Hyperbaric oxygen preconditioning ameliorates blood-brain barrier damage induced by hypoxia through modulation of tight junction proteins in an in vitro model

Aim To explore the effects of hyperbaric oxygen preconditioning (HBOP) on the permeability of blood-brain barrier (BBB) and expression of tight junction proteins under hypoxic conditions in vitro. Methods A BBB in vitro model was constructed using the hCMEC/D3 cell line and used when its trans-endothelial electrical resistance (TEER) reached 80-120 Ω · cm2 (tested by Millicell-Electrical Resistance System). The cells were randomly divided into the control group cultured under normal conditions, the group cultured under hypoxic conditions (2%O2) for 24 h (hypoxia group), and the group first subjected to HBOP for 2 h and then to hypoxia (HBOP group). Occludin and ZO-1 expression were analyzed by immunofluorescence assay. Results Normal hCMEC/D3 was spindle-shaped and tightly integrated. TEER was significantly reduced in the hypoxia (P = 0.001) and HBOP group (P = 0.014) compared to control group, with a greater decrease in the hypoxia group. Occludin membranous expression was significantly decreased in the hypoxia group (P = 0.001) compared to the control group, but there was no change in the HBOP group. ZO-1 membranous expression was significantly decreased (P = 0.002) and cytoplasmic expression was significantly increased (P = 0.001) in the hypoxia group compared to the control group, although overall expression levels did not change. In the HBOP group, there was no significant change in ZO-1 expression compared to the control group. Conclusion Hyperbaric oxygen preconditioning protected the integrity of BBB in an in vitro model through modulation of occludin and ZO-1 expression under hypoxic conditions

The use of heart rate to estimate oxygen consumption of free-ranging black-browed albatrosses Diomedea melanophrys

Heart rates (fh) and rates of oxygen consumption (V(dot)O2) were measured in eight black-browed albatrosses (Diomedea melanophrys) when walking on a treadmill, with the aim of using fh to predict V(dot)O2 in free-ranging albatrosses. The resulting relationship between the variables was: V(dot)O2 (ml min-1) = [0.0157fh (beats min-1)]1.60, r2=0.80, P<0.001. In addition to the calibration procedure, six of the albatrosses were injected with doubly labelled water (DLW), and fh and V(dot)O2 were monitored continuously over a 3 day period while the birds were held in a respirometer. During the 3 day period, the birds were walked for up to 3&shy;4 h day-1 in bouts lasting approximately 0.5 h. The heart rate data were used to estimate the metabolic rates of these birds using the above regression. Estimates of metabolic rate derived from fh, DLW and respirometry did not differ (ANOVA; P=0.94), primarily because of the variance between individual birds. There was also no significant difference between the different estimates obtained from the different equations used to calculate energy expenditure from the DLW technique (ANOVA; P=0.95). Mean estimates of V(dot)O2 from fh under active and inactive conditions differed from measured values of V(dot)O2 by -5.9 % and -1.7 % respectively. In addition, the estimates of V(dot)O2 from fh at different walking speeds did not differ significantly from the measured values. It appears that, in the black-browed albatross, fh is as good a predictor of the mean metabolic rate of free-ranging birds as DLW or time&shy;energy budgets combined with either respirometry or DLW. However, the method should be applied to as many individuals and as many instances of a particular behaviour as possible. The heart rate technique offers potential for much more detailed analyses of the daily energy budgets of these birds, and over much longer periods, than has previously been possible

Estimation of daily energy expenditure from heart rate and doubly labeled water in exercising geese

We investigated whether daily O2, consumption (Vo2) could be predicted from heart rate (f(H)) in five exercising barnacle geese (Branta leucopsis) and compared the accuracy of this method with that of the doubly labeled water (DLW) method. The regressions of Vo2 on f(H), based on incremental speed tests, differed among individual birds. The O2 pulse (i. e., Vo2/f(H)) progressively increased with exercise level from 0.22 mL O2 heartbeat-1 during resting to an estimated 0.47 mL O2 heartbeat-1 during flight. Daily Vo2 was generally underestimated (-3.9%) by (individual) resting O2 pulses but overestimated (+8.4%) by linear regressions of Vo2 on f(H). However, it was well predicted (+0.8%) by the O2 pulses appropriate for each exercise level. When using relationships derived from the group of birds, the estimations were generally improved (-3.3% for resting O2 pulse, -0.03% for appropriate O2 pulse) but poorer (+13.6%) for the group linear regression. Some of these predictions were better than the estimation of daily CO2 production (Vco2) by the two-compartment model of the DLW method (average algebraic error of +0.9%). We conclude that f(H) can be used to estimate daily energy expenditure in birds accurately provided that (1) its application is limited to the range of exercise levels in which f(H) has been calibrated against Vo2 and (2a) Vo2-f(H) relationships are determined for each individual bird or (2b) the f(H) measurements of several free-ranging birds are averaged. Heart rate can also be used to indicate within-day variation in energy expenditure

Energetics of diving in macaroni penguins

Heart rate (fH), abdominal temperature (Tab) and diving depth were measured in thirteen free-ranging breeding female macaroni penguins. Measurement of these variables allowed estimation of the mass-specific rate of oxygen consumption (V˙O·) while diving and investigation of the physiological adjustments that might facilitate the diving behaviour observed in this species. In common with other diving birds, macaroni penguins showed significant changes in fH associated with diving, and these variables accounted for 36% of the variation in dive duration. When V˙O· was calculated for dives of different durations, 95.3% of dives measured were within the calculated aerobic dive limit (cADL) for this species. Mean fH for all complete dive cycles was 147±6 beats min–1. When this fH is used to estimate V˙O· of 26.2±1.4 ml min–1 kg–1 then only 92.8% of dives measured were within the cADL. Significant changes in abdominal temperature were not detected within individual dives, though the time constant of the measuring device used may not have been low enough to record these changes if they were present. Abdominal temperature did decline consistently during bouts of repeated diving of all durations and the mean decrease in Tab during a diving bout was 2.32±0.2°C. There was a linear relationship between bout duration and the magnitude of this temperature drop. There was no commensurate increase in dive duration during dive bouts as Tab declined, suggesting that macaroni penguins are diving within their physiological limits and that factors other than Tab are important in determining the duration of dives and dive bouts. Lowered Tab will in turn facilitate lower metabolic rates during diving bouts, but it was not possible in the present study to determine the importance of this energy saving and whether it is occurs actively or passively

Feeding, fasting and foraging success during chick rearing in macaroni penguins

Foraging behaviour and energy expenditure were measured continuously throughout the chick-rearing period of free-ranging macaroni penguins Eudyptes chrysolophus. These data were integrated with values obtained from the literature on body mass, assimilation efficiency, body reserve consumption and deposition rates, chick growth and energy expenditure and energy content of food in a new type of algorithm to predict (with 95% confidence limits [CL]) foraging success and daily changes in body mass. A successfully breeding pair of macaroni penguins will capture 111.7 kg (95% CL: 79.4 to 158.0 kg) of prey during the chick-rearing period. The crucial phase of the chick rearing period was around the time that chicks crèche, when prey consumption rates more than doubled as the male assisted in foraging and recovered from a long fast. Female macaroni penguins extracted 2.28 (1.60 to 3.26) and males extracted 2.84 (2.02 to 3.99) g of prey from their environment for every minute spent submerged during foraging. Only 15.3 (14.7 to 15.6)% of all prey consumed was fed to chicks. While food capture rates increase in the middle of the breeding season, this may be more a function of greater food availability than a response to demands from their chick. Male and female macaroni penguins have differing breeding strategies with the male showing the characteristics of a capital then income breeder while the female has a strategy that shows characteristics of both capital and income strategies simultaneously. The high synchronicity and precise timing of the macaroni penguin breeding season and timing of the increase in prey capture rates suggest an influx of prey to their foraging area during the middle of the breeding season. A depletion of prey resources in the foraging area used during the breeding season could affect foraging success and have profound effects on the body condition and composition of this species and its ability to raise chicks successfully

Behavioural flexibility during year-round foraging in macaroni penguins

Penguins are major consumers in the marine environment. However, like many top predators, very little information exists on their foraging behaviour outside the breeding season. We investigated the foraging behaviour of the macaroni penguin Eudyptes chrysolophus continuously for 2 consecutive years, from the end of December 2001. This allowed us to investigate whether foraging behaviour varied between sexes, years or phases of the annual cycle. Male penguins tended to dive deeper and longer than female penguins, but at a lower frequency, probably as a result of their larger body size. There was little variation in foraging behaviour between the 2 years studied, although neither year included a notable period of low Antarctic krill abundance. Diving behaviour varied substantially within years and general linear models were used to investigate this variability. In summary, all penguins tended to dive deeper, longer and more efficiently during their winter migration than during the summer breeding season. The penguins dived predominantly during daylight hours at all times of the year, but appeared to be more constrained by daylight during the short winter days. Several diving variables including dive duration, dive rate and amount of time spent diving were significantly related to day length and these associations were stronger during winter than summer. The macaroni penguin shows flexibility in its foraging behaviour as it adapts to differing constraints and challenges during its annual cycle

The use of data loggers to determine the energetic and physiology of aquatic birds and mammals

By deploying a data logger specifically designed for the purpose, it was possible to record heart rate, fH (beats/min), from free-ranging gentoo penguins, Pygoscelis papua, and Antarctic fur seals, Arctocephalus gazella, at the British Antarctic Survey Base at Bird Island. The heart rate data were then converted into oxygen consumption (VO2, mlO2 min-1 kg-1) and/or energy expenditure (W/kg) using equations that had been derived from calibration experiments. In these experiments the relationships between fH and VO2 were determined in animals at rest and while exercising at different levels on a treadmill or in a static water channel (penguins) and in a variable speed flume (California sea lions, Zalophus californianus, as surrogate fur seals) or in a static water channel (fur seals). The validity of using these relationships was tested by recording simultaneously fH, VO2 by direct respirometry and VCO2 by the doubly labelled water (DLW) technique in six penguins and in six California sea lions during 72 h and 24 h, respectively, at various levels of activity. For the penguins, both indirect methods gave mean algebraic errors within 2% of the measured VO2, whereas for the sea lions, the mean algebraic errors were 36.4% for the DLW method and 2.7% for the fH method. The range of errors was greater for the DLW method, in both species. Field data from 15 penguins indicate that the fH method provides data that are comparable to those obtained using the DLW method, but with the added advantage that they can be broken down into the energy costs for specific types of behaviour. The implanted data loggers also recorded the temperature of the abdominal cavity (T(ab)) and it was evident that this routinely decreased by approximately 2 degrees C during diving bouts and by a maximum of almost 5 degrees C. Such temperature decreases, particularly if representative of similar decreases in other tissues, may at least partly explain why the energy costs of travelling to and from the foraging site and of foraging itself are similar to those for penguins resting in water at 5 degrees C. Field data from 15 female fur seals indicate that, when the animals are ashore, there is good agreement between the values for mean energy expenditure obtained by the fH and DLW methods. However, when the animals are at sea, the values obtained by DLW are substantially greater than those obtained by fH. When the at-sea values are corrected for the apparent overestimations referred to above, there is good agreement between the data obtained using the two methods. The data derived from fH indicate that, as with the penguins, the energy expenditures during travelling to and from the foraging site and during foraging are similar to those of fur seals resting in water at 7 degrees C

Do seasonal changes in metabolic rate facilitate changes in diving behaviour?

Macaroni penguins were implanted with data loggers to record heart rate (fH), abdominal temperature (Tab) and diving depth during their pre-moult trip (summer) and winter migration. The penguins showed substantial differences in diving behaviour between the seasons. During winter, mean and maximum dive duration and dive depth were significantly greater than during summer, but the proportion of dives within the calculated aerobic dive limit (cADL) did not change. Rates of oxygen consumption were estimated from fH. As winter progressed, the rate of oxygen consumption during dive cycles (sO2DC) declined significantly and mirrored the pattern of increase in maximum duration and depth. The decline in sO2DC was matched by a decline in minimum rate of oxygen consumption (sO2min). When sO2min was subtracted from sO2DC, the net cost of diving was unchanged between summer and winter. We suggest that the increased diving capacity demonstrated during the winter was facilitated by the decrease in sO2min. Abdominal temperature declined during winter but this was not sufficient to explain the decline in sO2min. A simple model of the interactions between sO2min, thermal conductance and water temperature shows how a change in the distribution of fat stores and therefore a change in insulation and/or a difference in foraging location during winter could account for the observed reduction in sO2min and hence sO2DC