[Electrodynamics of interactions in electrolyte solutions and their biological significance].

Attention is drawn to the fact that the interaction of charges in aqueous solutions of electrolytes, such as media having physiological characteristics, depends not only on the distance between interacting charges but also on the frequency that determines their dynamics. This fact has significant consequences for some biological processes and their kinetics. The analysis of reasons for charge shielding, including the dynamic effects, shows that, even at distances exceeding the Debye length, electric interactions in systems similar to physiological are effective provided that charges move with frequencies higher than 250 MHz. For each electrolyte solution, the threshold frequency (Maxwell frequency) can be found, which determines the transition from the conducting to the dielectric mode of interactions of charges in physiological solutions.

[Visual evoked potentials in rabbit's visual cortex reflect variations in orientation and intensity of lines].

Amplitude variations of visual evoked potentials (VEP) in rabbit were studied using changes of three types of stimuli: lines with different orientations (0-90 degree) but constant in intensity, lines with different intensities but constant in orientation, and complex stimuli with different intensities and different orientations. Factor analysis of component N85 of VEP to stimuli with varying orientation and constant intensity revealed two-dimensional sensorial space of orientations. Also, the two-dimensional achromatic sensorial space was revealed for stimuli different only in intensities. In experiments with complex stimuli, two versions of stimulation were used. In the first version, four stimuli with varying orientation from 0 to 38.58 degrees were of 5 cd/m2 in intensity, the remaining four stimuli (from 51.44 to 90 degrees) were of 15 cd/m2 in intensity. In the sensorial space, stimuli with different intensities were disposed on the plane formed by the first two significant factors in the opposite quadrants, whereas within each quadrant, stimuli were arranged according to their orientation from minimum to maximum degrees. It is suggested that, in this version of stimulation, the interaction between two characteristics (intensity and orientation) took place with clear-cut dominance of the factor of intensity. In the second version of the experiments, also eight complex stimuli were used. Each stimulus was characterized by specific combination of orientation (one of the eight directions in the range from 0 to 90 degrees) and intensity (one of the eight intensities in the range from 5 to 21 cd/m2). Three or four significant factors were revealed in each test. Only the plane of intensity of sensorial space (XIX2) formed by two significant factors was revealed in the overwhelming majority of cases. On this plane, stimuli were arranged according to their intensities. This fact can be explained by specific (twilight) type of rabbit's vision with predominant discrimination of intensities. However, some findings suggest that visual evoked potentials reflect simultaneous processing of two characteristics of visual stimuli (intensity and orientation) being indicative of a possibility of the complex stimuli analysis in the primary visual cortex.

Effect of Triton X-100 on the physical properties of liposomes.

The interaction of the nonionic detergent Triton X-100 with phospholipid bilayers of liposomes made of egg yolk phosphatidylcholine was studied through the behavior of several physical properties. The dielectric permittivity spectra between 30 kHz and 13 MHz, the viscosity, the density, and the d.c. conductivity (1 kHz) of aqueous liposomes suspensions at various mole ratios were measured at 22 degrees C. For detergent-to-phospholipid ratios lower than 3, a dielectric relaxation process of characteristic frequency of about 50 kHz was recorded. This process does not appear for the liposomes in water, and becomes smaller and smaller for detergent-to-phospholipid ratios higher than 3. The viscosity of these suspensions showed a biphasic behavior, being remarkably increased by the detergent for concentration ratios lower than 3. The measured d.c. conductivity of these samples showed no relation with this process, being slightly increased when the detergent content is increased. As a conclusion of these results a well defined concentration range appears where the phospholipid organization changes forming highly asymmetrical structures.

Electric birefringence as a means of studying the effect of anaesthetics on liposomes.

Birefringence can be induced in liposome suspensions using electric fields. The fields interact predominantly with anisotropic electrical polarisabilities which give rise to induced dipole moments. Using pulsed electric fields, the optical and electrical polarisabilities and the geometrical size of the liposomes can be measured simultaneously. These parameters have been found to be very sensitive to the presence of small amounts of fluidising additives of polar and ionic nature. Illustrative data are presented for the influence of the amines ammonium chloride, methyl ammonium chloride and lignocaine and of benzyl alcohol on phosphatidylcholine/serine liposomes. Structural changes in the vesicle membranes were detected, which appeared to correlate with the biological functions, thus indicating that electric birefringence is a rapid and useful method for studying interactive phenomena in lipid membrane systems.

Effect of additives on liposomes: an electric birefringence study.

Under the influence of an electric field, vesicles in suspension partially deform or orientate, rendering the medium optically birefringent. The amplitudes of the birefringence under fields of variable amplitude lead to evaluation of the anisotropy of the electrical delta alpha and optical delta G polarisabilities of the vesicles. By using pulsed fields, rates of establishment and decay of birefringence enable vesicle sizes d to be measured. Samples of 9:1 phosphatidylcholine-phosphatidylserine liposome suspension in water were studied in the presence of various additives, including sucrose, an antibiotic (streptomycin), a steroid (dexamethasone), an anaesthetic (lignocaine) and a fluidising agent (benzyl alcohol). The changes in the three parameters delta alpha, delta G and d were different for each additive and are thought to be indicative of the mode of interaction of each. Electric birefringence also appears to be a rapid means of detecting structure changes.

[The perceptive color space of the rabbit]. / Pertseptivnoe tsvetovoe prostranstvo krolika.

Discrimination of colors was studied using instrumental learning paradigm in three rabbits (Oryctolagus cuniculus). The rabbits were able to discriminate all but red stimuli by their color. The red stimulus could not be discriminated from the black one. The confusion matrix composed of probabilities of instrumental reactions was subjected to factor analysis in order to reveal the basic axes of the color perceptual space. The four-dimensional spherical structure of perceptual color space was obtained, which was different from that of trichromatic species in a reduction of color axes in red and yellow parts. The evidence characterizes rabbit as a protanopic animal.

[The discrimination by the rabbit of light intensities and the plotting of its achromatic space]. / Razlichenie krolikom intensivnostei sveta i postroenie ego akhromaticheskogo prostranstva.

Elaboration of differential instrumental conditioned reflexes in rabbits showed that probabilities of responses to differential stimuli were inversely related to differences in intensity between conditioned and differential stimuli. Factor analysis of a response probability matrix revealed two orthogonal axes. They could be interpreted as the axes of brightness and darkness in achromatic space of a rabbit. Lights of different intensities were located on a semicircle in accordance with their intensities. The experiments imply that light intensities are coded by excitation vectors composed of responses of brightness and darkness neurons.

[Effects of the intersensory action of sound on the performance of a simple motor reaction to light in the cat]. / Effekty mezhsensornogo deistviia zvuka na vypolnenie prostoi dvigatel'noi reaktsii koshki na svet.

In 6 alert cats, placing responses to light and their latencies with added sound stimuli were investigated. The latency recovery cycles demonstrated that in cases of sound-light intervals 750-0 ms and light-sound intervals 0-75 ms the latencies to light were reduced, the maximum of this effect being at sound-light intervals 250-200 ms. Latency to light was enhanced at light-sound intervals 100-350 ms, the maximum being at 100-200 ms. Spatial location of sound source affected the latencies: when the sound source spatially coincided with the light source, the effect of latency shortening was most obvious.

[The effects of electric stimulation of the visual cortex of the cat in a behavior model of placing reaction]. / Effekty élektricheskogo razdrazheniia zritel'noi kory mozga koshki na povedencheskoi modeli postanovki lapy na oporu.

In 5 alert cats, the dependence of latency and probability of placing reaction on the parameters of electrical stimulation of visual cortex (the pulse duration and frequency in a series, number of pulses in a series) was studied. The values of current parameters were analogous to those that aroused human phosphens. The results revealed the conformity of the dependence of phosphens and cat's motor reaction on the current parameters. An addition of sound or electrocutaneous stimuli to the current stimulation decreases the threshold of the motor reaction and increases its probability. It is particularly obvious in case of weak and middle intensity currents when the probability of correct reactions to the current is insignificant.

[Transcutaneous electrostimulation of the primary elements of the visual system in children after the extraction of a congenital cataract]. / Chreskozhnaia élektrostimuliatsiia pervichnykh élementov zritel'noi sistemy u detei posle ékstraktsii vrozhdennoi katarakty.

Courses of transcutaneous electrostimulation of the visual analyzer periphery according to E. B. Kompaneets were administered to 31 children (56 eyes) aged 4 to 12 because of low vision acuity after congenital cataract extraction. The amplitude of stimulating pulses was from 150 to 400 microA. The first course consisted of 5-8 sessions, repeated courses of 4 sessions. The results were assessed by vision acuity check-ups and recordings of visual [correction of auditory] evoked potentials (AEP). Vision acuity improved from 0.1 to 0.9 after a course of treatment. AEP amplitude was reduced in all the patients to 15.4 microV on an average, the time of the pulse conduction in the auditory system was normal (113.2 ms). Electrostimulation effects on the AEP were negligible. Electrostimulation may be recommended to children with low vision acuity and low values of the AEP amplitude after congenital cataract extraction.

Ordered collagen membranes: production and characterization.

A collagen membrane with microscopic order is presented. The membranes were produced with acid-soluble collagen, using two different methods to obtain orientation. The product was characterized by mean of UV and IR spectra, scanning electronic microscopy, optical microscopy and laser diffractometry. The results clearly show a high level of order in the membranes obtained by both techniques. Permeability for rifamycin, ascorbic acid and NaCl was also measured. Due to the characteristics of the membranes, they have a potential application for treatment of surface injuries.

Evoked potentials in the rabbit visual cortex reflect changes in line orientation and intensity.

Changes in the amplitudes of evoked potentials in the visual cortex of conscious rabbits in response to substitution of flashing lines of different orientations (0-90 degrees ) but constant intensity were studied, along with interneurons of different intensities but constant orientation, and complex stimuli with simultaneous changes in flash orientation and intensity. Factor analysis of the results showed that analysis of the N85 peak of evoked potentials produced by substitution of stimuli with different orientations but constant intensity identified a two-dimensional sensory space for orientations. An achromatic sensory space was also detected using substitution of lines of different intensities but constant orientation. Substitution of complex stimuli involved two versions of the experiment. In the first version, four stimuli in the initial orientations (0-38.58 degrees ) had an intensity of 5 cd/m(2), the other stimuli (with orientations of 51.44-90 degrees ) were presented at an intensity of 15 cd/m(2). On the plane of the sensory space formed by the first two significant factors, stimuli with different intensities were located in different quadrants of the circle, while within the quadrants themselves, the stimuli were located in accord with their orientations, from lower values to greater. It is suggested that in this version, an interaction between orientation and intensity attributes was seen on the single plane of the sensory space, with a clear predominance of the intensity factor. The other experimental version also included eight complex stimuli, each complex having its own orientation (one of eight over the range 0-90 degrees ) and intensity (also one of eight, in the range 5-21 cd/m(2)). In all experiments involving substitution of complex stimuli, factor analysis identified three to four significant factors. In the vast majority of cases, only the sensory space plane X1, X2 was found, this being formed by two significant factors. On this plane, the stimuli were located in order of changes in intensity. This may be associated with the fact that rabbits are crepuscular animals, such that stimulus brightness is the most important attribute. However, in some cases, potentials in the rabbit brain also demonstrated simultaneous processing of two visual stimulus attributes, i.e., intensity and orientation. This may be evidence indicating analysis of complex stimuli in the primary visual cortex.

[Characteristics of the response of rabbit visual cortex neurons to intracortical electric stimulation]. / Kharakteristiki reaktsii neironov zritel'noi kory krolika na vnutrikorkovuiu élektricheskuiu stimuliatsiiu.

Responses of visual cortex neurons to single and rhythmical intracortical electrical stimulation were investigated in rabbits. Stimulating and recording electrodes were separated by 0.7-1.2 mm. Thresholds of responses to single stimuli were in general about 150-180 microA, to serial stimuli -- 30-60 microA. Latency of the first spike was 5-15 ms, but probability of discharge was very low (3-6%). The length of the inhibitory phrase in the response increased in a half of the investigated neurons with the increase in the stimulus strength. Spontaneous activity after a series of stimuli increased during 4-6 s. Repeated single stimuli induced in about a half of the investigated neurons the same types of dynamic modifications in activity, as those produced by light stimulation. However, in response to electrical stimulation more neurons developed discharge sensitization and less habituation. It is supposed that intracortical stimulation induces in the visual cortex excitation of local hypercolumns and inhibition of the neighbouring ones.