Biomedical subjects

J Bures

Publications and source records attributed to J Bures.

At least 19 recordsLinked to original sources

PubMed1992

Can rats solve a simple version of the traveling salesman problem?

Whereas correct tours through the radial arm maze are almost equally long, free choice mazes with multiple goals scattered in an open field allow the animal to select the shortest one from a multitude of correct tours. Thirteen rats were trained (at 10 trials per day) to visit an array of cylindrical feeders in an open field (40 x 100 cm) with reward available only when visiting the last feeder of the set. In Expt. 1 with eight feeders arranged in five different configurations the rats made after 10 days of training 1 error in the first 8 choices and incidence of errorless trials was about 20%. In Expt. 2. the use of six feeders in a rectangular (A) or double triangle (B) configuration increased the incidence of errorless trials to 60%. Expt. 3 showed that performance in the 6-feeder maze was significantly impaired by 6 mg/kg ketamine or 0.25 mg/kg scopolamine but not by lower dosages of these drugs. Tours generated on errorless trials (each feeder visited only once) during 10 days of Expt. 2 were analyzed. Six places can be visited in 6! = 720 different closed tours the lengths of which (in arbitrary units) range from 6.00 to 10.12 for A and from 6.83 to 10.47 for B. Whereas random generation of correct routes yielded only 5% of the shortest tours, they were clearly preferred by rats (41% in A and 45% in B). The apparent proficiency of rats in this optimization problem is probably not due to cognitive comparison of the possible correct routes but rather to following a simple rule 'Always go to the nearest not yet visited feeder'.

Animals↗

PubMed1992

Differential involvement of gustatory insular cortex and amygdala in the acquisition and retrieval of conditioned taste aversion in rats.

Lesion studies of the role of the gustatory insular cortex (GC) and amygdala (Am) in conditioned taste aversion (CTA) are confounded by the irreversibility of the intervention. Functional ablation methods allow more specific influencing of different phases of CTA acquisition and retrieval. Bilateral tetrodotoxin (TTX) blockade of GC (10 ng) or Am (3 ng) before or after saccharin drinking in rats with chronically implanted intracerebral cannulae showed that GC is indispensable for the initial processing of the taste stimulus but not for the association of the gustatory trace with the symptoms of LiCl poisoning. Gustatory signals can by-pass the blocked Am, the inactivation of which, however, impairs the gustatory trace-poisoning association. TTX injection into both GC and Am impairs CTA retrieval more than isolated blockade of either of these structures. It is argued that GC and Am implement processing of gustatory and visceral signals, respectively, but that formation and consolidation of the CTA engram proceeds outside forebrain, probably at the level of the brainstem.

Amygdala↗

PubMed1992

Vasopressin administration via microdialysis into the septum interferes with the acquisition of spatial memory in rats.

The role of vasopressin (AVP) in the septohippocampal system in spatial memory was studied in 27 male hooded rats of the Long-Evans strain. The rats were implanted with a septal microdialysis probe and assigned to 3 groups. Two days later, they were trained on 3 consecutive days (12 daily trials) to locate the hidden underwater platform in the Morris water maze (MWM) while the probes were perfused with either artificial cerebrospinal fluid (aCSF) or aCSF containing vasopressin or the V1 antagonist d(CH2)5Tyr(Me)AVP (AAVP). Another group of rats (n = 8) remained untreated. Groups receiving microdialysis of aCSF or AAVP acquired the MWM task at the same rate as untreated animals. On the other hand, place navigation learning was significantly impaired by microdialysis of AVP during all sessions. The results indicate that endogenous AVP (at least that affecting the V1 receptor subtype) is not indispensable for the acquisition of spatial memories in the MWM, whereas excessive presence of synthetic AVP interferes with spatial learning.

Animals↗

PubMed1992

Time-dependent disruption of passive avoidance acquisition by post-training intra-amygdala injection of tetrodotoxin in rats.

The role of the amygdala (AM) in the consolidation of the passive avoidance reaction (PAR) has been examined with the tetrodotoxin (TTX)-induced functional block of this structure. Rats were trained in the step-through PAR and anesthetized with ketamine. TTX injected immediately after acquisition into both AM (2 x 10 ng) significantly reduced avoidance of the dark compartment in the retrieval test performed two days later. The amnesic effect was significant when the acquisition--TTX delay was prolonged to 90 min but not to 6 h or 24 h. Earlier research indicated that TTX blockade of the parabrachial nuclei caused similar PAR disruption when elicited 24 h but not 48 h after acquisition. Comparison of the TTX-induced retrograde amnesias indicates that the two structures play different roles in the formation of the PAR engram.

Amnesia, Retrograde↗

PubMed1992

Postacquisition injection of tetrodotoxin into the parabrachial nuclei elicits partial disruption of passive avoidance reaction in rats.

The recent discovery that post-trial functional blockade of the parabrachial nuclei by intracerebral injection of 10 ng tetrodotoxin (TTX) disrupts acquisition of conditioned taste aversion (CTA) (Ivanova & Bures, 1990a,b) has prompted attempts to ascertain the role of this structure in other types of inhibitory learning. In Experiment 1, rats with implanted parabrachial cannulae were trained in a step-through avoidance task and received bilateral TTX (2 x 10 ng) immediately after the acquisition trial; they displayed significantly weakened avoidance of the shock compartment 2 days later. In Experiment 2, rats were anesthetized with pentobarbital (50 mg/kg) immediately after passive avoidance acquisition and received parabrachial TTX 15 min later; whereas anesthesia alone left the passive avoidance reaction (PAR) unaffected, TTX elicited similar disruption as in unanesthetized animals. In Experiment 3, TTX was injected in anesthetized animals 0, 1, 2, or 4 days after PAR acquisition. The amnesic effect was significant when the acquisition-TTX delay had been prolonged to 24 but not to 48 or 96 h. Since CTA is disrupted by reversible blockade of parabrachial nuclei and of the adjacent reticular formation elicited up to 4 days after acquisition (Ivanova & Bures, 1990b), PAR seems to be impaired to a lesser degree and for a shorter time than CTA by similar TTX treatment.

Amygdala↗

PubMed1992

Rat exploratory behavior controlled by intracranial self-stimulation improves the study of place cell activity.

This report is limited to the description of a procedure that should help to resolve the question whether firing fields of hippocampal place cells are relatively stable or modifiable by learning. Rats implanted with lateral hypothalamic electrodes for rewarding intracranial self-stimulation (ICSS) were trained to explore a circular open field (100 cm in diameter) while their locomotion was tracked by a computerized video system which also delivers ICSS whenever the animal's exploration has met certain experimenter defined criteria. The 3 following conditions were examined. (1) Homogeneous exploration of the entire field: ICSS was delivered after the animal repeatedly visited 5 equal segments of the field (central annulus and remainders of the 4 quadrants), entered randomly located circular areas of the field, and/or traveled a criterion distance. (2) Place field contingent reward or non-reward: ICSS was delivered when the animal entered a circular area (23 cm in diameter) corresponding to the place field after a previous visit to a similar area outside the place field. These conditions were reversed in the following task. (3) Delayed reward: ICSS was delivered when the animal entered the circular area and remained in it for 2 s. Each condition was tested for 600 s or until 50 ICSS were delivered. The behavioral procedures described make it possible to propose an experimental protocol that allows examination of the same place cell under conditions of homogeneous exploration with a segment condition or randomly distributed reward and under conditions with the place field signaling reward or non-reward. The delayed reward condition increases the accuracy of the target location and allows assessment of the phasic versus tonic nature of the place cell firing.

Animals↗

PubMed1992

Lateralized contributions of the cerebral cortex, parabrachial nucleus, and amygdala to acquisition and retrieval of passive avoidance reaction in rats: a functional ablation study.

Reversible blockade of the neocortex by spreading depression and of the parabrachial nucleus (PBN) and amygdala (AMG) by tetrodotoxin (TTX) injection was used to study lateralization of passive avoidance reaction (PAR) engrams in rats. In Experiment 1, PAR acquisition was not disrupted by posttrial TTX applied into the PBN or AMG or into both of these structures in the same hemisphere but was impaired when the AMG and PBN were blocked in opposite hemispheres. In Experiment 2, retrieval of PAR acquired with intact brain was not impaired by unilateral TTX blockade of the AMG. In Experiment 3, PAR was acquired with posttrial TTX blockade of the AMG and PBN in one hemisphere. Full or partial block of PAR retrieval was induced by functional decortication of the contra- or ipsilateral hemisphere, respectively, whereas blockade of either AMG was ineffective. It is concluded that PAR acquisition requires ipsilateral interaction of the AMG and PBN and that the two hemicortices contribute differentially to the retrieval of engrams formed under such conditions.

Amygdala↗

PubMed1991

Acquisition of conditioned taste aversion in rats is mediated by ipsilateral interaction of cortical and mesencephalic mechanisms.

The possibility to lateralize the neural circuits mediating conditioned taste aversion (CTA) has been examined by combination of functional hemidecortication and unilateral tetrodotoxin (TTX) injection into the parabrachial nucleus (PBN). Rats drinking saccharin (CS) during cortical spreading depression (CSD) in the right hemisphere and receiving unilateral PBN injection of TTX (3 ng) shortly before i.p. injection of lithium chloride (LiCl) (US) formed CTA when CSD and TTX were applied to the same hemisphere but not when applied to different hemispheres. Rats drinking saccharin with intact brain and receiving unilateral TTX overlapping with LiCl administration learned a weak CTA, the retrieval of which was disrupted by either ipsilateral or contralateral CSD during retention testing. It is concluded that CTA acquisition requires cooperation of ipsilateral cortical and subcortical centers but that formation of unilateral subcortical CTA engram does not warrant lateralization of the retrieval process.

Animals↗

PubMed1991

Synchronisation of tongue and forepaw movements in the rat: a model of instrumental muscle synergy.

Acquisition of new skills is often implemented by the formation of coordinated movements of functionally unrelated muscles. This situation was modelled in rats trained to lick at a retractable spout which was automatically withdrawn after termination of every lick but could be returned by pressing and releasing a lever placed 4 cm below the spout. Rats (n = 12) learned to perform short presses (50 ms) synchronized with the lick cycle in a way allowing continuous drinking. When the distance of the lever from the box was increased from 5 mm to 12.5 mm or when the force required for lever operation was raised from 20 g to 90 g, the lick-press interval increased in multiples of the interlick interval. Licking ceased during the lever pressing but regular timing of subsequent licks indicated uninterrupted activity of the licking generator. It is concluded that the coordination of orofacial and forelimb muscles engaged in licking and lever pressing, respectively, is accomplished by propagation of the activity of the lick generator to cortical and subcortical motor centers.

Animals↗

PubMed1991

Reversal of 'handedness' in rats is achieved more effectively by training under peripheral than under central blockade of the preferred forepaw.

Reversal of forepaw preference was studied in rats under conditions of peripheral (bracelet) or central (inactivation of contralateral motor cortex and caudate nucleus by intracerebral injection of tetrodotoxin) preferred limb block. Persisting change of the forepaw preferred when reaching for food into a tubular feeder was achieved on the average after 91 (n = 27) and 211 (n = 26) reaches, respectively. When tested in another task (recovering food pellets from a horizontal shelf accessible through a narrow slit below the ceiling of the test box) same rats displayed identical (45%) and opposite (15%) preference or were ambidextrous (40%). Forced change of handedness on the tubular feeder task was accompanied by similar change of preference on the shelf task in only 17% rats. It is concluded that rather independent lateralisation of the two tasks reflects differential contribution of the corticospinal, rubrospinal and ventromedial motor systems. Reversal training proceeds faster with peripheral blockade which establishes not only the new preference but also inhibits the original one.

Animals↗

PubMed1991

Re-entry waves of Leao's spreading depression between neocortex and caudate nucleus.

About 40% of spreading depression (SD) waves elicited from the parieto-occipital cortex of anesthetised rats penetrated through the temporal lobe structures (amygdala) into the caudate nucleus. Almost 70% of these SD waves did not terminate in the caudate but returned to the cortex and spread through it toward the site of SD initiation. Longer cortico-caudate (5.9 +/- 0.1 min) than caudate-cortical (4.7 +/- 0.2 min) conduction times suggest that SD enters and leaves caudate through routes of different length. SD waves elicited by KCl microinjection into the caudate reached frontal and parieto-occipital cortical electrodes with latencies indicating that the transit point is 5 mm closer to the rostral than to the caudal electrode. The region best satisfying this condition corresponds to rostral claustrum. The directionally biased SD conduction through the transit zone provides a re-entry path for cortico-caudate-cortical SD propagation and forms thus a natural reverberator the small dimensions of which preclude generation of repetitive SD waves.

Animals↗

PubMed1991

Extent of the tetrodotoxin induced blockade examined by pupillary paralysis elicited by intracerebral injection of the drug.

Spatial extent and duration of the functional blockade elicited by intracerebral injection of tetrodotoxin (TTX) was examined in rats anesthetized with pentobarbital. Pupillary diameter was measured under dissecting microscope before and up to 24 h after injection of TTX (10 ng/l microliters saline) into or 1.0, 1.5 and 2.0 mm lateral from the Edinger-Westphal nucleus. TTX administration elicited mydriasis the latency of which was directly and amplitude indirectly proportional to the target-injection distance. The maximum mydriasis attained 3.4 mm, lasted 2 h and slowly decayed over subsequent 20 h. Impulse transmission and conduction was blocked in a spherical volume of tissue about 3 mm in diameter the development of which could be approximated by diffusion from an instantaneous point source. Completeness and full reversibility make the TTX block a convenient research tool.

Animals↗

PubMed1991

Integration of neocortical embryonal grafts with the neocortex of host rats examined by Leao's spreading cortical depression.

Cortical spreading depression (SD) was used to assess the density and organization of neural elements in neocortical transplants and their connectivity with the host brain. Embryonal neocortex (E14) was transplanted into cavities in the frontoparietal cortex of 3-month-old rats. SD elicited in the cortex of anesthetized host rats (n = 12) 3 to 8 months after transplantation did not penetrate into the grafts. SD could be elicited in large transplants but did not propagate to the surrounding host neocortex. Spontaneous unit activity in the transplants was affected by SD elicited in the neocortex of the host rats anesthetized with urethane. Most units (n = 49) displayed excitatory-inhibitory (52%) or inhibitory (29%) reactions, whereas purely excitatory reactions were less frequent (8%). The results suggest that the packing density of neurons in the transplant can support SD but that the conditions at the graft-host boundary (glial scar, scarcity of neurons) stop SD propagation. High reactivity of the graft neurons to SD in the host neocortex indicates that afferentation from the host brain represents an important, predominantly excitatory contribution to the spontaneous activity of the transplant.

Animals↗

PubMed1991

Neuroscience in Czechoslovakia.

The collapse of the communist regime in Czechoslovakia revealed not only the disastrous state of the Czechoslovak economy but also the serious problems that Czechoslovak science faces. Understanding the present situation and determining the best way to improve it requires careful analysis of the development of science during the past 40 years.

Animals↗

PubMed1991

Brain stem mechanisms of conditioned taste aversion learning in rats.

Acquisition of conditioned taste aversion (CTA) in rats is not prevented by functional decortication, anesthesia or hypothermia applied after intake of the flavored fluid and maintained throughout the action of the poison but is disrupted by bilateral application of 10 ng tetrodotoxin (TTX) into the parabrachial nuclei. The blockade is directly proportional to TTX dosage, indirectly proportional to distance of the injection site from parabrachial nuclei and equally affects CTAs using different CS (saccharin, NaCl) and different US (LiCl, carbachol, amphetamine, cycloheximide). CTA is disrupted by TTX applied up to 4 but not 8 days after a single CS-US pairing. TTX fails to disrupt overtrained CTA and elicits only a weak anterograde amnesia when applied 1 but 2 or more days before CTA acquisition. It is concluded that the parabrachial nuclei and the adjacent reticular formation probably represent the neural substrate of the permanent CTA engram the protracted consolidation of which is disrupted by prolonged cessation of impulse which is disrupted by prolonged cessation of impulse activity in the information storing network.

Amnesia↗

PubMed1991

[Colicinogeny in nonspecific intestinal inflammations and colorectal cancer].

Colicins are proteinaceous substances produced by Escherichia coli strains and related bacteria of Enterobacteriaceae family. They are considered to be an important factor in preserving the balance of the intestinal microflora. Their antibiotic action on susceptible bacteria is supplemented with cytotoxicity for several pro- and eukaryotic cells. The large bowel is a natural site of their action. Besides of enhancing oxidoreductive activity of leukocytes in vitro, colicins are also believed to influence inflammatory reaction in vivo. For these reasons, the first part of the present work was concerned with studying colicinogeny in nonspecific inflammatory bowel diseases (IBD). No significant difference has been found out in colicinogeny between a total of 93 IBD-related and 160 healthy controls. In testing leukocyte migration inhibition, colicins of autologous E. coli were used as antigens. The migration index out of normal range showed 36% patients with ulcerative colitis (5/14), 80% patients with Crohn's disease (12/15), and only one clinically healthy control subject (1/16; 6%). The obtained results are considered to be proof of cellular hypersensitivity of IBD patients to colicins of their own E. coli strains. In several colicins the antitumorous effect has been reported in both the in vitro and in vivo experimentation. The second part of this work was concerned with colicinogeny in colorectal cancer. Colicinogenic E. coli were evidenced in 42 subjects (40%) from 105 patients with colorectal carcinoma. Controls showed colicinogenic E. coli in 102/160 clinically healthy subjects (64%), and the difference was as significant as p less than 0.05. In colorectal cancer group, the subjects with proved colicinogeny showed lesser amounts of colicinogenic E. coli strains in contrast with non-colicinogenic ones. In colorectal cancer patients with colicinogenic E. coli strains, B and M colicins were of most frequent occurrence in them no antitumorous effect has been experimentally stated. If changes of colicinogeny were only either the manifestation or consequence of tumor disease, so both the presence or absence of colicinogenic E. coli would have been dependent of clinical patients's condition, stage of disease (in accord with Dukes) or correlated with the tumor markers. For these accounts, a total of 28 colorectal cancer patients underwent a colicinogenic study. However, no colicinogeny dependence was evidenced of either clinical condition or Dukes stage, showing no correlation with any of cancer markers investigated (carcinoembryonic antigen, CA 19-9, alfa-1-fetoprotein, alfa-1-orosomucoid, Cancer serum index, sialic acid, lysozyme).(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1991

[Plasmapheresis in the treatment of Crohn's disease].

Crohn's disease is a disease with unknown etiology of which immunological mechanisms participate. As standard treatment is sometimes ineffective, in 15 patients therapeutic plasmapheresis was used. Before plasmapheresis and immediately after it some immunological parameters were assessed. In the serum a significant drop of all immunoglobulins of the basic classes was recorded: (P less than 0.05) and of circulating immunocomplexes (P less than 0.02). Marked clinical improvement was observed in three patients, which as compared with data in the literature, is somewhat less. The cause is in the author's opinion in the selection of patients (plasmapheresis is usually most successful in patients with marked activity of the disease and non-intestinal symptoms) even in case of less active plasma exchange. Despite this plasmapheresis can be recommended in patients with a poor response to common conservative treatment and in some of them we may expect a marked therapeutic effect with a favourable influence on the prognosis of the disease.

Adolescent↗

PubMed1990

[Excretion of phenol and p-cresol in the urine in fasting obese individuals and in persons treated with total enteral nutrition].

In the literature it is maintained that phenol and p-cresol are produced in humans in the gut by bacteria from dietary protein. Both substances are absorbed from the small intestine and excreted in the urine. If the urinary output of phenol and p-cresol depends really on the dietary protein intake it should decline to zero values during fasting and correlate with the protein supply into the gut. The objective of the present work was therefore to investigate the urinary phenol and p-cresol excretion in fasting obese subjects (21 fasting subjects, 7 subjects with modified fasts--Nutramine R-350) and in subjects treated by complete enteral nutrition by a nasojejunal tube (8 patients with Crohn's disease, 8 with another disease of the gastrointestinal tract). Phenol and p-cresol in 24-hour urine specimens were assessed by gas chromatography in all four groups always on the 1st, 7th and 14th day. In fasting obese subjects the phenol and p-cresol values did not decline (the difference of values from the assumed zero value is significant z = 0.000055). There was no difference between patients with a complete and modified fast. The phenol and p-cresol values did not correlate mutually, nor with the protein intake, nitrogen balance and cumulated nitrogen balance. There are great individual differences in the urinary phenol and p-cresol excretion and it does not depend on the oral dietary protein intake, as hitherto assumed. It has most probably more complex causes and the decisive factor seems to be the metabolic activity of the intestinal bacterial microflora.

Adult↗