bluuebunny/crossref_metadata_2025 huggingface dataset:
PSD-93 Knock-Out Mice Reveal That Neuronal MAGUKs Are Not Required for Development or Function of Parallel Fiber Synapses in Cerebellum
Authors: McGee Aaron W. , Topinka J. Rick , Hashimoto Kouichi , Petralia Ronald S. , Kakizawa Sho , Kauer Frederick , Aguilera-Moreno Andrea , Wenthold Robert J. , Kano Masanobu , Bredt David S.
Published: April 2018

Membrane-associated guanylate kinases (MAGUKs) are abundant postsynaptic density (PSD)-95/discs large/zona occludens-1 (PDZ)-containing proteins that can assemble receptors and associated signaling enzymes at sites of cell–cell contact, including synapses. PSD-93, a postsynaptic neuronal MAGUK, has three PDZ domains that can bind to specific ion channels, including NMDA δ2 type glutamate receptors, as well as Shaker and inward rectifier type K+channels, and can mediate clustering of these channels in heterologous cells. Genetic analyses ofDrosophilashow that MAGUKs play critical roles in synaptic development because mutations ofdiscs largedisrupt the subsynaptic reticulum and block postsynaptic clustering of Shaker K+channels. It is uncertain whether MAGUKs play an essential role in the development of central synapses. There are four neuronal MAGUKs with overlapping expression patterns in the mammalian brain; however, we find PSD-93 is the only MAGUK expressed in cerebellar Purkinje neurons. Therefore, we targeted disruption of PSD-93 in mouse. Despite the absence of MAGUK immunoreactivity in Purkinje neurons from the knock-outs, these mice have no structural or functional abnormality in cerebellum. Both the dendritic architecture and the postsynaptic localization of PSD-93 interacting proteins remain intact at light and electron microscopic levels in the knock-outs. Postsynaptic Purkinje cell responses, monosynaptic climbing fiber innervation, and cerebellar-dependent behaviors are also normal. Our data demonstrate that MAGUK proteins of the PSD-93/95 family are not essential for development of certain central synapses but may instead participate in specialized aspects of synaptic signaling and plasticity.
Reconstruction of Target Speed for the Guidance of Pursuit Eye Movements
Authors: Priebe Nicholas J. , Churchland Mark M. , Lisberger Stephen G.
Published: April 2018

We studied how object speed is reconstructed from the responses of motion-selective cells for the generation of a behavior that is tightly linked to the speed of visual motion. In theory, the speed of an object could be estimated either from the speed tuning of the active population of motion-selective cells or from the rate of displacement of activation across the cortical map of visual space. We measured the pursuit eye movements evoked by stimuli containing two conflicting motion components: a local component designed to excite motion-selective cells with a particular speed tuning and a displacement component designed to excite cells with a sequence of spatial receptive fields. Pursuit eye movements were driven primarily by the local-motion component and were affected to only a small degree by the rate of target displacement across visual space. Extracellular single-unit recordings using the same stimuli revealed that the responses of cells in the middle temporal visual area (MT) depended primarily on the local-motion component but were influenced by the displacement component to the same degree as were pursuit eye movements. We conclude that the initiation of pursuit is consistent with a reconstruction of target speed based on the speed tuning of the active population of MT cells.
3,4-Methylenedioxymethamphetamine (Ecstasy)-Induced Learning and Memory Impairments Depend on the Age of Exposure during Early Development
Authors: Broening Harry W. , Morford LaRonda L. , Inman-Wood Sandra L. , Fukumura Masao , Vorhees Charles V.
Published: April 2018

Use of 3,4-methylenedioxymethamphetamine (MDMA; ecstasy) has increased dramatically in recent years, yet little is known about its effects on the developing brain. Neonatal rats were administered MDMA on days 1–10 or 11–20 (analogous to early and late human third trimester brain development). MDMA exposure had no effect on survival but did affect body weight gain during treatment. After treatment, body weight largely recovered to 90–95% of controls. MDMA exposure on days 11–20 resulted in dose-related impairments of sequential learning and spatial learning and memory, whereas neonatal rats exposed on days 1–10 showed almost no effects. At neither stage of exposure did MDMA-treated offspring show effects on swimming ability or cued learning. Brain region-specific dopamine, serotonin, and norepinephrine changes were small and were not correlated to learning changes. These findings suggest that MDMA may pose a previously unrecognized risk to the developing brain by inducing long-term deleterious effects on learning and memory.
Preferential Cytoplasmic Localization of δ-Opioid Receptors in Rat Striatal Patches: Comparison with Plasmalemmal μ-Opioid Receptors
Authors: Wang Hong , Pickel Virginia M.
Published: April 2018

The activation of δ-opioid receptors (DORs) in the caudate-putamen nucleus (CPN) produces regionally distinct changes in motor functions, many of which are also influenced by opioids active at μ-opioid receptors (MORs). These actions most likely occur in MOR-enriched patch compartments in the CPN. To determine the functional sites for DOR activation and potential interactions involving MOR in these regions, immunoperoxidase and immunogold–silver labeling methods were applied reversibly for the ultrastructural localization of DOR and MOR in single rat brain sections containing patches of the CPN. DOR immunoreactivity was commonly seen within the cytoplasm of spiny and aspiny neurons, many of which also expressed MOR. In dendrites and spines, DOR labeling was preferentially localized to membranes of the smooth endoplasmic reticulum and spine apparatus, whereas MOR showed a prominent plasmalemmal distribution. DOR- and/or MOR-labeled spines received asymmetric, excitatory synapses, some of which showed notable perforations, suggesting the involvement of these receptors in activity-dependent synaptic plasticity. DORs were more frequently detected than were MORs within axon terminals that formed either asymmetric synapses with spine heads or symmetric synapses with spine necks. Our results suggest that in striatal patches, DORs, often in cooperation with MORs, play a direct modulatory role in controlling the postsynaptic excitability of spines, whereas presynaptic neurotransmitter release onto spines is mainly influenced by DOR activation. In comparison with MOR, the prevalent association of DOR with cytoplasmic organelles that are involved in intracellular trafficking of cell surface proteins suggests major differences in availability of these receptors to extracellular opioids.
Genetic Control of the Mouse Cerebellum: Identification of Quantitative Trait Loci Modulating Size and Architecture
Authors: Airey David C. , Lu Lu , Williams Robert W.
Published: April 2018

To discover genes influencing cerebellum development, we conducted a complex trait analysis of variation in the size of the adult mouse cerebellum. We analyzed two sets of recombinant inbred BXD strains and an F2 intercross of the common inbred strains, C57BL/6J and DBA/2J. We measured cerebellar size as the weight or volume of fixed or histologically processed tissue. Among BXD recombinant inbred strains, the cerebellum averages 52 mg (12.4% of the brain) and ranges 18 mg in size. In F2 mice, the cerebellum averages 62 mg (12.9% of the brain) and ranges ∼20 mg in size. Five quantitative trait loci (QTLs) that significantly control variation in cerebellar size were mapped to chromosomes 1 (Cbs1a), 8 (Cbs8a), 14 (Cbs14a), and 19 (Cbs19a,Cbs19b). In combination, these QTLs can shift cerebellar size an appreciable 35% of the observed range. To assess regional genetic control of the cerebellum, we also measured the volume of the cell-rich, internal granule layer (IGL) in a set of BXD strains. The IGL ranges from 34 to 43% of total cerebellar volume. The QTLCbs8ais significantly linked to variation in IGL volume and is suggestively linked to variation in the number of cerebellar folia. The QTLs we have discovered are among the first loci shown to modulate the size and architecture of the adult mouse cerebellum.
Bilateral Integration of Whisker Information in the Primary Somatosensory Cortex of Rats
Authors: Shuler Marshall G. , Krupa David J. , Nicolelis Miguel A. L.
Published: April 2018

The isomorphic representation of the contralateral whisker pad in the rodent cerebral cortex has served as a canonical example in primary somatosensory areas that the contralateral body surface is spatially represented as a topographic map. By characterizing responses evoked by multiwhisker stimuli, we provide direct evidence that the whisker region of the rat primary somatosensory cortex (SI) integrates information from both contralateral and ipsilateral whisker pads. The proportions of SI neurons responsive to ipsilateral whisker stimuli, as well as their response probabilities, increased with the number of ipsilateral whiskers stimulated. Under bilateral whisker stimulation, the responses of 95% of neurons recorded were affected by stimulation of ipsilateral whiskers. Contralateral tactile responses of SI neurons were profoundly influenced by preceding ipsilateral stimuli and vice versa. This effect depended on both the spatial location and the relative timing of bilateral whisker stimuli, leading to both spatial and temporal asymmetries of interaction. Bilateral whisker stimulation resulted in only modest changes in evoked response latency. Previous ipsilateral stimulation was also shown to affect tactile responses evoked by later ipsilateral stimuli. Inactivation of the opposite SI abolished ipsilaterally evoked responses as well as their influence on subsequently evoked contralateral responses in the intact SI. Based on these results, we conclude that the rat SI integrates information from both whisker pads and propose that such interactions may underlie the ability of rats to discriminate bilateral tactile stimuli.
In VivoResetting of the Hamster Circadian Clock by 5-HT7Receptors in the Suprachiasmatic Nucleus
Authors: Ehlen J. Christopher , Grossman Gregory H. , Glass J. David
Published: April 2018

Serotonin (5-HT) has been strongly implicated in the regulation of the mammalian circadian clock located in the suprachiasmatic nuclei (SCN); however, its role in behavioral (nonphotic) circadian phase resetting remains elusive. Central to this issue are divergent lines of evidence that the SCN may, or may not, be a target for the phase-resetting effects of 5-HT. We have addressed this question using a novel reverse-microdialysis approach for timed perfusions of serotonergic and other agents to the Syrian hamster SCN with durations equivalent to the increases inin vivo5-HT release during phase-resetting behavioral manipulations. We found that 3 hr perfusions of the SCN with either 5-HT or the 5-HT1A,7receptor agonist 2-dipropylamino-8-hydroxy-1,2,3,4-tetrahydro-naphthalene (8-OH-DPAT) at midday advanced the phase of the free-running circadian rhythm of wheel-running assessed using an Aschoff type II procedure. Phase shifts induced by 8-OH-DPAT were enhanced more than threefold by pretreatment with the 5-HT synthesis inhibitorpara-chlorophenylalanine. Phase advances induced by SCN 8-OH-DPAT perfusion were significantly inhibited by the 5-HT2,7receptor antagonist ritanserin and by the more selective 5-HT7receptor antagonist DR4004, implicating the 5-HT7receptor in mediating this phase resetting. Concurrent exposure to light during the 8-OH-DPAT perfusion abolished the phase advances. Furthermore, coperfusion of the SCN with TTX, which blockedin vivo5-HT release, did not suppress intra-SCN 8-OH-DPAT-induced phase advances. These results indicate that 5-HT7receptor-mediated phase resetting in the SCN is markedly influenced by the degree of postsynaptic responsiveness to 5-HT and by photic stimulation. Finally, 5-HT may act directly on SCN clock cells to inducein vivononphotic phase resetting.
Glycosylation Alters Steady-State Inactivation of Sodium Channel Nav1.9/NaN in Dorsal Root Ganglion Neurons and Is Developmentally Regulated
Authors: Tyrrell Lynda , Renganathan Muthukrishnan , Dib-Hajj Sulayman D. , Waxman Stephen G.
Published: April 2018

Na channel NaN (Nav1.9) produces a persistent TTX-resistant (TTX-R) current in small-diameter neurons of dorsal root ganglia (DRG) and trigeminal ganglia. Nav1.9-specific antibodies react in immunoblot assays with a 210 kDa protein from the membrane fractions of adult DRG and trigeminal ganglia. The size of the immunoreactive protein is in close agreement with the predicted Nav1.9 theoretical molecular weight of 201 kDa, suggesting limited glycosylation of this channel in adult tissues. Neonatal rat DRG membrane fractions, however, contain an additional higher molecular weight immunoreactive protein. Reverse transcription-PCR analysis did not show additional longer transcripts that could encode the larger protein. Enzymatic deglycosylation of the membrane preparations converted both immunoreactive proteins into a single faster migrating band, consistent with two states of glycosylation of Nav1.9. The developmental change in the glycosylation state of Nav1.9 is paralleled by a developmental change in the gating of the persistent TTX-R Na+current attributable to Nav1.9 in native DRG neurons. Whole-cell patch-clamp analysis demonstrates that the midpoint of steady-state inactivation is shifted 7 mV in a hyperpolarized direction in neonatal (postnatal days 0–3) compared with adult DRG neurons, although there is no significant difference in activation. Pretreatment of neonatal DRG neurons with neuraminidase causes an 8 mV depolarizing shift in the midpoint of steady-state inactivation of Nav1.9, making it indistinguishable from that of adult DRG neurons. Our data show that extensive glycosylation of rat Nav1.9 is developmentally regulated and changes a critical property of this channel in native neurons.
Estimating Transmitter Release Rates from Postsynaptic Current Fluctuations
Authors: Neher Erwin , Sakaba Takeshi
Published: April 2018

A method is presented that allows one to estimate transmitter release rates from fluctuations of postsynaptic current records under conditions of stationary or slowly varying release. For experimental applications, we used the calyx of Held, a glutamatergic synapse, in which “residual current,” i.e., current attributable to residual glutamate in the synaptic cleft, is present. For a characterization of synaptic transmission, several postsynaptic parameters, such as the mean amplitude of the miniature postsynaptic current and an apparent single channel conductance, have to be known. These were obtained by evaluating variance and two more higher moments of the current fluctuations. In agreement with Fesce et al. (1986), we found both by simulations and by analyzing experimental records that high-pass filtering of postsynaptic currents renders the estimates remarkably tolerant against nonstationarities. We also found that release rates and postsynaptic parameters can be reliably obtained when release rates are low (∼10 events/msec). Furthermore, during a long-lasting stimulus, the transmitter release at the calyx of Held was found to decay to a low, stationary rate of 10 events/msec after depletion of the “releasable pool” of synaptic vesicles. This stationary release rate is compatible with the expected rate of recruitment of new vesicles to the release-ready pool of vesicles. MiniatureEPSC (mEPSC) size is estimated to be similar to the value of spontaneously occurring mEPSC under this condition.
Axonal Rejoining Inhibits Injury-Induced Long-Term Changes inAplysiaSensory NeuronsIn Vitro
Authors: Bedi Supinder S. , Glanzman David L.
Published: April 2018

Injury ofAplysiasensory neurons, both in the CNS and in dissociated cell culture, produces long-term changes in these cells, among which are hyperexcitability and enhanced neuritic outgrowth (hypermorphogenesis). These long-term, injury-induced changes are attributable, in part, to the generation of new intrinsic cellular signals. Little is known, however, about the signals that maintain homeostasis within sensory neurons. To elucidate the role of homeostatic signals inAplysiasensory neurons, we investigated how axonal rejoining alters the cellular consequences of axotomy. Sensory neurons in dissociated cell culture were axotomized. In some cases, the distal segment of the severed axon was then removed; in other cases, the proximal and distal segments of the severed axon were permitted to rejoin. If the severed distal segment was left unmolested, then axonal rejoining invariably occurred within 7 hr. Surprisingly, we found that the characteristic long-term cellular consequences of axotomy were suppressed by axonal rejoining. The long-term axotomy-induced changes were not inhibited merely by contact between the severed axon and another, uninjured sensory neuron. These results indicate that long-term changes in sensory neurons induced by injury are attributable, in part, to prolonged disruption of a retrograde homeostatic signal that originates in the distal segment of the growing neurite and chronically suppresses hyperexcitability and hypermorphogenesis.
Axon Branching Requires Interactions between Dynamic Microtubules and Actin Filaments
Authors: Dent Erik W. , Kalil Katherine
Published: April 2018

Cortical neurons innervate many of their targets by collateral axon branching, which requires local reorganization of the cytoskeleton. We coinjected cortical neurons with fluorescently labeled tubulin and phalloidin and used fluorescence time-lapse imaging to analyze interactions between microtubules and actin filaments (F-actin) in cortical growth cones and axons undergoing branching. In growth cones and at axon branch points, splaying of looped or bundled microtubules is accompanied by focal accumulation of F-actin. Dynamic microtubules colocalize with F-actin in transition regions of growth cones and at axon branch points. In contrast, F-actin is excluded from the central region of the growth cone and the axon shaft, which contains stable microtubules. Interactions between dynamic microtubules and dynamic actin filaments involve their coordinated polymerization and depolymerization. Application of drugs that attenuate either microtubule or F-actin dynamics also inhibits polymerization of the other cytoskeletal element. Importantly, inhibition of microtubule or F-actin dynamics prevents axon branching but not axon elongation. However, these treatments do cause undirected axon outgrowth. These results suggest that interactions between dynamic microtubules and actin filaments are required for axon branching and directed axon outgrowth.
Functional Regeneration in a Rat Parkinson's Model after Intrastriatal Grafts of Glial Cell Line-Derived Neurotrophic Factor and Transforming Growth Factor β1-Expressing Extra-Adrenal Chromaffin Cells of the Zuckerkandl's Organ
Authors: Espejo Emilio Fernandez , Gonzalez-Albo M. Carmen , Moraes Joao-Paulo , El Banoua Fadwa , Flores Juan A. , Caraballo Isabel
Published: April 2018

Intrabrain transplantation of chromaffin cell aggregates of the Zuckerkandl's organ, an extra-adrenal paraganglion that has never been tested for antiparkinsonian treatment, induced gradual improvement of functional deficits in parkinsonian rats. These beneficial effects were related to long survival of grafted cells, striatal reinnervation, and enhancement of dopamine levels in grafted striatum. Grafted cells were not dopaminergics, but they expressed glial cell line-derived neurotrophic factor (GDNF) and transforming growth factor-β1. These factors were detected in the host striatal tissue, indicating that chromaffin cells secreted them after grafting. Because glial cell line-derived neurotrophic factor possesses neurorestorative properties over dopaminergic neurons, and transforming growth factor-β1is a cofactor that potentiates the neurotrophic actions of GDNF, functional regeneration was likely caused by the chronic trophic action of neurotrophic factors delivered by long-surviving grafted cells. This work should stimulate research on the clinical applicability of transplants of the Zuckerkandl's organ in Parkinson's disease.
Expression of a Variant Form of the Glutamate Transporter GLT1 in Neuronal Cultures and in Neurons and Astrocytes in the Rat Brain
Authors: Chen Weizhi , Aoki Chiye , Mahadomrongkul Veeravan , Gruber Christian E. , Wang Guang Jian , Blitzblau Rachel , Irwin Nina , Rosenberg Paul A.
Published: April 2018

To identify glutamate transporters expressed in forebrain neurons, we prepared a cDNA library from rat forebrain neuronal cultures, previously shown to transport glutamate with high affinity and capacity. Using this library, we cloned two forms, varying in the C terminus, of the glutamate transporter GLT1. This transporter was previously found to be localized exclusively in astrocytes in the normal mature brain. Specific antibodies against the C-terminal peptides were used to show that forebrain neurons in culture express both GLT1a and GLT1b proteins. The pharmacological properties of glutamate transport mediated by GLT1a and GLT1b expressed in COS-7 cells and in neuronal cultures were indistinguishable. Both GLT1a and GLT1b were upregulated in astrocyte cultures by exposure to dibutyryl cAMP. We next investigated the expression of GLT1bin vivo. Northern blot analysis of forebrain RNA revealed two transcripts of ∼3 and 11 kb that became more plentiful with developmental age. Immunoblot analysis showed high levels of expression in the cortex, hippocampus, striatum, thalamus, and midbrain. Pre-embedding electron microscopic immunocytochemistry with silver-enhanced immunogold detection was used to localize GLT1bin vivo. In the rat somatosensory cortex, GLT1b was clearly expressed in neurons in presynaptic terminals and dendritic shafts, as well as in astrocytes. The presence of GLT1b in neurons may offer a partial explanation for the observed uptake of glutamate by presynaptic terminals, for the preservation of input specificity at excitatory synapses, and may play a role in the pathophysiology of excitotoxicity.
Endosomal Compartments Serve Multiple Hippocampal Dendritic Spines from a Widespread Rather Than a Local Store of Recycling Membrane
Authors: Cooney James R. , Hurlburt Jamie L. , Selig David K. , Harris Kristen M. , Fiala John C.
Published: April 2018

Endosomes are essential to dendritic and synaptic function in sorting membrane proteins for degradation or recycling, yet little is known about their locations near synapses. Here, serial electron microscopy was used to ascertain the morphology and distribution of all membranous intracellular compartments in distal dendrites of hippocampal CA1 pyramidal neurons in juvenile and adult rats. First, the continuous network of smooth endoplasmic reticulum (SER) was traced throughout dendritic segments and their spines. SER occupied the cortex of the dendritic shaft and extended into 14% of spines. Several types of non-SER compartments were then identified, including clathrin-coated vesicles and pits, large uncoated vesicles, tubular compartments, multivesicular bodies (MVBs), and MVB–tubule complexes. The uptake of extracellular gold particles indicated that these compartments were endosomal in origin. Small, round vesicles and pits that did not contain gold were also identified. The tubular compartments exhibited clathrin-coated tips consistent with the genesis of these small, presumably exosomal vesicles. Approximately 70% of the non-SER compartments were located within or at the base of dendritic spines. Overall, only 29% of dendritic spines had endosomal compartments, whereas 20% contained small vesicles. Small vesicles did not colocalize in spines with endosomes or SER. Three-dimensional reconstructions revealed that up to 20 spines shared a recycling pool of plasmalemmal proteins rather than maintaining independent stores at each spine.
Depletion of Cholinergic Amacrine Cells by a Novel Immunotoxin Does Not Perturb the Formation of Segregated On and Off Cone Bipolar Cell Projections
Authors: Günhan Emine , Choudary Prabhakara V. , Landerholm Thomas E. , Chalupa Leo M.
Published: April 2018

Cone bipolar cells are the first retinal neurons that respond in a differential manner to light onset and offset. In the mature retina, the terminal arbors of On and Off cone bipolar cells terminate in different sublaminas of the inner plexiform layer (IPL) where they form synapses with the dendrites of On and Off retinal ganglion cells and with the stratified processes of cholinergic amacrine cells. Here we first show that cholinergic processes within the On and Off sublaminas of the IPL are present early in development, being evident in the rat on the day of birth, ∼10 d before the formation of segregated cone bipolar cell axons. This temporal sequence, as well as our previous finding that the segregation of On and Off cone bipolar cell inputs occurs in the absence of retinal ganglion cells, suggested that cholinergic amacrine cells could provide a scaffold for the subsequent in-growth of bipolar cell axons. To test this hypothesis directly, a new cholinergic cell immunotoxin was constructed by conjugating saporin, the ribosome-inactivating protein toxin, to an antibody against the vesicular acetylcholine transporter. A single intraocular injection of the immunotoxin caused a rapid, complete, and selective loss of cholinergic amacrine cells from the developing rat retina. On and Off cone bipolar cells were visualized using an antibody against recoverin, the calcium-binding protein that labels the soma and processes of these interneurons. After complete depletion of cholinergic amacrine cells, cone bipolar cell axon terminals still formed their two characteristic strata within the IPL. These findings demonstrate that the presence of cholinergic amacrine cells is not required for the segregation of recoverin-positive On and Off cone bipolar cell projections.
The C Domain of Netrin UNC-6 Silences Calcium/Calmodulin-Dependent Protein Kinase- and Diacylglycerol-Dependent Axon Branching inCaenorhabditis elegans
Authors: Wang Qun , Wadsworth William G.
Published: April 2018

Second messenger systems mediate neuronal responses to extracellular factors that elicit axon branching, turning, and guidance. We found that mutations inCaenorhabditis elegansthat affect components of second messenger systems, a G-protein subunit, phospholipase Cβ, diacylglycerol (DAG) kinase, and calcium/calmodulin-dependent protein kinase (CaMKII), have no obvious effect on axon responses to UNC-6 except in animals in which the N-terminal fragment, UNC-6ΔC, is expressed. In these animals, the mutations enhance or suppress ectopic branching of certain axons. Netrin UNC-6 is an extracellular protein that guides circumferential migrations, and UNC-6ΔC has UNC-6 guidance activity. We propose that the guidance response elicited by the UNC-6 N-terminal domains involves mechanisms that can induce branching that is sensitive to CaMKII- and DAG-dependent signaling, and that the UNC-6 C domain is required incisto the N-terminal domains to silence the branching and to maintain proper axon morphology.
Odorant-Induced Olfactory Receptor Neural Oscillations and Their Modulation of Olfactory Bulbar Responses in the Channel Catfish
Authors: Nikonov Alexander A. , Parker James M. , Caprio John
Published: April 2018

Peripheral waves (PWs) in the channel catfish are odorant-induced neural oscillations of synchronized populations of olfactory receptor neurons (ORNs) that appear after the initial ∼500 msec of the response. The mean dominant frequency during the initial 2 sec of PW activity is ∼28 Hz, declining to ∼20 Hz in the last sec of a 5 sec stimulus. Recordings of PWs from different regions of a single olfactory lamella and simultaneously from widely separated lamellae within the olfactory organ suggest that PWs are initiated in the sensory epithelium within each olfactory lamella. Simultaneous recordingsin vivofrom the olfactory organ [electro-olfactogram (EOG) or integrated neural activity], local field potentials (LFPs) from the olfactory bulb (OB), and single and few-unit activity from OB neurons were performed. Cross-correlation analysis of simultaneously recorded odor-induced OB LFPs and either EOG or ORN neural activity showed that oscillations occurring within the OB were lower (<20 Hz) than those of PWs; however, during PW activity, OB LFPs increased both their magnitude and dominant frequencies and became correlated with the PWs. Also during odorant-induced PW activity, the responses of different OB neurons with similar odorant specificity became phase locked to each other and to both the PWs and OB LFPs. PWs are hypothesized to function to strengthen the synaptic transfer of olfactory information at specific glomeruli within the OB.
Alterations in Exocytosis Induced by Neuronal Ca2+Sensor-1 in Bovine Chromaffin Cells
Authors: Pan Chien-Yuan , Jeromin Andreas , Lundstrom Kenneth , Yoo Seung Hyun , Roder John , Fox Aaron P.
Published: April 2018

A variety of Ca2+binding proteins are known to play an integral role in catecholamine release from synapses as well as secretory cells, such as chromaffin cells. TheDrosophilaprotein frequenin and its mammalian homolog neuronal Ca2+sensor-1 (NCS-1) belong to a family of Ca2+sensors with EF hands that bind Ca2+and then interact with other proteins. Frequenin/NCS-1 has been shown to enhance exocytotic activity in addition to altering Ca2+channel regulation. To better understand how NCS-1 regulates stimulus–secretion coupling, bovine chromaffin cells were infected with Semliki Forest virus (SFV) vectors containing the rat NCS-1 gene. Cells were studied in the perforated whole-cell patch-clamp configuration. Membrane capacitance was monitored as an indicator of exocytosis–endocytosis. Exocytosis elicited by membrane depolarization was not significantly different between cells infected with SFV expressing green fluorescent protein (GFP) or GFP plus NCS-1, except that the overexpression of NCS-1 resulted in a faster rundown in exocytosis. When cells were stimulated with histamine, NCS-1 overexpression led to higher exocytosis, as well as [Ca2+]ielevation. Immunocytochemistry showed a similar distribution of NCS-1 and phosphatidylinositol 4-kinase β (PI4Kβ). NCS-1 and PI4Kβ coimmunoprecipitate, opening up the possibility that the two proteins directly interact. These results suggest that NCS-1 may regulate cellular activity through the modulation of the phosphatidylinositol signaling pathway.
Specificity of Glomerular Targeting by Olfactory Sensory Axons
Authors: Treloar Helen B. , Feinstein Paul , Mombaerts Peter , Greer Charles A.
Published: April 2018

Axons from olfactory sensory neurons (OSNs) expressing a specific odorant receptor (OR) project to specific subsets of glomeruli in the olfactory bulb (for review, see Mombaerts, 1999, 2001). The aim of this study was to examine the trajectories that subsets of axons from OSNs expressing the same OR follow within the olfactory nerve and olfactory nerve layer (ONL) of adult mice. Using confocal microscopy, we generated serial reconstructions of axons from M72-IRES-tauGFP-expressing OSNs as they coursed within the ONL and into glomeruli. GFP-expressing axons were loosely aggregated in the outer ONL; however, as they entered the inner ONL, the majority fasciculated with other GFP-expressing axons before entering the glomerular neuropil. Although the vast majority of axons entered the glomerulus from the directly apposed ONL, some followed tortuous courses through and/or around adjacent glomeruli before terminating in the target glomerulus. Similar observations were made on subpopulations of axons in M71-IRES-tauGFP and P2-IRES-tauGFP mice. Ultrastructural analyses of labeled M72 glomeruli showed no evidence of axodendritic synapses other than those with GFP-labeled axon terminals. These data are consistent with the notion that OSN axons are highly precise in targeting glomeruli and that glomeruli, in turn, are highly homogeneous with regard to the OR expressed by the innervating OSNs. Because some single axons could follow idiosyncratic trajectories to the target glomerulus, it appears that stable homotypic fasciculation is not a prerequisite for correct targeting.
Effects of Reversible Inactivation of the Neonatal Ventral Hippocampus on Behavior in the Adult Rat
Authors: Lipska Barbara K. , Halim Nader D. , Segal Pavan N. , Weinberger Daniel R.
Published: April 2018

Rats with neonatal excitotoxic damage of the ventral hippocampus display in adulthood a variety of abnormalities reminiscent of schizophrenia and are used as an animal model of this disorder. In the present study, we hypothesized that transient inactivation of ventral hippocampal activity during a critical developmental period may be sufficient to disrupt normal maturation of relevant brain systems and produce similar lasting behavioral changes. We infused tetrodotoxin (TTX) or artificial CSF into the ventral hippocampus on postnatal day 7 (P7) and assessed behavioral changes in response to stress, amphetamine, and (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine maleate in juvenile (P35) and young adult (P56) rats. In adulthood, rats infused neonatally with TTX displayed motor hyperactivity after pharmacological stimulation and after stress compared with sham controls. Analogous TTX infusions in adult animals did not alter these behaviors later in life. These data suggest that transient loss of ventral hippocampal function during a critical time in maturation of intracortical connections permanently changes the development of neural circuits mediating certain dopamine- and NMDA-related behaviors. These results represent a potential new model of aspects of schizophrenia without involving a gross anatomic lesion.
Reduction of Stress-Induced Behavior by Antagonism of Corticotropin-Releasing Hormone 2 (CRH2) Receptors in Lateral Septum or CRH1Receptors in Amygdala
Authors: Bakshi Vaishali P. , Smith-Roe Stephanie , Newman Sarah M. , Grigoriadis Dimitri E. , Kalin Ned H.
Published: April 2018

Although corticotropin-releasing hormone (CRH), a regulator of stress responses, acts through two receptors (CRH1and CRH2), the role of CRH2in stress responses remains unclear. Knock-out mice without the CRH2gene exhibit increased stress-like behaviors. This profile could result either directly from the absence of CRH2receptors or indirectly from developmental adaptations. In the present study, CRH2receptors were acutely blocked by α-helical CRH (αhCRH, CRH1/CRH2antagonist; 0, 30, 100, and 300 ng) infusion into the lateral septum (LS), which abundantly expresses CRH2but not CRH1receptors. Freezing, locomotor activity, and analgesia were tested after infusion. Intra-LS αhCRH blocked shock-induced freezing without affecting activity or pain responses; infusions into lateral ventricle or nucleus of the diagonal band had no effects. The same behavioral profile was obtained withd-Phe-CRH(12–41)(100 ng), another CRH1/CRH2antagonist. A selective CRH1antagonist (NBI27914), in doses that reduced freezing on intra-amygdala (central nucleus) infusion (0, 0.2, and 1.0 μg), did not affect freezing when infused into the LS.Ex vivoautoradiography revealed that binding of [125I]sauvagine, a mixed CRH1/CRH2agonist, was prevented in the LS by previous intra-LS infusion of αhCRH but not NBI27914.In vitrostudies demonstrated that [125I]sauvagine binding in the LS could be inhibited by a CRH1/CRH2antagonist but not by the selective CRH1receptor antagonist, confirming that in the LS, αhCRH antagonized exclusively CRH2receptors. Acute antagonism of CRH2receptors in the LS thus produces a behaviorally, anatomically, and pharmacologically specific reduction in stress-induced behavior, in contrast to results of recent knock-out studies, which induced congenital and permanent CRH2removal. CRH2receptors may thus represent a potential target for the development of novel CRH system anxiolytics.
Dopamine Enhances EPSCs in Layer II–III Pyramidal Neurons in Rat Prefrontal Cortex
Authors: Gonzalez-Islas Carlos , Hablitz John J.
Published: April 2018

Dopaminergic inputs to the prefrontal cortex (PFC) are important for the integration of neuronal signals, the formation of working memory, and the establishment of memory fields. A detailed characterization of cellular mechanisms underlying the effects of dopamine on PFC is still emerging. We have examined how dopamine affects excitatory synaptic transmission in the PFC using whole-cell patch-clamp recording from visually identified layer II–III pyramidal cellsin vitro. Bath application of dopamine significantly enhanced EPSC amplitudes. Pharmacologically isolated AMPA and NMDA receptor-mediated EPSCs were increased to a similar extent. Application of the specific D1-like receptor agonist SKF38393 [(±)-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol hydrobromide] significantly increased EPSC amplitude, whereas the D2-like receptor agonist quinpirole had no effect. Responses to pressure-applied glutamate were also enhanced by dopamine, indicating a postsynaptic mechanism. Inclusion of the Ca2+chelator BAPTA in the recording pipette blocked the dopamine enhancement. When the PKA inhibitory peptide PKI [5–24] was included in the recording pipette, dopamine did not affect EPSCs. Similarly, when the Ca2+/calmodulin-kinase II (CaMKII) inhibitory peptide was present in the pipette, dopamine enhancement of EPSCs was not observed in any of the cells tested. These results indicate that EPSC enhancement may be attributable to a postsynaptic signaling cascade involving Ca2+, PKA, and CaMKII.
Early Exposure to Common Anesthetic Agents Causes Widespread Neurodegeneration in the Developing Rat Brain and Persistent Learning Deficits
Authors: Jevtovic-Todorovic Vesna , Hartman Richard E. , Izumi Yukitoshi , Benshoff Nicholas D. , Dikranian Krikor , Zorumski Charles F. , Olney John W. , Wozniak David F.
Published: April 2018

Recently it was demonstrated that exposure of the developing brain during the period of synaptogenesis to drugs that block NMDA glutamate receptors or drugs that potentiate GABAAreceptors can trigger widespread apoptotic neurodegeneration. All currently used general anesthetic agents have either NMDA receptor-blocking or GABAAreceptor-enhancing properties. To induce or maintain a surgical plane of anesthesia, it is common practice in pediatric or obstetrical medicine to use agents from these two classes in combination. Therefore, the question arises whether this practice entails significant risk of inducing apoptotic neurodegeneration in the developing human brain. To begin to address this problem, we have administered to 7-d-old infant rats a combination of drugs commonly used in pediatric anesthesia (midazolam, nitrous oxide, and isoflurane) in doses sufficient to maintain a surgical plane of anesthesia for 6 hr, and have observed that this causes widespread apoptotic neurodegeneration in the developing brain, deficits in hippocampal synaptic function, and persistent memory/learning impairments.
Fibroblast Growth Factor Receptor 3 Signaling Regulates the Onset of Oligodendrocyte Terminal Differentiation
Authors: Oh Luke Y. S. , Denninger Adam , Colvin Jennifer S. , Vyas Aditee , Tole Shubha , Ornitz David M. , Bansal Rashmi
Published: April 2018

Fibroblast growth factor receptor (FGFR) signaling is essential for nervous system development. We have shown that, in the normal postnatal brain, the spatial and temporal expression pattern of FGFR3 parallels the appearance of differentiated oligodendrocytes and that in culture FGFR3 is expressed maximally at the critical stage in the lineage at which oligodendrocyte late progenitors (Pro-OLs) enter terminal differentiation. Therefore, FGFR3 expression is positioned ideally to have an impact on oligodendrocyte differentiation. In support of this we show that, during the onset and active phase of myelination in FGFR3-deficient mice, there are reduced numbers of differentiated oligodendrocytes in the forebrain, cerebellum, hindbrain, and spinal cord. Furthermore, myelination is delayed in parallel. Delay of oligodendrocyte differentiation also is observed in primary cell culture from this mutant. On the other hand, no differences are observed in the survival or proliferation of oligodendrocyte progenitors. This suggests that the decrease in the number of differentiated oligodendrocytes is attributable to a delay in the timing of their differentiation process. Astrocytes also express FGFR3, and in mice lacking FGFR3 there is an enhancement of the astrocytic marker glial fibrillary acidic protein expression in a region-specific manner. Thus our findings suggest that there are cell type- and region-specific functions for FGFR3 signaling and in particular emphasize a prominent role for FGFR3 as part of a system regulating the onset of oligodendrocyte terminal differentiation.
Locally Born Olfactory Bulb Stem Cells Proliferate in Response to Insulin-Related Factors and Require Endogenous Insulin-Like Growth Factor-I for Differentiation into Neurons and Glia
Authors: Vicario-Abejón Carlos , Yusta-Boyo Marı́a J. , Fernández-Moreno Carmen , de Pablo Flora
Published: April 2018

After late embryogenesis, new neurons are continuously added to the olfactory bulb (OB) from stem cells located in the forebrain subventricular zone. Nonetheless, stem cells have not been described within the embryonic olfactory bulb. Here we report the isolation of local olfactory bulb stem cells from the embryonic day 12.5–14.5 mouse embryo. These cells were 99.2% nestin positive and proliferated extensively in culture to at least 150 cell doublings. Clonal analysis demonstrated that neurons (TuJ1+), astrocytes (GFAP+), and oligodendrocytes (O4+) could be generated from single-plated cells, indicating that they are multipotent. At least 90% of proliferating cells expressed insulin-like growth factor-I (IGF-I), (pro)insulin, and their cognate receptors; these growth factors collaborated with fibroblast growth factor-2 plus epidermal growth factor (EGF) to promote stem cell proliferation and sphere formation. Cells fromIgf-I−/−mice, however, proliferated as extensively as didIgf-I+/+cells. Differentiation and survival of stem cell-generated neurons and glia showed strong dependence on exogenous IGF-I, but oligodendrocyte differentiation also required insulin at low concentration. Furthermore, the percentages of stem cell-generated neurons, astrocytes, and oligodendrocytes were markedly lower in the cultures prepared from theIgf-I−/−mice compared with those ofIgf-I+/+. Concordantly, lack of IGF-I resulted in abnormal formation of the olfactory bulb mitral cell layer and altered radial glia morphology. These results support the presence within the embryonic mouse olfactory bulb of stem cells with specific requirements for insulin-related growth factors for proliferation or differentiation. They demonstrate that IGF-I is an endogenous factor regulating the differentiation of stem and other precursor cells within the olfactory bulb.
Role of the G-Protein-Coupled Receptor GPR12 as High-Affinity Receptor for Sphingosylphosphorylcholine and Its Expression and Function in Brain Development
Authors: Ignatov Atanas , Lintzel Julia , Hermans-Borgmeyer Irm , Kreienkamp Hans-Jürgen , Joost Patrick , Thomsen Susanne , Methner Axel , Schaller H. Chica
Published: April 2018

Lysophospholipids are bioactive molecules influencing numerous cellular processes such as proliferation, differentiation, and motility. As extracellular ligands, they interact with specific members of the G-protein-coupled receptor family. We show in this paper that the lysophospholipid sphingosylphosphorylcholine is a high-affinity ligand for the orphan G-protein-coupled receptor GPR12. Heterologous expression of GPR12 in Chinese hamster ovary cells and in frog oocytes revealed a high-affinity interaction with sphingosylphosphorylcholine in the nanomolar range. Blockade of its action by pertussis toxin was taken as evidence that GPR12 is coupled to an inhibitory G-protein. In the adult mouse brain, GPR12 was expressed in the limbic system. During mouse embryonal development, GPR12 transcripts were detected in the CNS, especially in areas where neuronal differentiation occurs. Consistent with this we found that cultures of embryonal cerebral cortical neurons responded to sphingosylphosphorylcholine with an increase in synaptic contacts. The GPR12-expressing hippocampal cell line HT22 reacted to sphingosylphophorylcholine with an increase in cell proliferation and cell clustering. Other receptors known to interact at nanomolar concentrations with sphingosylphosphorycholine were expressed neither in the developing cerebral cortex nor in the HT22 cell line. We therefore hypothesize that sphingosylphosphorylcholine, most likely by interaction with GPR12, has positive effects on the differentiation and maturation of postmitotic neurons and that it may also influence the proliferation of neuronal precursor cells.
Activity of Different Classes of Neurons of the Motor Cortex during Locomotion
Authors: Beloozerova Irina N. , Sirota Mikhail G. , Swadlow Harvey A.
Published: April 2018

This study examines the activity of different classes of neurons of the motor cortex in the rabbit during two locomotion tasks: a simple (on a flat surface) and a complex (overstepping a series of barriers) locomotion. Four classes of efferent neurons were studied: corticocortical (CC) neurons with ipsilateral projection (CCIs), those with contralateral projection (CCCs), descending corticofugal neurons of layer V (CF5s), and those of layer VI (CF6s). In addition, one class of inhibitory interneurons (SINs) was investigated. CF5 neurons and SINs were the only groups that were strongly active during locomotion. In most of these neurons a clear-cut modulation of discharge in the locomotion rhythm was observed. During simple locomotion, CF5s and SINs were preferentially active in opposite phases of the step cycle, suggesting that SINs contribute to formation of the step-related pattern of CF5s. Transition from simple to complex locomotion was associated with changes of the discharge pattern of the majority of CF5 neurons and SINs. In contrast to CF5 neurons, other classes of efferent neurons (CCI, CCC, CF6) were much less active during both simple and complex locomotion. That suggests that CC interactions, both within a hemisphere (mediated by CCIs) and between hemispheres (mediated by CCCs), as well as corticothalamic interactions via CF6 neurons are not essential for motor coordination during either simple or complex locomotion tasks.
Derangements of Hippocampal Calcium/Calmodulin-Dependent Protein Kinase II in a Mouse Model for Angelman Mental Retardation Syndrome
Authors: Weeber Edwin J. , Jiang Yong-Hui , Elgersma Ype , Varga Andrew W. , Carrasquillo Yarimar , Brown Sarah E. , Christian Jill M. , Mirnikjoo Banefsheh , Silva Alcino , Beaudet Arthur L. , Sweatt J. David
Published: April 2018

Angelman syndrome (AS) is a disorder of human cognition characterized by severe mental retardation and epilepsy. Recently, a mouse model for AS (Ube3amaternal null mutation) was developed that displays deficits in both context-dependent learning and hippocampal long-term potentiation (LTP). In the present studies, we examined the molecular basis for these LTP and learning deficits. Mutant animals exhibited a significant increase in hippocampal phospho-calcium/calmodulin-dependent protein kinase II (CaMKII), specifically at sites Thr286and Thr305, with no corresponding change in the levels of total CaMKII. In addition, mutants show a reduction in CaMKII activity, autophosphorylation capability, and total CaMKII associated with postsynaptic density. These findings are the first to implicate misregulation of CaMKII as a molecular cause for the neurobehavioral deficits in a human learning disorder.