bluuebunny/crossref_metadata_2025 huggingface dataset:
Membrane Potential and Firing Rate in Cat Primary Visual Cortex
Authors: Carandini Matteo , Ferster David
Published: April 2018

We have investigated the relationship between membrane potential and firing rate in cat visual cortex and found that the spike threshold contributes substantially to the sharpness of orientation tuning. The half-width at half-height of the tuning of the spike responses was 23 ± 8°, compared with 38 ± 15° for the membrane potential responses. Direction selectivity was also greater in spike responses (direction index, 0.61 ± 0.35) than in membrane potential responses (0.28 ± 0.21).

Threshold also increased the distinction between simple and complex cells, which is commonly based on the linearity of the spike responses to drifting sinusoidal gratings. In many simple cells, such stimuli evoked substantial elevations in the mean potential, which are nonlinear. Being subthreshold, these elevations would be hard to detect in the firing rate responses. Moreover, just as simple cells displayed various degrees of nonlinearity, complex cells displayed various degrees of linearity.

We fitted the firing rates with a classic rectification model in which firing rate is zero at potentials below a threshold and grows linearly with the potential above threshold. When the model was applied to a low-pass-filtered version of the membrane potential (with spikes removed), the estimated values of threshold (−54.4 ± 1.4 mV) and linear gain (7.2 ± 0.6 spikes · sec−1 · mV−1) were similar across the population. The predicted firing rates matched the observed firing rates well and accounted for the sharpening of orientation tuning of the spike responses relative to that of the membrane potential.

As it was for stimulus orientation, threshold was also independent of stimulus contrast. The rectification model accounted for the dependence of spike responses on contrast and, because of a stimulus-induced tonic hyperpolarization, for the response adaptation induced by prolonged stimulation. Because gain and threshold are unaffected by visual stimulation and by adaptation, we suggest that they are constant under all conditions.
Heterogeneous Conductance Levels of Native AMPA Receptors
Authors: Smith T. Caitlin , Wang Lu-Yang , Howe James R.
Published: April 2018

The single-channel properties of AMPA receptors can affect information processing in neurons by influencing the amplitude and kinetics of synaptic currents, yet little is known about the unitary properties of native AMPA receptorsin situ. Using whole-cell and outside-out patch-clamp recordings from granule cells in acute cerebellar slices, we found that migrating granule cells begin to express AMPA receptors before they arrive in the internal granule cell layer and receive synaptic input. At saturating agonist concentrations, the open probability of channels in outside-out patches from migrating cells was very high, allowing us to identify patches that contained only one or two active channels. Analysis of the single-channel activity in these patches showed that individual AMPA receptors exhibit as many as four distinguishable conductance levels. The conductance levels observed varied substantially for different channels, although on average the values fell within the range of unitary conductances estimated previously for synaptic AMPA receptors. In contrast to patches from migrating granule cells, we rarely observed directly resolvable single-channel currents in patches excised from the somata of granule cells in the internal granular layer, even though these cells gave large AMPA receptor whole-cell currents. We did, however, detect AMPA receptors with apparent unitary conductances of <1 pS in patches from both migrating and mature granule cells. Our results suggest that granule cells express a heterogeneous population of AMPA receptors, a subset of which are segregated to postsynaptic sites after synaptogenesis.
Functional Correlation of GABAAReceptor α Subunits Expression with the Properties of IPSCs in the Developing Thalamus
Authors: Okada Masayoshi , Onodera Kayoko , Van Renterghem Catherine , Sieghart Werner , Takahashi Tomoyuki
Published: April 2018

GABAAreceptor α1 and α2 subunits are expressed differentially with ontogenic period in the brain, but their functional roles are not known. We have recorded GABAAreceptor-mediated IPSCs from laterodorsal (LD) thalamic relay neurons in slices of rat brain at various postnatal ages and found that decay times of evoked IPSCs and spontaneous miniature IPSCs undergo progressive shortening during the first postnatal month. With a similar time course, expression of transcripts and proteins of GABAAreceptor α2 subunit in LD thalamic region declined, being replaced by those of α1 subunit. To further address the causal relationship between α subunits and IPSC decay time kinetics, we have overexpressed GABAAreceptor α1 subunit together with green fluorescent protein in LD thalamic neurons in organotypic culture using recombinant Sindbis virus vectors. Miniature IPSCs recorded from the LD thalamic neurons overexpressed with α1 subunit had significantly faster decay time compared with control expressed with β-galactosidase. We conclude that the α2-to-α1 subunit switch underlies the developmental speeding in the decay time of GABAergic IPSCs.
Neural Cell Adhesion Molecule-Stimulated Neurite Outgrowth Depends on Activation of Protein Kinase C and the Ras–Mitogen-Activated Protein Kinase Pathway
Authors: Kolkova Kateryna , Novitskaya Vera , Pedersen Nina , Berezin Vladimir , Bock Elisabeth
Published: April 2018

The signal transduction pathways associated with neural cell adhesion molecule (NCAM)-induced neuritogenesis are only partially characterized. We here demonstrate that NCAM-induced neurite outgrowth depends on activation of p59fyn, focal adhesion kinase (FAK), phospholipase Cγ (PLCγ), protein kinase C (PKC), and the Ras–mitogen-activated protein (MAP) kinase pathway. This was done using a coculture system consisting of PC12-E2 cells grown on fibroblasts, with or without NCAM expression, allowing NCAM–NCAM interactions resulting in neurite outgrowth. PC12-E2 cells were transiently transfected with expression plasmids encoding constitutively active forms of Ras, Raf, MAP kinase kinases MEK1 and 2, dominant negative forms of Ras and Raf, and the FAK-related nonkinase. Alternatively, PC12-E2 cells were submitted to treatment with antibodies to the fibroblast growth factor (FGF) receptor, inhibitors of the nonreceptor tyrosine kinase p59fyn, PLC, PKC and MEK and an activator of PKC, phorbol-12-myristate-13-acetate (PMA). MEK2 transfection rescued cells treated with all inhibitors. The same was found for PMA treatment, except when cells concomitantly were treated with the MEK inhibitor. Arachidonic acid rescued cells treated with antibodies to the FGF receptor or the PLC inhibitor, but not cells in which the activity of PKC, p59fyn, FAK, Ras, or MEK was inhibited. Interaction of NCAM with a synthetic NCAM peptide ligand, known to induce neurite outgrowth, was shown to stimulate phosphorylation of the MAP kinases extracellular signal-regulated kinases ERK1 and ERK2. The MAP kinase activation was sustained, because ERK1 and ERK2 were phosphorylated in PC12-E2 cells and primary hippocampal neurons even after 24 hr of cultivation on NCAM-expressing fibroblasts. Based on these results, we propose a model of NCAM signaling involving two pathways: NCAM–Ras–MAP kinase and NCAM–FGF receptor–PLCγ–PKC, and we propose that PKC serves as the link between the two pathways activating Raf and thereby creating the sustained activity of the MAP kinases necessary for neuronal differentiation.
DM-GRASP Is Necessary for Nonradial Cell Migration during Chick Diencephalic Development
Authors: Heffron Daniel S. , Golden Jeffrey A.
Published: April 2018

Cell migration is fundamental to normal CNS development. Radial migration, along radial glial fibers, has been the principal pathway studied, however, nonradial or tangential cell migration has increasingly been identified at all levels of the CNS. Receptors, cell adhesion molecules, and extracellular matrix molecules have all been shown to participate in radial cell migration. In contrast, the molecular basis of nonradial cell migration has only recently begun to be elucidated. Using replication defective retroviral vectors we have determined the location and time when nonradial cell migration begins in the developing chick diencephalon. We have identified three molecules that are expressed in spatially and temporally restricted domains that are consistent with them playing a role in nonradial cell migration. One of these molecules, DM-GRASP, a transmembrane protein with five extracellular Ig domains, is expressed on the nonradially migrating cells in addition to axons. To test the hypothesis that DM-GRASP participates in guiding nonradial cell migration, we injected a replication-defective retroviral vector used for lineage tracing followed by a DM-GRASP blocking antibody. Embryos injected with the blocking antibody showed a near complete block in nonradial cell migration specifically where DM-GRASP is expressed. Furthermore, morphological analyses revealed disruption of the normal architecture of the diencephalon indicating nonradial cell migration is necessary for normal morphological development of the brain. Our data indicate that DM-GRASP is necessary for nonradial cell migration in the chick diencephalon and have provided a system to further explore the function of nonradial cell migration during CNS development.
Striatonigrostriatal Pathways in Primates Form an Ascending Spiral from the Shell to the Dorsolateral Striatum
Authors: Haber Suzanne N. , Fudge Julie L. , McFarland Nikolaus R.
Published: April 2018

Clinical manifestations in diseases affecting the dopamine system include deficits in emotional, cognitive, and motor function. Although the parallel organization of specific corticostriatal pathways is well documented, mechanisms by which dopamine might integrate information across different cortical/basal ganglia circuits are less well understood. We analyzed a collection of retrograde and anterograde tracing studies to understand how the striatonigrostriatal (SNS) subcircuit directs information flow between ventromedial (limbic), central (associative), and dorsolateral (motor) striatal regions. When viewed as a whole, the ventromedial striatum projects to a wide range of the dopamine cells and receives a relatively small dopamine input. In contrast, the dorsolateral striatum (DLS) receives input from a broad expanse of dopamine cells and has a confined input to the substantia nigra (SN). The central striatum (CS) receives input from and projects to a relatively wide range of the SN. The SNS projection from each striatal region contains three substantia nigra components: a dorsal group of nigrostriatal projecting cells, a central region containing both nigrostriatal projecting cells and its reciprocal striatonigral terminal fields, and a ventral region that receives a specific striatonigral projection but does not contain its reciprocal nigrostriatal projection. Examination of results from multiple tracing experiments simultaneously demonstrates an interface between different striatal regions via the midbrain dopamine cells that forms an ascending spiral between regions. The shell influences the core, the core influences the central striatum, and the central striatum influences the dorsolateral striatum. This anatomical arrangement creates a hierarchy of information flow and provides an anatomical basis for the limbic/cognitive/motor interface via the ventral midbrain.
Peripheral Odor Coding in the Rat and Frog: Quality and Intensity Specification
Authors: Duchamp-Viret Patricia , Duchamp André , Chaput Michel A.
Published: April 2018

In mammals, two recent studies have shown recently that one odor molecule can be recognized by several molecular olfactory receptors (ORs), and a single OR can recognize multiple odor molecules. In addition, one olfactory receptor neuron (ORN) may respond to different stimuli chosen as representative of distinct odor qualities. The aim of the present study was to analyze quality and intensity coding abilities of rat single ORNs, comparing them with previous extensive data gathered in the frog to get insight into the generality of olfactory coding mechanisms over vertebrates.

Response properties of 90 rat ORNs to different odors or to one odor at different concentrations were analyzed. In the rat and the frog, odor quality appears to be specified through the identity of activated ORNs.

However, rat ORNs have higher response thresholds. This lower sensitivity may be interpreted as an increase in selectivity of rat ORNs for low or medium odor intensities. In these conditions, the lower proportion of activated ORNs could be counterbalanced by their number, as well as by their higher glomerular convergence ratio in the olfactory bulb. From amphibians to mammals, the olfactory system appears to use universal mechanisms based on a combinatorial-coding mode that may allow quasi-infinite possibilities of adaptation to various olfactory environments.
Modest Neuropsychological Deficits Caused by Reduced Noradrenaline Metabolism in Mice Heterozygous for a Mutated Tyrosine Hydroxylase Gene
Authors: Kobayashi Kazuto , Noda Yukihiro , Matsushita Natsuki , Nishii Kazuhiro , Sawada Hirohide , Nagatsu Toshiharu , Nakahara Daiichiro , Fukabori Ryoji , Yasoshima Yasunobu , Yamamoto Takashi , Miura Masami , Kano Masanobu , Mamiya Takayoshi , Miyamoto Yoshiaki , Nabeshima Toshitaka
Published: April 2018

Tyrosine hydroxylase (TH) is the initial and rate-limiting enzyme for the biosynthesis of catecholamines that are considered to be involved in a variety of neuropsychiatric functions. Here, we report behavioral and neuropsychological deficits in mice carrying a single mutated allele of the TH gene in which TH activity in tissues is reduced to ∼40% of the wild-type activity. In the mice heterozygous for the TH mutation, noradrenaline accumulation in brain regions was moderately decreased to 73–80% of the wild-type value. Measurement of extracellular noradrenaline level in the frontal cortex by the microdialysis technique showed a reduction in high K+-evoked noradrenaline release in the mutants. The mutant mice displayed impairment in the water-finding task associated with latent learning performance. They also exhibited mild impairment in long-term memory formation in three distinct forms of associative learning, including active avoidance, cued fear conditioning, and conditioned taste aversion. These deficits were restored by the drug-induced stimulation of noradrenergic activity. In contrast, the spatial learning and hippocampal long-term potentiation were normal in the mutants. These results provide genetic evidence that the central noradrenaline system plays an important role in memory formation, particularly in the long-term memory of conditioned learning.
The Evolution of Lipophilin Genes from Invertebrates to Tetrapods: DM-20 Cannot Replace Proteolipid Protein in CNS Myelin
Authors: Stecca Barbara , Southwood Cherie M. , Gragerov Alexander , Kelley Kevin A. , Friedrich Victor L. , Gow Alexander
Published: April 2018

The proteolipid protein (PLP) gene encodes two myelin-specific protein isoforms, DM-20 and PLP, which are members of the highly conserved lipophilin family of transmembrane proteins. While the functions of this family are poorly understood, the fact that null mutations of thePLPgene cause leukodystrophy in man is testament to the importance of DM-20 and PLP in normal CNS function. PLP differs from DM-20 by the presence of a 35 amino acid domain exposed to the cytoplasm, which is not encoded by other lipophilin genes and appears to have arisen in amphibians ∼300 million years before present. However, the lipophilin gene family can be traced back at least 550 million years and is represented inDrosophilaand silkworms. Thus, from an evolutionary perspective PLP can reasonably be anticipated to perform functions in CNS myelin that cannot be accomplished by other lipophilins. Herein we use a novel knock-in strategy to generate mice expressing wild-type levels of aPlpgene that has been modified to encode only DM-20. Although DM-20 is incorporated into functional compact myelin sheaths in young animals, our data show that the 35 amino acid PLP-specific peptide is required to engender the normal myelin period and to confer long-term stability on this multilamellar membrane.
Identification of Proteins in the Postsynaptic Density Fraction by Mass Spectrometry
Authors: Walikonis Randall S. , Jensen Ole N. , Mann Matthias , Provance D. William , Mercer John A. , Kennedy Mary B.
Published: April 2018

Our understanding of the organization of postsynaptic signaling systems at excitatory synapses has been aided by the identification of proteins in the postsynaptic density (PSD) fraction, a subcellular fraction enriched in structures with the morphology of PSDs. In this study, we have completed the identification of most major proteins in the PSD fraction with the use of an analytical method based on mass spectrometry coupled with searching of the protein sequence databases. At least one protein in each of 26 prominent protein bands from the PSD fraction has now been identified. We found 7 proteins not previously known to be constituents of the PSD fraction and 24 that had previously been associated with the PSD by other methods. The newly identified proteins include the heavy chain of myosin-Va (dilute myosin), a motor protein thought to be involved in vesicle trafficking, and the mammalian homolog of the yeast septin protein cdc10, which is important for bud formation in yeast. Both myosin-Va and cdc10 are threefold to fivefold enriched in the PSD fraction over brain homogenates. Immunocytochemical localization of myosin-Va in cultured hippocampal neurons shows that it partially colocalizes with PSD-95 at synapses and is also diffusely localized in cell bodies, dendrites, and axons. Cdc10 has a punctate distribution in cell bodies and dendrites, with some of the puncta colocalizing with PSD-95. The results support a role for myosin-Va in transport of materials into spines and for septins in the formation or maintenance of spines.
Functional Coupling between Neurons and Glia
Authors: Alvarez-Maubecin Veronica , García-Hernández Fernando , Williams John T. , Van Bockstaele Elisabeth J.
Published: April 2018

Neuronal–glial interactions play an important role in information processing in the CNS. Previous studies have indicated that electrotonic coupling between locus ceruleus (LC) neurons is involved in synchronizing the spontaneous activity. The results of the present study extend the functional electrotonic coupling to interactions between neurons and glia. Spontaneous oscillations in the membrane potential were observed in a subset of glia. These oscillations were synchronous with the firing of neurons, insensitive to transmitter receptor antagonists and disrupted by carbenoxolone, a gap junction blocker. Hyperpolarization of neurons with [Met]5enkephalin blocked the oscillations in glia. Selective depolarization of glia with a glutamate transporter substrate (l-α-aminoadipic acid) increased the neuronal firing rate, suggesting that changes in the membrane potential of glia can modulate neuronal excitability through heterocellular coupling. Dye-coupling experiments further confirmed that small molecules could be transferred through gap junctions between these distinct cell types. No dye transfer was observed between neurons and oligodendrocytes or between astrocytes and oligodendrocytes, suggesting that the junctional communication was specific for astrocytes and neurons. Finally, immunoelectron microscopy studies established that connexins, the proteins that form gap junctions, were present on portions of the plasmalemma, bridging the cytoplasm of neurons and glia in LC. This heterocellular coupling extends the mechanisms by which glia participate in the network properties of the LC in which the degree of coupling is thought to influence cognitive performance.
Local Directional Cues Control Growth Polarity of Dopaminergic Axons Along the Rostrocaudal Axis
Authors: Nakamura Shin-ichiro , Ito Yasuko , Shirasaki Ryuichi , Murakami Fujio
Published: April 2018

The vertebrate CNS is composed of a variety of longitudinal axonal tracts extending rostrally and caudally. Although recent studies have demonstrated that chemoattraction and chemorepulsion play key roles in axon guidance along the circumferential axis in the neural tube of the vertebrate, mechanisms of axonal elongation along the longitudinal axis, and most importantly, what determines rostrocaudal polarity of axonal growth, remains unknown. Here, we examined the mechanism that guides midbrain dopaminergic axons rostrally, using flat whole-mount preparations of embryonic rat brain bothin vivoandin vitro.

At embryonic day 11 (E11) and early stage E12, dopaminergic neurons in the ventral midbrain extended short axons dorsally. By middle stage E12, these axons had increased in number, some deflecting rostrally and others caudally. At E13, almost all axons showed rostrally oriented growth heading toward the forebrain targets. Inin vitrowhole-mount preparations prepared from an E12 embryo and cultured for 24 hr, these axons showed rostrally oriented growth, but when they were forced to grow on substratum of reversed rostrocaudal polarity, they turned abruptly and grew following the polarity of the reversed midbrain substratum. These results suggest that local directional cues in the midbrain guide these axons rostrally and support the idea that substratum-associated polarized cues play an important role in axon guidance along the longitudinal axis.
Uncoupling of Myelin Assembly and Schwann Cell Differentiation by Transgenic Overexpression of Peripheral Myelin Protein 22
Authors: Niemann Stephan , Sereda Michael W. , Suter Ueli , Griffiths Ian R. , Nave Klaus-Armin
Published: April 2018

We have generated previously transgenic rats that overexpress peripheral myelin protein 22 (PMP22) in Schwann cells. In the nerves of these animals, Schwann cells have segregated with axons to the normal 1:1 ratio but remain arrested at the promyelinating stage, apparently unable to elaborate myelin sheaths. We have examined gene expression of these dysmyelinating Schwann cells using semiquantitative reverse transcription-PCR and immunofluorescence analysis. Unexpectedly, Schwann cell differentiation appears to proceed normally at the molecular level when monitored by the expression of mRNAs encoding major structural proteins of myelin. Furthermore, an aberrant coexpression of early and late Schwann cell markers was observed. PMP22 itself acquires complex glycosylation, suggesting that trafficking of the myelin protein through the endoplasmic reticulum is not significantly impaired. We suggest that PMP22, when overexpressed, accumulates in a late Golgi–cell membrane compartment and uncouples myelin assembly from the underlying program of Schwann cell differentiation.
Insulin-Like Growth Factor I Stimulates Dendritic Growth in Primary Somatosensory Cortex
Authors: Niblock Mary M. , Brunso-Bechtold Judy K. , Riddle David R.
Published: April 2018

The temporal and spatial distributions of several growth factors suggest roles in the regulation of neuronal differentiation in the neocortex. Among such growth factors, the insulin-like growth factors (IGF-I and -II) are of particular interest because they are available to neurons from multiple sources under independent control. IGF-I is produced by many neurons throughout the brain and also by cells in the cerebral vasculature. IGF-II is found at high levels in the CSF, and both IGF-I and IGF-II cross the blood–brain barrier. Thus, the IGFs may act as both paracrine and endocrine regulators of neuronal development. As an initial step toward understanding the influence of IGFs in the developing cerebral cortex, the present study examined the effects of IGF-I and of the neurotrophins brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) on the dendritic complexity of layer 2 pyramidal neurons. The results demonstrate that IGF-I increased the branching and total extent of both apical and basal dendrites of pyramidal cells in organotypic slices of rat primary somatosensory cortex. BDNF and NT-3 also enhanced dendritic development, but the two neurotrophins increased the extent of only basal, not apical, dendrites and promoted greater elongation than was seen after IGF-I treatment. These results provide direct evidence that IGF-I can regulate the dendritic elaboration of cortical neurons and indicate that endogenous IGFs may influence dendritic differentiation and the formation of cortical connections. In addition, IGF-dependent regulation of dendritic structure may represent a link between age-related declines in IGFs and cognitive deficits seen in senescence.
Toward Understanding the Biology of a Complex Phenotype: Rat Strain and Substrain Differences in the Sensorimotor Gating-Disruptive Effects of Dopamine Agonists
Authors: Swerdlow Neal R. , Martinez Zoe A. , Hanlon Faith M. , Platten Amanda , Farid Marjan , Auerbach Pamela , Braff David L. , Geyer Mark A.
Published: April 2018

Sensorimotor gating, measured by prepulse inhibition (PPI) of the startle reflex, is reduced in schizophrenia patients and in rats treated with dopamine agonists. Strain differences in the sensitivity to the PPI-disruptive effects of dopamine agonists may provide insight into the genetic basis for human population differences in sensorimotor gating. We reported strain differences in the sensitivity to the PPI-disruptive effects of the D1/D2 agonist apomorphine in adult rats, with greater sensitivity in Harlan Sprague Dawley (SDH) versus Wistar (WH) rats. However, Kinney et al. (1999) recently reported opposite findings, using Bantin-Kingman Sprague Dawley (SDBK) and Wistar (WBK) rats; in fact, SDBK rats did not exhibit clear apomorphine-induced reductions in sensorimotor gating. These new findings of Kinney et al. (1999) directly conflict with over 15 years of results from our laboratories and challenge interpretations from a large body of literature. The present studies carefully assessed drug effects on sensorimotor gating in SD versus W strains, across rat suppliers (H vs BK). Significantly greater SDH than WH apomorphine sensitivity in PPI measures was observed in both adult and 18 d pups, confirming that these strain differences are both robust and innate. These strain differences in apomorphine sensitivity were not found in adult BK rats. Supplier differences in sensitivity (SDH > SDBK) were also evident in the PPI-disruptive effects of D1 but not D2-family agonists; PPI was clearly disrupted by quinpirole in both SDH and SDBK rats. These findings demonstrate robust, innate, neurochemically specific, and apparently heritable phenotypic differences in an animal model of sensorimotor gating deficits in human neuropsychiatric disorders.
Prolonged Synaptic Currents and Glutamate Spillover at the Parallel Fiber to Stellate Cell Synapse
Authors: Carter Adam G. , Regehr Wade G.
Published: April 2018

Although neurons often fire in bursts, most of what is known about glutamate signaling and postsynaptic receptor activation is based on experiments using single stimuli. Here we examine the activation of ionotropic glutamate receptors by bursts at the parallel fiber to stellate cell synapse. We show that brief stimulus trains generate prolonged AMPA receptor (AMPAR)- and NMDA receptor (NMDAR)-mediated EPSCs recorded in whole-cell voltage clamp. These EPSCs contrast with the rapid AMPAR-mediated EPSC evoked by a single stimulus. The prolonged AMPAR-mediated EPSC is promoted by high-frequency and high-intensity trains and can persist for hundreds of milliseconds. This EPSC is also increased byl-trans-2,4-PDC, an inhibitor of glutamate transporters, suggesting that these transporters usually limit the synaptic response to trains. These prolonged EPSCs reflect both receptor properties and a long-lasting glutamate signal. In addition, several experiments demonstrate that glutamate spillover can contribute to receptor activation. First, imaging stimulus-evoked changes in presynaptic calcium establishes that distinct parallel fiber bands can be activated. Second, activation of parallel fibers that do not directly synapse onto a given stellate cell can evoke indirect AMPAR- and NMDAR-mediated EPSCs in that cell. Third, experiments using the use-dependent NMDAR blocker MK-801 show that these indirect EPSCs reflect glutamate spillover in response to trains. Together, these findings indicate that stimulus trains can generate a sustained and widespread glutamate signal that can in turn evoke large and prolonged EPSCs mediated by ionotropic glutamate receptors. These synaptic properties may have important functional consequences for stellate cell firing.
Activation of Mitogen-Activated Protein Kinases after Transient Forebrain Ischemia in Gerbil Hippocampus
Authors: Sugino Toshiyuki , Nozaki Kazuhiko , Takagi Yasushi , Hattori Itaro , Hashimoto Nobuo , Moriguchi Tetsuo , Nishida Eisuke
Published: April 2018

We investigated the expression, activation, and distribution of c-Jun N-terminal kinases (JNKs), p38 mitogen-activated protein kinases (p38s) and extracellular signal-regulated kinases (ERKs) using Western blotting and immunohistochemistry in gerbil hippocampus after transient forebrain ischemia to clarify the role of these kinases in delayed neuronal death (DND) in the CA1 subfield. Immunoblot analysis demonstrated that activities of JNK, p38, and ERK in whole hippocampus were increased after 5 min of global ischemia. We used an immunohistochemical study to elucidate the temporal and spatial expression of these kinases after transient global ischemia. The immunohistochemical study showed that active JNK and p38 immunoreactivities were enhanced at 15 min of reperfusion and then gradually reduced and disappeared in the hippocampal CA1 region. On the other hand, in CA3 neurons, active JNK and p38 immunoreactivities were enhanced at 15 min of reperfusion and peaked at 6 hr of reperfusion and then gradually reduced but was continuously detected 72 hr after ischemia. Active ERK immunoreactivity was observed transiently in CA3 fibers and dentate gyrus. Pretreatment with SB203580, a p38 inhibitor, but not with PD98059, an ERK kinase 1/2 inhibitor, reduced ischemic cell death in the CA1 region after transient global ischemia by inhibiting the activity of p38. These findings indicate that the p38 pathway may play an important role in DND during brain ischemia in gerbil. Components of the pathway are important target molecules for clarifying the mechanism of neuronal death.
The L1-Type Cell Adhesion Molecule Neuroglian Influences the Stability of Neural Ankyrin in theDrosophilaEmbryo But Not Its Axonal Localization
Authors: Bouley Michael , Tian Ming-Zhu , Paisley Kerry , Shen Yu-Chi , Malhotra Jyoti Dhar , Hortsch Michael
Published: April 2018

Ankyrins are linker proteins, which connect various membrane proteins, including members of the L1 family of neural cell adhesion molecules, with the submembranous actin–spectrin skeleton. Here we report the cloning and characterization of a second, novelDrosophilaankyrin gene (Dank2) that appears to be the result of a gene duplication event during arthropod evolution. TheDrosophilaL1-type protein neuroglian interacts with products from bothDrosophilaankyrin genes. Whereas the previously described ankyrin gene is ubiquitously expressed during embryogenesis, the expression ofDank2is restricted to the nervous system in theDrosophilaembryo. The absence of neuroglian protein in a neuroglian null mutant line causes decreased levels of Dank2 protein in most neuronal cells. This suggests that neuroglian is important for the stability of Dank2 protein. However, neuroglian is not required for Dank2 axonal localization. In temperature-sensitiveneuroglianmutants in which neuroglian protein is mislocated at the restrictive temperature to an intracellular location in the neuronal soma, Dank2 protein can still be detected along embryonic nerve tracts.
Interaction of the Postsynaptic Density-95/Guanylate Kinase Domain-Associated Protein Complex with a Light Chain of Myosin-V and Dynein
Authors: Naisbitt Scott , Valtschanoff Juli , Allison Daniel W. , Sala Carlo , Kim Eunjoon , Craig Ann Marie , Weinberg Richard J. , Sheng Morgan
Published: April 2018

NMDA receptors interact directly with postsynaptic density-95 (PSD-95), a scaffold protein that organizes a cytoskeletal– signaling complex at the postsynaptic membrane. The molecular mechanism by which the PSD-95-based protein complex is trafficked to the postsynaptic site is unknown but presumably involves specific motor proteins. Here we demonstrate a direct interaction between the PSD-95-associated protein guanylate kinase domain-associated protein (GKAP) and dynein light chain (DLC), a light chain subunit shared by myosin-V (an actin-based motor) and cytoplasmic dynein (a microtubule-based motor). A yeast two-hybrid screen with GKAP isolated DLC2, a novel protein 93% identical to the previously cloned 8 kDa dynein light chain (DLC1). A complex containing PSD-95, GKAP, DLC, and myosin-V can be immunoprecipitated from rat brain extracts. DLC colocalizes with PSD-95 and F-actin in dendritic spines of cultured neurons and is enriched in biochemical purifications of PSD. Immunogold electron microscopy reveals a concentration of DLC in the postsynaptic compartment of asymmetric synapses of brain in which it is associated with the PSD and the spine apparatus. We discuss the possibility that the GKAP/DLC interaction may be involved in trafficking of the PSD-95 complex by motor proteins.
Postsynaptic Scaffolds of Excitatory and Inhibitory Synapses in Hippocampal Neurons: Maintenance of Core Components Independent of Actin Filaments and Microtubules
Authors: Allison Daniel W. , Chervin Adam S. , Gelfand Vladimir I. , Craig Ann Marie
Published: April 2018

The mechanisms responsible for anchoring molecular components of postsynaptic specializations in the mammalian brain are not well understood but are presumed to involve associations with cytoskeletal elements. Here we build on previous studies of neurotransmitter receptors (Allison et al., 1998) to analyze the modes of attachment of scaffolding and signal transducing proteins of both glutamate and GABA postsynaptic sites to either the microtubule or microfilament cytoskeleton. Hippocampal pyramidal neurons in culture were treated with latrunculin A to depolymerize actin, with vincristine to depolymerize microtubules, or with Triton X-100 to extract soluble proteins. The synaptic clustering of PSD-95, a putative NMDA receptor anchoring protein and a core component of the postsynaptic density (PSD), was unaffected by actin depolymerization, microtubule depolymerization, or detergent extraction. The same was largely true for GKAP, a PSD-95-interacting protein. In contrast, the synaptic clustering of Ca2+/calmodulin-dependent protein kinase II (CaMKII)α, another core component of the PSD, was completely dependent on an intact actin cytoskeleton and was partially disrupted by detergent. Drebrin and α-actinin-2, actin-binding proteins concentrated in spines, were also dependent on F-actin for synaptic localization but were unaffected by detergent extraction. Surprisingly, the subcellular distributions of the inhibitory synaptic proteins GABAAR and gephyrin, which has a tubulin-binding motif, were unaffected by depolymerization of microtubules or actin or by detergent extraction. These studies reveal an unsuspected heterogeneity in the modes of attachment of postsynaptic proteins to the cytoskeleton and support the idea that PSD-95 and gephyrin may be core scaffolding components independent of the actin or tubulin cytoskeleton.
The MAPK/ERK Cascade Targets Both Elk-1 and cAMP Response Element-Binding Protein to Control Long-Term Potentiation-Dependent Gene Expression in the Dentate GyrusIn Vivo
Authors: Davis Sabrina , Vanhoutte Peter , Pagès Christiane , Caboche Jocelyne , Laroche Serge
Published: April 2018

The mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) signaling cascade contributes to synaptic plasticity and to long-term memory formation, yet whether MAPK/ERK controls activity-dependent gene expression critical for long-lasting changes at the synapse and what the events underlying transduction of the signal are remain uncertain. Here we show that induction of long-term potentiation (LTP) in the dentate gyrusin vivoleads to rapid phosphorylation and nuclear translocation of MAPK/ERK. Following a similar time course, the two downstream transcriptional targets of MAPK/ERK, cAMP response element-binding protein (CREB) and the ternary complex factor Elk-1, a key transcriptional-regulator of serum response element (SRE)-driven gene expression, were hyperphosphorylated and the immediate early gene zif268 was upregulated. The mRNA encoding MAP kinase phosphatase MKP-1 was upregulated at the time point when MAPK/ERK phosphorylation had returned to basal levels, suggesting a negative feedback loop to regulate deactivation of MAPK/ERK. We also show that inhibition of the MAPK/ERK cascade by the MAPK kinase MEK inhibitor SL327 prevented CREB and Elk-1 phosphorylation, and LTP-dependent gene induction, resulting in rapidly decaying LTP. In conclusion, we suggest that Elk-1 forms an important link in the MAP kinase pathway to transduce signals from the cell surface to the nucleus to activate the genetic machinery necessary for the maintenance of synaptic plasticity in the dentate gyrus. Thus, MAPK/ERK activation is required for LTP-dependent transcriptional regulation and we suggest this is regulated by two parallel signaling pathways, the MAPK/ERK-Elk-1 pathway targeting SRE and the MAPK/ERK-CREB pathway targeting CRE.
Cell Cycle Control of Schwann Cell Proliferation: Role of Cyclin-Dependent Kinase-2
Authors: Tikoo Ravi , Zanazzi George , Shiffman Dov , Salzer James , Chao Moses V.
Published: April 2018

Schwann cell proliferation is regulated by multiple growth factors and axonal signals. However, the molecules that control growth arrest of Schwann cells are not well defined. Here we describe regulation of the cyclin-dependent kinase-2 (CDK2) protein, an enzyme that is necessary for the transition from G1 to S phase. Levels of CDK2 protein were elevated in proliferating Schwann cells cultured in serum and forskolin. However, when cells were grown with either serum-free media or at high densities, CDK2 levels declined to low levels. The decrease in CDK2 levels was associated with growth arrest of Schwann cells. The modulation of CDK2 appears to be regulated at the transcriptional level, because CDK2 mRNA levels and its promoter activity both decline during cell cycle arrest. Furthermore, analysis of the CDK2 promoter suggests that Sp1 DNA binding sites are essential for maximal activation in Schwann cells. Together, these data suggest that CDK2 may represent a significant target of developmental signals that regulate Schwann cell proliferation and that this regulation is mediated, in part, through regulation of Sp1 transcriptional activity.
c-Fos Expression in GABAergic, Serotonergic, and Other Neurons of the Pontomedullary Reticular Formation and Raphe after Paradoxical Sleep Deprivation and Recovery
Authors: Maloney Karen J. , Mainville Lynda , Jones Barbara E.
Published: April 2018

The brainstem contains the neural systems that are necessary for the generation of the state of paradoxical sleep (PS) and accompanying muscle atonia. Important for its initiation are the pontomesencephalic cholinergic neurons that project into the pontomedullary reticular formation and that we have recently shown increase c-Fos expression as a reflection of neural activity in association with PS rebound after deprivation in rats (Maloney et al., 1999). As a continuation, we examined in the present study c-Fos expression in the pontomedullary reticular and raphe neurons, including importantly GABAergic neurons [immunostained for glutamic acid decarboxylase (GAD)] and serotonergic neurons [immunostained for serotonin (Ser)].

Numbers of single-labeled c-Fos+ neurons were significantly increased with PS rebound only in the pars oralis of the pontine reticular nuclei (PnO), where numbers of GAD+/c-Fos+ neurons were conversely significantly decreased. c-Fos+ neurons were positively correlated with PS, whereas GAD+/c-Fos+ neurons were negatively correlated with PS, suggesting that disinhibition of reticular neurons in the PnO from locally projecting GABAergic neurons may be important in the generation of PS. In contrast, through the caudal pons and medulla, GAD+/c-Fos+ cells were increased with PS rebound, covaried positively with PS and negatively with the electromyogram (EMG). In the raphe pallidus-obscurus, Ser+/c-Fos+ neurons were positively correlated, in a reciprocal manner to GAD+/c-Fos+ cells, with EMG, suggesting that disfacilitation by removal of a serotonergic influence and inhibition by imposition of a GABAergic influence within the lower brainstem and spinal cord may be important in the development of muscle atonia accompanying PS.
Predicting Vulnerability to Acoustic Injury with a Noninvasive Assay of Olivocochlear Reflex Strength
Authors: Maison Stéphane F. , Liberman M. Charles
Published: April 2018

Permanent noise-induced damage to the inner ear is a major cause of hearing impairment, arising from exposures occurring during both work- and pleasure-related activities. Vulnerability to noise-induced hearing loss is highly variable: some have tough, whereas others have tender ears. This report documents, in an animal model, the efficacy of a simple nontraumatic assay of normal ear function in predicting vulnerability to acoustic injury. The assay measures the strength of a sound-evoked neuronal feedback pathway to the inner ear, the olivocochlear efferents, by examining otoacoustic emissions created by the normal ear, which can be measured with a microphone in the external ear. Reflex strength was inversely correlated with the degree of hearing loss after subsequent noise exposure. These data suggest that one function of the olivocochlear efferent system is to protect the ear from acoustic injury. This assay, or a simple modification of it, could be applied to human populations to screen for individuals most at risk in noisy environments.
Chemical Determinants of the Rat Electro-Olfactogram
Authors: Scott John W. , Brierley Tracy , Schmidt Frederick H.
Published: April 2018

The chemical properties that determine the distribution of the electro-olfactogram were studied after exposure of a large area of the rat olfactory epithelium. Multiple electrodes were placed along the rostral border of endoturbinate IV on the midline of the nasal cavity. This array of electrodes spanned a region containing the four receptor gene expression zones described for the rat. The response to a series of odorants containing only carbon, hydrogen, and oxygen was strongly related to electrode position. For most hydrocarbons, the responses were progressively larger toward the ventral epithelium. The only exceptions were aromatic hydrocarbons, which evoked nearly equal response sizes across the epithelium. Ketones and aldehydes evoked relatively larger dorsal responses than did hydrocarbons with similar structures. Aromatic ketones and aldehydes evoked systematically larger responses from the dorsal part of the epithelium. The response profiles for most odorants were well described by a linear fit to the electrode position along the dorsal–ventral position on the epithelium. However, a few bicyclic odorants and carboxylic acids evoked significantly nonlinear profiles. It is concluded that there is a systematic distribution of odorant sensitivity across this part of the epithelium and that this sensitivity is related to general chemical properties. Other evidence suggests that these properties extend to other parts of the epithelium. This spatial sensitivity of the epithelium to odorants probably contributes to olfactory coding in parallel with the convergence of axons from olfactory sensory neurons expressing the same receptor type.
Traumatic Brain Injury Alters the Molecular Fingerprint of TUNEL-Positive Cortical NeuronsIn Vivo: A Single-Cell Analysis
Authors: O'Dell Dianne M. , Raghupathi Ramesh , Crino Peter B. , Eberwine James H. , McIntosh Tracy K.
Published: April 2018

The cerebral cortex is selectively vulnerable to cell death after traumatic brain injury (TBI). We hypothesized that the ratio of mRNAs encoding proteins important for cell survival and/or cell death is altered in individual damaged neurons after injury that may contribute to the cell's fate. To investigate this possibility, we used amplified antisense mRNA (aRNA) amplification to examine the relative abundance of 31 selected candidate mRNAs in individual cortical neurons with fragmented DNA at 12 or 24 hr after lateral fluid percussion brain injury in anesthetized rats. Only pyramidal neurons characterized by nuclear terminal deoxynucleotidyl transferase-mediated biotinylated dUTP nick end labeling (TUNEL) reactivity with little cytoplasmic staining were analyzed. For controls, non-TUNEL-positive neurons from the cortex of sham-injured animals were obtained and subjected to aRNA amplification. At 12 hr after injury, injured neurons exhibited a decrease in the relative abundance of specific mRNAs including those encoding for endogenous neuroprotective proteins. By 24 hr after injury, many of the mRNAs altered at 12 hr after injury had returned to baseline (sham-injured) levels except for increases in caspase-2 and bax mRNAs. These data suggest that TBI induces a temporal and selective alteration in the gene expression profiles or “molecular fingerprints” of TUNEL-positive neurons in the cerebral cortex. These patterns of gene expression may provide information about the molecular basis of cell death in this region after TBI and may suggest multiple avenues for therapeutic intervention.
A Temperature-Sensitive Paralytic Mutant Defines a Primary Synaptic Calcium Channel inDrosophila
Authors: Kawasaki Fumiko , Felling Ryan , Ordway Richard W.
Published: April 2018

Neurotransmission at chemical synapses involves regulated exocytosis of neurotransmitter from the presynaptic terminal. Neurotransmitter release is thought to be triggered by calcium influx through specific classes of voltage-gated calcium channels. Here we report genetic and functional analysis implicating a specific calcium channel gene product in neurotransmitter release. We have isolated a temperature-sensitive paralytic allele of theDrosophilacalcium channel α1 subunit gene,cacophony(cac). This mutant, referred to ascacTS2, allows functional analysis of synaptic transmission after acute perturbation of a specific α1 subunit. Electrophysiological analysis at neuromuscular synapses revealed that neurotransmitter release incacTS2is markedly reduced at elevated temperatures, indicating thatcacencodes a primary α1 subunit functioning in synaptic transmission. These observations further define the molecular basis of voltage-gated calcium entry at synapses and provide a new starting point for further genetic analysis of synaptic mechanisms.