PubMed Health⌕ Search

Biomedical subjects

M Paré

Publications and source records attributed to M Paré.

31 records · Page 2Linked to original sources
PubMed1996

Saccadic reaction time in the monkey: advanced preparation of oculomotor programs is primarily responsible for express saccade occurrence.

1. The introduction of a period of darkness between the disappearance of an initial fixation target and the appearance of a peripheral saccade target produces a general reduction in saccadic reaction time (SRT)-known as the gap effect- and often very short latency express saccades. To account for these phenomena, premotor processes may be facilitated by release of visual fixation and advanced preparation of saccadic programs. The experiments described in this paper were designed to test the relevance of the ocular fixation disengagement and oculomotor preparation hypotheses by identifying the influence of different factors on SRTs and the occurrence of express saccades in the monkey. 2. The SRTs of two monkeys were measured in two behavioral paradigms. A peripheral saccade target appeared at the time of disappearance of a central fixation target in the no-gap task, whereas a 200-ms period of no stimuli was interposed between the fixation target disappearance and the saccade target appearance in the gap task. The distribution of SRTs in these tasks was generally bimodal; the first and second mode was composed of express and regular saccades, respectively. We measured the mean SRT, mean regular saccade latency, mean express saccade latency, and percentage of express saccades in both tasks. We also estimated the gap effect, i.e., the difference between the SRTs in no-gap trial and the SRTs in gap trials. 3. Once the animals were trained to make saccades to a single target location and produce express saccades, SRTs in both no-gap and gap trials displayed a broad tuning with respect to the spatial location of the trained target when the target location was varied randomly in a block of trials. Express saccades were made only to a restricted region of the visual field surrounding the trained target location. A gap effect was present for nearly all target locations tested, irrespective of express saccade occurrence. Finally, the probability of generating an express saccade at the trained target location decreased with the introduction of uncertainty about target location. 4. The occurrence of express saccades increased with the duration of the visual and nonvisual (gap) fixation that the animal was required to maintain before the onset of a saccade target. The gap duration was effective in reducing the mean SRT for gaps < or = 300 ms, and it was more influential than comparable variation in the visual fixation duration. 5. The occurrence of express saccades made to targets of identical eccentricity increased when the initial eye fixation position was shifted eccentric in a direction opposite to the saccade direction. Concomitantly, mean SRT decreased by approximately 2 ms for each 1-deg change in initial eye fixation position. 6. The occurrence of express saccades depended upon contextual factors, i.e., on both the behavioral task (no-gap or gap) and the latency of the saccade that the monkey executed to the same target in the preceding trial. The highest percentage of express saccades was observed after an express saccade in a no-gap trial, whereas the lowest percentage was obtained after a regular saccade in a gap trial. 7. These findings indicate that training-dependent express saccades are restricted to a specific spatial location dictated by the training target, and their incidence is facilitated by high predictability of target presentation, long-duration foreperiod, absence of visual fixation, eccentric initial eye position opposite to the saccade direction, and express saccade occurrence in the previous trial. The release of fixation afforded by the gap accounts for the general gap effect, but has only a modulatory influence on express saccade generation. We conclude that advanced motor preparation of saccadic programs generally reduces SRT and is primarily responsible for the occurrence of express saccades, which therefore may be caused mainly by neuronal changes restricted to a specific locus-coding for the trained movemen

Analysis of Variance↗
PubMed1996

[Blaschkolinear eruption with biological signs of lupus].

INTRODUCTION: Acquired inflammatory dermatoses of the adult with a blaschkolinear arrangement are rare. Their cause is unknown. CASE REPORT: We report the case of a 35-year-old man who presented an unilateral skin eruption covering the forearm and with secondary blaschkolinear extension to the arm, the axillary region and the chest. In this particular case, the patient was positive for RNP type anti-nuclear antibodies and direct immunofluorescence was positive in both biopsies of the lesions and of healthy skin. The eruption lasted 6 months and regressed spontaneously. DISCUSSION: Such cases are exceptional and the nosology is difficult to establish. A particular form of lupus erythematosus? Fortuitous coexpression of lupus antibodies and blaschkitis in an adult?

Adult↗
PubMed1994

The fixation area of the cat superior colliculus: effects of electrical stimulation and direct connection with brainstem omnipause neurons.

The superior colliculus has long been recognized as an important structure in the generation of saccadic displacements of the visual axis. Neurons with presaccadic activity encoding saccade vectors are topographically organized and form a "motor map." Recently, neurons with fixation-related activity have been recorded at the collicular rostral pole, at the area centralis representation or fixation area. Another collicular function which deals with the maintenance of fixation behavior by means of active inhibition of orientation commands was then suggested. We tested that hypothesis as it relates to the suppression of gaze saccades (gaze = eye in space = eye in head + head in space) in the head-free cat by increasing the activity of the fixation cells at the rostral pole with electrical microstimulation. Long stimulation trains applied before gaze saccades delayed their initiation. Short stimuli, delivered during the gaze saccades, transiently interrupted both eye and head components. These results provide further support for a role in fixation behavior for collicular fixation neurons. Brainstem omnipause neurons also exhibit fixation-related activity and have been shown to receive a direct excitatory input from the superior colliculus. To determine whether the collicular projection to omnipause neurons arises from the fixation area, the deep layers of the superior colliculus were electrically stimulated either at the rostral pole including the fixation area or in more caudal regions where stimulation evokes orienting responses. Forty-nine neurons were examined in three cats. 61% of the neurons were found to be orthodromically excited by single-pulse stimulation of the rostral pole, whereas only 29% responded to caudal stimulation. In addition, stimuli delivered to the rostral pole activated, on average, omnipause neurons at shorter latencies and with lower currents than those applied in caudal regions. These results suggest that excitatory inputs to omnipause neurons from the superior colliculus are principally provided by the fixation area, via which the superior colliculus could play a role in suppression of gaze shifts.

Animals↗
PubMed1994

Gaze shifts evoked by stimulation of the superior colliculus in the head-free cat conform to the motor map but also depend on stimulus strength and fixation activity.

In our previous paper we demonstrated that electrical microstimulation of the fixation area at the rostral pole of the cat superior colliculus (SC) elicits no gaze movement but, rather, transiently suppresses eye-head gaze saccades. In this paper, we investigated the more caudal region of the SC and its interaction with the fixation area. In the alert head-free cat, suprathreshold stimulation in the anterior portion of the SC but outside the fixation area evoked small saccadic shifts of gaze consisting mainly of an eye movement, the head's contribution being small. Stimulating more posteriorly elicited large gaze saccades consisting of an ocular saccade combined with a rapid head movement. At these latter stimulation sites, craniocentric (goal-directed) eye movements were evoked when the cat's head was restrained. The amplitude of eye-head gaze saccades elicited at a particular stimulation site increased with stimulus duration, current strength, and pulse rate, until a constant or "unit" value was reached. The peak velocity of gaze shifts depended on both pulse rate and current strength. The movement direction was not affected by stimulus parameters. The unit gaze vector evoked, in the head-free condition, by stimulating one collicular site was similar to that coded by efferent neurons recorded at that site, thereby indicating a retinotopically coded gaze error representation on the collicular motor map which is not revealed by stimulating the head-fixed animal. Evoked gaze saccades were found to be influenced by fixation behavior. The amplitude of evoked gaze shifts was reduced if stimulation occurred when the hungry animal fixated a food target. Electrical activation of the collicular fixation area was found to mimic well the effects of natural fixation on evoked gaze shifts. Taken together, our results support the view that the overall distribution and level of collicular activity contributes to the encoding of the metrics of gaze saccades. We suggest that the combined levels of activity at the site being stimulated and at the fixation area influence the amplitude of evoked gaze saccades through competition. When stimulation is at low intensities, fixation-related activity reduces the amplitude of evoked gaze saccades. At high activation levels, the site being stimulated dominates and the gaze vector is specified only by that site's collicular output neurons, from which arises the close correspondence between the unit-evoked gaze saccades and the neurally coded gaze vector at that site.

Animals↗
PubMed1992

Up-regulation of 5-hydroxytryptamine2 and neurokinin-1 receptors associated with serotonin/substance P hyperinnervation in the rat inferior olive.

The fate of serotonin and substance P receptors following serotonin/substance P hyperinnervation of CNS tissue was investigated in the inferior olivary complex of adult rats subjected to earlier intraventricular administration of 5,6-dihydroxytryptamine. [3H]8-hydroxy-2-(Dl-n-propylamino)tetralin, [3H]5-hydroxytryptamine, [3H]ketanserin and [125I]Bolton-Hunter-substance P were respectively used to label 5-hydroxytryptamine1A, 5-hydroxytryptamine1B, 5-hydroxytryptamine2 and neurokinin-1 receptor sites for quantitative ligand binding autoradiography. Only 5-hydroxytryptamine2 and neurokinin-1 sites were detected in the normal or serotonin/substance P-hyperinnervated inferior olivary complex. In the normal inferior olivary complex, the density of [3H]ketanserin binding (5-hydroxytryptamine2 receptors) was relatively low, being the highest in pars a of the caudal medial accessory olive and the principal olive; moderate in pars c of the caudal medial accessory olive; truly low in the medial and the lateral dorsal accessory olive, nucleus b and pars b of the caudal medial accessory olive; and negligible in the middle medial accessory olive, rostral medial accessory olive and the smaller subnuclei. [125I]Bolton-Hunter-substance P binding (neurokinin-1 receptors) appeared denser, being highest in nucleus beta and the middle medial dorsal accessory olive; moderate in the three portions of the caudal medial accessory olive, the lateral dorsal accessory olive and the dorsal cap of Kooy; low in the rostral medial accessory olive, the ventrolateral outgrowth and the dorsomedial cell column; and very low or null in the principal olive and the medial dorsal accessory olive. After serotonin/substance P hyperinnervation, there were striking increases in the apparent density of both populations of receptor. [3H]Ketanserin binding was now stronger in the most olivary subnuclei, including some in which it had not been found in the normal, such as the middle and the rostral medial accessory olive. [125I]Bolton-Hunter-substance P binding showed even greater elevations in a few subnuclei, such as the principal olive and the dorsomedial cell column; it was now detectable in the medial dorsal accessory olive, unchanged in the dorsal cap of Kooy and the ventrolateral outgrowth, and slightly decreased in the lateral dorsal accessory olive. The normal and altered distributions of both ligands did not match the respective patterns of serotonin and substance P innervation and hyperinnervation previously demonstrated with immunocytochemistry. In some sectors of the inferior olivary complex where both transmitters are presumably co-localized, there was no overlap in the distribution of the respective binding sites either in the normal or in the hyperinnervated state.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Virotoxins polymerize actin and induce membrane fragmentation in cytoplasmic preparations of Amoeba proteus.

Virotoxins and phalloidin are peptides that induce actin polymerization in vitro. We have compared the effect of five virotoxins and phalloidin on the ultrastructure of spread preparations of Amoeba proteus cytoplasm. Like phalloidin, the five virotoxins induce polymerization of cytoplasmic actin. Moreover, the virotoxins, but not phalloidin, induce membrane fragmentation in small spherical vesicles. We, therefore, conclude that these virotoxins may have another membrane-bound target besides actin.

Actins↗
PubMed1990

Gaze-related activity of brainstem omnipause neurons during combined eye-head gaze shifts in the alert cat.

Studies undertaken in head-restrained animals have long implicated the omnipause neurons (OPNs) in the initiation of saccadic eye movements. These inhibitory neurons discharge tonically but cease firing just before and during saccades in all directions. By recording from OPNs in alert behaving head-unrestrained cats, we have demonstrated that the activity of these cells is related to the displacement of the visual axis in space (gaze), which is the sum of the eye movement relative to the head and head movement relative to space. OPNs were found to exhibit a complete cessation of discharge for a period equivalent to the duration of the gaze shift, and not to the duration of either the rapid eye movement or the head movement components. In large gaze shifts, OPNs were silent even when the eye was immobile in the orbit, as long as the gaze shift was not completed. The results of this study show that OPNs are controlled by neural elements that take into account the actual position of the visual axis relative to its final desired position irrespective of the trajectory of the eye in the orbit or of whether the head is moving or not.

Animals↗
PubMed1987

Innervation and reinnervation of rat inferior olive by neurons containing serotonin and substance P: an immunohistochemical study after 5,6-dihydroxytryptamine lesioning.

Serotonin (5-HT) and substance P (SP) immunoreactive axon terminals were visualized in the inferior olivary complex (IOC) of adult rats, 1 to 2 weeks or 6 to 12 months after cerebro-ventricular injection of 5,6-dihydroxytryptamine (5,6-DHT). In normal or saline-injected controls of the same age, there was some overlap between the respective distributions of 5-HT- and SP-immunostained axonal varicosities among the various subdivisions of IOC. At short time intervals after the 5-HT axotomy, almost as many degenerating axonal profiles showed immunoreactivity to SP as to 5-HT throughout the IOC, suggesting the coexistence of both transmitters within the same fibres. A few areas continued to exhibit characteristic patches of 'normal-looking' SP immunoreactivity, consistent with a distinct innervation by SP fibres without coexistent 5-HT. At prolonged survival times after 5,6-DHT treatment, there was a massive increase in the number-and striking similarity in the distribution-of IOC axonal varicosities immunostained for SP as well as for 5-HT. This neo-innervation involved certain subdivisions of the IOC normally receiving fibres of either type (e.g. dorsal accessory olive), but also others normally poor in 5-HT and/or SP (e.g. medial accessory olive). It remains to be determined if this abundance of 5-HT-SP terminals in the 'hyperinnervated' IOC reflected a particular capacity to express both transmitters in regenerating 5-HT neurons.

5,6-Dihydroxytryptamine↗
PubMed1986

Retrograde labeling of neurons in the brain stem following injections of [3H]choline into the rat spinal cord.

In an attempt to identify cholinergic neurons in the brain stem which project to the spinal cord, [3H]choline (100, 20, 10, 5 or 1 microCi) was injected into the upper cervical spinal cord in 55 rats. The animals were killed 20 h later and the brains processed for autoradiography of diffusible substances. At all doses of [3H]choline, cells were consistently, retrogradely labeled in the medical medullary reticular formation, the lateral vestibular nucleus, the dorsolateral pontine tegmentum and the red nucleus. The retrogradely labeled cells were found to be moderately to darkly stained for acetylcholinesterase. Injection of [3H]noradrenaline (50 microCi) into the upper cervical spinal cord resulted in retrograde labeling of cells in the locus coeruleus, subcoeruleus and the ventrolateral pontine tegmentum, that correspond in position to the neurons of the A6, A7 and A5 catecholamine cell groups, respectively. Injection of [3H]serotonin (20 microCi) into the upper cervical spinal cord was associated with retrograde labeling of cells in the raphe pallidus, obscurus and magnus nuclei that correspond in position to those of the B1, B2 and B3 serotonin cell groups, respectively. Injection of True Blue into the upper cervical spinal cord was followed by retrograde labeling of a large number of cells located in the areas where cells were retrogradely labeled by [3H]choline, [3H]noradrenaline and [3H]serotonin, and additionally, in the solitary tract nucleus, the lateral, parvicellular medullary reticular formation, the caudal and oral pontine reticular formation, the mesencephalic reticular formation and the superior colliculus. These results indicate that from the cervical spinal cord, [3H]choline selectively retrogradely labels a certain population of non-monaminergic, acetylcholinesterase-positive cells localized in the medial medullary, and secondarily the dorsolateral pontine, reticular formation, the lateral vestibular nucleus, and the red nucleus.

Animals↗
PubMed1982

Long-term degeneration renders central tracts refractory to penetration by regenerating optic fibers.

We have examined time-dependent changes in the ability of degenerating central pathways in the goldfish to be penetrated by regenerative axons. We have found that when a tract has degenerated for 2--5 weeks it is readily penetrated by regenerating optic fibers. However, tracts which degenerated for any longer than 6 weeks, before being exposed to the regenerating fibers, were only sparsely penetrated by them. We conclude that over a period of no less than 6 weeks, degenerating central tracts in the goldfish change their character and become relatively refractory to penetration by regenerating axons.

Animals↗
PubMedDate not supplied

Determinants of health counseling practices in hospitals: the patient's perspective.

We conducted a survey of 518 patients who had been admitted to three hospitals for selected medical, surgical, and obstetrical conditions. All patients came from the same city. One of the hospitals had put forward health promotion and disease prevention as a formal goal. Almost 40% of the respondents reported that they received health counseling during their hospital stay. Logistic regression analyses revealed that medical care processes and organizational factors were more important than patient characteristics in determining health counseling. The only patient characteristic that was positively related to health counseling was "perceived poor health status." Favorable conditions for the development of health counseling included having an attending physician different from the one who treated the patient before entering the hospital, an adequate number of physician visits, and a longer length of stay. Being admitted to a medical ward rather than a surgical or an obstetrical ward also was associated with more frequent health counseling. No significant differences were found among hospitals. Finally, having a general practitioner rather than a specialist as attending physician did not make a difference. These findings support the view that although hospitals have an important and legitimate role to play in health promotion, organizational and institutional obstacles to implementing such practices must not be ignored.

Adult↗