Spread of fast thermowaves through the cerebral cortex produced by visual stimulation

Thermowaves spreading through the cerebral cortex were observed and investigated during acute experiments on white rats using a new technique — that of thermoencephaloscopy (TES) through the intact skull. These waves were induced by regular visual stimulation (at intervals of 1.5–3 min) or by initiating one of the flashes and spread through the cortex along trajectories of five basic types; amplitude of thermowaves: 0.005–0.1°C; length: 10–15 mm; duration 1.2–11.4 sec; velocity: 1–33 mm/sec; extent of pathway: 2–56 mm. They appeared with a high degree of probability (of 0.92) during the interval between 15 sec before and 26 sec after the flash. Numbers of moving waves declined by the point of stimulus application and rose by 7–8 sec after the flash. Waves arose in 50% of cases in the contralateral visual cortex (areas 17 and 18a), spreading to the midline and crossing to the ipsilateral hemisphere (areas 17, 18a, and 7). Local waves moving along a circular trajectory were also discovered in the contralateral visual cortex. Several types of wave, differing in trajectory, also arose in the ipsilateral visual cortex. Mechanisms and possible significance of this effect are examined.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 4, pp. 467–475, July–August, 1989.     

Isolation and characteristics of endonuclease tightly bound to alpha-polymerase from the rat liver

Three major polypeptides are found in purified DNA polymerase alpha from rat liver: 160, 77 and 58 kDa. The electrophoretic analysis has identified polypeptide 160 kDa as the catalytically active subunit of DNA polymerase alpha. The other two polypeptides showed no DNA polymerase activity. Individual polypeptide p77 kDa purified by sodium dodecyl sulfate polyacrylamide gel electrophoresis was used to produce antibodies in rabbits. Immunoblot analysis indicated that the complex DNA polymerase alpha-3'-5'-exonuclease contained polypeptide p77 kDa. To elucidate the function of the p77 kDa protein we have prepared an immunoabsorbent column with antibodies against the p77 kDa polypeptide. The antibody column purified p77 kDa protein was homogeneous according to sodium dodecyl sulfate gel electrophoresis. The activity of alpha-polymerase was increased approximately 10-fold as a result of purification of DNA polymerase alpha from the p77 kDa protein. The in vitro experiments showed the identity of the p77 kDa polypeptide to endonuclease. It cleaved both single-stranded and double-stranded DNA. The function of endonuclease p77 kDA in complex with DNA polymerase alpha remains obscure.     

Stability of multienzyme systems with feedback regulation: a graph theoretical approach

Stability of multienzyme systems with feedback regulation has been analyzed on the basis of the Lienard-Chipart criteria. The rules governing the topological graph construction for multienzyme systems have been developed. A theorem about correspondence of the graph constructed and coefficients of the characteristic polynomial of linearized kinetic equations is proved. The graph-theoretical stability analysis proposed is illustrated by a number of examples of multienzyme systems with feedback regulation.     

Telomeres and P-element of Drosophila melanogaster contain sequences that replicate autonomously in Saccharomyces cerevisiae

Summary We have isolated restriction fragments from a shotgun collection of Drosophila DNA which function as autonomously replicating sequences (ARS) in Saccharomyces cerevisiae and hybridize with telomeric regions of the 2L, 2R, 4, and X chromosomes. In an independently obtained set of D. melanogaster clones five fragments hybridize in situ with telomeres and a number of internal sites. Two of them also contain ARSs. A Drosophila mobile P-element also possesses ARS activity in yeast.     

Different properties of two groups of orientation discriminators in the cat visual cortex

The properties of 149 neurons, divided into two groups, were investigated during acute experiments on immobilized cats. These consisted of "timers" (37%) in which latency of response and time taken for reaction to peak changed in an orientation range of not more than 10 msec. The remaining 63% consisted of "scanners" [2]. "Timers" reliably differed from "scanners" in their shorter latent periods, rising time of discharge rate, duration of response, and higher rate of impulsation at all orientations of the stimulus. "Scanners" display greater orientational tuning and "scan" much more frequently throughout the orientation range. The pattern of acuity of orientational tuning is counterphasic during response in neurons of these two groups, while the distribution of their preferred orientation is complementary in nature. Both timers and scanners were found in the orientation columns of the visual cortex on most occasions, with the latter predominating. Columns consisting of only timers or scanners were met with more seldom. The significance of the differences between the properties of the two groups of neurons in the visual cortex is discussed with a view to orientational discrimination.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 1, pp. 85–92, January–February, 1986.     

Characteristics of dynamic reorganization of receptive fields of cortical and geniculate visual neurons of cat in response to changes in photic stimulation parameters

The effect of parameters of local photic stimulation of different points of the receptive field on the characteristics of dynamic reorganization of receptive fields of cortical and geniculate visual neurons within microintervals of time observed previously was studied in computer-controlled experiments on unanesthetized, curarized cats. Dependence on the degree of widening of the receptive field and the temporal characteristics of this process on the background illumination level, intensity, contrast, area, duration, energy, and orientation of a local rectangular or circular photic stimulus flashing in random order at 100 points of the tested part of the visual field was studied. It was concluded that the background illumination level and the intensity, size, duration, and orientation of the stimulus have a specific effect on dynamic reorganization of the receptive field. The effects of all the parameters studied on the dynamics of the receptive field were shown to be nonlinear functions with optimal values that differed for different cells. The possible functional role of this effect and also the probability that it may participate in information coding in the visual system are discussed.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 15, No. 4, pp. 339–346, July–August, 1983.     

Orientation selectivity of visual cortical neurons at different stimulus intensities in cats

Orientation selectivity of 24 neurons in area 17 of the visual cortex at different intensities of test bars of light, flashing against a constant light background in the center of the receptive field, was investigated in acute experiments on immobilized cats. Five neurons were invariant in orientation tuning to stimulus intensity (contrast): Although the magnitude of the response and acuteness of orientation selectivity were modified, preferential orientation was unchanged. More than half of the cells studied (13) were classed as noninvariant, for their preferential orientation was significantly shifted by 22–90° with a change in contrast. Small shifts of the peak of orientation selectivity, not statistically significant, were observed for the other neurons. Invariant neurons, unlike noninvariant, were characterized by preferential horizontal and vertical orientation, a lower frequency of spontaneous and evoked discharges, and the more frequent presence of receptive fields of simple type. The mechanisms of the change of orientation selectivity during contrast variation and also the different use of the two types of cells in orientation detection operations are discussed.     

Dynamics of orientational tuning of feling visual cortex neurons under the effects of sombrevine

Dynamics of orientational tuning in 59 primary visual cortex neurons were investigated before and after sombrevine-induced anesthesia during acute experiments on immobilized cats using temporal slice techniques. A dynamic shift in preferred orientation of a flashing light strip, during which peak amplitude of spike discharges was noted (at an angle of between 22 and 157°) occurred as response developed in two-thirds of the cells. We had previously named this effect "scanning the orientational range" [9]. Scanning declined significantly in 45% of the sample, culminating in complete disappearance of this effect in some cells following sombrevine action. Scanning intensified in 30%, while dynamics of tuning remained unchanged in 25% of units. Sombrevine administration induced change in the preferred stimulus orientation of 60% of the neurons (referred to as "unstable" cells) and remained constant in "stable" cells (= 40%). Dynamic changes in preferred stimulus orientation were 2.5 times as high as those of stable cells in the waking state. The scanning effect declined significantly in 60% of "unstable" neurons under the action of anesthesia and remained unchanged in not more than 6%. At the same time, orientational tuning did not alter in the "stable" cell group in 46% of units, either declining (25%) or increasing (29%) in the remaining scanning ranges.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 1, pp. 107–113, January–February, 1990.     

Tuning for cruciform stimuli in visual cortex neurons of cat

In the primary visual cortex of an immobilized awake cat, nearly one-third of the neurons studied (8 out of 22) were found to respond to flashing cruciform light stimuli 1.5–4 times better than to single stimulations with the strips of preferred orientation. It is suggested that such neurons can detect angles and line intersections.Neirofiziologiya/Neurophysiology, Vol. 25, No. 5, pp. 362–364, September–October, 1993.