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Biomedical subjects

S Reinis

Publications and source records attributed to S Reinis.

At least 19 recordsLinked to original sources
PubMed2002

[ Physiology of consciousness. II].

At present, no plausible theory or even working hypothesis of the formation of human consciousness based on physiological processes of the central nervous system has been proposed. An obvious and principal obstacle is, how an immaterial process, consciousness, may arise from any material processes, and vice versa. For this reason, it is extremely difficult to propose such a hypothesis. Therefore, a working hypothesis is proposed based on well known interactions of the human consciousness with quantum submicroscopic processes.

Central Nervous System↗
PubMed1997

Heat-excited and heat-inhibited neurones in the ventroposterior nucleus of thalamus of anaesthetized rats.

The activities of 39 single cells, located in the ventroposterior nucleus of the rat thalamus, were recorded from rats deeply anaesthetized with xylazine and ketamine. The activity of each neurone was recorded before and during noxious tail heating. In all, 17 neurones were excited, 11 were inhibited, and 11 were not affected by the noxious stimulation. The possible function of each type of response in the coding of nociceptive information is discussed.

Anesthetics, Dissociative↗
PubMed1996

[The physiology of consciousness].

Since 1990, the number of papers on the biological basis of consciousness has increased sharply. Some aspects of consciousness, such as its localization in the brain structure, relation of conscious and unconscious processes, selective attention and the waking state may be analyzed by objective means. According to the model proposed by Dennett and Kinsbourne (1990) and called Multiple Drafts Model, there is no isolated module in the brain structure where consciousness is located. Conscious experience is a serial stream of activity integrating various sources of information. All conscious processes are generated in various parts of the central nervous system and the state of consciousness moves throughout the brain structure. Consciousness is therefore not identical with the global activity of the brain. Information may enter the consciousness or stay out of it in relation to the actual contents of the conscious process. Experimental data supporting this notion were obtained by electrophysiology, positron emission tomography, nuclear magnetic resonance, measuring of blood flow and other metabolic methods. These studies indicate that the state of consciousness is characterized by an increased neuronal activity and they may show which part of the brain is activated at any given moment. Of all brain areas involved in conscious processes, the role of the frontal lobe is widely documented in clinical and physiological papers. Entry of any information into consciousness requires about 350 to 500 ms of neuronal activity. Subjective timing of conscious recognition of events in the outside world is then retroactively returned to the moment when the information enters the neural processing. Recent research indicates that the gap between the humanistic and neurophysiological approach becomes gradually narrowed. Still, we have to keep in mind that the basic question about the ideal or materialistic character of consciousness remains open.

Brain↗
PubMed1995

A correlogram analysis of the activity in the rostral ventromedial medulla of awake rats and in rats anesthetized with ketamine or pentobarbital following the administration of morphine.

The spiking activity of single units and their corresponding mass activity in the rostral ventromedial medulla (RVM) was recorded simultaneously in rats that were either awake or anesthetized with pentobarbital or ketamine. Autocorrelograms and cross-correlograms were calculated to illustrate the distribution of interspike intervals under each of these conditions. The spontaneous activity in both anesthetized groups, but not the awake group, displayed a low incidence for short intervals (about 1-36 ms) between spikes. However, this low incidence of short interspike intervals was found in some awake rats following the administration of subanesthetic dosages of ketamine, pentobarbital, or morphine. The occurrences, or lack of occurrences of these short interspike intervals may be a marker for the anesthetized state of the rat. A basal spiking pattern, as illustrated by three different types of correlograms, was observed, and these basal patterns did not usually change after the administration of morphine to awake or anesthetized rats, even though the cells became excited or inhibited. Cross-correlograms revealed that the synapses between "on" and "off" cells might sometimes be inhibitory, while at other times they might be excitatory; however, cells of the same class mainly shared excitatory connections. In summary, ketamine and pentobarbital do alter the firing patterns of individual neurons in the RVM, but, no matter what state the rat is in, the activity of individual RVM neurons is strongly related to the activity of other neurons in the local network.

Action Potentials↗
PubMed1993

Two distinct unit activity responses to morphine in the rostral ventromedial medulla of awake rats.

Past research investigating the rostral ventromedial medulla (RVM) in anesthetized animals has found two distinct classes of cells, ON and OFF, noted for their distinct responses to noxious stimuli and to morphine. However, only one class (ON) has been found in the awake animal paradigm. We report in this paper that we have found both the ON and OFF cell responses to morphine in the awake rat.

Animals↗
PubMed1993

Investigating the role of anaesthetics on the rostral ventromedial medulla: implications for a GABAergic link between ON and OFF cells.

Two classes of cells in the rostral ventromedial medulla (RVM), ON and OFF, are important in the descending modulation of noxious input. It is thought that these two cell classes communicate, at a local level, with each other to control the RVM's descending modulation. Systemic morphine was given to rats anaesthetized with either pentobarbital (a GABA agonist) or with ketamine (a non-competitive NMDA receptor antagonist) and xylazine. The spiking activity of the ON and OFF cells was recorded. The typical ON cell inhibition by morphine was observed in rats under both anaesthetics. However, the OFF cell excitatory response to morphine was seen in the ketamine but not in the pentobarbital-anaesthetized animals. The implications for a GABAergic connection between these two classes of cells are discussed.

Anesthetics↗
PubMed1993

Simultaneous multi- and single-unit recordings in the rostral ventromedial medulla of ketamine-anaesthetized rats, and the cross-correlogram analysis of their interactions.

In anaesthetized rats, neurons located in the rostral ventromedial medulla (RVM) are classified by their differential responses to noxious stimulation. "On" cells are excited by noxious stimulation, "off" cells are inhibited and "neutral" cells are unaffected. Past research has primarily investigated the activity of these cells in lightly barbiturate anaesthetized animals while inducing a tail flick reflex. We recorded neuronal activity in the RVM of deeply ketamine-xylazine anaesthetized rats using a novel method of recording single- and multiunit activity simultaneously with one electrode. Under this anaesthetic paradigm we were able to record RVM cells which responded to noxious tail heating in the same manner as on and off cells without inducing a tail flick. A cross-correlogram analysis was done between the two levels of activity. It demonstrated that the RVM is a highly coordinated system in both the spontaneous period and the noxious evoked activity period. Through this technique it was also shown that both on and off cells fire simultaneously in the ketamine-xylazine paradigm.

Anesthesia↗
PubMed1992

Method of analysis of local neuronal circuits in the vertebrate central nervous system.

Although a considerable amount of knowledge has been accumulated about the activity of individual nerve cells in the brain, little is known about their mutual interactions at the local level. The method presented in this paper allows the reconstruction of functional relations within a group of neurons as recorded by a single microelectrode. Data are sampled at 10 or 13 kHz. Prominent spikes produced by one or more single cells are selected and sorted by K-means cluster analysis. The activities of single cells are then related to the background firing of neurons in their vicinity. Auto-correlograms of the leading cells, auto-correlograms of the background cells (mass correlograms) and cross-correlograms between these two levels of firing are computed and evaluated. The statistical probability of mutual interactions is determined, and the statistically significant, most common interspike intervals are stored and attributed to real pairs of spikes in the original record. Selected pairs of spikes, characterized by statistically significant intervals between them, are then assembled into a working model of the system. This method has revealed substantial differences between the information processing in the visual cortex, the inferior colliculus, the rostral ventromedial medulla and the ventrobasal complex of the thalamus. Even short 1-s records of the multiple neuronal activity may provide meaningful and statistically significant results.

Animals↗
PubMed1988

Mass correlograms of multiple neuronal activity in the cat's extrastriate cortex.

Electrical activity of a population of visually responsive cells located in the vicinity of a single functionally defined neuron was recorded in the area 18 of the cat's cerebral cortex with a single tungsten microelectrode. The correlograms calculated from the mass activity record showed an existence of a rhythmic neuronal firing with an average interval near to 3 ms. When the system was activated by a visual stimulus, a line at an optimal angle moving in an optimal direction, the rhythmic activity became regular, acquiring an oscillatory sinusoidal character. This rhythmic pattern cannot be easily recognized when the activity of a single neuron is recorded. It is possible that such rhythmic activity involving large numbers of neurons contributes to the recognition of the velocity and position of the visual stimulus.

Animals↗
PubMed1988

Lack of homogeneity of receptive fields of visual neurons in the cortical area 18 of the cat.

The receptive fields of "complex" neurons within area 18 of the cerebral cortex of the cat were determined by a computer-assisted method using a moving light bar substantially shorter than the long diameter of the receptive field as a visual stimulus. The visual cells repeatedly generated nerve impulses when the stimulus crossed well-defined "active points" within their receptive fields. Outside of these active points, the cells remained silent. It is suggested that the receptive fields are formed by a discontinuous accumulation of such active points. When the electrical activities of two neighbouring visual neurons are recorded simultaneously, their active points do not coincide. In addition, some active points were located outside the most prominent excitatory part of the receptive field of the studied cells. Individual visual cells typically differ in the number and distribution of active points. Since these cells best respond to a stimulus moving in a certain direction, it is suggested that they may act as direction of movement and/or velocity detectors. Alternate firing of a number of neighboring cells connected to a distributed pattern of peripheral receptors may form a system which is able to code for velocity and direction of the moving stimulus.

Action Potentials↗
PubMed1986

Effect of head tilt on visual cortical cell function in the intact and labyrinthectomized cat.

The area of the receptive field, its length and width, its position in the visual field, the peristimulus time (PST) histogram (i.e., the response to successive moving light-bar stimuli), the directional preference, the velocity gradient, and the intertrial (spontaneous) firing rate were studied electrophysiologically in complex cortical visual cells in Brodmann's area 18. These characteristics were explored after head tilt, in immobilized cats, both in intact and in bilaterally labyrinthectomized animals. In intact animals (in 64 cells), most of these characteristics changed after head tilts of 10, 20, 30, or 40 degrees to the right or to the left of the horizontal plane. There was always one specific head position in which the receptive field area was at its smallest. In labyrinthectomized animals (in 29 cells), the lengths, widths, and the areas of the receptive fields were only minimally altered during identical tilts. Similarly, in the labyrinthectomized cats, head tilts (40 degrees, to the right or left) caused no substantial changes in the shape and duration of the PST histogram, compared with those in intact cats. No two visual cortical cells responded to head tilts in exactly the same manner. Such uniqueness in response is probably of importance during visual image analysis; in particular, as it relates to cortical reconstruction of stable visual images during continuously changing head movements and positions.

Animals↗
PubMed1985

Effects of nitrous oxide on the functional characteristics of cells in the extrastriate cortex of the cat.

The directional preferences, receptive field areas, peristimulus-time (PST) histograms and spontaneous activities of 112 feline visual cortical (area 18) cells were studied before, during, and after the administration of nitrous oxide. These cellular characteristics were altered by nitrous oxide inhalation; some quite substantially. The data indicate that the functional characteristics of cortical visual cells, such as the receptive field and the directional preference, are variable; and, among other factors, depend also on the anaesthetic administered to the animal.

Animals↗
PubMed1984

Cluster analysis of visual cortical responses evoked by moving lines.

The cortical evoked responses to a bar of light (line) moving in 8 different directions across the visual field of 6 unanaesthetized, immobilized cats were compared in 18 experimental sessions. The shape of the response is unique for each direction. This is particularly apparent during the first 350 msec of the response. Cluster analysis of the evoked potentials reveals that the recognition of the direction of the moving line is probably less distinct when the line moves in a downward direction. This finding is more pronounced in the left hemisphere. The results of the cluster analysis indicate that the technique may be a useful tool in the analysis and classification of large numbers of evoked potentials. Furthermore, such clustering may eventually reveal some of the physiological mechanisms that contribute to the shape of the evoked response.

Animals↗
PubMed1984

The transneuronal transport of proline within the mouse visual system: some characteristics of the [3H]-proline containing material.

Following the intraocular injection of tritiated proline in the mouse, the progressive transport of radioactivity in the brain and the nature of the cortical material(s) to which the label is bound was examined. About 35-40% of the radioactivity that was present in the cerebral cortex at four weeks post-injection was extractable with either distilled water or various buffers. By using 0.1% SDS this value can be increased up to 94%. Polyacrylamide gel electrophoresis of the extracted proteins showed that a major part of the radioactivity is accumulated in one band of proteins. This heavily labeled band could not be identified in the homolateral parietooccipital cortex or in the frontal cortex. Similarly, SDS electrophoresis of the SDS-extracted proteins also demonstrated the presence of a major band of proteins whose molecular weight was estimated at approximately 68,000 daltons. The protein was purified by ammonium sulfate precipitation and DEAE-Sephadex separation.

Animals↗
PubMed1984

Effects of deuterium oxide and galvanic vestibular stimulation on visual cortical cell function.

/he spontaneous and evoked unit activities of complex visual cortical cells were recorded from Brodmann's area 18 in immobilized, unanesthetized cats before, during, and after stimulation of the vestibular system. The vestibular system was stimulated by intravenous injection of deuterium oxide (D2O)--a noted nystagmogenic agent (14)--or by direct galvanic stimulation of the labyrinth. Measures of the receptive-field areas, poststimulus time histograms, directional preferences, and the optimal speed of the light bar stimulating the cell were obtained before and after the application of D2O. Directional preferences were determined in a novel manner, using a method derived from a hierarchical clustering technique (19). Data were collected and analyzed from a) visual cortical cells in cats with intact labyrinths, b) visual cortical cells in cats following bilateral labrinthectomies, and c) nonvisual cortical cells in cats with intact labyrinths. In cats with intact labyrinths, D2O changed the optimal length of the light bar that was able to stimulate the cortical cell as well as the path on which it evoked the response of the cell. Both values, which constitute the receptive field of the cell, changed approximately proportionately. This effect usually lasts for less than 4.5 h. The other cellular characteristics were also altered by the D2O. Galvanic stimulation of the labyrinth resembles, in its effects, the injection of D2O. In labyrinth-intact cats, the time course of area 18 spontaneous activity dramatically increased 30 min or more after D2O was administered. It peaked 2-3 h later and still had not returned to preinjection levels even 7 h after the D2O administration. In bilaterally labyrinthectomized cats, the spontaneous activity of the visual cells (and the other cellular characteristics studied) did not change following D2O administration. In nonvisual cells from labyrinth-intact cats, the spontaneous activity demonstrated a slight but significant decrease over time after D2O injection. (The other measures, however, did not change.) In pilot studies (about 2 wk prior to the electrophysiological experiments), the cats were injected with D2O. Within 8-10 min afterward, signs of positional nystagmus commenced; and within 30 min, problems in maintaining balance were noted. This continued for 7-8 h before disappearing. In the labyrinthectomized animals, such effects were not observed. These results, therefore, add support to other evidence that suggests that D2O works directly through the vestibular apparatus to produce the effects it does (and not through interference with certain cellular processes).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Deuterium oxide modification of neuronal characteristics in the visual cortex of the cat.

The receptive field area and the spontaneous activity of complex visual cortical cells were investigated in the cat before, and after, the administration of deuterium oxide (D2O). In cats with intact labyrinths, the receptive field area of the cell usually expands, and the spontaneous activity increases. In bilaterally labyrinthectomized animals, these changes are absent. Also, D2O does not alter the spontaneous firing rate in non-visual cortical cells in normal cats.

Animals↗