bluuebunny/crossref_metadata_2025 huggingface dataset:
The cAMP–Protein Kinase A Signal Transduction Pathway Modulates Ethanol Consumption and Sedative Effects of Ethanol
Authors: Wand Gary , Levine Michael , Zweifel Larry , Schwindinger William , Abel Ted
Published: April 2018

Ethanol and other drugs of abuse modulate cAMP–PKA signaling within the mesolimbic reward pathway. To understand the role of the cAMP–PKA signal transduction in mediating the effects of ethanol, we have studied ethanol consumption and the sedative effects of ethanol in three lines of genetically modified mice. We report that mice with the targeted disruption of one Gsα allele as well as mice with reduced neuronal PKA activity have decreased alcohol consumption compared with their wild-type littermates. Genetic reduction of cAMP–PKA signaling also makes mice more sensitive to the sedative effects of ethanol, although plasma ethanol concentrations are unaffected. In contrast, mice with increased adenylyl cyclase activity resulting from the transgenic expression of a constitutively active form of Gsα in neurons within the forebrain are less sensitive to the sedative effects of ethanol. Thus, the cAMP–PKA signal transduction pathway is critical in modulating sensitivity to the sedative effects of ethanol as well as influencing alcohol consumption.
Membrane Bistability in Olfactory Bulb Mitral Cells
Authors: Heyward Philip , Ennis Matthew , Keller Asaf , Shipley Michael T.
Published: April 2018

Whole-cell patch-clamp recordings were used to investigate the electrophysiological properties of mitral cells in rat main olfactory bulb brain slice preparations. The majority of mitral cells are bistable. These cells spontaneously alternate between two membrane potentials, separated by ∼10 mV: a relatively depolarized potential (upstate), which is perithreshold for spike generation, and a relatively hyperpolarized potential (downstate), in which spikes do not occur. Bistability occurs spontaneously in the absence of ionotropic excitatory or inhibitory synaptic inputs. Bistability is voltage dependent; transition from the downstate to the upstate is a regenerative event activated by brief depolarization. A brief hyperpolarization can switch the membrane potential from the upstate to the downstate. In response to olfactory nerve (ON) stimulation, mitral cells in the upstate are more likely to fire an action potential than are those in the downstate. ON stimulation can switch the membrane potential from the downstate to the upstate, producing a prolonged and amplified depolarization in response to a brief synaptic input. We conclude that bistability is an intrinsic property of mitral cells that is a major determinant of their responses to ON input.
Functional Interaction between Opioid and Cannabinoid Receptors in Drug Self-Administration
Authors: Navarro M. , Carrera M. R. A. , Fratta W. , Valverde O. , Cossu G. , Fattore L. , Chowen J. A. , Gómez R. , del Arco I. , Villanúa M. A. , Maldonado R. , Koob G. F. , de Fonseca F. Rodrı́guez
Published: April 2018

The present study was designed to explore the relationship between the cannabinoid and opioid receptors in animal models of opioid-induced reinforcement. The acute administration of SR141716A, a selective central cannabinoid CB1 receptor antagonist, blocked heroin self-administration in rats, as well as morphine-induced place preference and morphine self-administration in mice. Morphine-dependent animals injected with SR141716A exhibited a partial opiate-like withdrawal syndrome that had limited consequences on operant responses for food and induced place aversion. These effects were associated with morphine-induced changes in the expression of CB1 receptor mRNA in specific nuclei of the reward circuit, including dorsal caudate putamen, nucleus accumbens, and septum. Additionally, the opioid antagonist naloxone precipitated a mild cannabinoid-like withdrawal syndrome in cannabinoid-dependent rats and blocked cannabinoid self-administration in mice. Neither SR141716A nor naloxone produced any intrinsic effect on these behavioral models. The present results show the existence of a cross-interaction between opioid and cannabinoid systems in behavioral responses related to addiction and open new strategies for the treatment of opiate dependence.
Metabotropic Glutamate Receptor 5-Induced Phosphorylation of Extracellular Signal-Regulated Kinase in Astrocytes Depends on Transactivation of the Epidermal Growth Factor Receptor
Authors: Peavy Richard D. , Chang Mike S. S. , Sanders-Bush Elaine , Conn P. Jeffrey
Published: April 2018

G-protein-coupled receptors (GPCRs) induce the phosphorylation of mitogen-activated protein (MAP) kinase by actions on any of a number of signal transduction systems. Previous studies have revealed that activation of the Gq-coupled metabotropic glutamate receptor 5 (mGluR5) induces phosphorylation of the MAP kinase extracellular signal-regulated kinase 2 (ERK2) in cultured rat cortical astrocytes. We performed a series of studies to determine the mechanisms underlying mGluR5-induced phosphorylation of MAP kinase in these cells. Interestingly, our studies suggest that mGluR5-mediated ERK2 phosphorylation is dependent on the activation of Gαqbut is not mediated by the activation of phospholipase Cβ1, activation of protein kinase C, or increases in intracellular calcium. Studies with peptide inhibitors suggest that this response is not dependent on Gβγsubunits. However, the activation of ERK2 was dependent on activation of the epidermal growth factor (EGF) receptor and activation of a Src family tyrosine kinase. Furthermore, activation of mGluR5 induced an association of this receptor and the EGF receptor, suggesting the formation of a signaling complex involved in the activation of ERK2. These data suggest that mGluR5 increases ERK2 phosphorylation in astrocytes by a novel mechanism involving the activation of Gαqand both receptor and nonreceptor tyrosine kinases but that is independent of the activation of phospholipase Cβ1.
Synapse-Forming Axons and Recombinant Agrin Induce Microprocess Formation on Myotubes
Authors: Uhm Chang-Sub , Neuhuber Birgit , Lowe Brian , Crocker Virginia , Daniels Mathew P.
Published: April 2018

We examined cell-surface behavior at nerve–muscle contacts during synaptogenesis in cocultures of rat ventral spinal cord (VSC) neurons and myotubes. Developing synapses in 1-d-old cocultures were identified by the presence of axon-induced acetylcholine receptor (AChR) aggregation. Identified regions were then examined by transmission and scanning electron microscopy. The myotube surface near contacts with axons that induced AChR aggregation typically displayed ruffles, microvilli, and filopodia (microprocesses), indicating motility of the myotube surface. At some of these contact sites microprocesses were wrapped around the axon, resulting in the partial or total “submersion” of the axon within the myotube contours. Sites of myotube contact with somata and dendrites of the same neurons showed much less evidence of motility and surface interaction than sites of contact with axons. Moreover, the distance between opposed membranes of axons and myotubes was smaller than between dendrites or somata and myotubes, suggesting stronger adhesion of axons. These results suggest polarized expression of molecules involved in the induction of microprocess formation and adhesion in developing VSC neurons. We therefore tested the ability of agrin, which is preferentially secreted by axons, to induce microprocess formation in myotubes. Addition of recombinant C-terminal agrin to culture medium resulted in formation of microprocesses within 3 hr. Myotubes transfected with full-length rat agrin constructs displayed numerous filopodia, as revealed by fluorescence microscopy. The results suggest that the induction of muscle cell surface motility may be linked to the signaling processes that trigger the initial formation of the neuromuscular junction.
Neocortical Cell Migration: GABAergic Neurons and Cells in Layers I and VI Move in a Cyclin-Dependent Kinase 5-Independent Manner
Authors: Gilmore Edward C. , Herrup Karl
Published: April 2018

The adult mammalian cerebral cortex arises from a complex series of neuronal migrations. The primitive layer known as the preplate is split into an outer marginal zone and an inner subplate by invading cortical plate neurons in an “inside-out” pattern of layering with respect to time of neuronal origin. In cyclin-dependent kinase 5 (Cdk5)-deficient mice (cdk5−/−), the earliest born cortical neurons split the preplate, but later born neurons arrest below the subplate, resulting in an ectopic “outside-in” layer of neurons normally destined for layers II–V. We have pursued this analysis incdk5−/−↔ wild-type chimeric mice coupled with experiments in cell culture.In vitromigration assays show no difference in migrational ability between embryoniccdk5−/−and wild-type neurons. Incdk5−/−chimeras, layers I and VI are made up of both mutant and wild-type genotype neurons, whereas layers II–V contain predominantly wild-type cells. In addition, a thin layer of neurons is found below layer VI, made up ofcdk5−/−cells; bromodeoxyuridine labeling suggests that these neurons were destined for layers II–V. Scatteredcdk5−/−cells are found throughout layers II–V, but these neurons are always found to be GABAergic. The findings suggest that Cdk5 is not required for migration of either the deepest cortical plate neurons or the GABAergic neurons from the ganglionic eminences. The migration of layer II–V pyramidal neurons, however, is intrinsically blocked by Cdk5 deficiency, thus suggesting that different neuronal cell types use distinct mechanisms of migration.
Structure and Emergence of Specific Olfactory Glomeruli in the Mouse
Authors: Potter Steve M. , Zheng Chen , Koos David S. , Feinstein Paul , Fraser Scott E. , Mombaerts Peter
Published: April 2018

Olfactory sensory neurons (OSNs) expressing a given odorant receptor (OR) gene project their axons to a few specific glomeruli that reside at recognizable locations in the olfactory bulb. Connecting ∼1000 populations of OSNs to the ∼1800 glomeruli of the mouse bulb poses a formidable wiring problem. Additional progress in understanding the mechanisms of neuronal connectivity is dependent on knowing how these axonal pathways are organized and how they form during development. Here we have applied a genetic approach to this problem. We have constructed by gene targeting novel strains of mice in which either all OSNs or those that express a specific OR gene, M72 or M71, also produce green fluorescent protein (GFP) or a fusion of tau with GFP. We visualized OSNs and their axons in whole mounts with two-photon laser scanning microscopy. The main conclusion we draw from the three-dimensional reconstructions is the high degree of morphological variability of mature glomeruli receiving axonal input from OR-expressing OSNs and of the pathways taken by the axons to those glomeruli. We also observe that axons of OR-expressing OSNs do not innervate nearby glomeruli in mature mice. Postnatally, a tangle of axons from M72-expressing OSNs occupies a large surface area of the bulb and coalesces abruptly into a protoglomerulus at a reproducible stage of development. These results differ in several aspects from those reported for the development of glomeruli receiving input from OSNs expressing the P2 OR, suggesting the need for a more systematic examination of OR-specific glomeruli.
Erythropoietin Regulates theIn VitroandIn VivoProduction of Neuronal Progenitors by Mammalian Forebrain Neural Stem Cells
Authors: Shingo Tetsuro , Sorokan S. Todd , Shimazaki Takuya , Weiss Samuel
Published: April 2018

Recent studies have shown that neurogenesis is enhanced after hypoxia and that erythropoietin (EPO), an inducible cytokine, is produced in the brain as part of the intrinsic hypoxia response. Thus, we asked whether EPO might regulate neurogenesis by forebrain neural stem cells (NSCs). We found that EPO receptors are expressed in the embryonic germinal zone during neurogenesis as well as in the adult subventricular zone, which continues to generate neurons throughout adulthood. Cultured NSCs exposed to a modest hypoxia produced two- to threefold more neurons, which was associated with an elevation in EPO gene expression. The enhanced neuron production attributable to hypoxia was mimicked by EPO and blocked by coadministration of an EPO neutralizing antibody. EPO appears to act directly on NSCs, promoting the production of neuronal progenitors at the expense of multipotent progenitors. EPO infusion into the adult lateral ventricles resulted in a decrease in the numbers of NSCs in the subventricular zone, an increase in newly generated cells migrating to the olfactory bulb, and an increase in new olfactory bulb interneurons. Infusion of anti-EPO antibodies had the opposite effect: an increase in the number of NSCs in the subventricular zone and a decrease in the number of newly generated cells migrating to the bulb. These findings suggest that EPO is an autocrine–paracrine factor, capable of regulating the production of neuronal progenitor cells by forebrain NSCs.
The Permissive Cue Laminin Is Essential for Growth Cone TurningIn Vivo
Authors: Bonner Jennifer , O'Connor Timothy P.
Published: April 2018

The proper guidance of migrating growth cones relies on the balance of multiple guidance cues in the embryonic environment. In addition to guidance cues, growth cones are in contact with other substrates that may contribute to the pathfinding of neurons. For example, in the developing insect peripheral nervous system, pioneer neurons migrate on and between layers of the basal lamina. Previous studies have demonstrated that one basal lamina molecule, laminin, promotes outgrowth of many classes of neuronsin vitro. In this study, the simple grasshopper nervous system was used to investigate the role of laminin in neuronal pathfinding. Laminin expression precedes axonogenesis of the Tibial (Ti1) pioneer neurons in the developing limb bud, and expression continues during outgrowth and guidance of the pioneer neurons. The role of a nidogen-binding motif on laminin was investigated using subunit-specific antibodies and peptides as blocking reagentsin vivo. Antibodies and peptides that block the nidogen-binding site on laminin resulted in stalled Ti1 axon migration, predominantly at the precise location where they normally turn ventrally. After prolonged culturing, Ti1 axons remained stalled at the same location. Therefore, although Ti1 axons were capable of outgrowth in the presence of blocking reagents, they were not able to navigate an essential turn. This study indicates that the interaction of the Ti1 growth cone with the nidogen-binding site on laminin is vital for neuronal pathfindingin vivoand suggests that permissive cues may be essential for growth cone steering.
Long-Term Potentiation of Thalamocortical Transmission in the Adult Visual CortexIn Vivo
Authors: Heynen Arnold J. , Bear Mark F.
Published: April 2018

It has been suggested that NMDA receptor-dependent synaptic strengthening, like that observed after long-term potentiation (LTP), is a mechanism by which experience modifies responses in the neocortex. We report here that patterned (theta burst) stimulation of the dorsal lateral geniculate nucleus reliably induces LTP of field potentials (FPs) evoked in primary visual cortex (Oc1) of adult ratsin vivo. The response enhancement is saturable, long-lasting, and dependent on NMDA receptor activation. To determine the laminar locus of these changes, current source density (CSD) analysis was performed on FP profiles obtained before and after LTP induction. LTP was accompanied by an enhancement of synaptic current sinks located in thalamorecipient (layer IV and deep layer III) and supragranular (layers II/III) cell layers. We also examined immunocytochemical labeling for the immediate early gene zif-268 1 hr after induction of LTP. In concert with the laminar changes observed in CSD analyses, we observed a significant increase in the number of zif-268-immunopositive neurons in layers II–IV that occurred over a wide extent of Oc1. Last, we investigated the functional consequences of LTP induction by monitoring changes in visually evoked potentials. After LTP, we observed that the cortical response to a full-field flash was significantly enhanced and that responses to grating stimuli were increased across a range of spatial frequencies. These findings are consistent with growing evidence that primary sensory cortex remains plastic into adulthood, and they show that the mechanisms of LTP can contribute to this plasticity.
Selective Perceptual Impairments After Perirhinal Cortex Ablation
Authors: Buckley Mark J. , Booth Michael C. A. , Rolls Edmund T. , Gaffan David
Published: April 2018

It has been suggested that the primate perirhinal cortex contributes exclusively to memory. However, recent studies in macaque monkeys have implied that the perirhinal cortex may also contribute to object perception. To investigate whether the perirhinal cortex does contribute to perception, we devised several perceptual oddity tasks in which monkeys had to choose which stimulus of several presented concurrently on a touch screen was different. Macaques with bilateral perirhinal cortex ablations were selectively impaired relative to controls at perceptually discriminating the odd stimulus when the odd stimulus was a different object and when the discrimination could not be done on the basis of simple differences in features between the stimuli. They remained unimpaired relative to controls on discriminating the odd stimulus when the odd stimulus was a different color, a different shape, or a different size even when these discriminations were extremely difficult. They were also impaired on human and monkey face oddity tasks and oddity tasks with scenes containing objects. Therefore, we reject the notion that the macaque perirhinal cortex has a role exclusive to memory and conclude that the macaque perirhinal cortex does contribute to perception. We argue that the perirhinal cortex is neither specialized for perception nor memory processes alone, but rather, is specialized for processing stimuli that require processing at a more abstract level such as at the level of an object and that the perirhinal cortex contributes to both memory and perception of such stimuli.
Control of Serotonergic Function in Medial Prefrontal Cortex by Serotonin-2A Receptors through a Glutamate-Dependent Mechanism
Authors: Martı́n-Ruiz Raúl , Puig M. Victoria , Celada Pau , Shapiro David A. , Roth Bryan L. , Mengod Guadalupe , Artigas Francesc
Published: April 2018

We examined thein vivoeffects of the hallucinogen 4-iodo-2,5-dimethoxyamphetamine (DOI). DOI suppressed the firing rate of 7 of 12 dorsal raphe (DR) serotonergic (5-HT) neurons and partially inhibited the rest (ED50= 20 μg/kg, i.v.), an effect reversed by M100907 (5-HT2Aantagonist) and picrotoxinin (GABAAantagonist). DOI (1 mg/kg, s.c.) reduced the 5-HT release in medial prefrontal cortex (mPFC) to 33 ± 8% of baseline, an effect also antagonized by M100907. However, the local application of DOI in the mPFC increased 5-HT release (164 ± 6% at 100 μm), an effect antagonized by tetrodotoxin, M100907, and BAY × 3702 (5-HT1Aagonist) but not by SB 242084 (5-HT2Cantagonist). The 5-HT increase was also reversed by NBQX (AMPA–KA antagonist) and 1S,3S-ACPD (mGluR 2/3 agonist) but not by MK-801 (NMDA antagonist). AMPA mimicked the 5-HT elevation produced by DOI. Likewise, the electrical–chemical stimulation of thalamocortical afferents and the local inhibition of glutamate uptake increased the 5-HT release through AMPA receptors. DOI application in mPFC increased the firing rate of a subgroup of 5-HT neurons (5 of 10), indicating an enhanced output of pyramidal neurons. Dual-label fluorescence confocal microscopic studies demonstrated colocalization of 5-HT1Aand 5-HT2Areceptors on individual cortical pyramidal neurons.

Thus, DOI reduces the activity of ascending 5-HT neurons through a DR-based action and enhances serotonergic and glutamatergic transmission in mPFC through 5-HT2Aand AMPA receptors. Because pyramidal neurons coexpress 5-HT1Aand 5-HT2Areceptors, DOI disrupts the balance between excitatory and inhibitory inputs and leads to an increased activity that may mediate its hallucinogenic action.
Adaptation to Temporal Contrast in Primate and Salamander Retina
Authors: Chander Divya , Chichilnisky E. J.
Published: April 2018

Visual adaptation to temporal contrast (intensity modulation of a spatially uniform, randomly flickering stimulus) was examined in simultaneously recorded ensembles of retinal ganglion cells (RGCs) in tiger salamander and macaque monkey retina. Slow contrast adaptation similar to that recently discovered in salamander and rabbit retina was observed in monkey retina. A novel method was developed to quantify the effect of temporal contrast on steady-state sensitivity and kinetics of light responses, separately from nonlinearities that would otherwise significantly contaminate estimates of sensitivity. Increases in stimulus contrast progressively and reversibly attenuated and sped light responses in both salamander and monkey RGCs, indicating that a portion of the contrast adaptation observed in visual cortex originates in the retina. The effect of adaptation on sensitivity and kinetics differed in simultaneously recorded populations of ON and OFF cells. In salamander, adaptation affected the sensitivity of OFF cells more than ON cells. In monkey, adaptation affected the sensitivity of ON cells more than OFF cells. In both species, adaptation sped the light responses of OFF cells more than ON cells. Functionally defined subclasses of ON and OFF cells also exhibited asymmetric adaptation. These findings indicate that contrast adaptation differs in parallel retinal circuits that convey distinct visual signals to the brain.
The Neuronal Apoptosis Inhibitory Protein Is a Direct Inhibitor of Caspases 3 and 7
Authors: Maier Johannes K. X. , Lahoua Zahia , Gendron Nathalie H. , Fetni Raouf , Johnston Anne , Davoodi Jamshid , Rasper Dita , Roy Sophie , Slack Ruth S. , Nicholson Donald W. , MacKenzie Alex E.
Published: April 2018

The neuronal apoptosis inhibitory protein (NAIP) was identified as a candidate gene for the inherited neurodegenerative disorder spinal muscular atrophy. NAIP is the founding member of a human protein family that is characterized by highly conserved N-terminal motifs called baculovirus inhibitor of apoptosis repeats (BIR). Five members of the human family of inhibitor of apoptosis proteins including NAIP have been shown to be antiapoptotic in various systems. To date, a mechanism for the antiapoptotic effect of NAIP has not been elucidated. To investigate NAIP function, we found cytoprotection of NAIP-expressing primary cortical neurons treated to undergo caspase-3-dependent apoptosis. The additional treatment of these neurons with the pancaspase inhibitor boc-aspartyl(OMe)-fluoromethylketone did not result in increased survival. Similar cytoprotective effects were obtained using HeLa cells transiently transfected with a NAIP N-terminal construct and treated to undergo a caspase-3-dependent cell death. To examine whether NAIP inhibits caspases directly, recombinant N-terminal NAIP protein containing BIR domains was overexpressed, purified, and tested for caspase inhibition potential. Our results demonstrate that inhibition of caspases is selective and restricted to the effector group of caspases, withKivalues as low as ∼14 nmfor caspase-3 and ∼45 nmfor caspase-7. Additional investigations with NAIP fragments containing either one or two NAIP BIRs revealed that the second BIR and to a lesser extent the third BIR alone are sufficient to mediate full caspase inhibition.
Long-Term Depression in the Adult HippocampusIn VivoInvolves Activation of Extracellular Signal-Regulated Kinase and Phosphorylation of Elk-1
Authors: Thiels Edda , Kanterewicz Beatriz I. , Norman Eric D. , Trzaskos James M. , Klann Eric
Published: April 2018

Protein kinase cascades likely play a critical role in the signaling events that underlie synaptic plasticity and memory. The extracellular signal-regulated kinase (ERK) cascade is suited well for such a role because its targets include regulators of gene expression. Here we report that the ERK cascade is recruited during long-term depression (LTD) of synaptic strength in area CA1 of the adult hippocampusin vivoand selectively impacts on phosphorylation of the nuclear transcription factor Elk-1. Using a combination ofin vivoelectrophysiology, biochemistry, pharmacology, and immunohistochemistry, we found the following: (1) ERK phosphorylation, including phosphorylation of nuclear ERK, and ERK phosphotransferase activity are increased markedly, albeit transiently, after the induction of NMDA receptor-dependent LTD at the commissural input to area CA1 pyramidal cells in the hippocampus of anesthetized adult rats; (2) LTD-inducing paired-pulse stimulation fails to produce lasting LTD in the presence of the ERK kinase inhibitor SL327, which suggests that ERK activation is necessary for the persistence of LTD; and (3) ERK activation during LTD results in increased phosphorylation of Elk-1 but not of the transcription factor cAMP response element-binding protein. Our findings indicate that the ERK cascade transduces signals from the synapse to the nucleus during LTD in hippocampal area CA1in vivo, as it does during long-term potentiation in area CA1, but that the pattern of coupling of the ERK cascade to transcriptional regulators differs between the two forms of synaptic plasticity.
Dysfunctional Light-Evoked Regulation of cAMP in Photoreceptors and Abnormal Retinal Adaptation in Mice Lacking Dopamine D4 Receptors
Authors: Nir Izhak , Harrison Joseph M. , Haque Rashidul , Low Malcolm J. , Grandy David K. , Rubinstein Marcelo , Iuvone P. Michael
Published: April 2018

Dopamine is a retinal neuromodulator that has been implicated in many aspects of retinal physiology. Photoreceptor cells express dopamine D4 receptors that regulate cAMP metabolism. To assess the effects of dopamine on photoreceptor physiology, we examined the morphology, electrophysiology, and regulation of cAMP metabolism in mice with targeted disruption of the dopamine D4 receptor gene. Photoreceptor morphology and outer segment disc shedding after light onset were normal in D4 knock-out (D4KO) mice. Quinpirole, a dopamine D2/D3/D4 receptor agonist, decreased cAMP synthesis in retinas of wild-type (WT) mice but not in retinas of D4KO mice. In WT retinas, the photoreceptors of which were functionally isolated by incubation in the presence of exogenous glutamate, light also suppressed cAMP synthesis. Despite the similar inhibition of cAMP synthesis, the effect of light is directly on the photoreceptors and independent of dopamine modulation, because it was unaffected by application of the D4 receptor antagonistl-745,870. Nevertheless, compared with WT retinas, basal cAMP formation was reduced in the photoreceptors of D4KO retinas, and light had no additional inhibitory effect. The results suggest that dopamine, via D4 receptors, normally modulates the cascade that couples light responses to adenylyl cyclase activity in photoreceptor cells, and the absence of this modulation results in dysfunction of the cascade. Dark-adapted electroretinogram (ERG) responses were normal in D4KO mice. However, ERG b-wave responses were greatly suppressed during both light adaptation and early stages of dark adaptation. Thus, the absence of D4 receptors affects adaptation, altering transmission of light responses from photoreceptors to inner retinal neurons. These findings indicate that dopamine D4 receptors normally play a major role in regulating photoreceptor cAMP metabolism and adaptive retinal responses to changing environmental illumination.
The Mitochondrial Toxin 3-Nitropropionic Acid Induces Striatal Neurodegeneration via a c-Jun N-Terminal Kinase/c-Jun Module
Authors: Garcia Marta , Vanhoutte Peter , Pages Christiane , Besson Marie-Jo , Brouillet Emmanuel , Caboche Jocelyne
Published: April 2018

Impairments in mitochondrial energy metabolism are thought to be involved in most neurodegenerative diseases, including Huntington's disease (HD). Chronic administration of 3-nitropropionic acid (3-NP), a suicide inhibitor of succinate dehydrogenase, causes prolonged energy impairments and replicates most of the pathophysiological features of HD, including preferential striatal degeneration. In this study, we analyzed one of the mechanisms that could account for this selective 3-NP-induced striatal degeneration. In chronically 3-NP-infused rats, the time course of motor behavioral impairments and histological abnormalities was determined. Progressive alterations of motor performance occurred after 3 d. By histological analysis and terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end-labeling staining, we found a selective neurodegenerescence in the striatum, occurring first in its dorsolateral (DL) part. Activation of c-Jun N-terminal kinase (JNK) was analyzed from brain sections of these rats, using immunocytochemical detection of its phosphorylated form. Activation of JNK occurred progressively and selectively in the DL of the striatum and was followed by c-Jun activation and expression in the same striatal region. To elucidate the role of the JNK/c-Jun module in 3-NP-induced striatal degeneration, we then used primary striatal neurons in culture, in which we replicated neuronal death by application of 3-NP. We found strong nuclear translocation of activated JNK that was rapidly followed by phosphorylation of the transcription factor c-Jun. Overexpression of a dominant negative version of c-Jun, lacking its transactivation domain and phosphorylation sites for activated JNK, completely abolished 3-NP-induced striatal neurodegeneration. We thus conclude that a genetic program controlled by the JNK/c-Jun module is an important molecular event in 3-NP-induced striatal degeneration.
Serotonin Release Evoked by Tail Nerve Stimulation in the CNS ofAplysia: Characterization and Relationship to Heterosynaptic Plasticity
Authors: Marinesco Stéphane , Carew Thomas J.
Published: April 2018

Considerable experimental evidence suggests that serotonin (5-HT) at sensory neuron→motor neuron (SN→MN) synapses, as well as other neuronal sites, contributes importantly to simple forms of learning such as sensitization and classical conditioning inAplysia. However, the actual release of 5-HT in the CNS induced by sensitizing stimuli such as tail shock has not been directly demonstrated. In this study, we addressed this question by (1) immunohistochemically labeling central 5-HT processes and (2) directly measuring with chronoamperometry the release of 5-HT induced by pedal tail nerve (P9) shock onto tail SNs in the pleural ganglion and their synapses onto tail MNs in the pedal ganglion.

We found that numerous 5-HT-immunoreactive fibers surround both the SN cell bodies in the pleural ganglion and SN axons in the pedal ganglion. Chronoamperometric detection of 5-HT performed with carbon fiber electrodes implanted in the vicinity of tail SN somata and synapses revealed an electrochemical 5-HT signal lasting ∼40 sec after a brief shock of P9. 5-HT release was restricted to discrete subregions (modulatory fields) of the CNS, including the vicinity of tail SN soma and synapses ipsilateral to the stimulation. Increasing P9 shock frequency augmented the amplitude of the 5-HT signal and, in parallel, increased SN excitability and SN synaptic transmission onto tail MNs. However, the relationship between the amount of 5-HT release and the two forms of SN plasticity was not uniform: SN excitability increased in a graded manner with increased 5-HT release, whereas synaptic facilitation exhibited a highly nonlinear relationship. The development of chronoamperometric techniques inAplysianow paves the way for a more complete understanding of the contribution of the serotonergic modulatory pathway to memory processing in this system.
Role of Primate Substantia Nigra Pars Reticulata in Reward-Oriented Saccadic Eye Movement
Authors: Sato Makoto , Hikosaka Okihide
Published: April 2018

To test the hypothesis that the basal ganglia are related to reward-oriented saccades, we examined activity of substantia nigra pars reticulata (SNr) neurons by using a one-direction-rewarded version of the memory-guided saccade task (1DR). Many SNr neurons changed (decreased or increased) their activity after and before a visual cue (post-cue and pre-cue activity). Post-cue decreases or increases tended to be larger to a contralateral cue. They were often modulated prospectively by the presence or absence of reward, either positively (enhanced in the rewarded condition) or negatively (enhanced in the nonrewarded condition). The positive reward modulation was more common among decreasing type neurons, whereas no such preference was observed among increasing type neurons. The reward-contingent decrease in SNr neuronal activity would facilitate rewarded saccades by inducing disinhibition in superior colliculus (SC) neurons. In contrast, the increase in SNr activity would suppress a saccade less selectively (rewarded or nonrewarded) by augmenting inhibition of SC neurons. The post-cue activity was often preceded by anticipatory pre-cue activity. Most typically, post-cue decrease was preceded by pre-cue decrease, selectively when the contralateral side was rewarded. This would reinforce the reward-oriented nature of SNr neuronal activity. The decreases and increases in SNr activity may be derived directly and indirectly, respectively, from the caudate (CD), where neurons show reward-contingent pre-cue and post-cue activity. These results suggest that the CD–SNr–SC mechanism would promote saccades oriented to reward.
Coding and Monitoring of Motivational Context in the Primate Prefrontal Cortex
Authors: Watanabe Masataka , Hikosaka Kazuo , Sakagami Masamichi , Shirakawa Shu-ichiro
Published: April 2018

The prefrontal cortex is involved in acquiring and maintaining information about context, including the set of task instructions and/or the outcome of previous stimulus–response sequences. Most studies on context-dependent processing in the prefrontal cortex have been concerned with such executive functions, but the prefrontal cortex is also involved in motivational operations. We thus wished to determine whether primate prefrontal neurons show evidence of representing the motivational context learned by the monkey. We trained monkeys in a delayed reaction task in which an instruction cue indicated the presence or absence of reward. In random alternation with no reward, the same one of several different kinds of food and liquid rewards was delivered repeatedly in a block of ∼50 trials, so that reward information would define the motivational context. In response to an instruction cue indicating absence of reward, we found that neurons in the lateral prefrontal cortex not only predicted the absence of reward but also represented more specifically which kind of reward would be omitted in a given trial. These neurons seem to code contextual information concerning which kind of reward may be delivered in following trials. We also found prefrontal neurons that showed tonic baseline activity that may be related to monitoring such motivational context. The different types of neurons were distributed differently along the dorsoventral extent of the lateral prefrontal cortex. Such operations in the prefrontal cortex may be important for the monkey to maximize reward or to modify behavioral strategies and thus may contribute to executive control.
G-Protein α Subunit Isoforms Couple Differentially to Receptors that Mediate Presynaptic Inhibition at Rat Hippocampal Synapses
Authors: Straiker Alex J. , Borden Catherine R. , Sullivan Jane M.
Published: April 2018

Presynaptic receptors that are coupled to heterotrimeric G-proteins are found throughout the brain and are responsible for modulating synaptic transmission. At least 10 G-protein-coupled receptors (GPCRs) reduce transmission in hippocampal neurons. Additionally, hippocampal neurons express up to 17 different Gα, Gβ, and Gγ subunits, making for a striking array of possible heterotrimer compositions and GPCR–heterotrimer interactions. The identity of the Gα subunit is likely a critical determinant in coupling specificity between GPCRs and their molecular effectors mediating presynaptic inhibition. We studied the role of four Gαi/osubunits (Gαo1, Gαi1,Gαi2, and Gαi3) in mediating presynaptic inhibition in hippocampal neurons by expressing pertussis toxin-insensitive (PTx-ins) Gαi/omutants. PTx treatment of these cells disrupts coupling of endogenous subunits, leaving only the mutant Gα subunits to couple with native GPCRs and βγ subunits. Successful rescue of presynaptic inhibition indicates that the expressed mutant Gα subunit can couple to the GPCR of interest. All four PTx-ins Gα subunits rescued presynaptic inhibition by adenosine A1 receptors. A PTx-ins Gα subunit also rescued adenosine A1-mediated inhibition of spontaneous vesicle fusion frequency. Of the remaining GPCRs tested, cannabinoid CB1, somatostatin, and GABABreceptors displayed an α subunit-dependent selectivity in binding to G-protein heterotrimers, whereas group III metabotropic glutamate receptor-mediated inhibition was not rescued by expression of any of the four PTx-ins Gα subunits. Differential coupling of G-protein α subunits may be a means of achieving specificity between different GPCRs and their molecular targets for mediating presynaptic inhibition.
A Proximal Promoter Domain Containing a Homeodomain-Binding Core Motif Interacts with Multiple Transcription Factors, Including HoxA5 and Phox2 Proteins, and Critically Regulates Cell Type-Specific Transcription of the Human Norepinephrine Transporter Gene
Authors: Kim Chun-Hyung , Hwang Dong-Youn , Park Jae-Joon , Kim Kwang-Soo
Published: April 2018

Expression of the norepinephrine transporter (NET), which mediates the reuptake of norepinephrine into presynaptic nerve terminals, is restricted to noradrenergic (NA) neurons. We have demonstrated previously that the 9.0 kb upstream sequences and the first intron residing in the 5′ untranslated area are critical for high-level and NA cell-specific transcription. Here, using transient transfection assays, we show that 4.0 kb of the 5′ upstream sequences contains sufficient genetic information to drive reporter gene expression in an NA cell type-specific manner. Three functional domains appear to be potentially important for the regulation ofhuman NET(hNET) gene transcription: an upstream enhancer region at −4.0 to −3.1 kb, a proximal domain at −133 to −75 bp, and a middle silencer region between these two domains. DNase I footprinting analysis of the proximal promoter region shows that a subdomain at −128 to −80 bp is protected in a cell-specific manner. We provide evidence that multiple protein factors interact with the proximal promoter domain to critically regulate the transcriptional activity of thehNETgene. In the middle of this proximal subdomain resides a homeodomain (HD)-binding core motif, which interacts with HD factors, including Phox2a and HoxA5, in an NA-specific manner. Cotransfection analyses suggest that HoxA5 and Phox2a may transactivate thehNETgene promoter. Together with previous studies indicating direct activation of dopamine β-hydroxylase transcription by Phox2a/2b, the present results support a model whereby Phox2 proteins may coordinately regulate the phenotypic specification of NA neurons by activating both NA biosynthetic and reuptake genes.
Cell Density and N-Cadherin Interactions Regulate Cell Proliferation in the Sensory Epithelia of the Inner Ear
Authors: Warchol Mark E.
Published: April 2018

Sensory hair cells in the inner ears of nonmammalian vertebrates can regenerate after injury. In many species, replacement hair cells are produced by the proliferation of epithelial supporting cells. Thus, the ability of supporting cells to undergo renewed proliferation is a key determinant of regenerative ability. The present study used cultures of isolated inner ear sensory epithelia to identify cellular signals that regulate supporting cell proliferation. Small pieces of sensory epithelia from the chicken utricle were cultured in glass microwells. Under those conditions, cell proliferation was inversely related to local cell density. The signaling molecules N-cadherin, β-catenin, and focal adhesion kinase were immunolocalized in the cultured epithelial cells, and high levels of phosphotyrosine immunoreactivity were present at cell–cell junctions and focal contacts of proliferating cells. Binding of microbeads coated with a function-blocking antibody to N-cadherin inhibited ongoing proliferation. The growth of epithelial cells was also affected by the density of extracellular matrix molecules. The results suggest that cell density, cell–cell contact, and the composition of the extracellular matrix may be critical influences on the regulation of sensory regeneration in the inner ear.
Spontaneous Retinal Activity Is Tonic and Does Not Drive Tectal Activity during Activity-Dependent Refinement in Regeneration
Authors: Kolls Bradley J. , Meyer Ronald L.
Published: April 2018

During development, waves of activity periodically spread across retina to produce correlated activity that is thought to drive activity-dependent ordering in optic fibers. We asked whether similar waves of activity are produced in the retina of adult goldfish during activity-dependent refinement by regenerating optic fibers. Dual-electrode recordings of spontaneous activity were made at different distances across retina but revealed no evidence of retinal waves in normal retina or during regeneration. Retinal activity was tonic and lacked the episodic bursting associated with waves. Cross-correlation analysis showed that the correlated activity that was normally restricted to near neighbors (typically seen across 100–200 μm and absent at >500 μm) was not altered during regeneration. The only change associated with regeneration was a twofold reduction in ganglion cell firing rates. Because spontaneous retinal activity is known to be sufficient to generate refinement during regeneration in goldfish, we examined its effect on tectal activity. In normal fish, acutely eliminating retinal activity with TTX rapidly reduced tectal unit activity by >90%. Surprisingly, during refinement at 4–6 weeks, eliminating retinal activity had no detectable effect on tectal activity. Similar results were obtained in recordings from torus longitudinalis. After refinement at 3 months, tectal activity was again highly dependent on ongoing retinal activity. We conclude that spontaneous retinal activity drives tectal cells in normal fish and after regeneration but not during activity-dependent refinement. The implications of these results for the role of presynaptic activity in refinement are considered.
Intravitreal Injection of the Attenuated Pseudorabies Virus PRV Bartha Results in Infection of the Hamster Suprachiasmatic Nucleus Only by Retrograde Transsynaptic Transport via Autonomic Circuits
Authors: Pickard Gary E. , Smeraski Cynthia A. , Tomlinson Christine C. , Banfield Bruce W. , Kaufman Jessica , Wilcox Christine L. , Enquist Lynn W. , Sollars Patricia J.
Published: April 2018

Intravitreal injection of the attenuated strain of pseudorabies virus (PRV Bartha) results in transneuronal spread of virus to a restricted set of central nuclei in the rat and mouse. We examined the pattern of central infection in the golden hamster after intravitreal inoculation with a recombinant strain of PRV Bartha constructed to express enhanced green fluorescent protein (PRV 152). Neurons in a subset of retinorecipient nuclei [i.e., suprachiasmatic nucleus (SCN), intergeniculate leaflet, olivary pretectal nucleus (OPN), and lateral terminal nucleus] and autonomic nuclei [i.e., paraventricular hypothalamic nucleus and Edinger–Westphal nucleus (EW)] are labeled by late stages of infection. Infection of the EW precedes infection in retinorecipient structures, raising the possibility that the SCN becomes infected by retrograde transsynaptic infection via autonomic (i.e., EW) circuits. We tested this hypothesis in two ways: (1) by removing the infected eye 24 hr after PRV 152 inoculation, well before viral infection first appears in the SCN; and (2) by examining central infection after intravitreal PRV 152 injection in animals with ablation of the EW. The pattern and time course of central infection were unchanged after enucleation, whereas EW ablation before intravitreal inoculation eliminated viral infection in the SCN. The results of EW lesions along with known connections between EW, OPN, and SCN indicate that intravitreal injection of PRV Bartha produces a retrograde infection of the autonomic innervation of the eye, which subsequently labels a restricted set of retinorecipient nuclei via retrograde trans-synaptic infection. These results, taken together with other genetic data, indicate that the mutations in PRV Bartha render the virus incapable of anterograde transport. PRV Bartha is thus a retrograde transsynaptic marker in the CNS.
Imaging Attentional Modulation of Pain in the Periaqueductal Gray in Humans
Authors: Tracey Irene , Ploghaus Alexander , Gati Joseph S. , Clare Stuart , Smith Steve , Menon Ravi S. , Matthews Paul M.
Published: April 2018

Pain is an unpleasant sensory and emotional experience usually triggered by stimulation of peripheral nerves and often associated with actual or potential tissue damage. It is well known that pain perception for patients and normal subjects can be modulated by psychological factors, such as attention, stress, and arousal. Our understanding of how this modulation occurs at a neuroanatomical level is poor. Here we neuroanatomically defined a key area in the network of brain regions active in response to pain that is modulated by attention to the painful stimulus. High-resolution functional magnetic resonance imaging was used to define brain activation to painful heat stimulation applied to the hand of nine normal subjects within the periaqueductal gray region. Subjects were asked to either focus on or distract themselves from the painful stimuli, which were cued using colored lights. During the distraction condition, subjects rated the pain intensity as significantly lower compared with when they attended to the stimulus. Activation in the periaqueductal gray was significantly increased during the distraction condition, and the total increase in activation was predictive of changes in perceived intensity. This provides direct evidence supporting the notion that the periaqueductal gray is a site for higher cortical control of pain modulation in humans.