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At least 1,621 records · Page 90Linked to original sources
PubMed1992

Interhemispheric communication following unilateral cerebrovascular lesions.

39 patients with a single small cerebrovascular lesion (20 in the right, 19 in the left hemisphere) were subjected to a simple reaction time (RT) task with visual stimuli flashed to the visual field either ipsilateral or contralateral to the cerebral lesion. The subject responded always with the ipsilateral hand. The crossed-uncrossed difference (CUD), i.e. the RT when both stimulus and response occur on the same side minus the RT when stimulus and response occur on opposite sides, is assumed to assess the transit time of information through callosal fibers, and in normal people is about 3-5 msec. In our patients the mean CUD, expressed as the difference between contralateral and ipsilateral responses, was 20 msec. Patients with parietal lesions had still longer CUDs, 37 msec on the average. There was no statistical difference in CUDs between right and left brain-damaged patients. The CUD in brain-damaged patients was of the same order of magnitude as that found in acallosal or split-brain patients. Nonetheless, the present findings are interpreted as reflecting the intrahemispheric rather than the interhemispheric delay in information transmission, with the possible additive effect of an asymmetrical orienting of attention.

Brain↗
PubMed1985

Intracranial teratoma associated with agenesis of the corpus callosum.

Several intracranial tumors are known to occur in conjunction with agenesis of the corpus callosum. We report the occurrence of a teratoma with callosal agenesis, an association not previously described, and suggest that the tumor's ventral location may serve to differentiate it from other lesions.

Adult↗
PubMed1998

Bilateral medial frontal infarction in a case of azygous anterior cerebral artery stenosis.

We describe the unusual case of a 63-year-old woman with a history of arterial hypertension who presented a sudden weakness of the lower limbs followed by mutism, akinesia and dyspraxia. Magnetic resonance images showed a bilateral medial frontal infarction. Digital subtraction angiography documented a right azygous anterior cerebral artery with severe stenosis in its sub-callosal tract; the left anterior cerebral artery showed mild hypoplasia with only sub-frontal and fronto-polar branches. No embolic source was documented. Afterwards the patient presented a gradual and partial recovery of both motor and cognitive functions.

Angiography, Digital Subtraction↗
PubMedDate not supplied

The effects of high-frequency microstimulation of the cortex on interhemisphere synchronization in the rat motor cortex.

Studies were carried out on long-term changes in the synchronization of neuronal activity in networks including callosal cells of the opposite hemispheres evoked by high-frequency microstimulation in the motor cortex of anesthetized rats. The level of synchronization was assessed in terms of the amplitude and width of peaks located symmetrically on cross-correlograms relative to the coordinate origin. Tetanization predominantly decreased synchronization in a group of initially background-active neurons, while there was a significant number of synchronously firing neurons in a group of cells which became activated. "Super-narrow" peaks appeared in interhemisphere interactions. There was a correlation between the type of modification of "narrow" (<20 msec) and "intermediate" (30-80 msec) peaks and changes in the efficiencies of mono- and polysynaptic connections.

Animals↗
PubMedDate not supplied

Background gamma-oscillations in neuronal networks with interhemisphere connections.

Results obtained in studies of the high-frequency components of EEG recordings and in modeling, determining the conditions for the appearance of gamma oscillations in interneuronal interactions, were compared with features of the background gamma oscillations recorded in the activity of interacting neurons located in symmetrical loci of the right and left hemisphere motor areas in anesthetized rats. Similarities in high frequencies extracted from EEG recordings and in the most commonly observed gamma oscillation frequencies suggested that these oscillations may represent one of the mechanisms underlying the high-frequency EEG component. Published modeling data indicating that the formation of these oscillations involves reciprocal inhibitory connections, along with our own data that interhemisphere oscillations are seen 1.5 times more commonly than ipsilateral oscillations, suggested that transcallosal inhibition is more effective than inhibition between neighboring cells. Simultaneously extracted background oscillations in the interacting activity of callosal cells and neighboring cells could be different, as could those characterizing the activity of individual neurons. It is suggested that these differences underlie the functional heterogeneity of local cortical neuronal networks and explain the fact that these networks contain various types of inhibitory neurons.

Animals↗
PubMedDate not supplied

Post-tetanic changes in background gamma oscillations in interhemisphere interactions.

Experiments conducted on the motor cortex of anesthetized rats were performed to study the effects of high-frequency microstimulation of one of the hemispheres on oscillation parameters in neuronal networks containing callosal cells. Before tetanization, there were three modes in the distribution of gamma oscillation periods, corresponding to frequencies of 40-60, 70-100, and 100-200 Hz. In cells active in pre-tetanization background conditions, the three modes were retained after tetanization; there was a relative increase in the number of oscillatory interactions in that part of the gamma range (40-60 Hz) which dominated before tetanization. The distribution of oscillation periods in neurons which became active in background conditions after tetanization contained the same three modes. Tetanization resulted in a relative decrease in the number of oscillatory interactions and the number of neuron pairs in which additional synchronization occurred, along with a reduction in the extent of oscillations, which is evidence of reduced synchronization. Existing modeling data taken together with the present results led to the suggestion that these post-tetanization changes were based on a modification of the efficiency of excitatory and inhibitory inputs to neurons in both hemispheres.

Anesthesia↗
PubMed2003

A primary CNS lymphoma in spontaneous remission for 3.5 years after initial detection of the lesions by MRI.

We describe the clinicopathological features of a patient with an autopsy-proven primary CNS lymphoma, who had a relatively long remission period after onset. A 61-year-old man experienced disorientation and gait disturbance. A ventriculoperitoneal shunt operation was performed, based on the diagnosis of hydrocephalus due to aqueductal stenosis, after which his symptoms subsided. Three months later, T2-weighted magnetic resonance imaging (MRI) revealed high-intensity lesions in the corpus callosum and tectum. However, he remained asymptomatic for the next three and a half years, during which periodic MRI studies constantly detected the lesions. At the age of 65 years, he suffered respiratory and consciousness disturbances, and his general condition gradually deteriorated. MRI studies disclosed that the callosal lesion had spontaneously disappeared, whereas the tectal lesion had developed to become an enhanced linear lesion with a tendency to spread on the dorsal side of the brain stem. Examination of the cerebrospinal fluid disclosed a markedly elevated beta2-microglobulin content, and a tentative diagnosis of malignant lymphoma was made. Steroid pulse therapy had little effect, and the patient died four years after presentation. Examination at autopsy disclosed a malignant, large B-cell lymphoma that had diffusely infiltrated the cerebrum and brain stem. In the corpus callosum, a small number of residual lymphoma cells were seen around the vessels. Therefore, the initially detected lesions in the corpus callosum and tectum might have been attributable to lymphoma, and the unusual clinical and radiological features of this case provide further information that might aid in diagnosis and help to ensure prompt treatment.

Brain Neoplasms↗
PubMed2001

Ultrastructural effects of cellulose biosynthesis inhibitor herbicides on developing cotton fibers.

Cotton fibers are often utilized as a model system to investigate cellulose biosynthesis and cell wall elongation. In this study, we grew cotton fibers in vitro, with ovules dissected at day zero post anthesis as the explant source, in the presence of three herbicides that inhibit cellulose biosynthesis. Cultures were sampled for electron microscopy and immunocytochemistry 1-2 days after beginning the treatments. After dichlobenil treatment, the fibers were much shorter than the controls and assumed a variety of abnormal shapes, from shortened versions of the control fiber to nearly spherical. The inner layers of the fiber wall often contained juxtaposed electron-translucent and -transparent areas; this layer reacted strongly with antibodies to callose. Cellulase-gold labeling in these newly developed fibers grown in the presence of dichlobenil was present at only about 3% of the control labeling. After treatment with either isoxaben or flupoxam, the fibers assumed spherical shapes and frequently (more than 60% of fibers) exhibited a new cell plate within the fiber, indicating that cell division had occurred, a process that rarely occurred in the controls. Unlike the dichlobenil-treated fibers, fibers grown in the presence of isoxaben or flupoxam contained an extensive accumulation of chiefly deesterified pectins, replacing the entire wall with an elaborated version of the pectin sheath found in control cotton fibers. These data indicate that all three herbicides are effective disrupters of cellulose biosynthesis and cause radical changes in cell wall structure and composition. Moreover, these data indicate that the composition of the walls may influence indirectly cell cycle kinetics, keeping these fiber cells in a more meristematic mode.

Benzamides↗
PubMed1996

The development of the corpus callosum in semilobar and lobar holoprosencephaly.

OBJECTIVE: The objective of this study was to determine whether and how a true corpus callosum develops in milder cases of holoprosencephaly. MATERIALS AND METHODS: The MR scans of seven patients with holoprosencephaly and a callosum-like structure were reviewed. The anatomy of the callosum-like structure and the pericallosal anatomy were evaluated. RESULTS: Six of the seven cases had a posterior corpus callosum. The seventh case was indeterminate because lack of myelination prevented confirmation that the callosum-like structure consisted only of white matter. In each case the posterior corpus callosum formed posterior to white matter which spanned the interhemispheric fissure beneath a layer of cortical gray matter. CONCLUSION: A posterior corpus callosum can develop in holoprosencephaly because the first callosal axons use the white matter of the undivided hemispheres as a bridge to cross the interhemispheric fissure.

Agenesis of Corpus Callosum↗
PubMed1999

[Polydactyly of the foot].

Polydactyly may be preaxial or tibial (hallux-side), postaxial or ulnar (side of the little toe) and central (middle toes). The duplication may appear at the distal and medial phalanges or at the whole digit. The metatarsal bone may be part wise or completely duplicated, the accessory toes may share only one metatarsal. Surgical intervention may be indicated in shoe problems, for esthetic reasons or, especially in duplication of the metatarsales, because of secondary deviation of the toes and therefore shoe problems or plantar callosities. Preoperative analysis including x-ray is of great importance to achieve good functional and cosmetic results.

Adolescent↗
PubMed2004

An extensive microarray analysis of AAL-toxin-induced cell death in Arabidopsis thaliana brings new insights into the complexity of programmed cell death in plants.

A T-DNA knockout of the Arabidopsis homologue of the tomato disease resistance gene Asc was obtained. The asc gene renders plants sensitive to programmed cell death (PCD) triggered by the fungal AAL toxin. To obtain more insights into the nature of AAL-toxin-induced cell death and to identify genes of potential importance for PCD, we carried out transcription profiling of AAL-toxin-induced cell death in this knockout with an oligonucleotide array representing 21,500 Arabidopsis genes. Genes responsive to reactive oxygen species (ROS) and ethylene were among the earliest to be upregulated, suggesting that an oxidative burst and production of ethylene played a role in the activation of the cell death. This notion was corroborated by induction of several genes encoding ROS-generating proteins, including a respiratory burst oxidase and germin oxalate oxidase. Cytochemical studies confirmed the oxidative burst and, in addition, showed synthesis of callose, a feature of the hypersensitive response. A diverse group of transcription factors was also induced. These events were followed by repression of most of the auxin-regulated genes known to be involved in growth and developmental responses. All photosynthesis-related genes were repressed. Blocking the synthesis of ethylene or NO significantly compromised cell death. In addition, we identified a heterogeneous group of early-induced genes, some of them never before associated with PCD. The group of early-induced genes included a number of proteases that were previously implicated in developmentally regulated types of PCD, suggesting a more principal role for these proteases in the PCD process. These findings provide new insights into the molecular mechanisms of plant PCD.

Apoptosis↗
PubMed1997

Structures and functions of annexins in plants.

The first evidence that higher plants contain annexins was presented in 1989. Since that time, annexins have been purfied and characterized from a variety of plant sources. Analyses of the deduced proteins encoded by annexin cDNAs indicate that the majority of these plant annexins possess the characteristic four repeats of 70 to 75 amino acids and possess motifs proposed to be involved in Ca2+ binding. Like animal annexins, plant annexins bind Ca2+ and phospholipids and are abundant proteins, but there are indications that the number of distinct plant annexin genes may be considerably fewer than that found in animals. Regarding function, a number of studies show that various members of the annexin family of plants may play roles in secretion and/or fruit ripening, show interaction with the enzyme callose (1.3-beta-glucan) synthase, possess intrinsic nucleotide phosphodiesterase activity, bind to F-actin, and/or have peroxidase activity.

Actins↗
PubMed2005

Identification of two novel genes for blackleg resistance in Brassica napus.

Blackleg, caused by Leptosphaeria maculans, is a major disease of Brassica napus. Two populations of B. napus DH lines, DHP95 and DHP96, with resistance introgressed from B. rapa subsp. sylvestris, were genetically mapped for resistance to blackleg disease with restriction fragment length polymorphism markers. Examination of the DHP95 population indicated that a locus on linkage group N2, named LepR1, was associated with blackleg resistance. In the DHP96 population, a second locus on linkage group N10, designated LepR2, was associated with resistance. We developed BC1 and F2 populations, to study the inheritance of resistance controlled by the genes. Genetic analysis indicated that LepR1 was a dominant nuclear allele, while LepR2 was an incompletely dominant nuclear resistance allele. LepR1 and LepR2 cotyledon resistance was further evaluated by testing 30 isolates from Canada, Australia, Europe, and Mexico. The isolates were from B. napus, B. juncea, and B. oleracea and represented different pathogenicity groups of L. maculans. Results indicated that LepR1 generally conferred a higher level of cotyledon resistance than LepR2. Both genes exhibited race-specific interactions with pathogen isolates; virulence on LepR1 was observed with one isolate, pl87-41, and two isolates, Lifolle 5, and Lifolle 6, were virulent on LepR2. LepR1 prevented hyphal penetration, while LepR2 reduced hyphal growth and inhibited sporulation. Callose deposition was associated with resistance for both loci.

Ascomycota↗
PubMed2003

At what stage of manual visual reaction time does interhemispheric transmission occur: controlled or ballistic?

Interhemispheric transfer (IT) time through the corpus callosum can be measured with a manual reaction time (RT) to lateralized visual stimuli (the so-called Poffenberger paradigm) by subtracting mean RT of faster uncrossed hemifield-hand combinations (not requiring an IT) from slower crossed combinations (requiring an IT). That the corpus callosum is involved in IT has been demonstrated by its dramatic lengthening in patients with a section of the corpus callosum. However, it is still unclear whether the signal transmitted by the corpus callosum concerns perceptual or motor stages of RT. To try and cast light on this question, in a first experiment we tested normal subjects on a partially modified Poffenberger paradigm with stop trials intermingled with go trials. In the former, subjects are supposed to refrain from responding following a stop signal (stop-signal paradigm). This paradigm can tease apart the contribution of the controlled and ballistic stages to overall RT and, used together with the Poffenberger task, enables one to assess the stage at which IT occurs. The controlled stage lies before the point of no return, i.e. the point beyond which the response cannot be inhibited, and concerns perceptual and pre-motor processes, while the ballistic stage occurs after the point of no return and concerns the motoric aspect of the response. We found that the slower responses typically obtained in the crossed conditions were more likely to be inhibited than the faster uncrossed responses and this suggests that IT occurs prior to the point of no return. Since the precise locus of the point of no return is uncertain, in a second experiment we used response force as a dependent variable reflecting the activation of the motor cortex. We found that none of the force parameters studied differed between crossed and uncrossed conditions while the temporal parameters confirmed the presence of an advantage of the uncrossed combinations. Altogether these results suggest that callosal IT of visuomotor information occurs at the stage of controlled (perceptual and pre-motor) processes and rule out the possibility of an IT at the motoric stage.

Adult↗
PubMed2003

Modulation of interhemispheric inhibition during passive movement of the upper limb reflects changes in motor cortical excitability.

We investigated modulation of inhibition of motor evoked potentials in the left forearm musculature attributable to changes in corticomotor excitability induced by passive rhythmic movement of the right limb. In the first experiment, eight healthy volunteers pre-activated their left flexor carpi radialis (FCR) in a simple isometric contraction (2.5-7.5% MVC) while their right hand underwent passive wrist flexion-extension. Transcranial magnetic (TMS) or electrical (TES) stimulation was applied to the right motor cortex and responses recorded from the test (left) limb in eight phases of the wrist flexion-extension cycle of the passively driven right limb. In half of the trials TMS conditioning was applied to the left motor cortex. The conditioning stimulus significantly inhibited TMS-evoked responses in the test FCR muscle, whereas TES-evoked responses did not appear to be inhibited. For TMS-evoked responses only, inhibition in the static pre-activated left FCR was modulated such that inhibition was greater when the right wrist was passively flexing than when it was extending. In the second experiment TMS was applied to the right motor cortex, contralateral to the test (left) limb, with the right hand either passively extending or flexing through the neutral position. Conditioning was applied to the left motor cortex at a range of intensities adjusted to threshold for flexion and extension movements. No difference was evident in the maximum magnitude of inhibition between the extension and flexion conditions. We propose there is an increased absolute threshold for recruitment and a decreased gain of inhibitory callosal pathways during extension phases of the wrist flexion-extension cycle.

Adolescent↗
PubMed2006

Intermanual interactions during initiation and production of rhythmic and discrete movements in individuals lacking a corpus callosum.

Three individuals lacking a corpus callosum, two due to callosotomy and one agenesis, and three age-matched healthy controls were tested on a bimanual task in which a discrete or rhythmic arm movement was initiated following a visual signal while the other arm produced continuous, rhythmic movements. The control participants initiated the secondary, rhythmic movement in phase with the ongoing rhythmic base movement and the two limbs were coupled in an inphase mode across the duration of the trial. In contrast, the acallosal individuals failed to show phase entrainment at the initiation of the secondary, rhythmic movements. Moreover, the callosotomy patients exhibited weak coupling between the rhythmically moving limbs while the individual with callosal agenesis consistently synchronized in an antiphase mode. The control participants exhibited increased perturbation of the ongoing base movement when initiating a discrete movement; for the acallosal participants, the base movement was similarly perturbed in both secondary movement conditions. These results are consistent with the hypothesis that intermanual interactions observed during bimanual movements arise from various levels of control, and that these are distinct for discrete and rhythmic movements. Temporal coupling during rhythmic movements arises in large part from transcallosal interactions between the two hemispheres. The imposition of a secondary movement may transiently disrupt an ongoing rhythmic movement even in the absence of the corpus callosum. This may reflect subcortical interactions associated with response initiation, or, due to dual task demands, a transient shift in attentional resources.

Agenesis of Corpus Callosum↗
PubMed2000

Coordination disorders in patients with Parkinson's disease: a study of paced rhythmic forearm movements.

Whereas the consequences of Parkinson's disease (PD) for the performance of single-limb movements are well documented (i.e., bradykinesia, akinesia, rigidity, and tremor), fairly little is known about its implications for the coordination between limb movements. To help resolve this situation an experiment was conducted in which 11 PD patients and 11 control subjects performed rhythmic forearm movements at a comfortable amplitude in the in-phase, antiphase, and single-arm mode at pacing frequencies ranging from 0.5 to 3 Hz. The PD group displayed marked coordination problems over and above the known clinical motor symptoms of PD. The performance of both the in-phase and antiphase modes was significantly affected in the PD group compared to the control group; furthermore, the variability of relative phase was significantly increased in this group. These observations were not caused by problems to synchronize the movements with the external pacing signal. In addition to the bimanual coordination problems, involuntary mirror movements (MM) were observed in the single-arm control trials that were significantly larger in the PD group (4.4% of the amplitude of the moving arm) than in the control group (2.3%), suggesting a reduced ability to suppress a basic in-phase coupling of the arms. In the PD group, MM were largest during movements of the least-affected arm. These parkinsonian coordination problems are interpreted in terms of recent evidence on the neural organization of bimanual coordination, suggesting that they are due to cortical rather than callosal dysfunction.

Aged↗
PubMed2001

Lipid peroxidation in the postnatal rat brain. Formation of 4-hydroxynonenal in the supraventricular corpus callosum of postnatal rats.

Lipid peroxidation is known to be associated with many neurodegenerative diseases and with traumatic brain injury, but its occurrence in the normal developing brain has not been reported. The present study was carried out using a specific antibody that recognises proteins modified by the end-product of lipid peroxide decomposition, 4-hydroxynonenal (HNE), to evaluate evaluate possible lipid peroxidation products in the brains of developing rats by immunocytochemistry and electron microscopy. Moderately dense labelling was observed in the supraventricular corpus callosum in the 7- and 8-day-old rats, whilst very dense labelling was observed in the same region, in the 9- and 10-day-old rats. Very little immunoreactivity was observed at 14 days, and no staining was observed in the corpus callosum in adult rats. HNE staining was not observed in neuronal cell bodies that give rise to callosal axons in the overlying cerebral cortex. Electron microscopy showed dense HNE staining on the basal laminae of blood vessels and on the plasma membranes of unmyelinated axons. Large numbers of rounded cells with features of oligodendrocyte precursor cells were labelled by Perl's stain in the supraventricular corpus callosum at postnatal day 7 and postnatal day 10, i.e. at times corresponding to high levels of HNE immunoreactivity. In contrast, very few such cells were observed in the adult brain, corresponding to the very little or no Perl's staining in the adult. These results suggest that lipid peroxidation observed in the supraventricular corpus callosum at postnatal day 10 could result from an accumulation of iron in this region, at this time.

Aging↗