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PubMed1983

Effects on binocular activation of cells in visual cortex of the cat following the transection of the optic tract.

Cells in area 17 of the cortex are generally activated either directly through a retino-thalamic pathway or indirectly via a contralateral hemisphere-callosal pathway. The aim of the present experiment was to evaluate the effects of eliminating this second pathway on the binocular activation of cells in the primary visual cortex. The optic tract was sectioned on one side in 18 cats and unit activity was recorded in the contralateral hemisphere. This hemisphere should receive normal thalamo-cortical inputs but no visual callosal input. These animals were compared to 21 normal cats. Extracellular electrophysiological recordings were carried out in the conventional way using tungsten microelectrodes and N2O anaesthesia. Results indicated that the proportion of binocular cells found in the cortex of tract sectioned animals was lower than that found in normal animals. However, this decrease in binocularity could be essentially attributed to cells having receptive fields situated to within 4 degrees of the vertical meridian of the visual field. These results are interpreted as being congruent with the demonstrated anatomo-physiological projections of the callosal system.

Animals↗
PubMed1992

Corpus callosum lesions after closed head injury in children: MRI, clinical features and outcome.

Thirty-four children who sustained moderate to severe closed head injury underwent magnetic resonance imaging (MRI). Eight (24%) had MRI evidence of corpus callosum injury, most commonly within the posterior body and splenium. In contradistinction to reports in adults, there was no definite relationship between callosal injury and lower initial Glasgow Coma Scale scores, nor was there a significantly higher incidence of primary brain-stem lesions, diffuse axonal shear injury or intraventricular hemorrhage. In none of these 8 children did the initial admission computed tomography show evidence of callosal injury. Callosal injuries on MRI are not necessarily a poor prognostic finding, the majority of the 8 children showing good functional recovery.

Adolescent↗
PubMed1982

The early formation of the corpus callosum: a light and electron microscopic study in foetal and neonatal rats.

A light and electron microscopic study of the developing corpus callosum was carried out in foetal and neonatal rats in order to determine the mode of growth of the earliest callosal axons across the midline and to investigate the potential role played by non-neuronal cells during the formation of the tract. The axons of the corpus callosum first cross the midline between the 18th and 19th days of gestation by traversing the anterodorsal aspect of the pre-existing hippocampal commissure. Prior to the appearance of the callosal axons at the midline, there is an aggregation of astrocyte processes anterior and dorsal to the hippocampal commissure. Careful examination of these processes in different planes of section shows that they are not organized in any obvious way that would provide a clearly defined path for the growing axons; nor are there any preferentially oriented extracellular spaces at the midline. No specialized membrane contacts could be seen between non-neuronal cell processes and the early callosal axons. Thus, there is no overt morphological evidence for an active role of non-neuronal cells in axon guidance in the initial formation of the corpus callosum. The development of the corpus callosum is accompanied by the formation of a temporary cavum septi pellucidi, which is always closed to the subarachnoid space. The cavum persists during the first postnatal week, after which time it becomes populated by cells of the lateral septal nuclei. Macrophages are present within the cavum and may play a role in its formation. Macrophages are also found within parts of the corpus callosum. No obvious degeneration of axons is seen in the corpus callosum during its early development.

Aging↗
PubMed1993

Cytological indication of the involvement of calcium and calcium-related proteins in the early responses of Bryonia dioica to mechanical stimulus.

The distribution of membrane-bound calcium, activated calmodulin, and callose synthesis was visualized in Bryonia dioica internodes before and after mechanical stimulus, using fluorescent probes, respectively, chlorotetracycline, fluphenazine, and aniline blue. Bright chlorotetracycline fluorescence remains localized in the plasma membrane of control cells, 30 s after stimulation calcium left the plasmalemma. A delocalization of activated calmodulin was observed after wounding and deposition of callose, which could not be detected before, appeared in the same times in most cells. The callose formation and the decrease in membrane-associated calcium suggest a rapid influx of calcium in the cytosol and an intervention of this ion in the cascade of the early events underlying Bryonia dioica thigmomorphogenesis.

Calcium↗
PubMed1996

Anterior callosotomy in the management of intractable epileptic seizures: significance of the extent of resection.

We report our series of twenty consecutive patients who underwent corpus callosotomy for medically intractable epilepsy. The follow-up is 6.7 +/- 0.5 years. Sixteen of 20 patients (80%) had a favourable outcome. Six patients have remained free of major generalized motor seizures, and ten further patients experienced significant sustained reduction in the severity and frequency of the seizures. The type of seizures associated with improved outcome were drop attacks, and generalized tonic-clonic seizures, in 11 of 13 (85%) and 14 of 18 (78%) of the patients, respectively. In order to establish the extent of necessary callosal resection to achieve seizure control, the outcome of patients was correlated with the extent of callosal sectioning on postoperative magnetic resonance imaging. This study confirms that an anterior callosal resection of two-thirds (or 65%) is sufficient to achieve significant improvement in seizure control with an acceptable morbidity in judiciously selected patients with medically intractable epilepsy. Results also suggest that the patient's history and clinical classification of the seizures have prognostic value as selection criteria for patients referred for this operation. In this series, no prognostic value was established for pre-operative electroencephalographic patterns, or neuroimaging findings.

Adolescent↗
PubMed2001

Corpus callosum: microsurgical anatomy and MRI.

The anatomy of the corpus callosum has received renewed interest during recent years due to the increasing number of callosotomies performed to treat intraventricular lesions, as well as some forms of generalized epilepsy. We have previously reported on the microsurgical anatomy of the corpus callosum and identified specific anatomical reference landmarks that can be used during surgery. In the present study we have continued the anatomical aspect of this earlier work in a larger number of cases, with in vitro observations (brain out of skull) being compared with the corresponding in vivo features seen in sagittal MRI slices. Fifty-three in vitro microsurgical callosotomies was performed and the data collected compared with a series of 57 in vivo normal MR callosal images. Callosal dimensions were measured on both the anatomical and MRI material, thus overcoming the problems associated with in vitro callosal deformation. Of the anatomical landmarks studied the distance from the genu of the corpus callosum to the bifurcation of the columns of the fornix was found to be useful for the intraoperative evaluation of the extent of rostral callosotomy, as it is not significantly changed in in vitro. The main microsurgical features of rostral callosotomy are presented.

Adult↗
PubMed2003

Electron tomographic analysis of post-meiotic cytokinesis during pollen development in Arabidopsis thaliana.

The mechanism of cell wall formation after male meiosis was studied in microsporocytes of Arabidopsis thaliana (L.) Heynh. by means of thin-section and immuno-electron microscopy and dual-axis electron tomography of high-pressure-frozen/freeze-substituted cells. The cellularization of four-nucleate microsporocytes involves a novel type of cell plate, called a post-meiotic-type cell plate. As in the syncytial endosperm, the microsporocyte cell plates assemble in association with mini-phragmoplasts. However, in contrast to the endosperm cell plates, post-meiotic type cell plates arise simultaneously across the entire division plane. Vesicles are transported along mini-phragmoplast microtubules by putative kinesin proteins and, prior to fusion, they become connected together by 24-nm-long linkers that resemble exocyst complexes. These vesicles fuse with each other to form wide tubules and wide tubular networks. In contrast to endosperm cell plates, the wide tubular networks in microsporocytes completely lack callose and do not appear to be constricted by dynamin rings. The most peripheral wide tubular networks begin to fuse with the plasma membrane before the more central cell plate assembly sites become integrated into a coherent cell plate. Fusion with the parental plasma membrane triggers callose synthesis and the wide tubular domains are converted into convoluted sheets. As the peripheral convoluted sheets accumulate callose and arabinogalactan proteins, they are converted into stub-like projections, which grow centripetally, i.e. toward the interior of the syncytium, fusing with the wide tubular networks already assembled in the division plane. We also demonstrate that the ribosome-excluding cell plate assembly matrix is delivered to the mini-phragmoplast with the first vesicles, and encompasses all the linked vesicles and intermediate stages in cell plate formation.

Arabidopsis↗
PubMed2006

Temporal and spatial appearance of wall polysaccharides during cellularization of barley (Hordeum vulgare) endosperm.

Barley endosperm begins development as a syncytium where numerous nuclei line the perimeter of a large vacuolated central cell. Between 3 and 6 days after pollination (DAP) the multinucleate syncytium is cellularized by the centripetal synthesis of cell walls at the interfaces of nuclear cytoplasmic domains between individual nuclei. Here we report the temporal and spatial appearance of key polysaccharides in the cell walls of early developing endosperm of barley, prior to aleurone differentiation. Flowering spikes of barley plants grown under controlled glasshouse conditions were hand-pollinated and the developing grains collected from 3 to 8 DAP. Barley endosperm development was followed at the light and electron microscope levels with monoclonal antibodies specific for (1-->3)-beta-D: -glucan (callose), (1-->3,1-->4)-beta-D: -glucan, hetero-(1-->4)-beta-D: -mannans, arabino-(1-->4)-beta-D: -xylans, arabinogalactan-proteins (AGPs) and with the enzyme, cellobiohydrolase II, to detect (1-->4)-beta-D: -glucan (cellulose). Callose and cellulose were present in the first formed cell walls between 3 and 4 DAP. However, the presence of callose in the endosperm walls was transient and at 6 DAP was only detected in collars surrounding plasmodesmata. (1-->3,1-->4)-beta-D: -Glucan was not deposited in the developing cell walls until approximately 5 DAP and hetero-(1-->4)-beta-D: -mannans followed at 6 DAP. Deposition of AGPs and arabinoxylan in the wall began at 7 and 8 DAP, respectively. For arabinoxylans, there is a possibility that they are deposited earlier in a highly substituted form that is inaccessible to the antibody. Arabinoxylan and heteromannan were also detected in Golgi and associated vesicles in the cytoplasm. In contrast, (1-->3,1-->4)-beta-D: -glucan was not detected in the cytoplasm in endosperm cells; similar results were obtained for coleoptile and suspension cultured cells.

Cell Wall↗
PubMed2001

The location of (1-3)-beta-glucan in the nucellar projection and in the vascular tissue of the crease in developing barley grain using a (1-3)-beta-glucan-specific monoclonal antibody.

Immunocytochemical localization of the (1-3)-beta-glucan, callose, in developing barley (Hordeum vulgare L.) grain was investigated using a specific monoclonal antibody and observed by means of confocal laser-scanning microscopy. The nucellar projection (NP) and vascular tissue (VT) of the crease cells were specifically labelled by this antibody at all stages of grain development. Maximum intensity of label was found in the NP at 12-15 days post anthesis; thereafter, label was localized in the VT of the crease. The location of (1-3)-beta-glucan in the NP and VT of the crease was also monitored by means of aniline blue-induced fluorescence of callose. The results obtained using both methods were found to be similar. The possible significance of the presence of callose in these tissues is discussed in relation to the uptake of assimilates into the developing grain.

Antibodies, Monoclonal↗
PubMed2005

Aluminium causes variable responses in actin filament cytoskeleton of the root tip cells of Triticum turgidum.

The effects of aluminium on the actin filament (AF) cytoskeleton of Triticum turgidum meristematic root tip cells were examined. In short treatments (up to 2 h) with 50-1000 microM AlCl3.6H2O, interphase cells displayed numerous AFs arrayed in thick bundles that lined the plasmalemma and traversed the endoplasm in different directions. Measurements using digital image analysis and assessment of the overall AF fluorescence revealed that, in short treatments, the affected cells possessed 25-30% more AFs than the untreated ones. The thick AF bundles were not formed in the Al-treated cells in the presence of the myosin inhibitors 2,3-butanedione monoxime (BDM) and 1-(5-iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine (ML-7), a fact suggesting that myosins are involved in AF bundling. In longer Al treatments, the AF bundles were disorganised, forming granular actin accumulations, a process that was completed after 4 h of treatment. In the Al-treated cells, increased amounts of callose were uniformly deposited along the whole surface of the cell walls. In contrast, callose formed local deposits in the Al-treated cells in the presence of cytochalasin B, BDM, or ML-7. These results favour the hypothesis that the actomyosin system in the Al-treated cells, among other roles, participates in the mechanism controlling callose deposition.

Actin Cytoskeleton↗
PubMed2006

Study of male sterility in Taiwania cryptomerioides Hayata (Taxodiaceae).

A study of male sterility over a period of three consecutive years on a conifer species endemic to Taiwan, Taiwania cryptomerioides Hayata (Taxodiaceae), was done for this article. With the aids of fluorescence and electron microscopic observations, the ontogenic processes in the fertile and sterile microsporangia are compared, using samples collected from Chitou Experimental Forest and Yeou-Shoei-Keng Clonal Orchard of the National Taiwan University, Nantou, Taiwan. The development of male strobili occurred from August to the end of March. Microsporogenesis starts with the formation of the archesporium and ends with the maturation of 2-celled pollen grains within the dehiscing microsporangium. Before meiosis, there was no significant difference in ultrastructure between the fertile and sterile microsporangia. Asynchronous pollen development with various tetrad forms may occur in the same microsporangium of either fertile or sterile strobili. However, a callose wall was observable in the fertile dyad and tetrad, but not in the sterile one. After dissolution of the callose wall, the fertile microspores were released into the locule, while some sterile microspores still retained as tetrads or dyads with intertwining of exine walls in the proximal faces. As a result, there was no well developed lamellated endexine and no granulate ectexine or intine in the sterile microspores. Eventually, the intracellular structures in sterile microspores were dramatically collapsed before anthesis. The present study shows that the abortion in pollen development is possibly attributed to the absence of the callose wall. The importance of this structure to the male sterility of T. cryptomerioides is discussed.

Cupressaceae↗
PubMed1979

Laminar origins and terminations of cortical connections of the occipital lobe in the rhesus monkey.

Cortical connections within the occipital lobe (areas 17, 18 and 19) of the rhesus monkey are investigated with the autoradiographic and horseradish peroxidase procedures. Two efferent systems, each with a specific laminar organization, are observed. (1) Rostrally directed connections, from area 17 to 18, area 18 to 19 and area 19 to the inferotemporal region (area TE), originate from neurons in layer IIIc (and, in area 19, from a small complement of neurons in layer Va), and terminate in and around layer IV. (2) In contrast, connections in the reverse direction ('caudally directed' connections), from area TE to 19, area 19 to 18, and area 18 to 17, originate from neurons in layers Vb, VI and, to a lesser extent, IIIa, and terminate mainly in layer I. In addition, the laminar organization of several intrinsic and callosal connections are observed. In trinsic connections within areas 18 and 19 originate from neurons in layers IIIc and, to a lesser extent, Va, and terminate in vertical bands in layers I to IV. Callosal connections from areas 18, 19, and the caudal inferotemporal region originate from neurons mainly in layer IIIc. From areas 18 and 19, these callosal connections terminate in vertical bands in layers I through IV. Thus, different cortical projection systems are characterized by specific laminar distributions of efferent terminations as well as of their neurons of origin.

Animals↗
PubMed1992

Fiber composition of the human corpus callosum.

The densities of fibers of different sizes were calculated in ten regions of the corpus callosum of twenty human brains (ten females, ten males). Light microscopic examination revealed a consistent pattern of regional differentiation of fiber types in the corpus callosum. Thin fibers are most dense in the anterior corpus callosum (genu), and decrease in density posteriorly towards the posterior midbody, where they reach a minimum. Towards the posterior corpus callosum (splenium), the density of thin fibers increases again, but in the posterior pole of the callosum the density decreases locally. Large-diameter fibers show a pattern complementary to that of thin fibers, having a peak of density in the posterior midbody and a local increase of density in the posterior pole of the corpus callosum. Across subjects, the overall density of callosal fibers had no significant correlation with callosal area and an increased callosal area indicated an increased total number of fibers crossing through. Considering different fiber sizes, this was only true for small diameter fibers, whose large majority is believed to interconnect association cortex. No sex differences in fiber composition of the corpus callosum were found.

Adult↗
PubMed1982

Changing relation between onset of myelination and axon diameter range in developing feline white matter.

The size spectra of unmyelinated, ensheathed and initially myelinating CNS axons were examined by electron microscopy in the spinal cord ventral funiculus and the corpus callosum of the cat during development. The first myelin sheaths appeared 4 weeks before and 3 weeks after birth in the spinal and callosal areas, respectively. De novo myelination had largely ceased by 4 months in the ventral funiculus and by 7 months in the corpus callosum. The result show that the diameter ranges, within which spinal and callosal axons undergo primary ensheathment and initial myelination, are markedly different if similar levels of myelination are compared. In both areas, these diameter ranges shift towards smaller sizes with development. However, spinal and callosal axons, which undergo primary ensheathment and initial myelination simultaneously, present comparable diameter ranges. The findings support the view that other factors than the absolute physical size of the axon trigger initiation of CNS myelination. In this respect the developmental stage of the animal appears to play an important role.

Animals↗
PubMed1993

Corpus callosum morphometry and dichotic listening performance: individual differences in functional interhemispheric inhibition?

We examined the relationship between midsagittal corpus callosum area, as seen by magnetic resonance imaging, and behavioral laterality effects from a dichotic listening task requiring cross-callosal relay of an auditory signal, in 60 healthy young adults. Four patients with complete forebrain commissurotomy were also given the dichotic listening task, confirming that in this task, the report of left ear items is dependent on callosal pathways. Contrary to our predictions, callosum measures were unrelated to either a laterality measure or to inferior (typically left) ear performance. Surprisingly, superior (typically right) ear accuracies, which do not depend on cross-callosal sensory transfer, were significantly and negatively correlated with callosum size. These findings show that normal variations in callosum size do not appear to contribute significantly to individual differences in hemispheric specialization. Callosum size may, instead, be associated with degree of functional interhemispheric inhibition.

Acoustic Stimulation↗
PubMed1996

Interhemispheric transfer time differences related to aging and gender.

The difference in simple reaction times to unstructured stimuli contralateral to the hand used for response ('crossed' responses) and those stimuli ipsilateral to the hand used for response ('uncrossed' responses)--or crossed-uncrossed difference (CUD) is assumed to be a reliable index of interhemispheric transfer time (IHTT). Studies using the CUD paradigm with acallosal patients as well as a variety of populations with known variations in callosal size or functioning have demonstrated that such callosal differences are reflected in differences in recorded CUD times. Recent studies have suggested that elderly individuals show a reduction in size of the corpus callosum, particularly in the anterior region. In order to assess any potential change in callosal transfer efficiency with aging. CUDs were obtained from elderly (60+ years) and younger subjects (18 30 years). The elderly subjects showed a significantly elongated CUD compared to younger subjects, with elderly females contributing the greatest increase. No significant gender differences were found for younger subjects. In addition, an unexpected trend for an overall right field reaction time advantage was found for all subgroups, accompanied by a larger calculated CUD for right hand responses than for left hand responses.

Adolescent↗
PubMed1986

Microanatomy of the anterior cerebral artery.

The microanatomic features of the anterior cerebral artery were studied in 30 unfixed human brains which were injected with tinted polyester resin via cannulation of the internal carotid arteries under microscopic dissection. The outer diameter, length, and number of perforating branches were measured for each of the following vessels: anterior cerebral artery (proximal A1 segment, distal A2 segment), anterior communicating artery, and recurrent artery of Heubner. The perforating branches of the proximal segment of the anterior cerebral artery penetrated the brain at the anterior perforated substance, lateral chiasm, and optic tracts. The perforating branches of the anterior communicating artery penetrated the brain at the lamina terminalis, anterior perforated substance, and medial chiasm. The first 5 mm of the distal anterior cerebral artery (A2) had perforating branches penetrating the brain at the gyrus rectus and olfactory sulcus. The recurrent artery of Heubner originated from the A2 segment of the anterior cerebral artery in 57% of the cases, from the anterior cerebral artery-anterior communicating artery junction in 35%, and from the A1 segment in 8%. The depth of the interhemispheric fissure at the genu was 36.0 +/- 0.5 mm and at the midbody of the corpus callosum, 35.0 +/- 0.5 mm. Extension of the dissection to approach the anterior communicating artery from the genu of the corpus callosum using the anterior interhemispheric route was an additional 31.7 +/- 0.7 mm. The callosal arterial supply from the anterior cerebral artery showed short callosal branches in all brain specimens and long callosal vessels in 10% of the specimens.

Cerebral Arteries↗
PubMed1991

Rhyming and the right hemisphere.

Subjects determined whether two successively presented and orthographically different words rhymed with each other. The first word was presented at fixation and the second was presented either to the left or to the right of fixation, either alone (unilateral presentation) or accompanied by a distractor word in the other visual hemifield (bilateral presentation). Subjects were more accurate when the words did not rhyme, when presentation was unilateral, and when the target was flashed to the right visual hemifield. It was predicted that bilateral presentation would produce interference when information from both visual fields was processed by one hemisphere (callosal relay), but not when each of the two hemispheres performed a task independently (direct access). That is, callosal relay tasks should show greater laterality effects with bilateral presentations, whereas direct access tasks should show similar laterality effects with both bilateral and unilateral presentations. Greater laterality effects were observed for bilaterally presented rhyming words, but nonrhyming words showed similar laterality effects for both bilateral and unilateral presentations. These results suggest that judgment of nonrhyming words can be performed by either hemisphere, but that judgment of rhyming words requires callosal relay to the left hemisphere. The absence of a visual field difference with nonrhyming word pairs suggests further that judgment of nonrhyming word pairs may be accomplished by the right hemisphere when presentation is to the left visual field.

Adult↗