| 1. |
- Altimiras, Jordi, 1967-, et al.
(författare)
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Intrinsic autoregulation of cardiac output in rainbow trout (Oncorhynchus mykiss) at different heart rates
- 2004
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Ingår i: J Exp Biol. - : The Company of Biologists. ; 207:Pt 2, s. 195-201
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Tidskriftsartikel (refereegranskat)abstract
- Intrinsic regulation of the heart in teleosts is partly driven by central venous pressure, which exerts a modulatory role on stroke volume according to the well-known Frank-Starling mechanism. Although this mechanism is well understood from heart perfusion studies, less is known about how this mechanism operates in vivo, where heart rate varies markedly. We used zatebradine, a bradycardic agent, to attain resting heart rates in surgically instrumented animals. A dose of zatebradine of 2.79+/-0.47 mg l(-1) decreased heart rate by half, from 44.4+/-4.19 beats min(-1) to 22.1+/-1.9 beats min(-1). Zatebradine had no significant effect on the peripheral vasculature and no inotropic effects, so was a suitable pharmacological agent with which to manipulate heart rate. When heart rate halved, cardiac output dropped to 87.5+/-4.6% of the control value, due to the concomitant increase in stroke volume to 165+/-13%. In vivo recordings of venous pressure at varying heart rates indicated that the partial compensation in cardiac output was possible through an increase in pressure in the sinus venosus, from -0.06+/-0.04 kPa at a control heart rate of 58.3+/-3.5 beats min(-1) (N=10) to 0.07+/-0.05 kPa after injection of zatebradine (4 mg kg(-1)). The operation of the so-called time-dependent autoregulatory mechanism was further demonstrated in perfused hearts. The positive pressures recorded in the sinus venosus at low heart rates coincident with non-invasive measurements in trout suggest that atrial filling in trout is more dependent on the build-up of pressure in the venous circulation (vis-a-tergo filling) than a suction mechanism during ventricular contraction (vis-a-fronte filling).
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| 2. |
- Balkenius, Anna, et al.
(författare)
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Colour constancy in diurnal and nocturnal hawkmoths
- 2004
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Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 207:19, s. 3307-3316
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Tidskriftsartikel (refereegranskat)abstract
- Diurnal and nocturnal hawkmoths have been shown to use colour vision for flower discrimination. Here, we present evidence that the nocturnal hawkmoth Deilephila elpenor and the diurnal hawkmoth Macroglossum stellatarum also have colour constancy. Colour constancy was shown in D. elpenor in two multiple-choice experiments with five different bluish colour patches under white and blue illumination and with five yellowish colour patches under white, blue and yellow illumination. The mechanism underlying colour constancy in both species was investigated in two dual-choice experiments. The choice behaviour is consistent with the use of the von Kries coefficient law. Although the moths have colour constancy, they react to the colour of the illumination. They make fewer choices when tested under the changed illumination, where they never receive a reward, compared with the training illumination. Even if colour constancy can be explained by a von Kries adaptation mechanism, the fact that the animals discriminate between different illuminations indicates that some additional process must be involved.
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| 3. |
- Barclay, C J, et al.
(författare)
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Initial mechanical efficiency of isolated cardiac muscle
- 2003
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Ingår i: Journal of Experimental Biology. - 0022-0949 .- 1477-9145. ; 206:Pt 16, s. 2725-32
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to determine whether the initial mechanical efficiency (ratio of work output to initial metabolic cost) of isolated cardiac muscle is over 60%, as has been reported previously, or whether it is approximately 30%, as suggested by an estimate based on the well-established net mechanical efficiency (ratio of work output to total, suprabasal energy cost) of 15%. Determination of initial efficiency required separation of the enthalpy output (i.e. heat + work) into initial and recovery components. The former corresponds to energy produced by reactions that use high-energy phosphates and the latter to energy produced in the regeneration of high-energy phosphates. The two components were separated mathematically. Experiments were performed in vitro (30 degrees C) using preparations dissected from rat left ventricular papillary muscles (N=13). Muscle work output and heat production were measured during a series of 40 contractions using a contraction protocol designed to mimic in vivo papillary muscle activity. Net mechanical efficiency was 13.3+/-0.7%. The total enthalpy output was 2.16 times greater than the initial enthalpy output, so that initial mechanical efficiency was 28.1+/-1.2%.
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| 4. |
- Bäckman, Johan, et al.
(författare)
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Harmonic oscillatory orientation relative to the wind in nocturnal roosting flights of the swift Apus apus.
- 2002
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Ingår i: Journal of Experimental Biology. - 1477-9145. ; 205:Pt 7, s. 905-910
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Tidskriftsartikel (refereegranskat)abstract
- Swifts regularly spend the night flying at high altitude. From previous studies based on tracking radar observations, we know that they stay airborne during the night and prefer to orient themselves into the wind direction with an increased angular concentration with increasing wind speed. In this study, we investigated the orientation relative to the wind of individual swifts by frequency (discrete Fourier transform) and autocorrelation analysis based on time series (10s intervals) of the angle between the swifts' heading and the wind direction for radar trackings of long duration (9-60 min). The swifts often showed a significant harmonic oscillation of their heading direction relative to the wind, with a frequency mostly in the range 1-17 mHz, corresponding to cycle periods of 1-16 min. The swifts also sometimes performed circling flights at low wind speeds. Wind speed ranged from 1.3 to 14.8 m s(-1), and we expected to find different patterns of orientation at different wind speeds, assuming that the swifts adapt their orientation to avoid substantial displacement during their nocturnal flights. However, oscillatory orientation was found at all wind speeds with variable frequencies/periods that did not show any consistent relationship with wind speed. It remains to be shown whether cyclic heading changes are a regular feature of bird orientation.
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| 5. |
- Crossley, II, Dane A., et al.
(författare)
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Ontogeny of baroreflex control in the American alligator Alligator mississippiensis
- 2003
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Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 0022-0949 .- 1477-9145. ; 206, s. 2895-2902
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Tidskriftsartikel (refereegranskat)abstract
- Baroreflex regulation appears in different species at different points in embryonic development. This study was designed to understand the development of the baroreflex in embryos of the American alligator at four different points of embryonic development (60%, 70%, 80% and 90% of a total incubation period of 72 days) and in 1-week-old hatchlings. Data from a separate study on 1-year-old alligators were included for comparison. The gain of the cardiac limb of the baroreflex was calculated from heart rate changes triggered by pharmacological manipulation of arterial pressure with sodium nitroprusside and phenylephrine. The results demonstrated that a vagally mediated hypertensive baroreflex was present during the final 30% of alligator development. A hypotensive baroreflex was not present in embryos but appeared in hatchlings, mediated by a combined effect of vagal and sympathetic efferents. Absolute baroreflex gain was maximal at 80% of incubation (41.22 beats kPa–1 min–1) and dropped thereafter, reaching a minimum in 1-year-old alligators (9.69 beats kPa–1 min–1). When the baroreflex gain was normalized to resting arterial pressure and heart rate, the maximum gain was observed in 1-year-old alligators (normalized index of 2.12 versus 0.75 in hatchlings and 0.69 as the highest gain in embryos). In conclusion, baroreflex regulation appeared during embryonic development with a substantial gain. These findings indicate that embryonic development is a period of preparation for cardiovascular regulatory mechanisms that will be necessary in adult life and that the baroreflex control mechanism is required for cardiovascular control during ontogeny.
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| 6. |
- Dacke, Marie, et al.
(författare)
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Twilight orientation to polarised light in the crepuscular dung beetle Scarabaeus zambesianus
- 2003
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Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 206:9, s. 1535-1543
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Tidskriftsartikel (refereegranskat)abstract
- The polarisation pattern of skylight offers many arthropods a reference for visual compass orientation. The dung beetle Scarabaeus zambesianus starts foraging at around sunset. After locating a source of fresh droppings, it forms a ball of dung and rolls it off at high speed to escape competition at and around the dung pile. Using behavioural experiments in the field and in the laboratory, we show that the beetle is able to roll along a straight path by using the polarised light pattern of evening skylight. The receptors used to detect this skylight cue can be found in the ommatidia of the dorsal rim area of the eye, whose structures differ from the regular ommatidia in the rest of the eye. The dorsal rim ommatidia are characterised by rhabdoms with microvilli oriented at only two orthogonal orientations. Together with the finding that the receptors do not twist along the length of the rhabdom, this indicates that the photoreceptors of the dorsal rim area are polarisation sensitive. Large rhabdoms, a reflecting tracheal sheath and a lack of screening pigments make this area of the eye well adapted for polarised light detection at low light levels. The fan-shaped arrangement of receptors over the dorsal rim area was previously believed to be an adaptation to polarised light analysis, but here we argue that it is simply a consequence of the way that the eye is built.
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| 7. |
- Dircksen, Heinrich, 1954-, et al.
(författare)
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Two orcokinins and the novel octapeptide orcomyotropin in the hindgut of the crayfish Orconectes limosus : identified myostimulatory neuropeptides originating together in neurones of the terminal abdominal ganglion
- 2000
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Ingår i: Journal of Experimental Biology. - 0022-0949 .- 1477-9145. ; 203:18, s. 2807-2818
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Tidskriftsartikel (refereegranskat)abstract
- The tridecapeptides Asn(13)-orcokinin and Val(13)-orcokinin, two known members of the orcokinin neuropeptide family native to crustaceans, and a novel octapeptide, orcomyotropin, FDAFTTGFamide, have been identified from extracts of hindguts of the crayfish Orconectes limosus using an isolated hindgut contractility bioassay, high-performance liquid chromatography, microsequencing and mass spectrometry. All three peptides display strong inotropic actions on crayfish hindguts. Orcomyotropin showed higher potency than the two orcokinins. Threshold concentration was approximately 5 x 10(-12)mol l(-1)versus 10(-10)mol l(-1) for the two orcokinins. An approximately fivefold increase in contraction amplitude was observed with 10(-9)mol l(-1) orcomyotropin and 10(-7)mol l(-1) of the orcokinins. Asn(13)- and Val(13)-orcokinin did not differ significantly with regard to their biological effects. Semi-isolated crayfish hearts and locust oviducts did not respond to the three peptides. Immunocytochemistry using antisera against Asn(13)-orcokinin and orcomyotropin showed that these neuropeptides are co-localized in approximately 80-90 neurones of the terminal abdominal ganglion that have been shown to innervate the entire hindgut muscularis via the intestinal nerve. The neurones form elaborate terminal branches preferentially on longitudinal hindgut muscles. Orcomyotropin is a novel crustacean member of the GF-amide family of myotropic and/or allatotropic neuropeptides from annelids, molluscs and insects.
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| 8. |
- Gudmundsson, G A, et al.
(författare)
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Sanderlings (Calidris alba) have a magnetic compass: Orientation experiments during spring migration in Iceland
- 2000
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Ingår i: Journal of Experimental Biology. - 1477-9145. ; 203:20, s. 3137-3144
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Tidskriftsartikel (refereegranskat)abstract
- The migratory orientation of sanderlings (Calidris alba) was investigated with cage experiments during the spring migration in southwest Iceland. Sanderlings were exposed to 90 degrees counterclockwise-shifted magnetic fields under both clear skies and natural overcast. Clear sky control tests resulted in a northerly mean direction, in agreement with predictions based on ringing recovery data and earlier visual observations of departing flocks. Sanderlings closely followed experimental deflections of magnetic fields when tested under clear skies. Control experiments under natural overcast resulted in a bimodal distribution approximately coinciding with the magnetic north-south axis. Overcast tests did not reveal any predictable response to the experimental treatment, but instead resulted in a non-significant circular distribution. The time of orientation experiments in relation to the tidal cycle affects the motivation of the birds to depart, as shown by the lower directional scatter of headings of individuals tested within the appropriate tidal window under clear skies. Sanderlings were significantly more likely to become inactive under overcast conditions than under clear sky conditions. The results demonstrate, for the first time, that a wader species such as the sanderling possesses a magnetic compass and suggest that magnetic cues are of primary directional importance. However, overcast experiments indicate that both celestial and geomagnetic information are needed for sanderlings to realize a seasonally appropriate migratory orientation.
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| 9. |
- Hays, G. C., et al.
(författare)
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The diving behaviour of green turtles undertaking oceanic migration to and from Ascension Island: dive durations, dive profiles and depth distribution
- 2001
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Ingår i: Journal of Experimental Biology. - 1477-9145. ; 204:23, s. 4093-4098
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Tidskriftsartikel (refereegranskat)abstract
- Satellite telemetry was used to record the submergence duration of green turtles (Chelonia mydas) as they migrated from Ascension Island to Brazil (N=12 individuals) while time/depth recorders (TDRs) were used to examine the depth distribution and dive profiles of individuals returning to Ascension Island to nest after experimental displacement (N=5 individuals). Satellite telemetry revealed that most submergences were short (<5 min) but that some submergences were longer (>20 min), particularly at night. TDRs revealed that much of the time was spent conducting short (24 min), shallow (approximately 0.91.5 m) dives, consistent with predictions for optimisation of near-surface travelling, while long (typically 2030 min), deep (typically 1020 m) dives had a distinctive profile found in other marine reptiles. These results suggest that green turtles crossing the Atlantic do not behave invariantly, but instead alternate between periods of travelling just beneath the surface and diving deeper. These deep dives may have evolved to reduce silhouetting against the surface, which would make turtles more susceptible to visual predators such as large sharks.
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| 10. |
- Hedenström, Anders, et al.
(författare)
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Field estimates of body drag coefficient on the basis of dives in passerine birds
- 2001
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Ingår i: Journal of Experimental Biology. - 1477-9145. ; 204:6, s. 1167-1175
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Tidskriftsartikel (refereegranskat)abstract
- During forward flight, a bird's body generates drag that tends to decelerate its speed. By flapping its wings, or by converting potential energy into work if gliding, the bird produces both lift and thrust to balance the pull of gravity and drag. In flight mechanics, a dimensionless number, the body drag coefficient (C-D,C-par), describes the magnitude of the drag caused by the body. The drag coefficient depends on the shape (or streamlining), the surface texture of the body and the Reynolds number. It is an important variable when using flight mechanical models to estimate the potential migratory flight range and characteristic flight speeds of birds, Previous wind tunnel measurements on dead, frozen bird bodies indicated that C(D,pa)r is 0.4 for small birds, while large birds should have lower values of approximately 0.2. More recent studies of a few birds flying in a wind tunnel suggested that previous values probably overestimated C-D,C-par. We measured maximum dive speeds of passerine birds during the spring migration across the western Mediterranean. When the birds reach their top speed, the pull of gravity should balance the drag of the body land wings), giving us an opportunity to estimate C-D,C-par. Our results indicate that C-D,C-par decreases with increasing Reynolds number within the range 0.17-0.77, with a mean C-D,C-par of 0.37 for small passerines, A somewhat lower mean value could not be excluded because diving birds may control their speed below the theoretical maximum, Our measurements therefore support the notion that 0.4 (the 'old' default value) is a realistic value of C-D,C-par for Small passerines.
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