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PubMed2002

Does "callosal relay" explain ear advantage in dichotic monitoring?

Pairs of consonant-vowel (CV) syllables were dichotically presented to a large sample of healthy subjects (n = 263) who were instructed to monitor for the presence of a target CV (/ta/) which could occur in either ear. The subjects responded by pressing a response button, allowing the recording of reaction times (RTs) and number of correct responses. The investigated sample comprised consistent right-handers (CRH), consistent left-handers (CLH), and mixed-handers (MH). It was found that right-ear targets were detected more frequently and faster than left-ear targets, both in CRH and MH subjects. CLH subjects, on the other hand, responded faster to targets presented to the left ear but there was no ear advantage in terms of the correct responses. The RT data were used to examine whether they are compatible with the callosal relay model of language lateralisation. It was found that the predictions made by the callosal relay model were supported by the RT data for all groups.

Journal Article↗
PubMed1983

Callosal apraxia.

A 43-year-old woman suffered a spontaneous corpus callosum disconnection, resulting in apraxia and apraxic agraphia confined to the left hand. She initially had a functionally total callosal disconnection. With time, the splenium of the corpus callosum became functional, and a computerized tomographic scan performed five months after the onset showed infarction of only the body of the corpus callosum. Concomitant with this improvement in callosal function, the apraxia changed from ideational (loss of the concept of skilled movements) to classic ideomotor apraxia. A temporal analysis of this case provided support for Liepmann's (Liepmann, 1900; Liepmann and Maas, 1970) hypothesis that there is a centre for visuokinaesthetic (space-time) engrams in the left hemisphere of right-handed patients that controls skilled motor acts in either hand. This patient's recovery also allowed us a better understanding of the mechanisms underlying various types of apraxia.

Adult↗
PubMed2000

Anterior and posterior callosal contributions to simultaneous bimanual movements of the hands and fingers.

In order to study the role of the corpus callosum in two-handed coordination we tested callosotomy subjects while they attempted to initiate simultaneous discrete movements with both hands. We observed four split-brain patients, including one pre- and post-operatively, as well as normal and epileptic control subjects. Split-brain patients made button presses that were less synchronous than either normal or epileptic controls. Although split-brain patients' average performance did not always differ from control subjects, callosotomy resulted in a 3-fold increase in the variability with which 'simultaneous' movements were initiated. The one subject tested pre- and post-callosotomy showed distinct changes in movement initiation synchrony after both the anterior and the posterior stages of the surgery. These changes suggest that anterior and posterior callosal fibres may make unique contributions to bimanual synchronization, depending on whether responses are self-initiated or in reaction to a visual stimulus. This study demonstrates that neural communication across anterior and posterior fibres of the corpus callosum strongly influences the temporal precision of bimanual coordination. Specifically, callosal transmission affects the degree of bilateral synchrony with which simple simultaneous hand and finger movements are initiated.

Adolescent↗
PubMed1995

Callosal neurones give rise to zinc-rich boutons in the rat visual cortex.

Sodium selenide was used as a retrograde tracer to assess the callosal origin of zinc-rich boutons in the neocortex of the rat. Selenide injections were placed in the lateral end of area Oc1 (area 17). Zinc present in synaptic boutons precipitated as zinc selenide and was transported retrogradely to the parent cell bodies. In addition to the ipsilateral labelling, contralateral retrogradely labelled somata were mainly observed along the border between areas Oc1 and Oc2L (area 18a). Labelled neurones were present in layer 2-3 and layer 6. In contrast to tracing studies with peroxidase, no labelled neurone was observed in layers 4 and 5 except at the inner border of layer 5. This study reveals the chemical heterogeneity of callosal projections, which may be divided into zinc-rich and zinc-poor systems.

Animals↗
PubMed1997

Activation of pollen tube callose synthase by detergents. Evidence for different mechanisms of action.

In pollen tubes of Nicotiana alata, a membrane-bound, Ca(2+)-independent callose synthase (CalS) is responsible for the biosynthesis of the (1,3)-beta-glucan backbone of callose, the main cell wall component. Digitonin increases CalS activity 3- to 4-fold over a wide range of concentrations, increasing the maximum initial velocity without altering the Michaelis constant for UDP-glucose. The CalS activity that requires digitonin for assay (the latent CalS activity) is not inhibited by the membrane-impermeant, active site-directed reagent UDP-pyridoxal when the reaction is conducted in the absence of digitonin. This is consistent with digitonin increasing CalS activity by the permeabilization of membrane vesicles. A second group of detergents, including 3-[(3-cholamidopropyl)dimethylammonio]-1-propane-sulfonate (CHAPS), Zwittergent 3-16, and 1-alpha-lysolecithin, activate pollen tube CalS 10- to 15-fold, but only over a narrow range of concentrations just below their respective critical micellar concentrations. This activation could not be attributed to any particular chemical feature of these detergents. CHAPS increases maximum initial velocity and decreases the Michaelis constant for UDP-glucose and activates CalS even in the presence of permeabilizing concentrations of digitonin. Inhibition studies with UDP-pyridoxal indicate that activation by CHAPS occurs by recruitment of previously inactive CalS molecules to the pool of active enzyme. The activation of pollen tube CalS by these detergents therefore resembles activation of the enzyme by trypsin.

Cholic Acids↗
PubMed1982

Callose induction in cowpea by uridine diphosphate glucose and calcium phosphate-boric Acid treatments.

Calcium phosphate-boric acid treatments and UDP-glucose both elicited aniline blue fluorescent, periodic acid-Schiff's reagent-resistant, deposits in association with the cell walls of cowpea (Vigna sinensis [Torner] Savi cv. Early Ramshorn) tissue. Those deposits induced by calcium phosphateboric acid treatment ultrastructurally resembled the "wound callose" commonly triggered by cell damage; they were formed in seemingly intact cells of stems and leaves and their formation was associated with an increase in the surface density of rough endoplasmic reticulum in the cell cytoplasm. In contrast, UDP-glucose induced a more rapid accumulation of aniline blue fluorescent material, but only at the cut edges of stem slices. Comparative light and electron microscopy indicated that the material was incorporated into the walls of the damaged cells, even when such cells were devoid of organized cytoplasm. These results indicate a difference in the mode and site of synthesis between wound callose and that elicited by exogenous UDP-glucose. They support the hypothesis that externally supplied UDP-glucose cannot be utilized by intact cells.

Journal Article↗
PubMed1986

Influence of Free Fatty Acids, Lysophosphatidylcholine, Platelet-Activating Factor, Acylcarnitine, and Echinocandin B on 1,3-beta-d-Glucan Synthase and Callose Synthesis.

The activity of 1,3-beta-d-glucan synthase assayed in the presence of digitonin in a microsomal preparation from suspension-cultured cells of Glycine max can be fully inhibited by unsaturated fatty acids, trienoic acids being most effective. Lysophosphatidylcholine, platelet-activating factor, acylcarnitine, and Echinocandin B can also fully inhibit the enzyme. Inhibition is observed both when the enzyme is activated by Ca(2+) or by trypsinization. At low amounts some of the substances can also cause stimulation. These effects all may result from a displacement of certain endogenous phospholipids necessary for optimal activity of the 1,3-beta-d-glucan synthase.In the absence of digitonin the enzyme activity is greatly stimulated by lysophosphatidylcholine, platelet-activating factor, acylcarnitine, and Echinocandin B within a certain concentration range, presumably by rendering the microsomal vesicles permeable to the substrate and Ca(2+). Dibucaine does not cause such an effect.Acylcarnitine and Echinocandin B at low concentrations can induce callose synthesis in vivo; this effect is enhanced by chitosan. At higher concentrations the two substances and polyunsaturated fatty acids cause severe electrolyte leakage. The effects are discussed in regard to the induction of callose synthesis by enforced Ca(2+) influx, and its modulation by membrane lipids.

Journal Article↗
PubMed1991

Developmental Regulation of the (1,3)-beta-Glucan (Callose) Synthase from Tomato : Possible Role of Endogenous Phospholipases.

Activity levels of UDP-glucose: (1,3)-beta-glucan (callose) synthase in microsomal membranes of pericarp tissue from tomato fruit (Lycoperisicon esculentum Mill, cv Rutgers) were determined during development and ripening. Addition of the phospholipase inhibitors O-phosphorylcholine and glycerol-1-phosphate to homogenization buffers was necessary to preserve enzyme activity during homogenization and membrane isolation. Enzyme activity declined 90% from the immature green to the red ripe stage. The polypeptide composition of the membranes did not change significantly during ripening. The enzyme from immature fruit was inactivated by exogenously added phospholipases A(2), C, and D. These results suggest that the decline in callose synthase activity during ontogeny may be a secondary effect of endogenous lipase action.

Journal Article↗
PubMed2006

Spatial coordination of aluminium uptake, production of reactive oxygen species, callose production and wall rigidification in maize roots.

Aluminium (Al) toxicity associated with acid soils represents one of the biggest limitations to crop production worldwide. Although Al specifically inhibits the elongation of root cells, the exact mechanism by which this growth reduction occurs remains controversial. The aim of this study was to investigate the spatial and temporal dynamics of Al migration into roots of maize (Zea mays L.) and the production of the stress response compound callose. Using the Al-specific fluorescent probe morin, we demonstrate the gradual penetration of AI into roots. Al readily accumulates in the root's epidermal and outer cortical cell layers but does not readily penetrate into the inner cortex. After prolonged exposure times (12-24 h), Al had entered all areas of the root apex. The spatial and temporal accumulation of Al within the root is similarly matched by the production of the cell wall polymer callose, which is also highly localized to the epidermis and outer cortical region. Exposure to Al induced the rapid production of reactive oxygen species and induced a significant rigidification of the cell wall. Our results suggest that Al-induced root inhibition in maize occurs by rigidification of the epidermal layers.

Aluminum↗
PubMed1994

Juvenile visual callosal axons in kittens display origin- and fate-related morphology and distribution of arbors.

In kittens, callosal axons originating either from medial area 17 (transient axons) or near the 17/18 border (mostly permanent axons) were labelled with anterogradely transported biocytin; they were reconstructed by computer from serial sections, and their morphologies compared at different ages. During the first and second postnatal weeks both sets of axons branched profusely in the white matter of the lateral gyrus and the number of branches increased with age. The most common type of axon ending was the growth cone; others may have been collapsing growth cones, branches in the process of elimination or early synaptic boutons. Axons from medial area 17 distributed over a broad territory, including the 17/18 border where callosal axons terminate in the adult cat, but without aiming specifically at any one area. The majority of axons and their branches terminated in the white matter or at the bottom of layer VI; exceptionally they extended further into the cortex. Most of the axons originating near the 17/18 border were different from those described above, and the difference increased with age. Although they also terminated profusely in the white matter of the lateral gyrus, most of the branches terminated near the contralateral 17/18 border; they frequently entered the grey matter up to the superficial layers and branched into it. During the third week, axons from medial area 17 were rarely found to extend beyond the corpus callosum, probably because they were in the process of being eliminated. In contrast, axons originating near the 17/18 border had increased their number of branches in the grey matter. In conclusion, during the first and second postnatal weeks axons grew and differentiated according to their origin, and this anticipated whether they would be maintained or eliminated. Neurotrophic signals, possibly from the white matter or the subplate, and growth-inhibiting signals from area 17 may be involved in this process.

Aging↗
PubMed1994

Computational structure of visual callosal axons.

We analysed the activation profiles obtained by simulating invasion of an orthodromic action potential in eleven anterogradely filled and serially reconstructed terminal arbors of callosal axons originating and terminating in areas 17 and 18 of the adult cat. This was done in order to understand how geometry relates to computational properties of axons. In the simulation, conduction from the callosal midline to the first bouton caused activation latencies of 0.9-3.2 ms, compatible with published electrophysiological values. Activation latencies of the total set of terminal boutons varied across arbors between 0.3 and 2.7 ms. Arbors distributed boutons in tangentially segregated terminal columns spanning one or, more often, several layers. Individual columns of one axon were frequently activated synchronously or else with a few hundred microseconds of each other. Synchronous activation of spatially separate columns is achieved by: (i) long primary or secondary branches of similar calibre running nearly parallel to each other for several millimetres; (ii) variations in the calibre of branches serially fed to separate columns by the same primary or secondary branch; (iii) exchange of high-order or preterminal branches across columns. The long, parallel branches blatantly violate principles of axonal economy. Simulated alterations of the axonal arbors indicate that similar spatiotemporal patterns of activity could, in principle, be obtained by less axon-costly architectures. The structure of axonal arbors, therefore, may not be determined solely by the type of spatiotemporal activation profiles it achieves in the cortex but also by other constraints, in particular those imposed by developmental mechanisms.

Action Potentials↗
PubMed1996

Growth of callosal terminal arbors in primary visual areas of the cat.

In kittens ranging in age between postnatal day (P) 5 and P150, callosal axons originating near the 17/18 border were anterogradely labelled with biocytin and reconstructed from serial sections. At the end of the first postnatal week most of the axons begin to invade the cortex near the 17/18 border with multiple branches; some axons already span the grey matter up to layer 1. Branches tend to grow into the grey matter in loose bundles </=100 microm in diameter, separated by empty spaces of comparable width. In the following weeks additional branches are produced in the grey matter; this appears to blur the initial bundled distribution, although by the end of the first postnatal month the branches are distributed in discrete patches similar to the adult terminal columns. Although a few boutons (presumably synaptic boutons) are found in the white matter/subplate region at earlier ages, they appear in the grey matter from P12 onwards. Their number per axon increases with age, reaching adult values about the end of the first month. Subsequently the number of boutons continues to increase and remains above adult values at P50, P65 and P80; it then decreases, reaching adult levels by P150. During the first month boutons tend to be more numerous in the infragranular layers, but then the trend reverses in favour of the supragranular layers. In most cases, the distribution of boutons spares layer IV partially or completely. From the onset boutons are distributed in radial columns whose diameter increases with age. They maintain selective laminar and columnar distributions through the period of rapid and exuberant increase. These distributions do not appear to be sharpened further by the reduction in the number of boutons to adult levels. On the whole, callosal terminal arbors differentiate through stages of exuberant, albeit progressively constrained, growth involving both progressive and regressive events. Comparisons with previous work suggest that visual activity might finely shape the arbor, from the onset of synaptogenesis onwards.

Animals↗
PubMed1975

Angiographic signs of corpus callosal tumors: a reappraisal.

Angiographic findings of eleven corpus callosal tumors are analyzed. Three new angiographic signs are demonstration of the lateral ventricular roof veins, spreading of the septal veins, and actual demonstration of corpus callosal thickening. In contrast to traditional concepts, diagnostic abnormalities were angiographically demonstrated in all eleven cases. Biplane angiotomography is of vital importance in the angiographic diagnosis of this frequently subtle tumor.

Adult↗
PubMed1997

Three kinetically distinct Ca2+-independent depolarization-activated K+ currents in callosal-projecting rat visual cortical neurons.

Three kinetically distinct Ca2+-independent depolarization-activated K+ currents in callosal-projecting rat visual cortical neurons. J. Neurophysiol. 78: 2309-2320, 1997. Whole cell, Ca2+-independent, depolarization-activated K+ currents were characterized in identified callosal-projecting (CP) neurons isolated from postnatal day 7-16 rat primary visual cortex. CP neurons were identified in vitro after in vivo retrograde labeling with fluorescently tagged latex microbeads. During brief (160-ms) depolarizing voltage steps to potentials between -50 and +60 mV, outward K+ currents in these cells activate rapidly and inactivate to varying degrees. Three distinct K+ currents were separated based on differential sensitivity to 4-aminopyridine (4-AP); these are referred to here as IA, ID, and IK, because their properties are similar (but not identical) K+ currents termed IA, ID, and IK in other cells. The current sensitive to high (>/=100 mu M) concentrations of 4-AP (IA) activates and inactivates rapidly; the current blocked completely by low (</=50 mu M) 4-AP (ID) activates rapidly and inactivates slowly. A slowly activating, slowly inactivating current (IK) remains in the presence of 5 mM 4-AP. IA, ID, and IK also were separated and characterized in experiments that did not rely on the use of 4-AP. All CP cells express all three K+ current types, although the relative densities of IA, ID, and IK vary among cells. The experiments here also have revealed that IA, ID, and IK display similar voltage dependences of activation and steady state inactivation, whereas the kinetic properties of the currents are distinct. At +30 mV, for example, mean +/- SD activation taus are 0. 83 +/- 0.24 ms for IA, 1.74 +/- 0.49 ms for ID, and 14.7 +/- 4.0 ms for IK. Mean +/- SD inactivation taus for IA and ID are 26 +/- 7 ms and 569 +/- 143 ms, respectively. Inactivation of IK is biexponential with mean +/- SD inactivation time constants of 475 +/- 232 ms and 3,128 +/- 1,328 ms; approximately 20% of the 4-AP-insensitive current is noninactivating. For all three components, activation is voltage dependent, increasing with increasing depolarization, whereas inactivation is voltage independent. Both IA and IK recover rapidly from steady state inactivation with mean +/- SD recovery time constants of 38 +/- 7 ms and 79 +/- 26 ms, respectively; ID recovers an order of magnitude more slowly (588 +/- 274 ms). The properties of IA, ID, and IK in CP neurons are compared with those of similar currents described previously in other mammalian central neurons and, in the accompanying paper, the roles of these conductances in regulating the firing properties of CP neurons are explored.

4-Aminopyridine↗
PubMed1997

Role of voltage-gated K+ currents in mediating the regular-spiking phenotype of callosal-projecting rat visual cortical neurons.

Role of voltage-gated K+ currents in mediating the regular-spiking phenotype of callosal-projecting rat visual cortical neurons. J. Neurophysiol. 78: 2321-2335, 1997. Whole cell current- and voltage-clamp recordings were combined to examine action potential waveforms, repetitive firing patterns, and the functional roles of voltage-gated K+ currents (IA, ID, and IK) in identified callosal-projecting (CP) neurons from postnatal (day 7-13) rat primary visual cortex. Brief (1 ms) depolarizing current injections evoke single action potentials in CP neurons with mean +/- SD (n = 60) durations at 50 and 90% repolarization of 1.9 +/- 0.5 and 5.5 +/- 2.0 ms, respectively; action potential durations in individual cells are correlated inversely with peak outward current density. During prolonged threshold depolarizing current injections, CP neurons fire repetitively, and two distinct, noninterconverting "regular-spiking" firing patterns are evident: weakly adapting CP cells fire continuously, whereas strongly adapting CP cells cease firing during maintained depolarizing current injections. Action potential repolarization is faster and afterhyperpolarizations are more pronounced in strongly than in weakly adapting CP cells. In addition, input resistances are lower and plateau K+ current densities are higher in strongly than in weakly adapting CP cells. Functional studies reveal that blockade of ID reduces the latency to firing an action potential, and increases action potential durations at 50 and 90% repolarization. Blockade of ID also increases firing rates in weakly adapting cells and results in continuous firing of strongly adapting cells. After applications of millimolar concentrations of 4-aminopyridine to suppress IA (as well as block ID), action potential durations at 50 and 90% repolarization are further increased, and firing rates are accelerated over those observed when only ID is blocked. Using VClamp/CClamp and the voltage-clamp data in the preceding paper, mathematical descriptions of IA, ID, and IK are generated and a model of the electrophysiological properties of rat visual cortical CP neurons is developed. The model is used to simulate the firing properties of strongly adapting and weakly adapting CP cells and to explore the functional roles of IA, ID, and IK in shaping the waveforms of individual action potentials and controlling the repetitive firing properties of these cells.

4-Aminopyridine↗
PubMed2000

Somesthetic disconnection syndromes in patients with callosal lesions.

Somesthetic disconnection syndromes were investigated in relation to the sites of lesions in the corpus callosum in 3 patients with callosal lesions, in order to identify the callosal regions responsible for the interhemispheric transfer of somesthetic information. Cases 1 and 2 with lesions in the posterior truncus exhibited transfer deficits of discriminative sensations between the left and right hands, left-sided tactile anomia and left-sided somesthetic alexia. Case 3 with lesions in the posteroventral part of the posterior truncus showed no signs of somesthetic disconnection syndromes. The results suggest the importance of the anterior and/or dorsal part of the posterior truncus of the corpus callosum for interhemispheric transfer of the discriminative sensations and integrated somesthetic information necessary for tactile naming and somesthetic reading.

Adult↗
PubMed1982

Visual callosal, corticotectal and corticogeniculate projections in golden hamsters.

Visual callosal projections were identified in the hamster by terminal degeneration after total transection of the corpus callosum. A dense trilaminar callosal terminal field was observed to form a belt around area 17. The subcortical projections from area 17 were studied using the autoradiographic method. Evidence for a topographic organization is presented for projections from area 17 to the superior colluculus, the dorsal and ventral nuclei of the lateral geniculate body. The totography of the projections are in accord with known patterns of distribution of the retina upon these structures in the hamster.

Animals↗
PubMed1996

Hereditary painful callosities with associated features.

'Hereditary painful callosities' defines an autosomal dominant nummular palmoplantar keratoderma characterized by the development of painful keratotic lesions over pressure points. Two unrelated patients with hereditary painful callosities with other familial acral abnormalities are reported. To our knowledge subtotal congenital leukonychia and symmetrical bone duplication of great toes have not been previously described in association with this disorder.

Adult↗