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  • 1
    ISSN: 1432-1912
    Keywords: Microdialysis ; 5-HT release ; Chronic antidepressant ; Citalopram ; 5-HT reuptake inhibitor ; Tolerance ; Autoreceptors ; Frontal cortex Dorsal hippocampus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Rats were administered the selective serotonin (5-HT) uptake blocker citalopram or saline for 14 days to determine if prolonged treatment would lead to changes in extracellular 5-HT or autoreceptor sensitivity. One day after drug withdrawal, dialysis probes were implanted in the frontal cortex and dorsal hippocampus. Dialysis experiments were carried out using chloral hydrate anesthetized rats. The experimental protocol comprised the administration of three consecutive drug challenges: (1) After stable baseline levels were obtained, citalopram was infused through the dialysis probes to locally block uptake in the forebrain. (2) Subsequently, a 5-HT1B receptor agonist (RU24969 or CP93,129) was infused through the probe to test for changes in terminal autoreceptor sensitivity. (3) Last, citalopram was administered systemically to test the effect of indirect activation of somatodendritic autoreceptors. Under these conditions, with uptake already blocked locally in the forebrain, systemic citalopram produces a decrease in extracellular 5-HT, an effect that can be inhibited by pretreatment with antagonists of 5-HT1A receptors. The results indicate that during local infusion of citalopram extracellular 5-HT was significantly higher in the dorsal hippocampus of the chronic citalopram as compared to saline treatment group. This difference persisted throughout the full time course of the experiment. However, the decreases in 5-HT levels produced by local infusion of a 5-HT1B receptor agonist or after systemic citalopram administration were not significantly different between the chronic citalopram and saline treated groups. There were no significant differences between chronic citalopram and saline treated animals in frontal cortex. These results suggest that prolonged inhibition of 5-HT uptake may produce a selective change in the regulation of release from median raphe 5-HT neurons, but this change could not be clearly linked to a change in nerve terminal or somatodendritic autoreceptor sensitivity.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1912
    Keywords: Key words Microdialysis ; 5-HT release ; Chronic antidepressant ; Citalopram ; 5-HT reuptake inhibitor ; Tolerance ; Autoreceptors ; Frontal cortex ; Dorsal hippocampus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Rats were administered the selective serotonin (5-HT) uptake blocker citalopram or saline for 14 days to determine if prolonged treatment would lead to changes in extracellular 5-HT or autoreceptor sensitivity. One day after drug withdrawal, dialysis probes were implanted in the frontal cortex and dorsal hippocampus. Dialysis experiments were carried out using chloral hydrate anesthetized rats. The experimental protocol comprised the administration of three consecutive drug challenges: (1) After stable baseline levels were obtained, citalopram was infused through the dialysis probes to locally block uptake in the forebrain. (2) Subsequently, a 5-HT1B receptor agonist (RU24969 or CP93,129) was infused through the probe to test for changes in terminal autoreceptor sensitivity. (3) Last, citalopram was administered systemically to test the effect of indirect activation of somatodendritic autoreceptors. Under these conditions, with uptake already blocked locally in the forebrain, systemic citalopram produces a decrease in extracellular 5-HT, an effect that can be inhibited by pretreatment with antagonists of 5-HT1A receptors. The results indicate that during local infusion of citalopram extracellular 5-HT was significantly higher in the dorsal hippocampus of the chronic citalopram as compared to saline treatment group. This difference persisted throughout the full time course of the experiment. However, the decreases in 5-HT levels produced by local infusion of a 5-HT1B receptor agonist or after systemic citalopram administration were not significantly different between the chronic citalopram and saline treated groups. There were no significant differences between chronic citalopram and saline treated animals in frontal cortex. These results suggest that prolonged inhibition of 5-HT uptake may produce a selective change in the regulation of release from median raphe 5-HT neurons, but this change could not be clearly linked to a change in nerve terminal or somatodendritic autoreceptor sensitivity.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-2967
    Keywords: carbon dioxide ; sequestration ; plume ; pH ; toxicity ; zooplankton
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Feasibility studies suggest that the concept of capturing CO2 from fossil fuel power plants and discharging it to the deep ocean could help reduce atmospheric CO2 concentrations. However, the local reduction in seawater pH near the point of injection is a potential environmental impact. Data from the literature reporting on toxicity of reduced pH to marine organisms potentially affected by such a plume were combined into a model expressing mortality as a function of pH and exposure time. Since organisms exposed to real plumes would experience a time‐varying pH, methods to account for a variable exposure were reviewed and a new method developed based on the concept of isomortality. In part II of this paper, the method is combined with a random‐walk model describing the transport of passive organisms through a low pH plume leading to a Monte‐Carlo‐like risk assessment which is applied to several candidate CO2 injection scenarios.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-2967
    Keywords: carbon dioxide ; plume ; pH ; random walk ; diffusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract A method to evaluate aquatic mortality given a pollutant distribution is presented and applied to several sample low pH plumes representing various ocean CO2 disposal schemes. The method is an improvement over current analysis because it integrates the mortality due to time‐varying exposure to low pH with the probabilistic experiences of passive organisms subject to turbulent lateral diffusion as they pass through the plume. For the examples presented, the plume was discretized laterally into lanes and longitudinally by time steps, and a random walk model accounting for the scale‐dependent nature of relative diffusion was used to simulate the organism pathways over one time step. From these simulations, the probability that an organism will be in a given lane, $$\dot \jmath $$ , one time step after it starts from an initial lane, $$i$$ , was determined for all combinations of $$i$$ and $$\dot \jmath $$ . These probabilities were used to find the number of organisms following each of the possible pathways, and the mortality to the organisms due to their time varying exposure to low pH was determined by using the toxicity model described in part I of this paper. The integrated method allows the impact of the plume to be described in terms of total organism mortality as well as spatial deficit of organisms.
    Type of Medium: Electronic Resource
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