The Experts below are selected from a list of 99 Experts worldwide ranked by ideXlab platform
Antanas Kuras - One of the best experts on this subject based on the ideXlab platform.
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Inhibition of Dendritic L-Type Calcium Current by Memantine in Frog Tectum
Medicina-buenos Aires, 2013Co-Authors: Armantas Baginskas, Antanas Kuras, Artūras GrigaliūnasAbstract:The aim of the study was to explore the effects of memantine on responses elicited in the frog tectum by the bursts of spikes of moderate strength of a single Retina Ganglion Cell and to gain an insight about the effect of memantine on the L-type Ca2+ current. Material and Methods. The experiments were performed in vivo on adult frogs (Rana temporaria). An individual Retina Ganglion Cell (or its retinotectal fiber) was stimulated by current pulses delivered through a multichannel stimulating electrode positioned on the Retina. Responses to the discharge of a single Retinal Ganglion Cell were recorded in the tectum by an extraCellular carbonfiber microelectrode positioned in the terminal arborization of the retinotectal fiber in the tectum layer F. The solution of memantine (1-amino-3,5-dimethyladamantane) hydrochloride (30 or 45 μM) was applied onto the surface of the tectum by perfusion at a rate of 0.4 mL/min. Results. Memantine (30–45 μM) largely inhibited the L-type Ca2+ channel-mediated slow negative wave and late discharges seen in the tectum responses without any effect on fast synaptic retinotectal transmission. Conclusions. Our results suggest that the neuroprotective effect of memantine could arise not only through the inhibition of the NMDA receptor current but also through the suppression of the L-type Ca2+ current.
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presynaptic nicotinic potentiation of a frog retinotectal transmission evoked by discharge of a single Retina Ganglion Cell
Neuroscience Research, 2011Co-Authors: Armantas Baginskas, Vilija Kuraite, Antanas KurasAbstract:Abstract It was demonstrated in our previous studies of the frog retinotectal transmission that retinotectal synaptic potentials are enhanced by a factor of 1.5 due to the tonic presynaptic nicotinic potentiation, caused by the ambient level of the acetylcholine in the frog tectum. Furthermore, the results of those studies have indicated that the mechanism of the nicotinic potentiation is only partially exploited, because the application of the cholinergic agonist had increased the retinotectal transmission more than 2 times above the level of the tonic potentiation. The purpose of the present study was to explore this additional potentiation. We have shown that: (1) Bursts of 4–10 action potentials of a frog Retina Ganglion Cell gave rise to an increase (phasic potentiation) of the retinotectal transmission 1.4–2.2 times, depending on the burst strength, that lasted tens of seconds. (2) This increase has been mediated through the presynaptic nicotinic acetylcholine receptors activated by the endogenous acetylcholine released into the tectum during relatively strong bursts of the Retina Ganglion Cell. (3) Two types of the nicotinic acetylcholine receptors are co-localized in the presynaptic terminals of the individual retinotectal input to the tectum layer F – high-affinity (tonic) and low-affinity (phasic) nicotinic receptors.
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L-Type Ca^2+ current in frog tectal recurrent neurons determines the NMDA receptor activation on efferent neuron
Experimental Brain Research, 2008Co-Authors: Armantas Baginskas, Antanas KurasAbstract:The activity patterns of a neuronal network originate from the intrinsic properties and synaptic interactions of the constituent neurons. Our recent studies support this view, showing that the discharge of a single frog Retina Ganglion Cell brings an elementary neuronal network of the tectum (tectum column) to a suprathreshold activity of two distinct levels that are related to the activation of the slow L-type calcium current in dendrites of the recurrent pear-shaped neurons (lower level) and the NMDA receptors in neurons (higher level) of the tectum column. We show in the present study that the dendritic slow L-type calcium current is necessary for the NMDA receptor activation in the tectum column. A small decrease of this current prevents the NMDA receptor activation and, hence, the transition of the network to the higher activity level, at which the efferent neuron of the network fires. So, the activity of the frog tectum column can be effectively controlled through the intrinsic properties of the recurrent pear-shaped neurons of the column.
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L-Type Ca2+ current in frog tectal recurrent neurons determines the NMDA receptor activation on efferent neuron
Experimental Brain Research, 2008Co-Authors: Armantas Baginskas, Antanas KurasAbstract:The activity patterns of a neuronal network originate from the intrinsic properties and synaptic interactions of the constituent neurons. Our recent studies support this view, showing that the discharge of a single frog Retina Ganglion Cell brings an elementary neuronal network of the tectum (tectum column) to a suprathreshold activity of two distinct levels that are related to the activation of the slow L-type calcium current in dendrites of the recurrent pear-shaped neurons (lower level) and the NMDA receptors in neurons (higher level) of the tectum column. We show in the present study that the dendritic slow L-type calcium current is necessary for the NMDA receptor activation in the tectum column. A small decrease of this current prevents the NMDA receptor activation and, hence, the transition of the network to the higher activity level, at which the efferent neuron of the network fires. So, the activity of the frog tectum column can be effectively controlled through the intrinsic properties of the recurrent pear-shaped neurons of the column.
Armantas Baginskas - One of the best experts on this subject based on the ideXlab platform.
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Inhibition of Dendritic L-Type Calcium Current by Memantine in Frog Tectum
Medicina-buenos Aires, 2013Co-Authors: Armantas Baginskas, Antanas Kuras, Artūras GrigaliūnasAbstract:The aim of the study was to explore the effects of memantine on responses elicited in the frog tectum by the bursts of spikes of moderate strength of a single Retina Ganglion Cell and to gain an insight about the effect of memantine on the L-type Ca2+ current. Material and Methods. The experiments were performed in vivo on adult frogs (Rana temporaria). An individual Retina Ganglion Cell (or its retinotectal fiber) was stimulated by current pulses delivered through a multichannel stimulating electrode positioned on the Retina. Responses to the discharge of a single Retinal Ganglion Cell were recorded in the tectum by an extraCellular carbonfiber microelectrode positioned in the terminal arborization of the retinotectal fiber in the tectum layer F. The solution of memantine (1-amino-3,5-dimethyladamantane) hydrochloride (30 or 45 μM) was applied onto the surface of the tectum by perfusion at a rate of 0.4 mL/min. Results. Memantine (30–45 μM) largely inhibited the L-type Ca2+ channel-mediated slow negative wave and late discharges seen in the tectum responses without any effect on fast synaptic retinotectal transmission. Conclusions. Our results suggest that the neuroprotective effect of memantine could arise not only through the inhibition of the NMDA receptor current but also through the suppression of the L-type Ca2+ current.
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presynaptic nicotinic potentiation of a frog retinotectal transmission evoked by discharge of a single Retina Ganglion Cell
Neuroscience Research, 2011Co-Authors: Armantas Baginskas, Vilija Kuraite, Antanas KurasAbstract:Abstract It was demonstrated in our previous studies of the frog retinotectal transmission that retinotectal synaptic potentials are enhanced by a factor of 1.5 due to the tonic presynaptic nicotinic potentiation, caused by the ambient level of the acetylcholine in the frog tectum. Furthermore, the results of those studies have indicated that the mechanism of the nicotinic potentiation is only partially exploited, because the application of the cholinergic agonist had increased the retinotectal transmission more than 2 times above the level of the tonic potentiation. The purpose of the present study was to explore this additional potentiation. We have shown that: (1) Bursts of 4–10 action potentials of a frog Retina Ganglion Cell gave rise to an increase (phasic potentiation) of the retinotectal transmission 1.4–2.2 times, depending on the burst strength, that lasted tens of seconds. (2) This increase has been mediated through the presynaptic nicotinic acetylcholine receptors activated by the endogenous acetylcholine released into the tectum during relatively strong bursts of the Retina Ganglion Cell. (3) Two types of the nicotinic acetylcholine receptors are co-localized in the presynaptic terminals of the individual retinotectal input to the tectum layer F – high-affinity (tonic) and low-affinity (phasic) nicotinic receptors.
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L-Type Ca^2+ current in frog tectal recurrent neurons determines the NMDA receptor activation on efferent neuron
Experimental Brain Research, 2008Co-Authors: Armantas Baginskas, Antanas KurasAbstract:The activity patterns of a neuronal network originate from the intrinsic properties and synaptic interactions of the constituent neurons. Our recent studies support this view, showing that the discharge of a single frog Retina Ganglion Cell brings an elementary neuronal network of the tectum (tectum column) to a suprathreshold activity of two distinct levels that are related to the activation of the slow L-type calcium current in dendrites of the recurrent pear-shaped neurons (lower level) and the NMDA receptors in neurons (higher level) of the tectum column. We show in the present study that the dendritic slow L-type calcium current is necessary for the NMDA receptor activation in the tectum column. A small decrease of this current prevents the NMDA receptor activation and, hence, the transition of the network to the higher activity level, at which the efferent neuron of the network fires. So, the activity of the frog tectum column can be effectively controlled through the intrinsic properties of the recurrent pear-shaped neurons of the column.
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L-Type Ca2+ current in frog tectal recurrent neurons determines the NMDA receptor activation on efferent neuron
Experimental Brain Research, 2008Co-Authors: Armantas Baginskas, Antanas KurasAbstract:The activity patterns of a neuronal network originate from the intrinsic properties and synaptic interactions of the constituent neurons. Our recent studies support this view, showing that the discharge of a single frog Retina Ganglion Cell brings an elementary neuronal network of the tectum (tectum column) to a suprathreshold activity of two distinct levels that are related to the activation of the slow L-type calcium current in dendrites of the recurrent pear-shaped neurons (lower level) and the NMDA receptors in neurons (higher level) of the tectum column. We show in the present study that the dendritic slow L-type calcium current is necessary for the NMDA receptor activation in the tectum column. A small decrease of this current prevents the NMDA receptor activation and, hence, the transition of the network to the higher activity level, at which the efferent neuron of the network fires. So, the activity of the frog tectum column can be effectively controlled through the intrinsic properties of the recurrent pear-shaped neurons of the column.
Jacob Engelmann - One of the best experts on this subject based on the ideXlab platform.
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spatial resolution of an eye containing a grouped Retina Ganglion Cell morphology and tectal physiology in the weakly electric fish gnathonemus petersii
The Journal of Comparative Neurology, 2013Co-Authors: Roland Pusch, Hansjoachim Wagner, Gerhard Von Der Emde, Jacob EngelmannAbstract:The Retina of the weakly electric fish Gnathonemus petersii is a so-called grouped Retina where photoreceptors are bundled. These bundles are regarded as functional units and this type of Retinal specialization is uniquely found in teleosts. To understand how this anatomical organization influences visual information processing we investigated the morphology and distribution of Retinal Ganglion Cells (GCs) and the response properties of Retinal afferents terminating in the major retinorecipient area, the optic tectum. GCs were classified based on their dendritic morphology (dendritic field diameters 280 μm: giant GCs). Within these classes subtypes were distinguished based on the ramification patterns of the dendrites in the sublaminae of the inner plexiform layer. Properties of presumed optic nerve terminals were investigated in the optic tectum using extraCellular recordings. Physiological classes could be observed based on their response to visual stimuli (on; off; on-off, and fast units). Receptive field sizes and spatiotemporal properties were classified and the topographical representation of the visual space was mapped in the tectum. Gratings of low spatial frequencies were best responded to and followed up to high temporal frequencies (>30 Hz). Most of the recorded units were directionally selective. No evidence of distorted topographies in the tectum was found, i.e., no overrepresentation of the Retina was seen in the tectum opticum. The grouped Retina of G. petersii seems to be optimized for the detection of large, fast objects in an environment of low optical quality. J. Comp. Neurol. 521:4075-4093, 2013. © 2013 Wiley Periodicals, Inc.
Paola Bovolenta - One of the best experts on this subject based on the ideXlab platform.
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secreted frizzled related proteins modulate pathfinding and fasciculation of mouse Retina Ganglion Cell axons by direct and indirect mechanisms
The Journal of Neuroscience, 2015Co-Authors: Severine Marcos, Francisco Nietolopez, Africa Sandonis, Marcos Julian Cardozo, Fabiana Di Marco, Pilar Esteve, Paola BovolentaAbstract:Retina Ganglion Cell (RGC) axons grow along a stereotyped pathway undergoing coordinated rounds of fasciculation and defasciculation, which are critical to establishing proper eye–brain connections. How this coordination is achieved is poorly understood, but shedding of guidance cues by metalloproteinases is emerging as a relevant mechanism. Secreted Frizzled Related Proteins (Sfrps) are multifunctional proteins, which, among others, reorient RGC growth cones by regulating intraCellular second messengers, and interact with Tolloid and ADAM metalloproteinases, thereby repressing their activity. Here, we show that the combination of these two functions well explain the axon guidance phenotype observed in Sfrp1 and Sfrp2 single and compound mouse mutant embryos, in which RGC axons make subtle but significant mistakes during their intraRetinal growth and inappropriately defasciculate along their pathway. The distribution of Sfrp1 and Sfrp2 in the eye is consistent with the idea that Sfrp1/2 normally constrain axon growth into the fiber layer and the optic disc. Disheveled axon growth instead seems linked to Sfrp-mediated modulation of metalloproteinase activity. Indeed, Retinal explants from embryos with different Sfrp -null alleles or explants overexpressing ADAM10 extend axons with a disheveled appearance, which is reverted by the addition of Sfrp1 or an ADAM10-specific inhibitor. This mode of growth is associated with an abnormal proteolytic processing of L1 and N -cadherin, two ADAM10 substrates previously implicated in axon guidance. We thus propose that Sfrps contribute to coordinate visual axon growth with a dual mechanism: by directly signaling at the growth cone and by regulating the processing of other relevant cues.
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Morphogen signaling at the vertebrate growth cone: a few cases or a general strategy?
Journal of Neurobiology, 2005Co-Authors: Paola BovolentaAbstract:Axon navigation relies on the competence of growth cones to sense and interpret attractive and repulsive guidance cues present along their trajectory. For most neurons, this process is mediated by a limited number of conserved families of ligand-receptor signaling systems, including Ephrin/Eph, Netrins/DCC-Unc5, Slits/Robo, and Semaphorins/Plexin-Neuropilin. Recent studies have demonstrated that some neurons respond also to well-known secreted signaling molecules, best known for their roles as morphogens, such as BMP7, SHH, FGF8, and Wnt. Thus, Retina Ganglion Cell axon navigation is influenced by FGF, SHH, and possibly BMP signaling. Similarly, commissural neurons in the spinal cord respond sequentially to the activity of BMP, SHH, and Wnt to extend toward and away from their intermediate target, the floor plate. The data that support this conclusion will be summarized and how morphogens may signal at the growth cone will be discussed. © 2005 Wiley Periodicals, Inc. J Neurobiol 64: 405–416, 2005
Beatriz L. Caputto - One of the best experts on this subject based on the ideXlab platform.
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Short term labeling of proteins, gangliosides and glycoproteins of the optic tract of chickens exposed to light or darkness
Neurochemistry International, 2003Co-Authors: A.m. Marchionatti, Beatriz L. Caputto, Ranwel CaputtoAbstract:Abstract In contrast with previous findings of the labeling of the glycosidic moieties of the gangliosides and glycoproteins in chickens injected with N-[ 3 H ] acetylmannosamine , the labeling of the Ganglion Cell layer and optic tectum proteins of chicks exposed to light after an intraocular injection of [ 3 H]proline showed no differences with those of their counterpart chickens that remained in darkness. The same failure in finding a difference was met when the cytosolic or the particulate proteins or the acid soluble fraction in the Retina were compared. Cycloheximide and puromycin inhibited the labeling of Retina and optic tectum proteins, gangliosides and glycoproteins in both illumination conditions. Since the labelings in the optic tectum appeared more inhibited than those in the Retina Ganglion Cell layer it was concluded that cycloheximide and puromycin, besides the synthesis of those compounds, also inhibit their axonal transport. On the basis of these contrasting results the working hypothesis is advanced that light stimulation enhances the activity of the Golgi apparatus but not (or less) that of the polyribosomes.
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Light Exposue Activates Retina Ganglion Cell Lysophosphatidic Acid Acyl Transferase and Phosphatidic Acid Phosphatase by a c‐fos‐Dependent Mechanism
Journal of Neurochemistry, 2001Co-Authors: G. A. De Arriba Zerpa, Mario E. Guido, D. F. Bussolino, S. J. Pasquare, P. I. Castagnet, N. M. Giusto, Beatriz L. CaputtoAbstract:Abstract : We previously reported that the biosynthesis of phospholipids in the avian Retina is altered by light stimulation, increasing significantly in anglion Cells in light and in photoreceptor Cells in dark. In the present work, we have determined that light significantly increases the incorporation of [3H]glycerol into Retina Ganglion Cell glycerophospholipids in vivo by a Fos-dependent mechanism because an oligonucleotide antisense to c-fos mRNA substantially blocked the light-dark differences. We also studied in viro the enzyme activities of phosphatidate phosphohydrolase (PAPase), lysophosphatidate acyl transferase (AT II), and phosphatidylserine synthase from Retinas of chickens exposed to light or dark. Higher PAPase I and AT II activities were found in incubations of Retinal Ganglion Cells from animals exposed to light ; no increase was observed in preparations obtained from light-exposed animals reated with the c-fos antisense oligonucleotide. No light-dark differences were found in phosphatidylserine synthase activity. These findings support the idea that a coordinated photic regulation of PAPase I and AT II is taking place in Retina Ganglion Cells. This constitutes a reasonable mechanism to obtain an overall increased synthesis of glycerophospholipids in stimulated Cells that is mediated by the expression of Fos-like proteins.
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Light exposure stimulates the activity of ganglioside glycosyltransferases of Retina Ganglion Cells
Neurochemistry International, 1997Co-Authors: D. F. Bussolino, Mario E. Guido, Beatriz L. CaputtoAbstract:Abstract In chicks submitted to light stimulation, the synthesis of gangliosides of the Retina Ganglion Cell increases with respect to chicks maintained in the dark. In an attempt to elucidate if the activation of glycosyltransferases participates in the establishment of these light-dark differences detected in vivo, we examined the activity of a key ganglioside glycosyltransferase, the GalNAc-T (N-acetylgalactosaminyltransferase) that converts GM3 to GM2, in the Retina Ganglion Cells isolated from light and dark exposed chicks. We found that GalNAc-T and other glycosyltransferases are active in these Ganglion Cell preparations; the kinetic parameters for GalNAc-T were similar to those previously reported for chick Retina. The other glycosyltransferase activites assayed were the galactosyltransferase (Gal-T2) that converts GM2 to GM1 and the N-acetylneuraminyltransferase (Sialyl-T1) that converts lactosylceramide to GM3. The three glycosyltransferase activities were higher in the Ganglion Cell preparations obtained from chicks exposed to light compared to those maintained in the dark. For the GalNAc-T activity, the differences disappear when the Cell preparations are sonicated or if the assays are carried out in the presence of detergents or if the end product of the reaction is added to the incubates. The results indicate that the activation of the glycosyltransferases is part of the phenomenon required for Cells to achieve the precise rate of synthesis of gangliosides needed in vivo. © 1997 Elsevier Science Ltd
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Labeling of Retina and optic tectum phospholipids in chickens exposed to light or dark.
Journal of Neurochemistry, 1990Co-Authors: Mario E. Guido, Beatriz L. CaputtoAbstract:: The labeling of Retina Ganglion Cell and optic tectum phospholipids was determined in chickens given an intraocular injection of 32P and then either exposed to light or maintained in the dark. Significantly higher labeling was found in the optic tectum phospholipids of light-exposed compared with dark-maintained animals after 3-24 h of labeling. In the Ganglion Cells, the labeling of phospholipids increased in dark with respect to light at 15 and 30 min of labeling; from 60 min to 24 h, the labeling of phospholipids was significantly higher in light with respect to dark, even if the precursor pool showed a higher labeling in dark at all times studied. When labeling was allowed to proceed in the dark for 30 min and then half of the animals were exposed to light for 15 min, the labeling of Ganglion Cell phospholipids of light-exposed animals was significantly higher than those of animals kept in the dark. No individual phospholipid accounted for the differences observed in the labeling of the total phospholipid pool. These results are interpreted as an increase in the biosynthesis of phospholipids in the Ganglion Cell somas in light with respect to dark.