Targeting of cyclic AMP degradation to beta 2-adrenergic receptors by beta-arrestins

Catecholamines signal through the beta2-adrenergic receptor by promoting production of the second messenger adenosine 3',5'-monophosphate (cAMP). The magnitude of this signal is restricted by desensitization of the receptors through their binding to beta-arrestins and by cAMP degradation by phosphodiesterase (PDE) enzymes. We show that beta-arrestins coordinate both processes by recruiting PDEs to activated beta2-adrenergic receptors in the plasma membrane of mammalian cells. In doing so, the beta-arrestins limit activation of membrane-associated cAMP-activated protein kinase by simultaneously slowing the rate of cAMP production through receptor desensitization and increasing the rate of its degradation at the membrane.     

On the origin of interictal activity in human temporal lobe epilepsy in vitro

The origin and mechanisms of human interictal epileptic discharges remain unclear. Here, we describe a spontaneous, rhythmic activity initiated in the subiculum of slices from patients with temporal lobe epilepsy. Synchronous events were similar to interictal discharges of patient electroencephalograms. They were suppressed by antagonists of either glutamatergic or gamma-aminobutyric acid (GABA)-ergic signaling. The network of neurons discharging during population events comprises both subicular interneurons and a subgroup of pyramidal cells. In these pyramidal cells, GABAergic synaptic events reversed at depolarized potentials. Depolarizing GABAergic responses in neurons downstream to the sclerotic CA1 region contribute to human interictal activity.     

Ocular responses to linear motion are inversely proportional to viewing distance

Eye movements exist to improve vision, in part by preventing excessive retinal image slip. A major threat to the stability of the retinal image comes from the observer's own movement, and there are visual and vestibular reflexes that operate to meet this challenge by generating compensatory eye movements. The ocular responses to translational disturbances of the observer and of the scene were recorded from monkeys. The associated vestibular and visual responses were both linearly dependent on the inverse of the viewing distance. Such dependence on proximity is appropriate for the vestibular reflex, which must transform signals from Cartesian to polar coordinates, but not for the visual reflex, which operates entirely in polar coordinates. However, such shared proximity effects in the visual reflex could compensate for known intrinsic limitations that would otherwise compromise performance at near viewing.     

Free radical generation assays: new methodology for accelerated oxidation studies at low temperature in complex food matrices

A novel method for the rapid screening of antioxidant efficacy and oxidative stability in food and feed matrices has been developed. The analyses are described as free radical generation (FRG) assays. The new procedure combines the use of azo-initiators with analytical equipment that is widely used for antioxidant research such as the oxidative stability instrument and the oxygen bomb. The use of initiators instead of high temperatures as a driving force to increase the rate of oxidation improves the correlation between the accelerated screening of foodstuffs and real shelf life. The improved correlation can be mainly explained by the fact that food products are analyzed in their original status, maintaining all interfacial phenomena of the food matrix. Furthermore, the lower temperature of analysis reduces differences between the reaction kinetics of the assay and those of the oxidation during actual shelf life. Consequently, the correlation between the accelerated analysis and shelf life is improved, particularly when compared to accelerated oxidation at high temperatures. The FRG assays could be used successfully to evaluate the efficacy of natural antioxidants in heat-sensitive food products such as emulsions and meat products. A good correlation was observed between the accelerated tests and the oxidation parameters obtained from standard shelf-life evaluation. It was possible to successfully compare the efficacy of several antioxidants and to predict shelf life for these heat-sensitive food matrices.     

Liquid chromatographic and spectroscopic characterization of pentamidine isethionate and impurities in bulk drug and injectables

A liquid chromatographic (LC) method is described for evaluating purity of pentamidine isethionate (PI), a life-saving drug used in the treatment of Pneumocystis carinii pneumonia, which is a leading cause of death in persons with acquired immunodeficiency syndrome (AIDS). Six potential impurity compounds were synthesized to test the selectivity of the chromatographic system and to permit quantitation of impurities in various lots of PI products. The drug and impurities were separated with gradient elution on a cyano-bonded LC column. The analytic system provided information on the identities and levels of impurities in early experimental lots of PI. These results assisted the manufacturer in altering reaction conditions and purification procedures to ensure that succeeding lots were within the specification limits, i.e., no more than 0.4% of any single impurity or 0.7% of total impurities found in the final product.     

Comparison of spectroscopic techniques for the determination of Kjeldahl and ammoniacal nitrogen content of farmyard manure

The feasibility of determining the nitrogen content of farmyard manure using infrared spectroscopy was investigated. Fifteen samples each of cattle, pig, and turkey manure were analyzed by three infrared techniques: Fourier transform mid-infrared (MIR), using attenuated total reflection (ATR); near-infrared reflectance (NIR-R); and near-infrared optothermal photoacoustic (NIR-OT). The near-infrared measurements were made at wavelengths determined respectively by four (NIR-OT) and five (NIR-R) band-pass filters. The total nitrogen (using the Kjeldahl method) and volatile (ammoniacal) nitrogen contents of all samples were measured by wet chemistry. Internally cross-validated (ICV) partial least-squares (PLS) regression was then used to obtain calibrations for the nitrogen content. The data sets obtained by each technique were treated separately. Within these sets, data from each manure type were treated both separately and combined: the best predictive ability was obtained by combining data from all three manure types. From the combined data set, the residual standard deviations and correlation coefficients for the ICV-predicted versus actual Kjeldahl nitrogen content were, respectively, 6772 mg/kg dry wt, 0.862 (MIR); 9434 mg/kg dry wt, 0.771 (NIR-OT); and 8943 mg/kg dry wt, 0.865 (NIR-R). For the ammoniacal nitrogen content, the residual standard deviations and correlation coefficients were 3869 mg/kg dry wt, 0.899 (MIR); 6079 mg/kg dry wt, 0.820 (NIR-OT); and 3498 mg/kg dry wt, 0.961 (NIR-R).     

Vigilance behaviour of polar bears (Ursus maritimus) in the context of wildlife-viewing activities at Churchill, Manitoba, Canada

Viewing of polar bears (Ursus maritimus) from tundra vehicles has been offered at Churchill, Manitoba since the early 1980s. This form of wildlife viewing has provided a unique and safe way for tourists to learn about polar bears. However, these activities have largely been carried out without examining possible effects on polar bear behaviour. We studied vigilance behaviour (a scanning of the immediate vicinity and beyond) of resting polar bears to evaluate impacts from tundra vehicle activity. Focal animal sampling was used to examine whether a difference in vigilance behaviour existed when vehicles were present. We recorded the numbers of head-ups, vigilance bout length, and between-bout intervals for polar bears. In general, the frequency of head-ups increased, and the between-bout intervals decreased for male bears, when vehicles were present. Female bears behaved opposite to males. The vigilance bout lengths did not differ significantly between vehicle presence and absence. Vigilance behaviour of male bears was not magnified with increasing numbers of vehicles; therefore the threshold is one vehicle. We suggest that manipulative studies be conducted to examine how distances between vehicles and bears, tundra vehicle activity in the immediate vicinity of a bear during viewing, and noise of tourists affect increased vigilance.     

Soil phosphorus fractions after 111 years of animal manure and fertilizer applications

Accumulated soil P in agricultural soils is a major source of soluble and particulate forms of P entering water resources and degrading water quality. However, few research sites are currently available to evaluate the long-term effects of different cropping systems and fertility practices on soil inorganic and organic P accumulation. The objectives of this study were: (1) to compare the forms and quantity of different inorganic and organic soil P fractions in plots on Sanborn Field, which has been cultivated for 111 years; and (2) to assess the use of standard soil test P extractants for determining changes in soil P dynamics over time. A modified sequential P extraction procedure was used to separate labile and stable inorganic and organic P pools from surface soils collected on Sanborn Field in 1915, 1938, 1962, and 1999 from plots in continuous corn, continuous wheat, continuous timothy, and a corn-wheat-clover rotation amended with either manufactured fertilizers, horse or dairy manure or receiving no fertilization since 1888. Additional samples were collected from a native grass prairie site of a similar soil series to estimate soil characteristics at Sanborn Field before initial cultivation in 1888. Observed accumulation of Bray-1 P among fertilizer and manure treatments was attributed to over-application of P due to unrealistically high yield goals for each cropping system. Long-term cultivation of Sanborn Field increased soil bulk density and lowered soil pH and total organic C compared with native prairie. Fertilization either by addition of manufactured fertilizer or manure significantly increased inorganic resin-P and inorganic NaOH-extractable P. Applications of animal manure also significantly increased most organic P fractions compared with the unfertilized treatment. The native prairie had a larger proportion of total P in organic forms compared with cultivated plots, especially in organic NaOH-extractable P, but no significant decreases in either residual or total P were observed due to cultivation. This study confirms that soil P availability in cropping systems that are amended with predominantly organic P amendments may differ from conventional cropping systems relying on manufactured P fertilizers. However, no direct evidence was found to support the hypothesis that any individual inorganic or organic soil P fraction has a better relationship than conventional soil test P extractants with plant P uptake under contrasting organic and conventional fertility practices.