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  • 1
    Electronic Resource
    Electronic Resource
    Photosynthetic responses of Arctic sea-ice microalgae to short-term temperature acclimation (1989)
    Springer
    Polar biology 9 (1989), S. 437-442 
    Details
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In April-May 1986, sea-ice microalgae (southcastern Hudson Bay, Canadian Arctic) were acclimated to temperatures ranging from-1.5° to 10°C for short periods (3 h), after which photosynthesis and carboxylating enzyme activities were measured. P max b increased after acclimation to 10°C while photosynthetic parameters α, β and Ik as well as activities of PePC and PePCk did not show any significant change after temperature acclimation. Contrary to P max b , the activity of RuBPC was lower for algae acclimated to 3°-10°C, the observed response increasing with temperature. There was also a seasonal trend in the response of RuBPC, the ability to compensate for rapid temperature changes being higher in May. These results show that ice algae were photosynthetically adaptable in the range of temperatures tested. For RuBPC, adaptability developed seasonally when the environmental temperature started to fluctuate in May. Photosynthetic acclimatization to temperature may be of high ecological significance in extending the growth season of ice-algae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00443230
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Springtime coupling between ice algal and phytoplankton assemblages in southeastern Hudson Bay, Canadian Arctic (1993)
    Springer
    Polar biology 13 (1993), S. 441-449 
    Details
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Microalgal assemblages from the bottom ice, the ice-water interface and the water column were systematically sampled from April to June 1986, in southeastern Hudson Bay (Canadian Arctic). The taxonomic similarity between samples from the three environments was assessed using a clustering procedure. There were two groups that comprised samples from both the ice-water interface and the water column, while five other groups were made of samples originating from a single environment. Taxonomic compositions of the two mixed groups suggest two types of connexion between the ice-water interface and the water column, i.e. before the phytoplankton bloom, there was seeding of the water column by ice algae and, during ice melt, interfacial algae contributed to the water column communities that were otherwise typically phytoplankton. Overall, the phytoplankton community underwent a succession from pennate to centric diatoms. Sinking rates of algae from the ice-water interface were estimated using settling columns (SETCOL). The sinking rates increased seasonally (0.4–2.7 m d−1), which enhanced accessibility of ice-algal cells to the pelagic grazers. Ice algae contributed to water column production as they became accessible to the pelagic grazers, and also by seeding the water column before the phytoplankton bloom.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00233135
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of clonidine, dihydralazine and splanchnic nerve stimulation on the release of neuropeptide Y, MET-enkephalin and catecholamines from dog adrenal medulla (1993)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 348 (1993), S. 379-384 
    Details
    ISSN: 1432-1912
    Keywords: Catecholamines ; Neuropeptides ; Adrenal medulla ; Clonidine ; Dihydralazine ; Splanchnic nerve stimulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Various neuropeptides are costored together with catecholamines in the adrenal medulla. The concurrent release (evaluated by adrenal vein plasma levels) of these neuropeptides [neuropeptide Y (NPY), met-enkephaline (ME)] and catecholamines [adrenaline (A) and noradrenaline (NA)] from the adrenal gland was examined in chloralose-anesthetized dogs after intravenous administration of clonidine (10 μg/kg) and dihydralazine (1 mg/kg). These results were compared to those obtained after the stimulation of the right splanchnic nerve at 1, 5 and 10 Hz frequencies. The increment in the release of catecholamines and neuropeptides was evaluated for dihydralazine and splanchnic nerve stimulation. Dihydralazine (at its maximal effect) induced a significant preferential increase in catecholamines (expressed as mean (SEM): NA: 17.3 (5.4) fold, A: 13.1 (2.6) fold) and ME (16.0 (7.1) fold) versus basal values. However, the significant increase in NPY-LI was only 2.0 (0.4) times the baseline. Splanchnic nerve stimulation induced a frequency-dependent increase in catecholamines and neuropeptides. When the stimulation frequency was increased from 1 Hz to 5 Hz, NA and A levels increased 17.9 (4.3) and 14.0 (2.2) fold, respectively and ME levels 14.1 (3.0) fold. By contrast, NPY-LI was increased only 2.3 (0.3) fold under the same conditions. Increasing the stimulation frequency from 5 Hz to 10 Hz resulted in similar elevations of NA, ME, and NPY-LI adrenal plasma levels (about 4 times) whereas A only increased twice. Clonidine decreased catecholamine and ME adrenal plasma levels (the maximal percent decrease when compared with control values was about 75%) whereas NPY adrenal plasma levels remained unchanged. In conclusion, the present data indicate that (i) both adrenal ME and NA always exhibit corelease in a parallel fashion which is not the case for NPY art; (ii) different populations of chromaffin vesicles could be preferentially mobilized according to different physiological and pharmacological patterns.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00171337
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  • 4
    Electronic Resource
    Electronic Resource
    Is neuropeptide Y co-released with catecholamines in experimental arterial hypertension following sinoaortic denervation? (1992)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 345 (1992), S. 431-436 
    Details
    ISSN: 1432-1912
    Keywords: Catecholamines ; NPY ; Conscious dogs ; Sinoaortic denervation ; Yohimbine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The release of catecholamines and their co-neurotransmitter neuropeptide Y (NPY) was investigated in conscious dogs with neurogenic arterial hypertension elicited by sinoaortic denervation. One month after denervation, an elevation of catecholamine levels (measured by HPLC) without elevation of NPY-like immunoreactivity (NPY-LI) levels in plasma (evaluated by RIA) has been found. This dissociation could be explained by 1) a transient release of NPY during the first weeks after surgery, 2) a depletion of neuronal NPY due to the permanent sympathetic stimulation, or 3) an insufficient increase in sympathetic tone. To test these hypotheses, we investigated the time courses of catecholamine and NPY-LI levels in arterial plasma during the first five weeks after sinoaortic denervation and responses to yohimbine (an alpha2 antagonist which enhances transmitter release). Resting NPY-LI levels in plasma remained normal during the first five weeks after sinoaortic denervation. In normal dogs, a high dose of yohimbine (0.5 mg/kg i. v.) elevated both catecholamine (6-fold) and NPY-LI levels (1.5-fold), whereas a lower dose (0.05 mg/kg i. v.) induced a two fold elevation of catecholamine levels without changing NPY-LI concentrations. In sinoaortically denervated dogs, yohimbine elicited elevation of both catecholamines and NPY-LI whatever the dose used. Thus, neurogenic arterial hypertension in dogs seems to involve catecholamines but not NPY. Moreover, the present work suggests that a high level of sympathetic stimulation is required for a co-release of catecholamines and NPY.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00176621
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    Paper (German National Licenses)
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