Synaptic depression and short-term habituation are located in the sensory part of the mammalian startle pathway

Background  

Short-term habituation of the startle response represents an elementary form of learning in mammals. The underlying mechanism is located within the primary startle pathway, presumably at sensory synapses on giant neurons in the caudal pontine reticular nucleus (PnC). Short trains of action potentials in sensory afferent fibers induce depression of synaptic responses in PnC giant neurons, a phenomenon that has been proposed to be the cellular correlate for short-term habituation. We address here the question whether both this synaptic depression and the short-term habituation of the startle response are localized at the presynaptic terminals of sensory afferents. If this is confirmed, it would imply that these processes take place prior to multimodal signal integration, rather than occurring at postsynaptic sites on PnC giant neurons that directly drive motor neurons.     

Measurements of hyperon semileptonic decays at the CERN Super Proton Synchrotron

The charged hyperon beam at the CERN Super Proton Synchrotron (SPS) has been used to collect data on semileptonic decays of Σ^?, Ξ^?, andΛ. A magnetic channel selected 100 GeV/c negatively charged particles produced in the forward direction by interaction of a 210 GeV/c proton beam on a BeO target. The Σ^? and Ξ^? hyperons were concurrently identified in a DISC ?erenkov counter, and their decay products were analysed by a magnetic spectrometer. Electron-hadron discrimination was achieved by the combined use of lead glass and lead/scintillator counters, transition radiation detectors, and a ?erenkov counter. In this article we report results on the \(\Xi \to \Lambda \pi (\Lambda \to pe\bar v), \Xi \to \Lambda e\bar v(\Lambda \to p\pi ),\) and \(\Xi \to \sum ^0 e\bar v(\sum ^0 \to \Lambda \gamma ) (\Lambda \to p\pi )\) decay modes. Samples of 7,111 \(\Lambda \to pe\bar v, 2,608 \Xi \to \Lambda e\bar v\) , and \(154 \Xi \to \Sigma ^0 e\bar v\) were used in our analysis. The branching ratio measurements gave values of (8.57±0.36)×10^?4, (5.64±0.31)×10^?4, and (0.87±0.17)×10^?4 for \(\Lambda \to pe\bar v, \Xi \to \Lambda e\bar v\) , and \( \Xi \to \sum ^0 e\bar v\) , respectively. Measurements of the Λ polarization and of the centre-of-mass distributions yield the axial vector to vector form factor ratio,g ₁/f ₁=+0.70±0.03 for \(\Lambda \to pe\bar v\) , andg ₁/f ₁=+0.25±0.05 for \(\Xi \to \Lambda e\bar v\) . The effects ofq ²-dependence off ₁ andg ₁ and of radiative corrections, the measurement of the weak magnetism termf ₂, and the effect of possible second-class current terms are discussed. Results on the \(\sum \to \Lambda e\bar v\) and \(\sum \to ne\bar v\) decay modes are reported in separate articles.     

Koordinationschemie funktioneller phosphorylide: III. Neue mangan- und rhenium-komplexe mit triphenylphosphonio-alkandithiocarboxylat-liganden

As strong nucleophiles, phosphorus ylids easily attack heteroallenes. The addition of isopropylidene triphenylphosphorane to carbon disulfide yields the zwitterionic adduct Ph₃PCMe₂CS₂^?, which reacts to bis(isopropylidene)-1,2,4-trithiolane by thermal or, coordinated to transition metals, photochemical activation according to a cycloaddition mechanism. By reaction of the betaine with manganese and rhenium carbonyl halides under exclusion of light, stable monomeric and dimeric fac-tricarbonyl complexes with the composition (CO)₃M?(X)S₂CCMe₂PPh₃ (M = Mn, Re; X = Cl, Br) are obtained which are distinguished by their spectra (IR, NMR, UV). The monomeric bromomanganese and -rhenium complexes are isomorphous and crystallize in the space group P2_frcase1/c (monoclinic, Z = 4).     

Degradation kinetics of the Alternaria mycotoxin tenuazonic acid in aqueous solutions

The degradation kinetics of the Alternaria mycotoxin tenuazonic acid (l-TA) in aqueous buffer were studied over a period of 4 months at different pH levels (3.5 and 7.0) and temperatures (4, 25 and 40 °C). l-TA and its degradation products were quantified by newly developed high-performance liquid chromatography methods with UV or electrospray multistage mass spectrometry detection. At pH 3.5, significant degradation occurred at 25 and 40 °C, the respective l-TA half-lives being 73.8 ± 0.4 and 14.0 ± 0.1 days. Two degradation processes, epimerization and hydrolysis, were evaluated kinetically. The hydrolytically formed iso-deacetyl TA (iso-DTA, epimeric mixture) was found to be the stable end product of l-TA degradation under the conditions of this study. This indicates that iso-DTA as well as the l-TA epimer u-TA are formed in aqueous beverage matrices.     

Optical coherent transient continuously programmed continuous processor

A novel technique for continuously programming an optical coherent transient spatial-spectral signal processor is proposed. The repeated application of two spatially distinct optical programming pulses to a nonpersistent hole-burning material writes an accumulated spatial-spectral population grating. An optical data stream is introduced on a third beam, resulting in a processor output signal that is spatially distinct from all the input pulses. Programming and processing take place simultaneously, asynchronously, and continuously. In the case of true-time delays, the efficiency that is achievable with currently available materials is of the order of that predicted for a perfect photon-gated device.     

Process parameters and their effect on grafting reactions in core/shell latexes

The grafting of methyl methacrylate (MMA) onto polybutadiene (PB) latexes prepared by seeded emulsion polymerization at 50°C was investigated as a function of: (a) initiator concentration used in the secondary polymerization, (b) monomer-to-polymer ratio, (c) the specific surface area of the seed latex, and (d) the degree of conversion. The thin layer chromatography/flame ionization detection (TLC/FID) technique was used to determine the proportion of graft copolymer in the core/shell latex, It was found that grafting PMMA onto PB depended upon the concentration of initiator, decreasing as the concentration was increased. The amount of grafting increased with increasing specific surface area of the seed latex, while the molecular weight of the acetone-soluble graft copolymer decreased. The amount of graft copolymer was found to decrease concurrently with increasing monomer-to-polymer ratio and degree of conversion. These results suggest a hydrogen abstraction mechanism in the formation of graft PB–PMMA through a chain transfer process.     

The orientational order parameters of a dendritic liquid crystal organo-siloxane tetrapode oligomer, determined using polarized infrared spectroscopy

The observed macroscopic anisotropic properties such as the components of infrared (IR) absorbances of liquid crystals are expressed in terms of the order parameters of the long molecular axis, molecular, and phase biaxiality. The order parameters of the organo-siloxane tetrapode liquid crystal of zero dendritic order (G0) in its nematic and smectic phases have been determined using results of the polarized IR spectroscopic measurements on a planar homogenously and hometropic aligned cells. The spatial components of the absorbances for the vibrational bands (in the mesogenic unit, terminal chains, and spacer) have been measured and analyzed. For the laboratory reference system, the apparent orientational order parameter S of the mesogen unit shows a significant drop in the transition from the nematic to the smectic phase while the phase biaxiality order parameter P increases to almost 0.4 in the smectic phase. This result shows that the director is tilted out of the sample plane in the smectic phase. The molecular biaxiality parameter D is found to be positive both for the nematic and smectic phases. This suggests that the carbonyl dipoles are oriented close to the tilt plane. For the vibrational bands in the chains, low values of S and D indicative of their low orientational order are obtained. As a result of the interaction among the molecules in the tilted smectic phases, the transition dipoles show positive correlations for the transversal and negative for the longitudinal dipoles.