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PubMed2002

Comparative subcellular immunolocation of polypeptides associated with xylan and callose synthases in French bean (Phaseolus vulgaris) during secondary wall formation.

The Golgi apparatus of plant cells is thought to be the main site of synthesis of cell wall matrix polysaccharides and the terminal glycosylation of glycoproteins. Much of this evidence still depends on earlier biochemical studies employing subcellular fractionation. However acquiring pure Golgi membranes is still difficult and the question of spatial organisation of glycosyl transferases can be addressed by immunolocation of the enzymes. An antibody to a xylan synthase-associated polypeptide from French bean, the enzyme which synthesises the core polysaccharide for secondary wall xylan, has been raised and shown to inhibit its activity. Xylan is deposited in secondary thickenings and the xylan synthase was only detected in appreciable amounts in developing xylem cells. The location within the Golgi stack was observed throughout the dictyosomes. Some enzyme subunits were also detected in post-Golgi vesicles. A second antibody to a non-catalytic M(r) 65000 subunit of beta 1,3- glucan (callose) synthase was used for a comparative study. Although the bulk of this enzyme has been detected in previous studies at plasmamembrane-wall interfaces in sieve plates and stressed tissue, a Golgi-location can be observed in root tip meristematic cells during cell plate formation. The enzyme was present throughout the stacks. Callose was also immunolocated in a similar manner to xylan in secondary walls and thickenings and in pits in developing xylem. In these cells, the callose synthase was detected at the surface of the growing thickenings and the plasmamembrane within the pits.

Blotting, Western↗
PubMed1997

Regional differences of callosal connections in the granular zones of the primary somatosensory cortex in rats.

The primary somatosensory cortex (SI) in rats is cytoarchitectonically divided into three zones: the granular, peri-, and dysgranular zones. To examine callosal connections in the granular zone that bears representation of the body somatosensory map, the distribution of lectin-conjugated horse-radish peroxidase labeis was explored in the right SI after single or multiple injections into the granular zone of the left SI. After injections in the upper and lower law regions, many labeled cell bodies and dense terminal labeling were found in the regions homotopical to the injection sites. Both kinds of labels were densely seen in layers II-III and V, less densely in layer VI. Densely labeled terminals were also observed in layer I. In layer IV, many terminals and a few cell bodies were labeled in the septa, while labeling inside the barrels was sparse or absent. After injections in other regions, i.e., those representing the facial whiskers, fore- and hindlimbs, or trunk in the granular zone, labeled callosal cell bodies and terminals were sparse or absent, except in the septa of the posteromedial barrel subfield representing the facial whiskers. The results clearly show that the density of callosal connection in the granular zone differs in different subfields, and that at least the jaw regions in the granular zones of both hemispheres are directly interconnected, in contrast to the previous assumption that only the dysgranular zone mediates information transmission between the granular zones of both sides.

Animals↗
PubMedDate not supplied

Callosal changes in obstructive hydrocephalus: observations with FLAIR imaging, and diffusion MRI.

Sagittal and transverse fluid attenuated inversion recovery (FLAIR) images were obtained in age-matched 16 normal individuals, and 24 patients with obstructive hydrocephalus. The inner (inferior) callosal surface, which is covered by ependyma, was electronically measured ranging from 0.15 to 0.25 cm (mean= 0.20+/-0.02 cm) in normal individuals. This region was thicker in hydrocephalus cases due to transcallosal accumulation of water, ranging from 0.29 to 1.10 cm (mean= 0.65+/-0.30 cm). Furthermore, there was a prominent difference between mild hydrocephalus and moderate-to-severe hydrocephalus cases that in mild hydrocephalus the ranges were 0.29-0.40 cm (mean= 0.34+/-0.03 cm), and in moderate-to-severe hydrocephalus the ranges were 0.50-1.10 cm (mean= 0.80+/-0.22 cm). It is concluded that especially sagittal FLAIR images could be useful for identifying especially milder forms of hydrocephalus by evaluation of the appearance and thickness of the inner callosal layer. Twelve patients with moderate-to-severe obstructive hydrocephalus, and eight of the controls were studied with diffusion MRI, using the echo-planar trace imaging. In moderate-to-severe hydrocephalus patients apparent diffusion coefficient (ADC) values from the inner callosal surface were high, similar to that of transependymal resorption of water, ranging from 1.30 to 2.20 x 10 x (-3)mm(2)/s (mean: 1.78+/-0.27 x 10 x (-3) mm(2)/s), compared to the normal ADC values of the splenium in controls: 0.78+/-0.12 x 10 x (-3) mm(2)/s.

Adolescent↗
PubMedDate not supplied

Callosally projecting neurons in the macaque monkey V1/V2 border are enriched in nonphosphorylated neurofilament protein.

Previous immunohistochemical studies combined with retrograde tracing in macaque monkeys have demonstrated that corticocortical projections can be differentiated by their content of neurofilament protein. The present study analyzed the distribution of nonphosphorylated neurofilament protein in callosally projecting neurons located at the V1/V2 border. All of the retrogradely labeled neurons were located in layer III at the V1/V2 border and at an immediately adjacent zone of area V2. A quantitative analysis showed that the vast majority (almost 95%) of these interhemispheric projection neurons contain neurofilament protein immunoreactivity. This observation differs from data obtained in other sets of callosal connections, including homotypical interhemispheric projections in the prefrontal, temporal, and parietal association cortices, that were found to contain uniformly low proportions of neurofilament protein-immunoreactive neurons. Comparably, highly variable proportions of neurofilament protein-containing neurons have been reported in intrahemispheric corticocortical pathways, including feedforward and feedback visual connections. These results indicate that neurofilament protein is a prominent neurochemical feature that identifies a particular population of interhemispheric projection neurons at the V1/V2 border and suggest that this biochemical attribute may be critical for the function of this subset of callosal neurons.

Animals↗
PubMed2002

Dichotic listening in patients with splenial and nonsplenial callosal lesions.

The authors found splenial lesions to be associated with left ear suppression in dichotic listening of consonant-vowel syllables. This was found in both a rapid presentation dichotic monitoring task and a standard dichotic listening task, ruling out attentional limitations in the processing of high stimulus loads as a confounding factor. Moreover, directed attention to the left ear did not improve left ear target detection in the patients, independent of callosal lesion location. The authors' data may indicate that auditory callosal fibers pass through the splenium more posterior than previously thought. However, further studies should investigate whether callosal fibers between primary and secondary auditory cortices, or between higher level multimodal cortices, are vital for the detection of left ear targets in dichotic listening.

Adult↗
PubMed2006

Callosal involvement in a lateralized stroop task in alcoholic and healthy subjects.

To investigate the role of interhemispheric attentional processes, 25 alcoholic and 28 control subjects were tested with a Stroop match-to-sample task and callosal areas were measured with magnetic resonance imaging. Stroop color-word stimuli were presented to the left or right visual field (VF) and were preceded by a color cue that did or did not match the word's color. For matching colors, both groups showed a right VF advantage; for nonmatching colors, controls showed a left VF advantage, whereas alcoholic subjects showed no VF advantage. For nonmatch trials, VF advantage correlated with callosal splenium area in controls but not alcoholic subjects, supporting the position that information presented to the nonpreferred hemisphere is transmitted via the splenium to the hemisphere specialized for efficient processing. The authors speculate that alcoholism-associated callosal thinning disrupts this processing route.

Adult↗
PubMed1983

Interocular transfer in cats with early callosal transection.

The visual system is capable of reorganization following experimental interventions, provided that these are carried out before the 'critical period' early in life. Direct evidence suggests that this plasticity may also apply to the commissural system. In the present experiment, we sectioned the posterior two-thirds of the corpus callosum in kittens either before this structure attained maturity, as defined by various anatomical and physiological parameters, or after callosal maturation but before the end of the critical period for most other visual functions. As adult, further transection of the optic chiasma was carried out and these animals were then compared with adult split-brain cats for their ability to transfer monocularly learned pattern discriminations from one hemisphere to the other. Our results indicate that only the first group of animals with the earlier callosal transection demonstrated significant interhemispheric transfer. This suggests that the secondary commissural system is subject to at least some degree of functional plasticity. However, its critical period is very brief and possibly pre-dates the optimal activation of the callosal pathway.

Age Factors↗
PubMed2001

Biosynthesis of (1-->3)-beta-D-glucan (callose) by detergent extracts of a microsomal fraction from Arabidopsis thaliana.

The aim of this work was to develop a biochemical approach to study (1-->3)-beta-D-glucan (callose) biosynthesis using suspension cultures of Arabidopsis thaliana. Optimal conditions for in vitro synthesis of callose corresponded to an assay mixture containing 50 mM Mops buffer, pH 6.8, 1 mM UDP-glucose, 8 mM Ca2+ and 20 mM cellobiose. The enzyme was Ca2+-dependent, and addition of Mg2+ to the reaction mixture did not favour cellulose biosynthesis. Enzyme kinetics suggested the existence of positive homotropic cooperativity of (1-->3)-beta-D-glucan synthase for the substrate UDP-glucose, in agreement with the hypothesis that callose synthase consists of a multimeric complex containing several catalytic subunits. Detergents belonging to different families were tested for their ability to extract and preserve membrane-bound (1-->3)-beta-D-glucan synthase activity. Cryo-transmission electron microscopy experiments showed that n-octyl-beta-D-glucopyranoside allowed the production of micelle-like structures, whereas vesicles were obtained with Chaps and Zwittergent 3-12. The morphology and size of the (1-->3)-beta-D-glucans synthesized in vitro by fractions obtained with different detergents were affected by the nature of the detergent tested. These data suggest that the general organization of the glucan synthase complexes and the properties of the in vitro products are influenced by the detergent used for protein extraction. The reaction products synthesized by different detergent extracts were characterized by infrared spectroscopy, methylation analysis, 13C-NMR spectroscopy, electron microscopy and X-ray diffraction. These products were identified as linear (1-->3)-beta-D-glucans having a degree of polymerization higher than 100, a microfibrillar structure, and a low degree of crystallinity.

Arabidopsis↗
PubMed1996

Bilateral symmetry detection: testing a 'callosal' hypothesis.

At the end of the 19th century Mach observed that vertical symmetry is more easily perceived than is symmetry at other orientations, and proposed this resulted from bilateral symmetry in the visual system. Numerous studies of symmetry detection have been conducted, but none has been concentrated on Mach's proposal. Recent interpretations of Mach's hypothesis suggest the corpus callosum mediates the vertical-symmetry advantage. In this 'callosal' hypothesis it is suggested that the detectability of symmetry should be narrowly tuned around vertical, and that presentation of patterns away from fixation should disrupt the vertical advantage. We found that the vertical advantage was disrupted by presentation of patterns 1.2 deg from fixation, while detection of symmetry at other orientations was not disrupted. At fixation the orientation tuning was at least within +/- 10 degrees of vertical. The detection of vertical symmetry at fixation was found to be anomalous in two subjects born without a corpus callosum as compared with controls, but relatively normal for presentation off fixation. The three experiments reported are in agreement with some of the predictions derived from the callosal hypothesis. It appears that the callosal hypothesis may account for the relative advantage of vertical symmetry at fixation, but other mechanisms must operate to detect symmetry at other orientations and positions.

Adult↗
PubMed1999

Cross-modal reorganization of callosal connectivity without altering thalamocortical projections.

Mammalian cerebral cortex is composed of a multitude of different areas that are each specialized for a unique purpose. It is unclear whether the activity pattern and modality of sensory inputs to cortex play an important role in the development of cortical regionalization. The modality of sensory inputs to cerebral cortex can be altered experimentally. Neonatal diversion of retinal axons to the auditory thalamus (cross-modal rewiring) results in a primary auditory cortex (AI) that resembles the primary visual cortex in its visual response properties and topography. Functional reorganization could occur because the visual inputs use existing circuitry in AI, or because the early visual inputs promote changes in AI's circuitry that make it capable of constructing visual receptive field properties. The present study begins to distinguish between these possibilities by exploring whether the callosal connectivity of AI is altered by early visual experience. Here we show that early visual inputs to auditory thalamus can reorganize callosal connections in auditory cortex, causing both a reduction in their extent and a reorganization of the pattern. This result is distinctly different from that in deafened animals, which have widespread callosal connections, as in early postnatal development. Thus, profound changes in cortical circuitry can result simply from a change in the modality of afferent input. Similar changes may underlie cortical compensatory processes in deaf and blind humans.

Afferent Pathways↗
PubMed2006

Arrangement of fiber tracts forming Probst bundle in complete callosal agenesis: report of two cases with an evaluation by diffusion tensor tractography.

We report two patients with complete callosal agenesis in whom Probst bundles in both hemispheres could be depicted by diffusion tensor tractography (DTT). While one patient had no associated telencephalic anomaly other than callosal agenesis, the other had cortical dysplasia in the right frontal lobe. Although Probst bundles in the three normal hemispheres were well developed, that in the hemisphere which was affected by cortical dysplasia was small and poorly developed. DTT also showed that the fibers from the frontal pole ran more on the inner side of the Probst bundle than those from a more caudal region of the frontal lobe. Furthermore, fibers from the orbital gyri ran along the outermost side of Probst bundle. The arrangement of these fiber tracts in Probst bundle may reflect the developmental process of callosal fibers in their normal formation.

Adult↗
PubMed1998

Speech lateralisation in callosal agenesis assessed by the dichotic fused words test.

Child patients with left-hemisphere damage (n = 2), with total callosal agenesis (n = 2), and with partial callosal agenesis or hypotrophy (n = 3) were submitted to dichotic verbal stimulation by the Fused Words Test. The controls were nine normal children, right-, left-, and mixed-handed. As expected, the left-injured patients presented a massive advantage of the ear contralateral to the intact hemisphere. Among the controls the right-handers showed a significant right-ear prevalence, whereas left-and mixed-handers exhibited rather inconsistent earasymmetries. The major finding of this study is the striking difference in perceptual asymmetry between partial and total acallosals. Based on the notion that the dichotic verbal asymmetry is an effect of the underlying functional asymmetry for language, these findings are interpreted as an indication that development of the unilateral speech control is influenced by the presence, during ontogenesis, of callosal connections.

Journal Article↗
PubMed1989

Anterior callosal haemorrhage. A partial interhemispheric disconnection syndrome.

The interhemispheric disconnection syndrome secondary to a callosal haemorrhage is exceedingly uncommon. In the present study, 3 patients with haemorrhages restricted to the corpus callosum are presented. All 3 developed a partial anterior interhemispheric disconnection syndrome: unilateral tactile anomia, unilateral agraphia, unilateral apraxia, difficulty in copying drawings, dyscalculia as well as abnormalities of somaesthetic transfer and the 'alien hand' sign. The study of these cases allowed a close examination of the association between deficits in the transfer of specific neuropsychological information and the precise topography of callosal damage. Variability in the lateralization of cognitive functions, and possible mechanisms underlying the production of callosal haemorrhages after the rupture of saccular aneurysms are also discussed.

Adult↗
PubMed2002

Sound localization in callosal agenesis and early callosotomy subjects: brain reorganization and/or compensatory strategies.

In order to evaluate the callosal involvement in sound localization, the present study examined the response accuracy of acallosal and early callosotomized subjects to monaural and binaural auditory targets presented in three-dimensional space. In these subjects, bilateral localization cues, such as interaural time and level differences, are integrated at the cortical and subcortical levels without the additional support of the callosal commissure. Because acallosal and early-callosotomized subjects have developed with this reduced source of binaural activation of cortical cells, they might have perfected their ability to use monaural sound localization cues. This hypothesis was tested by assessing localization performance under both binaural and monaural listening conditions. Five subjects with callosal agenesis, one callosotomized subject operated early in life and 19 control subjects were asked to localize broad-band noise bursts (BBNBs) of fixed intensity in the horizontal plane in an anechoic chamber. BBNBs were delivered through randomly selected loudspeakers. Two conditions were tested: (i) localization of a stationary sound source; and (ii) localization of a moving sound source. Listeners had to report the apparent stimulus location by pointing to its perceived position on a graduated perimeter. The results indicated that the acallosal subjects were less accurate than controls, but only in the binaural moving sound condition. More interestingly, in the monaural testing conditions, some of the acallosal subjects and the early-callosotomized subject performed significantly better than control subjects. This suggests that, because of the absence of the corpus callosum, these subjects compensate for their reduced access to cortically determined binaural cues by making more efficient use of monaural cues.

Acoustic Stimulation↗
PubMedDate not supplied

Morphogenesis of callosal arbors in the parietal cortex of hamsters.

The morphogenesis of callosal axons originating in the parietal cortex was studied by anterograde labeling with Phaseolus lectin or biocytin injected in postnatal (P) hamsters aged 7-25 days. Some labeled fibers were serially reconstructed. At P7, some callosal fibers extended as far as the contralateral rhinal fissure, with simple arbors located in the homotopic region of the opposite cortical gray matter, and two or three unbranched sprouts along their trajectory. From P7 to P13, the homotopic arbors became more complex, with branches focused predominantly, but not exclusively, in the supra- and infragranular layers of the homotopic region. Simultaneously, the lateral extension of the trunk axon in the white matter became shorter, finally disappearing by P25. Arbors in the gray matter were either bilaminar (layers 2/3 and 5) or supragranular. A heterotopic projection to the lateral cortex was consistently seen at all ages; the heterotopic arbors follow a similar sequence of events to that seen in homotopic regions. These observations document that callosal axons undergo regressive tangential remodeling during the first postnatal month, as the lateral extension of the trunk fiber gets eliminated. Radially, however, significant arborization occurs in layer-specific locations. The protracted period of morphogenesis suggests a correspondingly long plastic period for this system of cortical fibers.

Animals↗
PubMed2005

Selective age-related degradation of anterior callosal fiber bundles quantified in vivo with fiber tracking.

The corpus callosum, the principal white matter structure enabling interhemispheric information transfer, is heterogeneous in its microstructural composition, heterotopic in its anteroposterior cortical connectivity, and differentially susceptible to aging. In vivo characterization of callosal features is possible with diffusion tensor imaging (DTI), a magnetic resonance imaging method sensitive to the detection of white matter's linear structure. We implemented a quantitative fiber tracking approach to examine age-related variation in regional microstructural characteristics [fractional anisotropy (FA) and apparent diffusion coefficient (ADC)] of callosal fibers in 10 younger (29 +/- 5 years) and 10 older (72 +/- 5 years) healthy adults. Fiber tracking was performed on 2.5 mm isotropic voxels collected at 3 T. Fiber targets comprised the midsagittal corpus callosum, divided into six regions based on known callosal anatomical projections. FA and ADC for each voxel of each fiber identified were determined; lower FA and higher ADC reflect degraded microstructural tissue integrity. Older subjects had lower FA (P < 0.002), higher ADC (P < 0.006), and fewer (P < 0.005) fibers than younger subjects. Group x region interactions indicated disproportionately lower FA (P = 0.0001) and higher ADC (P < 0.006) in the older than younger group in frontal fiber bundles relative to posterior bundles. As a test of the functional significance of the fiber bundle metrics, the older subjects were administered the Stroop Task, which showed significant correlations between regional fiber bundle integrity and performance. These results validate this quantitative fiber tracking approach and confirm the selective vulnerability of frontal white matter systems to normal aging, likely substrates of age-related declines in cognitive processes dependent on prefrontal circuitry integrity.

Adult↗
PubMed2006

Neuroplasticity in human callosal dysgenesis: a diffusion tensor imaging study.

Callosal dysgenesis (CD) is observed in many neurodevelopmental conditions, but its subjacent mechanisms are unknown, despite extensive research on animals. Here we employ magnetic resonance diffusion tensor imaging and tractography in human CD to reveal the aberrant circuitry of these brains. We searched particularly for evidence of plasticity. Four main findings are described--1) in the presence of a callosal remnant or a hypoplastic corpus callosum (CC), fibers therein largely connect the expected neocortical regions; 2) callosal remnants and hypoplastic CCs display a fiber topography similar to normal; 3) at least 2 long abnormal tracts are formed in patients with defective CC: the well-known Probst bundle (PB) and a so far unknown sigmoid, asymmetrical aberrant bundle connecting the frontal lobe with the contralateral occipitoparietal cortex; and 4) whereas the PB is topographically organized and has an ipsilateral U-connectivity, the sigmoid bundle is a long, heterotopic commissural tract. These observations suggest that when the developing human brain is confronted with factors that hamper CC fibers to cross the midline, some properties of the miswired fibers are maintained (such as side-by-side topography), whereas others are dramatically changed, leading to the formation of grossly abnormal white matter tracts.

Adult↗
PubMed2003

Synthesis of a callosic substance during rhizoid differentiation in Spirogyra.

Spirogyra living in running water is anchored to the substratum by rhizoids that form at the ends of the filaments. A new terminal cell differentiates into a rhizoid cell if the filament is injured. The mode of growth changes from diffuse to tip growth when rhizoid differentiation begins. In this study, we found that a callosic substance was synthesized during rhizoid differentiation. Decreasing the cell turgor, lowering extracellular Ca2+ or adding Gd3+, all inhibited the commencement of rhizoid differentiation as well as synthesis of the callose-like substance at the tip of the terminal cell. A callosic substance was also synthesized during formation of the conjugation tube.

Calcium↗