Biomedical subjects

A Rosier

Publications and source records attributed to A Rosier.

11 recordsLinked to original sources

PubMed1998

Human brain activity related to speed discrimination tasks.

The regional cerebral blood-flow (rCBF) pattern of the human brain was measured using positron emission tomography (PET) while subjects viewed, detected, judged the speed of a moving random dot pattern (RDP) or compared speeds of successive RDPs. In all four conditions, retinal input was identical. Two additional conditions, continuous presentation of a moving and a stationary RDP, were included to identify human MT/V5 (hMT/V5). Both speed discrimination tasks involved the right cuneus and right lingual gyrus and to a lesser degree the left lingual gyrus and a more anterior lingual region in the right hemisphere. There was, however, little or no differential activity over hMT/V5 during either speed discrimination. Direct comparison of the two speed discrimination tasks revealed higher activity in the right middle fusiform gyrus, a result reminiscent of that obtained in earlier studies using orientation and direction as the attribute to be discriminated. These results confirm that processing in the human visual cortex is task dependent and underscore the role of the middle fusiform gyrus in temporal comparison of simple attributes.

Adult↗

PubMed1998

Regions in the human brain activated by simultaneous orientation discrimination: a study with positron emission tomography.

In order to compare regional cerebral activity involved in simultaneous as opposed to successive orientation discrimination, we used positron emission tomography to measure regional cerebral blood flow, in two threefold sets of conditions, in a large number of subjects. The first such triad involved simultaneous orientation discrimination, orientation identification and detection, with all tasks using the same pair of gratings. The second triad consisted of successive orientation discrimination with its corresponding identification and detection tasks. Comparisons between tasks within each triad isolate attention to orientation and, respectively, spatial or temporal comparison. The subtraction of detection from simultaneous discrimination revealed activation of right fusiform, right lingual, left precentral, left cingulate and left temporal cortex, in addition to right insula, cerebellum and left thalamus. Only the fusiform, insular and precentral activations remained when the corresponding identification was subtracted from simultaneous discrimination. In contrast, most of the non-visual activation sites remained when simultaneous discrimination was compared with successive discrimination, which also revealed a left lingual activation. These experiments provide further evidence for task-dependent processing in the human visual system and suggest that the right fusiform cortex is involved in spatial as much as temporal comparisons.

Adult↗

PubMed1998

Human brain regions involved in direction discrimination.

To obtain further evidence for the functional specialization and task-dependent processing in the human visual system, we used positron emission tomography to compare regional cerebral blood flow in two direction discrimination tasks and four control tasks. The stimulus configuration, which was identical in all tasks, included the motion of a random dot pattern, dimming of a fixation point, and a tone burst. The discrimination tasks comprised the identification of motion direction and successive direction discrimination. The control tasks were motion detection, dimming detection, tone detection, and passive viewing. There was little difference in the activation patterns evoked by the three detection tasks except for decreased activity in the parietal cortex during the detection of a tone. Thus attention to a nonvisual stimulus modulated different visual cortical regions nonuniformly. Comparison of successive discrimination with motion detection yielded significant activation in the right fusiform gyrus, right lingual gyrus, right frontal operculum, left inferior frontal gyrus, and right thalamus. The fusiform and opercular activation sites persisted even after subtracting direction identification from successive discrimination, indicating their involvement in temporal comparison. Functional magnetic resonance imaging (fMRI) experiments confirmed the weak nature of the activation of human MT/V5 by successive direction discrimination but also indicated the involvement of an inferior satellite of human MT/V5. The fMRI experiments moreover confirmed the involvement of human V3A, lingual, and parietal regions in successive discrimination. Our results provide further evidence for the functional specialization of the human visual system because the cortical regions involved in direction discrimination partially differ from those involved in orientation discrimination. They also support the principle of task-dependent visual processing and indicate that the right fusiform gyrus participates in temporal comparison, irrespective of the stimulus attribute.

Acoustic Stimulation↗

PubMed1998

Scopolamine-induced impairment of delayed recognition of abstract visual shapes.

Since the limbic system, whose involvement in cognitive processes is well documented, constitutes a major central cholinergic area, the effect of cholinergic drugs on cognitive tasks has been studied extensively. In the present study, we used a long-term visual recognition task to evaluate the persistence of the scopolamine-induced anterograde amnesia beyond drug clearance intervals. Following memorization of a list of abstract shapes, subjects were evaluated on recognition performance immediately after encoding, and after a 3-day interval. Administration of scopolamine (0.4-0.8 mg) 70 min prior to encoding induced a significant (8-16%) deficit in delayed recognition performance. In contrast, a scopolamine challenge on delayed recognition following a drug-free encoding did not influence memory performance. In contrast, even at peak levels, scopolamine did not alter immediate recognition, detection or visual discriminative performances. Hence, the presence of scopolamine during the encoding of the shapes induced a significant long-term memory deficit that persisted after scopolamine clearance. Therefore, this paradigm is useful for imaging regional brain activation during impaired recognition without the confounding direct effects of scopolamine on cerebral blood flow or metabolism, two physiological variables underlying the indirect measurement of brain activation.

Adult↗

PubMed1997

Positron-emission tomography imaging of long-term shape recognition challenges.

Long-term visual memory performance was impaired by two types of challenges: a diazepam challenge on acquisition and a sensory challenge on recognition. Using positron-emission tomography regional cerebral blood flow imaging, we studied the effect of these challenges on regional brain activation during the delayed recognition of abstract visual shapes as compared with a baseline fixation task. Both challenges induced a significant decrease in differential activation in the left fusiform gyrus, suggesting that this region is involved in the automatic or volitional comparison of incoming and stored stimuli. In contrast, thalamic differential activation increased in response to memory challenges. This increase might reflect enhanced retrieval attempts as a compensatory mechanism for restoring recognition performance.

Adult↗

PubMed1996

Visualisation of loss of 5-HT2A receptors with age in healthy volunteers using [18F]altanserin and positron emission tomographic imaging.

We used [18F]altanserin and positron emission tomography (PET) to image serotonin 5-HT2A receptors in humans. The highest [18F]altanserin uptake is found in the cerebral cortex, with specific-to-nonspecific binding ratios varying from 0.53 to 1.91 in humans between 24 and 48 years of age. In all neocortical regions studied, [18F]altanserin uptake correlates negatively with age. No correlations were found between age and uptake in the cerebellum, the regional cerebral blood flow, or the time course of metabolization of [18F]altanserin. The reduction in cerebral 5-HT2A receptor binding thus directly reflects the loss of specific 5-HT2A receptors with age.

Adult↗

PubMed1996

Diazepam decreases performance in a long-term memory task using visual shapes.

We designed a memory task involving visual recognition sensitive enough to demonstrate the long-term amnesic effect of diazepam. Following memorization of a list of abstract visual stimuli (Fourier), subjects were evaluated on recognition performance immediately following acquisition and after a 3-day drug clearance interval. Administration of 15 mg diazepam 1 h before acquisition imposed a significant (10-24%) deficit only in delayed recognition. In contrast, a drug-free acquisition followed by a diazepam-challenged delayed recognition did not influence recognition. Moreover, 1 h after administration, diazepam did not significantly impair detection or visual discriminative performances. Given the persistence of an important deficit in recognition memory in the absence of any drug, this paradigm promises to be useful for studying regional cerebral blood flow during long-term memory performance.

Adolescent↗

PubMed1996

Variability of energy metabolism and nuclear T3-receptors within the skeletal muscle tissue of pigs different with respect to the halothane gene.

Energy metabolism of skeletal muscle tissue of pigs growing from approximately 12 to 18 kg (12 homozygous halothane negative, HH; 16 heterozygotes, Hh; 17 homozygous halothane susceptible, hh) was measured in vivo using 31P nuclear magnetic resonance (NMR) spectroscopy. Data for intracellular pH, phosphocreatine (PCr), phosphomonoesters (PME), and ATP were analyzed by canonical discriminant analysis, an artificial neural network approach, and analysis of variance. Within the hh pigs, two subpopulations could be distinguished before the application of halothane treatment. Some of the hh pigs had a high PME concentration in the biceps femoris muscle (hh(pme+)), whereas others had a low concentration (hh(pme-)) (2.18 +/- .12 for hh(pme+) vs 1.68 +/- .12 mM for hh(pme-), P < .004). The hh(pme+) pigs were statistically different from HH pigs for pH (P < .03), PME (P < .004), and PCr (P < .008) before halothane treatment. The hh(pme-) pigs were not different from the Hh and HH pigs with respect to PME when measured before halothane treatment (P > .05). However, intracellular pH (P < .03) and PCr (P < .008) of the hh(pme-) pigs were different from those of HH pigs (7.15 vs 7.19 for pH and 38.7 vs 35.1 for PCr, respectively). When combining intracellular pH, PME, and PCr within a canonical discriminant analysis, all were measured before halothane treatment, Hh pigs were found to be different from HH pigs (Mahalanobis distance different from zero, P < .02). In a second experiment, growth rate, depth of longissimus muscle, and maximal binding capacity of nuclear T3-receptors of skeletal muscle tissue were different (P < .05, P < .002, and P < .02, respectively) among pigs selected from the same genetic lines. Of the variability in depth of the longissimus muscle, 22% was explained by variability in maximal binding capacity of nuclear T3-receptors. These results, if confirmed with a large number of pigs, might open new possibilities for selection procedures for leanness because, with respect to halothane susceptibility, a shift between genotypic and phenotypic variability was observed.

Adenosine Triphosphate↗

PubMed1994

Partial colocalization of the GABAA receptor with parvalbumin and calbindin D-28K in neurons of the visual cortex and the dorsal lateral geniculate nucleus of the cat.

Monoclonal antibodies to a synthetic peptide fragment of the beta 1-subunit of the bovine central GABAA/benzodiazepine receptor were used to investigate immunocytochemically the distribution of this receptor in the visual system of the cat. Labeled neurons were observed in all layers of the visual cortex and the dorsal lateral geniculate nucleus. About half of the total cortical or geniculate neuronal population was found to be positive. To further identify immunocytochemically these GABAA receptor expressing cells, double stainings were undertaken with, on one hand, the monoclonal antibodies directed against the receptor complex, and on the other hand polyclonal antisera directed against cat muscle parvalbumin or chicken calbindin D-28K. A high degree of colocalization between either of the two calcium binding proteins and the GABAA receptor was found in the upper layers (I, II and III) of the visual cortex and in the A and C laminae of the dorsal lateral geniculate nucleus; all calbindin D-28K-positive cells were immunoreactive for the GABAA receptor. The parvalbumin-positive cells, scattered throughout all layers of the dorsal lateral geniculate nucleus and the visual cortex, except cortical layer I, were also all positive for the GABAA receptor. However, a large proportion of all GABAA receptor bearing cells were negative for one of the calcium binding proteins.

Animals↗

PubMed1994

Visualization of gamma-aminobutyric acid A receptors on proopiomelanocortin-producing neurons in the rat hypothalamus.

It has recently been shown that gamma-aminobutyric acid (GABA) and central-type benzodiazepine receptor agonists inhibit the expression of the POMC gene and the release of POMC-derived peptides from hypothalamic neurons. To determine whether the inhibitory effect of GABA could be accounted for by a direct action on POMC neurons, we investigated the localization of the beta 1-subunit of the GABAA-benzodiazepine-receptor complex in the arcuate nucleus. Using a monoclonal antibody raised against a synthetic fragment of the beta 1-subunit, we demonstrate the presence of GABAA receptor on POMC neurons. The proportion of POMC neurons that exhibit immunoreactivity for the beta 1-subunit of the GABAA receptor was not significantly different in the posterior portion (73.0-76.0%) and anterior portion (61.3-62.7%) of the arcuate nucleus. The data also revealed that in the arcuate nucleus, a majority of neurons that were immunostained by the antibody to the beta 1-subunit were not POMC positive. The present results support the concept that GABAA and central-type benzodiazepine receptor agonists exert a direct inhibitory action on POMC neurons. The data also indicate the existence of subsets of POMC neurons within the arcuate nucleus.

Amino Acid Sequence↗

PubMed1993

Immunocytochemical detection of astrocyte GABAA receptors in cat visual cortex.

A nine amino-acid peptide derived from the beta 1-subunit of the bovine GABAA receptor was used for immunization of mice and subsequent production of monoclonal antibodies (MAb). In view of the later immunocytochemical application of the MAb to sections of cat visual cortex, the MAb were characterized on similar tissue. The GABAA receptor was isolated by affinity chromatography of protein material obtained from cat cortical gray matter. The antibodies were characterized by SDS-PAGE, followed by immunoblotting and immunoadsorption. Immunocytochemical staining with the MAb revealed labeled cells throughout all layers of the cat visual cortex as well as within the white matter. The morphology of most stained cells in the white matter and of some cells in the cortical gray matter closely resembled that of astrocytes. Double immunocytochemical staining with an antiserum against glial fibrillary acidic protein (GFAP), followed by light microscopic examination, indeed confirmed that astrocytes in both white and gray matter in the cat cortex possess GABAA receptors.

Amino Acid Sequence↗