Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Callosities”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources
PubMed1995

Effects of neonatal enucleation on the organization of callosal linkages in striate cortex of the rat.

Lewis and Olavarria ([1995] J. Comp. Neurol. 361:119-137) showed that the mediolateral organization of callosal linkages differs markedly between medial and lateral regions of striate cortex in the rat. Thus, callosal fibers originating from medial regions of striate cortex interconnect loci that are mirror-symmetric with respect to the midsagittal plane. In contrast, fibers from lateral regions of striate cortex show a reversed pattern of connections: tracer injections into the 17/18a border produce retrograde cell labeling in regions medial to the contralateral 17/18a border, whereas injections placed somewhat medial to the 17/18a border label cells located at the contralateral 17/18a border. Based on the interpretation that callosal fibers from lateral striate cortex connect retinotopically corresponding loci (Lewis and Olavarria [1995] J. Comp. Neurol. 361:119-137) we propose here that the development of the reversed pattern of connections in lateral portions of striate cortex is guided by activity-dependent cues originating from spontaneously active ganglion cells in temporal retina. In the present study we have attempted to falsify this hypothesis by investigating the effects of neonatal bilateral enucleation on the organization of callosal linkages in striate cortex of the rat. Once enucleated rats reached adulthood, we studied the mediolateral organization of callosal connections by placing small injections of different fluorescent tracers into different loci within medial and lateral striate cortex. The analysis of the distribution of retrogradely labeled callosal cells indicated that connections from lateral portions of striate cortex were no longer organized in a reversed fashion, rather, they resembled the mirror image pattern normally found in the medial callosal region, i.e., injections at the 17/18a border produced labeled cells at the opposite 17/18a border, whereas injections into slightly more medial regions produced labeled cells in the opposite, mirror-symmetric location. In addition, we found that enucleation does not alter the organization of callosal linkages in medial portions of striate cortex. Thus, by showing that enucleation significantly changes the pattern of connections from lateral portions of striate cortex, the present study does not falsify, but rather strengthens the hypothesis that interhemispheric correlated activity driven from the temporal retinal crescent guides the normal development of reversed callosal linkages in lateral portions of rat striate cortex. Furthermore, the present study shows that, in the absence of the eyes, the pattern of callosal linkages in lateral portions of striate cortex resembles the mirror image pattern normally found only in medial striate cortex.

Animals↗
PubMed1995

Overall pattern of callosal connections in visual cortex of normal and enucleated cats.

The effect of neonatal bilateral enucleation on the overall distribution of callosal connections in striate and extrastriate visual cortex of the cat was studied using tangential sections from the physically unfolded and flattened cortex. Callosal neurons were labeled by administering the anatomical tracer horseradish peroxidase directly to the transected corpus callosum. The pattern of callosal connections in binocularly enucleated cats showed both consistent differences and consistent similarities with the pattern in normal cats. In agreement with previous studies, it was found that callosal labeling at the 17/18 border of enucleated cats was considerably sparser than in normal cats. Moreover, we found that the strip containing the majority of labeled cells at the 17/18 border was narrower than in normal cats. In both normal and enucleated cats, scattered cells were distributed on either side of the 17/18 callosal strip, well into areas 17 and 18. In much of extrastriate cortex, the pattern of callosal connectivity in enucleated cats looked surprisingly normal. Details of the callosal pattern that were consistently found in normal cats could also be recognized in binocularly enucleated cats, such as two to four bridges of labeling spanning areas 18 and 19. Also, four zones that were free of callosal connectivity in area 7, on the banks of the suprasylvian sulcus, and in the posterior suprasylvian sulcus were found in both normal and enucleated cats. Finally, as in normal cats, dense cell labeling occurred on the crown of the suprasylvian gyrus at its posterior end, from which it extended laterally across both banks of the suprasylvian sulcus and into the fundus of this sulcus. The results of this study suggest that, although the stabilization of callosal connections at the 17/18 border region appears to depend on visual input, this input plays a less prominent role in the stabilization of callosal connections in extrastriate visual cortex.

Animals↗
PubMed1984

Neonatal superior collicular lesions alter visual callosal development in hamster.

Visual callosal connections were examined using autoradiographic (ARG) and horseradish peroxidase (HRP) techniques in normal adult hamsters, and in adults subjected to ablation of the superficial tectal laminae at birth. Additional ARG and HRP experiments were carried out in hamsters 1-27 days of age in order to describe the normal development of this pathway. Neonatal collicular lesions, which deprived visual cortical neurons of a major terminal zone in the midbrain, substantially altered the visual callosal pathway. In the lesioned animals, the numbers of supragranular callosal cells in the 17-18a border region and lamina VI callosal neurons in medial area 17 were significantly greater than normal. The ARG experiments demonstrated additional clearcut abnormalities in the visual callosal pathway of the lesioned hamsters. First, the mediolateral extent of the supragranular callosal zone around the 17-18a border was increased. Secondly, dense label was visible over lower layer V and lamina VI throughout area 17. Finally, labelling in lamina I could also be observed across the entire mediolateral extent of area 17. Experiments in the developing hamsters suggested that some of the abnormalities observed in the lesioned animals may have resulted from the maintenance of normally transient developmental states. During the first postnatal week, both callosal cells and anterograde labelling were evenly distributed throughout the dorsal posterior neocortex, but only in the subplate region. During the second postnatal week, supragranular callosal cells were also labelled in both medial and lateral area 17, but from their first appearance, they were always most numerous in the 17-18a border region. At the same time callosal axons invaded the supragranular laminae, but only near the 17-18a border. By the end of the second postnatal week, the visual callosal pathway was very similar to that in the adult.

Animals↗
PubMed1998

Paradoxically greater interhemispheric transfer deficits in partial than complete callosal agenesis.

Symptoms of interhemispheric disconnection are typically much less severe in callosal agenesis than after surgical section of the corpus callosum. Sperry [Sperry, R. W., Plasticity of neural maturation. Developmental Biology, 1968, 2 (Suppl.), 306-327.] has attributed this difference to two interconnected factors: (1) the callosal section is usually performed after the brain has lost the maximal degree of functional plasticity associated with the early stages of development and (2) the removal of an already formed structure is more disruptive for functional brain organization than the failure of the same structure to develop. It has been suggested that functional compensation is less efficient if callosal agenesis is partial rather than complete [Dennis, M., Impaired sensory and motor differentiation with corpus callosum agenesis: A lack of callosal inhibition during ontogeny? Neuropsychologia, 1976, 14, 455-469.]. This suggestion is supported by the present findings of partial left-hand anomia, partial left-field alexia and poor tactile cross-localization in a subject with a congenital absence of the posterior part of the corpus callosum due to an arteriovenous malformation. In agreement with many previous studies, similar, though more severe, symptoms of interhemispheric disconnection were found in a subject with a complete section of the corpus callosum, but not in a subject with complete callosal agenesis. Praxic control of the left hand on verbal commands was severely deficient in the callosotomy subject, but it was normal in the subject with callosal hypogenesis. The lesser degree of compensation in partial compared to complete callosal agenesis may be explained by a reduced pressure to develop extracallosal means of interhemispheric communication, contingent on the partial existence of callosal connections, as well as by the later occurrence in development of the causes of callosal hypogenesis compared to those of total callosal agenesis.

Agenesis of Corpus Callosum↗
PubMed1992

Topographic organization, number, and laminar distribution of callosal cells connecting visual cortical areas 17 and 18 of normally pigmented and Siamese cats.

The callosal connections between visual cortical areas 17 and 18 in adult normally pigmented and "Boston" Siamese cats were studied using degeneration methods, and by transport of WGA-HRP combined with electrophysiological mapping. In normal cats, over 90% of callosal neurons were located in the supragranular layers. The supragranular callosal cell zone spanned the area 17/18 border and extended, on average, some 2-3 mm into both areas to occupy a territory which was roughly co-extensive with the distribution of callosal terminations in these areas. The region of the visual field adjoining the vertical meridian that was represented by neurons in the supragranular callosal cell zone was shown to increase systematically with decreasing visual elevation. Thus, close to the area centralis, receptive-field centers recorded from within this zone extended only up to 5 deg into the contralateral hemifield but at elevations of -10 deg and -40 deg they extended as far as 8 deg and 14 deg, respectively, into this hemifield. This suggests an element of visual non-correspondence in the callosal pathway between these cortical areas, which may be an essential substrate for "coarse" stereopsis at the visual midline. In the Siamese cats, the callosal cell and termination zones in areas 17 and 18 were expanded in width compared to the normal animals, but the major components were less robust. The area 17/18 border was often devoid of callosal axons and, in particular, the number of supragranular layer neurons participating in the pathway were drastically reduced, to only about 25% of those found in the normally pigmented adults. The callosal zones contained representations of the contralateral and ipsilateral hemifields that were roughly mirror-symmetric about the vertical meridian, and both hemifield representations increased with decreasing visual elevation. The extent and severity of the anomalies observed were similar across individual cats, regardless of whether a strabismus was also present. The callosal pathway between these visual cortical areas in the Siamese cat has been considered "silent," since nearly all neurons within its territory are activated only by the contralateral eye. The paucity of supragranular pyramidal neurons involved in the pathway may explain this silence.

Albinism↗
PubMed1989

Segregation and overlap of callosal and association neurons in frontal and parietal cortices of primates: a spectral and coherency analysis.

The spatial relations between selected classes of association and callosal neurons were studied in the frontal and parietal lobes of the macaque monkey using retrogradely transported fluorescent dyes. Fast blue and nuclear yellow were injected in the left frontal (areas 4 and 6) and right posterior parietal (area 5) cortices, respectively. These injections led to the retrograde labeling, in the right frontal cortex, of callosal neurons projecting homotopically and association neurons projecting to ipsilateral area 5; in the left superior parietal lobule, of callosal neurons projecting to contralateral area 5 and association neurons projecting to the ipsilateral frontal lobe. In both frontal and parietal cortices, callosal and association neurons were located in layers III and V-VI; a few neurons were also found in layer II. The contribution of layers V-VI to the callosum was significantly higher in areas 4 and 6 than in area 5. Only a small number of neurons (less than 1%) were double labeled. Spectral analyses were used to characterize the spatial periodicities of the distributions of callosal and association neurons. In areas 4, 6, and 5, both association and callosal spectra were dominated by a strong elevation in the range of low spatial frequencies, corresponding to periodicities in cell density with a peak-to-peak distance of about 8 mm. This indicated an arrangement of these corticocortical cells in the form of bands. The latter displayed various shapes and orientations and were composed of more discrete assemblies of cell clusters of about 400-1000 microns width. Their presence was revealed in the power spectra by a small elevation in the range of high spatial frequencies. The coherency analysis assessed the degree of linear relationships for each spatial frequency, and therefore the degree of similarity, between callosal and association cell distributions, together with their phase relations. Little coherency was found in areas 4 and 6 between bands of callosal and association neurons, which suggests that the 2 cell populations are differently and independently distributed in the tangential domain, with no simple phase relations. The overall mean coherency was higher in area 5 than in the frontal cortex: callosal and association bands were more similar in shape, with more extensive zones of overlap. These data indicate that callosal and association neurons share common principles of spatial organization despite the great regional variability of their interrelations in the tangential cortical domain.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2001

A longitudinal study of callosal atrophy and interhemispheric dysfunction in relapsing-remitting multiple sclerosis.

OBJECTIVES: To determine if callosal atrophy and interhemispheric dysfunction can be detected in the early stages of relapsing-remitting multiple sclerosis (MS) and to evaluate their progression in relation to the disability and evolution of lesions seen on magnetic resonance imaging during a 5-year period. METHODS: We compared 30 patients who had clinically definite early-onset replasing-remitting MS and mild disability with control subjects. Regional and segmental callosal size and extent of white matter abnormalities on magnetic resonance imaging, as well as performance on tasks exploring interhemispheric transfer of motor, auditory, and sensory information were assessed. Patients with MS were evaluated at baseline and after 5 years. Physical disability was determined at both times using the Expanded Disability Status Scale score. RESULTS: Patients with MS were seen with significant callosal atrophy and functional impairment of interhemispheric transfer at baseline that worsened during the 5-year study. A significant correlation was found between the magnitude of disability and the severity of morphological and functional callosal involvement at baseline. This association persisted at year 5. Baseline clinical characteristics such as age and prestudy relapse rate were unrelated to callosal size or interhemispheric performance. However, the number of baseline T2-weighted lesions was correlated with callosal involvement and this relation persisted at year 5. CONCLUSION: Patients who had relapsing-remitting MS in the early stages of the disease and mild disability had significant callosal involvement that progressed over time. The relationship between disability, T2-weighted lesions load, and degree of morphological and functional callosal impairment confirm the potential value of using callosal dysfunction as a surrogate marker of disease progression in MS.

Adult↗
PubMed1990

Occipital cortex in man: organization of callosal connections, related myelo- and cytoarchitecture, and putative boundaries of functional visual areas.

Human area 17 is known to contain a single (the primary) visual area, whereas areas 18 and 19 are believed to contain multiple visual areas (defined as individual representations of the contralateral visual hemifield). This is known to be the case in monkeys, where several boundaries between visual areas are characterized by bands of callosal afferents and/or by changes in myeloarchitecture. We here describe the pattern of callosal afferents in (human) areas 17, 18, and 19 as well as their cortical architecture and we infer the position of some visual areas. Sections from occipital lobes of 6 human brains with unilateral occipital infarctions have been silver-impregnated for degenerating axons, thereby revealing callosal afferents to the intact occipital cortex. Their tangential distribution is discontinuous, even in cases with large lesions. A band of callosal afferents straddles the area 17/18 boundary, whereas the remainder of area 17 and a 15-45 mm wide stripe of area 18 adjacent to the callosal band along the 17/18 border are free of them. Patches of callosal afferents alternate with callosal-free regions more laterally in area 18 and in area 19. We conclude that, in man, a second visual area (analogue of V2) lies in area 18, horseshoe-shaped around area 17, and includes the inner part of the acallosal stripe adjacent to the callosal band along the 17/18 boundary. The outer part of this acallosal stripe belongs to a third visual area, which may contain dorsally the analogue of V3 and ventrally that of VP. Thus the lower parts of the second and third visual areas lie on the lingual gyrus, whereas the analogue of the macaque's fourth visual area probably lies on the fusiform gyrus. Although the proposed subdivision of the occipital cortex relies largely on the pattern of callosal afferents, some putative human visual areas appear to have distinct architectonic features. The analogue of V2 is rather heavily myelinated and its layer III contains large pyramidal neurons. Its upper part is not well delimited laterally since adjacent "V" has similar architecture. Its lower part, however, differs clearly from the adjacent "VP," which is lightly myelinated and lacks the large pyramids in layer III. The cortex lateral to "VP" is heavily myelinated and contains fairly large pyramids in layers III and V. The myeloarchitecture of the lateral part of the occipital cortex is not uniform; a very heavily myelinated region stands out in the lateral part of area 19, near the occipito-temporal junction.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1994

Tangential organization of callosal connectivity in the cat's visual cortex.

Cells and/or terminals of corticocortical pathways in mammalian visual cortex often have a discontinuous distribution across the surface of the cortex. A modular organization of cortical function has been shown to underlie the tangential segregation of many inputs and outputs. Here, we present evidence that the callosal pathway in the visual cortex of the cat follows these general principles. Large injections of wheat germ agglutinin-horseradish peroxidase or biotinylated dextran amine were made in areas 17 and 18, and callosal labeling was analyzed in tangential sections. The band of callosal cells and terminals straddling the border of areas 17 and 18 was not uniform but varied in density in a complicated fashion. Fluctuations in density of callosal connections became more clear 2-3 mm lateral or medial to the 17/18 border, as the callosal labeling became less dense. Here, regular fluctuations with a periodicity of about 1 mm in area 17, and slightly greater than 1 mm in area 18 were apparent. Cytochrome oxidase staining in areas 17 and 18 showed a pattern of dense blobs with the same spacing as the callosal labeling in these areas, and the blobs were found to align with the patches of callosal labeling. Larger, more irregularly spaced stripes of callosal labeling extended from the lateral part of area 18 across area 19 and into more lateral visual areas. These results suggest that the callosal pathway in the cat's visual cortex has a patchy distribution similar to many ipsilateral corticocortical projections, and that the columnar system marked by cytochrome oxidase is important for the organization of (interhemispheric) corticocortical connectivity in cats.

Animals↗
PubMed1980

The postnatal development of visual callosal connections in the absence of visual experience or of the eyes.

Counts of callosal neurons retrogradely labeled by horseradish peroxidase (visualized using multiple substrates) were obtained in areas 17 and 18 of five kittens reared with their eyelids bilaterally sutured and of three kittens which had undergone bilateral enucleation on postnatal days 1--4. These counts were compared with those obtained in normal adult cats. The normal adult distribution of the callosal neurons results from the gradual postnatal reduction of a more widespread juvenile population. Binocular visual deprivation by lid suturing dramatically decreases the final number of callosal neurons and narrows their region of distribution (callosal zone) in areas 17 and 18. A less severe reduction in the final number of callosal neurons is caused by bilateral enucleation, which also increases the width of the callosal zone compared to that of normal cats. Thus, visual experience is necessary for the normal stabilization of juvenile callosal connections. However, since some callosal neurons form connections in the absence of vision, other influences capable of stabilizing juvenile callosal neurons also exist. These influences are probably antagonized by destabilizing influences or inhibited, when the eyes are intact.

Aging↗
PubMed1982

Distribution patterns and individual variations of callosal connections in the albino rat.

After complete callosotomy the distribution of degeneration products was re-investigated in adult albino rats. Three to seven days post operation, coronal, horizontal and "flattened" sections were impregnated according to the new methods of Gallyas et al. (1980) which stain degenerating axons and terminals, respectively. The regional distribution patterns of callosal terminals were directly visualized with dark field illumination at low magnification. With this technique the distribution pattern of axons and terminals could be compared between different cortical regions and individuals. Callosal terminals tend to accumulate in patches or bands along the borders of cortical regions and areas. The concentration of callosal terminals was especially high at the common corners of more than two cortical areas. The callosal system shows a rather constant distribution pattern which is composed of column shaped subunits. Considerable individual variations were recognized concerning the number, position, shape, density and contiguity of the columnar units either occupied by callosal connections or empty. Although the laminar distribution of callosal terminals shows some similarities in different areas of the cortex, there is no common laminar pattern characteristic either for the whole neocortex or for any cortical region. The comparison between consecutive sections stained either for degenerating fibers or degenerating axon terminals revealed that the callosal axons do not determine directly the arrangement and packing density of callosal synapses. Whatever determines the position and amount of callosal synapses this influence seems to be exerted via translation into the columnar organization.

Animals↗
PubMed1985

Proliferation of thalamic afferents in cerebral cortex altered by callosal deafferentation.

In area 41, the auditory region of rat neocortex, callosal afferents project to layers I through III and thalamic afferents project to deep layer III through IV. Thus, these two extrinsic systems of afferents project simultaneously to only a narrow lamina in mid to low layer III. For this study, this narrow region of overlap is quantitatively examined to determine the distribution of callosal and thalamic afferents by observing degenerating terminals produced by separate callosal and thalamic lesions. The results show that of all asymmetric synapses observed in the neuropil of this narrow zone, 84% are dendritic spines and the balance are dendritic shafts. Although both callosal and thalamic afferents prefer to synapse with dendritic spines in the neuropil, 78% of the thalamic afferents synapse with dendritic spines while 93% of the callosal afferents synapse with dendritic spines. Vaughan & Foundas (1982) have shown that 3 months after callosal lesions in 1-month-old animals, additional thalamic axons have grown into, and proliferated in, this part of mid to low layer III. Quantitative analysis of the distribution of the degenerating thalamic axon terminals in these long-term callosally lesioned animals has been used to determine whether the proliferating thalamic afferents demonstrate any specificity in the pattern of synapses they make or whether the callosally deafferented neurons determine the pattern of synapses. The results indicate that thalamic axons do exhibit axon specificity, for after they have proliferated into the callosal domain, 80% of the degenerating terminals synapse with dendritic spines and 20% synapse with shafts. This distribution is most comparable to the normal distribution of thalamic axons in this region.

Animals↗
PubMed1984

Heterotopic and homotopic callosal connections in rat visual cortex.

Heterotopic and homotopic callosal projections of rat visual cortex are evaluated. Callosal termination zones in visual cortex are identified with a degeneration technique following complete section of the corpus callosum. The zones which receive callosal afferents are the lateral one-third of area 17, an anteroposterior strip in dorsal and in ventral areas 18a, and 4 patches in area 18b. Following a large injection of lectin-bound horseradish peroxidase (WGA-HRP) into visual cortex, many retrogradely labeled neurons are found in the medial two-thirds of area 17 which does not receive callosal afferents, as well as in the lateral, callosal-recipient zone. These data suggest that heterotopic callosal pathways exist in visual cortex. Injections of tritiated amino acids into restricted parts of visual cortex show the following heterotopic connections: lateral area 17 projects to dorsal area 18a; medial area 17 projects to lateral area 17 and dorsal area 18a; area 18a projects to lateral area 17 and anteromedial area 18b; area 18b projects to lateral area 17, dorsal area 18a, heterotopic sites in area 18b, and to area 29d . Heterotopic connections are generally less dense than homotopic ones. In addition, heterotopic connections are generally less dense than homotopic ones. In addition, heterotopic projections terminate in the supragranular layers. This contrasts with the homotopic afferents of areas 17 and 18a which have additional strong projections to layer V. The distribution of label through the depth of the cortex in some of the callosal recipient zones has been quantified. Injections of WGA-HRP restricted to areas 17, 18a or 18b corroborate the presence of each of the heterotopic connections described above. Heterotopic afferents originate mostly from layer V neurons, whereas homotopic afferents arise from neurons primarily in layers II-V. Like the afferents, the numbers of callosal projection cells in heterotopic regions are substantially less than that in homotopic sites. heterotopic callosal connections may be one factor responsible for binocular vision and also may provide the basis for large, nonoriented receptive fields of units in layer V of rodent visual cortex.

Animals↗
PubMed1995

Late loss of connections during callosal development in Siamese cats.

Siamese cats are hypopigmented mutants which have abnormal retino-geniculo-cortical pathways. The callosal pathway between areas 17 and 18 of the two cortical hemispheres also exhibits abnormalities: projections arising from the supragranular layers are more widely distributed but greatly reduced in number compared to normally pigmented (NP) cats, whereas those from the infragranular layers are more widespread and more numerous than normal (Berman and Grant, Visual Sci., 9 (1992). Here we examine the development of these abnormalities, using pathway tracing combined with quantitative analyses of the projection in normal and Siamese kittens at different postnatal ages. In neonatal kittens of both strains studied prior to natural eye-opening supragranular layer callosal projections arose throughout areas 17 and 18, with those from the infragranular layers restricted more to the region of the area 17/18 border. Between postnatal days 10 and 30 there was a similar, major (approximately 50%) reduction in the number and distribution of supragranular layer callosal projections from the two areas. The reductions in the normal kittens largely established the adult pattern of projection, but in the Siamese kittens twice as many callosal neurons were present than in adults of the mutant genotype and this situation persisted at the end of the second postnatal month. There was also a major (> or = 50%) reduction in the number and distribution of infragranular layer callosal projections in the NP kittens after eye-opening, but in the mutants such reductions did not occur. Thus the sequence of callosal development in the Siamese cat differs markedly for its two laminar components and by comparison with normal animals: an abnormally late loss of the main source of callosal projections occurs from the upper cortical layers, while the lower layers maintain an early exuberancy. We conclude that abnormal callosal connectivity in these mutants does not result from a misrouting of growing callosal axons, but from subsequent alterations to different mechanisms of cortical pathway development.

Animals↗
PubMed2005

Quantitative determination of callose in tree roots.

The formation of callose in tree roots has been suggested as a physiological indicator of aluminum (Al) toxicity. Quantifying callose in the roots in forest soils, however, is hampered by the presence of autofluorescent materials in the roots that disturb the measurement of callose by fluorescence spectrophotometry. Tannins in the roots cause these measurement problems. Here we report on the measurement of callose in the root apices of European chestnut (Castanea sativa) seedlings collected in an acidified forest soil. The callose was quantified with a modified protocol which included three washing steps with polyvinylpolypyrrolidone (PVPP) before the callose was extracted. This procedure reduced the autofluorescence by about 50%. With the use of water or ethanol alone, callose could be measured in only about 15% of the root samples, whereas with the use of PVPP callose could be determined in 95% of the samples. This improved method could help to evaluate the effects of Al toxicity on tree roots grown in forest soils, where callose is detected as a physiological indicator.

Fagaceae↗
PubMed1990

Callosal projections in rat somatosensory cortex are altered by early removal of afferent input.

During the first postnatal week, the distribution of callosal projection neurons in the rat somatosensory cortex changes from a uniform to a discontinuous pattern. To determine if this change is influenced by afferent inputs to the somatosensory cortex, the effect of both early unilateral infraorbital nerve section and unilateral removal of the dorsal thalamus on the distribution of callosal projections in rat somatosensory cortex was examined. One month after either of the above manipulations at birth, the tangential distribution of callosal projections in the somatosensory cortex was examined using the combined retrograde and anterograde transport of horseradish peroxidase. Both manipulations alter the distribution of callosal projection neurons and terminations in the somatosensory cortex. After infraorbital nerve section, the distribution of callosal projections is altered in the contralateral primary somatosensory cortex. The abnormalities observed are consistent with the altered distribution of thalamocortical projections. In addition, consistent abnormalities were observed in the pattern of callosal projections of the second somatosensory area of both hemispheres. Most notably, they are absent in a portion of the region that contains the representation of the mystacial vibrissae and sinus hairs in this area. Thalamic ablation resulted in highly aberrant patterns of callosal projections in the somatosensory cortex on the operated side, where abnormal bands and clusters of callosal projections were observed in apparently random locations. These results are interpreted as evidence that both peripheral and central inputs influence the maturational changes in the distribution of callosal projection neurons.

Afferent Pathways↗
PubMed2004

Induction of callose in roots of Norway spruce seedlings after short-term exposure to aluminum.

Callose (1,3-beta-glucan) is a suggested physiological indicator of aluminum (Al) toxicity in crop plants. It is not known if callose serves a similar function in forest trees, because quantitative data on callose formation in tree roots are limited, particularly under controlled conditions. To evaluate callose as a physiological indicator of Al toxicity in tree roots, we quantified callose formation in roots of Norway spruce (Picea abies (L.) Karst.) seedlings. Seedlings were grown in simulated soil solutions in the presence or absence (control) of Al under controlled conditions. In seedlings grown in solutions containing 280 microM Al, callose concentrations in roots were twice as high as control values after 6 h of Al treatment and 5 times higher than control values after 1 day. Thereafter, root callose concentrations gradually decreased and were only twice as high as control values after 7 days. The presence of various Al concentrations in the simulated soil solutions indicated that callose was induced by a relatively low Al concentration (84 microM). We conclude that callose in tree roots is an indicator of Al toxicity.

Aluminum↗
PubMed2004

More than a leak sealant. The mechanical properties of callose in pollen tubes.

While callose is a well-known permeability barrier and leak sealant in plant cells, it is largely unknown whether this cell wall polymer can also serve as a load-bearing structure. Since callose occurs in exceptionally large amounts in pollen, we assessed its role for resisting tension and compression stress in this cell. The effect of callose digestion in Solanum chacoense and Lilium orientalis pollen grains demonstrated that, depending on the species, this cell wall polymer represents a major stress-bearing structure at the aperture area of germinating grains. In the pollen tube, it is involved in cell wall resistance to circumferential tension stress, and despite its absence at the growing apex, callose is indirectly involved in the establishment of tension stress resistance in this area. To investigate whether or not callose is able to provide mechanical resistance against compression stress, we subjected pollen tubes to local deformation by microindentation. The data revealed that lowering the amount of callose resulted in reduced cellular stiffness and increased viscoelasticity, thus indicating clearly that callose is able to resist compression stress. Whether this function is relevant for pollen tube mechanics, however, is unclear, as stiffened growth medium caused a decrease in callose deposition. Together, our data provide clear evidence for the capacity of cell wall callose to resist tension and compression stress, thus demonstrating that this amorphous cell wall substance can have a mechanical role in growing plant cells.

Cell Wall↗