Cochlear microphonics and the initiation of spikes in the auditory nerve: correlation of single-unit data with neural and receptor potentials recorded from the round window

On the basis of comparisons of responses of guinea pig ganglion cells and inner hair cells to intense low-frequency tones, Sellick et al. [Hear. Res. 7, 199-221 (1982)] have proposed that basal inner hair cells can be depolarized (and thus, VIII-N. spikes generated) by the extracellular microphonic generated during hyperpolarization of outer hair cells. VIII-N. data for the chinchilla have been presented that, to a first approximation, support such a hypothesis [Ruggero and Rich, J. Acoust. Soc. Am. 73, 2096-2108 (1983)]. However, an apparent discrepancy exists in our results, vis à vis Sellick et al.'s hypothesis, in that basal fiber near-threshold responses precede maximal negativity of the round window microphonic (i.e., maximal hyperpolarization of outer hair cells) by up to 90 degrees (but generally less than 45 degrees), depending on frequency. It is shown here that the discrepancy is resolved if certain nonlinear phase changes and overall distortion of the microphonic waveshapes, both of which occur at intense stimulus levels, are taken into account. It is also shown that compound action potentials (AP's), superimposed on the round window microphonics, can be identified at multiple times within each stimulus cycle, closely matching the near-threshold response phases of single-unit excitation. AP1 is nearly synchronous with the negative-to-positive transition of round window microphonics and with the excitation of fibers innervating apical-to-middle cochlear regions. AP2 is synchronous with the positive-to-negative transition of the microphonics and with the excitation of basal fibers. One or two other AP's probably reflect "peak splitting" in the responses of both basal and apical fibers.     

Dimer asymmetry in superoxide dismutase studied by molecular dynamics simulation

Summary Molecular dynamics (MD) simulations of 100 ps have been carried out to study the active-site behaviour of the Cu,Zn superoxide dismutase dimer (SOD) in water. The active site of each subunit was monitored during the whole simulation by calculating the distances between functional residues and the catalytic copper. The results indicate that charge orientation is maintained at each active site but the solvent accessibility varies. Analysis of the MD simulation, carried out by using the atomic displacement covariance matrix, has shown a different intra-subunit correlation pattern for the two monomers and the presence of inter-subunit correlations. The MD simulation presented here indicates an asymmetry in the two active sites and different dynamic behaviour of the two SOD subunits.     

Mechanisms of peroxidic oxygen transfer to organic substrates : Oxidation of organic sulphides by chromium(vi)oxide diperoxide

The oxidation of organic sulphides (n-Bu₂S, PhSCH₃, Tolyl-SCH₃, p-Cl-C₆H₄SCH₃, and Ph₂S by (HMPT)CrO(O₂)₂1′ in CHCl₃ has been studied. The reaction produces the corresponding sulphoxides in nearly quantitative yields according to a 2:1 stoichiometry of sulphide to metaldiperoxide. A second-order-overall (order one in each of the reagents) kinetic law is obeyed. In parallel, the oxidation of organic sulphides by (HMPT)MoO(O₂)₂1' has been studied. Kinetic data, the observed rate laws, and the effect of inhibitors (HMPT, DABCO) have pointed out that-although 1' is significantly more reactive than 1′—considerable similarity exists between the two metaldiperoxides, in that both appear to act as electrophilic oxidizers. Also, through ¹H, ³¹P and ¹³C NMR investigations have permitted to assess the relevance of equilibria (HMPT)MO(O₂₂ MO(O₂)₂ + HMPT [with M = Mo(VI) or Cr(VI)]in solution, whereas no NMR evidence could be found for significant substrate coordination under the given conditions.     

Determination of Hyaluronic Acid in a Chitosan-Based Formulation by RP C18 and HILIC LC–ESI-MS: an Evaluation of Matrix Effect

Two simple and fast C18 and HILIC liquid chromatography–electrospray mass spectrometry methods for the determination of hyaluronic acid (HA) in a mucoadhesive chitosan-based formulation were developed and validated. The performances of both methods were compared in terms of validation parameters and matrix effect. A simple sample preparation method based on sulphuric acid-based degradation was optimized for the detection of HA fragments (i.e. m/z 380 2-mer, m/z 759 4-mer, m/z 1,138 8-mer and m/z 1,518 16-mer). By operating under selected ion-monitoring mode, excellent selectivity towards chitosan fragments was obtained. For validation, good linearity, detection limits (<4 μg mL⁻¹) and precision (RSD % < 16 %) were generally obtained on matrix with both columns. However, HILIC column exhibited improved performances in terms of HA fragment separation and selectivity. By analyzing on the C18 column the chitosan-based formulation and sample extracts from pig mucosa treated with the formulation, matrix effects exhibited a dependence of signal suppression degree (ranging from 37 to 83 %) as a function of the HA fragment dimension. The HILIC column afforded instead a significantly reduced suppression degree (ranging from 1 to 16 %) and a better separation. These findings demonstrated the improved performances of the HILIC column with respect to conventional C18 mechanism for the analysis of HA fragments in complex matrices.

     

Un'osservazione sulle funzioni booleane simmetriche

Sommario In un'algebra di Boole si considerano le funzioni simmetriche rispetto al coniugio su un sottoinsieme delle variabili. Si danno delle rappresentazioni di tali funzioni in funzione delle funzioni simmetriche elementari.

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Summary In a Boolean Algebra, the functions which are symmetric with respect to conjugation on a subset of the variables are considered. A representation of such functions by means of the elementary symmetric functions is given.

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Il presente lavoro è stato eseguito mentre l'autore era teaching assistant presso l'University of California at Los Angeles (UCLA).     

Detection of XY behavior in weakly anisotropic quantum antiferromagnets on the square lattice

We consider the Heisenberg antiferromagnet on the square lattice with S=1/2 and very weak easy-plane exchange anisotropy; by means of the quantum Monte Carlo method, based on the continuous-time loop algorithm, we find that the thermodynamics of the model is highly sensitive to the presence of tiny anisotropies and is characterized by a crossover between isotropic and planar behavior. We discuss the mechanism underlying the crossover phenomenon and show that it occurs at a temperature which is characteristic of the model. The expected Berezinskii-Kosterlitz-Thouless transition is observed below the crossover: a finite range of temperatures consequently opens for experimental detection of noncritical 2D XY behavior. Direct comparison is made with uniform susceptibility data relative to the S=1/2 layered antiferromagnet Sr2CuO2Cl2.     

Near Field Stimulated Time of Flight Mass Surface Analyzer

This work describes a groundbreaking process that provides a direct highly localized measurement of the atomic mass on surfaces at room temperature. Employing an original system that joins a scanning tunneling microscopy (STM) device and a time of flight (TOF) mass analyzer, we could previously ionize surface atoms by the combination of an optical laser pulse and an electric pulse at the STM tip. Desorbed ions from a localized area were accelerated and detected by a TOF chamber. We will demonstrate in this paper that high localization and mass discrimination can be obtained even without the aid of an electric pulse from the tip. We reduced the angle of incidence of the laser beam to zero (laser beam parallel to the sample surface). In this condition we were able to demonstrate for the first time ionic desorption at a confinement level of the order of 5-10nm, an order of magnitude better than previous configurations.This paper was originally presented at the 11th Optical Near Field Workshop, which was held on June 28, 2002 at Tokyo Institute of Technology, Yokohama, organized by the Optical Near Field Group of the Optical Society of Japan, an affiliate of the Japan Society of Applied Physics.