Electrochemical sensing telomere-bending motions caused by hTRF1

It has been reported that human telomeric repeat binding factor 1 (hTRF1) may cause telomeric DNA bent; however there is no direct evidence, thus controversy still exists. In this work, the interaction between hTRF1 and a simulated telomeric DNA was investigated by using electrochemical method. While the telomeric DNA was immobilized on a gold electrode surface, a guanine-quadruplex-hemin complex was linked at the end of the DNA to serve as an electrochemical signal reporter. If hTRF1 made the telomeric tracts bent, electrochemical response from "off" to "on" could be observed. Therefore, this electrochemical method could give direct evidence whether hTRF1 binding to telomeric DNA would induce a shallow distortion of the DNA molecules, and a new way to explore the structural information of telomere was also proposed in this paper.     

Spatio-temporally averaged positions of moving objects

This study investigated the case where a spatial offset was periodically and momentarily introduced between two vernier components during their excursion, to determine how such an offset affects the relative localization of the components. If the object in motion is perceived at a position averaged over a limited spatio-temporal range, spatial offsets in a moving vernier should be perceived accordingly. This prediction was confirmed by the outcome of the first experiment. A second experiment was performed to inquire into the relationship between vernier threshold and the averaging of spatial offset, and also the spatio-temporal limit of the integrative process. The upper temporal limit of the averaging was estimated to be about 50 ms, and the spatial extent of positional modulation was shown to have a significant effect on the detection of vernier offset. It was found that the larger the extent over which the vernier positions were distributed, the smaller the offset detected between them. It is suggested that spatial offset can be detected directly, perhaps by some mechanism sensitive to the phase relationship of the components of visual patterns.     

Computational model for perception of objects and motions

Perception of objects and motions in the visual scene is one of the basic problems in the visual system. There exist ‘What’ and ‘Where’ pathways in the superior visual cortex, starting from the simple cells in the primary visual cortex. The former is able to perceive objects such as forms, color, and texture, and the latter perceives ‘where’, for example, velocity and direction of spatial movement of objects. This paper explores brain-like computational architectures of visual information processing. We propose a visual perceptual model and computational mechanism for training the perceptual model. The computational model is a three-layer network. The first layer is the input layer which is used to receive the stimuli from natural environments. The second layer is designed for representing the internal neural information. The connections between the first layer and the second layer, called the receptive fields of neurons, are self-adaptively learned based on principle of sparse neural representation. To this end, we introduce Kullback-Leibler divergence as the measure of independence between neural responses and derive the learning algorithm based on minimizing the cost function. The proposed algorithm is applied to train the basis functions, namely receptive fields, which are localized, oriented, and bandpassed. The resultant receptive fields of neurons in the second layer have the characteristics resembling that of simple cells in the primary visual cortex. Based on these basis functions, we further construct the third layer for perception of what and where in the superior visual cortex. The proposed model is able to perceive objects and their motions with a high accuracy and strong robustness against additive noise. Computer simulation results in the final section show the feasibility of the proposed perceptual model and high efficiency of the learning algorithm.     

Spontaneous discrimination of possible and impossible objects by newly hatched chicks

Four-month-old infants can integrate local cues provided by two-dimensional pictures and interpret global inconsistencies in structural information to discriminate between possible and impossible objects. This leaves unanswered the issue of the relative contribution of maturation of biologically predisposed mechanisms and of experience with real objects, to the development of this capability. Here we show that, after exposure to objects in which junctions providing cues to global structure were occluded, day-old chicks selectively approach the two-dimensional image that depicted the possible rather than the impossible version of a three-dimensional object, after restoration of the junctions. Even more impressively, completely naive newly hatched chicks showed spontaneous preferences towards approaching two-dimensional depictions of structurally possible rather than impossible objects. These findings suggest that the vertebrate brain can be biologically predisposed towards approaching a two-dimensional image representing a view of a structurally possible three-dimensional object.     

Subcortical discrimination of unperceived objects during binocular rivalry

Rapid identification of behaviorally relevant objects is important for survival. In humans, the neural computations for visually discriminating complex objects involve inferior temporal cortex (IT). However, less detailed but faster form processing may also occur in a phylogenetically older subcortical visual system that terminates in the amygdala. We used binocular rivalry to present stimuli without conscious awareness, thereby eliminating the IT object representation and isolating subcortical visual input to the amygdala. Functional magnetic resonance imaging revealed significant brain activation in the left amygdala but not in object-selective IT in response to unperceived fearful faces compared to unperceived nonface objects. These findings indicate that, for certain behaviorally relevant stimuli, a high-level cortical representation in IT is not required for object discrimination in the amygdala.     

Behavioral discrimination of prey with various defense mechanisms by the lizardEumeces okadae

Predatory behavior of the lizardEumeces okadae upon 40 kinds of potential prey was observed under laboratory conditions. Prey items eaten byE. okadae were those having no particular defense mechanisms. Invertebrates with chemical repellants (phenol, alkaloids and cyanide), dense and long hairs around the body, and with lethal or poisonous bites were rejected. Sensory modalities for prey discrimination varied between the well eaten (preferred) and completely rejected (undesirable) prey. Almost all tasty prey were attacked on sight, while undesirable ones were rejected at various stages using visual and chemical senses. Despite the keen chemical prey discrimination ability inEumeces, this study demonstrated thatE. okadae did not always use chemical cues for prey discrimination. Fast predatory attacks immediately after visual discrimination are directed toward preferred and probably agile prey.     

Behavioral responses of Escherichia coli to changes in temperature caused by electric shock.

The behavioral response of Escherichia coli to electric shock in 10(-2) M potassium phosphate plus 10(-4) M potassium EDTA was studied. When presented with a 150-V/cm electric shock that lasted 250 ms, the bacteria at first exclusively ran, then exclusively tumbled, and finally returned to their original running and tumbling. This response is due to increased temperature caused by the electric shock, i.e., to thermotaxis, and it is mediated by the chemotaxis machinery. A more severe electric shock, 150 V/cm for 550 ms, caused cells to tumble immediately, and then they went back to their original running and tumbling. The mechanism of that response is unknown since, unlike known thermotaxis, it does not require the chemotaxis machinery.     

A simple strategy for detecting moving objects during locomotion revealed by animal-robot interactions

An important role of visual systems is to detect nearby predators, prey, and potential mates, which may be distinguished in part by their motion. When an animal is at rest, an object moving in any direction may easily be detected by motion-sensitive visual circuits. During locomotion, however, this strategy is compromised because the observer must detect a moving object within the pattern of optic flow created by its own motion through the stationary background. However, objects that move creating back-to-front (regressive) motion may be unambiguously distinguished from stationary objects because forward locomotion creates only front-to-back (progressive) optic flow. Thus, moving animals should exhibit an enhanced sensitivity to regressively moving objects. We explicitly tested this hypothesis by constructing a simple fly-sized robot that was programmed to interact with a real fly. Our measurements indicate that whereas walking female flies freeze in response to a regressively moving object, they ignore a progressively moving one. Regressive motion salience also explains observations of behaviors exhibited by pairs of walking flies. Because the assumptions underlying the regressive motion salience hypothesis are general, we suspect that the behavior we have observed in Drosophila may be widespread among eyed, motile organisms.     

Legionnaires' disease caused by Legionella dumoffii in distilled water.

Five cases of Legionnaires'' disease caused by Legionella dumoffii were identified within an 11-month period in a hospital in the Quebec City area. In four cases bacterial isolates were obtained from clinical specimens, and in one case seroconversion was demonstrated. All the patients had been admitted to hospital within 10 days before diagnosis. Two of the patients were immunosuppressed children. Only 1 of the 40 hot water samples from the hospital yielded L. dumoffii; however, 6 of 11 distilled water samples contained the bacterium. All the patients had been exposed to distilled water, four through respiratory therapy equipment and one through a room humidifier. Following the use of sterile distilled water in the apparatus, no further cases were identified. This is the first reported outbreak of Legionnaires'' disease caused by L. dumoffii, and it is the first time that nosocomial legionellosis has been linked to contaminated distilled water in Canada.     

Separate colour-opponent mechanisms underlie the detection and discrimination of moving chromatic targets.

Current opinion holds that human colour vision is mediated primarily via a colour-opponent pathway that carries information about both wavelength and luminance contrast (type I). However, some authors argue that chromatic sensitivity may be limited by a different geniculostriate pathway, which carries information about wavelength alone (type II). We provide psychophysical evidence that both pathways may contribute to the perception of moving, chromatic targets in humans, depending on the nature of the visual discrimination. In experiment 1, we show that adaptation to drifting, red-green stimuli causes reductions in contrast sensitivity for both the detection and direction discrimination of moving chromatic targets. Importantly, the effects of adaptation are not directionally specific. In experiment 2, we show that adaptation to luminance gratings results in reduced sensitivity for the direction discrimination, but not the detection of moving chromatic targets. We suggest that sensitivity for the direction discrimination of chromatic targets is limited by a colour-opponent pathway that also conveys luminance-contrast information, whereas the detection of such targets is limited by a pathway with access to colour information alone. The properties of these pathways are consistent with the known properties of type-I and type-II neurons of the primate parvocellular lateral geniculate nucleus and their cortical projections. These findings may explain the known differences between detection and direction discrimination thresholds for chromatic targets moving at low to moderate velocities.     

Responses of the goldfish head lateral line to moving objects

We investigated how fibers in the anterior lateral line nerve of goldfish, Carassius auratus, respond to water motions generated by an object that was moved alongside the fish. Motion direction was from anterior to posterior or opposite, object diameter was between 0.1 and 4 cm and the distance between object and fish varied between 1 and 6 cm. Fibers exhibited monophasic responses characterized by a transient increase in discharge rate, biphasic responses consisting of an increase followed by a decrease in discharge rate or vice versa, or triphasic responses characterized by a rate increase followed by a decrease and again an increase or by the inverse pattern. In two-thirds of the fibers response patterns depended on object motion direction. Of these, about 60% responded to a reversal of motion direction with an inversion of the response pattern. Our results differ from previous data obtained from posterior lateral line nerve fibers in the relative proportions of the observed response patterns, and by a much smaller proportion of fibers that exhibited a direction-dependent response. These differences can be explained by the fact that the spatial orientations of the neuromasts on the head are more heterogenuous than on the trunk.     

Responses of the goldfish trunk lateral line to moving objects

We recorded the responses of single afferent fibers in the posterior lateral-line nerve of the goldfish, Carassius auratus, to a small object moving in the water. Responses consisted of a dominant and reproducible pattern of discharge which was characterized by excitation followed by inhibition or vice versa. The pattern depended on the direction in which the object moved and was inverse when the direction was reversed. About half of the fibers continued to discharge bursts of spikes for a long time after the object had passed the fish. These spike bursts were not reproducible from one stimulus presentation to the next. In many fibers, the pattern of the response changed with speed and lateral distance of the moving object. Response strength increased with increasing object speed and decreasing lateral distance. Measurements of water motions revealed that the object generated complex water movements, aspects of which were reflected in the discharges of primary lateral-line afferents. The observed uniformity of the responses in the periphery suggests that many, but not all, of the response patterns of central lateral-line units to moving objects are due to additional information processing by the central nervous system and not to peripheral hydrodynamic effects. Accepted: 6 October 1997     

Human pressure perception values for constant and moving one- and two-point discrimination.

Despite the need to evaluate sensibility for accurate diagnosis and the need to record the degree of sensation achieved in the postoperative period, the clinician has been without the ability to measure human pressure perception accurately. Traditionally, the Semmes-Weinstein monofilaments were used to measure the static one-point discrimination threshold. A new sensory testing instrument, the Pressure-Specifying Sensory Device, was used to obtain normative data from the index and little finger of the dominant hand in 35 people ranging in age from 16 to 83 with no known neurologic impairment. Pressure perceptions for static one- and two-point discrimination (s1PD, s2PD) and moving one- and two-point discrimination (m1PD, m2PD) were recorded. The mean values (+/- SD) were 0.13 +/- 0.06, 0.24 +/- 0.12, 0.22 +/- 0.10, and 0.26 +/- 0.13 gm/mm2 for s1PD, s2PD, m1PD, and m2PD, respectively, on the index finger and 0.07 +/- 0.05, 0.16 +/- 0.12, 0.17 +/- 0.07, and 0.21 +/- 0.14 gm/mm2 for s1PD, s2PD, m1PD, and m2PD, respectively, for the little finger. The little finger was significantly more sensitive than the index finger (p less than 0.001). There was no significant change in pressure perception with increasing age.     

Behavioral interferences modify the acceleration in memory decay caused by diazepam

A staircase maze has been used to test the modification induced by a chronic administration of different doses of diazepam in the decay of the rat performance caused by an interruption of 20 days in the daily training. The possibility that behavioral interferences modify the diazepam effect has been examined by testing the rat in an open field or in a Y maze during the interruption of the training in the staircase maze. The diazepam effect on the rat behavior in the staircase maze increased linearly with the doses; an intercalated training in the open field increased the diazepam effect, while an intercalated training in a Y maze completely abolished the increase of forgetting caused by diazepam.     

Loss of function in phenylketonuria is caused by impaired molecular motions and conformational instability

A significant share of patients with phenylalanine hydroxylase (PAH) deficiency benefits from pharmacological doses of tetrahydrobiopterin (BH(4)), the natural PAH cofactor. Phenylketonuria (PKU) is hypothesized to be a conformational disease, with loss of function due to protein destabilization, and the restoration of enzyme function that is observed in BH(4) treatment might be transmitted by correction of protein misfolding. To elucidate the molecular basis of functional impairment in PAH deficiency, we investigated the impact of ten PAH gene mutations identified in patients with BH(4)-responsiveness on enzyme kinetics, stability, and conformation of the protein (F55L, I65S, H170Q, P275L, A300S, S310Y, P314S, R408W, Y414C, Y417H). Residual enzyme activity was generally high, but allostery was disturbed in almost all cases and pointed to altered protein conformation. This was confirmed by reduced proteolytic stability, impaired tetramer assembly or aggregation, increased hydrophobicity, and accelerated thermal unfolding--with particular impact on the regulatory domain--observed in most variants. Three-dimensional modeling revealed the involvement of functionally relevant amino acid networks that may communicate misfolding throughout the protein. Our results substantiate the view that PAH deficiency is a protein-misfolding disease in which global conformational changes hinder molecular motions essential for physiological enzyme function. Thus, PKU has evolved from a model of a genetic disease that leads to severe neurological impairment to a model of a treatable protein-folding disease with loss of function.     

On localization of moving objects in the visual system of cats

In cortical areas direction-specific receptive fields occur systematically. Direction specifity is based on unsymmetric coupling of neurons. Such a coupling allows an exact localization of moved stimuli. For this task, the asymmetry in the time domain is compensated for by a spatial asymmetry.This research was supported by DFG grant Se251/9. Professor W. von Seelen was in charge of the project