Ventilatory and behavioural responses of the marbled sole Pseudopleuronectes yokohamae to progressive hypoxia

This study identified ventilatory and behavioural responses in the marbled sole Pseudopleuronectes yokohamae under experimentally induced progressive decreases in dissolved oxygen (DO) levels. Ventilation frequency showed an increase with decreasing DO levels from normoxia to 2·75 mg O₂ l^?1, followed by a decrease in ventilation frequency at decreased DO levels from 2·00 to 0·75 mg O₂ l^?1. At DO levels below 2·00 mg l^?1, behaviours at the bottom were suppressed, whereas avoidance behaviours increased. A decrease in avoidance behaviours was observed from 1·00 to 0·75 mg O₂ l^?1. Upside‐down reversal and incapacitation at DO levels of 1·00–0·75 mg O₂ l^?1 suggested that sublethal effects on P. yokohamae were induced. The responses observed before the sublethal DO level could be interpreted as an effort to maintain oxygen uptake, reduce routine activities and facilitate avoidance. The observed DO level thresholds that induce behavioural responses, in addition to sublethal effects, indicate hypoxia‐tolerance that is important for understanding the effects of hypoxia on coastal ecosystems.     

Flow increases tolerance of heat and hypoxia of an aquatic insect

Recent experiments support the idea that upper thermal limits of aquatic insects arise, at least in part, from a lack of sufficient oxygen: rising temperatures typically stimulate metabolic demand for oxygen more than they increase rates of oxygen supply from the environment. Consequently, factors influencing oxygen supply, like water flow, should also affect thermal and hypoxia tolerance. We tested this hypothesis by measuring the effects of experimentally manipulated flows on the heat and hypoxia tolerance of aquatic nymphs of the giant salmonfly (Plecoptera: Pteronarcys californica), a common stonefly in western North America. As predicted, stoneflies in flowing water (10 cm s⁻¹) tolerated water that was approximately 4°C warmer and that contained approximately 15% less oxygen than did those in standing water. Our results imply that the impacts of climate change on streamflow, such as changes in patterns of precipitation and decreased snowpack, will magnify the threats to aquatic insects from warmer water temperatures and lower oxygen levels.     

Control of ventilatory movements in the aquatic insect Corydalus comutus: central effect of hypoxia

ABSTRACT. The influence of hypoxia and hypercapnia on the ventilatory rhythm of the hellgrammite Corydalus cornutus L. (Megaloptera) was studied. In intact animals the frequency of rhythmic retractions and protractions of abdominal gills is increased by hypoxia (10% O₂, 90% N₂) but no ventilatory response is elicited by hypercapnia (1–5% CO₂, 20% O₂, 75–79% N₂).
The ventilatory motor pattern was examined by recording extracellularly from the gill retractor muscle or its efferent nerve. In response to hypoxia (8% 0₂, 92% N₂), there are decreases in the cycle-time, the interspike interval, and the burst length of the gill retractor motorneuron. In addition, previously quiescent motorneurons associated with gill protraction are recruited.
Individual ganglia or small groups of abdominal ganglia can be isolated both from the central ganglionic chain and from the periphery by selective cutting of roots and connectives. When exposed to hypoxia, preparations that include the first abdominal ganglion show characteristic changes in the ventilatory motor pattern similar to those in intact animals. Thus sensitivity to oxygen appears to be located centrally and not peripherally. In small animals (head width < 7 mm), abdominal ganglia 2–3 and 2–7 respond characteristically to hypoxia, but in larger animals (head width > 9 mm), chains of ganglia lacking abdominal ganglion 1 fail to respond. In larger animals oxygen sensitivity may thus be concentrated in abdominal ganglion 1, whereas in smaller animals the ability to initiate a ventilatory response to hypoxia is distributed among the abdominal ganglia.     

The behavioural and physiological response of Atlantic cod Gadus morhua L. to short-term acute hypoxia

The average rate of swimming speed and the physiological status or stress of individual Atlantic cod Gadus morhua was monitored in response to short-term acute (STA) hypoxia ( i.e. partial pressure of oxygen,     , reduced from 20·9 to 4·3 kPa within 1 h at 10° C). The STA hypoxic response of Atlantic cod was associated with a large primary increase (+29%) and a large secondary decrease (−54%) in swimming speed as well as major physiological stress ( e.g. plasma cortisol = 214·7 ng ml⁻¹ and blood lactate = 2·41 mmol l⁻¹).     

Respiratory responses of Oreochromis niloticus (Pisces, Cichlidae) to environmental hypoxia under different thermal conditions

The oxygen uptake ( V O₂), breathing frequency ( f _R), breath volume ( V _S.R), gill ventilation ( V G) and oxygen extraction (%) from the ventilatory current of four groups of Oreochromis niloticus during graded hypoxia were measured under the following acclimation temperatures: 20. 25. 30 and 35°C. The critical oxygen tensions ( P O₂), determined from V O₂ v. P O₂ of inspired water at each experimental temperature were, respectively. 19±1±3±1. 18±0±4±9, 29±7± 4±1 and 30±2± 0.6 mmHg. The f _R remained nearly constant during the reductions of O₂ at all the temperatures studied. V G increased discretely from normoxic levels until the P O₂ was reached, below which it assumed extremely high values (17-fold higher or more). The increases observed in V G resulted, at all the acclimation temperatures, in an elevation in V _S.R rather than in f _R. The extraction of O₂ decreased gradually from normoxia until the P O₂ was reached, below which an abrupt reduction of extraction was recorded, except at 35°C when fish showed a gradual reduction in extraction just below the tension of 80 mmHg.     

Swimming alters responses to hypoxia in the Adriatic sturgeon Acipenser naccarii

When the Adriatic sturgeon Acipenser naccarii was exposed to progressive hypoxia under static conditions, it exhibited a linear decline in O₂ uptake, behaving as an 'oxyconformer'. When, however, it was allowed to swim at a low sustained speed, it could regulate O₂ uptake down to a mean ± s . e . critical ( P _crit) of 4·9 ± 0·5 kPa ( n = 6). At moderate levels of hypoxia, static fish exhibited significant reductions in arterial blood O₂ content, and increases in plasma lactate, which were not observed in swimming animals.     

低压低氧大鼠摄氧量测定装置

目的：设计并制作一种用于测定模拟不同海拔低压低氧环境中大鼠摄氧量的装置。方法：该装置容积约为0．01m3。它包括动物舱、参照舱、高度表、高度升降速率表、动物舱与参照舱间气压差感应和氧气自动补偿装置、低范围气压计、钠石灰和氯化钙、小风扇、温度湿度表、循环水温度控制装置、真空泵。利用该装置检测大鼠在平原（50m）、4000m和6000m模拟海拔环境中的摄氧量。结果：大鼠在平原（50m,北京）、4000m和6000m模拟海拔环境中的摄氧量分别为（24．4±2．1）、（10．8±2．0）和（8．8±1．6）ml／（kg·min）（x±s,n=10）,随着海拔高度的升高其摄氧量逐渐降低。结论：本文制作的低压低氧动物摄氧量测定装置可用于测定不同海拔环境中大鼠的摄氧量。     

FMRFamide-like immunoreactivity in the metathoracic ganglion of the locust (Schistocerca gregaria)

Summary The distribution of FMRFamide-like immunoreactivity in the metathoracic ganglion of the locust, Schistocerca gregaria, has been investigated in serial semithin transverse sections with the use of the peroxidase-antiperoxidase (PAP) technique. The topographical distribution of approximately 120 immunopositive neurons was established. Antiserum against bovine pancreatic polypeptide (BPP) stains the same ganglionic cells as FMRFamide-antiserum, yet this staining is largely blocked after preabsorption to FMRFamide. A comparison of these results with those from other studies suggests that there may be more than one type of endogenous RFamide-like peptide.     

The occurrence of aerial respiration in Rhinelepis strigosa during progressive hypoxia

Rhinelepis strigosa did not surface for air breathing in normoxic or moderate hypoxic water. This species initiated air breathing when the P _io₂ in the water reached 22 ± 1 mmHg. Once begun, the air-breathing frequency increased with decreasing P _io₂. Aquatic oxygen consumption was 21·0 ± 1·9ml O₂ kg⁻¹h⁻¹ in normoxic water, and was almost constant during progressive hypoxia until the P _io₂ reached 23·9 mmHg, considered the critical oxygen tension (P_co₂). Gill ventilation increased until close to the P _co₂ (7·9-fold) as a consequence of a greater increase in ventilatory volume than in breathing frequency. Gill oxygen extraction was 42 ± 5% and decreased with hypoxia, but under severe hypoxia returned to values characteristic of normoxic. The critical threshold for air breathing was coincident with the P_co₂ during aquatic respiration. This suggests that the air-breathing response is evoked by the aquatic oxygen tension at which the respiratory mechanisms fail to compensate for environmental hypoxia, and the gill O₂ uptake becomes insufficient to meet O₂ requirements.     

A micro-CT approach for determination of insect respiratory volume

Variation in the morphology of the insect tracheal system can strongly affect respiratory physiology, with implications for everything from pest control to evolution of insect body size. However, the small size of most insects has made measuring the morphology of their tracheal systems difficult. Historical approaches including light microscopy and scanning and transmission electron microscopy (SEM, TEM) are technically difficult, labor intensive, and can introduce preparation artifacts. More recently, synchrotron X-ray microtomography (SR-μCT) has allowed for detailed analysis of tracheal morphology of diverse insects. However, linear accelerators required for SR-μCT are not readily available, making the approach unavailable for most labs. Recent advancements in microcomputed tomography (μCT) have made possible fine resolution of internal morphology of very small insects. However, μCT has never been used to quantify insect tracheal system dimensions. We measured respiratory volume of a grasshopper (Schistocerca americana) by analysis of high resolution μCT scans. Volume estimates from μCT closely matched volume estimates by water displacement as well as literature estimates for this species. The μCT approach may thus provide a widely available, cost-effective, and straightforward approach to characterizing the internal morphology of insect respiratory systems.     

Physiological hypoxia restrains the senescence-associated secretory phenotype via AMPK-mediated mTOR suppression

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Ventilatory mechanisms and the effect of hypoxia and temperature on the embryonic lesser spotted dogfish

Small, intermediate and large-sized embryos of the dogfish Scyliorhinus canicula utilize different ventilatory methods; small and intermediate embryos rely on body movement alone to stir either the jelly or sea water in the capsule, large embryos use conventional pharyngeal pumping to pump water through the case. The effects of environmental changes in O₂ tension (0.5–100% air saturation) and temperature (6–18°C) upon ventilatory mechanisms in the developing embryo in situ were studied using non-invasive ultrasonography. All three embryo classes increased ventilation rate with rising temperature: for small embryos, y=2.02x+3.295 ( P <0.01); for intermediate embryos, y=3.51x+0.395 ( P <0.01); and for large embryos, y=3.81x+9.39 ( P <0.01); where y=ventilatory frequency (tail beats min⁻¹ or pump cycles min⁻¹) and x=temperature (°C). Q ₁₀ (6–16°C)=5.0, 2.45, and 2.08 for small, intermediate and large embryos, respectively; corresponding Q ₁₀ (8–18°C) values were 2.09, 2.62, and 2.02. It is suggested that the extreme response of small embryos to 6°C is related to a different state of development in either chemoreceptors or muscle blocks. There was no significant change in ventilatory frequency induced by chronic (2 h) hypoxia. Dogfish embryos are oxyconformers at 8°C but oxyregulators at higher temperatures. Water flow through an eggcase occupied by a large embryo was studied also. Water enters the open eggcase of a large embryo, drawn in by the buccal/opercular pump of the respiring embryo, via holes at the posterior end of the eggcase. Expired water exits holes at the anterior end of the eggcase. The mean residence time for water in the case is 50 s at 8°C, giving a transit velocity of 1.36 mm s⁻¹.     

Tolerance, behaviour and oxygen consumption in the sand goby, Pomatoschistus minutus (Pallas), exposed to hypoxia

Behavioural and metabolic reactions of Pomatoschistus minutus (Pallas) exposed to various degrees of hypoxia were studied. At 15°C and 20‰ mortality was 50% at 15.2% oxygen saturation. Avoidance and oxygen saturation showed a linear inverse relationship. At levels lower than 60% saturation increased activity occurred; avoidance was significant at 30% saturation. Active, routine and standard MO₂ correlated linearly with weight at 6 and 15°C (salinity = 19‰). During hypoxia at 15°C routine MO₂ rose significantly at 60–50% and 40–30% saturation expressed either as MO₂ during longer periods at night or MO₂ at shorter intervals during the day. Standard MO₂ was unaffected by hypoxia at 15°C. Haemoglobin concentration was significantly increased when P. minutus was acclimatized to 35% saturation.     

慢性间断性低氧大鼠认知功能和脑胆碱能神经元的进行性变化

目的：探讨慢性间断性低氧（CIH）大鼠认知功能的进行性变化及其与脑胆碱能神经元变化的关系。方法：成年雄性SD大鼠40只,随机均分为对照组、慢性间断性低氧1,3,5周组。应用Morris水迷宫检测认知功能的变化;利用HE染色在光镜下计数前额叶皮层和海马坏死神经元数;利用免疫组化方法检测前额叶皮层和海马胆碱乙酰转移酶（ChAT）阳性表达。结果：CIH各组大鼠学习记忆能力呈进行性下降趋势;与对照组比较,CIH5w组出现明显学习记忆功能障碍（P〈0.05）。CIH各组前额叶皮层和海马变性坏死神经元数增多,且随低氧时间延长,上述改变呈慢性进行性加重趋势。CIH各组前额叶皮层和海马ChAT阳性表达逐渐下降;与对照组比较,CIH3w组和CIH5w组前额叶皮层和海马ChAT阳性表达明显减少,差异具有显著性（P〈0.05）。结论：慢性间断性低氧大鼠认知功能进行性下降与前额叶皮层和海马神经元病理性损伤、ChAT表达进行性减少有关。