Brain correlates of automatic visual change detection.

A number of studies support the presence of visual automatic detection of change, but little is known about the brain generators involved in such processing and about the modulation of brain activity according to the salience of the stimulus. The study presented here was designed to locate the brain activity elicited by unattended visual deviant and novel stimuli using fMRI. Seventeen adult participants were presented with a passive visual oddball sequence while performing a concurrent visual task. Variations in BOLD signal were observed in the modality-specific sensory cortex, but also in non-specific areas involved in preattentional processing of changing events. A degree-of-deviance effect was observed, since novel stimuli elicited more activity in the sensory occipital regions and at the medial frontal site than small changes. These findings could be compared to those obtained in the auditory modality and might suggest a "general" change detection process operating in several sensory modalities.

Schizophrenia and frontal cortex: where does it fail?

Schizophrenia is characterized by cognitive, social, and emotional impairments and by psychotic symptoms. Neuroimaging studies have reported abnormalities within the prefrontal cortex and it has been hypothesized that schizophrenia results from poor or miswired anatomical/functional connections. We have compared the functional connectivity within the frontal cortex in control and schizophrenic subjects during the realization of a Continuous Performance Task. The connectivity pattern within the frontal cortex was uncovered by the analysis of the correlation matrix computed from the fMRI time series in frontal areas for 14 schizophrenic patients and 14 control subjects. In control subjects, the right dorsolateral prefrontal cortex (DLFCr) activity correlated i) positively with the left dorsolateral prefrontal cortex and the posterior part of the supplementary motor area, ii) negatively with the medial and anterior/inferior part of the frontal cortex. In the schizophrenic group, these relations were abolished or strongly lowered. The negative relation between the DLFCr and the medial frontal cortex has been proposed to play a key role in setting a harmonious balance between the direction of attention to the external world and the expression of the individual believes and self-referential activities, and therefore, the impaired relation of right DLFCr with other frontal areas could explain a distorted perception of external world in relation with internal motivations.

Decision-making in a changing world: a study in autism spectrum disorders.

To learn to deal with the unexpected is essential to adaptation to a social, therefore often unpredictable environment. Fourteen adults with autism spectrum disorders (ASD) and 15 controls underwent a decision-making task aimed at investigating the influence of either a social or a non-social environment, and its interaction with either a stable (with constant probabilities) or an unstable (with changing probabilities) context on their performance. Participants with ASD presented with difficulties in accessing underlying statistical rules in an unstable context, a deficit especially enhanced in the social environment. These results point out that the difficulties people with ASD encounter in their social life might be caused by impaired social cues processing and by the unpredictability associated with the social world.

Susceptibility of differentiated thyrocytes in primary culture to undergo apoptosis after exposure to hydrogen peroxide: relation with the level of expression of apoptosis regulatory proteins, Bcl-2 and Bax.

Thyrocytes, that generate and use hydrogen peroxide (H2O2) to synthesize thyroid hormones, undergo apoptosis, as do most cell types, when exposed in vitro to H2O2. We have studied 1) the kinetics and the amplitude of the apoptotic response to H2O2 and 2) the relationship between the extent of the apoptosis-inducing effect of H2O2, the H2O2 degradation activity, and the level of expression of apoptosis regulatory proteins, Bcl-2 and Bax, in pig thyrocytes in primary culture. Cells were seeded at high density to obtain confluent monolayers and were cultured in the presence of TSH to maintain the expression of differentiation. H2O2 (10-300 microM) induced the appearance of cells with fragmented DNA (terminal transferase deoxy-UTP-fluorescein isothiocyanate nick end labeling-positive cells) at a maximum of 3-4 h after H2O2 addition and then the detachment of apoptotic cells from the cell monolayer. The proportion of detached cells increased with H2O2 concentration and amounted to up to 30% of the initial cell number after 24 h. The transient effect of H2O2 was related to its rapid degradation by cells and culture medium components (rate constant, approximately 0.1 min(-1)). Iterative additions of H2O2 produced cumulative apoptotic waves. The amplitude of the apoptotic response of thyrocytes to H2O2 progressively increased with the time of culture, up to 4-fold from days 1-8. This was not related to a change in the capacity of thyrocytes to degrade H2O2. During the same period of culture, the Bcl-2 cell content progressively decreased, whereas that of Bax concomitantly increased; thus, the Bcl-2/Bax ratio varied from about 6 on day 1 to 0.5 on day 10. These data show that the susceptibility of thyrocytes to undergo apoptosis increases with the time of culture and that the pronounced changes in the apoptotic status ofthyrocytes might be linked to coordinate modifications of the level of expression of pro- and antiapoptotic regulatory proteins.

Cell-to-cell communication in the anterior pituitary: evidence for gap junction-mediated exchanges between endocrine cells and folliculostellate cells.

The ability of rat anterior pituitary cells to communicate through gap junctions (GJ) was studied using a fluorescent molecule, Lucifer Yellow (LY), which freely passes through GJ channels. The probe was introduced into the cell cytoplasm by using either the cut-end loading method on intact tissue, or cell microinjection on cultured cells. The identification of communicating cells was performed by immunofluorescence labeling of specific hormones in endocrine cells and of S100 protein in folliculostellate (FS) cells. Rat anterior pituitary cells in their physiological organization, i.e. in the intact tissue, exhibited a high level of coupling through GJ. LY-labeled cells were found up to 300-microns apart from its site of introduction. The communicating cells were primarily PRL cells, GH cells, and FS cells. Only a few LH, TSH, and ACTH cells were labeled with LY. Anterior pituitary cells, isolated from the rat tissue by mild protease treatment and cultured for 3 days, reestablished functional GJ as demonstrated by microinjection of LY into individual cells. By immunolabeling of specific hormones and/or S100 protein, we found a GJ coupling between FS cells, and between FS cells and endocrine cells, including PRL cells. The communication between FS cells was by far the most frequent. In conclusion, we demonstrate the presence of functional GJ between anterior pituitary cells of the same type and between anterior pituitary cells having distinct differentiated functions.

Mapping of corticotropic cells in the normal human pituitary.

We accomplished the first mapping of corticotropic cells in the whole human adult pituitary. Corticotropic cells were identified by immunocytochemistry (ICC) and quantified by image analysis on 12 pituitaries obtained from people who had died suddenly. An overall view of each pituitary was given by 15-21 sections (mean 18 sections) at 300-micron intervals on six slides. Each section was systematically treated by indirect immunoperoxidase using an anti-ACTH[17-39] polyclonal antiserum. All the measures were done with a x 6.3 objective lens, each field (0. 5 mm2) being considered as the unit area. The mean pituitary density (surface of labeled cells/total surface) of corticotropic cells (9.5 +/- 3.0% per 0. 5 mm2) is significantly higher in men (11.5 +/- 5.1%) than in women (7.0 +/- 1.3%). This difference is due to an inverse relationship between the corticotropic cell density and the weight of the pituitary, which is higher in women than in men. The mean diameter of corticotropic cells is 14.9 micron and their total number per pituitary is approximately 10(7) cells. We confirmed that the spatial distribution of corticotropic cells is nonuniform: they are mainly distributed in the anteromedian part of the anterior lobe. In addition, our results demonstrated that the inferior part of the pituitary contained three times more corticotropic cells than the superior part (mean density 18.0% vs 6.0%) and the anterior part twice as many as the posterior part (mean density 12.3% vs 6.8%). On the horizontal plane, the pituitary was divided into eight zones, in which the mean of area was 2.5-21.0%. The maximal cell density may reach 40-60%. The use of this map should help the pathologist to recognize if there is corticotropic hyperplasia in a small pituitary fragment surgically removed from a patient with Cushing's disease. On the basis of this study, we put forward some criteria for diagnosing corticotropic hyperplasia.

Early induction of ornithine decarboxylase occurs simultaneously with inositol phosphate accumulation in concanavalin A-stimulated rat thymocytes.

Stimulation of rat thymocytes with the lectin ConA produced an early peak of ornithine decarboxylase (ODC) activity within 10 min. This ODC induction appeared as early as the well-known inositol phosphate accumulation following mitogenic stimulation, and may be part of the signal transduction mechanism. The distribution of counts among the inositol phosphates was constant during the overall time of Concanavalin A (ConA) stimulation. We conclude that early induction of pre-existing ODC may be independent of protein kinase C action.

Benzodiazepine analogues inhibit arachidonate-induced aggregation and thromboxane synthesis in human platelets.

1. Benzodiazepine analogues inhibit human platelet aggregation induced by arachidonate with an EC50 value of 0.68 microM for PK 11195, the most potent analogue used. 2. There was a highly significant correlation between the inhibition of arachidonate-induced aggregation and the affinity for the peripheral-type of benzodiazepine binding sites. 3. There was no significant correlation between the inhibition of the platelet activating factor (PAF)-induced aggregation and the binding to the peripheral-type of benzodiazepine binding sites. 4. The inhibition of platelet aggregation seems to result from the inhibition of arachidonic acid cyclo-oxygenation, since the synthesis of thromboxane and 12-hydroxy-heptadecatrienoic acid, both cyclo-oxygenase products, was reduced. 5. Our results suggest that peripheral-type of benzodiazepine binding sites on human platelets could be linked to cyclo-oxygenase.

H2O2 induces apoptosis of pig thyrocytes in culture.

Apoptosis might be involved in the reduction of the thyroid cell population in physiopathological situations such as goitre involution and autoimmune deleterious processes. Up to now, little attention has been paid to the apoptotic phenomenon in the normal thyroid gland the specialized metabolism of which is expected to generate reactive oxygen species. Indeed, thyroid cells have the capacity to synthesize H2O2. In this study, we have analyzed the capacity of H2O2 to trigger apoptosis of pig thyrocytes in culture to try to determine whether thyrocytes exhibit a particular resistance to apoptosis induced by an oxidative stress. We show that exposure of thyrocytes cultured as monolayers to exogenous H2O2 induced cell death with characteristics of apoptosis. The effect of H2O2 was concentration-dependent; apoptotic cells were already observed after exposure to 50 micro M H2O2. At high concentrations (millimolar range), H2O2 exerted toxic effects leading to rapid cell disruption. Within the first hour after the onset of exposure to 50-300 micro M H2O2, early signs of apoptosis, i.e. DNA fragmentation, appeared in a low (0.1-1%) but definite fraction of thyrocytes. The proportion of adherent cells exhibiting DNA fragmentation remained fairly constant after 6, 15 and 24 h. During the 24-h period, an increasing number of cells detached from the culture dish and up to 30-40% of cells in suspension displayed apoptotic features. The fraction of cells that lost contact with the culture dish amounted to up to 25% 24 h after addition of 300 micro M H2O2. In conclusion, as reported for other cell types, low H2O2 concentrations are capable of triggering apoptosis in thyrocytes cultured as monolayers. Thyrocytes that undergo apoptosis secondarily lose contact with neighbour cells and the substratum; cell detachment from the monolayer probably happens within 1-2 h after initiation of DNA fragmentation. Our data show that the apoptotic commitment can take place many hours after initiation of the oxidative stress.

Comparison of basal and noradrenaline stimulated methylation of chloroform-extractable products in synaptosomal preparations from the rat brain.

Noradrenaline addition increases (S-adenosyl-L-methionine)-methylation of chloroform extractable products in the rat brain synaptosomal preparation. The characteristics of this methylation (MgCl2 dependence, S-adenosyl-L-methionine concentration dependence) are different from those of phosphatidylethanolamine methylase. The greatest increase was induced by noradrenaline in the 10(-4) M concentration range; preincubation of noradrenaline with the membranes, before S-adenosyl-L-methionine addition, was necessary. The TLC analysis of chloroform extractable products showed that: methylation of phosphatidylethanolamine derivatives was increased and the production of another unknown product (corresponding to that described by Wazer et al., Life Sci. 32, 2535, 1983) was more enhanced.

Kinetics of tryptophan accumulation into synaptosomes of various regions of rat brain.

The kinetics of synaptosomal tryptophan accumulation has been determined in five regions of the rat brain. For tryptophan concentrations ranging from 2.5 -- 20 microM, we found an active uptake in all the structures studied, i.e.: Corpus striatum, midbrain, brainstem, hypothalamus and cerebral cortex + hippocampus. The Vm of tryptophan uptake was highest in the cortex, followed in descending order by corpus striatum, hypothalamus, midbrain and brainstem, while the Km was highest in the cortex, then in descending order corpus striatum, brainstem, midbrain and hypothalamus. In spite of the possible nonspecific high affinity tryptophan uptake into serotoninergic neurons, we found a correlation between the Vm of tryptophan uptake and the different results in the literature concerning uptake and release of serotonin. These observations might indicate a correlation between the Vm of tryptophan uptake and the functional activity of serotonergic neurons.

Relationships between pathological diagnosis and clinical parameters in acromegaly.

From our series of 185 somatotropic adenomas with acromegaly, we found that sparsely granulated adenomas were more frequent (56%) than densely granulated ones. Immunocytochemistry detected growth hormone (GH) plurihormonal adenomas in 68% of patients. GH-alpha-subunit (alpha SU) and GH-alpha SU-prolactin (PRL) were more frequent (38%) than GH monohormonal adenomas (32%). The colocalization of GH and alpha SU in the same cell was obvious in many tumors. In contrast, colocalization of GH and PRL was demonstrated in only 25% of GH-PRL adenomas. The relationships between age, sex, tumor size, GH and PRL plasma levels, granularity, and percentage of GH-, alpha SU-, and PRL-immunoreactive cells were established in 105 acromegalic patients by three statistical methods, mainly by a principal component analysis. Correlations were found between the percentage of alpha SU- and GH-immunoreactive cells, and between densely granulated character and the percentage of GH-immunoreactive cells. Tumor size was not correlated with alpha SU, but was positively correlated with PRL plasma levels. Patients' age and percentage of GH-immunoreactive cells were inversely related to tumor size. Plurisecretion and sparsely granulated aspect are not related to age and tumor size.

A neural network elicited by parametric manipulation of the attention load.

We used a parametric experimental design to identify the rCBF variations related to a continuous variation of the attention load. The experiment involved goal-directed visual tasks. The length of time during which the subject's attention was engaged toward the external stimulus was taken as the factor of interest. The neural network revealed areas that positively (left cerebellum, bilateral MT/V5 complex and superior parietal lobule, right inferior temporal lobe and dorsolateral prefrontal cortex) or negatively (precuneus, anterior cingulate and medial superior frontal cortex) correlate with the attention load. Results demonstrate that the activity of these areas varies continuously as a function of the variation in the attention load.

New aspects of motion perception: selective neural encoding of apparent human movements.

Perception of apparent motion operates somewhat differently for objects and human figures. Depending on the interstimulus interval, the latter d may give rise to either perception of a direct path (i.e. biologically impossible) or indirect path (i.e. biologically possible). Here, PET was used to investigate whether a change in brain activity accompanies this perceptual shift. We found neural encoding of apparent motion to be a function of the intrinsic properties of the stimulus presented (object vs human) as well as the kind of human movement path perceived (biomechanically possible vs impossible). Motor and parietal cortex were only involved for possible motion which suggests that these regions are selectively activated to process actions which conform to the capabilities of the observer.

How the brain perceives causality: an event-related fMRI study.

Detection of the causal relationships between events is fundamental for understanding the world around us. We report an event-related fMRI study designed to investigate how the human brain processes the perception of mechanical causality. Subjects were presented with mechanically causal events (in which a ball collides with and causes movement of another ball) and non-causal events (in which no contact is made between the balls). There was a significantly higher level of activation of V5/MT/MST bilaterally, the superior temporal sulcus bilaterally and the left intraparietal sulcus to causal relative to non-causal events. Directing attention to the causal nature of the stimuli had no significant effect on the neural processing of the causal events. These results support theories of causality suggesting that the perception of elementary mechanical causality events is automatically processed by the visual system.

Incorporation of arachidonic and docosahexaenoic acids into phospholipids of rat brain membranes.

The incorporation of [3H]arachidonic acid (20:4n-6) into rat brain membranes and its mobilization in response to norepinephrine, a relevant neuromediator were studied. The most efficient [3H]20:4n-6 incorporation was in inositol glycerophospholipids (PI) where it reached a plateau after 10 min incubation, while this incorporation was very weak in choline glycerophospholipids (PC). In contrast, the esterification of docosahexaenoic acid, another polyunsaturated fatty acid occurring at high level in brain, was similar in PI and PC, the incorporation in PI being 8-fold lower than that of 20:4n-6. The newly esterified [3H]20:4n-6 was exclusively found in the 1,2-diacyl subclasses of PI and PC. The bulk of incorporation was in the 18:0/20:4n-6 molecular species of 1,2-diacyl-glycerophosphoinositol and in 16:0/20:4n-6 + 18:1/20:4n-6 molecular species of 1,2-diacyl-glycerophosphocholine, which agrees with the usual location of 20:4n-6 in brain phospholipid classes. Upon norepinephrine treatment, [3H]20:4n-6 was not released from PC, but was dose-dependently decreased in PI, the release being significant from 10(-5) M of the agonist. These results suggest that 20:4n-6 exhibits a high specific turnover in brain PI and is mobilized from this class upon relevant neuromediator stimulation. The acellular system used preserved the specificity of enzymes catalyzing the polyunsaturated fatty acid incorporation and release and could be helpful for studying their turn over in brain.

Increase of GABA-stimulated diazepam binding after lipid methylation in membrane preparations from rat brain.

Incubation of membrane preparations from rat brain with S-adenosyl-L-methionine resulted in methylation of the lipid fraction. Neither [3H]diazepam nor [3H]muscimol (a gamma-aminobutyric acid (GABA) agonist) binding was affected by this incubation. In contrast, when [3H]diazepam binding was stimulated by GABA, the methylation caused both a decrease of the minimal GABA concentration needed to produce its effect (10(-9) M instead of 10(-7) M) and an enhancement (from 36 to 66% over basal) of the GABA-stimulated [3H]diazepam binding.

Increase of in vitro brain [3H]muscimol binding after L-homocysteine administration to rat.

L-Homocysteine intraperitoneal injections to the rat induced 50-70% inhibition of phosphatidyl-N-methyltransferase activity. A 30-40% increase of muscimol (a gamma-aminobutyric acid (GABA) agonist) binding was observed; Scatchard plot analysis showed an increase of the number of sites. [3H]Diazepam binding was not modified.

12-HETE inhibits the binding of PGH2/TXA2 receptor ligands in human platelets.

12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE), the end-lipoxygenase product of arachidonic acid in platelets has been previously shown to prevent PGH2/TxA2-induced aggregation. From the present study, we show that 12-HETE inhibits the binding of [125I]-PTA-OH, a thromboxane antagonist, to platelet membranes with an IC50 of 8 microM. This value is in accordance with previously reported 12-HETE concentrations required to prevent the aggregation induced by TxA2 mimetics, the methano analogues of PGH2, U44069 and U46619. When [3H]-U44069 was used as a thromboxane agonist to label intact platelets, 12-HETE also inhibited its binding. We conclude that part of the inhibitory effect of 12-HETE on PGH2/TxA2-induced aggregation might be the result of interacting with PGH2/TxA2 receptor sites.

Phosphatidylethanolamine methylation in leukocyte membrane preparations from allergic subjects: an unexpected result.

We studied the incorporation of [3H]methyl from [3H]methyl-S-adenosylmethionine into leukocyte phospholipids. A higher incorporation in leukocytes from control subjects than from allergic subjects was noticed.