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  • 1. AXELSSON, M
    et al.
    DAVISON, B
    FORSTER, M
    NILSSON, S
    BLOOD-PRESSURE CONTROL IN THE ANTARCTIC FISH PAGOTHENIA-BORCHGREVINKI1994Inngår i: Journal of Experimental Biology, ISSN 0022-0949, E-ISSN 1477-9145, Vol. 190, s. 265-279Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The mechanisms of cardiovascular control in the Antarctic fish Pagothenia borchgrevinki were investigated during rest and swimming exercise using pharmacological tools to reveal the nature of the control systems involved. Simultaneous and continuous recordings of ventral and dorsal aortic blood pressure, heart rate and ventral aortic blood flow (cardiac output) were made using standard cannulation procedures and a single-crystal Doppler flowmeter. Exercise produced a clear and consistent decrease in dorsal aortic blood pressure caused by a decrease in systemic vascular resistance. At the same time, ventral aortic blood pressure increased owing to the combined effects of a markedly increased cardiac output (by about 80 %) and branchial vasoconstriction. Judged from the effects of the alpha-adrenoceptor antagonist prazosin, control of the branchial vasculature involves an alpha-adrenoceptor-mediated vasoconstriction, in addition to more traditional cholinergic vasoconstrictor and beta-adrenoceptor-mediated dilatory mechanisms. The range of heart rates is large, from 3-4 beats min(-1) in individual fish during hypertensive bradycardia to about 28 beats min(-1) after atropine treatment. Both chronotropic and inotropic effects are responsible for a marked increase in cardiac output during exercise. The increase in blood pressure caused by adrenaline injection was due largely to an increase in cardiac output, while direct effects on the systemic vasculature were small and transient. The increase in cardiac output, in turn, was due solely to an adrenergic stimulation of stroke volume. A barostatic bradycardia, often seen in other vertebrates in response to adrenaline injection, was absent and it is possible that a decrease in heart rate was offset by direct adrenergic stimulation of the heart. Angiotensin II (Ang II) produced consistent hypertension by systemic vasoconstriction. In contrast to the effects of adrenaline injection, the hypertension caused by Ang II was accompanied by a marked bradycardia. This could be abolished by atropine, suggesting a cholinergic vagal reflex of the type found in other vertebrates.

  • 2. AXELSSON, M
    et al.
    DAVISON, W
    FORSTER, ME
    FARRELL, AP
    CARDIOVASCULAR-RESPONSES OF THE RED-BLOODED ANTARCTIC FISHES PAGOTHENIA-BERNACCHII AND P-BORCHGREVINKI1992Inngår i: Journal of Experimental Biology, ISSN 0022-0949, E-ISSN 1477-9145, Vol. 167, s. 179-201Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of this study was to investigate cardiac performance and cardiovascular control in two red-blooded nototheniid species of antarctic fishes, Pagothenia bernacchii (a benthic fish) and P. borchgrevinki (a cryopelagic fish), and to make comparisons with existing information on haemoglobin-free antarctic teleosts. In quiescent P. bernacchii at 0-degrees-C ventral aortic pressure (PVA) was 3.09 kPa and cardiac output (Q) was 17.6 ml min-1 kg-1, with a heart rate (fH) of 10.5 beats min-1 and stroke volume of 1.56 ml kg-1. Following atropine treatment, Q was maintained but heart rate increased and stroke volume decreased. Resting heart rate resulted from an inhibitory cholinergic tone of 80.4 % and an excitatory adrenergic tone of 27.5 %. The intrinsic heart rate was 21.7 beats min-1 at 0-degrees-C. In quiescent P. borchgrevinki at 0-degrees-C, PVA was 3.6 kPa, Q was 29.6 ml min-1 kg-1 and stroke volume was 2.16 ml kg-1. The resting heart rate in P. borchgrevinki of 11.3 beats min-1 resulted from an inhibitory cholinergic tone of 54.5 % and an excitatory adrenergic tone of 3.2 %. The intrinsic heart rate was 23.3 beats min-1. P. bernacchii maintained Q during a progressive decrease in water oxygen tension from 20 to 6.7 kPa, but fH was increased significantly. Thus, although there is cholinergic control of the heart, no hypoxic bradycardia was observed. Recovery from hypoxia was associated with increases in Q and fH; stroke volume returned to control values. PvA declined in recovery as total vascular resistance decreased. Hypoxic exposure following atropine treatment resulted in progressive increases in PVA, Q and stroke volume; fH decreased during the recovery period. Hypoxic exposure in P. borchgrevinki produced similar cardiovascular responses to those observed in P. bernacchii. During an acute increase in water temperature from 0 to 5-degrees-C, P. bernacchii regulated Q and total vascular resistance. Stroke volume decreased as fH increased. The intrinsic heart rate had a Q10 of 1.96 over this temperature range. P. bernacchii maintained chronotropic inhibition up to a temperature of 2.5-3.0-degrees-C. However, by 5-degrees-C this chronotropic inhibition of the heart rate was lost. Infusion of adrenaline into the ventral aorta of P. bernacchii resulted in significant increases in Q, fH, PVA and total vascular resistance. Infusion of adrenaline after atropine treatment caused similar cardiovascular changes without the change in fH. P. borchgrevinki could sustain swimming in a water tunnel at approximately 1 body length per second for 6-10 min. During the bout of swimming there was a doubling of ventilation frequency, a 75 % increase in Q as fH doubled and a decrease in total vascular resistance. Similarities exist between these two red-blooded antarctic teleosts and haemoglobin-free channichthyids. These include a low PvA, associated with a low vascular resistance, and a high cardiac stroke volume. Ventricle mass is somewhat larger than in temperate species of teleosts, especially considering the low aortic pressures developed by the heart. The absence of a sustained bradycardia in P. bernacchii during hypoxia or an adrenaline-induced increase in PVA is unusual. This may in part reflect the very high inhibitory cholinergic tone to the heart, the highest value found in resting fish.

  • 3. Franklin, Craig. E.
    et al.
    Farrell, Anthony P.
    Altimiras, Jordi
    Axelsson, Michael
    Thermal dependence of cardiac function in arctic fish: implications of a warming world2013Inngår i: Journal of Experimental Biology, ISSN 0022-0949, E-ISSN 1477-9145, Vol. 216, nr 22, s. 4251-4255Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    With the Arctic experiencing one of the greatest and most rapid increases in sea temperatures in modern time, predicting how Arctic marine organisms will respond to elevated temperatures has become crucial for conservation biology. Here, we examined the thermal sensitivity of cardiorespiratory performance for three closely related species of sculpins that inhabit the Arctic waters, two of which, Gymnocanthus tricuspis and Myoxocephalus scorpioides, have adapted to a restricted range within the Arctic, whereas the third species, Myoxocephalus scorpius, has a wider distribution. We tested the hypothesis that the fish restricted to Arctic cold waters would show reduced cardiorespiratory scope in response to an increase in temperature, as compared with the more eurythermal M. scorpius. As expected from their biogeography, M. scorpioides and G. tricuspis maximised cardiorespiratory performance at temperatures between 1 and 4 degrees C, whereas M. scorpius maximised performance over a wider range of temperatures (1-10 degrees C). Furthermore, factorial scope for cardiac output collapsed at elevated temperature for the two high-latitude species, negatively impacting their ability to support aerobically driven metabolic processes. Consequently, these results concurred with our hypothesis, suggesting that the sculpin species restricted to the Arctic are likely to be negatively impacted by increases in ocean temperatures.

  • 4. Gronroos, Johanna
    et al.
    Muheim, Rachel
    Akesson, Susanne
    Orientation and autumn migration routes of juvenile sharp- tailed sandpipers at a staging site in Alaska2010Inngår i: Journal of Experimental Biology, ISSN 0022-0949, E-ISSN 1477-9145, Vol. 213, nr 11, s. 1829-1835Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Arctic waders are well known for their impressive long-distance migrations between their high northerly breeding grounds and wintering areas in the Southern hemisphere. Performing such long migrations requires precise orientation mechanisms. We conducted orientation cage experiments with juvenile sharp-tailed sandpipers (Calidris acuminata) to investigate what cues they rely on when departing from Alaska on their long autumn migration flights across the Pacific Ocean to Australasia, and which possible migration routes they could use. Experiments were performed under natural clear skies, total overcast conditions and in manipulated magnetic fields at a staging site in Alaska. Under clear skies the juvenile sharp-tailed sandpipers oriented towards SSE, which coincides well with reported sun compass directions from their breeding grounds in Siberia towards Alaska and could reflect their true migratory direction towards Australasia assuming that they change direction towards SW somewhere along the route. Under overcast skies the sandpipers showed a mean direction towards SW which would lead them to Australasia, if they followed a sun compass route. However, because of unfavourable weather conditions (headwinds) associated with overcast conditions, these south-westerly directions could also reflect local movements. The juvenile sharp-tailed sandpipers responded clearly to the manipulated magnetic field under overcast skies, suggesting the use of a magnetic compass for selecting their courses.

  • 5. Sundin, L
    et al.
    Axelsson, M
    Davison, W
    Forster, M E
    Cardiovascular responses to adenosine in the Antarctic fish Pagothenia borchgrevinki1999Inngår i: Journal of Experimental Biology, ISSN 0022-0949, E-ISSN 1477-9145, Vol. 202, nr 17, s. 2259-2267Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have investigated the effects of adenosine on the cardiovascular system of the Antarctic fish Pagothenia borchgrevinki. Continuous measurements of ventral and dorsal aortic blood pressures, heart rate (f(H)) and ventral aortic blood flow (cardiac output, (Q)over dot) were made using standard cannulation techniques and a single-crystal Doppler flowmeter, On line measurements of arterial P-O2 were made using an oxygen electrode connected to an extracorporeal loop. Adenosine (10 nmol kg(-1)) and the specific A(1)-receptor agonist N-6-cyclopentyadenosine (CPA) elicited biphasic changes in the branchial and systemic resistances. While there was an initial decrease in the branchial resistance followed by an increase, the opposite was true for the systemic response. The resistance changes were significantly attenuated by aminophylline (a P-1-receptor antagonist) and 8-cyclopentyltheophylline (CPT; an A(1)-receptor antagonist). In addition, adenosine induced an aminophylline-sensitive decrease in the arterial P-O2. The reduction was attenuated when pre-injection arterial P-O2 was low. Adenosine and CPA also caused a marked reduction in f(H), with CPA being more potent. The bradycardia was blocked by aminophylline and CPT, demonstrating an involvement of A(1) receptors in this response.

  • 6. Sundin, L
    et al.
    Davison, W
    Forster, M
    Axelsson, M
    A role of 5-HT2 receptors in the gill vasculature of the Antarctic fish Pagothenia borchgrevinki1998Inngår i: Journal of Experimental Biology, ISSN 0022-0949, E-ISSN 1477-9145, Vol. 201, nr 14, s. 2129-2138Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study was conducted to describe the cardiovascular responses to intra-arterial injections of serotonin in the Antarctic fish Pagothenia borchgrevinki and to elucidate the underlying mechanisms, Immunohistochemistry was used to localise serotonin-containing cells within the gills, Simultaneous and continuous recordings of ventral and dorsal aortic blood pressure, heart rate and ventral aortic blood flow (cardiac output) were made using standard cannulation procedures in combination with Doppler flow measurement, An extracorporeal loop with an in-line oxygen electrode allowed continuous measurements of arterial oxygen pressure Pa-O2. Pre-branchial injection of serotonin (5-hydroxytryptamine, 5-HT) or the 5-HT2 receptor agonist alpha-methylserotonin increased the branchial vascular resistance and ventral aortic pressure, while the 5-HT1 receptor agonist piperazine was without effect, The branchial vasoconstriction produced by serotonin injection was completely blocked by the 5-HT1/5-HT2 receptor antagonist methysergide and the branchial vasoconstriction produced by alpha-methylserotonin injection was completely blocked by the specific 5-HT2 receptor antagonist LY53857, The results suggest that the 5-HT2 receptor alone mediates the branchial vasoconstriction. Serotonin also mediated a methysergide-sensitive reduction in Pa-O2, the reduction being greatest when the pre-injection Pa-O2 value was high, 5-HT-immunoreactive cells and nerve fibres were present within the gill tissues, All the 5-HT-immunoreactive cells were located on the efferent side of the filaments, but 5-HT-immunoreactive nerve fibres were found lining both of the branchial arteries, Our findings demonstrate a potential serotonergic control system for the gills in Pagothenia borchgrevinki. In contrast to its effects on the branchial vasculature, serotonin produced a methysergide-insensitive decrease in the systemic vascular resistance, However, neither the specific 5-HT1 nor 5-HT2 receptor agonists produced a decrease in the resistance of the systemic vasculature, The nature of the serotonergic receptor(s) inducing vasodilation in teleost fish is uncertain.

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