as the variance of external acceleration (VARm), was low and invariant in hypoxia. Warming (21 to 31°C) caused progressive tachycardia with no differences in fH between holding conditions. Mean VARm was, however, significantly higher in the tank during warming, with a positive relationship between VARm and fH across all temperatures. Therefore, spontaneous activity contributed to raising fH of fish in the tank during warming. Mean fH in respirometers had a highly significant linear relationship with mean rates of oxygen uptake, considering data from hypoxia and warming together. The high fH of confined seabream indicates that respirometry techniques may bias estimates of metabolic traits in some fishes, and that biologging on free-swimming fishes will provide more reliable insight into cardiac and behavioural responses to environmental stressors by fishes in their natural environment.

Cardiac and behavioural responses to hypoxia and warming in free-swimming gilthead seabream Sparus aurata

ABSTRACTCardiac and behavioural responses to hypoxia and warming were investigated in free-swimming gilthead seabream Sparus aurata equipped with biologging tags in the peritoneal cavity. After suitable recovery in a holding tank, heart rate (fH) and the variance of tri-axial body acceleration (VARm) were logged during exposure to stepwise progressive hypoxia or warming, comparing when either swimming in a tank or confined to individual respirometer chambers. When undisturbed under control conditions (normoxia, 21 °C), mean fH was significantly lower in tank than respirometers. In progressive hypoxia (100 - 15% oxygen saturation), mean fH in the tank was significantly lower than respirometers at oxygen levels until 40%, with significant bradycardia in both holding conditions below this. Mean VARm was low and invariant in hypoxia. Warming (21 to 31 °C) caused progressive tachycardia with no differences in fH between holding conditions. Mean VARm was, however, significantly higher in the tank during warming, with a positive relationship between VARm and fH across all temperatures. Therefore, spontaneous activity contributed to raising fH of fish in the tank during warming. Mean fH in respirometers had a highly significant linear relationship with mean rates of oxygen uptake, considering data from hypoxia and warming together. The high fH of confined S. aurata indicates that static respirometry techniques may bias estimates of metabolic traits in some fish species. Biologging on free-swimming fish revealed novel information about cardiac responses to environmental stressors, which may be closer to responses exhibited by fish in their natural environment.SUMMARY STATEMENTImplantable biologgers were used to provide the first measurements of cardiac responses to hypoxia and warming in a free-swimming fish, revealing that confinement in respirometer chambers raises heart rate, with consequences for estimates of metabolic rates.

P O 2 of the metathoracic ganglion in response to progressive hypoxia in an insect

Mammals regulate their brain tissue P O 2 tightly, and only small changes in brain P O 2 are required to elicit compensatory ventilation. However, unlike the flow-through cardiovascular system of vertebrates, insect tissues exchange gases through blind-ended tracheoles, which may involve a more prominent role for diffusive gas exchange. We tested the effect of progressive hypoxia on ventilation and the P O 2 of the metathoracic ganglion (neural site of control of ventilation) using microelectrodes in the American locust, Schistocerca americana . In normal air (21 kPa), P O 2 of the metathoracic ganglion was 12 kPa. The P O 2 of the ganglion dropped as air P O 2 dropped, with ventilatory responses occurring when ganglion P O 2 reached 3 kPa. Unlike vertebrates, insects tolerate relatively high resting tissue P O 2 levels and allow tissue P O 2 to drop during hypoxia, activity and discontinuous gas exchange before activating convective or spiracular gas exchange. Tracheated animals, and possibly pancrustaceans in general, seem likely to generally experience wide spatial and temporal variation in tissue P O 2 compared with vertebrates, with important implications for physiological function and the evolution of oxygen-using proteins.

Acute life-threatening respiratory distress syndrome in an infant due to a bronchogenic cyst

An 8-week-old infant was admitted to the hospital after an initially normal postpartum course with pronounced shortness of breath. Progressive hypoxia and a loss of consciousness occurred during the computer tomography examination, whereby the massively increased airway resistance hardly allowed ventilation. During a emergency thoracotomy, a bronchogenic cyst which had compressed the left main bronchus, was successfully extirpated.

THE EFFECT OF PRO-INFLAMMATORY CYTOKINE IL-1β ON THE CENTRAL AND PERIPHERAL RESPIRATORY CONTROL MECHANISMS ON THE BACKGROUND OF SEVERE HYPOXIA

Pro-inflammatory cytokine IL-1β, as inflammatory mediators participate in neuroimmune interactions in the central nervous system. It’s assumed that IL-1β affect the central and peripheral breathing control in acute hypoxia that occurs simultaneously with systemic inflammation. The purpose of this study was to evaluate the influence IL-1β on respiratory responses following progressive hypoxia and ability to survive after hypoxic apnea. We studied the influence of IL-1β (10 μg/kg) on respiration and the ability to survive acute hypoxic challenge in anesthetized Wistar rats. The response of tidal volume, breathing rate, minute lung ventilation, oxygen saturation, during acute hypoxia was examined using pneumotachography methods. Increasing hypoxia was created by rebreathing method. The results indicated that during progressive acute hypoxia animals given IL-1β were unable to sustain breathing efforts for as long as control rats. Following hypoxic apnea IL-1β decrease the ability to autoresuscitate compared with control groups. Thus IL-1β reduces the tolerance of animals to acute hypoxia and the ability to spontaneously autoresuscitate after apnea. We assume that that IL-1β inhibit inspiratory neurons and decrease the sensitivity of the carotid chemoreceptors to hypoxic stimulation.