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Biomedical subjects

J Bures

Publications and source records attributed to J Bures.

At least 235 records · Page 13Linked to original sources
PubMed1980

Post-ingestion interference with brain function prevents attenuation of neophobia in rats.

Attenuation of the neophobic rejection of novel flavours is mediated by a memorial process the properties of which were examined by testing its resistance to functional disruption. Rats maintained on a 24-h water deprivation schedule consumed only 3 ml of the novel apple juice but doubled its intake during the second presentation 2 days later. This attenuation of neophobia (AN) was prevented by pentobarbital anaesthesia (40 mg/kg) induced 0 and 1 h, but not 4 and 7 h, after the first apple juice presentation. AN was also disrupted by ether anaesthesia (5 min), hypothermia (20 degrees C body temperature), bilateral cortical spreading depression and electroconvulsive shock (50 mA, 1.5 sec) applied 0-1 h, but not 2 or more hours, after the first apple juice presentation. The results are consonant with the 'learned safety' hypothesis and indicate that a 2-4 h long continuous absence of noxious consequences of food ingestion is required to classify a gustatory stimulus as safe or neutral. Since interventions interfering with AN do not disrupt formation of conditioned taste aversion, the two forms of adaptive control of food selection are obviously mediated by fundamentally different neural mechanisms.

Anesthesia↗
PubMed1979

Circulation of cortical spreading depression around electrically stimulated areas and epileptic foci in the neocortex of rats.

Spreading depression (SD) elicited in the cerebral cortex of anaesthetized rats does not penetrate into epileptic foci (penicillin) or cortical regions subjected to repetitive electrical stimulation (6--10 Hz, 0.05--0.01 msec). The extent of the SD block, monitored by the absence of the slow potential change and preservation of spontaneous and evoked EEG activity, can be varied in certain limits by changing the stimulus parameters. When the diameter of the block in the parietal cortex is reduced at a time when its temporal boundary is circumvented by an SD wave, propagating in the rostral direction, a strip of cortical tissue between the block and sagittal sulcus is opened for SD which spreads through this route from the frontal to the occipital cortex and starts reverberating around the block. Other methods for eliciting SD reverberation employ removal of an additional block in a section of the circular pathway and directionally biased propagation around the stimulation point. SD reverberation lasting for at least 3 cycles was observed 109 times (median number of completed cycles 5.2, average cycle duration 4.4 +/- 0.1 min). It is suggested that SD reverberation around an epileptic focus can account for slow oscillations of ictal and interictal discharge and for recurrent seizures.

Animals↗
PubMed1979

Conditioning compensates the neglect due to unilateral 6-OHDA lesions of substantia nigra in rats.

The degree of the contralateral sensory neglect in rats with unilateral 6-OHDA lesions of substantia nigra was assessed by a conditioning procedure, employing lateralized CS. In the first experiment visual neglect (revealed by failure of the visually elicited placing reaction contralateral to the lesion) was shown to be accompanied by slower acquisition of a brightness discrimination task. The impairment was due to ipsilateral turning tendency rather then to visual deficit, however, since monocular relearning yielded equal savings with the ipsilateral and contralateral eyes. The second experiment showed that rats anesthetized with urethane reacted to noxious skin stimulation contralateral to the lesion with shorter-lasting EEG arousal than to ipsilateral stimulation of the same intensity. The electrophysiological asymmetry could be compensated by classical conditioning, i.e. by pairing habituated tactile stimuli with noxious tail shock. The conditioned arousal reaction could be elicited with the same efficiency from the neglected and intact body surface. It is concluded that neglect is due neither to a sensory nor to a motor failure, but that 6-OHDA lesions of substantia nigra in one hemisphere reduce the arousing efficiency of unconditioned stimuli and interfere with sensorimotor integrating mechanisms on the side contralateral to the lesion. Compensation of the neglect by conditioning indicates that the role of the nigrostriatal system can be partly substituted by other circuits.

Animals↗
PubMed1979

Radial maze type as a determinant of the choice behavior of rats.

Spatial memory of rats was examined in two types of radial mazes in which animals had to obtain food from 6-, 8-, or 12-different arms without repeating choices. In Maze 1 with tubular channels closed at the far end rats returned to the central platform by backing out from the just visited alley. In Maze 2 the tubular channels were equipped with one-way doors at both ends and the central platform was raised 5 cm above the floor. Rats leaving the far end of the alley returned to the central platform through a circular hole in its center. Performance was almost perfect in both apparatuses, but rats preferred to enter adjacent alleys in Maze 1 and widely separated alleys in Maze 2. These behaviors were significantly different from computer-simulated random choice from the set of correct solutions of the task. It is concluded that Maze 2 is better suited for repeated experiments with the same animal because the obligatory return to the center of the platform precludes the simplification of the task by response chaining.

Animals↗
PubMed1979

Asymmetry of optokinetic trace phenomena induced by unilateral 6-OHDA lesion of substantia nigra in the rabbit.

Prolonged (1 h) optokinetic nystagmus (OKN) is followed in darkness by reversed postoptokinetic nystagmus (RPN) lasting 20-30 min in intact rabbits. Unilateral 6-OHDA lesion (10 microgram/5 microliter) of left substantia nigra did not disturb symmetry of the OKN reactions to monocular stimulation of either eye but weakened RPN induced by stimulation of the right eye. This RPN asymmetry was unaffected by amphetamine (2.5 mg/kg) but was reversed by apomorphine (1 mg/kg). It is concluded that the nigrostriatal system contributes to the development of the neural trace underlying RPN.

Amphetamine↗
PubMed1979

Electrophysiological analysis of retrieval of conditioned taste aversion in rats. Unit activity changes in critical brain regions.

Gustatory discrimination testing shows that rats with an overtrained conditioned taste aversion (CTA) to isotonic LiCl stop salt intake after 1 to 2 licks at the LiCl spout and move to the adjacent water spout within 0.7 s. Activity of 526 neurones from the nucleus of the solitary tract, gustatory thalamus, gustatory cortex, lateral and ventromedial thalamus, and amygdala was recorded in naive or CTA trained rats during the above gustatory discrimination. Post-stimulus histograms (PSH) triggered by water or salt licks or by spout switching were plotted for single units. Population responses of various regions were obtained by integration of the statistically significant excitatory and inhibitory intervals in the individual PSHs. Lick related changes of unit activity were orserved in 52% and 65% of neurones in control and CTA trained rats, respectively. The CTA training increased the incidence of units in which salt licking influenced the activity less than water licking. Presentation of the aversive fluid induced inhibition of unit activity in the gustatory cortex, ventromedial hypothalamus, and amygdala and excitation in the lateral hypothalamus. The changes started 100 to 150 ms after spout switching and culminated 100 ms later. Activity of the solitary tract nucleus and gustatory thalamus was affected less consistently. The results indicate that the gustatory cortex, amygdala and hypothalamus participate in CTA retrieval but a more specific identification of the electrical correlates of memory readout and of drinking control was not possible.

Action Potentials↗
PubMed1979

Electrophysiological analysis of retrieval of conditioned taste aversion. Physiological techniques and data processing.

New techniques suitable for electrophysiological investigation of retrieval of conditioned taste aversion (CTA) were developed. The gustatory discrimination apparatus consisted of two parallel drinking spouts (20 mm apart) equipped with photoelectric lick sensors. The spouts contained water or the aversive fluid (0.15 M LiCl), respectively, and their position could be rapidly (50 ms) interchanged with a reversive electromotor. Licking at either spout and the position of the fluids were recorded on one channel of a tape recorder. Unit activity was picked up with tungsten microelectrodes (40 micrometers) inserted into the brain of a freely moving rat with a head-mounted microdrive system (weight 2 g), fixed to an implanted guiding cannula. The electrode was connected through a head-carried FET signal follower to a wide band integrated circuit amplifier and the unit activity was recorded in the other channel of the tape recorder. The records were evaluated using an off-line computer program (LINC 8) consisting of a spike detection subroutine followed by amplitude histogram analysis. The mean (M) and SD values were computed for uni- or bimodal amplitude distributions of the principal spike components. Spike falling within the M+/-2 SD range of the selected parameter were identified as single units and used for construction of post stimulus histograms triggered by licking or by spout switching.

Action Potentials↗
PubMed1979

Importance of colicinogeny for the course of acute bacillary dysentery.

The development of acute bacillary dysentery was followed in 23 patients involved in two outbreaks and in three sporadic, mutually unrelated cases. Repeated cultivations performed at 2-day intervals for 10 days yielded 386 identifiable strains of "opportune intestinal flora". Escherichia coli colicinogenic activity is one of the significant factors of gastrointestinal tract protection. The period of shigella excretion is significantly reduced (p less than 0.02) if an appropriate colicinogenic E. coli strain is present. Analysis of the results suggested a working hypothesis of differentiated approach to bacillary dysentery treatment in outbreaks. In the absence of a suitable colicinogenic flora neomycin therapy should be administered since it does not damage the natural colonizing flora (bacteroids, bifidobacters, aerobic lactobacilli); in the presence of a suitable colicinogenic flora, no antibiotic should be used as this would abolish the coli-flora.

Bacteriocins↗
PubMed1979

Reversed postoptokinetic nystagmus: a model of plasticity in the vestibuloocular system.

A simple manifestation of the memorial processes is the so called reversed postoptokinetic nystagmus (RPN), a trace phenomenon elicited in the rabbit by prolonged (60 min) optokinetic (OK) stimulation. Electrophysiological analysis of RPN indicated that the underlying neural trace is weakened, but not suppressed by spreading depression in the cerebral cortex or superior colliculus. An asymmetry of RPN is brought about by unilateral 6-OHDA lesion on substantia nigra. Electroconvulsive shock applied immediately after a period of OK stimulation blocks the subsequent RPN without interfering with OKN. About 70 percent of neurons in the vestibular complex changed their activity during OKN and RPK. The changes consisted in most cases of an excitation accompanying OKN and inhibition during RPN. The OKN-RPN related reacti6ns were also abundant in flocculus but significant activity changes during RPN were less frequent in this structure. Units in midbrain reticular formation reacted both during OKN and RPN in a similar fashion as the vestibular ones. On the other hand units in the cerebellar deep nuclei and brachium conjunctivum were only weakly influenced by OKN and/or RPN. It is suggested that the neural trace of RPN develops in the vestibular complex and vestibulocerebellum as a part of the process compensating the effect of continued optokinetic stimulation. Flocculus participates in input processing of the optokinetic stimulation whereas reticular formation mediates signal transmission to oculomotor and higher integrating centers. The trace, revealed by sudden cessation of the eliciting stimulus in absence of visual reference signals is probably the neural substrate of the so called motion habituation and visual hallucinations. As other compensatory phenomena in the motor system, RPN has features of instrumental (it improves the organisms control of environment) and classical (it is automatically established and involuntarily emitted) conditioning.

Animals↗
PubMed1978

Electrophysiological changes induced by paradoxical sleep deprivation and lithium chloride poisoning in rats.

In an attempt to analyze the disruption of conditioned taste aversion (CTA) caused by pre-acquisition paradoxical sleep deprivation (PSD), the effect of poisoning (0.15 M LiCl, 4% body weight) on the sleep--wakefulness pattern was studied in 12 rats with chronically implanted electrodes. The polygraphic recording showed that poisoning reduced the total sleep time in the subsequent 3 h from 57 to 42% and REM sleep from 6 to 2%. The lithium chloride effect was still more pronounced after 24-h REM sleep deprivation: the total sleep time decreased from 67 to 46% and REM sleep from 13 to 2%. The change of sleep--wakefulness pattern, most pronounced during the first hour of poisoning, gradually returned to normal but REM sleep was significantly reduced even 3 h after poisoning. It is concluded that 24-h PSD does not alleviate the subsequent poisoning. On the other hand, the lithium chloride induced reduction of post-acquisition REM sleep many enhance the learning impairment caused by pre-acquisition PSD.

Activity Cycles↗