Assessing temporary threshold shift in a bottlenose dolphin (Tursiops truncatus) using multiple simultaneous auditory evoked potentials

Hearing sensitivity was measured in a bottlenose dolphin before and after exposure to an intense 20-kHz fatiguing tone in three different experiments. In each experiment, hearing was characterized using both the auditory steady-state response (ASSR) and behavioral methods. In experiments 1 and 2, ASSR stimuli consisted of seven frequency-modulated tones, each with a unique carrier and modulation frequency. The tones were simultaneously presented to the subject and the ASSR at each modulation rate measured to determine the effects of the sound exposure at the corresponding carrier frequency. In experiment 3 behavioral thresholds and ASSR input-output functions were measured at a single frequency before and after three exposures. Hearing loss was frequency-dependent, with the largest temporary threshold shifts occurring (in order) at 30, 40, and 20 kHz. ASSR threshold shifts reached 40-45 dB and were always larger than behavioral shifts (19-33 dB). The ASSR input-output functions were represented as the sum of two processes: a low threshold, saturating process and a higher threshold, linear process, that react and recover to fatigue at different rates. The loss of the near-threshold saturating process after exposure may explain the discrepancies between the ASSR and behavioral threshold shifts.     

Underwater sound pressure variation and bottlenose dolphin (Tursiops truncatus) hearing thresholds in a small pool

Studies of underwater hearing are often hampered by the behavior of sound waves in small experimental tanks. At lower frequencies, tank dimensions are often not sufficient for free field conditions, resulting in large spatial variations of sound pressure. These effects may be mitigated somewhat by increasing the frequency bandwidth of the sound stimulus, so effects of multipath interference average out over many frequencies. In this study, acoustic fields and bottlenose dolphin (Tursiops truncatus) hearing thresholds were compared for pure tone and frequency modulated signals. Experiments were conducted in a vinyl-walled, seawater-filled pool approximately 3.7 x 6 x 1.5 m. Acoustic signals were pure tone and linear and sinusoidal frequency modulated tones with bandwidths/modulation depths of 1%, 2%, 5%, 10%, and 20%. Thirteen center frequencies were tested between 1 and 100 kHz. Acoustic fields were measured (without the dolphin present) at three water depths over a 60 x 65 cm grid with a 5-cm spacing. Hearing thresholds were measured using a behavioral response paradigm and up/down staircase technique. The use of FM signals significantly improved the sound field without substantially affecting the measured hearing thresholds.     

An open source ion gate pulser for ion mobility spectrometry

Excluding the ion source, an ion mobility spectrometer is fundamentally comprised of drift chamber, ion gate, pulsing electronics, and a mechanism for amplifying and recording ion signals. Historically, the solutions to each of these challenges have been custom and rarely replicated exactly. For the IMS research community few detailed resources exist that explicitly detail the construction and operation of ion mobility systems. In an effort to address this knowledge gap we outline a solution to one of the key aspects of a drift tube ion mobility system, the ion gate pulser. Bradbury-Nielsen or Tyndall ion gates are found in nearly every research-grade and commercial IMS system. While conceptually simple, these gate structures often require custom, high-voltage, floating electronics. In this report we detail the operation and performance characteristics of a wifi-enabled, MOSFET-based pulser design that uses a lithium-polymer battery and does not require high voltage isolation transformers. Currently, each output of this circuit follows a TTL signal with ~20 ns rise and fall times, pulses up to +/? 200 V, and is entirely isolated using fiber optics. Detailed schematics and source code are provided to enable continued use of robust pulsing electronics that ease experimental efforts for future comparison.     

Fully integrated PDMS/SU-8/quartz microfluidic chip with a novel macroporous poly dimethylsiloxane (PDMS) membrane for isoelectric focusing of proteins using whole-channel imaging detection

A fully integrated polydimethylsiloxane (PDMS)/modified PDMS membrane/SU-8/quartz hybrid chip was developed for protein separation using isoelectric focusing (IEF) mechanism coupled with whole-channel imaging detection (WCID) method. This microfluidic chip integrates three components into one single chip: (i) modified PDMS membranes for separating electrolytes in the reservoirs from the sample in the microchannel and thus reducing pressure disturbance, (ii) SU-8 optical slit to block UV light (below 300?nm) outside the channel aiming to increase detection sensitivity, and (iii) injection and discharge capillaries for continuous operation. Integration of all these components on a single chip is challenging because it requires fabrication techniques for perfect bonding between different materials and is prone to leakage and blockage. This study has addressed all the challenges and presented a fully integrated chip, which is more robust with higher sensitivity than the previously developed IEF chips. This chip was tested by performing protein and pI marker separation. The separation results obtained in this chip were compared with that obtained in commercial cartridges. Side-by-side comparison validated the developed chip and fabrication techniques.     

Use of a multifunctional column for the determination of deoxynivalenol in grains, grain products, and processed foods

Deoxynivalenol (DON), also known as vomitoxin, belongs to a class of naturally occurring mycotoxins produced by Fusarium spp. DON, 12, 13-epoxy-3,7 trihydroxytrichothec-9-en-8-one, is one of the most frequently detected mycotoxins in agricultural commodities worldwide. A method consisting of extraction, filtration, column cleanup, and RP-HPLC-UV separation and quantitation was validated for the determination of DON in grains (rice and barley), grain products (whole wheat flour, white flour, wheat germ, and wheat bran), and processed foods (bread, breakfast cereals, and pretzels). A 25 g test portion was extracted with 100 mL acetonitrile-water (84 + 16, v/v). After blending for 3 min, the supernatant was applied to a multifunctional column (MycoSep 225). The purified filtrate (2 mL) was evaporated to dryness and redissolved in the mobile phase. The toxins were then subjected to RP-HPLC-UV analysis. The accuracy and repeatability characteristics of the method were determined. Recoveries of DON added at levels ranging from 0.5 to 1.5 microg/g for all test matrixes were from 75 to 98%. SD and RSD(r) ranged from 0.7 to 11.6% and 0.9 to 12.7%, respectively. Within-laboratory HorRat values were from 0.1 to 0.7 for all matrixes analyzed. The method was found to meet AOAC method performance criteria for grains, grain products, and processed foods. The identity of DON in naturally contaminated test sample extracts was confirmed by HPLC/MS/MS analysis.     

Compound prioritization methods increase rates of chemical probe discovery in model organisms

Preselection of compounds that are more likely to induce a phenotype can increase the efficiency and reduce the costs for model organism screening. To identify such molecules, we screened ~81,000 compounds in Saccharomyces cerevisiae and identified ~7500 that inhibit cell growth. Screening these growth-inhibitory molecules across a diverse panel of model organisms resulted in an increased phenotypic hit-rate. These data were used to build a model to predict compounds that inhibit yeast growth. Empirical and in silico application of the model enriched the discovery of bioactive compounds in diverse model organisms. To demonstrate the potential of these molecules as lead chemical probes, we used chemogenomic profiling in yeast and identified specific inhibitors of lanosterol synthase and of stearoyl-CoA 9-desaturase. As community resources, the ~7500 growth-inhibitory molecules have been made commercially available and the computational model and filter used are provided.     

Rapid, in situ synthesis of bidentate ligands: chromatography-free generation of catalyst libraries

The parallel synthesis of chiral bidentate ligands and their subsequent use in situ for a catalytic process is described. The ligands thus prepared gave comparable results to those obtained when the ligands were synthesized and purified by conventional means. This includes oxazolines and other compounds of similar complexity, meaning that for the first time these valuable compounds have been brought into the field of combinatorial catalysis.     

Electron-transfer reactions at the plasma-liquid interface

Electrochemical reactions are normally initiated in solution by metal electrodes such as Pt, which are expensive and limited in supply. In this Communication, we demonstrate that an atmospheric-pressure microplasma can act as a gaseous, metal-free electrode to mediate electron-transfer reactions in aqueous solutions. Ferricyanide is reduced to ferrocyanide by plasma electrons, and the reduction rate is found to depend on discharge current. The ability to initiate and control electrochemical reactions at the plasma-liquid interface opens a new direction for electrochemistry based on interactions between gas-phase electrons and ionic solutions.     

Isomeric trimethylene and ethylene pendant-armed cross-bridged tetraazamacrocycles and in vitro/in vivo comparisions of their copper(II) complexes

Ethylene cross-bridged tetraamine macrocycles are useful chelators in coordination, catalytic, medicinal, and radiopharmaceutical chemistry. Springborg and co-workers developed trimethylene cross-bridged analogues, although their pendant-armed derivatives received little attention. We report here the synthesis of a bis-carboxymethyl pendant-armed cyclen with a trimethylene cross-bridge (C3B-DO2A) and its isomeric ethylene-cross-bridged homocyclen ligand (CB-TR2A) as well as their copper(II) complexes. The in vitro and in vivo properties of these complexes are compared with respect to their potential application as (64)Cu-radiopharmaceuticals in positron emission tomography (PET imaging). The inertness of Cu-C3B-DO2A to decomplexation is remarkable, exceeding that of Cu-CB-TE2A. Electrochemical reduction of Cu-CB-TR2A is quasi-reversible, whereas that of Cu-C3B-DO2A is irreversible. The reaction conditions for preparing (64)Cu-C3B-DO2A (microwaving at high temperature) are relatively harsh compared to (64)Cu-CB-TR2A (basic ethanol). The in vivo behavior of the (64)Cu complexes was evaluated in normal rats. Rapid and continual clearance of (64)Cu-CB-TR2A through the blood, liver, and kidneys suggests relatively good in vivo stability, albeit inferior to (64)Cu-CB-TE2A. Although (64)Cu-C3B-DO2A clears continually, the initial uptake is high and only about half is excreted within 22 h, suggesting poor stability and transchelation of (64)Cu to proteins in the blood and/or liver. These data suggest that in vitro inertness of a chelator complex may not always be a good indicator of in vivo stability.