Psychophysical correlates of contralateral efferent suppression. I. The role of the medial olivocochlear system in "central masking" in nonhuman primates

An extensive physiological literature, including experimental and clinical studies in humans, demonstrates that activation of the medial olivocochlear (MOC) efferent system, by either contralateral sound or electrical stimulation, can produce significant alterations in cochlear function and suggests a role for the MOC system in influencing the auditory behavior of binaural hearing. The present data are from psychophysical studies in nonhuman primates which seek to determine if the noted physiological changes in response to contralateral acoustic stimulation have a perceptual counterpart. Four juvenile Japanese macaques were trained to respond to the presence of 1-s sinusoids, presented to the test ear, in an operant reinforcement paradigm. Thresholds were compared for frequencies ranging from 1.0 to 4.0 kHz in quiet, with thresholds measured when continuous, two octave-band noise, centered on the test tone frequency, was presented in the contralateral ear. Contralateral noise was presented at levels of 10-60 dB above detection threshold for the test-tone frequency. While some variability was evident across subjects, both in the frequency distribution and magnitude (as a function of contralateral noise level), all subjects exhibited an increase, or suppression of thresholds in the presence of contralateral noise. On average, thresholds increased systematically with contralateral noise level, to a peak of 7 dB. In one subject, the threshold increase seen with contralateral noise was significantly reduced when the MOC was surgically sectioned on the floor of the IVth ventricle. The characteristics of the measured shifts in behavioral thresholds, in the presence of contralateral noise reported here, are qualitatively and quantitatively similar to both efferent physiological suppression effects and psychophysical central masking threshold shifts which have been reported previously. These data suggest that at least some aspects of "central masking" are efferent-mediated peripheral processes, and that the term "central masking" may be incorrect.     

Cryopreservation of the australian species Macropidia fuliginosa (Haemodoraceae) by vitrification

Somatic embryos were used to develop a cryopreservation protocol for Macropidia fuliginosa, a commercially-important species endemic to the south-west of Western Australia. Somatic embryos were allowed to develop from embryogenic callus for three weeks on an kinetin medium prior to processing. These were transferred and cultured on a agar solidified basal medium supplemented with 0 to 0.6 M sorbitol for 2 d prior to incubation in Plant Vitrification Solution Two (PVS2). Following this, embryos were then washed in 1 M sucrose solution (treated controls) or cooled in liquid nitrogen (LN). Cooled embryos were then warmed and washed in sucrose solution. Highest survival for cooled treatments (67.3%) was achieved by preculture with 0.4 M sorbitol, then incubation in PVS2. Further experimentation varying pre-culture duration (2 or 3 d) and incubation on either glycerol (0.8 M) or sorbitol (0.4 M) indicated that very high survival (90.6%) of embryos was achievable by adopting a 2 d preculture period on 0.8 M glycerol. The phenotype and growth rates of plants obtained using this protocol were similar to those of parent plants. This optimised procedure was then applied to tissue culture-derived shoot apices of the same clone also resulting in a high survival rate (84.4%).     

High-energy, high-power ytterbium-doped Q-switched fiber laser

We report on a Q -switched, cladding-pumped, ytterbium-doped large-mode-area fiber laser operating at 1090 nm that is capable of generating 2.3 mJ of output pulse energy at a 500-Hz repetition rate and more than 5 W of average output power at higher repetition rates in a high-brightness beam (M(2) = 3) . Using a similar fiber with a smaller core, we generated >0.5-mJ pulses in a diffraction-limited beam. Our results represent a threefold increase in pulse energy over previously published values for Q-switched fiber lasers and firmly establish fiber lasers as compact, multiwatt, multimillijoule pulse sources with large scope for both industrial and scientific applications.     

Probing the substrate specificity of the catalytically self-sufficient cytochrome P450 RhF from a Rhodococcus sp

Analysis of the substrate specificity of the self-sufficient cytochrome P450 RhF revealed that the enzyme tends to catalyse the dealkylation of substituted alkyl-aryl ethers with shorter alkyl moieties more readily than equivalent compounds with longer alkyl groups.     

High-throughput approaches for the discovery and optimization of new olefin polymerization catalysts

The discovery of new olefin polymerization catalysts is currently a time-intensive trial-and-error process with no guarantee of success. A fully integrated high-throughput screening workflow for the discovery of new catalysts for polyolefin production has been implemented at Symyx Technologies. The workflow includes the design of the metal-ligand libraries using custom-made computer software, automated delivery of metal precursors and ligands into the reactors using a liquid-handling robot, and a rapid primary screen that serves to assess the potential of each metalligand-activator combination as an olefin polymerization catalyst. "Hits" from the primary screen are subjected to secondary screens using a 48-cell parallel polymerization reactor. Individual polymerization reactions are monitored in real time under conditions that provide meaningful information about the performance capabilities of each catalyst. Rapid polymer characterization techniques support the primary and secondary screens. We have discovered many new and interesting catalyst classes using this technology.     

Design, synthesis, and biological evaluation of platensimycin analogues with varying degrees of molecular complexity

The molecular design, chemical synthesis, and biological evaluation of two distinct series of platensimycin analogues with varying degrees of complexity are described. The first series of compounds probes the biological importance of the benzoic acid subunit of the molecule, while the second series explores the tetracyclic cage domain. The biological data obtained reveal that, while the substituted benzoic acid domain of platensimycin is a highly conserved structural motif within the active compounds with strict functional group requirements, the cage domain of the molecule can tolerate considerable structural modifications without losing biological action. These findings refine our present understanding of the platensimycin pharmacophore and establish certain structure-activity relationships from which the next generation of designed analogues of this new antibiotic may emerge.     

Dilithium tetrabromonickelate (II) as a source of soft nucleophilic bromide : Reaction with epoxides

Dilithium tetrabromonickelate (II) in THF serves as a source of “soft” nucleophilic bromide and reacts regioselectively with epoxides to give bromohydrins in high yield.     

Anion sensing 'venus flytrap' hosts: a modular approach

A series of podands based on three hydrogen bonding 'arms' have been prepared and their affinities for simple inorganic anions measured.