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Biomedical subjects

J Bures

Publications and source records attributed to J Bures.

At least 181 records · Page 10Linked to original sources
PubMed1985

Motor learning in rats: modification of the pattern of reaching and licking by operant conditioning.

Motor learning was studied in computer controlled experiments in which the prolongation of a definite phase of a discrete movement was reinforced by intracranial selfstimulation or by the offer of water. In Experiment 1, rats slowed down the retraction phase of the lateralized reaching reaction from 300 ms to 512 ms. In Experiment 2, rats learned to follow computer generated spout movement by increasing the interlick interval or by alternating long and short licks.

Animals↗
PubMed1985

Substitution of natural conditioned and unconditioned stimuli by artificial stimuli does not prevent acquisition of conditioned taste aversion in rats.

Attempts to replace a natural conditioned stimulus (taste) by electrical stimulation and a natural unconditioned stimulus (gastrointestinal disorder) by intracranial application of harmaline in the conditioned taste aversion (CTA) paradigm are described. The taste is replaced either by electrical stimulation of taste receptors of the tongue or by intracranial self-stimulation of the lateral hypothalamus, both triggered by licking. Both stimuli lose their rewarding properties when paired with gastrointestinal distress whereas self-stimulation triggered by nose poking is not affected by the same procedure. The unconditioned stimulus was replaced successfully by intracerebral injection of harmaline hydrochloride. The effect of the injection of 3-6 micrograms harmaline into the region of the inferior olive is comparable to that of systemic injection of 10 mg/kg harmaline. Electrophysiological analysis of the effect of locally and systemically applied harmaline indicates that the drug probably elicits CTA by activation of bulbar structures including the lateral reticular nucleus and lateral vestibular nucleus.

Animals↗
PubMed1985

Is there an increased risk of colorectal cancer after cholecystectomy?

The incidence of cholecystectomy was not higher in 525 colorectal cancer patients than in subjects without colorectal cancer of the same age and sex living in the same region. If we did not include the persons who underwent cholecystectomy 1 or 2 years before the diagnosis or the examination was made, the number of cholecystectomy patients was the same in both groups. Right-sided and left-sided localizations of colon cancer after cholecystectomy did not differ from those without cholecystectomy. The tendency to right-sided colon cancer in women who have undergone cholecystectomy was not significant. Patients after cholecystectomy have no higher risk of colorectal cancer than persons without cholecystectomy.

Adult↗
PubMed1984

Effects of rewarding hypothalamic stimulation on plasma catecholamine levels in rats.

Plasma catecholamines were measured before, during and after exposure to lick-contingent rewarding hypothalamic stimulation, clock-triggered neutral hypothalamic stimulation, and licking maintained by water. Rewarding hypothalamic stimulation elicited a marked rise in plasma epinephrine levels which returned to baseline levels 3 min after the self-stimulation session. No changes in plasma epinephrine were observed under the latter two conditions. Increases in norepinephrine levels were more variable and seemed to correspond to motor activity being similar in the licking groups but unchanged with clock-triggered stimulation. These results indicate that stimulation of reward pathways may selectively influence adreno-medullary secretion.

Animals↗
PubMed1984

Sensory feedback modulates the central pacemaker of licking in rats.

The role of the tongue-spout contact in generation of regular licking has been examined in 10 rats trained to drink from a tube accessible through an 8-mm hole in the wall. Computer controlled retraction of the spout after completion of a photoelectrically monitored lick did not affect the timing and duration of the next lick in the burst, but the interlick interval and lick duration of subsequent licks were prolonged by about 10 ms. The effect was expressed the better the longer the series of licks (1 to 4) was emitted in the absence of the spout. It is argued that licking is a preprogrammed ballistic movement which can only be corrected after the last completed lick has been compared with the anticipated outcome.

Animals↗
PubMed1984

Central mediation of the conditioned taste aversion induced in rats by harmaline.

The assumption that drugs used as unconditioned stimuli in conditioned taste aversion (CTA) studies act centrally was tested by comparing the effects of systemic and intracerebral injections of harmaline hydrochloride (H) in 340 rats. Intraperitoneal injection of 5-20 mg/kg but not of 2.5 mg/kg H administered 5 min after 15-min saccharin (0.1%) drinking decreased saccharin-water preference in a two-choice retention test, performed 48 h later, from 55% to 20%. Since CTA was not diminished when H (10 mg/kg) was injected into rats anesthetised immediately after saccharin drinking by pentobarbital (40 mg/kg), H (1.7-50 micrograms) was administered intracerebrally to anesthetised rats fixed in the stereotaxic apparatus. Injection of 3-6 micrograms H into the inferior olive elicited CTA comparable to that of systemic injection of 10 mg/kg H. Injections of 6 and 50 micrograms H into cerebellum and bulbar reticular formation elicited weaker CTA while neocortical, hypothalamic and mesencephalic applications were ineffective. CTA could also be elicited when 50 micrograms but not 6 micrograms H was injected into the inferior olive 1 or 2 h after saccharin drinking. This delay-dependent effect and failure of non-contingent H administration to change saccharin preference indicates that the H-induced CTA is not contaminated by a non-specific increase in neophobia. It is concluded that H probably elicits CTA by activation of caudal bulbar structures, including the nucleus of the solitary tract, area postrema and lateral reticular formation.

Alkaloids↗
PubMed1984

Effects of lateralized reaching and cerebellar stimulation on unit activity of motor cortex and caudate nucleus in rats.

Rats trained to reach into a narrow tubular feeder for food were implanted with bipolar stimulation electrodes in the dentate nucleus (DNT) ipsilateral to the preferred forepaw. Unit activity was recorded in freely moving animals (N = 15) with capillary microelectrodes inserted with a head-mounted microdrive into the contralateral motor cortex and caudate nucleus. Single-pulse stimulation of the DNT, subthreshold for eliciting overt movement and for interfering with reaching, evoked in both structures short-lasting excitatory responses sometimes preceded by brief inhibition. Reach-triggered stimulation changed the perireach histograms of the motor cortex neurons (N = 46) not only by interference with the movement-related and stimulation-elicited activities in the poststimulus interval but also considerably prolonged the prereach excitation. The perireach histograms of caudate neurons (N = 50) were not changed by the reach-triggered DNT stimulation in the prereach or in the poststimulus interval, probably because the movement-related activity overrode the electrical perturbation. The results indicated that the impairment of reaching caused by DNT stimulation was due to disorganization of the neuronal activity patterns in the motor cortex rather than in the caudate nucleus. The earlier onset of movement-related excitation in the motor cortex during stimulus-triggering reaching reflects attempts to cope with the disturbance by predictive reorganization of the motor discharge.

Animals↗
PubMed1984

Unit activity of motor cortex during acoustically signalled reaching in rats.

Changes of unit activity, accompanying a discriminated instrumental reaction were studied in the motor cortex of rats (n = 15) trained to reach into a narrow tubular feeder for food pellets. A shutter opened the feeder for 1280 ms while the presence of food was signalled by 600 Hz (CS+) tone and its absence by a 3000 Hz (CS-) tone. The electrophysiological experiments were performed after the rats had developed a preference for reaching with the left or right forepaw and when their discriminations were 75% correct. Unit activity was recorded in the motor cortex contralateral to the preferred forepaw using capillary microelectrodes and a head-mounted microdrive. Post-stimulus histograms (PSHs) to CS+ (n = 71) showed an increase of firing rate in the first 120 ms after CS onset (40% units) and a tonic excitation (55% units) starting some 200 ms later. The second component was related to movement as revealed by simultaneously plotted peri-reach histograms. The first component was related to preparatory activity and was also present in the PSHs obtained during correct reactions to CS- (n = 29). Then, absence of reaching was manifested by inhibition replacing the second excitatory component. The first but not the second excitatory components were seen in the PSHs plotted during negative reactions to CS+ (n = 18). It is concluded that the conditioned stimuli elicit in the motor cortex preparatory activity preceding actual movement by 200-250 ms. The neuronal populations engaged in the preparatory activity and movement execution overlap.

Acoustic Stimulation↗
PubMed1984

Persistence of spatial memory in the Morris water tank task.

Persistence of the spatial memory record was examined in 30 rats overtrained in the working memory version of the Morris water tank task. In Experiment 1, the animal had to find during the acquisition trial an invisible underwater platform randomly located at one of 4 possible sites in the pool. Retention test was performed 1 min, 60 min, 4 h or 24 h later with the same position of the platform and same or changed position of the start. Whereas in the acquisition trials the rats reached the goal after 12 s on average, the latency in the retrieval trials increased with the acquisition-retrieval interval. It was 5 s with the 1-min delay and exponentially approached, but did not quite reach the acquisition trial latency with the 24-h delay. In Experiment 2 the rats were started from the same position of the tank to goal positions changing from trial to trial in a prearranged sequence. There were either 1-h or alternating 1-min and 2-h intervals between the 6 daily trials. The latencies were long during the first trial and whenever the goal changed and short when the goal remained the same as on the previous trial. The latencies were not significantly influenced by intertrial interval in the 1 min to 2 h range. It is concluded that the decay of spatial memory in the water tank task is slow and is little affected by proactive interference.

Animals↗
PubMed1984

The effect of hypothermia on the rat's spatial memory in the water tank task.

The effect of hypothermia on the retention of the water tank navigation task has been examined in 21 male hooded rats. After a 3-min swimming test on Day 1 the animals were trained on Days 2 and 3 (2 X 12 trials) to find a small submerged platform 1 cm below the surface of a large pool (120 cm in diameter) of opaque water. On Day 4, the rats were divided into three groups (n = 7) which were cooled to colonic temperatures of 22-24 degrees C (H1), 25-27 degrees C (H2), and 28-31 degrees C (H3), respectively, and given 12 retrieval trials in the water tank. Average escape latencies increased from 6 s in normothermic rats on Day 3 to 33, 19, and 12 s on Day 4 in the H1, H2, and H3 groups, respectively. Under the same testing conditions the performance of groups H1, H2, and H3 improved on Day 5 to 20, 8 and 6 s, respectively. It is concluded that spatial memory retrieval is resistant to mild hypothermia (30 degrees C), but that it is severely impaired at body temperatures below 25 degrees C. Reacquisition of the task is slowed down but not fully prevented in deep hypothermia.

Animals↗