bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Isolation and Identification of Spinal Neurons That Control Movement in the Xenopus Embryo
Authors: Dale Nicholas 
Published: April 2006

AbstractA procedure for isolating spinal neurons of the Xenopus embryo has been devised. Using a variety of methods four of the eight previously described categories of neuron can be distinguished in vitro. Firstly, since many anatomical features of the neurons survived dissociation, sensory neurons and glycinergic inhibitory interneurons could be identified after isolation using anatomical criteria. Secondly, by selective labelling of the neurons in the intact spinal cord with fluorescein‐conjugated dextran amines prior to dissociation, three classes of isolated neuron could be identified: motoneurons, putative excitatory interneurons and, once again, inhibitory interneurons. The identity of the inhibitory interneurons has been confirmed using glycine immunocytochemistry. The physiological properties of the isolated neurons were similar to those of their in vivo counterparts. The dissociated neurons exhibited strong membrane accommodation and outward rectification, both of which could be blocked by the injection of Cs+ ions. The neurons also retained their receptors for the agonists N‐methyl‐d‐aspartate, kainate, quisqualate, glycine and GABA. Both the membrane properties and pharmacological sensitivity of the isolated neurons therefore appeared to be unaltered by the dissociation procedure. Thus the four classes of neuron from the Xenopus embryonic nervous system that can be identified after isolation constitute the basis for a valid model for detailed study of how the properties of individual neurons contribute to the functioning of the circuitry that underlies locomotor pattern generation in vertebrates.
An Organotypic Spinal Cord‐Dorsal Root Ganglion‐Skeletal Muscle Coculture of Embryonic Rat. I. The Morphological Correlates of the Spinal Reflex Arc
Authors: Spenger Christian , Braschler Urs Felix , Streit Jürg , Lüscher Hans‐Rudolf 
Published: April 2006

AbstractThe cytoarchitecture of a spinal cord‐dorsal root ganglion ‐ skeletal muscle tissue coculture system was investigated at the level of the light microscope using a number of different staining techniques. In these cultures central synapses between dorsal root ganglion (DRG) cells and interneurons in the ventral spinal cord and between DRG cells and motoneurons were visualized by parvalbumin immunostaining and by intracellular horseradish peroxidase (HRP) filling of DRG cells. Skeletal muscle fibres regenerated in vitro first into multinucleated myotubes, and around day 8 in vitro into well differentiated muscle fibres with regular cross‐striation. At the same time newly formed motor endplates could be visualized using acetylcholinesterase staining. The axons of motoneurons could be traced retrogradely by local application of HRP to the regenerated muscle fibres. The motor axons sometimes gave off collaterals reminiscent of Renshaw collaterals at about 300 μm from the axon hillock. Intracellular filling of motoneurons with HRP revealed that only a minority of the motoneurons within a culture had reached their appropriate target. Comparing the dendrograms of the motoneurons which had innervated muscles to those which had not suggested that motoneurons innervating muscle tissue had more complex dendritic trees and larger somata than those which did not innervate muscle tissue. Peripheral neurites of parvalbumin‐immunoreactive DRG cells coiling around regenerated muscle fibres could be demonstrated in these cultures. These probably correspond to that part of the sensory muscle spindle apparatus which developed in vivo. However, only a few of the several hundred DRG cells found in every culture were parvalbumin‐immunoreactive, suggesting that the actual number of la and II afferents within the population of DRG cells in culture is very small. This study demonstrates that all the neural elements necessary for the segmental spinal reflexes develop and can be maintained for several weeks in vitro.
An Organotypic Spinal Cord‐Dorsal Root Ganglion‐Skeletal Muscle Coculture of Embryonic Rat. II. Functional Evidence for the Formation of Spinal Reflex Arcs In Vitro
Authors: Streit Jürg , Spenger Christian , Lüscher Hans‐Rudolf 
Published: April 2006

AbstractElectrical properties of motoneurons, muscle fibres and dorsal root ganglion (DRG) cells were studied in an organotypic coculture of embryonic rat spinal cord, dorsal root ganglia and skeletal muscle. The motoneurons were identified by their morphology and position in culture. Their size and input conductance were significantly larger than those of spinal interneurons. Intracellular current injection evoked action potentials in all motoneurons, but only evoked stable repetitive firing patterns in some. Excitability was correlated to somatic size and the rate of spontaneous excitatory input. It is suggested that the somatic growth and the increase in excitability is regulated by the excitatory afferents. The motoneurons showed spontaneous excitatory and inhibitory postsynaptic potentials and action potentials which disappeared with the application of various agents known to inhibit excitability or excitatory synaptic transmission. Excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs respectively) were distinguished by their shape, reversal potential and pharmacology. IPSPs could be depolarizing or hyperpolarizing in different cells. A higher percentage of cells with hyperpolarizing IPSPs was found in older cultures and in the presence of skeletal muscle, suggesting a reversal of the polarity of IPSPs with development. The spontaneous muscle contractions observed in the cultures could be due either to innervation, spontaneous oscillations of the membrane potential, or electrical coupling between neighbouring fibres. A small percentage of DRG cells showed spontaneous action potentials, all of which were found in cultures with spontaneous muscle contractions. The electrical stimulation of DRG afferents evoked mono‐ and polysynaptic EPSPs in motoneurons, endplate potentials and muscle contractions. The stimulation of the ventral horns evoked endplate potentials and muscle contractions via mono‐ or polysynaptic pathways. Together these results indicate that appropriate and functional contacts were established in the culture between myotubes and DRG cells, between DRG cells and motoneurons, and between motoneurons and muscle fibres.
Morphological Classification of Bipolar Cells of the Primate Retina
Authors: Boycott B. B. , Wässle H. 
Published: April 2006

AbstractBipolar cells were studied in Golgi‐Colonnier‐stained whole mounts of macaque monkey retinae. A piece of retina, at 6–7 mm eccentricity, was particularly well stained for the analysis of the different bipolar cell types. Many midget bipolar cells were encountered and the dichotomy into flat and invaginating midget bipolars was confirmed. Six types of diffuse cone bipolar cell are distinguished. They differ in their dendritic branching pattern, in the number of cones contacted–usually between five and ten–and in the shape and branching level of their axons. The size, shape and stratification of the axons were found to be the most reliable distinguishing features for classifying diffuse cone bipolar cells. The stratification of the axons in the inner plexiform layer (IPL), whether closer to the amacrine or ganglion cells, was used to name diffuse cone bipolar cells in the order DB1 to DB6. Blue cone and rod bipolar cells were confirmed as distinct types. Axon terminals of diffuse cone bipolars were found to tile their sublamina of the IPL in a territorial manner. From this the density of each type could be estimated, and it is shown that a single cone is likely to be in contact with as many as 15 individual diffuse bipolar cells, as well as two midget bipolars. The diffuse bipolar cells observed contact all the cone pedicles in their dendritic fields. It is, therefore, unlikely that they carry a chromatic signal into the inner retina. The presence of many midget bipolar cells, which make contact with one cone pedicle only, suggests that midget bipolars provide chromatic input to ganglion cells in peripheral retina as well as in the fovea. The data show that the P‐ and M‐cell pathways of the primate visual system are, to a significant extent, already anatomically discrete at the photoreceptor synapse.
The Organization of Projections from Subdivisions of the Auditory Cortex and Thalamus to the Auditory Sector of the Thalamic Reticular Nucleus in Galago
Authors: Conley Michael , Kupersmith Andrew C. , Diamond Irving T. 
Published: April 2006

AbstractAnterograde and retrograde transport techniques were used to study the connexions between different subdivisions of the auditory cortex and thalamus with the thalamic reticular nucleus in the prosimian, Galago. In particular, the goal was to determine whether the primary auditory nucleus, GMv, and its cortical target, area I of the auditory cortex (A I), project to a different region of the auditory sector of the reticular nucleus from the secondary auditory nuclei, GMmc and Po and their cortical targets outside A I. The results show that the projections to and from the auditory sector are indeed segregated: injections of wheatgerm agglutinin‐conjugated horseradish peroxidase into either GMmc or Po labelled cells and terminals along the medial, lateral and ventral borders of the auditory sector, forming a U‐shaped pattern. Projections from area II of the auditory cortex produced almost an identical pattern of the terminal labelling in the auditory sector. In contrast, injections into GMv‐labelled cells and terminals in the centre region of the auditory sector, in the ‘interior’ of the U‐shaped region. Projections from A I were distributed to both the U‐shaped border region and the central core of the auditory sector probably because A I received projections from GMmc, Po and GMv. The significance of these results depends on a comparison between the auditory and visual sectors of the reticular nucleus. Both sectors are divided into tiers or subsectors–one related to the primary relay nucleus, i.e. GLd or GMv, and the other related to the secondary relay nuclei, i.e. pulvinar nucleus, GMmc, Po, etc.
Axons Sprout and Microtubules Increase After Local Inhibition of RNA Synthesis, and Microtubules Decrease after Inhibition of Protein Synthesis: A Morphometric Study of Rat Sural Nerves
Authors: Bustos Jorge , Vial Juan D. , Faúndez Victor , Alvarez Jaime 
Published: April 2006

AbstractDrugs that inhibit RNA or protein synthesis are known to affect some functional properties of axons. In this context, we studied the ultrastructural effects of actinomycin‐D, an inhibitor of RNA synthesis, and cycloheximide and emetine, inhibitors of protein synthesis, in rat sural nerves. A silicone sleeve (4 mm long) loaded with drug was placed around the nerves and left for about a week. The ultrastructural alterations of axons and Schwann cells progressed over this period. After cycloheximide and emetine, the cytoplasm of Schwann cells was enlarged and the rough endoplasmic reticulum was prominent. After actinomycin‐D, the Schwann cells reached the stage of lysis. Nonmedullated were more affected than myelinated axons. After cycloheximide and emetine, the axoplasmic matrix decreased substantially but reversibly. Microtubules of nonmedullated fibres decreased by about 50%. Actinomycin‐D determined sprouting of axons and a rise of axonal microtubules; in nonmedullated axons, the normal inverse correlation between microtubular density and calibre gave way to a high and constant density for all axonal sizes. A few millimetres proximal and distal to the sleeve, the nerve tissue and the axonal microtubular content were close to normal, i.e. the effects of drugs were local. Present results suggest that the local turnover of amino acids in the axon is necessary to maintain the integrity of microtubule and neurofilament proteins. We propose that the Schwann cell down‐regulates the axonal cytomatrix.
Differential Distribution of Tau Proteins in Developing Cat Cerebral Cortex and Corpus Callosum
Authors: Riederer Beat M. , Innocenti Giorgio M. 
Published: April 2006

AbstractDuring the postnatal development of cat visual cortex and corpus callosum the molecular composition of tau proteins varied with age. In both structures, they changed between postnatal days 19 and 39 from a set of two juvenile forms to a set of at least two adult variants with higher molecular weights. During the first postnatal week, tau proteins were detectable with TAU‐1 antibody in axons of corpus callosum and visual cortex, and in some perikarya and dendrites in the visual cortex. At later ages, tau proteins were located exclusively within axons in all cortical layers and in the corpus callosum. Dephosphorylation of postnatal day 11 cortical tissue by alkaline phosphatase strongly increased tau protein immunoreactivity on Western blots and in numerous perikarya and dendrites in all cortical layers, in sections, suggesting that some tau forms had been unmasked. During postnatal development the intensity of this phosphate‐dependent somatodendritic staining decreased, but remained in a few neurons in cortical layers II and III. On blots, the immunoreactivity of adult tau to TAU‐1 was only marginally increased by dephosphorylation. Other tau antibodies (TAU‐2, B19 and BR133) recognized two juvenile and two adult cat tau proteins on blots, and localized tau in axons or perikarya and dendrites in tissue untreated with alkaline phosphatase. Tau proteins in mature tissue were soluble and not associated with detergent‐resistant structures. Furthermore, dephosphorylation by alkaline phosphatase resulted in the appearance of more tau proteins in soluble fractions. Therefore tau proteins seem to alter their degree of phosphorylation during development. This could affect microtubule stability as well as influence axonal and dendritic differentiation.
Cytotoxic Effect of Brain Macrophages on Developing Neurons
Authors: Théry Clotilde , Chamak Brigitte , Mallat Michel 
Published: April 2006

AbstractBrain macrophages are transiently present in different regions of the central nervous system during development or in the course of tissue remodelling following various types of injuries. To investigate the influence of these phagocytes on neuronal growth and survival, brain macrophages stemming from the cerebral cortex of rat embryos were added to neuronal primary cultures. A neurotoxic effect of brain macrophages was demonstrated by the reduction of the number of neurons bearing neurites within two days of contact between the two cell types. Neuronal death and phagocytosis were also directly observed in video recordings of living cultures. This toxicity involved the production by brain macrophages of reactive oxygen intermediates, as shown by the protective effect of catalase, a scavenger of H2O2. In addition, the respiratory bursts of brain macrophages were stimulated in the presence of neurons. These results suggest that brain macrophages could favour the appearance of neuroregressive events which occur either during neurogenesis or in neurodegenerative diseases, implying intracerebral recruitment of mononuclear phagocytes.
Facilitation and Delay Sensitivity of Auditory Cortex Neurons in CF‐FM Bats, Rhinolophus rouxi and Pteronotus p.parnellii
Authors: Schuller G. , O'Neill W. E. , Radtke‐Schuller S. 
Published: April 2006

AbstractResponses of auditory neurons to complex stimuli were recorded in the dorsal belt region of the auditory cortex of two taxonomically unrelated bat species, Rhinolophus rouxi and Pteronotus parnellii parnellii, both showing Doppler shift compensation behaviour. As in P.p.parnellii (Suga et al., J. Neurophysiol, 49, 1573–1626, 1983), cortical neurons of R. rouxi show facilitated responses to pairs of pure tones or frequency modulations. Best frequencies for the two components lie near the first and second harmonic of the echolocation call but are in most cases not harmonically related. Neurons facilitated by pairs of pure tones show little dependence on the delay between the stimuli, whereas pairs of frequency modulations evoke best facilitated responses at distinct best delays between 1 and 10 ms. Facilitated neurons are found in distinct portions of the dorsal cortical belt region, with a segregation of facilitated neurons responding to pure tones and to frequency modulations. Non‐facilitated neurons are found throughout the field. Neurons are topographically aligned with increasing best delays along a rostrocaudal axis. The best delays between 2 and 4 ms are largely overrepresented numerically, and occupy ˜56% of the cortical area containing facilitated neurons. A functional interpretation of the large overrepresentation of best delays ˜3ms is proposed. Facilitated neurons are located almost entirely within layer V of the dorsal field.
The Gene for Ciliary Neurotrophic Factor (CNTF) Maps to Murine Chromosome 19 and its Expression is Not Affected in the Hereditary Motoneuron Disease ‘Wobbler’ of the Mouse
Authors: Kaupmann Klemens , Sendtner Michael , Stöckli Kurt A. , Jockusch Harald 
Published: April 2006

AbstractThe cDNA for ciliary neurotrophic factor (CNTF), a polypeptide involved in the survival of motoneurons in mammals, has recently been cloned (Stöckli et al., Nature, 342, 920–923, 1989; Lin et al Science, 246, 1023–1025, 1989). We have now localized the corresponding gene Cntf to chromosome 19 in the mouse, using an interspecific cross between Mus spretus and Mus musculus domesticus. The latter was carrying the gene wobbler (wr) for spinal muscular atrophy. DNA was prepared from backcross individuals and typed for the segregation of species‐specific Cntf restriction fragments in relation to DNA markers of known chromosomal location. The M.spretus allele of Cntf cosegregated with chromosome 19 markers and mapped closely to Ly‐1 to a region of mouse chromosome 19 with conserved synteny to human chromosome 11q. Cntf is not linked to wr, and the expression of CNTF mRNA and protein appears close to normal in facial and sciatic nerves of affected (wr/wr) mice, suggesting that motoneuron degeneration of wobbler mice has its origin in defects other than reduced CNTF expression.
Monosynaptic Interjoint Reflexes and their Central Modulation During Fictive Locomotion in Crayfish
Authors: El Manira A. , DiCaprio R. A. , Cattaert D. , Clarac F. 
Published: April 2006

AbstractAn in vitro preparation of the crayfish nervous system has been utilized to study an interjoint reflex pathway and its variability during rhythmic locomotor activity. The coxo‐basal chordotonal organ (CBCO) is a joint stretch receptor spanning the second joint of walking legs in crayfish, where it encodes joint movements and position. Mechanical stimulation (stretch and release) of the CBCO and electrical stimulation of the CBCO nerve elicits reflex responses in promotor and remotor motor neurons innervating muscles moving the basal thoraco‐coxal (TC) leg joint. Promotor and remotor motor neurons receive monosynaptic excitatory inputs from at least four CBCO afferents, including both stretch‐ and release‐sensitive CBCO afferents. In a tonic preparation, in which there is no tendency to produce alternating bursts of activity in antagonistic motor neurons, the reflex responses were evoked during each cycle of imposed movement. However, when the preparation became rhythmic and produced bouts of fictive locomotion, the reflex responses were unstable and their gain was phasically modulated. Paired recordings indicate that such a modulation of the monosynaptic interjoint reflex could be due to both a phasic change in the excitability of the motor neurons and presynaptic inhibition that reduces the excitatory input from CBCO primary afferents.
Aspartate‐ and Glutamate‐like Immunoreactivities in Rat Hippocampal Slices: Depolarization‐induced Redistribution and Effects of Precursors
Authors: Gundersen V. , Ottersen O. P. , Storm‐Mathisen J. 
Published: April 2006

AbstractThe light microscopic localization of aspartate‐like immunoreactivity (Asp‐LI) was compared to that of glutamate‐like immunoreactivity (Glu‐LI) in hippocampal slices by means of specific polyclonal antibodies recognizing the amino acids fixed by glutaraldehyde. After incubation in Krebs' solution with normal (5 mM) or depolarizing concentrations of K+, and various additives, the slices were fixed with glutaraldehyde, resectioned and processed according to the peroxidase ‐ antiperoxidase procedure. At 5 mM K+, Glu‐LI was localized in nerve‐terminal like dots with a conspicuous laminar distribution, the highest Glu‐LI concentrations coinciding with the terminal fields of major excitatory pathways thought to use glutamate or aspartate as transmitters. The localization of Asp‐LI showed some similarity to that of Glu‐LI, but the laminar distribution was less differentiated and the immunoreactivity was much weaker. At 40 and 55 mM K+ the nerve terminal localizations of Glu‐LI and Asp‐LI were strongly reduced. Concomitantly, both immunoreactivities appeared in astroglial cells. These changes were Ca2+‐dependent. The nerve ending staining patterns of Asp‐LI and Glu‐LI could be sustained during depolarization if the medium was supplemented with glutamine (0.5 mM). Under these conditions Asp‐LI became more intense and its distribution approached that of Glu‐LI. This suggests that, when stimulated, some nerve endings can increase their reservoir of releasable aspartate. The presence of glutamine during depolarization strongly reduced glial Asp‐LI and Glu‐LI, possibly due to its providing nitrogen for conversion of glutamate to glutamine. α‐Ketoglutarate, another glia‐derived precursor of neuronal glutamate, was virtually ineffective in supporting Glu‐LI and Asp‐LI in nerve endings, and did not suppress Glu‐LI or Asp‐LI in glia. Our findings provide morphological support for the view that excitatory nerve endings under certain conditions can contain high levels of both aspartate and glutamate (possibly in the same terminals), and that aspartate as well as glutamate can be released synaptically. Further, they underline the importance of the glial supply of the nerve endings with precursor glutamine, which allows them to build up and sustain high concentrations of transmitter amino acids during release.
Localization of Sequences Determining Cell Type Specificity and NGF Responsiveness in the Promoter Region of the Rat Choline Acetyltransferase Gene
Authors: Ibáñez Carlos F. , Persson Håkan 
Published: April 2006

AbstractA genomic clone containing 7 kb of 5’flanking sequences from the rat choline acetyltransferase (ChAT) gene was isolated and shown to contain a TATA box‐like sequence and several consensus binding sites for the transcription factor AP1. Two constructs containing 450 and 1450 base pairs (bp), respectively, of 5’flanking sequences promoted expression of a fused chloramphenicol acetyltransfersase (CAT) gene when transfected into fibroblast FR3T3, Sertoli TM4, phaeochromocytoma PC12 and cholinergic neuronal SN6 cell lines. In contrast, a longer construct containing 3850 bp of 5’flanking sequence allowed CAT activity only in the cholinergic cell line SN6. CAT activity with this construct was suppressed in the three other cell lines, indicating that the distal region of the ChAT promoter contains a cell type‐specific silencer‐like element that restricts ChAT gene expression to cholinergic cells. Treatment of PC12 cells with nerve growth factor (NGF) increased the promoter activity of the ‐450 and ‐1450 constructs approximately four‐fold and allowed promoter activity from the ‐3850 construct, indicating that elements involved in NGF responsiveness of the ChAT promoter are contained in the first 450 bp of upstream sequence. These results support a model in which gene transcription controlled by cell‐type specific regulatory elements contribute to the establishment, maintenance and plasticity of the cholinergic transmitter phenotype in the nervous system.