bluuebunny/crossref_metadata_2025 huggingface dataset:
Maternal Deprivation Effect on the Infant’s Neural Stress Markers Is Reversed by Tactile Stimulation and Feeding But Not by Suppressing Corticosterone
Authors: van Oers Helga J.J. , de Kloet E. Ronald , Whelan Tara , Levine Seymour
Published: April 2018

After 24 hr of maternal deprivation, significant elevations in ACTH and the naturally occurring glucocorticoid corticosterone (CORT) are observed during the stress-hyporesponsive period. The deprived pups also showed in the paraventricular nucleus (PVN) a marked increase of stress-inducedc-fosmRNA and a reduction of corticotropin-releasing hormone (CRH) and glucocorticoid receptor (GR) mRNA; in hippocampal CA1, a reduction of the mineralocorticoid receptor (MR) and GR was observed. Here, we examined whether these changes are reversed by (1) preventing the elevations of CORT characteristic for the 11-d-old deprived pups by administering the synthetic glucocorticoid dexamethasone (DEX); or (2) reinstating some aspects of maternal behavior. The pups were either (1) left undisturbed, (2) stroked, or (3) stroked and episodically fed by cheek cannulation. At postnatal day 12, peripheral and neural stress markers were measured. Nondeprived animals served as controls.

Experiment 1 demonstrates that although CORT was kept low by DEX, the central effects on CORT receptors, CRH, andc-fosmRNA were still present, except for MR in hippocampal CA1. Experiment 2 shows that stroking alone prevented the stress-induced rise in ACTH andc-fosmRNA and in the reduction in CRH and MR mRNA. In pups that were fed and stroked, CORT and GR mRNA resembled nondeprived controls. In conclusion, the changes in peripheral endocrine responses and in the brain cannot be attributed to the effect of elevated CORT concentrations, which are characteristic of the maternally deprived neonate. However, reinstating some components of the dams’ nurturing behavior can reverse the effects evoked by maternal deprivation.
An Anatomical Substrate for the Spatiotemporal Transformation
Authors: Moschovakis A. K. , Kitama T. , Dalezios Y. , Petit J. , Brandi A. M. , Grantyn A. A.
Published: April 2018

The purpose of the present experiments was to test the hypothesis that the metrics of saccades caused by the activation of distinct collicular sites depend on the strength of their projections onto the burst generators. This study of morphofunctional correlations was limited to the horizontal components of saccades. We evoked saccades by stimulation of the deeper layers of the superior colliculus (SC) in alert, head-fixed cats. We used standard stimulus trains of 350 msec duration, 200 Hz pulse rate, and intensity set at two times saccade threshold in all experiments. Evoked saccades were analyzed quantitatively to determine the amplitude of the horizontal component of their “characteristic vectors”. This parameter is independent of eye position and was used as the physiological, saccade-related metric of the stimulation sites. Anatomical connections arising from these sites were visualized after anterograde transport of biocytin injected through a micropipette adjoining the stimulation electrode. The stimulation and injection sites were, therefore, practically identical. We counted boutons deployed in regions of the paramedian pontine reticular formation reported to contain long-lead and medium-lead burst neurons of the horizontal burst generator. Regression analysis of the normalized bouton counts revealed a significant positive correlation with the size of the horizontal component of the characteristic vectors. This data supports a frequent modelling assumption that the spatiotemporal transformation in the saccadic system relies on the graded strength of anatomical projections of distinct SC sites onto the burst generators.
Cocaine Acts as an Apparent Competitive Inhibitor at the Outward-Facing Conformation of the Human Norepinephrine Transporter: Kinetic Analysis of Inward and Outward Transport
Authors: Chen Nianhang , Justice Joseph B.
Published: April 2018

The inhibition by cocaine of inward and outward transport of dopamine (DA) at the cloned human norepinephrine transporter (hNET) and the relationship of the inhibitory patterns of cocaine to the conformational requirements of the transporter were investigated. This was done using rotating disk electrode voltammetry in transfected cells. The uphill uptake of external DA, the lack of inhibition by internal substrates on DA uptake, and the accelerated exchange of internal DA by externalm-tyramine support a carrier model in which the hNET alternates between outward-facing and inward-facing conformations. Cocaine exhibited competitive inhibition of DA uptake, which was insensitive to intracellular substrates. In contrast, the inhibition by cocaine of them-tyramine-induced DA efflux appeared noncompetitive relative to intracellular DA, but competitive relative to extracellularm-tyramine. Simultaneous measurement ofm-tyramine uptake and accompanying DA efflux at various concentrations of intracellular DA showed that cocaine did not alter the ratio of DA efflux tom-tyramine uptake. Moreover, cocaine displayed similar potency for inhibiting DA uptake and efflux. Additionally, the inhibition profile of cocaine was unrelated to the addition time of cocaine, simultaneously with or earlier than a substrate. All of the findings are consonant with a competitive interaction between cocaine and substrates at the outward-facing conformation of the hNET. This action directly prevents the inward transport of external substrates, thereby inhibiting the outward transport of internal substrates by reducing the availability of the inward-facing conformation. Consequently, the experimental inhibition pattern of cocaine depends on the conformation of the hNET to which the transported substrate is exposed.
Thiol Oxidation and Loss of Mitochondrial Complex I Precede Excitatory Amino Acid-Mediated Neurodegeneration
Authors: Sriram Krishnan , Shankar Susarla K. , Boyd Michael R. , Ravindranath Vijayalakshmi
Published: April 2018

Human ingestion of “chickling peas” from the plantLathyrus sativus, which contains an excitatory amino acid,l-BOAA (l-β-N-oxalylamino-l-alanine), leads to a progressive corticospinal neurodegenerative disorder, neurolathyrism. Exposure tol-BOAA, but not its optical enantiomerd-BOAA, causes mitochondrial dysfunction as evidenced by loss of complex I activityin vitroin male mouse brain slices andin vivoin selected regions of mouse CNS (lumbosacral cord and motor cortex). Loss of complex I activity in lumbosacral cord afterl-BOAA administration to mice was accompanied by concurrent loss of glutathione. The inhibited complex I activity in mitochondria isolated from lumbosacral cord of animals treated withl-BOAA rebounded after incubation with the thiol-reducing agent dithiothreitol, indicating that oxidation of protein thiols to disulfides was responsible for enzyme inhibition. The inhibition of complex I could be abolished by pretreatment with antioxidant thiols such as glutathione ester and α-lipoic acid. Chronic treatment of male mice, but not female mice, withl-BOAA resulted in loss of complex I activity and vacuolation and dendritic swelling of neurons in the motor cortex and lumbar cord, paralleling the regionality of the aforementioned biochemical effects on CNS mitochondria. These results support the view that thiol oxidation and concomitant mitochondrial dysfunction (also implicated in other neurodegenerative disorders), occurring downstream of glutamate receptor activation byl-BOAA, are primary events leading to neurodegeneration. Maintenance of protein thiol homeostasis by thiol delivery agents could potentially offer protection against excitotoxic insults such as those seen withl-BOAA.
Use-Dependent Decline of Paired-Pulse Facilitation atAplysiaSensory Neuron Synapses Suggests a Distinct Vesicle Pool or Release Mechanism
Authors: Jiang Xue-Ying , Abrams Thomas W.
Published: April 2018

We have characterized paired-pulse facilitation atAplysiasensory neuron-to-motoneuron synapses. This simple form of very short-term synaptic plasticity displayed an unusual feature: it decreased dramatically with repeated testing. Synaptic depression at these synapses and this use-dependent decrease in paired-pulse facilitation occurred independently of each other. Paired-pulse facilitation was inversely correlated with the size of the initial synaptic connection and was absent at stronger synapses. The use-dependent decrease in paired-pulse facilitation occurred at the same rate at large synapses as at small synapses, although the initial paired-pulse facilitation at large synapses was substantially smaller. Rates of synaptic depression were also independent of initial synaptic strength. Paired-pulse facilitation was blocked by presynaptic EGTA injection, but not by postsynaptic EGTA or BAPTA injection. These results indicate that presynaptic Ca2+influx plays a critical role in paired-pulse facilitation. However, the persistence of the decrease in paired-pulse facilitation for longer than 15 min suggests that Ca2+from the first paired action potential produces facilitation via a modulatory mechanism rather than by summating with Ca2+influx during the second paired action potential in activating the Ca2+binding sites that initiate exocytosis. This modulatory mechanism may not involve protein phosphorylation because paired-pulse facilitation was unaffected by the protein kinase inhibitors H7 and KN-62. These findings further suggest that release by the second paired action potential occurs at sites distinct from those that mediate release by the first action potential.
Gating of the L-Type Ca Channel in Human Skeletal Myotubes: An Activation Defect Caused by the Hypokalemic Periodic Paralysis Mutation R528H
Authors: Morrill James A. , Brown Robert H. , Cannon Stephen C.
Published: April 2018

The skeletal muscle L-type Ca channel serves a dual role as a calcium-conducting pore and as the voltage sensor coupling t-tubule depolarization to calcium release from the sarcoplasmic reticulum. Mutations in this channel cause hypokalemic periodic paralysis (HypoPP), a human autosomal dominant disorder characterized by episodic failure of muscle excitability that occurs in association with a decrease in serum potassium. The voltage-dependent gating of L-type Ca channels was characterized by recording whole-cell Ca currents in myotubes cultured from three normal individuals and from a patient carrying the HypoPP mutation R528H. We found two effects of the R528H mutation on the L-type Ca current in HypoPP myotubes: (1) a mild reduction in current density and (2) a significant slowing of the rate of activation. We also measured the voltage dependence of steady-state L-type Ca current inactivation and characterized, for the first time in a mammalian preparation, the kinetics of both entry into and recovery from inactivation over a wide range of voltages. The R528H mutation had no effect on the kinetics or voltage dependence of inactivation.
Nitric Oxide-Producing Islet Cells Modulate the Release of Sensory Neuropeptides in the Rat Substantia Gelatinosa
Authors: Aimar Patrizia , Pasti Lucia , Carmignoto Giorgio , Merighi Adalberto
Published: April 2018

The substantia gelatinosa of the spinal cord (lamina II) is the major site of integration for nociceptive information. Activation of NMDA glutamate receptor, production of nitric oxide (NO), and enhanced release of substance P and calcitonin gene-related peptide (CGRP) from primary afferents are key events in pain perception and central hyperexcitability. By combining reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase histochemistry for NO-producing neurons with immunogold labeling for substance P, CGRP, and glutamate, we show that (1) NO-producing neurons in lamina IIiare islet cells; (2) these neurons rarely form synapses onto peptide-immunoreactive profiles; and (3) NADPH diaphorase-positive dendrites are often in close spatial relationship with peptide-containing terminals and are observed at the periphery of type II glomeruli showing glutamate-immunoreactive central endings. By means of confocal fluorescent microscopy in acute spinal cord slices loaded with the Ca2+indicator Indo-1, we also demonstrate that (1) NMDA evokes a substantial [Ca2+]iincrease in a subpopulation of neurons in laminae I-II, with morphological features similar to those of islet cells; (2) a different neuronal population in laminae I-IIo, unresponsive to NMDA, displays a significant [Ca2+]iincrease after slice perfusion with either substance P and the NO donor 3morpholinosydnonimine (SIN-1); and (3) the responses to both substance P and SIN-1 are either abolished or significantly inhibited by the NK1receptor antagonist sendide. These results provide compelling evidence that glutamate released at type II glomeruli triggers the production of NO in islet cells within lamina IIiafter NMDA receptor activation. The release of substance P from primary afferents triggered by newly synthesized NO may play a crucial role in the cellular mechanism leading to spinal hyperexcitability and increased pain perception.
CREB in the Mouse SCN: A Molecular Interface Coding the Phase-Adjusting Stimuli Light, Glutamate, PACAP, and Melatonin for Clockwork Access
Authors: von Gall Charlotte , Duffield Giles E. , Hastings Michael H. , Kopp Michael D. A. , Dehghani Faramarz , Korf Horst-Werner , Stehle Jörg H.
Published: April 2018

The suprachiasmatic nucleus (SCN) is a central pacemaker in mammals, driving many endogenous circadian rhythms. An important pacemaker target is the regulation of a hormonal message for darkness, the circadian rhythm in melatonin synthesis. The endogenous clock within the SCN is synchronized to environmental light/dark cycles by photic information conveyed via the retinohypothalamic tract (RHT) and by the nocturnal melatonin signal that acts within a feedback loop. We investigated how melatonin intersects with the temporally gated resetting actions of two RHT transmitters, pituitary adenylate cyclase-activating polypeptide (PACAP) and glutamate. We analyzed immunocytochemically the inducible phosphorylation of the transcription factor Ca2+/cAMP response element-binding protein (CREB) in the SCN of a melatonin-proficient (C3H) and a melatonin-deficient (C57BL) mouse strain.In vivo, light-induced phase shifts in locomotor activity were consistently accompanied by CREB phosphorylation in the SCN of both strains. However, in the middle of subjective nighttime, light induced larger phase delays in C57BL than in C3H mice.In vitro, PACAP and glutamate induced CREB phosphorylation in the SCN of both mouse strains, with PACAP being more effective during late subjective daytime and glutamate being more effective during subjective nighttime. Melatonin suppressed PACAP- but not glutamate-induced phosphorylation of CREB. The distinct temporal domains during which glutamate and PACAP induce CREB phosphorylation imply that during the light/dark transition the SCN switches sensitivity between these two RHT transmitters. Because these temporal domains are not different between C3H and C57BL mice, the sensitivity windows are set independently of the rhythmic melatonin signal.
Amphetamine-Induced Behavior, Dopamine Release, and c-fosmRNA Expression: Modulation by Environmental Novelty
Authors: Badiani Aldo , Oates Matthew M. , Day Heidi E. W. , Watson Stanley J. , Akil Huda , Robinson Terry E.
Published: April 2018

We have shown recently that the psychomotor activating effects of amphetamine in the rat are much greater when this drug is administered in association with environmental novelty than when it is given in a home environment. The main purpose of the present study was to explore the neural basis of this phenomenon. We found, usingin situhybridization of c-fosmRNA, that the pattern of neuronal activation in the cortex, in the caudate, in the shell and core of the nucleus accumbens, and in other subcortical structures was markedly different when amphetamine (2.0 mg/kg, i.p.) was given in association with exposure to environmental novelty relative to when it was given at home. In most brain regions the magnitude of c-fosexpression was over two times greater in rats given amphetamine plus novelty than in rats given amphetamine alone. In contrast, anin vivomicrodialysis study indicated that environmental novelty did not affect amphetamine-induced dopamine release in either caudate or nucleus accumbens. Furthermore, a unilateral 6-hydroxydopamine lesion of the mesostriatal dopamine system reduced amphetamine- but not novelty-induced c-fosexpression. Finally, we found no differences in the amount of corticosterone secreted after exposure to novelty, amphetamine, or both, suggesting that corticosterone does not play a critical role in the ability of novelty to modulate amphetamine-induced psychomotor activation. In conclusion, it seems that environmental novelty alters the neurobiological effects of amphetamine independently of the primary neuropharmacological actions of this drug in the striatum.
Differential Regulation of Neurotrophin andtrkReceptor mRNAs in Catecholaminergic Nuclei during Chronic Opiate Treatment and Withdrawal
Authors: Numan Suzanne , Lane-Ladd Sarah B. , Zhang Lixin , Lundgren Kerstin H. , Russell David S. , Seroogy Kim B. , Nestler Eric J.
Published: April 2018

The neurotrophins brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) and their receptorstrkB andtrkC, respectively, are expressed in the locus coeruleus (LC) and ventral tegmental area (VTA), brain regions known to be involved in opiate addiction. Previously, administration of exogenous neurotrophins has been shown to oppose effects of chronic morphine treatment on LC and VTA neurons. However, the response of endogenous neurotrophins in LC and VTA to opiate treatment is unknown. In this study, BDNF, NT-3,trkB, andtrkC mRNAs were analyzed in these regions after chronic morphine treatment and during antagonist precipitated withdrawal. Although chronic morphine exposure resulted in only modest increases in BDNF and NT-3 mRNA expression in LC, precipitated withdrawal led to a marked, rapid, and prolonged increase in BDNF mRNA and a delayed decrease in NT-3 mRNA. Levels oftrkB andtrkC mRNAs, which were unchanged by chronic morphine treatment, were elevated in LC at 2 and 6 hr of withdrawal. By 20 hr,trkB mRNA levels in LC had returned to control, whereastrkC mRNA levels fell below control values. In contrast to the substantial alterations observed in LC, there was no regulation of the neurotrophins ortrkmRNAs within the VTA during chronic opiate treatment or withdrawal, with the exception of an increase intrkB mRNA at 6 hr of withdrawal. These results suggest that neurotrophins and their receptors per se may be involved in opiate-induced plasticity of the LC, whereas other mechanisms would appear to be involved in the VTA.
Presynaptic Effects of NMDA in Cerebellar Purkinje Cells and Interneurons
Authors: Glitsch M. , Marty A.
Published: April 2018

NMDA receptors (NMDARs) are generally believed to mediate exclusively postsynaptic effects at brain synapses. Here we searched for presynaptic effects of NMDA at inhibitory synapses in rat cerebellar slices. In Purkinje cells, application of NMDA enhanced the frequency of miniature IPSCs (mIPSCs) but not that of miniature EPSCs (mEPSCs). This increase in frequency was dependent on the external Mg2+concentration. In basket and stellate cells, NMDA induced an even larger mIPSC frequency increase than in Purkinje cells, whereas mEPSCs were again not affected. Moreover, NMDA induced an inward current in both types of interneuron, which translated into a small depolarization (∼10 mV for 30 μmNMDA) under current-clamp conditions. In paired recordings of connected basket cell–Purkinje cell synapses, depolarizations of 10–30 mV applied to the basket cell soma enhanced the frequency of postsynaptic mIPSCs, suggesting that somatic depolarization was partially transmitted to the terminals in the presence of tetrodotoxin. However, this effect was small and unlikely to account fully for the effects of NMDA on mIPSCs. Consistent with a small number of dendritic NMDARs, evoked EPSCs in interneurons had a remarkably small NMDA component. Evoked IPSCs at interneuron–interneuron synapses were inhibited by NMDA, and the rate of failures was increased, indicating again a presynaptic site of action. We conclude that activation of NMDARs in interneurons exerts complex presynaptic effects, and that the corresponding receptors are most likely located in the axonal domain of the cell.
TheCaenorhabditis elegansGeneunc-25Encodes Glutamic Acid Decarboxylase and Is Required for Synaptic Transmission But Not Synaptic Development
Authors: Jin Yishi , Jorgensen Erik , Hartwieg Erika , Horvitz H. Robert
Published: April 2018

The neurotransmitter GABA has been proposed to play a role during nervous system development. We show that theCaenorhabditis elegansgeneunc-25encodes glutamic acid decarboxylase (GAD), the GABA biosynthetic enzyme.unc-25is expressed specifically in GABAergic neurons. Null mutations inunc-25eliminate the UNC-25 protein or alter amino acids conserved in all known GADs, result in a complete lack of GABA, and cause defects in all GABA-mediated behaviors. Inunc-25mutants the GABAergic neurons have normal axonal trajectories and synaptic connectivity, and the size and shape of synaptic vesicles are normal. The number of synaptic vesicles at GABAergic neuromuscular junctions is slightly increased. Cholinergic ventral nerve cord neurons, which innervate the same muscles as GABAergic ventral cord neurons, have normal morphology, connectivity, and synaptic vesicles. We conclude that GAD activity and GABA are not necessary for the development or maintenance of neuromuscular junctions inC. elegans.
Identification of an Acute Ethanol Response Quantitative Trait Locus on Mouse Chromosome 2
Authors: Demarest Kristin , McCaughran James , Mahjubi Elham , Cipp Laura , Hitzemann Robert
Published: April 2018

A two-stage strategy was used to identify and confirm quantitative trait loci (QTLs) associated with the changes in locomotor activity induced by a 1.5 gm/kg ethanol challenge. For stage 1, putative QTLs were identified by analysis of the strain means for 25 strains of the BXD recombinant inbred (RI) series (males only). QTLs were identified on chromosomes 1, 2, 4, and 6. The activity response to chlordiazepoxide generated similar QTLs on chromosomes 2 and 6. None of the QTLs were similar to those generated from analysis of the saline response data. For stage 2, 900 male C57BL/6J (B6) × DBA/2J (D2) F2intercross animals were phenotyped for ethanol response, and the phenotypic extremes (those animals > and <1 SD from the mean) were identified. These extremes differed by >10,000 cm/15 min in their response to ethanol. The extreme progeny were used for a genome-wide scan both to confirm the putative RI-generated QTLs and to detect new QTLs. The F2analysis generated no new QTLs with logarithm of the likelihood for linkage (LOD) scores >3. For RI-generated QTLs, only the QTL on chromosome 2 was confirmed (LOD = 5.3). The position of the peak LOD was estimated to be 47 cM with a 20 cM 1 LOD support interval; this QTL accounted for 6% of the phenotypic variance. The 1 LOD support interval overlaps with QTLs previously identified for alcohol preference and acute ethanol withdrawal (Melo et al., 1996; Buck et al., 1997; Phillips et al., 1999).
Cross-Modulation of Synaptic Plasticity by β-Adrenergic and 5-HT1AReceptors in the Rat Basolateral Amygdala
Authors: Wang Su-Jane , Cheng Li-Liang , Gean Po-Wu
Published: April 2018

Neurotransmitter receptors are often colocalized in a neuron with other receptors, and activation of one receptor can either amplify or antagonize the response to a colocalized receptor. The aim of this study was to investigate the cross-regulation of synaptic transmission by β-adrenergic and serotonin 1A (5-HT1A) receptors and to elucidate their underlying mechanisms. Stimulation of presynaptic β-adrenergic receptors with isoproterenol (Iso) in the basolateral amygdala resulted in a long-lasting increase in synaptic transmission. This effect was mimicked by forskolin, an activator for adenylyl cyclase and a cAMP analog. In addition, the effect of forskolin was blocked by catalytic and regulatory site antagonists for cAMP-dependent protein kinase (PKA), indicating a PKA-mediated mechanism. Application of 5-HT depressed the synaptic transmission and blocked Iso- and forskolin-induced potentiation. The effect of 5-HT was mimicked by the selective 5-HT1Aagonist 8-hydroxy-dipropylaminotetralin and was blocked by the selective 5-HT1Aantagonist 1-(2-methoxyphenyl)-4[4-(2-phthalimido)butyl]piperazine, indicating its mediation by 5-HT1Areceptors. To determine the locus of interaction, Sp-cAMPS, a membrane-permeable activator of PKA, was applied, and the potentiation produced by Sp-cAMPS was completely blocked in slices pretreated with 5-HT. These results suggest that the interaction between the intracellular signaling pathways activated by 5-HT1Aand β-adrenergic receptors occurs at a step downstream from cAMP production.
Oxygen/Glucose Deprivation in Hippocampal Slices: Altered Intraneuronal Elemental Composition Predicts Structural and Functional Damage
Authors: Taylor Charles P. , Weber Mark L. , Gaughan Christopher L. , Lehning Ellen J. , LoPachin Richard M.
Published: April 2018

Effects of oxygen/glucose deprivation (OGD) on subcellular elemental composition and water content were determined in nerve cell bodies from CA1 areas of rat hippocampal slices. Electron probe x-ray microanalysis was used to measure percentage water and concentrations of Na, P, K, Cl, Mg, and Ca in cytoplasm, nucleus, and mitochondria of cells exposed to normal and oxygen/glucose deficient medium. As an early (2 min) consequence of OGD, evoked synaptic potentials were lost, and K, Cl, P, and Mg concentrations decreased significantly in all morphological compartments. As exposure toin vitroOGD continued, a negative DC shift in interstitial voltage occurred (∼5 min), whereas general elemental disruption worsened in cytoplasm and nucleus (5–42 min). Similar elemental changes were noted in mitochondria, except that Ca levels increased during the first 5 min of OGD and then decreased over the remaining experimental period (12–42 min). Compartmental water content decreased early (2 min), returned to control after 12 min of OGD, and then exceeded control levels at 42 min. After OGD (12 min), perfusion of hippocampal slices with control oxygenated solutions (reoxygenation) for 30 min did not restore synaptic function or improve disrupted elemental composition. Notably, reoxygenated CA1 cell compartments exhibited significantly elevated Ca levels relative to those associated with 42 min of OGD. When slices were incubated at 31°C (hypothermia) during OGD/reoxygenation, neuronal dysfunction and elemental deregulation were minimal. Results show thatin vitroOGD causes loss of transmembrane Na, K, and Ca gradients in CA1 neurons of hippocampal slices and that hypothermia can obtund this damaging process and preserve neuronal function.
Kainate Receptor-Mediated Responses in the CA1 Field of Wild-Type and GluR6-Deficient Mice
Authors: Bureau Ingrid , Bischoff Serge , Heinemann Steve F. , Mulle Christophe
Published: April 2018

Kainate receptors are abundantly expressed in the hippocampus. Mice with disruption of kainate receptor subunits allow the genetic dissection of the role of each kainate receptor subunits in the synaptic physiology of the hippocampus, as well as in excitotoxic processes. We have compared the action of domoate and kainate on CA1 pyramidal neurons in slices from wild-type and GluR6−/− mice. The difference in the amplitude of inward currents evoked by domoate and kainate between wild-type and GluR6−/− mice demonstrates the presence of functional kainate receptors in CA1 pyramidal neurons. Block of domoate-activated inward currents by the AMPA receptor antagonists 2,3-dihydroxy-6-nitro-7-sulfonyl-benzo(F)quinoxaline (1 μm) and 1-(4-aminophenyl)-3-methylcarbamyl-4-methyl7,8-methylenedioxy-3,4-dihydro-5H-2,3-benzodiazepine) (GYKI 53655) (50 μm) is complete in GluR6−/− mice but only partial in wild-type mice. In the presence of GYKI 53655, kainate receptor activation dramatically increases the frequency of spontaneous IPSCs in CA1 pyramidal cells from wild-type, as well as GluR6−/−, mice. This results from the kainate receptor-mediated activation of a sustained inward current and an increased action potential firing in afferent GABAergic interneurons of the CA1 field. These effects are observed in wild-type, as well as GluR6−/−, mice. Kainate receptors also decrease the amplitude of evoked IPSCs in CA1 pyramidal cells by increasing synaptic failures in wild-type and GluR6−/− mice. These results indicate that in CA1 pyramidal cells, distinct subtypes of kainate receptors mediate several functionally antagonistic effects.
Dynamic Potassium Channel Distributions during Axonal Development Prevent Aberrant Firing Patterns
Authors: Vabnick Ian , Trimmer James S. , Schwarz Thomas L. , Levinson S. Rock , Risal Dipesh , Shrager Peter
Published: April 2018

The distribution and function of Shaker-related K+channels were studied with immunofluorescence and electrophysiology in sciatic nerves of developing rats. At nodes of Ranvier, Na+channel clustering occurred very early (postnatal days 1–3). Although K+channels were not yet segregated at most of these sites, they were directly involved in action potential generation, reducing duration, and the refractory period. At ∼1 week, K+channel clusters were first seen but were within the nodal gap and in paranodes, and only later (weeks 2–4) were they shifted to juxtaparanodal regions. K+channel function was most dramatic during this transition period, with block producing repetitive firing in response to single stimuli. As K+channels were increasingly sequestered in juxtaparanodes, conduction became progressively insensitive to K+channel block. Over the first 3 weeks, K+channel clustering was often asymmetric, with channels exclusively in the distal paranode in ∼40% of cases. A computational model suggested a mechanism for the firing patterns observed, and the results provide a role for K+channels in the prevention of aberrant excitation as myelination proceeds during development.
Identification and Characterization of Early Glial Progenitors Using a Transgenic Selection Strategy
Authors: Chandross Karen J. , Cohen Rick I. , Paras Peter , Gravel Michel , Braun Peter E. , Hudson Lynn D.
Published: April 2018

To define the spatiotemporal development of and simultaneously select for oligodendrocytes (OLs) and Schwann cells (SCs), transgenic mice were generated that expressed a bacterial β-galactosidase (β-gal) and neomycin phosphotransferase fusion protein (βgeo) under the control of murine 2′3′-cyclic nucleotide 3′-phosphodiesterase (muCNP) promoters I and II. Transgenic β-gal activity was detected at embryonic day 12.5 in the ventral region of the rhombencephalon and spinal cord and in the neural crest. When cells from the rhombencephalon were cultured in the presence of G418, surviving cells differentiated into OLs, indicating that during development this brain region provides one source of OL progenitors. Postnatally, robust β-gal activity was localized to OLs throughout the brain and was absent from astrocytes, neurons, and microglia or monocytes. In the sciatic nerve β-gal activity was localized exclusively to SCs. Cultures from postnatal day 10 brain or sciatic nerve were grown in the presence of G418, and within 8–9 d exposure to antibiotic, 99% of all surviving cells were β-gal-positive OLs or SCs. These studies demonstrate that the muCNP-βgeo transgenic mice are useful for identifying OLs and SCs beginning at early stages of the glial cell lineage and throughout their development. This novel approach definitively establishes that the β-gal-positive cells identifiedin vivoare glial progenitors, as defined by their ability to survive antibiotic selection and differentiate into OLs or SCsin vitro. Moreover, this experimental paradigm facilitates the rapid and efficient selection of pure populations of mouse OLs and SCs and further underscores the use of cell-specific promoters in the purification of distinct cell types.
Prostaglandin E2Stimulates Amyloid Precursor Protein Gene Expression: Inhibition by Immunosuppressants
Authors: Lee Robert K. K. , Knapp Stefan , Wurtman Richard J.
Published: April 2018

Amyloid plaques that accumulate in the brains of patients with Alzheimer’s disease (AD) are primarily composed of aggregates of amyloid peptides that are derived from the amyloid precursor protein (APP). Overexpression of APP in cell cultures increases the formation of amyloidogenic peptides and causes neurodegeneration and cognitive dysfunction in transgenic mice. We now report that activation of prostaglandin E2(PGE2) receptors increases cAMP formation and stimulates overexpression of APP mRNA and holoprotein in primary cultures of cortical astrocytes. Levels of glial fibrillary acidic protein were also increased by PGE2treatment, suggesting that these cultured astrocytes resemble reactive astrocytes foundin vivo. The stimulation by PGE2of APP synthesis was mimicked or blocked by activators or inhibitors, respectively, of protein kinase A. Actinomycin D or cycloheximide also inhibited the increase in APP holoprotein stimulated by PGE2. Treatment of astrocytes with 8-Bromo-cAMP or forskolin for 24 hr also stimulated APP overexpression in cultured astrocytes. The immunosuppressants cyclosporin A and FK-506 inhibited the increase in APP mRNA and holoprotein levels caused by PGE2or by other treatments that elevated cellular cAMP levels; the inhibitory effect of FK-506 but not of cyclosporin A was attenuated by rapamycin. These results suggest that prostaglandins produced by brain injury or inflammation can activate APP transcription in astrocytes and that immunosuppressants may be used to prevent APP overexpression and possibly the pathophysiological processes underlying AD.
Purification and Characterization of Astrocyte Precursor Cells in the Developing Rat Optic Nerve
Authors: Mi Huaiyu , Barres Ben A.
Published: April 2018

The signaling interactions that control oligodendrocyte generation from their precursor cells have been studied intensively. Much less is known about how astrocyte generation is normally controlled. Here we report the purification and characterization of astrocyte precursor cells (APCs) from the developing rat optic nerve. APCs are antigenically distinct from astrocytes. Both cell types are Pax2+and vimentin+, whereas astrocytes are GFAP+and S100β+, and the precursor cells are A2B5+. In contrast to purified astrocytes, purified APCs rapidly die in serum-free culture but can be saved by basic fibroblast growth factor (bFGF) and glial growth factor 2 (GGF2). Unlike oligodendrocyte precursor cells, APCs do not differentiate by default; their differentiation into GFAP+cells is induced by ciliary neurotrophic factor (CNTF) or by leukemia inhibitory factor (LIF). Finally, the survival, proliferation, and differentiation of APCs were promoted by coculture with other embryonic optic nerve cell types but not with purified embryonic retinal ganglion cells, indicating that interactions with non-neuronal cells are likely to play an important role in controlling astrocyte generation in the developing optic nerve.
Activated Macrophages and Microglia Induce Dopaminergic Sprouting in the Injured Striatum and Express Brain-Derived Neurotrophic Factor and Glial Cell Line-Derived Neurotrophic Factor
Authors: Batchelor Peter E. , Liberatore Gabriel T. , Wong John Y. F. , Porritt Michelle J. , Frerichs Fenneke , Donnan Geoffrey A. , Howells David W.
Published: April 2018

Nigrostriatal dopaminergic neurons undergo sprouting around the margins of a striatal wound. The mechanism of this periwound sprouting has been unclear. In this study, we have examined the role played by the macrophage and microglial response that follows striatal injury. Macrophages and activated microglia quickly accumulate after injury and reach their greatest numbers in the first week. Subsequently, the number of both cell types declines rapidly in the first month and thereafter more slowly. Macrophage numbers eventually cease to decline, and a sizable group of these cells remains at the wound site and forms a long-term, highly activated resident population. This population of macrophages expresses increasing amounts of glial cell line-derived neurotrophic factor mRNA with time. Brain-derived neurotrophic factor mRNA is also expressed in and around the wound site. Production of this factor is by both activated microglia and, to a lesser extent, macrophages. The production of these potent dopaminergic neurotrophic factors occurs in a similar spatial distribution to sprouting dopaminergic fibers. Moreover, dopamine transporter-positive dopaminergic neurites can be seen growing toward and embracing hemosiderin-filled wound macrophages. The dopaminergic sprouting that accompanies striatal injury thus appears to result from neurotrophic factor secretion by activated macrophages and microglia at the wound site.
The Amyloid Precursor Protein Interacts with GoHeterotrimeric Protein within a Cell Compartment Specialized in Signal Transduction
Authors: Brouillet Emmanuel , Trembleau Alain , Galanaud Damien , Volovitch Michel , Bouillot Colette , Valenza Cécile , Prochiantz Alain , Allinquant Bernadette
Published: April 2018

The function of the β-amyloid protein precursor (βAPP), a transmembrane molecule involved in Alzheimer pathologies, is poorly understood. We recently reported the presence of a fraction of βAPP in cholesterol and sphingoglycolipid-enriched microdomains (CSEM), a caveolae-like compartment specialized in signal transduction. To investigate whether βAPP actually interferes with cell signaling, we reexamined the interaction between βAPP and GoGTPase. In strong contrast with results obtained with reconstituted phospholipid vesicles (Okamoto et al., 1995), we find that incubating total neuronal membranes with 22C11, an antibody that recognizes an N-terminal βAPP epitope, reduces high-affinity GoGTPase activity. This inhibition is specific of Gαoand is reproduced, in the absence of 22C11, by the addition of the βAPP C-terminal domain but not by two distinct mutated βAPP C-terminal domains that do not bind Gαo. This inhibition of GαoGTPase activity by either 22C11 or wild-type βAPP cytoplasmic domain suggests that intracellular interactions between βAPP and Gαocould be regulated by extracellular signals. To verify whether this interaction is preserved in CSEM, we first used biochemical, immunocytochemical, and ultrastructural techniques to unambiguously confirm the colocalization of Gαoand βAPP in CSEM. We show that inhibition of basal GαoGTPase activity also occurs within CSEM and correlates with the coimmunoprecipitation of Gαoand βAPP. The regulation of GαoGTPase activity by βAPP in a compartment specialized in signaling may have important consequences for our understanding of the physiopathological functions of βAPP.
Identification of the Kv2.1 K+Channel as a Major Component of the Delayed Rectifier K+Current in Rat Hippocampal Neurons
Authors: Murakoshi Hideyuki , Trimmer James S.
Published: April 2018

Molecular cloning studies have revealed the existence of a large family of voltage-gated K+channel genes expressed in mammalian brain. This molecular diversity underlies the vast repertoire of neuronal K+channels that regulate action potential conduction and neurotransmitter release and that are essential to the control of neuronal excitability. However, the specific contribution of individual K+channel gene products to these neuronal K+currents is poorly understood. We have shown previously, using an antibody, “KC,” specific for the Kv2.1 K+channel α-subunit, the high-level expression of Kv2.1 protein in hippocampal neuronsin situand in culture. Here we show that KC is a potent blocker of K+currents expressed in cells transfected with the Kv2.1 cDNA, but not of currents expressed in cells transfected with other highly related K+channel α-subunit cDNAs. KC also blocks the majority of the slowly inactivating outward current in cultured hippocampal neurons, although antibodies to two other K+channel α-subunits known to be expressed in these cells did not exhibit blocking effects. In all cases the blocking effects of KC were eliminated by previous incubation with a recombinant fusion protein containing the KC antigenic sequence. Together these studies show that Kv2.1, which is expressed at high levels in most mammalian central neurons, is a major contributor to the delayed rectifier K+current in hippocampal neurons and that the KC antibody is a powerful tool for the elucidation of the role of the Kv2.1 K+channel in regulating neuronal excitability.
Fas/Apo [Apoptosis]-1 and Associated Proteins in the Differentiating Cerebral Cortex: Induction of Caspase-Dependent Cell Death and Activation of NF-κB
Authors: Cheema Zulfiqar F. , Wade Stephen B. , Sata Masataka , Walsh Kenneth , Sohrabji Farida , Miranda Rajesh C.
Published: April 2018

The developing cerebral cortex undergoes a period of substantial cell death. The present studies examine the role of the suicide receptor Fas/Apo[apoptosis]-1 in cerebral cortical development. Fas mRNA and protein are transiently expressed in subsets of cells within the developing rat cerebral cortex during the peak period of apoptosis. Fas-immunoreactive cells were localized in close proximity to Fas ligand (FasL)-expressing cells. The Fas-associated signaling protein receptor interacting protein (RIP) was expressed by some Fas-expressing cells, whereas Fas-associated death domain (FADD) was undetectable in the early postnatal cerebral cortex. FLICE-inhibitory protein (FLIP), an inhibitor of Fas activation, was also expressed in the postnatal cerebral cortex. Fas expression was more ubiquitous in embryonic cortical neuroblasts in dissociated culture compared toin situwithin the developing brain, suggesting that the environmental milieu partly suppresses Fas expression at this developmental stage. Furthermore, FADD, RIP, and FLIP were also expressed by subsets of dissociated cortical neuroblasts in culture. Fas activation by ligand (FasL) or anti-Fas antibody induced caspase-dependent cell death in primary embryonic cortical neuroblast cultures. The activation of Fas was also accompanied by a rapid downregulation of Fas receptor expression, non-cell cycle-related incorporation of nucleic acids and nuclear translocation of the RelA/p65 subunit of the transcription factor NF-κB. Together, these data suggest that adult cortical cell number may be established, in part, by an active process of receptor-mediated cell suicide, initiatedin situby killer (FasL-expressing) cells and that Fas may have functions in addition to suicide in the developing brain.
Neural Encoding in Orbitofrontal Cortex and Basolateral Amygdala during Olfactory Discrimination Learning
Authors: Schoenbaum Geoffrey , Chiba Andrea A. , Gallagher Michela
Published: April 2018

Orbitofrontal cortex (OFC) is part of a network of structures involved in adaptive behavior and decision making. Interconnections between OFC and basolateral amygdala (ABL) may be critical for encoding the motivational significance of stimuli used to guide behavior. Indeed, much research indicates that neurons in OFC and ABL fire selectively to cues based on their associative significance. In the current study recordings were made in each region within a behavioral paradigm that allowed comparison of the development of associative encoding over the course of learning. In each recording session, rats were presented with novel odors that were informative about the outcome of making a response and had to learn to withhold a response after sampling an odor that signaled a negative outcome. In some cases, reversal training was performed in the same session as the initial learning. Ninety-six of the 328 neurons recorded in OFC and 60 of the 229 neurons recorded in ABL exhibited selective activity during evaluation of the odor cues after learning had occurred. A substantial proportion of those neurons in ABL developed selective activity very early in training, and many reversed selectivity rapidly after reversal. In contrast, those neurons in OFC rarely exhibited selective activity during odor evaluation before the rats reached the criterion for learning, and far fewer reversed selectivity after reversal. The findings support a model in which ABL encodes the motivational significance of cues and OFC uses this information in the selection and execution of an appropriate behavioral strategy.
Complete Compensation in Skilled Reaching Success with Associated Impairments in Limb Synergies, after Dorsal Column Lesion in the Rat
Authors: McKenna John E. , Whishaw Ian Q.
Published: April 2018

Each of the dorsal columns of the rat spinal cord conveys primary sensory information, by way of the medullary dorsal column nucleus, to the ventrobasal thalamus on the contralateral side; thus the dorsal columns are an important source of neural input to the sensorimotor cortex. Damage to the dorsal columns causes impairments in synergistic proximal or whole-body movements in cats and distal limb impairments in primates, particularly in multiarticulated finger movements and tactile foviation while handling objects, but the behavioral effects of afferent fiber lesions in the dorsal columns of rodents have not been described. Female Long–Evans rats were trained to reach with a forelimb for food pellets and subsequently received lesions of the dorsomedial spinal cord at the C2 level, ipsilateral to their preferred limb. Reaching success completely recovered within a few days of dorsal column lesion. Nevertheless, a detailed analysis of high-speed video recordings revealed that rotatory limb movements (aiming, pronation, supination, etc.) were irreversibly impaired. Compensation was achieved with whole-body and alternate limb movements. These results indicate the following: (1) in the absence of the dorsal columns, other sensorimotor pathways support endpoint success in reaching; (2) sensory input conveyed by the dorsal columns is important for both proximal and distal limb movements used for skilled reaching; and (3) detailed behavioral analyses in addition to endpoint measures are necessary to completely describe the effects of dorsal column lesions.
Differential Distribution of Three Members of a Gene Family Encoding Low Voltage-Activated (T-Type) Calcium Channels
Authors: Talley Edmund M. , Cribbs Leanne L. , Lee Jung-Ha , Daud Asif , Perez-Reyes Edward , Bayliss Douglas A.
Published: April 2018

Low voltage-activated (T-type) calcium currents are observed in many central and peripheral neurons and display distinct physiological and functional properties. Usingin situhybridization, we have localized central and peripheral nervous system expression of three transcripts (α1G, α1H, and α1I) of the T-type calcium channel family (CaVT). Each mRNA demonstrated a unique distribution, and expression of the three genes was largely complementary. We found high levels of expression of these transcripts in regions associated with prominent T-type currents, including inferior olivary and thalamic relay neurons (which expressed α1G), sensory ganglia, pituitary, and dentate gyrus granule neurons (α1H), and thalamic reticular neurons (α1I and α1H). Other regions of high expression included the Purkinje cell layer of the cerebellum, the bed nucleus of the stria terminalis, the claustrum (α1G), the olfactory tubercles (α1H and α1I), and the subthalamic nucleus (α1I and α1G). Some neurons expressed high levels of all three genes, including hippocampal pyramidal neurons and olfactory granule cells. Many brain regions showed a predominance of labeling for α1G, including the amygdala, cerebral cortex, rostral hypothalamus, brainstem, and spinal cord. Exceptions included the basal ganglia, which showed more prominent labeling for α1H and α1I, and the olfactory bulb, the hippocampus, and the caudal hypothalamus, which showed more even levels of all three transcripts. Our results are consistent with the hypothesis that differential gene expression underlies pharmacological and physiological heterogeneity observed in neuronal T-type calcium currents, and they provide a molecular basis for the study of T-type channels in particular neurons.