bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Influence of Magnesium lons on the NMDA Mediated Responses of Ventral Rhythmic Neurons in the Spinal Cord of Xenopus Embryos
Authors: Soffe S. R. , Roberts Alan 
Published: April 2006

Abstract Xenopus embryos immobilized in tubocurarine respond to natural skin stimulation with fictive swimming. This can also occur in saline without Mg2+ and is blocked by NMDA antagonists. Ventral spinal cord neurons which are rhythmically active during swimming are depolarized by bath applied N‐methyl‐D‐aspartate (NMDA) (in 1 μM tetrodotoxin (TTX) to block indirect effects). By using current clamp techniques this depolarization is shown to be partially blocked by 0.5 and 1 mM Mg2+ in a voltage‐dependent manner similar to that described in cultured neurons.Mg2+ partially and reversibly reduces the slow NMDA‐mediated component of excitatory post‐synaptic potentials (EPSPs) in ventral neurons. However, in 1 mM Mg2+ fictive swimming can still be evoked by natural stimulation. The frequency of swimming is slightly lower than in nominally 0 mM Mg2+, but the pattern of ventral root activity and synaptic drive to ventral neurons seems little affected. Fictive swimming can also be induced by applying NMDA to spinal preparations. In 0 mM Mg2+, such rhythmic activity is unstable and transient over a narrow NMDA concentration range. In 0.5 mM Mg2+, continuous rhythmic activity is induced over a wide range of NMDA concentrations. Lower spinal preparations need higher NMDA concentrations to induce activity.We conclude that the neurons rhythmically active in swimming have NMDA receptor channels which show a voltage dependent block in the presence of Mg2+. However, while Mg2+ exerts a powerful stabilizing influence on rhythmic activity induced in spinal embryos by exogenous NMDA, its influence on ‘naturally’ evoked fictive swimming is less clear. The fictive swimming machinery in the brain and spinal cord can produce stable swimming with or without Mg2+ induced voltage dependency of the NMDA channels.
Localization and Quantitative Autoradiography of Glutamatergic Ligand Binding Sites in Chick Brain
Authors: Henley Jeremy M. , Moratallo Rosario , Hunt Stephen P. , Barnard Eric A. 
Published: April 2006

AbstractThe anatomical localization of glutamate receptor subtype‐selective ligand binding sites was investigated in 1‐day‐old chick brain using quantitative autoradiography. Under the conditions used, the regional distributions of [3H]glutamate, [3H]AMPA (a selective quisqualate receptor ligand) and [3H]kainate binding sites are manifestly different. [3H]L‐glutamate binding is densely localized in the telencephalon, particularly in the neostriatum (2.8 pmol/mg protein). In addition, [3H]L‐glutamate labels the thalamus, the nucleus mesencephalicus lateralis pars dorsalis, the superficial layers of the optic tectum and the molecular layer of the cerebellum. [3H]AMPA binding sites are most densely localized in the hippocampus (0.90 pmol/mg protein), with an otherwise relatively uniform distribution of binding within the telencephalon. [3H]AMPA also labels the striatum griseum et fibrosum superficiale of the optic tectum and the molecular layer of the cerebellum. [3H]Kainate binding sites are extremely densely packed in the molecular layer of the cerebellum (10 pmol/mg protein). Other regions of [3H]kainate binding include the hyperstriatum and the thalamus. The binding of the NMDA receptor channel blocker [3H]MK‐801 is increased in the presence of 1 mM L‐glutamate. [3H]MK‐801 binding is generally widespread in the telencephalon but is notably absent from the ectostriatum. No evidence of [3H]MK‐801 binding sites was detected in the cerebellum, even in the presence of 1 mM L‐glutamate. The relatively high densities and the well‐defined localizations of the glutamate receptor subtype binding sites suggest that chick brain provides a useful system for the further study of excitatory amino acid receptors.
Omissions of Auditory Stimuli May Activate Frontal Cortex
Authors: Joutsiniemi S.‐L. , Hari R. 
Published: April 2006

AbstractWe measured, with a 7 channel SQUID gradiometer, cerebral magnetic responses, time‐locked to unpredictable and infrequent stimulus omissions (10% of stimuli) in an otherwise regular sequence of short tones, repeated once every 510 ms. In 10 out of 12 subjects broad responses with multiple peaks and with wide interindividual variability were detected. Attention clearly increased the observed signals. The magnetic field patterns evoked by stimulus omissions could be explained by single current dipoles, whose locations agree with activation of the posterolateral frontal cortex.
Roles of Glycinergic Inhibition and N‐Methyl‐D‐Aspartate Receptor Mediated Excitation in the Locomotor Rhythmicity of One Half of the Xenopus Embryo Central Nervous System
Authors: Soffe S. R. 
Published: April 2006

AbstractRecent investigations into the neural basis for swimming in Xenopus embryos have pointed to central roles played by N‐methyl‐D‐aspartate (NMDA) receptor‐mediated excitation acting within and glycinergic reciprocal inhibition acting between motor systems for the muscular antagonists on the two sides of the CNS. A ‘reduced’ preparation consisting of only one half of the CNS divided sagittally along its midline is used here to examine the basis for rhythmicity within each side in the absence of reciprocal connections. Divided preparations transected rostrally at levels between the otic capsule and the obex can all generate a rhythmic pattern of motor discharge similar to that which underlies swimming. All rhythm generation is blocked by the NMDA antagonist (+/ ‐)‐2‐amino‐5‐phosphonovaleric acid (APS) at 20 μM. However, neither glycinergic nor GABAergic inhibition is required for a basic rhythmicity since some rhythm persists in the presence of 10 μM strychnine and 50 μM bicuculline, though it is no longer sustained. In the divided spinal cord alone, rhythm generation requires extracellular Mg2+. If the most caudal segment of the divided hindbrain is left attached, extracellular Mg2+ is required only if strychnine is present. If more of the hindbrain is included, extracellular Mg2+ is no longer necessary for rhythm generation even in the presence of strychnine.It seems that rhythm generation by a single side of the spinal cord requires NMDA receptor‐mediated excitation together with the voltage dependency conferred on it by extracellular Mg2+, but not inhibition in order to occur. As more of the hindbrain is left attached, the requirement for extracellular Mg2+ becomes progressively less strong. For sustained rhythm generation, one side of the CMS requires both excitation and glycinergic inhibition.
Anatomical and Physiological Properties of GABAergic Neurotransmission in Organotypic Slice Cultures of Rat Hippocampus
Authors: Streit Peter , Thompson Scott M. , Gähwiler Beat H. 
Published: April 2006

AbstractThe anatomical and physiological properties of GABAergic inhibitory neurotransmission were investigated in organotypic slice cultures of rat hippocampus. Interneurons and terminal‐like elements containing GABA‐like immunoreactivity were numerous in tissue kept for 13–26 days in culture and showed a similar morphology and distribution to those known from investigations on the hippocampal formation in situ. Furthermore, after 8–30 days in culture, spontaneous and evoked IPSPs were observed in all CA3 pyramidal cells tested, resulting from an increase in chloride conductance, and were shown to be mediated by activation of GABA receptors. No functional decrement in the efficacy of GABAergic inhibitory synaptic transmission following chronic isolation and long‐term maintenance in vitro was noticed. In particular, neither the magnitude of the synaptic conductance underlying the inhibitory postsynaptic currents nor its reversal potential varied with time in culture. Taken together, the present physiological and immunohistochemical data show that GABAergic inhibition is well expressed in organotypic hippocampal slice cultures and is maintained over periods of at least 4 weeks in vitro.
Ultrastructural Characterization of Adrenocorticotrope Hormone (ACTH) Immunoreactive Fibres in the Mesencephalic Central Grey Substance of the Rat
Authors: Buma Pieter , Veening Jan , Nieuwenhuys Rudolf 
Published: April 2006

AbstractThe fine structural localization of fibres immunoreactive for the adrenocorticotrope hormone (ACTH) was studied in the mesencephalic central grey substance (MCG) of the male Wistar rat. Light microscopically, varicose ACTH‐immunoreactive fibres were found throughout the MCG in a dorsal, lateral and ventral, periventricular position. Electron microscopically, the immunoreactivity was most prominent in the direct vicinity of electron‐dense secretory granules in axonal varicosities, and, although to a lower degree, around other cytoplasmic organelles such as electron‐lucent synaptic vesicles, mitochondria and microtubules. With serial section analysis two types of ACTH‐immunoreactive varicosity were discerned. The first type is large, contains many, small electron‐lucent synaptic vesicles, that are located in the vicinity of a morphologically well‐defined synaptic contact. In this type of varicosity, large dense‐core secretory granules are scarce. Immunoreactivity is low or absent, particularly near the active zone. The second type is strongly immunoreactive. It always contains many large, dense‐core secretory granules; electron‐lucent vesicles are rare. The smaller varicosities of this type never make synaptic contacts, but a few of the larger varicosities have synaptic contacts with dendrites of MCG cells.
Absence of Wallerian Degeneration does not Hinder Regeneration in Peripheral Nerve
Authors: Lunn E. R. , Perry V. H. , Brown M. C. , Rosen H. , Gordon S. 
Published: April 2006

AbstractWallerian degeneration of the distal stump of a severed peripheral nerve involves invasion by myelomonocytic cells, whose presence is necessary for destruction of myelin and for initiating mitosis in Schwann cells (Beuche and Friede, 1984). Degeneration of the distal ends of the axons themselves is assumed to occur by autolytic mechanisms. We describe a strain of mice (C57BL/6/Ola) in which leucocyte invasion is slow and sparse. In these mice, confirming Beuche and Friede, myelin removal is extremely slow. A new finding is that axon degeneration is also very slow. This is a consequence of lack of recruitment of myelomonocytic cells for if such recruitment is prevented in other mouse strains by a monoclonal antibody against the complement type 3 receptor (Rosen and Gordon, 1987) axon degeneration is again slowed. We have also, surprisingly, found that nerve regeneration in the C57BL/6/Ola mice is not impeded by the presence of largely intact axons in the distal stump and absence of recruited cells, myelin debris and the absence of Schwann cell mitosis.
Degenerative Changes in Forebrain Cholinergic Nuclei Correlate with Cognitive Impairments in Aged Rats
Authors: Fischer Walter , Gage Fred H. , Björklund Anders 
Published: April 2006

AbstractDegenerative changes in the forebrain cholinergic nuclei have been studied morphometrically in behaviourally characterized aged female Sprague‐Dawley rats. In all regions analysed (medial septum, diagonal band of Broca, nucleus basalis, and striatum) the acetylcholinesterase‐positive neurons were reduced in both size and number in the aged (24‐months‐old) rats as compared to the young (3‐months‐old) controls. The overall reduction in cell size amounted to between 20 and 30% and the overall reduction in cell number to between 27 and 45%. Impairment in learning and/or memory performance in the aged rats, as assessed in the Morris' water‐maze task, was significantly correlated with both cholinergic cell size and cell number in the medial septum, and with cholinergic cell number in the diagonal band of Broca and in the striatum. In the nucleus basalis there was a trend in the same direction but it did not reach significance. In contrast to these degenerative changes in the cell body regions, no significant differences in cortical or hippocampal choline acetyltransferase activity were detected biochemically between the young and the aged rats, and the enzyme activity levels did not correlate with the degree of behavioural impairment in the aged rats.The present results provide evidence that all major forebrain cholinergic cell groups undergo degenerative changes with age in the rat, and that the most severe changes are found in those rats which display the most profound spatial learning impairments. Despite the severe changes at the cell body level, however, the choline acetyltransferase activity in the cortical projection areas are affected only to a minor degree, perhaps as a result of functional compensatory changes at the terminal level.
The Topographic Organization and Axis of Projection within the Visual Sector of the Rabbit's Thalamic Reticular Nucleus
Authors: Crabtree John W. , Killackey Herbert P. 
Published: April 2006

AbstractThe organization of the visual field representation within the thalamic reticular nucleus (TRN) of the rabbit was studied. Focal injections of horseradish peroxidase (HRP) and/or [3H]proline were made into visuocortical areas V1 and V2 and the dorsal lateral geniculate nucleus (dLGN). The resultant labelling in the thalamus was analysed.A single injection in V1 or V2 results in a single zone of terminal label within the TRN that is restricted to the dorsocaudal part of the sheet‐like nucleus. In comparisons of the zones of label following injections at two different cortical sites in V1, a medial to lateral shift in label across the thickness of the TRN sheet is accompanied by a medial to lateral shift in label in the dLGN; a dorsal to ventral shift in label within the plane of the TRN sheet is accompanied by a dorsal to ventral shift in label in the dLGN. Thus, like the dLGN the TRN receives a precise topographic projection from V1. In reconstructions from horizontal sections the zones of label within the TRN resemble ‘slabs’, which lie within the plane of the nucleus parallel to its borders. Thus, the slabs of visuocortical terminals and reticular dendrites are similarly oriented. As revealed by the orientation of the slabs, the lines of projection representing points in visual space are represented by the oblique rostrocaudal dimension of the TRN.Injections restricted to V1 produce terminal labelling that is confined to the outer two‐thirds of the TRN across its thickness, whilst those involving V2 result in terminal labelling within the inner one‐third of the nucleus. Thus, the adjacent cortical areas V1 and V2 project in a continuous fashion across the mediolateral dimension of the TRN. The organization of the map within the TRN, which was revealed by visuocortical injections, was confirmed by the pattern of retrograde labelling within the nucleus following geniculate injections of HRP.On the basis of these findings and those in other mammalian species, two major conclusions can be reached that alter our view of the TRN. First, rather than mapping onto the whole nucleus in a continuous fashion, the cortical projection to the TRN has significant discontinuities. Second, rather than integrating efferents from widespread cortical areas, the reticular dendrites are related to focal areas of cortex.
Noradrenaline‐Induced Inhibition of Voltage‐Sensitive Calcium Currents in NG108‐15 Hybrid Cells
Authors: Docherty R. J. , McFadzean I. 
Published: April 2006

AbstractThe effect of noradrenaline (NA) on voltage‐sensitive calcium currents in neuroblastoma × glioma hybrid (NG108‐15) cells has been studied using a whole‐cell clamp technique. NA inhibited calcium current. The EC50 for NA induced inhibition was 177 nM. The NA receptor involved had a similar pharmacological profile to α2 adrenoreceptors but did not respond to clonidine. NA inhibited calcium current by an amount which depended on both membrane potential and current amplitude. When current‐dependent inactivation of calcium current was maximal, NA was without effect. The data are consistent with a mechanism where NA enhances current‐dependent inactivation.
A Novel Type of Glial Cell Associated with Nodes of Ranvier in Rat Optic Nerve
Authors: Miller Robert H. , Fulton Barbara P. , Raff Martin C. 
Published: April 2006

AbstractUsing Golgi impregnation and intracellular injection of horseradish peroxidase, we show that the adult rat optic nerve contains two distinct types of astrocyte‐like glial cells: one has mainly radially oriented processes that terminate on blood vessels or on the pial surface; the other has mainly longitudinally oriented processes that associate with, and often terminate at, nodes of Ranvier, but do not end on blood vessels or the pial surface. The sequence of appearance of the two types of glial cells in the developing nerve, taken together with previous immunocytochemical findings, suggests that these cells may correspond to the two types of astrocytes previously described in cultures of perinatal optic nerve cells—those with mainly radially oriented processes corresponding to type‐1 astrocytes and those with mainly longitudinally oriented processes corresponding to type‐2 astrocytes. To our knowledge, this is the first description of a class of central nervous system (CNS) glial cell whose processes are primarily associated with nodes of Ranvier.
Expansion of the Central Hindpaw Representation Following Fetal Forelimb Removal in the Rat
Authors: Killackey Herbert P. , Dawson Douglas R. 
Published: April 2006

AbstractWe provide evidence that prenatal removal of a rat forelimb results in both a disruption of the anatomical representation which would normally correspond to the forepaw and in an enlargement of the adjacent hindpaw representation in the brainstem and cortex. This enlargement, which in some cases is as much as 100%, only occurs following complete forelimb amputation on embryonic day 17 (E17) or earlier. This coincides with the age at which forepaw afferents first arrive in the brainstem, suggesting to us that the expansion is permitted in part because ingrowing hindpaw afferents are in the presence of cuneate cells which have never been previously innervated; in animals older than E17, the expansion is prohibited by either an intrinsic age‐dependent change in the cuneate cells, or a change imposed upon them by forelimb afferents.The number of cells in dorsal root ganglia subserving the expanded hindpaw areas does not differ from normal suggesting that the expansion of hindpaw territory within the brainstem reflects an increased terminal arborization by a normal complement of primary hindpaw afferents.We interpret the cortical enlargement to be an upstream reflection of the brainstem events. In cortex, the enlargement seems to result from an invasion of the dysgranular cortex by thalamic afferents arising from the ventral posterior nucleus.
Involvement of D1 and D2 Dopamine Receptors in the Control of Horizontal Cell Electrical Coupling in the Turtle Retina
Authors: Piccolino M. , Demontis G. , Witkovsky P. , Strettoi E. , Cappagli G. C. , Porceddu M. L. , De Montis M. G. , Pepitoni S. , Biggio G. , Meller E. , Bohmaker K. 
Published: April 2006

AbstractWe studied the actions of D1 and D2 dopamine agonists and antagonists on the coupling of horizontal cell axons in the turtle retina by a combinationn of pharmacological and electrophysiological methods. Both D1 and D2 receptors were identified in membrane fractions by radioligand binding using [3H]‐SCH 23390 and [3H]‐spiperone, respectively. The KD of both receptor classes were identical (0.21 nM) but D1 receptor density exceeded that of D2 receptors by more than four‐fold. D1 agonists increased the activity of adenylate cyclase in a dose‐dependent manner, whereas D2 agonists were without significant effect by themselves, nor did D2 antagonists block the D1‐mediated increase in adenylate cyclase activity. Intracellular recordings and Lucifer Yellow dye injections were used to characterize the modifications of the receptive field profile of horizontal cell axons (H1AT) exposed to different pharmacological agents. Dopamine or D1 agonists (0.05–10 μM) induced a marked constriction of the H1AT receptive field, whereas D2 agonists elicited a small expansion of the receptive field. However, in the presence of a D1 antagonist, as well as IBMX to inhibit phosphodiesterase, D2 agonists (10–70 μM) induced a marked increase in the receptive field profile. These results indicate that both D1 and D2 dopamine receptors play a role in shaping the receptive field profile of the horizontal cell axon terminal in the turtle retina.
The Role of Horizontal Connections in Generating Long Receptive Fields in the Cat Visual Cortex
Authors: Bolz Jürgen , Gilbert Charles D. 
Published: April 2006

AbstractThe cells in the primary visual cortex possess numerous functional properties that are more complex and varied than those seen in the cortical input. These properties result from the network of intrinsic cortical connections running across the cortical layers and between cortical columns. In the current study we relate the long receptive fields that are characteristic of layer 6 cells to the input that these cells receive from layer 5. The axons of layer 5 pyramidal cells project over long distances within layer 6, enabling layer 6 cells to collect input from regions of cortex representing large parts of the visual field. When layer 5 was locally inactivated by injection of the inhibitory transmitter GABA, layer 6 cells lost sensitivity over the portion of their receptive fields corresponding to the inactivated region of layer 5. This suggests that the extensive convergence in the projection from layer 5 to layer 6 is responsible for generating the long receptive fields characteristic of the layer 6 cells.
Postnatal Development of Protein Kinase C‐like Immunoreactivity in the Cat Visual Cortex
Authors: Stichel Christine C. , Singer Wolf 
Published: April 2006

AbstractThe postnatal development of protein kinase C isozymes II and III (PkCII/III) was investigted in the cat visual cortex by applying immunohistochemical methods with a monoclonal antibody against PkC(II/III).PkC(II/III)‐like immunoreactivity was found in astrocytes and neurons. All astrocytes but only a few of the immunoreactive neurons were homogeneously labelled. The majority of the latter exhibited a punctate distribution of reaction product. The staining pattern of neurons and glial cells showed developmental changes until at least 18 months of age. These were characterized by (1) a gradual increase of immunolabelled astrocytes, (2) an abrupt appearance of immunopositive neurons at 4 weeks of age, (3) an aggregation of immunolabelled neurons in a well‐delineated band in lower layer IV between 4 weeks and 12 months of age, and (4) a decrease in number of PkC(II/III)‐positive neurons after 12 months of age.These developmental changes in the expression of PkC(II/III)‐like immunoreactivity correlate well with the time course and the laminar selectivity of experience‐dependent malleability. Moreover, they correspond closely to changes in several systems that contribute to PkC‐activation and are thought to be involved in use‐dependent neuronal plasticity. Thus, we consider these results as compatible with the hypothesis that the PkC isozymes II and III participate in cellular mechanisms underlying use‐dependent plasticity.