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PubMed2001

Cortical map asymmetries in the context of transcallosal excitatory influences.

There is long-standing disagreement among experimentalists about whether transcallosal interhemispheric influences are primarily excitatory or inhibitory. Past computational models exploring this issue have encountered a similar dilemma: inhibitory callosal influences best explain hemispheric functional asymmetries, but excitatory callosal influences best explain transcallosal diaschisis. We recently hypothesized that this dilemma might be resolved by assuming excitatory callosal influences and a subcortical mechanism for cross-midline inhibition. Here we explore the feasibility of this hypothesis by examining a model of map formation in corresponding left and right cortical regions. The results show for the first time that both map asymmetries and diaschisis-like changes can be produced in a single model, suggesting that subcortical inhibitory processes may contribute more to asymmetric cortical functionality than is generally recognized.

Brain Diseases↗
PubMed1993

An animal model of corpus callosum impingement as seen in patients with normal pressure hydrocephalus.

RATIONALE AND OBJECTIVES: Callosal impingement has been postulated to cause the symptoms associated with normal pressure hydrocephalus. The authors developed an animal model for the investigation of corpus callosum impingement by the falx cerebri. METHODS: The corpus callosum was compressed from above by a plastic blade and surgically placed in the interhemispheric fissure in adult Sprague-Dawley rats. Magnetic resonance imaging (MRI) was performed both preoperatively and postoperatively. The brains of the rats also were examined grossly at the time of autopsy. RESULTS: All rats survived the surgical procedure. MRI proved to be a suitable method to image the corpus callosum, to confirm the location of the blade, and to demonstrate the corpus callosum impingement. MRI correlated well with necroscopy sections. CONCLUSIONS: It was possible to surgically produce callosal impingement in rats, and this impingement could be confirmed by MRI. In the future, this rat model of callosal impingement will be used to search for evidence of changes in metabolism, neuroelectrical activity, behavior, and neuronal anatomy which are known or are thought to be associated with hydrocephalus.

Animals↗
PubMed1998

Collateral inhibition of transcallosal activity facilitates functional brain asymmetry.

The corpus callosum is the largest connection between the functionally asymmetric cerebral hemispheres. The objective of this study was to measure functional activity of callosal fiber tracts during speech processing. We analyzed the regional glucose metabolism of the corpus callosum and of speech-relevant cortical areas in 10 normal individuals at rest and during word repetition. We used three-dimensionally registered magnetic resonance imaging to visualize the individual brain morphology and high-resolution positron emission tomography for metabolic measurements. The task-induced metabolic changes of the callosal midbody and isthmus had a significant negative correlation with key regions of language processing in the left inferior frontal cortex (Brodmann's area 44) and in the right superior temporal cortex (Brodmann's area 22) (e.g., correlation of metabolic changes in the surface aspects of the right Brodmann's area 22 and the callosal midbody/isthmus: r = -0.91, P < 0.001). The study indicates that language processing in asymmetrically organized cortical areas inhibits the reciprocal transcallosal information exchange in favor of the lateralized mental operation. Our data agree with anatomic, electrophysiologic, and pharmacologic experiments that point to the important role of collateral inhibition for the transcallosal information exchange.

Adult↗
PubMed1979

Fucntional specialization and binocular interaction in the visual areas of rhesus monkey prestriate cortex.

If is is believed that neural mechanisms mediating stereoscopic vision may be localized in specific areas of the visual cortex, then it becomes necessary to be able to define these areas adequately. This is no easy matter in the rhesus monkey, an animal close to man, where the cytoarchitecturally uniform prestriate cortex is folded into deep sulci with secondary gyri. One way around this awkward problem is to use the callosal connections of the prestriate cortex as the anatomical landmarks. Callosal connections are restricted to regions at which the vertical meridian is represented. Since the visual fields, including the vertical meridian, are separately represented in each area, each has its own callosal connections. These are of great help in defining some of the boundaries of these areas, since the boundaries often coincide with the representation of the vertical meridian. With the visual areas thus defined anatomically, it becomes relatively easy to assign recordings to particular areas. Studies of binocular interactions in these areas reveal that most cells in all prestriate areas are binocularly driven. Hence, theoretically, all of the prestriate areas are candidates for stereoscopic mechanisms. The degree of binocular interaction varies from cell to cell. At the two extremes are cells which either respond to monocular stimulation only and are inhibited by binocular stimulation or ones which respond to binocular stimulation only. Changing, as opposed to fixed, disparity is signalled by two types of cells. In one category are cells activated in opposite directions for the two eyes. Such cells are always binocularly driven. In the other category are cells, some of which are monocularly activated, that are capable of responding to changing image size. In the monkey, both these categories of cells have so far been found in the motion area of the superior temporal sulcus only.

Animals↗
PubMed1980

A function of the corpus callosum in the Siamese cat.

Recordings were made from 180 single cells, or cell clusters, in the Clare-Bishop area of two Siamese cats. In one cat, the corpus callosum had been sectioned prior to recording and all cells were driven by the contralateral eye exclusively. In the other recordings were made before and after callosal section. Before callosal section, most cells were binocularly driven but dominated by the contralateral eye. There were striking examples of binocular interaction and some cells could only be activated by simultaneous binocular stimulation. After callosal section, cells were driven by the contralateral eye only. The same experiment performed in a normal cat revealed no change in binocularity following section of the corpus callosum. We conclude that one of the functions of the corpus callosum in the Siamese cat is to generate binocular neurons.

Animals↗
PubMed2001

Pollen germinates precociously in the anthers of raring-to-go, an Arabidopsis gametophytic mutant.

Pollen hydration is usually tightly regulated and occurs in vivo only when desiccated pollen grains acquire water from the female, thus enabling pollen tube growth. Pollen tubes are easily visualized by staining with decolorized aniline blue, a stain specific for callose. We identified a mutant, raring-to-go, in which pollen grains stained for callose before anther dehiscence. When raring-to-go plants are transferred to high humidity, pollen tubes dramatically elongate within the anther. As early as the bicellular stage, affected pollen grains in raring-to-go plants acquire or retain water within the anther, and precociously germinate. Thus, the requirement for contact with the female is circumvented. We used pollen tetrad analysis to show that raring-to-go is a gametophytic mutation, to our knowledge the first gametophytic mutation in Arabidopsis that affects early events in the pollination pathway. To aid in identifying raring-to-go alleles, we devised a new technique for screening pollen in bulk with decolorized aniline blue. We screened a new M(1) mutagenized population and identified several additional mutants with a raring-to-go-like phenotype, demonstrating the usefulness of this technique. Further, we isolated other mutants (gift-wrapped pollen, polka dot pollen, and emotionally fragile pollen) with unexpected patterns of callose staining. We suggest that raring-to-go and these other mutants may help dissect components of the pathway that regulates pollen hydration and pollen tube growth.

Arabidopsis↗
PubMed1991

Plasmodesmatal function is probed using transgenic tobacco plants that express a virus movement protein.

A gene encoding a temperature-sensitive mutant (MPP154A) of the 30-kilodalton movement protein (MP) of tobacco mosaic virus (TMV) was transformed into Nicotiana tabacum cv Xanthi. Transgenic plants expressing the MPP154A gene complemented local and systemic movement of an MP-defective mutant of TMV (U3/12MPfs) at the permissive temperature of 24 degrees C but not at 32 degrees C, the nonpermissive temperature. A microinjection procedure was used to investigate the effects of the modified TMV MP on plasmodesmatal size-exclusion limits. Movement of fluorescein isothiocyanate-labeled dextran (F-dextran), with an average molecular mass of 9.4 kilodaltons, was detected between leaf mesophyll cells of the transgenic plants at 24 degrees C; however, no movement of either 3.9-kilodalton or 9.4-kilodalton F-dextrans was detected when the transgenic plants were held for 6 hours (or longer) at 32 degrees C. When these plants were shifted back to 24 degrees C for 6 hours, cell-to-cell movement of the F-dextrans was again observed. Accumulation of MPP154A was not affected by the temperature regime, nor was the subcellular distribution of the MP altered. These results are consistent with a change in the protein conformation of MPP154A at the nonpermissive temperature, which gives rise to a protein that fails to modify the molecular size-exclusion limits of plasmodesmata to the same extent as wild-type MP. Surprisingly, at 32 degrees C, movement of the F-dextrans was inhibited in transgenic plants expressing the wild-type MP gene; however, the inhibition was transient and was no longer detected after 48 hours at this elevated temperature. This transient inhibition of plasmodesmatal function was alleviated with Sirofluor, an inhibitor of callose ([1----3]-beta-D-glucan) synthesis. This result provides experimental evidence that callose deposition is involved in regulating the molecular size-exclusion limit of plasmodesmata in plants. Sirofluor had no effect on the inhibition of F-dextran movement at 32 degrees C in plants expressing the MPP154A gene, indicating that callose formation was not responsible for the failure of the temperature-sensitive mutant protein to alter the size-exclusion limit of plasmodesmata.

Benzenesulfonates↗
PubMed1996

Decreased Susceptibility to Viral Disease of [beta]-1,3-Glucanase-Deficient Plants Generated by Antisense Transformation.

Antifungal class I [beta]-1,3-glucanases are believed to be part of the constitutive and induced defenses of plants against fungal infection. Unexpectedly, mutants deficient in these enzymes generated by antisense transformation showed markedly reduced lesion size, lesion number, and virus yield in the local-lesion response of Havana 425 tobacco to tobacco mosaic virus (TMV) and of Nicotiana sylvestris to tobacco necrosis virus. These mutants also showed decreased severity of mosaic disease symptoms, delayed spread of symptoms, and reduced yield of virus in the susceptible response of N. sylvestris to TMV. The symptoms of disease in the responses of both plant species were positively correlated with [beta]-1,3-glucanase content in a series of independent transformants. Taken together, these results provide direct evidence that [beta]-1,3-glucanases function in viral pathogenesis. Callose, a substrate for [beta]-1,3-glucanase, acts as a physical barrier to the spread of virus. Callose deposition in and surrounding TMV-induced lesions was increased in the [beta]-1,3-glucanase-deficient, local-lesion Havana 425 host, suggesting as a working hypothesis that decreased susceptibility to virus resulted from increased deposition of callose in response to infection. Our results suggest novel means, based on antisense transformation with host genes, for protecting plants against viral infection. These observations also raise the intriguing possibility that viruses can use a defense response of the host against fungal infection[mdash]production of [beta]-1,3-glucanases[mdash]to promote their own replication and spread.

Journal Article↗
PubMed1997

Spatial resolution and contrast sensitivity of single neurons in area 19 of split-chiasm cats: a comparison with primary visual cortex.

Electrophysiological recordings were carried out in the callosal recipient zone of area 19 in normal and split-chiasm cats and, for comparison purposes, at the border of areas 17 and 18 of split-chiasm cats. The influences of retinothalamic and callosal inputs on a single cortical neurons were thereby evaluated. Extracellular recordings of single cells were made in anaesthetized and paralysed cats in the zone representing the central visual field. Receptive field properties were assessed using sine wave gratings drifting in optimal directions. Results showed that in area 19 and areas 17/18 one-third of the cells were binocularly driven after section of the optic chiasm. In area 19, the spatial resolution and contrast sensitivity of cells driven via the dominant eye were similar in the normal and split-chiasm groups. In areas 17/18 and area 19 of split-chiasm cats, binocular cells showed significant interocular matching of their receptive field properties (spatial resolution and contrast threshold), although small differences were observed. These small interocular differences were related to the cell's ocular dominance rather than to the signal transmission route (thalamic or callosal).

Animals↗
PubMed1997

Organization of pyramidal cell apical dendrites and composition of dendritic clusters in the mouse: emphasis on primary motor cortex.

It has been proposed that neurons in sensory cortices are organized into modules that centre on clusters of apical dendrites belonging to layer V pyramidal neurons. In the present study, sections reacted for microtubule-associated protein (MAP2) were examined in order to determine the three-dimensional inter-relationships of pyramidal cell dendrites in mouse primary motor cortex (MsI) cortex. Results indicate that pyramidal cell dendrites in MsI cortex can be interpreted to be arranged in a modular fashion, and that these modules are organized similarly to those in the sensory areas of the cortex. Also included in the present study are experiments designed to determine if the clusters of apical dendrites, around which the modules are centred, are composed of dendrites belonging to one or to more than one type of projection cell. Callosal neurons in MsI cortex were labelled by the retrograde transport of horseradish peroxidase deposited onto severed callosal fibres in the contralateral hemisphere. Examination of tangential thin sections through layer IV of MsI cortex shows clusters of apical dendrites in which every dendrite is labelled with horseradish peroxidase. Adjacent clusters are composed of unlabelled dendrites, suggesting that the apical dendrites of callosal neurons aggregate to form clusters that are composed exclusively of dendrites belonging to this type of projection cell. These findings suggest a hitherto unsuspected degree of specificity in the cellular composition of cortical modules.

Animals↗
PubMed2006

Contribution of the corpus callosum to bilateral representation of the trunk midline in the human brain: an fMRI study of callosotomized patients.

Human brain studies have shown that the cutaneous receptors of trunk regions close to the midline are represented in the first somatosensory cortex (SI) of both hemispheres. The present study aims to establish whether in humans, as in non-human primates, the bilateral representation of the trunk midline in area SI depends on the corpus callosum. Data were obtained from eight callosotomized patients: three with complete callosal resection, one with a partial posterior resection including the splenium and the callosal trunk, and four with partial anterior resections sparing the splenium and in one case also the posterior part of the callosal trunk. The investigation was carried out with functional magnetic resonance imaging. Unilateral tactile stimulation was applied by rubbing ventral trunk regions close to the midline (about 20 x 10 cm in width) with a soft cotton pad (frequency 1 Hz). Cortical activation foci elicited by unilateral stimulation of cutaneous regions adjacent to the midline were detected in the contralateral post-central gyrus (PCG), in a region corresponding to the trunk ventral midline representation zone of area SI, as described in a previous study of intact subjects. In most patients, activation foci were also found in the ipsilateral PCG, again as in subjects with an intact corpus callosum. The data confirm that the skin regions adjacent to the trunk midline are represented bilaterally in SI, and indicate that ipsilateral activation is at least partially independent of the corpus callosum.

Abdomen↗
PubMed2005

Regulation of cell length in the Arabidopsis thaliana root by the ethylene precursor 1-aminocyclopropane- 1-carboxylic acid: a matter of apoplastic reactions.

Treatment of the Arabidopsis thaliana root with the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) immediately imposes a reduced maximal cell length beyond which further elongation is blocked. Here, we investigated possible apoplastic reactions involved in the inhibition of cell elongation. Five-day-old Arabidopsis seedlings were transferred to a growth medium supplemented with ACC and the effect on root cell length was recorded after 3 h of treatment. Altered characteristics in the apoplast of the nonelongating cells in the ACC-treated root, such as 'reactive oxygen species' (ROS) production and callose deposition, were detected using specific fluorochromes. The presence of functional hydroxyproline-rich glycoproteins (HRGPs) and the crosslinking of these cell-wall proteins are essential in limiting cell elongation. The ROS that drive the oxidative crosslinking of HRGPs, accumulate in the apoplast of cells in the zone where cell elongation stops. In the same cells, callose is deposited in the cell wall. The final cell length in the Arabidopsis root treated for a short period with ACC is determined in the zone of fast elongation. Both HRGPs crosslinking by ROS and callose deposition in the cell wall of this zone are suggested as causes for the reduced cell elongation.

Amino Acids, Cyclic↗
PubMed1996

Thinning of the corpus callosum in older alcoholic men: a magnetic resonance imaging study.

A brain image averaging technique was applied to three-dimensional magnetic resonance images to identify visually detectable brain volume abnormalities in chronically alcoholic men, compared with healthy control men. This technique, which was based on pixel-by-pixel statistical probability mapping, revealed a dramatic reduction in the area of the corpus callosum in older alcoholics (age 45 years or older), relative to age-matched controls. Subsequent analysis used anatomical landmarks to outline the borders of midsagittal sections of the corpus callosum in a larger group of alcoholics and controls, who spanned the adult age range from 23 to 71 years. This analysis revealed significant reduction, most prominent in the genu and body, of total callosal area in the alcoholic group relative to the control group; the results were the same whether raw area measures or head size plus age adjusted measure were analyzed. Significant thinning of the callosal body in alcoholics is usually attributed to the relatively rare, nutritional-deficient condition, Marchiafava-Bignami disease. However, callosal thinning was present in vivo in chronic alcoholics without clinical symptoms of severe liver disease, amnesia, or alcoholic dementia. These data suggest that chronic alcoholism can be characterized by a continuum of graded brain dysmorphology, rather than classical alcoholic-related subsyndromes, such as Marchiafava-Bignami disease.

Adult↗
PubMed1994

No differences in corpus callosum size by sex and aging. A quantitative study using magnetic resonance imaging.

To identify normal variations in the magnetic resonance imaging appearances of the corpus callosum with regard to sex and age, a prospective study was performed in 130 normal subjects. Callosal measurements were calculated by morphometric analysis. There were no significant sex differences in corpus callosum area or the callosal subregions. The absolute area did not decrease significantly with aging in normal males or females. However, age-related changes of callosal configuration were shown by a decrease in the ratio of the rostrum and genu to the splenium.

Adolescent↗
PubMed1987

The transfer of visual information across the corpus callosum: spatial and temporal properties in the cat.

1. The spatial and temporal characteristics of the visual information transmitted across the corpus callosum have been studied in normal cats by recording directly from the corpus callosum and in split-chiasm cats by means of visual evoked potentials (v.e.p.s) and single-unit recordings at the 17/18 border. 2. The modulation transfer functions (m.t.f.s) obtained by recording from the corpus callosum are comparable to the m.t.f.s evaluated by various techniques for the whole visual system of the cat. The spatial and temporal acuities, however, do not reach the values obtained behaviourally or estimated with cortical evoked potentials. 3. In split-chiasm cats, both v.e.p.s and single-unit recordings indicate that the contrast gain of the callosal pathway is considerably lower than the gain of the direct, geniculo-cortical system. Spatial and temporal acuities are lower for the callosal than for the direct system. 4. The same differences in contrast gain between the spatial m.t.f. obtained for the callosal and the direct system have been found in alert split-chiasm cats. 5. Our data suggest that the cross-talk between the hemispheres taking place across the corpus callosum is nearly abolished at low contrasts and high spatial and temporal frequencies.

Animals↗
PubMed2006

Functional and magnetic resonance imaging correlates of corpus callosum in normal pressure hydrocephalus before and after shunting.

BACKGROUND: Normal pressure hydrocephalus (NPH) is associated with corpus callosum abnormalities. OBJECTIVES: To study the clinical and neuropsychological effect of callosal thinning in 18 patients with idiopathic NPH and to investigate the postsurgical callosal changes in 14 patients. METHODS: Global corpus callosum size and seven callosal subdivisions were measured. Neuropsychological assessment included an extensive battery assessing memory, psychomotor speed, visuospatial and frontal lobe functioning. RESULTS: After surgery, patients showed improvements in memory, visuospatial and frontal lobe functions, and psychomotor speed. Two frontal corpus callosum areas, the genu and the rostral body, were the regions most related to the clinical and neuropsychological dysfunction. After surgery, total corpus callosum and four of the seven subdivisions presented a significant increase in size, which was related to poorer neuropsychological and clinical outcome. CONCLUSION: The postsurgical corpus callosum increase might be the result of decompression, re-expansion and increase of interstitial fluid, although it may also be caused by differences in shape due to cerebral reorganisation.

Aged↗
PubMed1995

Progression of atrophy of the corpus callosum with deterioration of cerebral cortical oxygen metabolism after carotid artery occlusion: a follow up study with MRI and PET.

In cerebrovascular disease, progression of brain atrophy may reflect an increase in ischaemic changes. The purpose of this study was to determine whether atrophy of the corpus callosum progresses in association with a deterioration in cerebral cortical oxygen metabolism after occlusion of the carotid artery. Magnetic resonance imaging and PET were used to serially evaluate six patients with occlusion of the unilateral internal carotid artery at intervals ranging from 12 to 50 months. One patient had no symptoms, one had a transient ischaemic attack, and four had a minor stroke. All patients had presented at most only subcortical lesions at the first evaluation. During follow up, no patient showed extension of subcortical lesions or recurrent stroke. The initial total callosal area:skull area ratio for the patients was significantly less than that for 14 age matched normal control subjects. The yearly decrease of callosal size in the patients, which differed significantly from zero and exceeded that in the controls, was significantly correlated with the deterioration in mean cerebral cortical oxygen metabolism. Three of the four patients who showed significant progression of callosal atrophy presented deterioration in haemodynamic states as well. It is concluded that in some patients atrophy of the corpus callosum progresses after occlusion of the carotid artery even in the absence of any overt episode of stroke, and that this atrophy is associated with deterioration in cerebral cortical oxygen metabolism. An increase in cerebral morphological changes with deterioration in cerebral metabolism related to ischaemia may occur after occlusion of the carotid artery, even in the absence of symptoms.

Aged↗
PubMed2000

Subjective experience, involuntary movement, and posterior alien hand syndrome.

The alien hand syndrome, as originally defined, was used to describe cases involving anterior corpus callosal lesions producing involuntary movement and a concomitant inability to distinguish the affected hand from an examiner's hand when these were placed in the patient's unaffected hand. In recent years, acceptable usage of the term has broadened considerably, and has been defined as involuntary movement occurring in the context of feelings of estrangement from or personification of the affected limb or its movements. Three varieties of alien hand syndrome have been reported, involving lesions of the corpus callosum alone, the corpus callosum plus dominant medial frontal cortex, and posterior cortical/subcortical areas. A patient with posterior alien hand syndrome of vascular aetiology is reported and the findings are discussed in the light of a conceptualization of posterior alien hand syndrome as a disorder which may be less associated with specific focal neuropathology than are its callosal and callosal-frontal counterparts.

Aged↗