Orienting reflex: "targeting reaction" and "searchlight of attention"

The concept of orienting reflex based on the principle of vector coding of cognitive and executive processes is proposed. The orienting reflex to non-signal and signal stimuli is a set of orienting reactions: motor, autonomic, neuronal, and subjective emphasizing new and significant stimuli. Two basic mechanisms can be identified within the orienting reflex: a "targeting reaction" and a "searchlight of attention". In the visual system the first one consists in a foveation of a target stimulus. The foveation is performed with participation of premotor neurons excited by saccadic command neurons of the superior colliculi. The "searchlight of attention" is based on the resonance of gamma-oscillations in the reticular thalamus selectively enhancing responses of cortical neurons (involuntary attention). The novelty signal is generated in novelty neurons of the hippocampus, which are selectively tuned to a repeatedly presented standard stimulus. The selective tuning is caused by the depression of plastic synapses representing a "neuronal model" of the standard stimulus. A mismatch of the novel stimulus with the established neuronal model gives rise to a "novelty signal" enhancing the novel input. The novelty signal inhibits current conditioned reflexes (external inhibition) contributing to redirecting the behavior. By triggering the expression of early genes the novelty signal initiates the formation of the long-term memory connected with neoneurogenesis.     

Slow Relaxation Process in DNA

A dynamic transition at temperatures 200–230K is observed in manyhydrated bio-polymers. It shows up as a sharp increase of the mean-squaredatomic displacements above this temperature range. We present neutronscattering data of DNA at different levels of hydration. The analysis showsthat the dynamic transition in DNA is related to a slow relaxation processin the MHz-GHz frequency range. This slow relaxation process iscompletely suppressed in the dry DNA sample where no dynamic transitionwas observed. The nature of the slow process is discussed. We ascribe it toa global relaxation of DNA molecule that involves cooperative motion ofmany base-pairs and backbone.     

Stability of microbial association in the process of industrial biofiltration cleaning of gaseous discharges

Results of industrial exploitation of a biofiltration plant tailored for purifying gaseous discharges of hazardous organic components such as toluene, cyclohexane, and xylene, are examined. Both numerical and compositional variations were monitored for a long-term (more than 1.5 years) utilization process in an association of microorganisms decomposing organic pollutants. A population of microbial association composed by one yeast and two bacterial strains in the biofilm on the surface of filtering sheets was abundant (10(8)-10(9) yeast cells/cm2 and 10(10)-10(11) bacterial cells/cm2) and stable during the whole period of monitoring. A microbial association in the culture medium averaging 10(6) yeast cells/l and 10(8) bacterial cells/l is more susceptible to technogenic impacts and seasonal fluctuations. Overall, the biofilter as an open and autonomic system maintained its microbial association, thereby providing a high-degree (93-98%) purification of industrial gaseous discharges from organic pollutants.     

Massive light-driven translocation of transducin between the two major compartments of rod cells: a novel mechanism of light adaptation

We report a new cellular mechanism of rod photoreceptor adaptation in vivo, which is triggered by daylight levels of illumination. The mechanism involves a massive light-dependent translocation of the photoreceptor-specific G protein, transducin, between the functional compartments of rods. To characterize the mechanism, we developed a novel technique that combines serial tangential cryodissection of the rat retina with Western blot analysis of protein distribution in the sections. Up to 90% of transducin translocates from rod outer segments to other cellular compartments on the time scale of tens of minutes. The reduction in the transducin content of the rod outer segments is accompanied by a corresponding reduction in the amplification of the rod photoresponse, allowing rods to operate in illumination up to 10-fold higher than would otherwise be possible.     

The reconstruction of the perceptual spaces of brightness and color on the basis of visual evoked potentials and their comparison with the data from behavioral trials

The visual evoked potentials to a change in color stimuli were studied. The amplitude of the N85 component was correlated with color discrimination. In cases when the brightness of one color was fixed and that of the other one changed, the amplitude dynamics of N85 was V-shaped with the minimum corresponding to the point of equal brightness of both colors. The N85 amplitude in this point serves as a measure of discrimination between stimuli chromaticity. The perceptual color space in rabbit (possessing two cone pigments) was constructed in accordance with the amplitudes of N85 to color change. This space represented a hypersphere in the four-dimensional Euclidean space. The perceptual spaces for brightness and color reconstructed on the basis of conditioning probabilities and N85 amplitudes evoked by replacement of colored and achromatic stimuli were shown to coincide. This suggests the common mechanism of the vector color coding.     

The connection of visual evoked potentials with the subjective differences between emotional expressions of the "schematic face"

Human cortical visual potentials (VEP) were studied to obtain electrophysiological data concerning face discrimination and to compare them with the direct estimates of differences between faces obtained in the previous publications. The present schematic faces varied in curvature of a mouth and/or declination of eyebrows. These features determined the emotional expression of the schematic faces. We recorded the VEP as the response to the instant replacement of one schematic face (referent stimulus) by an other one (test stimulus) rather then to presentation of a single stimulus. Thus we recorded direct electrophysiological differences between schematic faces. A characteristic feature of this approach was the application of the set of functionally connected test stimuli with monotonously increasing values of differences between the referent and test stimuli. In a result of analysis the complex of components P120-N180-P230 in sites O1, O2, P3, P4, T5, T6 was described. Interpeaks amplitudes of the components shows high correlations with subjective differences between the same pairs of stimuli as well as with physical (configurative) differences between stimuli measured as the angles of lines, defining curvature of a mouth and a declination of eyebrows. The highest correlation with subjective estimates of emotional differences between faces was shown by interpeaks amplitudes N180-P230 in sites O1 and P3. In the some time the interpeaks amplitudes P120-N180 in sites O1 and T5 reflected highest correlation between configurative measures and subjective estimates of stimuli differences.     

A new inhibitor of pyrimidine phosphorylase

5,5-Bis(hydroxymethyl)-2-oxo-[1-(2-trifluoromethyl)-3,3,3- trifluoropropionamido)-1-trifluoromethyl-2,2,2-trifluoroethyl- 1,3,2-dioxaphosphan (CA-423) is an in vitro inhibitor of the Escherichia coli uridine and thymidine phosphorylases. Unlike widely studied nucleoside analogues, this compound binds to the enzymes irreversibly. Its LD50 in mice was 40 mg/kg. Due to the involvement of pyrimidine phosphorylases in carcinogenesis and the relatively low toxicity of CA-423, it is promising for anticancer therapy.     

Influence of sodium concentration on changes of membrane capacitance associated with the electrogenic ion transport by the Na,K-ATPase

Electrogenic ion transport by the Na,K-ATPase was investigated in a model system of protein-containing membrane fragments adsorbed to a lipid bilayer. Transient Na⁺ currents were induced by photorelease of ATP from inactive caged ATP. This process was accompanied by a capacitance change of the membrane system. Two methods were applied to measure capacitances in the frequency range 1 to 6000 Hz. The frequency dependent capacitance increment, ΔC, was of sigmoidal shape and decreased at high frequencies. The midpoint frequency, f ₀, depended on the ionic strength of the buffer. At 150 mm NaCl f ₀ was about 200 Hz and decreased to 12 Hz at high ionic strength (1 M). At low frequencies (f≪f ₀) the capacitance increment became frequency independent. It was, however, dependent on Na⁺ concentration and on the membrane potential which was generated by the charge transferred. A simple model is presented to analyze the experimental data quantitatively as a function of two parameters, the capacitance of the adsorbed membrane fragments, C _P, and the potential of maximum capacitance increment, ψ ₀. Below 5 mm Na⁺ a negative capacitance change was detected which may be assigned to electrogenic Na⁺ binding to cytoplasmic sites. It could be shown that the results obtained by experiments with the presented alternating current method contain the information which is determined by current-relaxation experiments with cell membranes. Received: 3 November 1997 / Revised version: 19 February 1998 / Accepted: 21 February 1998