bluuebunny/crossref_metadata_2025 huggingface dataset:
Calcium Dependence of Retrograde Inhibition by Endocannabinoids at Synapses onto Purkinje Cells
Authors: Brenowitz Stephan D. , Regehr Wade G.
Published: April 2018

Many types of neurons release endocannabinoids from their dendrites in response to elevation of intracellular calcium levels. Endocannabinoids then activate presynaptic cannabinoid receptors, thereby inhibiting neurotransmitter release for tens of seconds. A crucial step in understanding the physiological role of this retrograde signaling is to determine its sensitivity to elevations of postsynaptic calcium. Here we determine and compare the calcium dependence of endocannabinoid-mediated retrograde inhibition at three types of synapses onto cerebellar Purkinje cells. Previous studies have shown that Purkinje cell depolarization results in endocannabinoid-mediated retrograde inhibition of synapses received from climbing fibers, granule cell parallel fibers, and inhibitory interneurons. Using several calcium indicators with a range of affinities, we performed a series ofin situandin vitrocalibrations to quantify calcium levels in Purkinje cells. We found that postsynaptic calcium levels of ∼15 μM are required for half-maximal retrograde inhibition at all of these synapses. In contrast, previous studies had suggested that endocannabinoid release could occur with slight elevations of calcium above resting levels, which implies that inhibition should be widespread and continuously modulated by subtle changes in intracellular calcium levels. However, our results indicate that such small changes in intracellular calcium are not sufficient to evoke endocannabinoid release. Instead, because of its high requirement for calcium, retrograde inhibition mediated by calcium-dependent endocannabinoid release from Purkinje cells will occur under more restricted conditions and with greater spatial localization than previously appreciated.
Functions of Fibroblast Growth Factor (FGF)-2 and FGF-5 in Astroglial Differentiation and Blood-Brain Barrier Permeability: Evidence from Mouse Mutants
Authors: Reuss Bernhard , Dono Rosanna , Unsicker Klaus
Published: April 2018

Multiple evidence suggests that fibroblast growth factors (FGFs), most prominently FGF-2, affect astroglial proliferation, maturation, and transition to a reactive phenotypein vitro, and after exogenous administration,in vivo. Whether this reflects a physiological role of endogenous FGF is unknown. Using FGF-2 and FGF-5 single- and double mutant mice we show now a region-specific reduction of glial fibrillary acidic protein (GFAP), but not of S100 in gray matter astrocytes. FGF-2 is apparently the major regulator of GFAP, because in mice deficient for FGF-2, GFAP is distinctly reduced in cortex and striatum, whereas in FGF-5-/-animals only a reduction in the midbrain tegmentum can be observed. In FGF-2-/-/FGF-5-/-double mutant animals, GFAP-immunoreactivity is reduced in all three brain regions. Cortical astrocytes cultured from FGF-2-/-/FGF-5-/-double mutant mice revealed reduced levels of GFAP, but not S100 as compared with wild-type littermates. This phenotype could be rescued by exogenous FGF-2 but not FGF-5 (10 ng/ml). Electron microscopy revealed reduced levels of intermediate filaments in perivascular astroglial endfeet. This defect was accompanied by enhanced permeability of the blood-brain barrier (BBB), as detected by albumin extravasation. Levels of the tight junction proteins Occludin and ZO-1 were reduced in blood vessels of FGF-2-/-/FGF-5-/-double mutant mice as compared with wild-type littermates. Our data support the notion that endogenous FGF-2 and FGF-5 regulate GFAP expression in a region-specific manner. The observed defect in astroglial differentiation is accompanied by a defect in BBB function arguing for an indirect or direct role of FGFs in the regulation of BBB permeabilityin vivo.
Gap Junctions Mediate Bystander Cell Death in Developing Retina
Authors: Cusato Karen , Bosco Alejandra , Rozental Renato , Guimarães Cinthya A. , Reese Benjamin E. , Linden Rafael , Spray David C.
Published: April 2018

During development of the retina, programmed cell death helps to establish the final size and distribution of various cell classes in distinct layers of the tissue. Here we show that dying cells in the developing ganglion and inner nuclear layers are clustered spatially and that gap junction inhibitors decrease the clustering of dying cells. To confirm the role of gap junctions in cell death, we induced targeted cell death via intracellular cytochromec(Cc) and examined the induced cells and their neighbors for apoptotic morphology or caspase-3 cleavage. These studies indicate that bystander killing extends to coupled cells.

Quantitative studies of bystander killing were performed by scrape-loading retinas with Ccin the presence of rhodamine dextran (RD; to identify Cc-loaded cells) and by counting pyknotic cells in cryosections. Although only 1.5% of control scrape-loaded cells (RD alone) showed apoptotic morphology, 97% of Ccscrape-loaded cells were pyknotic. Moreover, bystander killing extended to neighboring cells, not labeled with RD, and was reduced significantly by the gap junction inhibitors octanol and carbenoxolone. We hypothesize that dying cells in the retina generate a gap junction-permeant apoptotic signal that mediates bystander killing. This novel finding of naturally occurring bystander cell death may have important implications in the histogenesis and pathology of the nervous system.
Contribution of TWIK-Related Acid-Sensitive K+Channel 1 (TASK1) and TASK3 Channels to the Control of Activity Modes in Thalamocortical Neurons
Authors: Meuth Sven G. , Budde Thomas , Kanyshkova Tatyana , Broicher Tilman , Munsch Thomas , Pape Hans-Christian
Published: April 2018

The thalamocortical network is characterized by rhythmic burst activity during natural sleep and tonic single-spike activity during wakefulness. The change between these two activity modes is partially governed by transmitters acting on leak K+currents in the thalamus, although the nature of the constituting ion channels is not yet known. In the present study, the contribution of members of the two-pore domain K+channel family to the leak current was investigated using whole-cell patch-clamp techniques and molecular biological techniques. RT-PCR andin situhybridization revealed the expression of TWIK-related acid-sensitive K+channel 1 (TASK 1) and TASK3 channels in the rat dLGN. Voltage-clamp recordings of thalamocortical relay neurons in slice preparations demonstrated the existence of a current component sensitive to the TASK channel blocker bupivacaine, which reversed at the presumed K+equilibrium potential, showed outward rectification, and contributed ∼40% to the standing outward current at depolarized values of the membrane potential (-28 mV). The pharmacological profile was indicative of TASK channels, in that the current was sensitive to changes in extracellular pH, reduced by muscarine and increased by halothane, and these effects were occluded by a near-maximal action of bupivacaine. Pharmacological manipulation of this current under current-clamp conditions resulted in a shift between burst and tonic firing modes. It is concluded that TASK1 and TASK3 channels contribute to the muscarine- and halothane-sensitive conductance in thalamocortical relay neurons, thereby contributing to the change in the activity mode of thalamocortical networks observed during the sleep-wake cycle and on application of inhalational anesthetics.
Locus-Specific Rescue of GluRϵ1 NMDA Receptors in Mutant Mice Identifies the Brain Regions Important for Morphine Tolerance and Dependence
Authors: Inoue Makoto , Mishina Masayoshi , Ueda Hiroshi
Published: April 2018

Tolerance and physical dependence caused by chronic treatment of narcotics are good models to study basic neuronal plasticity. Activation of the NMDA subtype of the glutamate receptor has been implicated as an anti-opioid system in the development of morphine analgesic tolerance and dependence. The present study examines the specific role of the ϵ1 subunit of the NMDA receptor using mice lacking the gene encoding ϵ1 subunit of the NMDA receptor (GluRϵ1-/-mice). GluRϵ1-/-mice showed significant enhancement and prolongation of morphine anti-nociception, compared with wild-type GluRϵ1+/+mice. GluRϵ1-/-mice also showed a marked loss of the analgesic tolerance after repeated morphine treatments. In C57BL/6J mice treated with chronic morphine after tolerance paradigm, the GluRϵ1 protein expression significantly increased in periaqueductal gray matter (PAG), ventral tegmental area (VTA) and nucleus accumbens (NAc), but not amygdala or hippocampus. The rescue of GluRϵ1 protein by electroporation into the PAG and VTA, but not NAc of GluRϵ1-/-mice significantly reversed morphine analgesic tolerance liability. Similar attempts were also performed in the naloxone-precipitated physical dependence paradigm. GluRϵ1-/-mice showed marked loss of typical withdrawal abstinence behaviors, and significant enhancement of GluRϵ1 protein expression was only observed in NAc by chronic morphine treatments after dependence paradigm. The rescue of GluRϵ1 protein by electroporation into the NAc of GluRϵ1-/-mice significantly reversed the loss of abstinence behaviors. These findings suggest that GluRϵ1 has locus-specific roles in the development of morphine analgesic tolerance and physical dependence.
Abnormal Dysbindin Expression in Cerebellar Mossy Fiber Synapses in the mdx Mouse Model of Duchenne Muscular Dystrophy
Authors: Sillitoe Roy V. , Benson Matthew A. , Blake Derek J. , Hawkes Richard
Published: April 2018

The dystrophin-associated protein complex (DPC), comprising sarcoglycans, dystroglycans, dystrobrevins, and syntrophins, is a component of synapses both in muscle and brain. Dysbindin is a novel component of the DPC, which binds to β-dystrobrevin and may serve as an adaptor protein that links the DPC to an intracellular signaling cascade. Disruption of the DPC results in muscular dystrophy, and mutations in the human ortholog of dysbindin have been implicated in the pathogenesis of schizophrenia. In both cases, patients also present with neurological symptoms reminiscent of cerebellar problems. In the mouse cerebellum, dysbindin immunoreactivity is expressed at high levels in a subset of mossy fiber synaptic glomeruli in the granular layer. Lower levels of dysbindin immunoreactivity are also detected in Purkinje cell dendrites. In the cerebellar vermis, dysbindin-immunoreactive glomeruli are restricted to an array of parasagittal stripes that bears a consistent relationship to Purkinje cell parasagittal band boundaries as defined by the expression of the respiratory isoenzyme zebrin II/aldolase c. In a mouse model of Duchenne muscular dystrophy, themdxmutant, in which dystrophin is not expressed, there is a dramatic increase in the number of dysbindin-immunoreactive glomeruli in the posterior cerebellar vermis. Moreover, the topography of the terminal fields is disrupted, replacing the stripes by a homogeneous distribution. Abnormal synaptic organization in the cerebellum may contribute to the neurological problems associated with muscular dystrophy and schizophrenia.
Active Transport of the Survival Motor Neuron Protein and the Role of Exon-7 in Cytoplasmic Localization
Authors: Zhang Honglai L. , Pan Feng , Hong Daewha , Shenoy Shailesh M. , Singer Robert H. , Bassell Gary J.
Published: April 2018

Spinal muscular atrophy (SMA) is a neurodegenerative disease caused by deletion and/or mutation of the survival motor neuron protein Gene (SMN1) that results in the expression of a truncated protein lacking the C terminal exon-7. Whereas SMN has been shown to be an important component of diverse ribonucleoprotein (RNP) complexes, its function in neurons is unknown. We hypothesize that the active transport of SMN may be important for neurite outgrowth and that disruption of exon-7 could impair its normal intracellular trafficking. SMN was localized in granules that were associated with cytoskeletal filament systems and distributed throughout neurites and growth cones. Live cell imaging of enhanced green fluorescent protein (EGFP)-SMN granules revealed rapid, bidirectional and cytoskeletal-dependent movements. Exon-7 was necessary for localization of SMN into the cytoplasm but was not sufficient for granule formation and transport. A cytoplasmic targeting signal within exon-7 was identified that could completely redistribute the nuclear protein D-box binding factor 1 into the cytoplasm. Neurons transfected with SMN lacking exon-7 had significantly shorter neurites, a defect that could be rescued by redirecting the exon-7 deletion mutant into neurites by a targeting sequence from growth-associated protein-43. These findings provide the first demonstration of cytoskeletal-based active transport of SMN in neuronal processes and the function of exon-7 in cytoplasmic localization. Such observations provide motivation to investigate possible transport defects or inefficiency of SMN associated RNPs in motor neuron axons in SMA.
Semaphorin 3F Is Critical for Development of Limbic System Circuitry and Is Required in Neurons for Selective CNS Axon Guidance Events
Authors: Sahay Amar , Molliver Mark E. , Ginty David D. , Kolodkin Alex L.
Published: April 2018

Little is known about the role of class 3 semaphorins in the development of CNS circuitry. Several class 3 semaphorins, including semaphorin 3F (Sema3F) bind to the receptor neuropilin-2 to confer chemorepulsive responsesin vitro. To understand the role of Sema3F in the establishment of neural circuitryin vivo, we have generatedsema3Fnull andsema3Fconditional mutant mice. Inspection of the peripheral nervous system insema3Fnull mice reveals that Sema3F is essential for the proper organization of specific cranial nerve projections. Analysis of the CNS insema3Fnull mice reveals a crucial role for Sema3F in the rostral forebrain, midbrain, and hippocampus in establishing specificNpn-2(neuropilin-2)-expressing limbic tracts. Furthermore, we identify Sema3F and Npn-2 as the first guidance cue-receptor pair shown to be essential for controlling the development of amygdaloid circuitry. In addition, we provide genetic evidence in vertebrates for a neuronal requirement of a soluble axon guidance cue in CNS axon guidance. Our data reveal a requirement for neuronal Sema3F in the normal development of the anterior commissure in the ventral forebrain and infrapyramidal tract in the hippocampus. Thus, our results show that Sema3F is the principal ligand for Npn-2-mediated axon guidance eventsin vivoand is a critical determinant of limbic and peripheral nervous system circuitry.
Impaired NMDA Receptor-Mediated Postsynaptic Function and Blunted NMDA Receptor-Dependent Persistent Pain in Mice Lacking Postsynaptic Density-93 Protein
Authors: Tao Yuan-Xiang , Rumbaugh Gavin , Wang Guo-Du , Petralia Ronald S. , Zhao Chengshui , Kauer Frederick W. , Tao Feng , Zhuo Min , Wenthold Robert J. , Raja Srinivasa N. , Huganir Richard L. , Bredt David S. , Johns Roger A.
Published: April 2018

Modification of synaptic NMDA receptor (NMDAR) expression influences NMDAR-mediated synaptic function and associated persistent pain. NMDARs directly bind to a family of membrane-associated guanylate kinases (MAGUKs) that regulate surface and synaptic NMDAR trafficking in the CNS. We report here that postsynaptic density-93 protein (PSD-93), a postsynaptic neuronal MAGUK, is expressed abundantly in spinal dorsal horn and forebrain, where it colocalizes and interacts with NMDAR subunits NR2A and NR2B. Targeted disruption of the PSD-93 gene reduces not only surface NR2A and NR2B expression but also NMDAR-mediated excitatory postsynaptic currents and potentials, without affecting surface AMPA receptor expression or its synaptic function, in the regions mentioned above. Furthermore, mice lacking PSD-93 exhibit blunted NMDAR-dependent persistent pain induced by peripheral nerve injury or injection of Complete Freund's Adjuvant, although they display intact nociceptive responsiveness to acute pain. PSD-93 appears to be important for NMDAR synaptic targeting and function and to be a potential biochemical target for the treatment of persistent pain.
Differential Properties of Astrocyte Calcium Waves Mediated by P2Y1 and P2Y2 Receptors
Authors: Gallagher Conor J. , Salter Michael W.
Published: April 2018

Intercellular spread of Ca2+waves is the primary manifestation of cell-to-cell communication among astrocytes. Ca2+waves propagate via the release of a diffusible extracellular messenger that has been identified as ATP. In dorsal spinal astrocytes, Ca2+waves are mediated by activation of two functionally distinct subtypes of metabotropic purinoceptor: the P2Y1 receptor and a receptor previously classified as P2U. Here, we show that the P2U receptor is molecularly and pharmacologically identical to the cloned P2Y2 receptor. Both P2Y1 and P2Y2 receptors are necessary for full Ca2+wave propagation in spinal astrocytes. Conversely, heterologous expression of either P2Y1 or P2Y2 receptors is sufficient for Ca2+waves, and expressing these receptor subtypes together recapitulates the characteristics of Ca2+waves in spinal astrocytes. Thus, P2Y1 and P2Y2 receptors are both necessary and sufficient for propagation of Ca2+waves. Furthermore, we demonstrate that there are dramatic differences in the characteristics of Ca2+waves propagating through each receptor subtype: Ca2+waves propagating via P2Y2 receptors travel faster and further than those propagating via P2Y1 receptors. We find that the nucleotidase apyrase selectively blocks Ca2+wave propagation through P2Y2 receptors but accelerates Ca2+waves propagating through P2Y1 receptors. Taking our results together with those from the literature, we suggest that mediation of Ca2+waves by ATP leading to activation of two subtypes of receptor, P2Y1 and P2Y2, may be a general principle for gliotransmission in the CNS. Thus, processes that alter expression or function of these receptors may control the rate and extent of astrocyte Ca2+waves.
The Human Immunodeficiency Virus-1 Protein Tat and Its Discrete Fragments Evoke Selective Release of Acetylcholine from Human and Rat Cerebrocortical Terminals through Species-Specific Mechanisms
Authors: Feligioni Marco , Raiteri Luca , Pattarini Roberto , Grilli Massimo , Bruzzone Santina , Cavazzani Paolo , Raiteri Maurizio , Pittaluga Anna
Published: April 2018

The effect of the human immunodeficiency virus-1 protein Tat was investigated on neurotransmitter release from human and rat cortical nerve endings. Tat failed to affect the release of several neurotransmitters, such as glutamate, GABA, norepinephrine, and others, but it evoked the release of [3H]ACh via increase of cytosolic [Ca2+]. In human nerve terminals, the Tat effect partly depends on Ca2+entry through voltage-sensitive Ca2+channels, because Cd2+halved the Tat-evoked release. Activation of group I metabotropic glutamate receptors (mGluR) and mobilization of Ca2+from IP3-sensitive intraterminal stores are also involved, because the Tat effect was prevented by mGluR antagonists 2-methyl-6-(phenylethynyl)pyridine hydrochloride and 7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester and by the IP3receptor antagonists heparin and xestospongin C. Furthermore, the group I selective mGlu agonist (RS)-3,5-dihydroxyphenylglycine enhanced [3H]ACh release. In rat nerve terminals, the Tat-evoked release neither depends on external Ca2+ions entry nor on IP3-mediated mechanisms. Tat seems to cause mobilization of Ca2+from ryanodine-sensitive internal stores because its effect was prevented by both 8-bromo-cyclic adenosine diphosphate-ribose and dantrolene. The Tat-evoked release from human synaptosomes was mimicked by the peptide sequences Tat 32-62, Tat 49-86, and Tat 41-60. In contrast, the Tat 49-86 and Tat 61-80 fragments, but not the Tat 32-62 fragment, were active in rat synaptosomes. In conclusion, Tat elicits Ca2+-dependent [3H]ACh release by species-specific intraterminal mechanisms by binding via discrete amino acid sequences to different receptive sites on human and rat cholinergic terminals.
Response to Contrast of Electrophysiologically Defined Cell Classes in Primary Visual Cortex
Authors: Contreras Diego , Palmer Larry
Published: April 2018

Information processing in the visual cortex is critically dependent on the input-output relationships of its component neurons. The transformation of synaptic inputs into spike trains depends in turn on the host of intrinsic membrane properties expressed by neurons, which define established electrophysiological cell classes in the neocortex. Here we studied, with intracellular recordingsin vivo, how the electrophysiological cell classes in the primary visual cortex transform an increasing input, represented by stimulus contrast, into membrane depolarization and trains of action potentials. We used contrast as input because, regardless of their stimulus selectivity, primary visual cortical cells increase their firing rates in response to increases in luminance contrast. We found that both the spike rate response and the membrane potential response are best described by the hyperbolic ratio function when compared with linear, power, and logarithmic functions. In addition, both responses show similar parameter values and similar residual variance from the fits to all four functions. We also found that changes in membrane potential are similar, but firing rates differ strongly, between the established electrophysiological cell classes: fast spiking neurons show the highest firing rates, followed by fast rhythmic bursting, and regular spiking (RS) cells. In addition, among complex cells, RS cells from supragranular layers fired at higher rates than RS cells from infragranular layers. Finally, we show that the differences in firing rates between cell classes arise from differences in the slope of the relationship between membrane potential and spike rate.
Persistent Cue-Evoked Activity of Accumbens Neurons after Prolonged Abstinence from Self-Administered Cocaine
Authors: Ghitza Udi E. , Fabbricatore Anthony T. , Prokopenko Volodymyr , Pawlak Anthony P. , West Mark O.
Published: April 2018

Persistent neural processing of information regarding drug-predictive environmental stimuli may be involved in motivating drug abusers to engage in drug seeking after abstinence. The addictive effects of various drugs depend on the mesocorticolimbic dopamine system innervating the nucleus accumbens. We used single-unit recording in rats to test whether accumbens neurons exhibit responses to a discriminative stimulus (SD) tone previously paired with cocaine availability during cocaine self-administration. Presentation of the tone after 3-4 weeks of abstinence resulted in a cue-induced relapse of drug seeking under extinction conditions. Accumbens neurons did not exhibit tone-evoked activity before cocaine self-administration training but exhibited significant SDtone-evoked activity during extinction. Under extinction conditions, shell neurons exhibited significantly greater activity evoked by the SDtone than that evoked by a neutral tone (i.e., never paired with reinforcement). In contrast, core neurons responded indiscriminately to presentations of the SDtone or the neutral tone. Accumbens shell neurons exhibited significantly greater SDtone-evoked activity than did accumbens core neurons. Although the onset of SDtone-evoked activity occurred well before the earliest movements commenced (150 msec), this activity often persisted beyond the onset of tone-evoked movements. These results indicate that accumbens shell neurons exhibit persistent processing of information regarding reward-related stimuli after prolonged drug abstinence. Moreover, the accumbens shell appears to be involved in discriminating the motivational value of reward-related associative stimuli, whereas the accumbens core does not.
Presynaptic and Postsynaptic Mechanisms of a Novel Form of Homosynaptic Potentiation atAplysiaSensory-Motor Neuron Synapses
Authors: Jin Iksung , Hawkins Robert D.
Published: April 2018

Previous studies have shown that homosynaptic potentiation produced by rather mild tetanic stimulation (20 Hz, 2 sec) atAplysiasensory-motor neuron synapses in isolated cell culture involves both presynaptic and postsynaptic Ca2+(Bao et al., 1997). We have now investigated the sources of Ca2+and some of its downstream targets. Although the potentiation lasts >30 min, it does not require Ca2+influx through either NMDA receptor channels or L-type Ca2+channels. Rather, the potentiation involves metabotropic receptors and intracellular Ca2+release from both postsynaptic IP3-sensitive and presynaptic ryanodine-sensitive stores. In addition, it involves protein kinases, including both presynaptic and postsynaptic CamKII and probably MAP kinase. Finally, it does not require transsynaptic signaling by nitric oxide but it may involve AMPA receptor insertion. The potentiation, thus, shares components of the mechanisms of post-tetanic potentiation, NMDA- and mGluR-dependent long-term potentiation, and even long-term depression, but is not identical to any of them. These results are consistent with the more general idea that there is a molecular alphabet of basic components that can be combined in various ways to create novel as well as known types of plasticity.
Neuromuscular Development after the Prevention of Naturally Occurring Neuronal Death by Bax Deletion
Authors: Sun Woong , Gould Thomas W. , Vinsant Sharon , Prevette David , Oppenheim Ronald W.
Published: April 2018

The removal of excess neurons by programmed cell death (PCD) is believed to be critical for the proper development and function of the nervous system. A major role of this neuronal loss is to attain quantitative matching of neurons with their targets and afferents. Because motoneurons (MNs) inBaxknock-out (BaxKO) mice fail to undergo PCD in the face of normal target muscle development, we asked whether the excess rescued neurons inBaxKO mice can develop normally. We observed many small atrophied MNs in postnatalBaxKO mice, and these failed to innervate limb muscle targets. When examined embryonically during the PCD period, however, these excess MNs had initiated target innervation. To examine whether a limitation in trophic factor availability is responsible for postnatal MN atrophy and loss of innervation, we applied glial cell line-derived neurotrophic factor (GDNF) to neonatal mice. GDNF injection for 7-14 d induced the regrowth and reinnervation of muscle targets by atrophic MNs inBaxKO mice and prevented the normal postnatal death of MNs in wild-type mice. These results indicate that, although initially all of the MNs, including those rescued byBaxdeletion, are able to project to and innervate targets, because of limited target-derived signals required for maintaining innervation and growth, only a subpopulation can grow and retain target contacts postnatally. Although sensory neurons in the dorsal root ganglia are also rescued from PCD byBaxdeletion, their subsequent development is less affected than that of MNs.
Different Signals Control Laminar Specificity of Commissural and Entorhinal Fibers to the Dentate Gyrus
Authors: Zhao Shanting , Förster Eckart , Chai Xuejun , Frotscher Michael
Published: April 2018

The factors governing the characteristic laminated termination of hippocampal afferents are essentially unknown. Principally, diffusible factors of the target region, membrane-bound molecules on the ingrowing afferent fibers and on the postsynaptic target cells as well as molecules of the extracellular matrix (ECM), may play a role. Using slice cocultures as a model, we show that hyaluronic acid, an ECM molecule, is essential for the segregated, layer-specific termination of entorhinal fibers but not of commissural afferents to the mouse dentate gyrus. Laminar specificity of the latter, in contrast, is determined by the position of the postsynaptic granule cells. Thus, malpositioning of the granule cells in slice cultures from reeler mutant mice altered the projection of commissural fibers from cocultured wild-type hippocampus. In contrast, commissural fibers from reeler mouse hippocampus formed a normal, sharply delineated projection to the inner molecular layer of cocultured wild-type dentate gyrus, precluding a cell-autonomous effect of the reeler mutation on commissural neurons. Interestingly enough, entorhinal fibers formed their normal, sharply delineated projection in cocultured reeler dentate gyrus despite the malpositioning of the target granule cells. Because hyaluronan-associated molecules are likely to control the segregated termination of entorhinal fibers, we compared immunolabeling for neurocan and chondroitin sulfate in sections from reeler and wild-type mice and found it similar in both genotypes. Together these results show that different mechanisms underlie the formation of commissural and entorhinal fiber layers during the development of the dentate gyrus.
Functional Interaction between T2R Taste Receptors and G-Protein α Subunits Expressed in Taste Receptor Cells
Authors: Ueda Takashi , Ugawa Shinya , Yamamura Hisao , Imaizumi Yuji , Shimada Shoichi
Published: April 2018

Bitter taste perception is a conserved chemical sense against the ingestion of poisonous substances in mammals. A multigene family of G-protein-coupled receptors, T2R (so-called TAS2R or TRB) receptors and a G-protein α subunit (Gα), gustducin, are believed to be key molecules for its perception, but little is known about the molecular basis for its interaction. Here, we use a heterologous expression system to determine a specific domain of gustducin necessary for T2R coupling. Two chimeric Gα16 proteins harboring 37 and 44 gustducin-specific sequences at their C termini (G16/gust37 and G16/gust44) responded to different T2R receptors with known ligands, but G16/gust 23, G16/gust11, and G16/gust5 did not. The former two chimeras contained a predictedβ6 sheet, anα5 helix, and an extreme C terminus of gustducin, and all the domains were indispensable to the expression of T2R activity. We also expressed G16 protein chimeras with the corresponding domain from other Gαi proteins, cone-transducin (Gαt2), Gαi2, and Gαz (G16/t2, G16/i2, and G16/z). As a result, G16/t2 and G16/i2 produced specific responses of T2Rs, but G16/z did not. Because Gαt2 and Gαi2 are expressed in the taste receptor cells, these G-protein αi subunits may also be involved in bitter taste perception via T2R receptors. The present Gα16-based chimeras could be useful tools to analyze the functions of many orphan G-protein-coupled taste receptors.
Conditional Ablation of Striatal Neuronal Types Containing Dopamine D2 Receptor Disturbs Coordination of Basal Ganglia Function
Authors: Sano Hiromi , Yasoshima Yasunobu , Matsushita Natsuki , Kaneko Takeshi , Kohno Kenji , Pastan Ira , Kobayashi Kazuto
Published: April 2018

Dopamine (DA) exerts synaptic organization of basal ganglia circuitry through a variety of neuronal populations in the striatum. We performed conditional ablation of striatal neuronal types containing DA D2 receptor (D2R) by using immunotoxin-mediated cell targeting. Mutant mice were generated that express the human interleukin-2 receptor α-subunit under the control of theD2Rgene. Intrastriatal immunotoxin treatment of the mutants eliminated the majority of the striatopallidal medium spiny neurons and cholinergic interneurons. The elimination of these neurons caused hyperactivity of spontaneous movement and reduced motor activation in response to DA stimulation. The elimination also induced upregulation ofGADgene expression in the globus pallidus (GP) and downregulation of cytochrome oxidase activity in the subthalamic nucleus (STN), whereas it attenuated DA-induced expression of the immediate-early genes (IEGs) in the striatonigral neurons. In addition, chemical lesion of cholinergic interneurons did not alter spontaneous movement but caused a moderate enhancement in DA-induced motor activation. This enhancement of the behavior was accompanied by an increase in the IEG expression in the striatonigral neurons. These data suggest that ablation of the striatopallidal neurons causes spontaneous hyperactivity through modulation of the GP and STN activity and that the ablation leads to the reduction in DA-induced behavior at least partly through attenuation of the striatonigral activity as opposed to the influence of cholinergic cell lesion. We propose a possible model in which the striatopallidal neurons dually regulate motor behavior dependent on the state of DA transmission through coordination of the basal ganglia circuitry.
Prestin and the Dynamic Stiffness of Cochlear Outer Hair Cells
Authors: He David Z. Z. , Jia Shuping , Dallos Peter
Published: April 2018

The outer hair cell (OHC) lateral wall is a unique trilaminate structure consisting of the plasma membrane, the cortical lattice, and subsurface cisternae. OHCs are capable of altering their length in response to transmembrane voltage change. This so-called electromotile response is presumed to result from conformational changes of membrane-bound protein molecules, named prestin. OHC motility is accompanied by axial stiffness changes when the membrane potential of the cell is altered. During length changes, intracellular anions (mainly Cl-) act as extrinsic voltage sensors. In this study, we inquired whether the motor proteins are responsible for the voltage-dependent axial stiffness of OHCs, and whether ACh, the neurotransmitter of efferent neurons, modulates the stiffness of the cortical lattice and/or the stiffness of the motor protein. The experiments were done on isolated guinea pig OHCs in the whole-cell voltage-clamp mode. Axial stiffness was determined by loading a fiber of known stiffness onto the apical surface of the cells. Voltage-dependent stiffness and cell motility disappeared, and the axial stiffness of the cells significantly decreased after removal of intracellular Cl-. The result suggests that the stiffness of the motor protein is a major contributor to the global axial stiffness of OHCs. ACh was found to affect both the motor protein and other lateral wall stiffness components.
The Transmembrane Semaphorin Sema4D/CD100, an Inhibitor of Axonal Growth, Is Expressed on Oligodendrocytes and Upregulated after CNS Lesion
Authors: Moreau-Fauvarque Caroline , Kumanogoh Atsushi , Camand Emeline , Jaillard Céline , Barbin Gilles , Boquet Isabelle , Love Christopher , Jones E. Yvonne , Kikutani Hitoshi , Lubetzki Catherine , Dusart Isabelle , Chédotal Alain
Published: April 2018

Semaphorins are a family of secreted and membrane-bound proteins, known to regulate axonal pathfinding. Sema4D, also called CD100, was first isolated in the immune system where it is involved in B and T cell activation. We found that in the mouse, Sema4D is expressed in cells throughout the CNS white matter, with a peak during the myelination period. Double-labeling experiments with different markers of oligodendrocyte lineage such as olig1, olig2, platelet-derived growth factor receptor α, and proteolipid protein showed that Sema4D was expressed selectively by oligodendrocytes and myelin. The presence of Sema4D in myelin was confirmed using Western blot. Sema4D expression in myelinating oligodendrocytes was further observed using neuron-oligodendrocyte cocultures. Moreover, using stripe assay, we found that Sema4D is strongly inhibitory for postnatal sensory and cerebellar granule cell axons. This prompted us to examine whether Sema4D expression is modified after CNS injury. At 8 d after spinal cord lesions, Sema4D expression was strongly upregulated in oligodendrocytes at the periphery of the lesion. Sema4D-positive cells were not colabeled with the astrocyte marker GFAP, with the microglial and macrophagic marker isolectin B4, or with NG2, a marker of oligodendrocyte precursors. This upregulation was transient because from 1 month after the lesion, Sema4D expression was back to its normal level. These results indicate that Sema4D is a novel inhibitory factor for axonal regeneration expressed in myelin.
Short-Term Dynamics of a Mixed Chemical and Electrical Synapse in a Rhythmic Network
Authors: Mamiya Akira , Manor Yair , Nadim Farzan
Published: April 2018

In the rhythmically active pyloric circuit of the spiny lobster, the synapse between the lateral pyloric (LP) neuron and pyloric constrictor (PY) neuron has an inhibitory depressing chemical and an electrical component. To understand how the dynamics of the LP→PY synapse affect the relative firing times between these two neurons in an ongoing rhythm, we characterized the dynamics of the LP→PY synapse after a pharmacological block of ongoing activity. When a train of voltage pulses was applied to the voltage-clamped LP neuron, the inhibitory chemical component of the postsynaptic potential (PSP) in the PY neuron rapidly depressed. Thus, after the first few pulses, the PSP was either hyperpolarizing or depolarizing, depending on the interpulse duration, with shorter interpulse durations producing depolarizing PSPs. To characterize the synaptic response during rhythmic activity, we played back prerecorded realistic waveforms in the voltage-clamped LP neuron. After an initial transient, the resulting PSP in PY was always depolarizing, suggesting that in an ongoing rhythm, the electrical component of the synapse is dominant. However, our results indicate that the chemical component of the synapse acts to delay the peak time of the PSP and to reduce its amplitude, and that these effects become more important at slower cycle periods.
Fibroblast Growth Factor-Inducible-14 Is Induced in Axotomized Neurons and Promotes Neurite Outgrowth
Authors: Tanabe Katsuhisa , Bonilla Iris , Winkles Jeffrey A. , Strittmatter Stephen M.
Published: April 2018

For successful nerve regeneration, a coordinated shift in gene expression pattern must occur in axotomized neurons. To identify genes participating in axonal regeneration, we characterized mRNA expression profiles in dorsal root ganglia (DRG) before and after sciatic nerve transection. Dozens of genes are differentially expressed after sciatic nerve injury by microarray analysis. Induction of SOX11, FLRT3, myosin-X, and fibroblast growth factor-inducible-14 (Fn14) mRNA in axotomized DRG neurons was verified by Northern analysis andin situhybridization. TheFn14gene encodes a tumor necrosis-like weak inducer of apoptosis (TWEAK) receptor and is dramatically induced in DRG neurons after nerve damage, despite low expression in developing DRG neurons. Fn14 expression in PC12 cells is also upregulated by nerve growth factor treatment. Overexpression of Fn14 promotes growth cone lamelipodial formation and increases neurite outgrowth in PC12 cells. These Fn14 effects are independent of the ligand, TWEAK. Fn14 colocalizes with the Rho family GTPases, Cdc42 and Rac1. Furthermore, Fn14 physically associates with Rac1 GTPase in immunoprecipitation studies. The neurite outgrowth-promoting effect of Fn14 is enhanced by Rac1 activation and suppressed by Rac1 inactivation. These findings suggest that Fn14 contributes to nerve regeneration via a Rac1 GTPase-dependent mechanism.
The Contraceptive Agent Provera Enhances GABAAReceptor-Mediated Inhibitory Neurotransmission in the Rat Hippocampus: Evidence for Endogenous Neurosteroids?
Authors: Belelli Delia , Herd Murray B.
Published: April 2018

Neurosteroids typified by 5α-pregnan-3α-ol-20-one (5α3α) have emerged as the most potent endogenous positive modulators of the GABAAreceptor, the principal mediator of fast inhibitory transmission within the CNS. Neurosteroids can be synthesizedde novoin the brain in levels sufficient to modulate GABAAreceptor function and, thus, might play an important physiological-pathophysiological role. Indirect support for this proposal comes from the observation that neurosteroid action is region and neuron selective. However, the mechanism(s) that imparts specificity of action remains primarily elusive. Although neurosteroids are relatively promiscuous toward different GABAAreceptor isoforms, the contribution of local neurosteroid metabolism has been relatively unexplored. Here, we investigate the role of neurosteroid metabolism by using electrophysiological techniques to compare the actions of 5α3α and its metabolically stable synthetic analog ganaxolone on inhibitory neurotransmission in CA1 and dentate gyrus neurons. Furthermore, we evaluate the contribution of a key enzyme in neurosteroid metabolism [i.e., 3α-hydroxysteroidoxidoreductase (3α-HSOR)] to the inactivation of endogenous, or exogenously applied 5α3α. We show that low concentrations of ganaxolone, but not of 5α3α, enhance inhibitory transmission in dentate gyrus, whereas both steroids are similarly effective in CA1 neurons. Furthermore, inhibition of 3α-HSOR by the contraceptive agent Provera results in enhanced synaptic and extrasynaptic GABAAreceptor-mediated inhibition in the dentate gyrus but not in the CA1 region. Collectively, these findings advocate a crucial role for local steroid metabolism in shaping GABAAreceptor-mediated inhibition in a regionally dependent manner and suggest a novel action by the contraceptive agent on inhibitory centers in the CNS.
Multiplicative Gain Changes Are Induced by Excitation or Inhibition Alone
Authors: Murphy Brendan K. , Miller Kenneth D.
Published: April 2018

We model the effects of excitation and inhibition on the gain of cortical neurons. Previous theoretical work has concluded that excitation or inhibition alone will not cause a multiplicative gain change in the curve of firing rate versus input current. However, such gain changesin vivoare measured in the curve of firing rate versus stimulus parameter. We find that when this curve is considered, and when the nonlinear relationships between stimulus parameter and input current and between input current and firing ratein vivoare taken into account, then simple excitation or inhibition alone can induce a multiplicative gain change. In particular, the power-law relationship between voltage and firing rate that is induced by neuronal noise is critical to this result. This suggests an unexpectedly simple mechanism that may underlie the gain modulations commonly observed in cortex. More generally, it suggests that a smaller input will multiplicatively modulate the gain of a larger one when both converge on a common cortical target.
Neuroprotection by Nicotine in Mouse Primary Cortical Cultures Involves Activation of Calcineurin and L-Type Calcium Channel Inactivation
Authors: Stevens Tanya R. , Krueger Stefan R. , Fitzsimonds Reiko M. , Picciotto Marina R.
Published: April 2018

Regulation of intracellular calcium influences neuronal excitability, synaptic plasticity, gene expression, and neurotoxicity. In this study, we investigated the role of calcium in mechanisms underlying nicotine-mediated neuroprotection from glutamate excitotoxicity. Neuroprotection by nicotine in primary cortical cultures was not seen in knock-out mice lacking the β2 subunit of the nicotinic acetylcholine receptor (nAChR). Neuroprotection was partially blocked in wild-type cultures by α-bungarotoxin, an antagonist of the α7 nAChR subtype, suggesting a potential cooperative role for these subtypes. Pretreatment with nicotine decreased glutamate-mediated calcium influx in primary cortical cultures by 41%, an effect that was absent in cultures from knock-out mice lacking the β2 subunit of the nAChR. This effect was dependent on calcium entry through L-type channels during nicotine pretreatment in wild-type cultures. The ability of nicotine to decrease glutamate-mediated calcium influx was occluded by cotreatment with nifedipine during glutamate application, suggesting that nicotine pretreatment decreased subsequent activity of L-type calcium channels. Treatment with the calcineurin antagonists FK506 and cyclosporine during pretreatment eliminated both nicotine-mediated neuroprotection and the effects of nicotine on L-type channels. We conclude that neuroprotective effects of nicotine in cortical neurons involve both β2- and α7-containing nAChRs, activation of calcineurin, and decreased intracellular calcium via L-type channels.
Nonlinear Integration of Sensory Responses in the Rat Barrel Cortex: An Intracellular StudyIn Vivo
Authors: Higley Michael J. , Contreras Diego
Published: April 2018

To study integration of converging sensory inputs on single cortical neurons, we performed intracellular recordingsin vivoin the barrel cortex of the barbiturate-anesthetized rat. We deflected the principal whisker (PW) for each cell either alone or preceded (at 20, 50, and 100 msec) by the deflection of a small number of remote whiskers (RWs) far from the PW. The synaptic responses to both the PW and the RW were similar qualitatively and consisted of excitation followed by inhibition that comprised an early and a late component. The RW response was of smaller amplitude and more often subthreshold for action potential generation. The main effect of the RW deflection was a suppression of the subsequent response to the PW that was most pronounced at the 20 msec interval and decreased progressively at the 50 and 100 msec intervals. Suppression of the spike output of the cell was not caused by hyperpolarization (subtractive inhibition) but by a reduction in the EPSP amplitude (divisive inhibition), resulting in a highly sublinear summation of the two responses. The small decrease in input resistance caused by the RW responses is not consistent with synaptic shunting as the main cause of the reduction of the EPSP amplitude. Instead, our results suggest that suppression results from a decrease in the amount of synaptic input triggered by the PW, particularly the early excitation. We suggest that this process involves a reduction in reverberant granular cell excitation that is induced by PW deflection.
Responses of Human Motoneurons to Corticospinal Stimulation during Maximal Voluntary Contractions and Ischemia
Authors: Butler Jane E. , Taylor Janet L. , Gandevia Simon C.
Published: April 2018

The discharge frequency of human motoneurons declines during a sustained isometric maximal voluntary contraction (MVC) of elbow flexor muscles, but the cause is unresolved. We aimed to determine whether motoneurons were inhibited during a sustained fatiguing contraction of the elbow flexor muscles and whether this inhibition was caused by the discharge of group III and IV muscle afferents. Subjects performed brief MVCs before and after a fatiguing 2 min MVC. During maximal efforts, electromyographic responses recorded from the elbow flexor muscles were evoked by stimulation of the corticospinal tracts at the cervicomedullary level [cervicomedullary motor evoked potentials (CMEPs)] and by supramaximal stimulation over the brachial plexus (Mmax). This revealed a novel decrease in the size of the muscle response to corticospinal tract stimulation during fatigue. During the sustained MVCs, the size of CMEPs decreased to 81 ± 15 and 78 ± 15% of the control value for brachioradialis and biceps brachii, respectively (mean ± SEM;n= 8). This recovered within 15 sec after the fatiguing contraction. In a second set of studies, input from group III and IV muscle afferents was prolonged after the end of the fatiguing contraction by holding the muscle ischemic with a cuff inflated above arterial pressure. Despite the maintained discharge of group III and IV afferents, the CMEPs again recovered within 15 sec of the end of the sustained contraction. These results show a diminished output of spinal motoneurons to stimulation of corticospinal tracts during a fatiguing MVC; however, the mechanisms responsible for this decline are not attributable to activity in group III and IV muscle afferents.