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  • Springer  (9)
  • Munksgaard International Publishers
  • 1980-1984  (9)
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  • 1
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Simultaneous measurements of whole body proton flux and both unidirectional and net ion fluxes together with assessment of the blood acid-base, respiratory gas, electrolyte and lactate status were performed in white suckers (Catostomus commersoni) originating from a natural soft water lake ([Ca++]=0.18 meq·l−1) in Ontario, Canada. Fish were examined under control (pH∼ 6.8) and acidic conditions (pH∼4.3) in natural soft water at 19–20 °C. Resting blood composition was similar to that previously reported for this species in natural hard water except for a marked enhancement of both plasma pH and bicarbonate levels. Acute acid exposure promoted a significant net influx of protons (or loss of base) concomitant with a plasma acidosis of mixed origin (metabolic+respiratory) as well as whole body Na+, Cl−, Ca++ and K+ losses. Circulating ion levels in plasma were partially conserved by intracellular ion depletion. Radiotracer studies showed that net body losses of Na+ and Cl− ensued largely through stimulation of efflux components and, to a lesser extent, inhibition of inward transport. Cl− loss eventually exceeded Na+, suggesting transport of an unmeasured substance to maintain electroneutrality. A markedly reduced blood $$P_{O_2 }$$ , enhanced plasma $$P_{CO_2 }$$ , elevated blood lactate levels and significant hemoconcentration were also observed. Thus, disturbances in acid-base regulation, ionoregulation and respiratory function may all contribute to acid toxicity in white suckers in natural soft water.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The function of carbonic anhydrase (CA) in the Red Rock Crab,Cancer productus Randall, was investigated. CA activity was found to varying degrees in the gills and many other tissues but not in hemolymph. Crabs injected with acetazolamide, a specific CA inhibitor, demonstrated a significant hemolymph acidosis. Hemolymph CO2 tension ( $$Pa_{CO_2 }$$ ) and CO2 content ( $$Ca_{CO_2 }$$ ) also increased and remained significantly elevated for 96 h following treatment. No significant changes could be detected in either hemolymph oxygenation or ionic status (except for HCO 3 − ) as a result of acetazolamide treatment. Crabs treated with acetazolamide, and also exposed to air, exhibited a more pronounced hemolymph acidosis with significantly increased respiratory ( $$P_{CO_2 }$$ ) and metabolic (lactate) components compared with the control group. Upon reimmersion acetazolamide treated crabs showed a slower recovery of hemolymph pH compared with the control group and no significant removal of the total CO2 load induced by air exposure. No significant differences between experimental and control groups during air exposure and recovery could be detected in hemolymph oxygenation, ionic status, NH3+NH 4 + levels or respiratory and cardiac pumping frequency and so the effects of acetazolamide treatment were apparently limited to CO2 removal across the gills. These results indicate that branchial CA facilitates the removal of CO2 from the hemolymph of SW adaptedC. productus largely by catalyzing the dehydration of hemolymph HCO 3 − to molecular CO2 at the gill. It is also recognized that gill CA may also serve to hydrate molecular CO2 to H+ and HCO3/− for use as counterions for ionic uptake mechanisms. Crab gill CA thus appears to play an important role in CO2 excretion as well as hemolymph ionic regulation.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary At the onset of moderate swimming activity,Callinectes sapidus rapidly increased branchial ventilation, heart rate, and oxygen uptake, reaching steady state values in 2–3 min, with a half-time of 30 sec. Although O2 extraction efficiency decreased slightly (50% to 43%) upon reaching steady state, O2 uptake was increased 2.6 fold over resting (routine) levels. HemolymphP O 2 did not change during sustained (30–60 min) exercise, but a marked decrease in pH (7.60 to 7.10), associated with a 14-fold increase in hemolymph lactate concentration, caused decreases in both pre-and postbranchial O2 content due to a large hemocyanin Bohr shift. The effect of the Bohr shift on O2 binding, however, was minimized by an increase in hemocyanin O2 affinity induced by lactate ions; the influence of lactate on hemocyaninP 50 was shown to be the same in vivo and in vitro. As a result of the interaction between the Bohr and lactate effects, only slight increases were observed in the a-v O2 difference (13%) and the quantitative role of hemocyanin in oxygen transport (11%) during exercise. The increase in O2 delivery was therefore attributed primarily to a 2.3 fold increase in cardiac output (Fick estimate), resulting from increases in both heart rate (1.61 X) and stroke volume (1.42X). During exercise hemocyanin remained 21% oxygenated upon leaving the tissues, thus maintaining a substantial ‘venous O2 reserve’ which could be utilized to fuel more strenuous levels of exercise at least partly by aerobic pathways. The high hemolymph lactate levels, however, indicate that anaerobic metabolism makes a significant contribution to energy production even during moderate exercise. These results are similar to the respiratory and circulatory responses reported for other decapod crustaceans and fish during mild exercise.C. sapidus, however, appears to be highly resistant to fatigue, which correlates with its welldeveloped locomotor capabilities.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The isolatedBulla eye expresses a circadian rhythm in optic nerve impulse frequency. In an effort to learn more about the organization of theBulla retina and, specifically, about the organization of retinal elements involved in the circadian pacemaker system, we have recorded both intracellularly and extracellularly from retinal cells, as well as examined thick sections and scanning electron micrographs of the eye. We report that: 1. TheBulla retina contains approximately 1000 large photoreceptors with distinct villousbearing distal segments which form a layer around a solid lens. There is also a population of approximately 100 neurons which surround a neuropil at the base of the retina. 2. Electrical activity in the optic nerve consists of large compound action potentials and lower amplitude activity. Compound action potentials occur spontaneously in darkness and both types of optic nerve activities can be induced by light pulses. 3. Intracellular recording from the photoreceptor layer reveals four types of responses: (a) cells which depolarize in response to a light pulse and then transiently hyperpolarize before returning to resting levels, (b) cells which depolarize and then return to resting levels without a hyperpolarization, (c) spontaneously active cells which transiently hyperpolarize and then depolarize during a light pulse and (d) cells which depolarize upon illumination with the production of action potentials. 4. Intracellular recording from cells at the base of the retina reveals neurons which are spontaneously active and fire action potentials in exact synchrony with compound impulses in the optic nerve. These basal retinal neurons are electrically coupled to one another and are responsible for the compound optic nerve impulse. 5. We find that the most common type of photoreceptors (R-type) are electrically coupled to one another but we find no evidence that these photoreceptors make contact with basal retinal neurons. 6. Localized illumination of retinal layers with miniature light guides reveals that the photoreceptor layer is responsible for light-induced low amplitude optic nerve impulses. In constrast, the light-induced compound action potential response is generated by light sensitive neurons at the retinal base. 7. The photoreceptor layer exerts an inhibitory effect on basal retinal neurons. Illumination of the photoreceptor layer leads to a hyperpolarization in basal retinal neuron membrane potential. We think it is likely that this inhibition is mediated by a particular class of retinal cells, similar to H-type cells in theAplysia retina. 8. An explicit model for the organization of theBulla retina is proposed.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary We have used chronic, or long-term, intracellular recording combined with simultaneous extracellular recording of optic nerve activity to examine the neurophysiological basis of circadian rhythmicity in theBulla eye. We report that: 1. Continuous intracellular recordings from R-type photoreceptors were maintained for up to 28 h. These recordings reveal that in constant conditions R-type cells do not exhibit rhythms in membrane potential which correlate with the circadian rhythm in compound action potential frequency expressed by the eye. 2. Continuous intracellular recordings from basal retinal neurons were maintained for up to 74 h. These recordings reveal that in constant conditions basal retinal neurons exhibit clear circadian rhythms in membrane potential and action potential frequency which are synchronized with the circadian rhythm in compound action potential frequency. Action potentials in individual basal retinal neurons correlate one-for-one with the compound action potentials in the optic nerve over the entire circadian cycle. The basal retinal neurons depolarize during the active phase of the compound action potential rhythm (projected day), relative to their membrane potential during the inactive phase of the rhythm (projected night). 3. The phase relationship between the rhythm in basal retinal neuron membrane potential and action potential frequency is such that the rise in membrane potential from its most hyperpolarized point precedes, or is synchronous with, the increase in action potential frequency observed near projected dawn. This suggests that the membrane potential rhythm drives the circadian rhythm in impulse frequency. 4. The quantitative relationship between basal retinal neuron membrane potential and action potential frequency is not linear, and varies predictably with circadian phase. Following the interval of peak impulse frequency the rate of impulse production declines more rapidly than does the membrane potential. Also, the impulse frequency at a given membrane potential is lower during the falling phase of the circadian cycle than during the rising phase. 5. In conclusion, we find that the basal retinal neurons are at minimum a pacemaker output pathway, and are likely the circadian pacemaker itself. We find no role for the R-type photoreceptor in the generation of circadian rhythmicity by theBulla eye.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The isolatedBulla eye expresses a circadian rhythm in optic nerve impulse frequency. In an effort to determine the anatomical location of the circadian pacemaking system within the retina we surgically reduced the eye. We report that: 1. The approximately 1000 large photoreceptors which form a cell layer immediately surrounding the lens, are not required for the expression of a circadian rhythm. Eyes which are surgically reduced so that only the basal retinal neuron population remains, continue to express a circadian rhythm indistinguishable in period to intact eyes. 2. The photoreceptor layer is also not required for light-induced phase shifts of the ocular rhythm. Retinal fragments containing only basal retinal neurons can be phase advanced or delayed by 6 h light pulses provided at the appropriate circadian phase. 3. Of the approximately 100 basal retinal neurons in theBulla eye, only a small proportion are required for the expression of a circadian rhythm in optic nerve frequency. Ocular fragments with as few as 6 basal retinal neuron somata remain rhythmic, and exhibit a free-running period indistinguishable from intact eyes. 4. Intact basal retinal somata are required for the expression of a circadian rhythm in optic nerve impulse frequency. Retinal fragments consisting of an optic nerve with a small amount of neuropil region produce spontaneous action potentials without evidence for a circadian modulation. 5. An explicit model for the organization of the circadian pacemaker system in theBulla retina is proposed.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Molecular and cellular biochemistry 59 (1984), S. 57-80 
    ISSN: 1573-4919
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Although a long held tenet of biology has been that endogenous inhibitors can modulate cell proliferation, little progress was made in purifying any such inhibitor. This was largely due to the rarity of non-malignant cell cultures in which regulation of cell division was still operative, and to problems in separating cytotoxic and cytostatic effects in the complex biological extracts which were being studied. During the last decade, hepatic proliferation inhibitors of varying degrees of purity have been isolated using regenerating rat liver or hepatoma cell cultures as test systems. In these early studies, a number of inhibitors with differing molecular weights, physicochemical properties and biological responses were purified from liver cytosol and/or serum. Some of them could inhibit DNA synthesis or mitosis and thus were considered to be G1 or G2 inhibitors. However, experiments which could give precise answers about mechanisms of action could not be done until an inhibitor purified to homogeneity was available. Using well-characterized rat liver diploid epithelial cell cultures, which maintain a number of liver properties and which do not possess any transformation markers or malignant properties, we recently purified an hepatic proliferation inhibitor to a homogenous protein. It has a molecular weight of 26 000 daltons and an isoelectric point of 4.65. It specifically inhibits cell division and DNA synthesis in a number of non-malignant rat liver epithelial cell types, and has no effect on transformed liver cells, or hepatoma cells, in culture. Its effect is not mediated through destruction or sequestration of essential nutrients or calcium ions. Nor have preliminary experiments shown the hepatic proliferation inhibitor to interfere with the binding of epidermal growth factor to its receptors. The majority of the cells treated with the inhibitor are blocked in the G1 phase. Further experiments to study its mechanism of action and the inter-relationship, if any, between the cell cycle block induced by serum or nutrient deprivation, and the inhibitor-induced cycle block are in progress.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1573-3521
    Keywords: imagery ; mind-body dualism ; placebos ; psychological medicine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Psychology
    Notes: Abstract A previous paper traced the pre-Cartesian history of the concept of imagination as a causal variable in physiopathology. The present paper continues that history, showing the prohibitive impact of mind-body dualism and sampling the views of some eighteenth- and nineteenth-century supporters of the theory. Contemporary research has produced abundant evidence supporting the historic belief that imagination has an arousal function and a direct link to physiopathology. This literature is surveyed and possible therapeutic applications are discussed.
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