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PubMed2002

Studies on callose and cutin during the expression of competence and determination for organogenic nodule formation from internodes of Humulus lupulus var. Nugget.

Callose and cutin deposition were followed by staining with Aniline Blue and Nile Red and by immunolocalization using antibodies raised against callose. Along with morphogenesis induction from internodes of Humulus lupulus var. Nugget, a temporal and spatial differential deposition of callose and cutin was observed. A cutin layer showing bright yellow autofluorescence appears, surrounding cells or groups of cells committed to express morphogenic competence. This cutin layer that evolves to a randomly organized network appeared underneath a callose layer and may create a specific cellular environment with altered permeability and altered receptors providing conditions for entering the cell cycle. The incipient callose accumulation in control explants cultured on basal medium suggests the involvement of callose in the initiation of the morphogenic programme leading to nodule formation. A scanning electron microscopic study during the organogenic process showed that before shoot bud regeneration, the cutin layer increases in thickness and acquires a smooth texture. This cutin layer is specific to nodular organogenic regions and disappeared with plantlet regeneration. This layer may control permeability to water and solute transfer throughout plantlet regeneration.

Journal Article↗
PubMed2003

Callosal connections of dorso-lateral premotor cortex.

This study investigated the organization of the callosal connections of the two subdivisions of the monkey dorsal premotor cortex (PMd), dorso-rostral (F7) and dorso-caudal (F2). In one animal, Fast blue and Diamidino yellow were injected in F7 and F2, respectively; in a second animal, the pattern of injections was reversed. F7 and F2 receive a major callosal input from their homotopic counterpart. The heterotopic connections of F7 originate mainly from F2, with smaller contingent from pre-supplementary motor area (pre-SMA, F6), area 8 (frontal eye fields), and prefrontal cortex (area 46), while those of F2 originate from F7, with smaller contributions from ventral premotor areas (F5, F4), SMA-proper (F3), and primary motor cortex (M1). Callosal cells projecting homotopically are mostly located in layers II-III, those projecting heterotopically occupy layers II-III and V-VI. A spectral analysis was used to characterize the spatial fluctuations of the distribution of callosal neurons, in both F7 and F2, as well as in adjacent cortical areas. The results revealed two main periodic components. The first, in the domain of the low spatial frequencies, corresponds to periodicities of cell density with peak-to-peak distances of approximately 10 mm, and suggests an arrangement of callosal cells in the form of 5-mm wide bands. The second corresponds to periodicities of approximately 2 mm, and probably reflects a 1-mm columnar-like arrangement. Coherency and phase analyses showed that, although similar in their spatial arrangements, callosal cells projecting to dorsal premotor areas are segregated in the tangential cortical domain.

Amidines↗
PubMedDate not supplied

Thalamic ablations and neocortical development: alterations in thalamic and callosal connectivity.

Corticofugal pathways (callosal, intracortical, and subcortical) have initial axon outgrowth to many areas where no adult connections will persist. Corticofugal projections also demonstrate considerable reorganization after early damage. At the level of gross projections from specific thalamic nuclei to cortical cytoarchitectonic areas, early thalamocortical projections appear to show greater specificity for their targets than do corticofugal projections, and their potential for reorganization after early damage is not known. In this article, we explore the nature of the reorganization shown by the thalamocortical system after early thalamic lesions, and contrast it with reorganization of the origin of contralateral visual callosal projections in the same animals. Hamster pups were given electrolytic lesions in the posterior thalamus on the day of birth, damaging principally either the ventrobasal (somatosensory) or the dorsal lateral geniculate (visual) nucleus. After 30 d of age, HRP was implanted in either the somatosensory or the visual cortex, matching the area of implant with the intended thalamic lesion. The thalamus was reconstructed to determine the remaining nuclei, and the distribution of retrogradely labeled cells was plotted. For animals with HRP implants in visual cortex, the location of callosally projecting cells from the contralateral cortex was charted. These animals were compared to a group of normal adult animals with HRP implants approximately matched for size and location. In seven of eight adult animals with neonatal thalamic lesions, the remaining thalamus did not reorganize to innervate the thalamically denervated cortex. In contrast, the callosal projections from the contralateral visual cortex showed a wider tangential origin in the experimental animals compared to the controls. This expanded callosal projection included cells from temporal cortex, a projection not seen in normal animals. Thus, thalamocortical and callosal projection systems differ in both the magnitude and the nature of their reorganization after early damage.

Aging↗
PubMed2002

Differential rates of regional brain change in callosal and ventricular size: a 4-year longitudinal MRI study of elderly men.

Brain structure changes in size with normal aging, but the rate at which different structures change is controversial. We used magnetic resonance imaging (MRI) performed twice, 4 years apart, to compare rates of age-related size change of the corpus callosum, which has been inconsistently observed to thin with age, with change in the lateral ventricles, which are well established to enlarge. Subjects were 215 community dwelling, elderly men (70-82 years old at initial MRI), who were participants in a longitudinal study of cardiovascular risk factors. Percent change in size was significant for both the callosal and ventricular measures, but annual rate of ventricular expansion (2.9%) was significantly greater than annual rate of callosal thinning (-0.9%). Callosal regions showed statistically equivalent rates of shrinkage; ventricular dilatation was symmetrical. Neither callosal and ventricular rates of change correlated with each other (r = 0.01), nor did genu and splenium rates of change correlate with each other (r = 0.05). Tests of speeded processing were administered contemporaneously with both MRIs to examine functional ramifications of observed brain changes. Decline in the Mini-Mental State Examination was related to thinning of the splenium, and decline in Stroop test word reading was selectively related to thinning of the callosal body. These longitudinal data support the contentions that differential rates of change occur in different brain regions in normal aging, age-related callosal thinning contributes to functional declines, and rate of change in one region can be independent of rate of change in another region, even within a brain structure.

Aged↗
PubMedDate not supplied

The distribution of callosal connections correlates with the pattern of cytochrome oxidase stripes in visual area V2 of macaque monkeys.

In visual area V2 of monkeys, cytochrome oxidase (CO) histochemistry reveals a system of stripe-like subregions where densely labeled thick and thin stripes and pale interstripes can be recognized. Several lines of evidence suggest that CO stripe-like subregions are associated with functional streams in the visual cortex. In the present study, the distribution of retrogradely labeled callosal cells in V2 and the pattern of CO staining were correlated using tangential sections through the flattened cortex. Spectral and coherency analyses of the callosal and CO patterns were performed to assess quantitatively the degree of spatial correlation between these two patterns. The results showed that labeled callosal cells accumulated along the V1/V2 border and in finger-like bands that protruded up to 7-8 mm into V2. These callosal bands were in register with thick and thin CO stripes, with relatively few labeled callosal cells found in interstripe regions. This finding supports the notion that the distribution of callosal connections in the visual cortex is dictated not only by the topography of visual areas, but also by the arrangement of cortical functional streams. Further, these results extend to interhemispheric pathways the notion of functional specificity currently associated mainly with some visual intrahemispheric pathways.

Animals↗
PubMed2006

GABAergic and pyramidal neurons of deep cortical layers directly receive and differently integrate callosal input.

We studied the involvement of deep cortical layer neurons in processing callosal information in the rat. We observed with electron microscopy that both parvalbumin (PV)-labeled profiles and unlabeled dendritic spines of deep cortical layer neurons receive synapses from the contralateral hemisphere. Stimulation of callosal fibers elicited monosynaptic excitatory postsynaptic currents in both layer VI pyramidal neurons and gamma-aminobutyric acidergic (GABAergic) interneurons immunopositive for the vesicular GABA transporter and PV. Pyramidal cells had intrinsic electrophysiological properties and synaptic responses with slow kinetics and a robust N-metyhl-D-aspartate (NMDA) component. In contrast, GABAergic interneurons had intrinsic membrane properties and synaptic responses with faster kinetics and a less pronounced NMDA component. Consistent with these results, the temporal integration of callosal input was effective over a significantly longer time window in pyramidal neurons compared with GABAergic interneurons. Interestingly, callosal stimulation did not evoke feedforward inhibition in all GABAergic interneurons and in the majority of pyramidal neurons tested. Furthermore, retrogradely labeled layer VI pyramidal neurons of the contralateral cortex responded monosynaptically to callosal stimulation, suggesting interconnectivity between callosally projecting neurons. The data show that pyramidal neurons and GABAergic interneurons of deep cortical layers receive interhemispheric information directly and have properties supporting their distinct roles.

Animals↗
PubMed2006

Callose in root apices of European chestnut seedlings: a physiological indicator of aluminum stress.

We determined if callose formation in 1-cm-long root apices of European chestnut (Castanea sativa Mill.) seedlings is affected by naturally occurring high concentrations of aluminum (Al) under laboratory conditions and by low base saturation (BS) of soils under forest field conditions. Under controlled conditions in the laboratory, seedlings were treated with simulated soil solutions in the presence or absence (control) of Al. One day after exposing seedlings to a simulated soil solution containing 168 microM Al, callose formation in the root apices had increased significantly. After 7 days, callose concentration in root apices was significantly correlated with the concentration of free Al3+ ions recovered in the simulated soil solution and with the concentration of Al in fine roots. At four field sites in southern Switzerland, seedlings were grown for five months in either A-horizon soil with a BS above 17% or in a B-horizon soil with a BS below 5%. Callose concentrations were significantly higher in root apices in the B horizon than in the A horizon. Callose concentrations in root apices were negatively correlated with Ca/Al molar ratio in fine roots. We conclude that callose in the root apices of European chestnut could be a useful physiological parameter for assessing Al toxicity under both laboratory and field conditions.

Aluminum↗
PubMed1985

Chitosan-elicited callose synthesis in soybean cells as a ca-dependent process.

A new method for the rapid and quantitative fluorometric determination of callose is described. In suspension-cultured cells of Glycine max, synthesis of callose starts within 20 minutes of treatment with chitosan and parallels over hours the accumulation of 1,3-linked glucose in the wall. Poly-l-lysine also elicits callose synthesis. The effect of chitosan is enhanced by Polymyxin B at low concentrations; this antibiotic alone at higher concentrations can also induce callose synthesis. Callose synthesis is immediately stopped when external Ca(2+) is bound by ethylene glycolbis-(2-aminoethyl ether)-N,N'-tetraacetate or cation exchange beads, and partly recovers upon restoration of 15 micromolar Ca(2+).Callose synthesis is observed only when membrane perturbation causing electrolyte leakage from the cells is induced by one of the above treatments. It does not appear to be due to de novo synthesis or proteolytic activation of 1,3-beta-d-glucan synthase. It is concluded that this Ca(2+)-dependent enzyme is directly activated by the influx of Ca(2+) occurring concomitantly with the leakage of cell constituents. This suggestion is also discussed in conjunction with the chitosan-induced synthesis of phytoalexin in the same cells.

Journal Article↗
PubMed2001

A novel UDP-glucose transferase is part of the callose synthase complex and interacts with phragmoplastin at the forming cell plate.

Using phragmoplastin as a bait, we isolated an Arabidopsis cDNA encoding a novel UDP-glucose transferase (UGT1). This interaction was confirmed by an in vitro protein--protein interaction assay using purified UGT1 and radiolabeled phragmoplastin. Protein gel blot results revealed that UGT1 is associated with the membrane fraction and copurified with the product-entrapped callose synthase complex. These data suggest that UGT1 may act as a subunit of callose synthase that uses UDP-glucose to synthesize callose, a 1,3-beta-glucan. UGT1 also interacted with Rop1, a Rho-like protein, and this interaction occurred only in its GTP-bound configuration, suggesting that the plant callose synthase may be regulated by Rop1 through the interaction with UGT1. The green fluorescent protein--UGT1 fusion protein was located on the forming cell plate during cytokinesis. We propose that UGT1 may transfer UDP-glucose from sucrose synthase to the callose synthase and thus help form a substrate channel for the synthesis of callose at the forming cell plate.

Arabidopsis↗
PubMed2004

Beta-amino-butyric acid-induced resistance against necrotrophic pathogens is based on ABA-dependent priming for callose.

The non-protein amino acid beta-amino-butyric acid (BABA) protects plants against a wide range of pathogens. We have examined the effectiveness and mode of action of BABA on resistance against two necrotrophic pathogens. Treatment of Arabidopsis with BABA induced resistance against Alternaria brassicicola and Plectosphaerella cucumerina to a similar level by jasmonic acid (JA). Conversely, treatment with benzothiadiazole (BTH), a functional analogue of salicylic acid (SA), had no significant effect on the resistance against both pathogens. BABA-induced resistance against A. brassicicola and P. cucumerina was unaffected in the JA-insensitive mutant coi1-1 and the camalexin-deficient mutant pad3-1. Moreover, the expression of BABA-induced resistance was not associated with enhanced accumulation of camalexin or enhanced transcription of the JA-inducible PDF1.2 gene. The expression of BABA-induced resistance against P. cucumerina was unaffected in mutants impaired in ethylene (ET) and SA signalling, but was blocked in the abscisic acid (ABA)-deficient mutant aba1-5, the ABA-insensitive mutant abi4-1 and the callose-deficient mutant pmr4-1. Upon infection by both pathogens, BABA-treated plants showed an earlier and more pronounced accumulation of callose. Treatment with the callose-inhibitor 2-deoxy-D-glucose (2-DDG) reversed the BABA-induced resistance against A. brassicicola. Furthermore, primed callose deposition was absent in BABA-treated abi4-1 and pmr4-1 plants upon infection by P. cucumerina. Although the expression of BABA-induced resistance was not associated with enhanced transcription of the ABA-inducible RAB18 gene, application of ABA mimicked the effect of BABA on the level of callose accumulation and resistance. Hence, BABA-induced resistance against necrotrophic pathogens is based on primed callose accumulation, which is controlled by an ABA-dependent defence pathway.

Abscisic Acid↗
PubMed2003

Loss of a callose synthase results in salicylic acid-dependent disease resistance.

Plants attacked by pathogens rapidly deposit callose, a beta-1,3-glucan, at wound sites. Traditionally, this deposition is thought to reinforce the cell wall and is regarded as a defense response. Surprisingly, here we found that powdery mildew resistant 4 (pmr4), a mutant lacking pathogen-induced callose, became resistant to pathogens, rather than more susceptible. This resistance was due to mutation of a callose synthase, resulting in a loss of the induced callose response. Double-mutant analysis indicated that blocking the salicylic acid (SA) defense signaling pathway was sufficient to restore susceptibility to pmr4 mutants. Thus, callose or callose synthase negatively regulates the SA pathway.

Alleles↗
PubMed1995

Clinical and topographical range of callosal infarction: a clinical and radiological correlation study.

A prospective clinical and radiological correlation study was performed to determine the frequency, and the clinical and radiological features of callosal infarction. From 1 January 1993 to the end of December 1993 282 cases of cerebral infarction seen in the Neurology service of the University Hospital of Dijon were studied prospectively. Eight cases with callosal ischaemic lesions were identified by CT and MRI. A callosal disconnection syndrome occurred in only five of eight patients, related to a single, large infarct or several infarctions in the anterior part of the corpus callosum. Clinical features were characterised by left ideomotor apraxia, construction apraxia, and left agraphia in all five cases. Alien hand was noted in only two cases. There were gait disorders in three cases with MRI features of multiple lacunes in a large part of the corpus callosum, and also the subcortical areas of both hemispheres. It is emphasised that callosal infarctions are not rare and that they contribute to the clinical features of strokes. As well as the classic incomplete callosal disconnection syndrome, these callosal ischaemic lesions may induce non-specific gait disorders.

Aged↗
PubMed2003

Electrophysiological properties and input-output organization of callosal neurons in cat association cortex.

Intracellular recordings from association cortical areas 5 and 7 were performed in cats under barbiturate or ketamine-xylazine anesthesia to investigate the activities of different classes of neurons involved in callosal pathways, which were electrophysiologically characterized by depolarizing current steps. Excitatory postsynaptic potentials (EPSPs), inhibitory postsynaptic potentials (IPSPs), and/or antidromic responses were elicited by stimulating homotopic sites in the contralateral cortical areas. Differential features of EPSPs related to latencies, amplitudes, and slopes were detected in closely located (50 microm or less) neurons recorded in succession along the same electrode track. In contrast to synchronous thalamocortical volleys that excited most neurons within a cortical column, stimuli applied to homotopic sites in the contralateral cortex activated neurons at restricted cortical depths. Median latencies of callosally evoked EPSPs were 1.5 to 4 ms in various cortical cell-classes. Fast-rhythmic-bursting neurons displayed EPSPs whose amplitudes were threefold larger, and latencies two- or threefold shorter, than those found in the three other cellular classes. Converging callosal and thalamic inputs were recorded in the same cortical neuron. EPSPs or IPSPs were elicited by stimulating foci spaced by <1 mm in the contralateral cortex. In the overwhelming majority of neurons, latencies of antidromic responses were between 1.2 and 3.1 ms; however, some callosal neurons had much longer latencies, <or=18.5 ms. Some neurons were excited monosynaptically through the callosal pathway and identified antidromically from appropriate thalamic nuclei, thus revealing a callosal-corticothalamic pathway. Data are discussed in relation to the commissural spread of fast and slow normal oscillations as well as paroxysmal activities.

Animals↗
PubMed1994

Callosal atrophy in patients with lacunar infarction and extensive leukoaraiosis. An indicator of cognitive impairment.

BACKGROUND AND PURPOSE: It is unclear why only some patients with lacunar infarction and radiological evidence of diffuse white matter abnormalities have dementia. The purpose of this study is to investigate the value of callosal atrophy as an indicator of cognitive impairment. METHODS: We used magnetic resonance imaging to evaluate 11 right-handed male patients with lacunar infarction and extensive white matter hypodensities on computed tomography (8 with dementia and 3 without dementia). The midsagittal corpus callosum area on T1-weighted images was compared with the IQ determined by the Wechsler Adult Intelligence Scale. The relation between these parameters and cerebral oxygen metabolism measured with positron emission tomography was also evaluated in the 8 patients with dementia. RESULTS: All patients showed diffuse high-intensity areas in the bilateral hemispheric white matter on T2-weighted images. Compared with 19 age- and sex-matched right-handed normal control subjects, the patients had a significantly smaller callosal area. The severity of callosal atrophy, which varied from mild to severe, was significantly related to the total IQ. In the 8 demented patients, the total callosal area was significantly correlated with the mean level of oxygen metabolism in the cerebral white matter. CONCLUSIONS: In patients with lacunar infarction and diffuse white matter abnormalities, the presence of callosal atrophy may indicate cognitive impairment. Callosal atrophy may reflect the severity and extent of white matter damage associated with a decrease in oxygen metabolism, which may determine the severity of intellectual decline.

Adult↗
PubMed1987

Callosal and ipsilateral cortical connections of the body surface representations in SI and SII of tree shrews.

Injections of horseradish peroxidase (HRP) were used to study the connections of the first and second somatosensory areas (SI and SII) in tree shrews. The locations of callosally projecting neurons in SI were determined by placing large injections of HRP in the SI region of one cerebral hemisphere and determining the organization of SI of the other cerebral hemisphere with microelectrode mapping. Many callosally projecting neurons were revealed in lateral SI representing the face, especially the glabrous nose. A sparse scattering of callosally projecting neurons were located more centrally in SI in portions representing the forepaw; these neurons tended to be in cortex devoted to the dorsal hand and pads of the palm rather than the digits. Part of medial SI, representing the forelimb and trunk, had a moderately dense distribution of callosally projecting neurons. More restricted injections in SI indicated that callosally projecting neurons were largely within comparable portions of contralateral SI, although a few neurons projecting callosally to SI were located in SII and cortex caudal and rostral to SI. Large injections of HRP in SII labeled neurons throughout contralateral SII, including representations of the forepaw and hindpaw. More restricted injections in SII labeled neurons in somatotopically comparable parts of the contralateral SII. A few labeled neurons were also seen in somatotopically matched parts of contralateral SI. The results also demonstrated strong somatotopically organized connections between SI and SII of the same hemisphere, and connections of SI and SII with adjoining subdivisions of parietal and frontal cortex. The major thalamic projections to both SI and SII originated in the ventroposterior nucleus.

Afferent Pathways↗
PubMed1991

Guidance of callosal axons by radial glia in the developing cerebral cortex.

During development, columns of the mammalian cerebral cortex are formed by migration of neurons along fascicles of radial glia. Subsequently, axons of the corpus callosum connect reciprocal regions of each cerebral hemisphere. To determine whether the radial growth of callosal afferents through the developing cortex may be guided by particular cellular elements, we examined the ultrastructural relationship between callosal afferents and radial fibers in the early postnatal hamster sensorimotor cortex. Developing callosal axons and their growth cones were labeled with HRP injected into the cortex at 3 d postnatal when the growth cones have extended across the callosum and are just entering the contralateral cortex. An EM analysis of 30 HRP-labeled axons and their growth cones revealed that they extended upon fascicles of radial processes associated with migrating neurons. Reconstruction of seven of these growth cones, serially sectioned in their entirety, showed that growth cones were associated with the same radial fascicle as their axon. Growth cones also touched other cellular elements such as axons. However, the finding that callosal afferents, from the point at which they enter the cortex to their growth cones, were apposed to a continuous fascicle of radial fibers suggests that callosal axons are tracking along radial processes. We conclude that the majority of the radial processes within fascicles are likely to be glial, based on their relatively large diameters, electron-lucent cytoplasm with a regular array of microtubules, the presence of glycogen granules, occasional cytoplasmic protrusions lacking microtubules, and their consistent association with migrating neurons. We propose therefore that radial glia may serve a guidance function for growing callosal axons in their radial trajectory through the developing cerebral cortex.

Animals↗
PubMed1986

Interchange of callosal and association projections in the developing visual cortex.

Neurons projecting transitorily into the corpus callosum from area 17 of the cat were retrogradely labeled by the fluorescent tracer Fast Blue (FB) injected into contralateral areas 17 and 18 on postnatal days 1-5. During the second postnatal month these neurons were still labeled by the early injection, although they had eliminated their callosal axon. At this time, 15-20% of these neurons could be retrogradely relabeled by injections of Diamidino Yellow (DY) into ipsilateral areas 17 and 18, but few or none by similar injections in the other areas that receive from area 17 (19, 21a, PMLS, 20a, 20b, DLS). Similarly, area 17 neurons projecting transitorily to contralateral area PMLS during the first postnatal week could be relabeled by DY injections in ipsilateral areas 17 and 18 but not in PMLS. Already around birth, many transitorily callosal neurons in area 17 send bifurcating axons both to contralateral areas 17 and 18 and ipsilateral area 18. It is probable that during postnatal development some of these neurons selectively eliminate their callosal axon collaterals and maintain the projection to ipsilateral area 18. In fact, some transitorily callosal neurons in area 17 can be double-labeled by simultaneous perinatal injections of FB in contralateral areas 17 and 18 and of a new long-lasting retrograde tracer, rhodamine-conjugated latex microspheres, in ipsilateral area 18. The same neurons can then be relabeled by reinjecting ipsilateral area 18 with DY during the second postnatal month. This finding, however, does not exclude the possibility that some transitorily callosal neurons send an axon to ipsilateral area 18 after eliminating their callosal axon. In conclusion, area 17 neurons that project transitorily through the corpus callosum later participate, probably permanently, in ipsilateral corticocortical projections but selectively to areas 17-18. The mechanism responsible for this selectivity is unknown, but it may be related to the differential radial distribution (i.e., to birth date) of area 17 neurons engaged in the various corticocortical projections. The problems raised by the use of long-lasting retrograde fluorescent tracers in neurodevelopmental studies and by the quantification of results of double- and triple-labeling paradigms are also discussed.

Action Potentials↗
PubMed1997

Comparison of the distribution of parvalbumin-immunoreactive and other synapses onto the somata of callosal projection neurons in mouse visual and somatosensory cortex.

The distribution of synapses made by parvalbumin-immunoreactive (pv-ir) and nonimmunoreactive terminals was determined for the cell bodies of callosal projection neurons in the somatosensory and visual areas of mouse cerebral cortex. Callosal neurons were labeled by the retrograde transport of horseradish peroxidase applied to the contralateral hemisphere. The surface areas of somata belonging to callosal cells in somatosensory cortex ranged from 230 to 243 microm2 in size and received roughly one-third of their synapses from pv-ir terminals. Visual cortex, in contrast, contained two populations of callosal cell bodies: relatively large ones ranging in size from 255 to 279 microm2 that received 3-9% of their synapses from pv-ir terminals and smaller cell bodies that both in size (232-237 microm2) and in the proportion of synapses received from pv-ir terminals resemble the callosal cells examined in somatosensory cortex. That different functional areas of the cortex have populations of callosal cells similar in size, and displaying similar patterns of somatic synapses, supports the notion that a common plan of synaptic connectivity characterizes different functional areas. Results in visual cortex indicate that functional areas contain, in addition, area-specific patterns of synapses.

Animals↗