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Biomedical subjects

P Buser

Publications and source records attributed to P Buser.

At least 91 records · Page 5Linked to original sources
PubMed1986

Role of the extra-geniculate pathway in visual guidance. II. Effects of lesioning the pulvinar-lateral posterior thalamic complex in the cat.

Eight cats were trained to perform a paw movement towards a moving target. The target was a lever which moved at a variable speed across an aperture situated in front of the animal, from left to right or right to left at random, but only once per trial. The animals were trained until performances stabilized in terms of precision (correct movements versus misguided ones) and speed (response time distribution of correctly guided movements). Then they underwent bilateral electrolytic lesions restricted to the pulvinar nucleus (4 cats) or to the lateral posterior nucleus (4 cats). Pre- and postoperative performances were compared. The results showed a clear difference between the two nuclei; postoperative performances after pulvinar lesion were in the preoperative range, both for precision and response time, thus allowing this group to be considered as a control lesion group. On the other hand, a marked impairment in visual guidance followed lateral posterior lesions. This deficit affected both the precision and the speed of the response, with all cats showing a tendency to increase the response time of their efficient movements. This impairment disappeared progressively except for one animal, whose lesion was especially large. We suggest that the nucleus lateral posterior is involved in the control of visually guided movements; and its role as a component of the tecto-thalamo-cortical pathway is discussed.

Animals↗
PubMed1986

Brachium pontis lesions in cats partly reproduce the cerebellar dysfunction of voluntary reaching movements.

The pontocerebellar pathway in the brachium pontis (BP), is known to convey signals from various cortical and subcortical visual structures to the cerebellum. Recently, a cortico-pontocerebellar pathway involving the BP has been implicated in the control of visually guided movements, on the basis of anatomical and physiological data. To further test this hypothesis, using behavioural methods, we studied the effects of a bilateral interruption of these projections in the BP, on 5 cats fully trained to perform a forepaw movement towards a moving target-light. The postoperative deficit consisted of an impairment in precision, with a strong tendency to over-reach and and increase in reaction time, contrasting with an unimpaired movement time. Although there was some initial recovery, performance soon stabilized with a permanent impairment in accuracy and reaction time. These results are discussed in relation to the various sensory signals processed at the pontine level and forwarded to the cerebellum, and compared with the effects of motor dysfunction of cerebellar origin.

Animals↗
PubMed1985

[Eosinophilic lung infiltration during malaria prophylaxis with pyrimethamine-sulfadoxine (Fansidar)].

The case is reported of a 40-year-old woman who developed an eosinophilic lung infiltration during malaria prophylaxis with pyrimethamine-sulfadoxine (Fansidar). The patient had a severe condition with cough, fever, chills, dyspnea, weight loss and an unusual but characteristic radiologic picture. Corticosteroid medication was followed by a dramatic improvement in symptoms and complete resolution of the radiographic opacities within a few days. There was no recurrence after cessation of steroids. The authors believe that the cause of this lung disease was an allergic reaction to pyrimethamine-sulfadoxine (Fansidar). Some aspects of drug-induced eosinophilic pulmonary infiltrations are discussed.

Adult↗
PubMed1984

Receptive field sizes and responsiveness to light in area 18 of the adult cat after chiasmotomy. Postoperative evolution; role of visual experience.

Receptive field sizes to stimulation of the ipsilateral temporal retina were studied in area 18 of adult cats at different times after complete midsagittal section of the optic chiasm. A specific postoperative evolution could thus be noticed: immediately after section, the average area of the receptive fields was reduced, as compared to control preparations, owing to the disappearance of large fields located at more than 20 degrees of eccentricity. A progressive reappearance of these large fields occurred between 8 and 45 days after chiasmotomy, provided that the animal was placed in normal visual conditions during its postoperative period. No such recovery could be assessed after as long as 55 days, in animals kept in complete darkness after operation. Chiasmotomized cats also displayed a reduction of their percentage of light reactive cells with respect to controls, as expected from the suppression of the contralateral input. This percentage was at first very low and progressively increased, during postoperative recovery but again not when the animal had been kept in the dark. Finally, an increase of cells with "diffuse responses" was observed in the late postoperative recovery stage. This latter evolution also appeared to depend upon postoperative visual experience. On the other hand, no clear indication of an interhemispheric transfer could be obtained in these experiments, even at the 17-18 boundary.

Animals↗
PubMed1984

Visually guided movements in the cat: a test using a randomly moving target.

A new apparatus is described in which cats must perform a visually guided movement of the forepaw toward a quasi-randomly moving target in order to obtain a reward. The target is a small bulb fixed to the pen carrier of an XY plotter; it moves under a translucent screen and is only visible to the cat when the bulb comes on at the onset of each trial. Sine waves of variable frequency are applied to the X and Y channels, the resulting target trajectory being a complex Lissajous pattern, unpredictable for the animal. Response times of accurate presses (detected by a capacity detector) are calculated and various types of misreachings can be coded, allowing quantification of performance, and comparison between normal and lesioned cats.

Animals↗
PubMed1984

[Unit activity in the ventral tegmental area and the state of focused attention in the normal awake cat].

Our previous studies had indicated that electrocortical "beta" rhythms (37 Hz) that develop in the fronto-parietal area in waking, immobile and highly attentive cats, are under the control of a dopaminergic system originating from the ventral tegmental area (VTA). A single unit study has now shown that 9% of VTA cells displayed a sustained increased of their firing rate during each beta episode. These data indicate that VTA cells exert a "gate control" on the rhythmic thalamo-cortical beta system.

Animals↗
PubMed1983

Unilateral connections between amygdala and hippocampus in man. A study of epileptic patients with depth electrodes.

During stereotaxic explorations of patients suffering from intractable temporal or non-temporal epilepsies, isolated electrical shocks could be delivered through depth electrodes to either the amygdaloid nucleus or the hippocampus, recording of the elicited response being performed from hippocampus or amygdala, respectively, on the same side. All patients displayed hippocampal responses to amygdala stimulation, whatever the type of epilepsy diagnosed. On the other hand, amygdala responses to hippocampal single shocks were only observed in a majority of patients suffering temporal epilepsy, while such back to forth activation could seldom be assessed in a group of patients not clearly characterized as temporal epileptics. It is suggested that subtle changes in excitability of an (indirect) pathway from hippocampus to amygdala are revealed through this procedure of low intensity, short-lasting stimulation, as a correlate of the temporal epileptic process.

Amygdala↗
PubMed1983

[Responsive characteristics of the cells of cortex area 18 of the adult cat after chiastomy. Postoperative development; importance of the visual experience].

Patterns of unit responses in area 18 to stimulation of the ipsilateral temporal retina were studied in adult Cats at different times after complete midsagittal section of the optic chiasm. A specific postoperative evolution could thus be followed. Immediately after section, the percentage of cells reacting to light was reduced, as compared to control preparations, as well as the average areas of the receptive fields, owing to the disappearance of large eccentric fields. A progressive recovery of the normal reactive patterns occurred between 8 and 45 days after chiasmotomy, provided that the animal was placed in normal visual conditions during its postoperative period. No such recovery could be observed after 55 days, in animals kept in complete darkness after operation. Visual experience thus seems essential to this kind of functional recovery in the adult. Another characteristic of chiasmotomised Cats also appeared to depend upon postoperative visual experience, namely the development of cells with "diffuse" responses to light.

Animals↗
PubMed1982

Ventral mesencephalic tegmentum (VMT) controls electrocortical beta rhythms and associated attentive behaviour in the cat.

When a cat is immobile, very alert and displaying behaviour suggesting focused attention toward a target in its environment, beta rhythms (ca. 40 Hz) develop in the fronto-parietal cortical areas. After bilateral electrolytic lesions of the ventral mesencephalic tegmentum (VMT), these beta rhythms are suppressed (while other cortical activities, with other behavioural correlates, persist), and at the same time, attentive immobility is no longer observed: the same experimental situation as in the control now elicits locomotor hyperactivity. Arguments are produced, favouring the hypothesis that both behavioural immobility and the accompanying thalamocortical beta rhythms are controlled through one of the dopaminergic system that originate from the VMT and are distinct from the nigrostriatal one.

Animals↗
PubMed1982

Somatosensory rhythms in the awake cat: a single unit exploration of their thalamic concomitant in nucleus ventralis posterior and vicinity.

A microelectrode study was performed in n. ventralis posterior (VP) of the fully alert cat, to study the correlation between thalamic unit activity and the cortical synchronized 14 c/sec rhythms that develop in the somatic area I for forepaw and wrist projections, when the animal is in a state of "quiet waking". (i) Only a small proportion of VP cells underwent changes during the studied cortical rhythms. (ii) None of these cells were typical thalamo-cortical relay cells carrying tactile messages to the cortex. (iii) Cells altering their discharge were of two types, rhythmic (R) cells, discharging at the frequency of the cortical rhythms, and tonic (T) cells, displaying an overall, sustained change during the whole sequence of cortical 14 c/sec. (iv) Among R cells, some were long axon thalamo-cortical cells and others, likely to be interneurones. (v) Some T cells increased their firing rate during rhythmic trains, others came into silence during the same period. (vi) The thalamic circuitry responsible for this particular set of "quiet waking rhythms" is discussed.

Action Potentials↗
PubMed1981

Effects of lesioning the anterior suprasylvian cortex on visuo-motor guidance performance in the cat.

Seven cats were trained to press a lever that moved in front of them at an adjustable speed and at random from left to right or from right to left. Efficient presses were reinforced by food. After measuring accuracy and latency of pressing the lever, the animals underwent bilateral ablation of the suprasylvian (SS) cortex; in three animals the lesions involved its anterior aspect; in two animals, they were restricted to its middle portion; two other cats had lesions of both anterior and the middle SS cortex. No long-lasting postoperative deficits were observed in any group when the lever remained immobile. On the other hand, the scores after anterior SS lesions were severely deteriorated, when presses had to be performed on the moving lever. No such deficits were noticed when the ablations were restricted to the middle SS. These results suggest that the cat anterior suprasylvian cortex (that includes parts of areas 5 and 7) plays a determinant role in the spatial adjustment of a visually guided (or visually triggered) forelimb movement.

Animals↗
PubMed1980

[Parietal electrocortical rhythms in the cat: their relation to a behavior of focused attention and possible mesencephalic control through a dopaminergic pathway].

In the Cat, the development of an electrocortical rhythm at 40 Hz (fast "mu" rhythm) is observed in the parietal cortex whenever the subject immobilizes itself in an attitude of focused attention (e.g. when watching a mouse). This rhythm, as well as the accompanying behaviour, seems to be under the control of a dopaminergic mechanism originating from the ventral tegmental mesencephalic area (cellular dopaminergic group A 10).

Animals↗
PubMed1980

Structures involved in acquisition and performance of visually guided movements in the cat.

Cats were trained to press on a lever either fixed or moving at different speeds from left to right or right to left at random. In the first series of animals, the following bilateral lesions were performed after reaching criterion on the moving lever: (1) deep cutting of cortico-cortical fibers connecting visual and frontal cortex; (2) subtotal electrolytic destruction of n. ventralis lateralis of the thalamus (nVL); (3) ablation of the anterior (3a) or middle (3b) suprasylvian cortex. No postoperative deficits were noticed after lesions (1), (2), (1 + 2) or (3b). On the other hand, impairment was found after lesion (3a), strongly suggesting the role of the anterior suprasylvian cortex in visual guidance of the forepaw movement in cat. The second group of animals was first trained to press the fixed lever and then underwent bilateral n. VL lesions. After lesion, performance with fixed lever remained normal while the animals displayed a deficit with the moving lever. The conclusion is that the n. VL is essential only during the acquisition phase of the tested visuomotor performance.

Animals↗
PubMed1979

Central locomotor programming in the rabbit.

In decorticate, unanaesthetized and curarized rabbit preparations, with both hindlimbs deafferented, locomotor-like discharges were recorded from nerves to flexors and extensors and their time patterns were compared. The bursts of rhythmic activities recorded from nerves to several flexor muscles acting at either joint were shown to be synchronous, with no differences in their time of onset. The same was true for the extensors. Nerves to bifunctional muscles (biceps posterior, semi-tendinosus and tenuissimus) acting on two consecutive joints (knee flexors, hip extensors) could display two consecutive bursts in each locomotor cycle, one being pure flexor and the other an extensor discharge. It is shown here that this functional bivalence is programmed centrally and can be modulated, i.e. the relative importance of the flexor and the extensor bursts can be changed in a predictable way through afferent (proprioceptive or cutaneous) influences, or through activation of the descending monoaminergic pathways. In extreme cases, complete functional reversal was observed in these bifunctional muscle nerves.

Action Potentials↗
PubMed1979

[Visually guided movement in the cat: difference in the effects of a bilateral lesion of the thalamic nucleus ventralis lateralis performed either before or after training].

Bilatéral lesions of the thalamic nucleus ventralis lateralis were performed in cats, either after [1] or before [2] training to reach a moving target with the forepaw. In situation [1], lesions were ineffective; in situation [2] the animal never reached normal scores. VL thus seems to be essential only in the acquisition phase of the tested visuomotor performance.

Animals↗