bluuebunny/crossref_metadata_2025 huggingface dataset:
Collapsin-1/Semaphorin-III/D Is Regulated Developmentally in Purkinje Cells and Collapses Pontocerebellar Mossy Fiber Neuronal Growth Cones
Authors: Rabacchi Sylvia A. , Solowska Joanna M. , Kruk Barbara , Luo Yuling , Raper Jonathan A. , Baird Douglas H.
Published: April 2018

Most axons in the CNS innervate specific subregions or layers of their target regions and form contacts with specific types of target neurons, but the molecular basis of this process is not well understood. To determine whether collapsin-1/semaphorin-III/D, a molecule known to repel specific axons, might guide afferent axons within their cerebellar targets, we characterized its expression byin situhybridization and observed its effects on mossy and climbing fiber extension and growth cone sizein vitro. In newborn mice sema-D is expressed by cerebellar Purkinje cells in parasagittal bands located medially and in some cells of the cerebellar nuclei. Later, sema-D expression in Purkinje cells broadens such that banded expression is no longer prominent, and expression is detected in progressively more lateral regions. By postnatal day 16, expression is observed throughout the cerebellar mediolateral axis.

Collapsin-1 protein, the chick ortholog of sema-D, did not inhibit the extension of neurites from explants of inferior olivary nuclei, the source of climbing fibers that innervate Purkinje cells. In contrast, when it was applied to axons extending from basilar pontine explants, a source of mossy fiber afferents of granule cells, collapsin-1 caused most pontine growth cones to collapse, as evidenced by a reduction in growth cone size of up to 59%. Moreover, 63% of pontine growth cones arrested their extension or retracted. Its effects on mossy fiber extension and its distribution suggest that sema-D prevents mossy fibers from innervating inappropriate cerebellar target regions and cell types.
Generation of Tyrosine Hydroxylase-Producing Neurons from Precursors of the Embryonic and Adult Forebrain
Authors: Daadi Marcel M. , Weiss Samuel
Published: April 2018

We have explored the plastic ability of neuronal precursors to acquire different identities by manipulating their surrounding environment. Specifically, we sought to identify potential signals involved in the specification of forebrain dopaminergic neurons. Here we describe culture conditions under which tyrosine hydroxylase (TH) expression is induced in neuronal precursors, which were derived directly from the embryonic striatum and adult subependyma (SE) of the lateral ventricle or generated from multipotent forebrain stem cells. TH was successfully induced in all of these cell types by 24 hr exposure to basic fibroblast growth factor (FGF2) and glial cell conditioned media (CM). The greatest magnitude of the inductive action was on embryonic striatal precursors. Although FGF2 alone induced limited TH expression in striatal cells (1.1 ± 0.2% of neurons), these actions were potentiated 17.5-fold (19.6 ± 1.5% of neurons) when FGF2 was coadministered with B49 glial cell line CM. Of these TH-immunoreactive cells, ∼15% incorporated bromodeoxyuridine (BrdU), indicating that they were newly generated, and 95% coexpressed the neurotransmitter GABA. To investigate whether precursors of the adult forebrain subependyma were competent to respond to the instructive actions of FGF2+CM, they were first labeledin vivowith a pulse of BrdU. Although none of the cells expressed TH in control, 0.2% of total cells showed TH immunoreactivity in FGF2+CM-treated cultures. Under these same conditions only,in vitro-generated precursors from epidermal growth factor-responsive stem cells exhibited TH expression in 10% of their total neuronal progeny. Regulation of neurotransmitter phenotype in forebrain neuronal precursors, by the synergistic action of FGF2 and glial-derived diffusible factors, may represent a first step in understanding how these cells are generated in the embryonic and adult brain and opens the prospect for their manipulationin vitroandin vivofor therapeutic use.
Electrophysiological and Morphological Evidence for a GABAergic Nigrostriatal Pathway
Authors: Rodrı́guez Manuel , González-Hernández Tomás
Published: April 2018

The electrophysiological and neurochemical characteristics of the nondopaminergic nigrostriatal (NO-DA) cells and their functional response to the degeneration of dopaminergic nigrostriatal (DA) cells were studied. Three different criteria were used to identify NO-DA cells: (1) antidromic response to striatal stimulation with an electrophysiological behavior (firing rate, interspike interval variability, and conduction velocity) different from that of DA cells; (2) retrograde labeling after striatal injection of HRP but showing immunonegativity for DA cell markers (tyrosine hydroxylase, calretinin, calbindin-D28k, and cholecystokinin); and (3) resistance to neurotoxic effect of 6-hydroxydomine (6-OHDA). Our results showed that under normal conditions, 5–8% of nigrostriatal neurons are immunoreactive for GABA, glutamic acid decarboxylase, and parvalbumin, markers of GABAergic neurons, a percentage that reached 81–84% after 6-OHDA injection. Electrophysiologically, NO-DA cells showed a behavior similar to that found in other nigral GABAergic (nigrothalamic) cells. In addition, the 6-OHDA degeneration of DA cells induced a modification of their electrophysiological pattern similar to that found in GABAergic nigrothalamic neurons. Taken together, the present data indicate the existence of a small GABAergic nigrostriatal pathway and suggest their involvement in the pathophysiology of Parkinson’s disease.
Regulation of the UNC-18–Caenorhabditis elegansSyntaxin Complex by UNC-13
Authors: Sassa Toshihiro , Harada Shin-ichi , Ogawa Hisamitu , Rand James B. , Maruyama Ichiro N. , Hosono Ryuji
Published: April 2018

TheCaenorhabditis elegans unc-13,unc-18, andunc-64genes are required for normal synaptic transmission. The UNC-18 protein binds to theunc-64gene productC. eleganssyntaxin (Cesyntaxin). However, it is not clear how this protein complex is regulated. We show that UNC-13 transiently interacts with the UNC-18-Cesyntaxin complex, resulting in rapid displacement of UNC-18 from the complex. Genetic and biochemical evidence is presented that UNC-13 contributes to the modulation of the interaction between UNC-18 andCesyntaxin.
Presynaptic μ and δ Opioid Receptor Modulation of GABAAIPSCs in the Rat Globus PallidusIn Vitro
Authors: Stanford Ian M. , Cooper Alison J.
Published: April 2018

The role of enkephalin and the opioid receptors in modulating GABA release within the rat globus pallidus (GP) was investigated using whole-cell patch recordings made from visually identified neurons. Two major GP neuronal subtypes were classified on the basis of intrinsic membrane properties, action potential characteristics, the presence of the anomalous inward rectifier (Ih), and anode break depolarizations.

The μ opioid receptor agonist [d-Ala2-N-Me-Phe4-Glycol5]-enkephalin (DAMGO) (1 μm) reduced GABAAreceptor-mediated IPSCs evoked by stimulation within the striatum. DAMGO also increased paired-pulse facilitation, indicative of presynaptic μ opioid receptor modulation of striatopallidal input. In contrast, the δ opioid agonistd-Pen-[d-Pen2,5]-enkephalin (DPDPE) (1 μm) was without effect.

IPSCs evoked by stimulation within the GP were depressed by application of [methionine 5′]-enkephalin (met-enkephalin) (30 μm). Met-enkephalin also reduced the frequency, but not the amplitude, of miniature IPSCs (mIPSCs) and increased paired-pulse facilitation of evoked IPSCs, indicative of a presynaptic action. Both DAMGO and DPDPE reduced evoked IPSCs and the frequency, but not amplitude, of mIPSCs. However, spontaneous action potential-driven IPSCs were reduced in frequency by met-enkephalin and DAMGO, whereas DPDPE was without effect.

Overall, these results indicate that presynaptic μ opioid receptors are located on striatopallidal terminals and pallidopallidal terminals of spontaneously firing GP neurons, whereas presynaptic δ opioid receptors are preferentially located on terminals of quiescent GP cells. Enkephalin, acting at both of these receptor subtypes, serves to reduce GABA release in the GP and may therefore act as an adaptive mechanism, maintaining the inhibitory function of the GP in basal ganglia circuitry.
Endocytic Active Zones: Hot Spots for Endocytosis in Vertebrate Neuromuscular Terminals
Authors: Teng Haibing , Cole John C. , Roberts Richard L. , Wilkinson Robert S.
Published: April 2018

We have used a sensitive activity-dependent probe, sulforhodamine 101 (SR101), to view endocytic events within snake motor nerve terminals. After very brief neural stimulation at reduced temperature, SR101 is visualized exclusively at punctate sites located just inside the presynaptic membrane of each terminal bouton. The number of sites (∼26 sites/bouton) and their location (in register with postsynaptic folds) are similar to the number and location of active zones in snake motor terminals, suggesting a spatial association between exocytosis and endocytosis under these stimulus conditions. With more prolonged stimulation, larger SR101-containing structures appear at the bouton margins. Thus endocytosis occurs initially at distinct sites, which we call “endocytic active zones,” whereas further stimulation recruits a second endocytic paradigm.
A Lobster Phospholipase C-β That Associates with G-Proteins in Response to Odorants
Authors: Xu Fuqiang , McClintock Timothy S.
Published: April 2018

A cDNA clone encoding a protein of 1116 amino acids with significant homology to β-isoforms of phospholipase C was isolated from lobster olfactory organ cDNA libraries and named lobPLCβ. This cDNA hybridized predominantly to a 9 kb transcript in RNA from olfactory organ, pereiopod, brain, and eye-eyestalk and to several smaller minor transcripts only in eye-eyestalk. An antiserum raised to the C terminus of lobPLCβ detected immunoreactivity in a single 130 kDa band in olfactory aesthetasc hairs, olfactory organ, pereiopod, dactyl, and brain. In eye-eyestalk this 130 kDa band was abundant, and minor bands of 100, 79, and 57 kDa also were detected. In cross sections of the aesthetasc hairs, immunoreactivity was detected in the outer dendritic segments of the olfactory receptor neurons, the site of olfactory transduction. A complex odorant caused lobPLCβ immunoreactivity to increase in membrane fractions and decrease in soluble fractions of homogenates of aesthetasc hairs. The odorant also increased the amount of lobPLCβ in immunoprecipitates of Gαqand Gβfrom homogenates of aesthetasc hairs. These results support the conclusion that lobPLCβ mediates olfactory transduction.
GABAAReceptor Subunit Composition and Functional Properties of Cl−Channels with Differential Sensitivity to Zolpidem in Embryonic Rat Hippocampal Cells
Authors: Maric Dragan , Maric Irina , Wen Xiling , Fritschy Jean-Marc , Sieghart Werner , Barker Jeffery L. , Serafini Ruggero
Published: April 2018

Using flow cytometry in conjunction with a voltage-sensitive fluorescent indicator dye (oxonol), we have identified and separated embryonic hippocampal cells according to the sensitivity of their functionally expressed GABAAreceptors to zolpidem. Immunocytochemical and RT-PCR analysis of sorted zolpidem-sensitive (ZS) and zolpidem-insensitive (ZI) subpopulations identified ZS cells as postmitotic, differentiating neurons expressing α2, α4, α5, β1, β2, β3, γ1, γ2, and γ3 GABAAreceptor subunits, whereas the ZI cells were neuroepithelial cells or newly postmitotic neurons, expressing predominantly α4, α5, β1, and γ2 subunits. Fluctuation analyses of macroscopic Cl−currents evoked by GABA revealed three kinetic components of GABAAreceptor/Cl−channel activity in both subpopulations. We focused our study on ZI cells, which exhibited a limited number of subunits and functional channels, to directly correlate subunit composition with channel properties. Biophysical analyses of GABA-activated Cl−currents in ZI cells revealed two types of receptor-coupled channel properties: one comprising short-lasting openings, high affinity for GABA, and low sensitivity to diazepam, and the other with long-lasting openings, low affinity for GABA, and high sensitivity to diazepam. Both types of channel activity were found in the same cell. Channel kinetics were well modeled by fitting dwell time distributions to biliganded activation and included two open and five closed states. We propose that short- and long-lasting openings correspond to GABAAreceptor/Cl−channels containing α4β1γ2 and α5β1γ2 subunits, respectively.
Positionally Selective Growth of Embryonic Spinal Cord Neurites on Muscle Membranes
Authors: Wang H. , Chadaram S. R. , Norton A. S. , Lewis R. , Boyum J. , Trumble W. , Sanes J. R. , Laskowski M. B.
Published: April 2018

Motor neurons from distinct positions along the rostrocaudal axis generally innervate muscles or muscle fibers from corresponding axial levels. These topographic maps of connectivity are partially restored after denervation or transplantation under conditions in which factors of timing and proximity are eliminated. It is therefore likely that motor neurons and some intramuscular structures bear cues that bias synapse formation in favor of positionally matched partners. To localize these cues, we studied outgrowth of neurites from embryonic spinal cord explants on carpets of membranes isolated from perinatal rat muscles. Neurites from rostral (cervical) and caudal (lumbar) spinal cord slices exhibit distinct growth preferences. In many instances, rostrally derived neurites grew selectively on membranes from forelimb muscles or from a single thoracic muscle (the serratus anterior) when given a choice between these membranes and membranes from hindlimb muscles or laminin. Caudally derived neurites almost never exhibited such rostral preferences, but instead preferred membranes from hindlimb muscles or a single hindlimb muscle (the gluteus) to rostral muscles or laminin. Likewise, spinal neurites exhibited distinct position-related preferences for outgrowth on membranes of clonal myogenic cell lines derived from specific rostral and caudal muscles. Taken together these results suggest that the membranes of motor axons and myotubes bear complementary labels that vary with rostrocaudal position and regulate neuromuscular connectivity.
Depression Duration But Not Age Predicts Hippocampal Volume Loss in Medically Healthy Women with Recurrent Major Depression
Authors: Sheline Yvette I. , Sanghavi Milan , Mintun Mark A. , Gado Mokhtar H.
Published: April 2018

This study takes advantage of continuing advances in the precision of magnetic resonance imaging (MRI) to quantify hippocampal volumes in a series of human subjects with a history of depression compared with controls. We sought to test the hypothesis that both age and duration of past depression would be inversely and independently correlated with hippocampal volume. A sample of 24 women ranging in age from 23 to 86 years with a history of recurrent major depression, but no medical comorbidity, and 24 case-matched controls underwent MRI scanning. Subjects with a history of depression (post-depressed) had smaller hippocampal volumes bilaterally than controls. Post-depressives also had smaller amygdala core nuclei volumes, and these volumes correlated with hippocampal volumes. In addition, post-depressives scored lower in verbal memory, a neuropsychological measure of hippocampal function, suggesting that the volume loss was related to an aspect of cognitive functioning. In contrast, there was no difference in overall brain size or general intellectual performance. Contrary to our initial hypothesis, there was no significant correlation between hippocampal volume and age in either post-depressive or control subjects, whereas there was a significant correlation with total lifetime duration of depression. This suggests that repeated stress during recurrent depressive episodes may result in cumulative hippocampal injury as reflected in volume loss.
Single- and Multi-Whisker Channels in the Ascending Projections from the Principal Trigeminal Nucleus in the Rat
Authors: Veinante Pierre , Deschênes Martin
Published: April 2018

This study investigated the relationship between axonal projections and receptive field properties of whisker-sensitive cells in the principal trigeminal sensory nucleus of the rat. The labeling of small groups of trigeminothalamic axons with biotinylated dextran amine disclosed two broad classes of axons; a majority of fibers (68%;n= 107) project to a single barreloid of the ventral posteromedial nucleus, and the remaining group includes axons that innervate both the posterior group of the thalamus and the tectum. Additional terminal sites for axons of this latter group may include the pretectum, the zona incerta, the medial part of the medial geniculate nucleus, and the ventral posteromedial nucleus. Corresponding to these two classes of fibers, 67% of the cells in the principal trigeminal nucleus (n= 313) have single-whisker receptive fields, whereas the rest of the population have receptive fields composed of multiple whiskers. The tonic or phasic properties of the responses apparently bear no relation to the axonal projection patterns. Solid retrograde labeling of cells that project to the ventral posteromedial nucleus and intracellular staining revealed that single-whisker cells have small somata and narrow, barrelette-bounded dendritic trees. In contrast, multi-whisker neurons have large multipolar somata, expansive dendritic trees, and many respond antidromically to stimulation of the superior colliculus. Together, these results provide evidence for two main channels of vibrissal information: a single-whisker channel that links trigeminal barrelettes to their corresponding barreloids, and a multi-whisker channel that distributes principally in the posterior group and tectum.
Brain-Derived Neurotrophic Factor Modulates Nociceptive Sensory Inputs and NMDA-Evoked Responses in the Rat Spinal Cord
Authors: Kerr B. J. , Bradbury E. J. , Bennett D. L. H. , Trivedi P. M. , Dassan P. , French J. , Shelton D. B. , McMahon S. B. , Thompson S. W. N.
Published: April 2018

Central sensitization, the hyperexcitability of spinal processing that often accompanies peripheral injury, is a major component of many persistent pain states. Here we report that the neurotrophin, brain-derived neurotrophic factor (BDNF), is a modulator of excitability within the spinal cord and contributes to the mechanism of central sensitization. BDNF, localized in primary sensory neuron cell bodies and central terminals, potentiates nociceptive spinal reflex responses in anin vitrospinal cord preparation and induces c-fos expression in dorsal horn neurons. NMDA receptor-mediated responses, known as a major contributor to central sensitization, were significantly enhanced by exogenous BDNF. Systemic NGF treatment, a procedure that mimics peripheral inflammatory states, raises BDNF levels in sensory neurons and increases nociceptive spinal reflex excitability. This increased central excitability is reduced by trkB-IgG, a BDNF “antagonist.” We also show directly that inflammatory pain-related behavior depends on BDNF releasein vivo. Thus behavioral nociceptive responses induced by intraplantar formalin and by intraplantar carageenan are significantly attenuated by trkB-IgG. Hence BDNF is appropriately localized and regulated in inflammatory states and is sufficient and necessary for the expression of central sensitization in the spinal cord. We propose that BDNF may function as a modulator of central sensitization in pathological states, and our results suggest that pharmacological antagonism of BDNF may prove an effective and novel analgesic strategy for the treatment of persistent inflammatory pain states.
Neuronal Nitric Oxide Synthase mRNA Upregulation in Rat Sensory Neurons after Spinal Nerve Ligation: Lack of a Role in Allodynia Development
Authors: Luo Z. David , Chaplan S. R. , Scott B. P. , Cizkova D. , Calcutt N. A. , Yaksh T. L.
Published: April 2018

Pharmacological evidence suggests a functional role for spinal nitric oxide (NO) in the modulation of thermal and/or inflammatory hyperalgesia. To assess the role of NO in nerve injury-induced tactile allodynia, we examined neuronal NO synthase (nNOS) expression in the spinal cord and dorsal root ganglia (DRG) of rats with tactile allodynia because of either tight ligation of the left fifth and sixth lumbar spinal nerves or streptozotocin-induced diabetic neuropathy. RNase protection assays indicated that nNOS mRNA (1) was upregulated in DRG, but not spinal cord, neurons on the injury side beginning 1 d after nerve ligation, (2) peaked (∼10-fold increase) at 2 d, and (3) remained elevated for at least 13 weeks. A corresponding increase in DRG nNOS protein was also observed and localized principally to small and occasionally medium-size sensory neurons. In rats with diabetic neuropathy, there was no significant change in DRG nNOS mRNA. However, similar increases in DRG nNOS mRNA were observed in rats that did not develop allodynia after nerve ligation and in rats fully recovered from allodynia 3 months after the nerve ligation. Systemic treatment with a specific pharmacological inhibitor of nNOS failed to prevent or reverse allodynia in nerve-injured rats. Thus, regulation of nNOS may contribute to the development of neuronal plasticity after specific types of peripheral nerve injury. However, upregulation of nNOS is not responsible for the development and/or maintenance of allodynia after nerve injury.
Knockdown of AMPA Receptor GluR2 Expression Causes Delayed Neurodegeneration and Increases Damage by Sublethal Ischemia in Hippocampal CA1 and CA3 Neurons
Authors: Oguro Keiji , Oguro Noriko , Kojima Takashi , Grooms Sonja Y. , Calderone Agata , Zheng Xin , Bennett Michael V. L. , Zukin R. Suzanne
Published: April 2018

Considerable evidence suggests that Ca2+-permeable AMPA receptors are critical mediators of the delayed, selective neuronal death associated with transient global ischemia and sustained seizures. Global ischemia suppresses mRNA and protein expression of the glutamate receptor subunit GluR2 and increases AMPA receptor-mediated Ca2+influx into vulnerable neurons of the hippocampal CA1 before the onset of neurodegeneration. Status epilepticus suppresses GluR2 mRNA and protein in CA3 before neurodegeneration in this region. To examine whether acute downregulation of the GluR2 subunit, even in the absence of a neurological insult, can cause neuronal cell death, we performed GluR2 “knockdown” experiments. Intracerebral injection of antisense oligodeoxynucleotides targeted to GluR2 mRNA induced delayed death of pyramidal neurons in CA1 and CA3. Antisense-induced neurodegeneration was preceded by a reduction in GluR2 mRNA, as indicated byin situhybridization, and in GluR2 protein, as indicated by Western blot analysis. GluR2 antisense suppressed GluR2 mRNA in the dentate gyrus but did not cause cell death. The AMPA receptor antagonist 6-cyano-7-nitroquinoxiline-2,3-dione (CNQX) and the Ca2+-permeable AMPA receptor channel blocker 1-naphthyl acetyl spermine protected against antisense-induced cell death. This result indicates that antisense-induced cell death is mediated by Ca2+-permeable AMPA receptors. GluR2 antisense and brief sublethal global ischemia acted synergistically to cause degeneration of pyramidal neurons, consistent with action by a common mechanism. These findings demonstrate that downregulation of GluR2 is sufficient to induce delayed death of specific neuronal populations.
Loss of Postsynaptic GABAAReceptor Clustering in Gephyrin-Deficient Mice
Authors: Kneussel Matthias , Brandstätter Johann Helmut , Laube Bodo , Stahl Sabine , Müller Ulrike , Betz Heinrich
Published: April 2018

The tubulin-binding protein gephyrin, which anchors the inhibitory glycine receptor (GlyR) at postsynaptic sites, decorates GABAergic postsynaptic membranes in various brain regions, and postsynaptic gephyrin clusters are absent from cortical cultures of mice deficient for the GABAAreceptor γ2 subunit. Here, we investigated the postsynaptic clustering of GABAAreceptors in gephyrin knock-out (geph−/−) mice. Both in brain sections and cultured hippocampal neurons derived fromgeph−/− mice, synaptic GABAAreceptor clusters containing either the γ2 or the α2 subunit were absent, whereas glutamate receptor subunits were normally localized at postsynaptic sites. Western blot analysis and electrophysiological recording revealed that normal levels of functional GABAAreceptors are expressed ingeph−/− neurons, however the pool size of intracellular GABAAreceptors appeared increased in the mutant cells. Thus, gephyrin is required for the synaptic localization of GlyRs and GABAAreceptors containing the γ2 and/or α2 subunits but not for the targeting of these receptors to the neuronal plasma membrane. In addition, gephyrin may be important for efficient membrane insertion and/or metabolic stabilization of inhibitory receptors at developing postsynaptic sites.
Excitatory Synaptogenesis between IdentifiedLymnaeaNeurons Requires Extrinsic Trophic Factors and Is Mediated by Receptor Tyrosine Kinases
Authors: Hamakawa Toshiro , Woodin Melanie A. , Bjorgum Micki C. , Painter Sherry D. , Takasaki Mayumi , Lukowiak Ken , Nagle Gregg T. , Syed Naweed I.
Published: April 2018

Neurotrophic factors have well established roles in neuronal development and adult synaptic plasticity, but their precise role in synapse formation has yet to be determined. This paper provides the first direct evidence that neurotrophic factors in brain conditioned medium (CM) differentially regulate excitatory and inhibitory synapse formation. Somata of identified presynaptic and postsynaptic neurons were isolated from the CNS ofLymnaeaand were cultured in a soma–soma configuration in the presence (CM) or absence [defined medium (DM)] of trophic factors. In DM, excitatory synapses did not form. When they were paired in CM or in DM containingLymnaeaepidermal growth factor (EGF); however, all presynaptic neurons reestablished their specific excitatory synapses, which had electrical properties similar to those seenin vivo. CM-induced formation of excitatory synapses required transcription andde novoprotein synthesis, as indicated by the observations that synapse formation was blocked by the protein synthesis inhibitor anisomycin and the protein transcription blocker actinomycin D; the CM factor was inactivated by boiling. They were also blocked by receptor tyrosine kinase inhibitors (lavendustin A, genistein, K252a, and KT5926) but not by inactive analogs (genistin and lavendustin B), suggesting that the effect was mediated by receptor tyrosine kinases. These results, together with our previously published data, demonstrate that trophic factors are required for excitatory, but not inhibitory, synapse formation and extends the role of EGF from cell proliferation, neurite outgrowth, and survival to excitatory synapse formation.
K+Channel Expression Distinguishes Subpopulations of Parvalbumin- and Somatostatin-Containing Neocortical Interneurons
Authors: Chow A. , Erisir A. , Farb C. , Nadal M. S. , Ozaita A. , Lau D. , Welker E. , Rudy B.
Published: April 2018

Kv3.1 and Kv3.2 K+channel proteins form similar voltage-gated K+channels with unusual properties, including fast activation at voltages positive to −10 mV and very fast deactivation rates. These properties are thought to facilitate sustained high-frequency firing. Kv3.1 subunits are specifically found in fast-spiking, parvalbumin (PV)-containing cortical interneurons, and recent studies have provided support for a crucial role in the generation of the fast-spiking phenotype. Kv3.2 mRNAs are also found in a small subset of neocortical neurons, although the distribution of these neurons is different. We raised antibodies directed against Kv3.2 proteins and used dual-labeling methods to identify the neocortical neurons expressing Kv3.2 proteins and to determine their subcellular localization. Kv3.2 proteins are prominently expressed in patches in somatic and proximal dendritic membrane as well as in axons and presynaptic terminals of GABAergic interneurons. Kv3.2 subunits are found in all PV-containing neurons in deep cortical layers where they probably form heteromultimeric channels with Kv3.1 subunits. In contrast, in superficial layer PV-positive neurons Kv3.2 immunoreactivity is low, but Kv3.1 is still prominently expressed. Because Kv3.1 and Kv3.2 channels are differentially modulated by protein kinases, these results raise the possibility that the fast-spiking properties of superficial- and deep-layer PV neurons are differentially regulated by neuromodulators. Interestingly, Kv3.2 but not Kv3.1 proteins are also prominent in a subset of seemingly non-fast-spiking, somatostatin- and calbindin-containing interneurons, suggesting that the Kv3.1–Kv3.2 current type can have functions other than facilitating high-frequency firing.
Growth Factors and Taurine Protect against Excitotoxicity by Stabilizing Calcium Homeostasis and Energy Metabolism
Authors: El Idrissi Abdeslem , Trenkner Ekkhart
Published: April 2018

Taurine, brain derived neurotrophic factor (BDNF), and basic fibroblast growth factor (bFGF) are known to control the development of early postnatal cerebellar granule cells. This study attempted to investigate possible mechanisms of this control by determining neuronal survival, calcium homeostasis, and related calcium-mediated functions, as well as the site of action during glutamate-induced excitotoxicity in cultures of cerebellar granule cells. We report that stimulation of glutamate receptors induced a rapid increase in intracellular calcium concentrations ([Ca2+]i) and a decrease in mitochondrial energy metabolism. These effects of glutamate were time- and concentration-dependent and could be specifically blocked by glutamate receptor antagonists. Taurine and bFGF but not BDNF differently regulated [Ca2+]i, and preserved the mitochondrial energy metabolism in the presence of glutamate. The regulation of [Ca2+]iby bFGF and taurine required pretreatment of cells with these factors. Confocal microscope analysis of [Ca2+]iand45Ca2+uptake studies showed that bFGF reduced the magnitude of glutamate-induced calcium uptake with no apparent regulation thereafter. Taurine, on the other hand, did not affect the level of calcium uptake induced by glutamate but rather the duration of the maximal response; this maximal response was transient and returned to basal levels ∼10 min after glutamate receptor stimulation. We conclude from these data that bFGF and taurine prevent glutamate excitotoxicity through regulation of [Ca2+]iand mitochondrial energy metabolism. Furthermore, the neuroprotective role of taurine and bFGF was enhanced by their collaboration.
Anterograde and Retrograde Amnesia After Lesions to Frontal Cortex in Rats
Authors: Winocur Gordon , Moscovitch Morris
Published: April 2018

A socially acquired food-preference test was used to assess effects of lesions to the frontal cortex on anterograde and retrograde memory in rats. In Experiment 1, there was no effect of lesion when rats were administered a two-choice test in which the target food was to be selected in the presence of a single distractor. In Experiment 2, a three-choice memory test was administered in which the target food was presented along with two equally palatable alternatives. In the latter test, lesioned groups displayed anterograde amnesia that increased with the length of the interval between postoperative acquisition and test, and a severe retrograde amnesia that extended equally over the entire range of intervals between preoperative acquisition and test. This outcome, which contrasted with the pattern of memory loss previously observed in rats with hippocampal lesions on this test, was interpreted as evidence for the strategic role of the frontal lobes in directing response selection and retrieval processes in memory.
TheAplysia MytilusInhibitory Peptide-Related Peptides: Identification, Cloning, Processing, Distribution, and Action
Authors: Fujisawa Y. , Furukawa Y. , Ohta S. , Ellis T. A. , Dembrow N. C. , Li L. , Floyd P. D. , Sweedler J. V. , Minakata H. , Nakamaru K. , Morishita F. , Matsushima O. , Weiss K. R. , Vilim F. S.
Published: April 2018

Neuropeptides are a ubiquitous class of signaling molecules. In our attempt to understand the generation of feeding behavior inAplysia,we have sought to identify and fully characterize the neuropeptides operating in this system. Preliminary evidence indicated thatMytilusinhibitory peptide (MIP)-like peptides are present and operating in the circuitry that generates feeding inAplysia.MIPs were originally isolated from the bivalve molluscMytilus edulis,and related peptides have been identified in other invertebrate species, but no precursor has been identified. In this study, we describe the isolation and characterization of novelAplysiaMIP-related peptides (AMRPs) and their precursor. Several AMRPs appear to have some structural and functional features similar to vertebrate opioid peptides. We use matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to confirm that all 14 AMRPs predicted by the precursor are processed in isolated neurons. Northern analysis, whole-mountin situhybridization, and immunohistochemistry are used to map the abundant expression of these peptides in the CNS and peripheral tissues such as the digestive tract, vasculature, and the reproductive organs. Physiological studies demonstrate that the rank order of the inhibitory actions of these peptides is different for three target muscles. These results underscore the importance of using a multidisciplinary approach to identifying and characterizing the actions of neuropeptides in an effort to gain understanding of their role in systems of interest. The widespread distribution of the AMRPs indicates that they may be operating in many different systems ofAplysia.
Glutamate Transporters Contribute to the Time Course of Synaptic Transmission in Cerebellar Granule Cells
Authors: Overstreet Linda S. , Kinney Gregory A. , Liu Ying-Bing , Billups Daniela , Slater N. Traverse
Published: April 2018

Transporters are thought to assist in the termination of synaptic transmission at some synapses by removing neurotransmitter from the synapse. To investigate the role of glutamate transport in shaping the time course of excitatory transmission at the mossy fiber–granule cell synapse, the effects of transport impairment were studied using whole-cell voltage- and current-clamp recordings in slices of rat cerebellum. Impairment of transport byl-trans-pyrrolidine-2,4-dicarboxylate (PDC) produced a prolongation of the decay of the AMPA receptor-mediated current after a repetitive stimulus, as well as prolongation of single stimulus-evoked EPSCs when AMPA receptor desensitization was blocked. PDC also produced a prolongation of both single and repetitive-evoked NMDA receptor-mediated EPSCs. Enzymatic degradation of extracellular glutamate did not reverse the PDC-induced prolongation of AMPA receptor-mediated current after a repetitive stimulus, suggesting that transporter binding sites participate in limiting glutamate spillover. In current-clamp recordings, PDC dramatically increased the total area of the EPSP and the burst duration evoked by single and repetitive stimuli. These data indicate that glutamate transporters play a significant role in sculpting the time course of synaptic transmission at granule cell synapses, most likely by limiting the extent of glutamate spillover. The contribution of transporters is particularly striking during repetitive stimulus trains at physiologically relevant frequencies. Hence, the structural arrangement of the glomerulus may enhance the contribution of transporters to information processing by limiting the extent of glutamate spillover between adjacent synapses.
Coding of Sound Pressure Level in the Barn Owl's Auditory Nerve
Authors: Köppl Christine , Yates Graeme
Published: April 2018

Rate–intensity functions, i.e., the relation between discharge rate and sound pressure level, were recorded from single auditory nerve fibers in the barn owl. Differences in sound pressure level between the owl's two ears are known to be an important cue in sound localization. One objective was therefore to quantify the discharge rates of auditory nerve fibers, as a basis for higher-order processing of sound pressure level. The second aim was to investigate the rate–intensity functions for cues to the underlying cochlear mechanisms, using a model developed in mammals.

Rate–intensity functions at the most sensitive frequency mostly showed a well-defined breakpoint between an initial steep segment and a progressively flattening segment. This shape has, in mammals, been convincingly traced to a compressive nonlinearity in the cochlear mechanics, which in turn is a reflection of the cochlear amplifier enhancing low-level stimuli. The similarity of the rate–intensity functions of the barn owl is thus further evidence for a similar mechanism in birds. An interesting difference from mammalian data was that this compressive nonlinearity was not shared among fibers of similar characteristic frequency, suggesting a different mechanism with a more locally differentiated operation than in mammals.

In all fibers, the steepest change in discharge rate with rising sound pressure level occurred within 10–20 dB of their respective thresholds. Because the range of neural thresholds at any one characteristic frequency is small in the owl, auditory nerve fibers were collectively most sensitive for changes in sound pressure level within ∼30 dB of the best thresholds. Fibers most sensitive to high frequencies (>6–7 kHz) showed a smaller increase of rate above spontaneous discharge rate than did lower-frequency fibers.
Positive Modulation of AMPA Receptors Increases Neurotrophin Expression by Hippocampal and Cortical Neurons
Authors: Lauterborn Julie C. , Lynch Gary , Vanderklish Peter , Arai Amy , Gall Christine M.
Published: April 2018

This study investigated whether positive modulators of AMPA-type glutamate receptors influence neurotrophin expression by forebrain neurons. Treatments with the ampakine CX614 markedly and reversibly increased brain-derived neurotrophic factor (BDNF) mRNA and protein levels in cultured rat entorhinal/hippocampal slices. Acute effects of CX614 were dose dependent over the range in which the drug increased synchronous neuronal discharges; threshold concentrations for acute responses had large effects on mRNA content when applied for 3 d. Comparable results were obtained with a second, structurally distinct ampakine CX546. Ampakine-induced upregulation was broadly suppressed by AMPA, but not NMDA, receptor antagonists and by reducing transmitter release. Antagonism of L-type voltage-sensitive calcium channels blocked induction in entorhinal cortex but not hippocampus. Prolonged infusions of suprathreshold ampakine concentrations produced peak BDNF mRNA levels at 12 hr and a return to baseline levels by 48 hr. In contrast, BDNF protein remained elevated throughout a 48 hr incubation with the drug. Nerve growth factor mRNA levels also were increased by ampakines but with a much more rapid return to control levels during chronic administration. Finally, intraperitoneal injections of CX546 increased hippocampal BDNF mRNA levels in aged rats and middle-aged mice. The present results provide evidence of regional differences in mechanisms via which activity regulates neurotrophin expression. Moreover, these data establish that changes in synaptic potency produce sufficient network level physiological effects for inducing neurotrophin genes, indicate that the response becomes refractory during prolonged ampakine exposure, and raise the possibility of using positive AMPA modulators to regulate neurotrophin levels in aged brain.
Cannabinoids Decrease the K+M-Current in Hippocampal CA1 Neurons
Authors: Schweitzer Paul
Published: April 2018

Cannabinoid effects on sustained conductances that control neuronal excitability have not been investigated in brain. Here, intracellular voltage-clamp recordings were performed using the rat hippocampal slice preparation to study the postsynaptic effect of cannabinoid agonists on CA1 pyramidal neurons. Superfusion of the cannabimimetics WIN55212–2 or methanandamide onto CA1 neurons elicited an inward steady-state current that reversed near the equilibrium potential for K+and voltage-dependently activated from a threshold of approximately −70 mV. The cannabinoid receptor (CB1) antagonist SR141716 did not alter membrane properties but prevented this effect. Further investigation revealed that the inward current elicited by cannabinoids was caused by a decrease of the noninactivating voltage-dependent K+M-current (IM). Cannabinoids had no effect in slices pretreated with the M-channel blocker linopirdine. Assessment of theIMrelaxation indicated that cannabinoids decreasedIMin a concentration-dependent manner, with a maximum inhibition of 45 ± 3% with WIN55212–2 (EC50of 0.6 μm) and 41 ± 5% with methanandamide (EC50of 1 μm). Cannabinoids did not affect the inwardly rectifying cationic h-current (Ih). The cannabinoid-inducedIMdecrease was prevented by SR141716 but remained unaffected by the muscarinic receptor antagonist atropine. Conversely, the cholinergic agonist carbamylcholine decreasedIMin the presence of SR141716, indicating that cannabinoid and muscarinic receptor activation independently diminishIM. It is concluded that cannabinoids may postsynaptically augment the excitability of CA1 pyramidal neurons by specifically decreasing the persistent voltage-dependentIM.
Distinction among Neuronal Subtypes of Voltage-Activated Sodium Channels by μ-Conotoxin PIIIA
Authors: Safo Patrick , Rosenbaum Tamara , Shcherbatko Anatoly , Choi Deog-Young , Han Edward , Toledo-Aral Juan J. , Olivera Baldomero M. , Brehm Paul , Mandel Gail
Published: April 2018

The functional properties of most sodium channels are too similar to permit identification of specific sodium channel types underlying macroscopic current. Such discrimination would be particularly advantageous in the nervous system in which different sodium channel family isoforms are coexpressed in the same cell. To test whether members of the μ-conotoxin family can discriminate among known neuronal sodium channel types, we examined six toxins for their ability to block different types of heterologously expressed sodium channels. PIIIA μ-conotoxin blocked rat brain type II/IIA (rBII/IIA) and skeletal muscle sodium current at concentrations that resulted in only slight inhibition of rat peripheral nerve (rPN1) sodium current. Recordings from variant lines of PC12 cells, which selectively express either rBII/IIA or rPN1 channel subtypes, verified that the differential block by PIIIA also applied to native sodium current. The sensitivity to block by PIIIA toxin was then used to discriminate between rBII/IIA and rPN1 sodium currents in NGF-treated PC12 cells in which both mRNAs are induced. During the first 24 hr of NGF-treatment, PN1 sodium channels accounted for over 90% of the sodium current. However, over the ensuing 48 hr period, a sharp rise in the proportion of rBII/IIA sodium current occurred, confirming the idea, based on previous mRNA measurements, that two distinct sodium channel types appear sequentially during neuronal differentiation of PC12 cells.
c-fosControls the “Private Pathway” of Light-Induced Apoptosis of Retinal Photoreceptors
Authors: Wenzel Andreas , Grimm Christian , Marti Andreas , Kueng-Hitz Nicole , Hafezi Farhad , Niemeyer Günter , Remé Charlotte E.
Published: April 2018

White light (5 klux for 2 hr) induces apoptosis of rod photoreceptors in wild-type mice (c-fos+/+) within 24 hr, whereas rods ofc-fosknock-out mice (c-fos−/−) are protected (Hafezi et al., 1997b).

The range of this protection was tested by analyzing retinas ofc-fos+/+andc-fos−/−mice up to 10 d after exposure to threefold increased light intensities (15 klux for 2 hr). Inc-fos−/−mice, rods were unaffected, whereas they were destroyed inc-fos+/+mice. After light exposure, mitochondrial damage in rods was observed exclusively inc-fos+/+mice. Electroretinograms recorded 48 hr after exposure revealed a decrease of all components inc-fos+/+mice but indicated no light-induced loss of function inc-fos−/−mice. Thus, inc-fos−/−mice, light-induced apoptosis is blocked or its threshold is elevated more than threefold.

Increased activity of the transcription factor activator protein-1 (AP-1) in retinas of light-exposedc-fos+/+mice indicated an acute contribution of AP-1 to apoptosis induction. AP-1 activity increased already during exposure and peaked ∼6 hr thereafter, coinciding with the appearance of major morphological signs of apoptosis. Activated AP-1 mainly consisted of c-Fos/Jun heterodimers. Inc-fos−/−mice, AP-1 activity remained unchanged, indicating that no other Jun- or Fos-family member could substitute for c-Fos. Like damaging light,N-methyl-N-nitrosourea (MNU) induced AP-1 containing c-Fos inc-fos+/+mice and did not induce AP-1 inc-fos−/−mice. In contrast to light, however, MNU induced apoptosis in rods ofc-fos−/−mice. Thus, c-Fos is essential for a specific premitochondrial “private apoptotic pathway” induced by light but not for the execution of apoptosis induced by other stimuli.
Regulation of Calcineurin by Growth Cone Calcium Waves Controls Neurite Extension
Authors: Lautermilch Nathan J. , Spitzer Nicholas C.
Published: April 2018

Growth cones generate spontaneous transient elevations of intracellular Ca2+that regulate the rate of neurite outgrowth. Here we report that these Ca2+waves inhibit neurite extension via the Ca2+-dependent phosphatase calcineurin (CN) inXenopusspinal neurons. Pharmacological blockers of CN (cyclosporin A and deltamethrin) and peptide inhibitors of CN [theXenopusCN (xCN) autoinhibitory domain and African swine fever virus protein A238L] block the Ca2+-dependent reduction of neurite outgrowth in cultured neurons. Time-lapse microscopy of growing neurites demonstrates directly that the reduction in the rate of outgrowth by Ca2+transients is blocked by cyclosporin A. In contrast, expression of a constitutively active form of xCN in the absence of waves results in shorter neurite lengths similar to those seen in the presence of waves. The developmental expression pattern of xCN transcriptsin vivocoincides temporally with axonal pathfinding by spinal neurons, supporting a role of CN in regulating Ca2+-dependent neurite extension in the spinal cord. Ca2+wave frequency and Ca2+-dependent expression of GABA are not affected by inhibition or activation of CN. However, phosphorylation of the cytoskeletal element GAP-43, which promotes actin polymerization, is reduced by Ca2+waves and enhanced by suppression of CN activity. CN ultimately acts on the growth cone actin cytoskeleton, because disrupting actin microfilaments with cytochalasin D or stabilizing them with jasplakinolide negates the effects of suppressing or activating CN. Destabilization or stabilization of microtubules with colcemide or taxol results in Ca2+-independent inhibition of neurite outgrowth. The results identify components of the cascade by which Ca2+waves act to regulate neurite extension.