Biomedical subjects

Y Dalezios

Publications and source records attributed to Y Dalezios.

14 recordsLinked to original sources

PubMed2006

Eye position modulates the electromyographic responses of neck muscles to electrical stimulation of the superior colliculus in the alert cat.

Rapid gaze shifts are often accomplished with coordinated movements of the eyes and head, the relative amplitude of which depends on the starting position of the eyes. The size of gaze shifts is determined by the superior colliculus (SC) but additional processing in the lower brain stem is needed to determine the relative contributions of eye and head components. Models of eye-head coordination often assume that the strength of the command sent to the head controllers is modified by a signal indicative of the eye position. Evidence in favor of this hypothesis has been recently obtained in a study of phasic electromyographic (EMG) responses to stimulation of the SC in head-restrained monkeys (Corneil et al. in J Neurophysiol 88:2000-2018, 2002b). Bearing in mind that the patterns of eye-head coordination are not the same in all species and because the eye position sensitivity of phasic EMG responses has not been systematically investigated in cats, in the present study we used cats to address this issue. We stimulated electrically the intermediate and deep layers of the caudal SC in alert cats and recorded the EMG responses of neck muscles with horizontal and vertical pulling directions. Our data demonstrate that phasic, short latency EMG responses can be modulated by the eye position such that they increase as the eye occupies more and more eccentric positions in the pulling direction of the muscle tested. However, the influence of the eye position is rather modest, typically accounting for only 10-50% of the variance of EMG response amplitude. Responses evoked from several SC sites were not modulated by the eye position.

Action Potentials↗

PubMed2006

The local loop of the saccadic system closes downstream of the superior colliculus.

Models of the saccadic system differ in several respects including the signals fed back to their comparators, as well as the location and identity of the units that could serve as comparators. Some models place the comparator in the superior colliculus while others assign this role to the reticular formation. To test the plausibility of reticular models we stimulated electrically efferent fibers of the superior colliculus (SC) of alert cats along their course through the pons, in the predorsal bundle (PDB). Our data demonstrate that electrical stimulation of the PDB evokes saccades, even with stimuli of relatively low frequency (100 Hz), which are often accompanied by slow drifts. The velocity and latency of saccades are influenced by the intensity and frequency of stimulation while their amplitude depends on the intensity of stimulation and the initial position of the eyes. The dynamics of evoked saccades are comparable to those of natural, self-generated saccades of the cat and to those evoked in response to the electrical stimulation of the SC. We also show that PDB-evoked saccades are not abolished by lesions of the SC and that therefore antidromic activation of the SC is not needed for their generation. Our data clearly demonstrate that the burst generator of the horizontal saccadic system is located downstream of the SC. If it is configured as a local loop controller, as assumed by most models of the saccadic system, our data also demonstrate that its comparator is located beyond the decussation of SC efferent fibers, in the pons.

Analysis of Variance↗

PubMed1999

14C-deoxyglucose mapping of the monkey brain during reaching to visual targets.

The strategies used by the macaca monkey brain in controlling the performance of a reaching movement to a visual target have been studied by the quantitative autoradiographic 14C-DG method. Experiments on visually intact monkeys reaching to a visual target indicate that V1 and V2 convey visuomotor information to the cortex of the superior temporal and parietoccipital sulci which may encode the position of the moving forelimb, and to the cortex in the ventral part and lateral bank of the intraparietal sulcus which may encode the location of the visual target. The involvement of the medial bank of the intraparietal sulcus in proprioceptive guidance of movement is also suggested on the basis of the parallel metabolic effects estimated in this region and in the forelimb representations of the primary somatosensory and motor cortices. The network including the inferior postarcuate skeletomotor and prearcuate oculomotor cortical fields and the caudal periprincipal area 46 may participate in sensory-to-motor and oculomotor-to-skeletomotor transformations, in parallel with the medial and lateral intraparietal cortices. Experiments on split brain monkeys reaching to visual targets revealed that reaching is always controlled by the hemisphere contralateral to the moving forelimb whether it is visually intact or 'blind'. Two supplementary mechanisms compensate for the 'blindness' of the hemisphere controlling the moving forelimb. First, the information about the location of the target is derived from head and eye movements and is sent to the 'blind' hemisphere via inferior parietal cortical areas, while the information about the forelimb position is derived from proprioceptive mechanisms and is sent via the somatosensory and superior parietal cortices. Second, the cerebellar hemispheric extensions of vermian lobules V, VI and VIII, ipsilateral to the moving forelimb, combine visual and oculomotor information about the target position, relayed by the 'seeing' cerebral hemisphere, with sensorimotor information concerning cortical intended and peripheral actual movements of the forelimb, and then send this integrated information back to the motor cortex of the 'blind' hemisphere, thus enabling it to guide the contralateral forelimb to the target.

Animals↗

PubMed1999

Metabolic activity patterns in the monkey visual cortex as revealed by spectral analysis.

The metabolic activity pattern of the monkey visual cortex was mapped quantitatively with [14C]-2-deoxyglucose during the performance of a visually guided reaching task. After bandpass filtering of the reconstructed two-dimensional metabolic maps of areas V1 and V2, alternating bands of high and low metabolic activity were apparent in control and experimental hemispheres. The spatial arrangement of active bands was studied with two-dimensional spectral analysis, and bands were found to be more organized in the experimental monkey. In area V1 of the control monkey the spectral amplitude was spread over a wider range of directions and frequencies than in the experimental subject. The finding that layer IV is characterized by more complex spectra than layers I through III suggests the coexistence of more than one active columnar system in the geniculorecipient layer. In area V2, stripes running almost perpendicular to the V1/V2 border were found along with superimposed patches of enhanced metabolic activity. In the experimental hemispheres, the corresponding spectra were extremely sharp yielding a constant periodicity. It is suggested that the well-organized columnar arrangement within areas V1 and V2 of the experimental hemispheres emerges from the diffusely organized background network of activity patterns in the control state.

Algorithms↗

PubMed1998

An anatomical substrate for the spatiotemporal transformation.

The purpose of the present experiments was to test the hypothesis that the metrics of saccades caused by the activation of distinct collicular sites depend on the strength of their projections onto the burst generators. This study of morphofunctional correlations was limited to the horizontal components of saccades. We evoked saccades by stimulation of the deeper layers of the superior colliculus (SC) in alert, head-fixed cats. We used standard stimulus trains of 350 msec duration, 200 Hz pulse rate, and intensity set at two times saccade threshold in all experiments. Evoked saccades were analyzed quantitatively to determine the amplitude of the horizontal component of their "characteristic vectors". This parameter is independent of eye position and was used as the physiological, saccade-related metric of the stimulation sites. Anatomical connections arising from these sites were visualized after anterograde transport of biocytin injected through a micropipette adjoining the stimulation electrode. The stimulation and injection sites were, therefore, practically identical. We counted boutons deployed in regions of the paramedian pontine reticular formation reported to contain long-lead and medium-lead burst neurons of the horizontal burst generator. Regression analysis of the normalized bouton counts revealed a significant positive correlation with the size of the horizontal component of the characteristic vectors. This data supports a frequent modelling assumption that the spatiotemporal transformation in the saccadic system relies on the graded strength of anatomical projections of distinct SC sites onto the burst generators.

Animals↗

PubMed1998

Brain benzodiazepine binding in aged rats.

Membrane [3H]flunitrazepam binding to central and peripheral benzodiazepine binding sites was studied in four brain areas (cerebellum, cortex, striatum and midbrain) of young (age 2-4 months) and aged (> 24 months) rats. A generalized reduction in the density of central binding sites (Bmax) was observed in all brain areas examined in aged rats. This reduction is irrelevant of the brain area and, according to literature, may correspond to cell loss and/or differential expression of mRNAs coding for the subunits of the GABA/benzodiazepine receptor complex during ageing. In the case of the peripheral binding sites, there was a decrease of Bmax in all brain areas with the exception of the cerebellum. However, the percent reduction of peripheral binding sites varied significantly among the different brain areas. These data suggest a differential effect of ageing on brain benzodiazepine binding which may reflect the special role for each brain area during ageing.

Aging↗

PubMed1998

Anatomy and physiology of the primate interstitial nucleus of Cajal. II. Discharge pattern of single efferent fibers.

Anatomy and physiology of the primate interstitial nucleus of Cajal. II. Discharge pattern of single efferent fibers. J. Neurophysiol. 80: 3100-3111, 1998. Single efferent fibers of the interstitial nucleus of Cajal (NIC) were characterized physiologically and injected with biocytin in alert behaving monkeys. Quantitative analysis demonstrated that their discharge encodes a constellation of oculomotor variables. Tonic and phasic signals were related to vertical (up or down) eye position and saccades, respectively. Depending on how they encoded eye position, saccade velocity, saccade size, saccade duration, and smooth-pursuit eye velocity, fibers were characterized as regular or irregular, bi- or unidirectionally modulated, more or less sensitive, and reliable or unreliable. Further, fibers that did not burst for saccades (tonic) and fibers the eye-position and saccade-related signals of which increased in the same (in-phase) or in the opposite (anti-phase) directions were encountered. A continuum of discharge properties was the rule. We conclude that NIC efferent fibers send a combination of eye-position, saccade-, and smooth-pursuit-related signals, mixed in proportions that differ for different fibers, to targets of the vertical neural integrator such as extraocular motoneurons.

Animals↗

PubMed1998

New mechanism that accounts for position sensitivity of saccades evoked in response to stimulation of superior colliculus.

New mechanism that accounts for position sensitivity of saccades evoked in response to stimulation of superior colliculus. J. Neurophysiol. 80: 3373-3379, 1998. Electrical stimulation of the feline superior colliculus (SC) is known to evoke saccades whose size depends on the site stimulated (the "characteristic vector" of evoked saccades) and the initial position of the eyes. Similar stimuli were recently shown to produce slow drifts that are presumably caused by relatively direct projections of the SC onto extraocular motoneurons. Both slow and fast evoked eye movements are similarly affected by the initial position of the eyes, despite their dissimilar metrics, kinematics, and anatomic substrates. We tested the hypothesis that the position sensitivity of evoked saccades is due to the superposition of largely position-invariant saccades and position-dependent slow drifts. We show that such a mechanism can account for the fact that the position sensitivity of evoked saccades increases together with the size of their characteristic vector. Consistent with it, the position sensitivity of saccades drops considerably when the contribution of slow drifts is minimal as, for example, when there is no overlap between evoked saccades and short-duration trains of high-frequency stimuli.

Algorithms↗

PubMed1997

Spatial cortical patterns of metabolic activity in monkeys performing a visually guided reaching task with one forelimb.

The 2-[14C]deoxyglucose method was used to map the metabolic activity in the neocortex of monkeys (Macaca nemestrina) performing a visually guided reaching task with one forelimb. Monkeys received liquid reward for correct, single directional reaching movements, which were required at a rate of about 10 per minute. We estimated the weighted average of local glucose consumption within several neocortical areas, and we reconstructed quantitative, high-resolution, two-dimensional maps of the detailed spatiointensive patterns of activity. Our findings demonstrate the involvement of the striate and prestriate cortices, the inferior intraparietal and superior temporal visual association areas, the frontal eye field and the caudal periprincipal cortex, the primary somatosensory and the related superior intraparietal area, the primary and association auditory cortices, the superior temporal multimodal region, and the premotor, primary, supplementary, and cingulate motor areas. The visual cortex in the superior temporal and the intraparietal sulci, which is concerned with "where", was activated during visually guided reaching. In contrast, the inferior temporal visual association cortex, which is concerned with "what", was not involved in our study. We suggest that the activated direction-selective layer four of V1 and the thick stripes of V2 convey visuomotor information to the activated cortex in the posterior bank and the floor of the superior temporal sulcus, which may encode the constantly updated position of the moving forelimb. In parallel, the activated cortex in the ventral part and the lateral bank of the intraparietal sulcus may encode visuospatial information related to the localization of the visual target in the extrapersonal space. Furthermore, the dorsal part of the medial bank of the intraparietal sulcus may be involved in proprioceptive guidance of movement, based on the parallel metabolic effects shown only contralateral to the moving forelimb within this region and the forelimb representations in the primary somatosensory and motor cortices. Finally, the bilaterally activated network including the inferior postarcuate skeletomotor and prearcuate oculomotor cortical fields and the caudal periprincipal region 46 may participate in sensory and oculomotor to motor transformations, in parallel with the medial and lateral intraparietal cortices with which this network is reciprocally interconnected.

Animals↗

PubMed1996

Metabolic activity pattern in the motor and somatosensory cortex of monkeys performing a visually guided reaching task with one forelimb.

The [14C]deoxyglucose method was used to map the metabolic activity in the primary somatosensory and motor cortex in monkeys (Macaca nemestrina) performing a unimanual task. The task required visually guided reaching and target holding at a rate of about 10 movements per min. The entire dorsoventral extent of the cortical region lying between the posterior crown of the arcuate and the anterior crown of the intraparietal sulci was reconstructed on the sagittal plane, from horizontal sections aligned on the fundus of the central sulcus. The metabolic mapping of the control monkey demonstrated homogeneous activity all around the central sulcus, bilaterally. The mapped activity in the performing monkeys displayed two different patterns. The first pattern, contralateral to the moving forelimb, was characterized by several discrete regions of increased metabolic activity, which were symmetrically distributed in a mirror image fashion around the fundus of the central sulcus. These activated regions correspond to the lower body, forelimb, and mouth areas of representation of body parts in previously reported maps in primary motor and somatosensory cortical areas. The second activity pattern ipsilateral to the moving forelimb, displayed activated somatosensory and motor regions corresponding only to the lower body, and mouth representations. Our study provides a continuous, high resolution map of activity pattern in the entire primary motor and somatosensory cortices, which demonstrates that the reaching forelimb is controlled by a discrete subregion in the contralateral somatosensorimotor cortex, whereas other subregions of body representation are actively involved, bilaterally, during the performance of a relatively simple motor behaviour.

Animals↗

PubMed1996

Neuronal mechanisms of two-dimensional orienting movements in the cat. I. A quantitative study of saccades and slow drifts produced in response to the electrical stimulation of the superior colliculus.

To evaluate the metrics of rapid eye movements caused by the activation of distinct collicular microzones, the superior colliculus (SC) was electrically stimulated in alert behaving cats while their heads were restrained. A quantitative study of electrically induced rapid eye movements demonstrated that their amplitude and direction depended on the intensity of stimulation, the electrode location, and the initial position of the eyes, while their duration depended on the intensity of stimulation. When detailed quantitative procedures are employed, properties of saccades produced in response to the electrical stimulation of the feline SC resemble those of saccades elicited in response to the electrical stimulation of a variety of primate brain areas. Besides saccades, electrical stimulation of the feline SC gave rise to slow drifts whose amplitude and direction was also influenced by the initial position of the eyes. Because their size depended on the frequency of stimulation and their time course reflected mechanical properties of the oculomotor plant, induced slow drifts could be due to a more or less direct projection of the SC onto extraocular motoneurons. A model that includes such a variety of connections between the SC and extraocular motoneurons is presented and is shown to produce realistic combinations of fast and slow eye movements when its input is a step function of time. The present findings support the notion that an orbital mechanical factor underlies the eye position sensitivity of slow drifts and saccades evoked in response to the electrical stimulation of the SC.

Animals↗

PubMed1995

Interaction between [3H]flunitrazepam and [3H]GABA binding in the cerebellum of reeler mice.

It has been shown that in the cerebellum of reeler mutant mice GABA levels and GABA uptake increase while GABA binding decreases. This study shows that in the cerebellum of these mutants there is also an increase of benzodiazepine receptors. This increase is observed in cerebellar homogenates, in nuclei and in membranes. The increase in the density of central (i.e. clonazepam displacable) benzodiazepine receptors is primarily reflected in binding sites located in the GABA-receptor complex. In comparison to wild-type, GABA-modulin extracted from reeler cerebellum inhibits with a greater potency [3H]GABA binding. The increase in the central-type of benzodiazepine binding and its interaction with GABA binding, observed in cerebellar membranes, is interpreted as a functional response to the decrease in GABA binding and may reflect benzodiazepine receptor condensation and/or changes of subunit composition of the GABA/benzodiazepine receptor complex. The enhanced activity of reeler GABA-modulin reflects a functional response to the increased GABA levels in reeler cerebellum. The increase of the peripheral-type (i.e. PK 11195 displacable) of benzodiazepine receptors is probably due to metabolic changes that may accompany reeler cerebellar mutation. Differences in nuclear benzodiazepine binding between reeler and wild-type mice add a physiological importance to the nuclear binding of this drug.

Animals↗

PubMed1993

Nuclear benzodiazepine binding: possible interaction with thyroid hormone receptors.

The biochemical and pharmacological properties of nuclear [3H]flunitrazepam in brain tissues were studied. Nuclear [3H]flunitrazepam binding is saturable for both central and peripheral binding sites. Inosine and hypoxanthine displace nuclear [3H]flunitrazepam binding with greater potency than the membrane [3H]flunitrazepam binding. Triiodothyronine (T3) increases the maximum number of binding sites (Bmax) of nuclear [3H]flunitrazepam binding in vitro while thyroxine (T4) does not have any effect. Diazepam reduces the affinity of nuclear 125I-T3 binding in vitro, while the Bmax is not affected significantly. Mild digestion of chromatin, using micrococcal nuclease, reveals that a major portion of nuclear [3H]flunitrazepam binding sites are located on chromatin. These data suggest a functional role for nuclear benzodiazepine binding and a possible modulatory effect of benzodiazepines on T3 binding with its nuclear receptors.

Animals↗

PubMed1986

Comparative aspects of cerebellar [3H]flunitrazepam and [3H]GABA binding.

[3H]Flu and [3H]GABA binding has been studied in mice and Rabbit cerebellum (Ce). The Bmax of [3H]Flu binding in Ce membranes is similar in all mice strains examined and Rabbit. However, in Ce homogenate there are significant differences in both kd and Bmax. Subcellular distribution shows higher [3H]Flu binding in the nuclear than in the membranous fraction. However, the [3H]GABA binding is lower in the nuclear than the membranous fraction.

Animals↗