64 research outputs found
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Characterization of D-Aspartate Receptor Currents in Aplysia californica
No full textD-Aspartate (D-Asp) is an endogenous compound found in the central nervous system (CNS) of a variety of organisms. Despite its prevalence, however, relatively little understood of its physiological role. The prevailing theory is that D-Asp is an alternate agonist of N-methyl-D-aspartate receptor (NMDAR) channels. The goal of this work was to characterize the currents activated by D-Asp in neurons Aplysia californica, focusing on cells of the buccal S cluster (BSC). First, a general electrophysiological characterization was carried out, examining ion permeability, agonist dose-response, and the kinetics of activation, inactivation, and desensitization. D-Asp activated non-specific cation currents characterized by permeability to Na+ and K+. D-Asp-induced currents shared similar current-voltage relationships and time courses of activation and inactivation with L-glutamate (L-Glu)-induced currents. D-Asp currents, however, were subject to prolonged desensitization. Additionally, D-Asp activated currents independently of L-Glu, the known agonist of NMDAR channels, suggesting a non-NMDAR-dependent role of D-Asp. Next, select antagonists were used in an effort to pharmacologically characterize D-Asp receptor channels. These experiments suggested that D-Asp whole cell currents may be characterized by activation of multiple receptor sites, including NMDARS, excitatory amino acid transporters (EAATs), and a putative non-L-Glu D-Asp receptor. Furthermore, bath-applied D-Asp attenuated L-Glu-activated currents. Finally, D-Asp currents were compared to those evoked by acetylcholine (ACh) and serotonin (5-HT) in BSC cells. Results suggested that D-Asp activated receptor channels independently of ACh and 5-HT. Ten minute bath application of 5-HT was found to potentiate D-Asp current responses, likely through activation of a protein kinase C (PKC)-dependent mechanism, suggesting that D-Asp induced currents may be subject to synaptic plasticity associated with learning. While the identity of the putative D-Asp receptor remains elusive, the current work has advanced our understanding of the role D-Asp may play in the nervous system. These results should provide the groundwork for future studies aimed at identifying this unknown receptor channel, as well as investigation of the potential relationship of D-Asp receptor modulation to learning and memory in Aplysia, which may have relevance in higher organisms.</p
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Corrigendum
No full textPyroptotic neuronal cell death mediated by the AIM2 inflammasome Adamczak SE, de Rivero Vaccari JP, Dale G, Brand FJ 3rd, Nonner D, Bullock MR, Dahl GP, Dietrich WD, Keane RW Journal of Cerebral Blood Flow & Metabolism 2014; 34: 621–629
The transient potassium conductance of the somatic membrane of cultured embryonic rat neurons
No full textThe transient K conductance of rat central neurons was studied under voltage clamp. Currents were recorded through tight-seal pipettes from whole neurons or 3-8 m spheres of excised somatic membrane ('blebs'). Whole cells revealed a tetrodotoxin-sensitive Na current, followed by a K current that passed through a peak and was maintained at 60-90% of the peak during 300 ms. Somatic membrane isolated in the form of blebs also conducted Na and K currents, but the K current was mostly, and often exclusively, transient. This current was blocked by 4-aminopyridine (5 mM), but not affected by tetraethylammonium ion (1 mM).A transient K current was activated by depolarizations greater than 40 mV. Peak conductance increased in proportion to voltage with no indication of saturation up to +80 mV. Ensemble fluctuations suggested that less than 50% of the channels were open at the peak during a +40 mV depolarization. Steady-state inactivation was minimal after conditioning at 100 mV, and was complete at 50 to 30 mV. Recovery from inactivation followed a sigmoidal time course (half time ca. 50 ms at 90 mV, 25\sp\circC).Substitution of external Na by K ion altered activation, but not inactivation. In high K, a given depolarization activated a larger and more rapidly rising conductance that could be saturated. Substitution of 1 mM external Mg by 1 mM Ca, or addition of 0.5 mM Cd, slowed activation.The gating characteristics of the transient K current varied significantly from neuron to neuron. Half times of inactivation, although constant and stable for a given neuron varied from 5 to 65 ms at 25\sp\circC. Activation half-times ranged from 1 to 2 ms (+40 mV). The position on the voltage axis of peak conductance and steady-state inactivation curves varied over 30 mV. The degree of preceding inactivation did not affect the time course of the currents, suggesting channels of a given preparation were uniform in their inactivation properties.Possible kinetic models of the transient K channel gating are discussed. It appears that opening of these channels during activation involves a final reaction step that is weakly voltage dependent, and possibly ion dependent. The variability of the channel's gating properties is discussed in the context of mechanisms. (Abstract shortened with permission of author.)</p
Comparison of groundwater recharge estimation methods for the semi-arid Nyamandhlovu area, Zimbabwe
No full textThe Nyamandhlovu aquifer is the main water resource in the semi-arid Umguza district in Matebeleland North Province in Zimbabwe. The rapid increase in water demand in the city of Bulawayo has prompted the need to quantify the available groundwater resources for sustainable utilization. Groundwater recharge estimation methods and results were compared: chloride mass balance method (19–62 mm/year); water-table fluctuation method (2–50 mm/year); Darcian flownet computations (16–28 mm/year); 14C age dating (22–25 mm/year); and groundwater modeling (11–26 mm/year). The flownet computational and modeling methods provided better estimates for aerial recharge than the other methods. Based on groundwater modeling, a final estimate for recharge (from precipitation) on the order of 15–20 mm/year is believed to be realistic, assuming that part of the recharge water transpires from the water table by deep-rooted vegetation. This recharge estimate (2.7–3.6% of the annual precipitation of 555 mm/year) compares well with the results of other researchers. The advantages/disadvantages of each recharge method in terms of ease of application, accuracy, and costs are discussed. The groundwater model was also used to quantify the total recharge of the Nyamandhlovu aquifer system (20?×?106–25?×?106 m3/year). Groundwater abstractions exceeding 17?×?106 m3/year could cause ecological damage, affecting, for instance, the deep-rooted vegetation in the area.WatermanagementCivil Engineering and Geoscience
Aflad for nonner i begyndelsen af trykkekunsten
No full textEt håndskrevet afladsbrev givet til de Fattige Clarisser i Roskilde fortæller historien om Gutenbergs opfindelse, pavens indgriben og den cypriotiske krig imod de osmanniske tyrkere
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The transient potassium conductance of the somatic membrane of cultured embryonic rat neurons
No full textThe transient K conductance of rat central neurons was studied under voltage clamp. Currents were recorded through tight-seal pipettes from whole neurons or 3-8 m spheres of excised somatic membrane ('blebs'). Whole cells revealed a tetrodotoxin-sensitive Na current, followed by a K current that passed through a peak and was maintained at 60-90% of the peak during 300 ms. Somatic membrane isolated in the form of blebs also conducted Na and K currents, but the K current was mostly, and often exclusively, transient. This current was blocked by 4-aminopyridine (5 mM), but not affected by tetraethylammonium ion (1 mM).A transient K current was activated by depolarizations greater than 40 mV. Peak conductance increased in proportion to voltage with no indication of saturation up to +80 mV. Ensemble fluctuations suggested that less than 50% of the channels were open at the peak during a +40 mV depolarization. Steady-state inactivation was minimal after conditioning at 100 mV, and was complete at 50 to 30 mV. Recovery from inactivation followed a sigmoidal time course (half time ca. 50 ms at 90 mV, 25\sp\circC).Substitution of external Na by K ion altered activation, but not inactivation. In high K, a given depolarization activated a larger and more rapidly rising conductance that could be saturated. Substitution of 1 mM external Mg by 1 mM Ca, or addition of 0.5 mM Cd, slowed activation.The gating characteristics of the transient K current varied significantly from neuron to neuron. Half times of inactivation, although constant and stable for a given neuron varied from 5 to 65 ms at 25\sp\circC. Activation half-times ranged from 1 to 2 ms (+40 mV). The position on the voltage axis of peak conductance and steady-state inactivation curves varied over 30 mV. The degree of preceding inactivation did not affect the time course of the currents, suggesting channels of a given preparation were uniform in their inactivation properties.Possible kinetic models of the transient K channel gating are discussed. It appears that opening of these channels during activation involves a final reaction step that is weakly voltage dependent, and possibly ion dependent. The variability of the channel's gating properties is discussed in the context of mechanisms. (Abstract shortened with permission of author.)</p
Seed bank dynamics and germination ecology of fountain grass (Pennisetum setaceum)
No full textIn Hawaii, fountain grass (Pennisetum setaceum) is an aggressive, fire prone invader that out-competes native flora and forms monotypic stands with large amounts of dead mass that fuels fires. Wildfires eliminate native dry forest species and contribute to further spread of alien grasses, creating a grass/fire cycle. The presence of a fountain grass seed bank can increase the possibility of the reestablishment of this alien grass. Meanwhile, restoration efforts can benefit from the presence of native seeds in the seed bank. The goals of this study were: 1. to test the basic germination requirements of P. setaceum 2. to determine the seed bank composition in a degraded dry forest site, 3. to test the effectiveness of prescribed fire and large-scale aerial herbicide treatment in removing/suppressing fountain grass seed banks. Laboratory germination trials showed that P. setaceum does not require light for germination and seedlings can emerge from at least 5 cm soil depths. However, awns on the dispersal unit imply fountain grass may form predominantly surface layer seed banks. The soil seed bank at the study site is dominated by non-native species. Of the 23 species germinated from the seed bank, 3 native species and 20 alien species emerged; 3 of the alien species are grasses, 14 are herbaceous weeds, and 3 are woody species. Pennisetum setaceum forms a patchy seed bank with a maximum density of2040 seeds/m2.Field and lab tests show that fire and heat, respectively, are effective in killing fountain grass seeds. However, the heterogeneity of lava fields on which fountain grass occurs may provide refugia for seeds during fire events. While not statistically significant, some trends are evident in the data. The P. setaceum seed bank is reduced after the passage of fire, and input of seeds into the seed bank is suppressed by herbicide treatment. The sampling methodology employed is not robust enough to show differences in the seed bank after treatment. Smaller sub plots within the research site may be more appropriate to show treatment effects. Given the paucity of native species present in the seed bank, native seed augmentation will be necessary for restoration .M.S
On the validity of modeling concepts for the simulation of groundwater flow in lowland peat areas – case study at the Zegveld experimental field
No full textCivil Engineering and Geoscience
Differential Effects of Insulin on Choline Acetyltransferase and Glutamic Acid Decarboxylase Activities in Neuron‐Rich Striatal Cultures
No full textWe studied the effects of insulin, nerve growth factor (NGF), and tetrodotoxin (TTX) on cellular metabolism and the activity of glutamic acid decarboxylase (GAD) and choline acetyltransferase (ChAT) in neuron-rich cultures prepared from embryonic day 15 rat striatum. Insulin (5 micrograms/ml) increased glucose utilization, protein synthesis, and GAD activity in cultures plated over a range of cell densities (2,800-8,400 cells/mm2). TTX reduced GAD activity; NGF had no effect on GAD activity. Insulin treatment reversibly reduced ChAT activity in cultures plated at densities of greater than 4,000 cells/mm2, and the extent of this reduction increased with increasing cell density. The number of acetylcholinesterase-positive neurons was not reduced by insulin, suggesting that insulin acts by down-regulating ChAT rather than by killing cholinergic neurons. Insulin-like growth factor-1 (IGF-1) reduced ChAT activity at concentrations 10-fold lower than insulin, suggesting that insulin's effect on ChAT may involve the IGF-1 receptor. NGF increased ChAT activity; TTX had no effect on ChAT activity. These results suggest that striatal cholinergic and GABAergic neurons are subject to differential trophic control
Comparison of different base flow separation methods in a lowland catchment
No full textAssessment of water resources available in different storages and moving along different pathways in a catchment is important for its optimal use and protection, and also for the prediction of floods and low flows. Moreover, understanding of the runoff generation processes is essential for assessing the impacts of climate and land use changes on the hydrological response of a catchment. Many methods for base flow separation exist, but hardly one focuses on the specific behaviour of temperate lowland areas. This paper presents the results of a base flow separation study carried out in a lowland area in the Netherlands. In this study, field observations of precipitation, groundwater and surface water levels and discharges, together with tracer analysis are used to understand the runoff generation processes in the catchment. Several tracer and non-tracer based base flow separation methods were applied to the discharge time series, and their results are compared.WatermanagementCivil Engineering and Geoscience
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