bluuebunny/crossref_metadata_2025 huggingface dataset:
Mediation of Neuronal Apoptosis by Kv2.1-Encoded Potassium Channels
Authors: Pal Sumon , Hartnett Karen A. , Nerbonne Jeanne M. , Levitan Edwin S. , Aizenman Elias
Published: April 2018

Cellular K+efflux is a requisite event in the unfolding of apoptosis programs across many types of cells and death-inducing stimuli; however, the molecular identities of the ion channels mediating this key event have remained undefined. Here, we show that Kv2.1-encoded K+channels are responsible for the expression of apoptosis in cortical neuronsin vitro. Transient expression of two different dominant-negative forms of this subunit in neurons completely eliminated the enhancement of K+currents that normally accompanies the cell death process. Importantly, neurons deficient in functional Kv2.1-encoded K+channels were protected from oxidant and staurosporine-induced apoptosis. Finally, Chinese hamster ovary cells, which do not express endogenous voltage-gated K+channels, became substantially more sensitive to apoptosis after transient expression of wild-type Kv2.1. These results suggest that Kv2.1-encoded K+channels are necessary for the apoptotic signaling cascade in mammalian cortical neurons in culture and are sufficient for increasing the susceptibility to apoptogens in a nonexcitable cell.
GABABReceptor-Mediated Presynaptic Inhibition Has History-Dependent Effects on Synaptic Transmission during Physiologically Relevant Spike Trains
Authors: Ohliger-Frerking Patricia , Wiebe Sherman P. , Stäubli Ursula , Frerking Matthew
Published: April 2018

Presynaptic inhibition is a form of neuromodulation that interacts with activity-dependent short-term plasticity so that the magnitude, and sometimes even the polarity, of that activity-dependent short-term plasticity is changed. However, the functional consequences of this interaction during physiologically relevant spike trains are poorly understood. We examined the effects of presynaptic inhibition on excitatory synaptic transmission during physiologically relevant spike trains, using the GABABreceptor (GABABR) agonist baclofen to engage presynaptic inhibition and field EPSPs (fEPSPs) in hippocampal slices to monitor synaptic output. We examined the effects of baclofen on the relationship between an fEPSP during the spike train and the timing of spikes preceding that fEPSP, a relationship that we refer to as the history dependence of synaptic transmission. Baclofen alters this history dependence by causing no inhibition during short interspike intervals (ISIs) in the spike train but a maximal inhibition during long ISIs. This effect strengthens the dependence of the fEPSP on the first ISI preceding it. One consequence of this effect is that the apparent affinity of baclofen is strongly reduced during physiologically relevant spike trains when compared with conventional stimulus paradigms, and a second consequence is that the overall inhibition experienced by a synapse will vary considerably during repeated trials of a behavioral task. We conclude that GABABR-mediated presynaptic inhibition is more accurately described as a high-pass filter than as a simple inhibition, and that this filtering must be taken into account to accurately assess the effects of presynaptic inhibition under physiologically relevant conditions.
Nongenomic Glucocorticoid Inhibition via Endocannabinoid Release in the Hypothalamus: A Fast Feedback Mechanism
Authors: Di Shi , Malcher-Lopes Renato , Halmos Katalin Cs. , Tasker Jeffrey G.
Published: April 2018

Glucocorticoid negative feedback in the brain controls stress, feeding, and neural-immune interactions by regulating the hypothalamic—pituitary—adrenal axis, but the mechanisms of inhibition of hypothalamic neurosecretory cells have never been elucidated. Using whole-cell patch-clamp recordings in an acute hypothalamic slice preparation, we demonstrate a rapid suppression of excitatory glutamatergic synaptic inputs to parvocellular neurosecretory neurons of the hypothalamic paraventricular nucleus (PVN) by the glucocorticoids dexamethasone and corticosterone. The effect was maintained with dexamethasone conjugated to bovine serum albumin and was not seen with direct intracellular glucocorticoid perfusion via the patch pipette, suggesting actions at a membrane receptor. The presynaptic inhibition of glutamate release by glucocorticoids was blocked by postsynaptic inhibition of G-protein activity with intracellular GDP-β-S application, implicating a postsynaptic G-protein-coupled receptor and the release of a retrograde messenger. The glucocorticoid effect was not blocked by the nitric oxide synthesis antagonistNG-nitro-l-arginine methyl ester hydrochloride or by hemoglobin but was blocked completely by the CB1cannabinoid receptor antagonists AM251 [N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide] and AM281 [1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-4-morpholinyl-1H-pyrazole-3-carboxamide] and mimicked and occluded by the cannabinoid receptor agonist WIN55,212-2 [(β)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate], indicating that it was mediated by retrograde endocannabinoid release. Several peptidergic subtypes of parvocellular neuron, identified by single-cell reverse transcripton-PCR analysis, were subject to rapid inhibitory glucocorticoid regulation, including corticotropin-releasing hormone-, thyrotropin-releasing hormone-, vasopressin-, and oxytocin-expressing neurons. Therefore, our findings reveal a mechanism of rapid glucocorticoid feedback inhibition of hypothalamic hormone secretion via endocannabinoid release in the PVN and provide a link between the actions of glucocorticoids and cannabinoids in the hypothalamus that regulate stress and energy homeostasis.
Orexin Excites GABAergic Neurons of the Arcuate Nucleus by Activating the Sodium—Calcium Exchanger
Authors: Burdakov Denis , Liss Birgit , Ashcroft Frances M.
Published: April 2018

The neuropeptides orexins/hypocretins are essential for normal wakefulness and energy balance, and disruption of their function causes narcolepsy and obesity. Although much is known of the role of orexins in sleep/wake behavior, it remains unclear how they stimulate feeding and metabolism. One of the main targets of orexinergic neurons is the arcuate nucleus (ARC) of the hypothalamus, which plays a key role in feeding and energy homeostasis. By combining patch-clamp and RT-multiplex PCR analysis of individual neurons in mouse brain slices, we show that an electrophysiologically distinct subset of ARC neurons coexpress orexin receptors and glutamate decarboxylase-67 and are excited by orexin. Acting on postsynaptic orexin type 2 receptors, orexin activates a sodium—calcium exchange current, thereby depolarizing the cell and increasing its firing frequency. Because GABA is a potent stimulus for feeding, in both the ARC and its main projection site, these results suggest a mechanism for how orexin may control appetite.
NR2B and NR2D Subunits Coassemble in Cerebellar Golgi Cells to Form a Distinct NMDA Receptor Subtype Restricted to Extrasynaptic Sites
Authors: Brickley Stephen G. , Misra Charu , Mok M. H. Selina , Mishina Masayoshi , Cull-Candy Stuart G.
Published: April 2018

NMDA receptors (NMDARs) are thought to be tetrameric assemblies composed of NR1 and at least one type of NR2 subunit. The identity of the NR2 subunit (NR2A, -B, -C, -D) is critical in determining many of the functional properties of the receptor, such as channel conductance and deactivation time. Further diversity may arise from coassembly of more than one type of NR2 subunit, if the resulting triheteromeric assembly (NR1 plus two types of NR2) displays distinct functional properties. We have used gene-ablated mice (NR2D -/-) to examine the effects of the NR2D subunit on NMDAR channels and NMDAR EPSCs in cerebellar Golgi cells. These cells are thought to express both NR2B and NR2D subunits, a combination that occurs widely in the developing nervous system. Our experiments provide direct evidence that the low conductance NMDAR channels in Golgi cells arise from diheteromeric NR1/NR2D assemblies. To investigate whether a functionally distinct triheteromeric assembly was also expressed, we analyzed the kinetic and pharmacological properties of single-channel currents in isolated extrasynaptic patches. We found that after the loss of the NR2D subunit, the properties of the 50 pS NMDAR channels were altered. This result is consistent with the presence of a triheteromeric assembly (NR1/NR2B/NR2D) in cells from wild-type mice. However, we could find no difference in the properties of NMDAR-mediated EPSCs between wild-type and NR2D subunit ablated mice. Our experiments suggest that although both diheteromeric and triheteromeric NR2D-containing receptors are expressed in cerebellar Golgi cells, neither receptor type participates in parallel fiber to Golgi cell synaptic transmission. The presence of the NR2D subunit within an assembly may therefore result in its restriction to extrasynaptic sites.
Identification of a Novel, Membrane-Associated Neuronal Kinase, Cyclin-Dependent Kinase 5/p35-Regulated Kinase
Authors: Kesavapany Sashi , Lau Kwok-Fai , Ackerley Steven , Banner Steven J. , Shemilt Stephen J. A. , Cooper Jonathan D. , Leigh P. Nigel , Shaw Christopher E. , McLoughlin Declan M. , Miller Christopher C. J.
Published: April 2018

Here we characterize a novel neuronal kinase, cyclin-dependent kinase 5 (cdk5)/p35-regulated kinase (cprk). Cprk is a member of a previously undescribed family of kinases that are predicted to contain two N-terminal membrane-spanning domains and a long C terminus, which harbors a dual-specificity serine/threonine/tyrosine kinase domain. Cprk was isolated in a yeast two-hybrid screen using the neuronal cdk5 activator p35 as “bait.” Cprk interacts with p35 in the yeast-two hybrid system, binds to p35 in glutathione S-transferase fusion pull-down assays, and colocalizes with p35 in cultured neurons and transfected cells. In these cells, cprk is present with p35 in the Golgi apparatus. Cprk is expressed in a number of tissues but is enriched in brain and muscle and within the brain is found in a wide range of neuronal populations. Cprk displays catalytic activity inin vitrokinase assays and is itself phosphorylated by cdk5/p35. Cdk5/p35 inhibits cprk activity. Cdk5/p35 may therefore regulate cprk function in the brain.
Bone Marrow-Derived Cells Expressing Green Fluorescent Protein under the Control of the Glial Fibrillary Acidic Protein Promoter Do Not Differentiate into AstrocytesIn VitroandIn Vivo
Authors: Wehner Tim , Böntert Matthias , Eyüpoglu Ilker , Prass Konstantin , Prinz Marco , Klett Francisco Fernández , Heinze Matthias , Bechmann Ingo , Nitsch Robert , Kirchhoff Frank , Kettenmann Helmut , Dirnagl Ulrich , Priller Josef
Published: April 2018

Differentiation of bone marrow (BM) cells into astroglia expressing the glial fibrillary acidic protein (GFAP) has been reportedin vitroand after intracerebral or systemic BM transplantation. In contrast, recent data suggest that astrocytic differentiation does not occur from BM-derived cellsin vivo. Using transgenic mice that express the enhanced green fluorescent protein (GFP) under the control of the human glial fibrillary acidic protein (GFAP) promoter, we investigated the potential of adult murine BM-derived cells to differentiate into macroglia. In the brains of GFAP–GFP transgenic mice, astrocytes were brightly fluorescent from the expression of GFP. When BM from these animals was transplanted into lethally irradiated wild-type animals, the transgene was detected in the reconstituted hematopoietic system, but no GFP expression was found in the nervous system. In contrast, GFAP–GFP neuroectodermal anlage grafted into adult wild-type striatum gave rise to GFP-expressing astrocytes. Because cerebral ischemia has been suggested to promote the differentiation of BM-derived cells into astrocytes, BM chimeric mice were subjected to focal cerebral ischemia. No GFP-positive cells were found in the ischemic or contralateral hemispheres of these brains. Even after direct injection of GFAP–GFP transgenic BM cells into wild-type striatum, no GFP-expressing astroglia were detected. To test the hypothesis that thein vitroenvironment might be more permissible for astroglial differentiation, we cultured BM from mice that constitutively express GFP, BM cells expressing GFP from a retroviral vector, and BM from GFAP–GFP transgenic mice on astrocytes and on organotypic hippocampal slices. In all experimental paradigms, BM-derived cells were found to differentiate into ramified microglia but not into GFAP-expressing astrocytes.
Caspase-Dependent and -Independent Cell Death Pathways in Primary Cultures of Mesencephalic Dopaminergic Neurons after Neurotoxin Treatment
Authors: Han Baek S. , Hong Hyun-Seung , Choi Won-Seok , Markelonis George J. , Oh Tae H. , Oh Young J.
Published: April 2018

Although the cause of neuronal death in Parkinson's disease (PD) is mainly unknown, growing evidence suggests that both apoptotic and non-apoptotic death may occur in PD. Using primary cultures of mesencephalic dopaminergic neurons and the MN9D dopaminergic neuronal cell line, we attempted to evaluate specifically the existence of the mitochondrial apoptotic pathway, focusing on the mitochondrial release of cytochromecto the activation of the caspases after 6-hydroxydopamine (6-OHDA) or 1-methyl-4-phenylpyridinium (MPP+) treatment. Both immunofluorescent labeling and immunoblot analysis indicated mitochondrial release of cytochromecinto the cytosol after 6-OHDA or MPP+treatment. However, the appearance of activated caspase-3 immunoreactivity in tyrosine hydroxylase (TH)-positive neurons was detected only after 6-OHDA. Immunoblot and biochemical analysis also confirmed that activation of both caspase-9 and caspase-3 was induced by 6-OHDA, but not by MPP+. Consequently, cotreatment with a caspase inhibitor (zVAD-fmk) or with an antioxidant (N-acetylcysteine) not only deterred 6-OHDA-induced loss of TH-positive neurons but also abolished the appearance of activated caspase-3 in TH-positive neurons. In contrast, the same treatment did not spare MPP+-treated TH-positive neurons. Interestingly, a reconstitution assay indicated that the addition of ATP to the cytosolic fraction obtained from MPP+-treated cells was sufficient to activate both caspase-9 and caspase-3. Taken together, our results indicate that distinct mechanisms underlie neurotoxin-induced cell death. They also suggest that, after mitochondrial release of cytochromecin dopaminergic neurons after neurotoxin treatment, intracellular levels of ATP may constitute a critical factor in determining whether a neuron will die by a caspase-dependent or -independent pathway.
CXCR4 Regulates Interneuron Migration in the Developing Neocortex
Authors: Stumm Ralf K. , Zhou Chun , Ara Toshiaki , Lazarini Françoise , Dubois-Dalcq Monique , Nagasawa Takashi , Höllt Volker , Schulz Stefan
Published: April 2018

The chemotactic factors directing interneuron migration during cerebrocortical development are essentially unknown. Here we identify the CXC chemokine receptor 4 (CXCR4) in interneuron precursors migrating from the basal forebrain to the neocortex and demonstrate that stromal cell-derived factor-1 (SDF-1) is a potent chemoattractant for isolated striatal precursors. In addition, we show that CXCR4 is present in early generated Cajal-Retzius cells of the cortical marginal zone. In mice with a null mutation in CXCR4 or SDF-1, interneurons were severely underrepresented in the superficial layers and ectopically placed in the deep layers of the neocortex. In contrast, the submeningeal positioning of Cajal-Retzius cells was unaffected. Thus, our findings suggest that SDF-1, which is highly expressed in the embryonic leptomeninx, selectively regulates migration and layer-specific integration of CXCR4-expressing interneurons during neocortical development.
Phosphorylation of CREB and Mechanical Hyperalgesia Is Reversed by Blockade of the cAMP Pathway in a Time-Dependent Manner after Repeated Intramuscular Acid Injections
Authors: Hoeger-Bement Marie K. , Sluka Kathleen A.
Published: April 2018

Spinal activation of the cAMP pathway produces mechanical hyperalgesia, sensitizes nociceptive spinal neurons, and phosphorylates the transcription factor cAMP-responsive element binding protein (CREB), which initiates gene transcription. This study examined the role of the cAMP pathway in a model of chronic muscle pain by assessing associated behavioral changes and phosphorylation of CREB. Bilateral mechanical hyperalgesia of the paw was induced by administering two injections of acidic saline, 5 d apart, into the gastrocnemius muscle of male Sprague Dawley rats. Interestingly, the increases in immunoreactivity for CREB and phosphorylated CREB (p-CREB) in the spinal dorsal horn occur 24 hr, but not 1 week, after the second injection of acidic saline compared with pH 7.2 intramuscular injections. Spinal blockade of adenylate cyclase prevents the expected increase in p-CREB that occurs after intramuscular acid injection. The reversal of mechanical hyperalgesia by adenylate cyclase or protein kinase A inhibitors spinally follows a similar pattern with reversal at 24 hr, but not 1 week, compared with the vehicle controls. The p-CREB immunoreactivity in the superficial dorsal horn correlates with the mechanical withdrawal threshold such that increases in p-CREB are associated with decreases in threshold. Therefore, activation of the cAMP pathway in the spinal cord phosphorylates CREB and produces mechanical hyperalgesia associated with intramuscular acid injections. The mechanical hyperalgesia and phosphorylation of CREB depend on early activation of the cAMP pathway during the first 24 hr but are independent of the cAMP pathway by 1 week after intramuscular injection of acid.
Postsynaptic Density-95 Mimics and Occludes Hippocampal Long-Term Potentiation and Enhances Long-Term Depression
Authors: Stein Valentin , House David R. C. , Bredt David S. , Nicoll Roger A.
Published: April 2018

Previous studies have shown that overexpression of the protein PSD-95 (postsynaptic density-95) selectively enhances AMPA receptor-mediated synaptic responses in hippocampal pyramidal cells. To determine whether this effect is related to synaptic plasticity at these synapses, we examined whether PSD-95 expression mimics long-term potentiation (LTP), and also whether it influences LTP and long-term depression (LTD) in hippocampal slice cultures. Using simultaneous recording from transfected or infected cells and control pyramidal cells, we found that PSD-95, similar to LTP, increases the amplitude and frequency of miniature EPSCs. It also converts silent synapses to functional synapses, as does LTP. In addition, LTP is completely occluded in cells expressing PSD-95, whereas LTD is greatly enhanced. These results suggest that common mechanisms are involved in controlling synaptic AMPA receptors by PSD-95 and synaptic plasticity.
Expression of Laminin Receptors in Schwann Cell Differentiation: Evidence for Distinct Roles
Authors: Previtali Stefano C. , Nodari Alessandro , Taveggia Carla , Pardini Celia , Dina Giorgia , Villa Antonello , Wrabetz Lawrence , Quattrini Angelo , Feltri M. Laura
Published: April 2018

Schwann cells require laminin-2 throughout nerve development, because mutations in the α2 chain indystrophicmice interfere with sorting of axons before birth and formation of myelin internodes after birth. Mature Schwann cells express several laminin receptors, but their expression and roles in development are poorly understood. Therefore, we correlated the onset of myelination in nerve and synchronized myelinating cultures to the appearance of integrins and dystroglycan in Schwann cells. Only α6β1 integrin is expressed before birth, whereas dystroglycan and α6β4 integrin appear perinatally, just before myelination. Although dystroglycan is immediately polarized to the outer surface of Schwann cells,α6β4 appears polarized only after myelination. We showed previously that Schwann cells lacking β1 integrin do not relate properly to axons before birth. Here we show that the absence of β1 before birth is not compensated by other laminin receptors, whereas coexpression of both dystroglycan and β4 integrin is likely required for β1-null Schwann cells to myelinate after birth. Finally, both β1-null anddystrophicnerves contain bundles of unsorted axons, but they are predominant in different regions: in spinal roots indystrophicmice and in nerves in β1-null mice. We show that differential compensation by laminin-1, but not laminin receptors may partially explain this. These data suggest that the action of laminin is mediated by β1 integrins during axonal sorting and by dystroglycan, α6β1, and α6β4 integrins during myelination.
Glucocorticoids Play a Fundamental Role in Protecting the Brain during Innate Immune Response
Authors: Nadeau Sylvain , Rivest Serge
Published: April 2018

The innate immune system plays a crucial role in protecting the host against infectious microorganisms. An inappropriate control of this system may have profound consequences, because of the maintained production of specific proinflammatory molecules. Glucocorticoids are the most efficient endogenous molecules that provide negative feedback on proinflammatory signaling and gene expression. Here we show that activation of this system is not detrimental for the brain but a profound neurodegeneration takes place in animals treated with the glucocorticoid receptor inhibitor Mifepristone (RU486). This drug increased the inflammatory reaction induced by a single intracerebral bolus of lipopolysaccharide (LPS). Inhibition of tumor necrosis factor α (TNF-α) totally abolished the neurotoxic effect of the endotoxin, and chronic infusion of the cytokine mimicked the treatment combining RU486 and LPS. The neuronal damage caused by TNF-α is dependent on both nitric oxide and caspase pathways. In controlling the cerebral innate immunity and microglial TNF-α production, glucocorticoids play a major role in protecting the brain against bacterial cell wall components.
Plasticity of the GABAergic Phenotype of the “Glutamatergic” Granule Cells of the Rat Dentate Gyrus
Authors: Gutiérrez Rafael , Romo-Parra Héctor , Maqueda Jasmín , Vivar Carmen , Ramìrez Mónica , Morales Miguel A. , Lamas Mónica
Published: April 2018

The “glutamatergic” granule cells of the dentate gyrus transiently express a GABAergic phenotype when a state of hyperexcitability is induced in the adult rat. Consequently, granule cell (GC) activation provokes monosynaptic GABAergic responses in their targets of area CA3. Because GABA exerts a trophic action on neonatal CA3 and mossy fibers (MF) constitute its main input, we hypothesized that the GABAergic phenotype of the MF could also be transiently expressed early in life. We addressed this possibility with a multidisciplinary approach. Electrophysiological recordings in developing rats revealed that, until day 22–23 of age, glutamate receptor antagonists block the excitatory response evoked in pyramidal cells by GCs, isolating a fast metabotropic glutamate receptor-sensitive GABAergic response. In a clear-cut manner from day 23–24 of age, GC activation in the presence of glutamatergic antagonists was unable to evoke synaptic responses in CA3. Immunohistological experiments showed the presence of GABA and GAD67(glutamate decarboxylase 67 kDa isoform) in the developing GCs and their MF, and, using reverse transcription-PCR, we confirmed the expression of vesicular GABA transporter mRNA in the developing dentate gyrus and its downregulation in the adult. The GABAergic markers were upregulated and MF inhibitory transmission reappeared when hyperexcitability was induced in adult rats. Our data evidence for the first time a developmental and activity-dependent regulation of the complex phenotype of the GC. At early ages, the GABAergic input from the MF may add to the interneuronal input to CA3 to foster development, and, in the adult, it can possibly protect the system from enhanced excitability.
Alteration of Gene Expression by Chromosome Loss in the Postnatal Mouse Brain
Authors: Kaushal Dhruv , Contos James J. A. , Treuner Kai , Yang Amy H. , Kingsbury Marcy A. , Rehen Stevens K. , McConnell Michael J. , Okabe Masaru , Barlow Carrolee , Chun Jerold
Published: April 2018

Frequent chromosomal aneuploidy has recently been discovered in normal neurons of the developing and mature murine CNS. Toward a more detailed understanding of aneuploidy and its effects on normal CNS cells, we examined the genomes of cells in the postnatal subventricular zone (SVZ), an area that harbors a large number of neural stem and progenitor cells (NPCs), which give rise to neurons and glia. Here we show that NPCs, neurons, and glia from the SVZ are frequently aneuploid. Karyotyping revealed that ∼33% of mitotic SVZ cells lost or gained chromosomesin vivo, whereas interphase fluorescencein situhybridization demonstrated aneuploidy in postnatal-born cells in the olfactory bulb (OB)in vivo, along with neurons, glia, and NPCsin vitro. One possible consequence of aneuploidy is altered gene expression through loss of heterozygosity (LOH). This was examined in a model of LOH: loss of transgene expression in mice hemizygous for a ubiquitously expressed enhanced green fluorescent protein (eGFP) transgene on chromosome 15. Concurrent examination of eGFP expression, transgene abundance, and chromosome 15 copy number demonstrated that a preponderance of living SVZ and OB cells not expressing eGFP lost one copy of chromosome 15; the eGFP transgene was lost in these cells as well. Although gene expression profiling revealed changes in expression levels of several genes relative to GFP-expressing controls, cells with LOH at chromosome 15 were morphologically normal and proliferated or underwent apoptosis at rates similar to those of euploid cellsin vitro. These findings support the view that NPCs and postnatal-born neurons and glia can be aneuploidin vivoand functional gene expression can be permanently altered in living neural cells by chromosomal aneuploidy.
Neural Correlates of the Automatic Processing of Threat Facial Signals
Authors: Anderson Adam K. , Christoff Kalina , Panitz David , De Rosa Eve , Gabrieli John D. E.
Published: April 2018

The present study examined whether automaticity, defined here as independence from attentional modulation, is a fundamental principle of the neural systems specialized for processing social signals of environmental threat. Attention was focused on either scenes or faces presented in a single overlapping display. Facial expressions were neutral, fearful, or disgusted. Amygdala responses to facial expressions of fear, a signifier of potential physical attack, were not reduced with reduced attention to faces. In contrast, anterior insular responses to facial expressions of disgust, a signifier of potential physical contamination, were reduced with reduced attention. However, reduced attention enhanced the amygdala response to disgust expressions; this enhanced amygdala response to disgust correlated with the magnitude of attentional reduction in the anterior insular response to disgust. These results suggest that automaticity is not fundamental to the processing of all facial signals of threat, but is unique to amygdala processing of fear. Furthermore, amygdala processing of fear was not entirely automatic, coming at the expense of specificity of response. Amygdala processing is thus specific to fear only during attended processing, when cortical processing is undiminished, and more broadly tuned to threat during unattended processing, when cortical processing is diminished.
Presenilin Redistribution Associated with Aberrant Cholesterol Transport Enhances β-Amyloid ProductionIn Vivo
Authors: Burns Mark , Gaynor Kate , Olm Vicki , Mercken Marc , LaFrancois John , Wang Lili , Mathews Paul M. , Noble Wendy , Matsuoka Yasuji , Duff Karen
Published: April 2018

Epidemiology,in vitro, andin vivostudies strongly implicate a role for cholesterol in the pathogenesis of Alzheimer's disease (AD). We have examined the impact of aberrant intracellular cholesterol transport on the processing of the amyloid precursor protein (APP) in a mouse model of Niemann-Pick type C (NPC) disease. In the NPC mouse brain, cholesterol accumulates in late endosomes/lysosomes. This was associated with the accumulation of β-C-terminal fragments (CTFs) of APP, but the level of β-secretase and its activity were not affected. α-Secretase activity and secreted APPα generation were also not affected, suggesting CTFs increased because of decreased clearance. The level of presenilin-1 (PS-1) was unchanged, but γ-secretase activity was greatly enhanced, which correlated with an increase in Aβ40 and Aβ42 levels. These events were associated with abnormal distribution of PS-1 in the endosomal system. Our results show that aberrant cholesterol trafficking is associated with the potentiation of APP processing componentsin vivo, leading to an overall increase in Aβ levels.
The Neural Representation of Speed in Macaque Area MT/V5
Authors: Priebe Nicholas J. , Cassanello Carlos R. , Lisberger Stephen G.
Published: April 2018

Tuning for speed is one key feature of motion-selective neurons in the middle temporal visual area of the macaque cortex (MT, or V5). The present paper asks whether speed is coded in a way that is invariant to the shape of the moving stimulus, and if so, how. When tested with single sine-wave gratings of different spatial and temporal frequencies, MT neurons show a continuum in the degree to which preferred speed depends on spatial frequency. There is some dependence in 75% of MT neurons, and the other 25% maintain speed tuning despite changes in spatial frequency. When tested with stimuli constructed by adding two superimposed sine-wave gratings, the preferred speed of MT neurons becomes less dependent on spatial frequency. Analysis of these responses reveals a speed-tuning nonlinearity that selectively enhances the responses of the neuron when multiple spatial frequencies are present and moving at the same speed. Consistent with the presence of the nonlinearity, MT neurons show speed tuning that is close to form-invariant when the moving stimuli comprise square-wave gratings, which contain multiple spatial frequencies moving at the same speed. We conclude that the neural circuitry in and before MT makes no explicit attempt to render MT neurons speed-tuned for sine-wave gratings, which do not occur in natural scenes. Instead, MT neurons derive form-invariant speed tuning in a way that takes advantage of the multiple spatial frequencies that comprise moving objects in natural scenes.
Properties and Functional Role of Voltage-Dependent Potassium Channels in Dendrites of Rat Cerebellar Purkinje Neurons
Authors: Martina Marco , Yao Gui Lan , Bean Bruce P.
Published: April 2018

We characterized the properties and functional roles of voltage-dependent potassium channels in the dendrites of Purkinje neurons studied in rat cerebellar slices. Using outside-out patches formed ≤250 μm away from the soma, we found that depolarization-activated potassium channels were present at high density throughout the dendritic tree. Currents required relatively large depolarizations for activation (midpoint, approximately –10 mV), had rapid activation and deactivation kinetics, and inactivated partially (20–70% over 200 msec) with both fast (time constant, 15–20 msec) and slow (300–400 msec) components. Inactivating and noninactivating components were both blocked potently by external tetraethylammonium (half-block by 150 μm) and 4-aminopyridine (half-block by 110 μm). The voltage dependence, kinetics, and pharmacology suggest a predominant contribution by Kv3 family subunits, and immunocytochemical experiments showed staining for both Kv3.3 and Kv3.4 subunits in the dendritic tree. In the proximal dendrite, potassium channels were activated by passively spread sodium spikes recorded at the same position, and experiments using dual recordings showed that the channels serve to actively dampen back-propagation of somatic sodium spikes. In more distal dendrites, potassium currents were activated by voltage waveforms taken from climbing fiber responses, suggesting that they help shape these responses as well. The requirement for large depolarizations allows dendritic Kv3 channels to shape large depolarizing events while not disrupting spatial and temporal summation of smaller excitatory postsynaptic potentials.
Focal Deletion of the Adenosine A1 Receptor in Adult Mice Using an Adeno-Associated Viral Vector
Authors: Scammell Thomas E. , Arrigoni Elda , Thompson Margaret A. , Ronan Patrick J. , Saper Clifford B. , Greene Robert W.
Published: April 2018

Adenosine is a ubiquitous neuromodulator that increases sleep, inhibits seizures, and promotes neuroprotection. Many of these effects are mediated by A1 receptors, but A1 receptors are expressed in most brain regions, and distinguishing the precise site of action of adenosine is challenging. To test the role of adenosine in different hippocampal regions, we have used theCre-loxPsystem and an adeno-associated viral (AAV) vector to focally delete endogenous adenosine A1 receptors in the hippocampus. Microinjection of an AAV vector containing the gene for Cre recombinase induced intense, focal, neuron-specific recombination in reporter mice. In a separate line of mice with loxP sites flanking the major coding exon for the adenosine A1 receptor, this AAV-Cre markedly reduced A1 receptor mRNA and focally abolished the postsynaptic response to adenosine without any change in basic electrophysiologic properties. Adenosine inhibits signaling between CA3 and CA1 neurons, but it is unclear from pharmacologic studies whether this response is caused by presynaptic or postsynaptic effects. Deletion of A1 receptors from CA3 neurons abolished this response to adenosine, but deletion of A1 receptors from CA1 neurons had no effect, demonstrating a presynaptic site of action. This transduction knock-out technique holds enormous potential for dissecting the functions of different CNS pathways.
Four-Dimensional Migratory Coordinates of GABAergic Interneurons in the Developing Mouse Cortex
Authors: Ang Eugenius S. B. C. , Haydar Tarik F. , Gluncic Vicko , Rakic Pasko
Published: April 2018

We have used time-lapse multiphoton microscopy to map the migration and settling pattern of GABAergic interneurons that originate in the ganglionic eminence of the ventral forebrain and incorporate into the neocortex of the cerebral hemispheres. Imaging of the surface of the cerebral hemispheres in both explant cultures and brains of living mouse embryos revealed that GABAergic interneurons migrating within the marginal zone originate from three different sources and migrate via distinct and independent streams. After reaching their areal destination, interneurons descend into the underlying cortex to assume positions with isochronically generated, radially derived neurons. The dynamics and pattern of cell migration in the marginal zone (see movies, available atwww.jneurosci.org) suggest that the three populations of interneurons respond selectively to distinct local cues for directing their migration to the appropriate areas and layers of the neocortex. This approach opens a new avenue for study of normal and abnormal neuronal migration in their native environment and indicate that interneurons have specific programs for their areal and laminar deployment.
Wnt Regulation of Progenitor Maturation in the Cortex Depends on Shh or Fibroblast Growth Factor 2
Authors: Viti Jane , Gulacsi Alexandra , Lillien Laura
Published: April 2018

In the embryonic mouse cerebral cortex, progenitors in the ventricular zone (VZ) undergo a developmental change between embryonic day 13 (E13) and E15. This results in the generation of a secondary proliferative population and the appearance of a second germinal layer, the subventricular zone (SVZ). We have shown previously that bone morphogenetic proteins (BMPs) and fibroblast growth factor 2 (FGF2) act antagonistically to regulate the development of a subset of SVZ progenitors that normally express a high level of epidermal growth factor (EGF) receptors and divide in response to EGF. In the present study, we show that Wnt 7a, Wnt 7b, and Sonic hedgehog (Shh) promote progenitor maturation in explant cultures, as reported for FGF2. Wnts 7a and 7b also stimulate the proliferation of neurogenic progenitors and increase the number of cells that can generate primary neurospheres. To determine whether Wnts, FGF2, and Shh act independently or in a common pathway, each factor was inhibited in cortical explants. This revealed that endogenous Wnts, FGF2, and Shh normally contribute to progenitor maturation. Moreover, Wnt 7a depends on FGF2 or Shh to promote maturation but not proliferation. Maturation induced by blocking BMPs also depends on Shh. In contrast, FGF2 promotes maturation by a Shh-independent mechanism.In vivo, progenitors infected with a Wnt 7a retrovirus at E10.5 were found preferentially in the SVZ at E16.5. These findings suggest that Wnts depend on Shh or FGF2 to promote progenitor maturation to an SVZ state in the embryonic cortex.
Energy Contribution of Octanoate to Intact Rat Brain Metabolism Measured by13C Nuclear Magnetic Resonance Spectroscopy
Authors: Ebert Douglas , Haller Ronald G. , Walton Marlei E.
Published: April 2018

Glucose is the dominant oxidative fuel for brain, but studies have indicated that fatty acids are used by brain as well. We postulated that fatty acid oxidation in brain could contribute significantly to overall energy usage and account for non-glucose-derived energy production. [2,4,6,8-13C4]octanoate oxidation in intact rats was determined by nuclear magnetic resonance spectroscopy. We found that oxidation of13C-octanoate in brain is avid and contributes ∼20% to total brain oxidative energy production. Labeling patterns of glutamate and glutamine were distinct, and analysis of these metabolites indicated compartmentalized oxidation of octanoate in brain. Examination of liver and blood spectra revealed that label from13C-octanoate was incorporated into glucose and ketones, which enabled calculation of its overall energy contribution to brain metabolism: glucose (predominantly unlabeled) and13C-labeled octanoate can account for the entire oxidative metabolism of brain. Additionally, flux through anaplerotic pathways relative to tricarboxylic acid cycle flux (Y) was calculated to be 0.08 ± 0.039 in brain, indicating that anaplerotic flux is significant and should be considered when assessing brain metabolism.Ywas associated with the glutamine synthesis compartment, consistent with the view that anaplerotic flux occurs primarily in astrocytes.
Long-Term Depression of Presynaptic Release from the Readily Releasable Vesicle Pool Induced by NMDA Receptor-Dependent Retrograde Nitric Oxide
Authors: Stanton Patric K. , Winterer Jochen , Bailey Christopher P. , Kyrozis Andreas , Raginov Ivan , Laube Gregor , Veh Rüdiger W. , Nguyen Can Q. , Müller Wolfgang
Published: April 2018

Postsynaptic alterations are currently believed to be able to fully account for NMDA-receptor-dependent long-term depression (LTD) and long-term potentiation of synaptic strength, although there is also evidence supporting changes in presynaptic release. Using dualphoton laser scan microscopy ofN-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl) pyridinium dibromide (FM1-43) to directly visualize presynaptic vesicular release at Schaffer collateral–CA1 excitatory synapses in hippocampal slices, we demonstrate reduced vesicular release associated with LTD. Selective loading, by hypertonic shock, of the readily releasable vesicle pool (RRP) showed that LTD of release is a selective modification of release from the RRP. Presynaptic LTD of RRP release required activation of NMDA receptors, production and extracellular diffusion of the intercellular messenger NO, and activation of cGMP-dependent protein kinase.
Dual Modes of Endoplasmic Reticulum-to-Golgi Transport in Dendrites Revealed by Live-Cell Imaging
Authors: Horton April C. , Ehlers Michael D.
Published: April 2018

Organelles of the neuronal secretory pathway are critical for the addition of membrane that accompanies neuronal development, as well as for the proper localization of plasma membrane proteins necessary for polarity, synaptic transmission, and plasticity. Here, we demonstrate that two organizations of the secretory pathway exist in neurons: one requiring processing of membrane and lipids in the Golgi complex of the cell body and one in which endoplasmic reticulum (ER)-to-Golgi trafficking is localized to dendrites. Using time-lapse imaging of green fluorescent protein-tagged cargo proteins and compartment markers, we show that organelles of the secretory pathway, including ER, ER exit sites, and Golgi, are present and engage in trafficking in neuronal dendrites. We find that ER-to-Golgi trafficking involves highly mobile vesicular carriers that traffic in both the anterograde and retrograde directions throughout the dendritic arbor. Dendritic Golgi outposts, which appear developmentally during the phase of process outgrowth, are involved in the trafficking of both integral membrane proteins and the secreted neuronal growth factor BDNF. This distributed dendritic Golgi represents an organization of the secretory pathway unique among mammalian cells.
Muscarine-Induced Increase in Frequency of Spontaneous EPSCs in Purkinje Cells in the Vestibulo-Cerebellum of the Rat
Authors: Takayasu Yukihiro , Iino Masae , Furuya Nobuhiko , Ozawa Seiji
Published: April 2018

Cholinergic projections are relatively sparse in the cerebellum compared with other parts of the brain. However, some mossy fibers in the vestibulo-cerebellum are known to be cholinergic. To clarify the functional roles of cholinergic mossy fibers in the vestibulo-cerebellum, we investigated the effects of acetylcholine (ACh) on the membrane electrical properties of both granule cells and Purkinje cells in slices of the cerebellar vermis of the rat using whole-cell patch-clamp techniques. The bath application of ACh induced a marked increase in the frequency of spontaneous EPSCs (sEPSCs) in Purkinje cells specifically in the vestibulo-cerebellum. This effect of ACh was mimicked by muscarine but not by nicotine. It was abolished by application of either tetrodotoxin or the antagonist of AMPA receptors, indicating that the ACh-induced enhancement of sEPSCs occurred indirectly via the activation of neurons sending glutamatergic projections to Purkinje cells. In ∼15% of granule cells tested in the vestibulo-cerebellum, muscarine elicited membrane depolarization accompanied by a decrease in membrane conductance and increased the neuronal excitability. The muscarine-induced depolarization of granule cells in the vestibulo-cerebellum was attributable to the inhibition of standing-outward K+currents (IKSO) most likely via the activation of muscarinic M3receptors. Taken together, these results indicate that ACh increases the firing frequency of granule cells by inhibitingIKSO, which in turn increases the frequency of sEPSCs in Purkinje cells in the rat vestibulo-cerebellum.
Peroxisome Proliferator-Activated Receptor-α Activation as a Mechanism of Preventive Neuroprotection Induced by Chronic Fenofibrate Treatment
Authors: Deplanque Dominique , Gelé Patrick , Pétrault Olivier , Six Isabelle , Furman Christophe , Bouly Muriel , Nion Stéphane , Dupuis Bernard , Leys Didier , Fruchart Jean-Charles , Cecchelli Roméo , Staels Bart , Duriez Patrick , Bordet Régis
Published: April 2018

The treatment of ischemic strokes is limited to the prevention of cerebrovascular risk factors and to the modulation of the coagulation cascade during the acute phase. A new therapeutic strategy could be to preventively protect the brain against noxious biological reactions induced by cerebral ischemia such as oxidative stress and inflammation to minimize their neurological consequences. Here, we show that a peroxisome proliferator-activated receptor (PPAR-α) activator, fenofibrate, protects against cerebral injury by anti-oxidant and anti-inflammatory mechanisms. A 14 d preventive treatment with fenofibrate reduces susceptibility to stroke in apolipoprotein E-deficient mice as well as decreases cerebral infarct volume in C57BL/6 wild-type mice. The neuroprotective effect of fenofibrate is completely absent in PPAR-α-deficient mice, suggesting that PPAR-α activation is involved as a mechanism of the protection against cerebral injury. Furthermore, this neuroprotective effect appears independently of any improvement in plasma lipids or glycemia and is associated with (1) an improvement in middle cerebral artery sensitivity to endothelium-dependent relaxation unrelated to an increase in nitric oxide synthase (NOS) type III expression, (2) a decrease in cerebral oxidative stress depending on the increase in numerous antioxidant enzyme activities, and (3) the prevention of ischemia-induced expression of vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 in cerebral vessels without any change in NOS II expression. These data demonstrate that PPAR-α could be a new pharmacological target to preventively reduce the deleterious neurological consequences of stroke in mice and suggest that PPAR-α activators could preventively decrease the severity of stroke in humans.
Segregation of Amphetamine Reward and Locomotor Stimulation between Nucleus Accumbens Medial Shell and Core
Authors: Sellings Laurie H. L. , Clarke Paul B. S.
Published: April 2018

Convergent evidence suggests that amphetamine (AMPH) exerts its rewarding and locomotor stimulating effects via release of dopamine in the nucleus accumbens. However, there is no consensus as to the relative contributions of core and medial shell subregions to these effects. Moreover, the literature is based primarily on intracranial administration, which cannot fully mimic the drug distribution achieved by systemic administration. In the present study, the effects of bilateral 6-hydroxydopamine lesions of the accumbens core or medial shell on rewarding and locomotor stimulating effects of systemically administered amphetamine (0.75 mg/kg, i.p.) were examined in a conditioned place preference (CPP) procedure relying solely on tactile cues (floor texture). Residual dopamine innervation was quantified by [125I]-RTI-55 binding to the dopamine transporter. When lesions were performed before the conditioning phase, AMPH-induced locomotor stimulation and CPP magnitude were positively correlated with residual dopamine transporter binding in core and medial shell, respectively. Medial shell lesions did not affect morphine CPP, arguing that a sensory or mnemonic deficit was not responsible for the lesion-induced reduction in AMPH CPP. Medial shell lesions performed between the conditioning phase and the test day reduced the expression of amphetamine CPP. These results suggest that after systemic amphetamine administration, rewarding and locomotor stimulating effects of the drug are anatomically dissociated within the nucleus accumbens: the medial shell contributes to rewarding effects, whereas the core contributes to behavioral activation.
Fast Inhibition Underlies the Transmission of Auditory Information between Cochlear Nuclei
Authors: Needham Karina , Paolini Antonio G.
Published: April 2018

A direct commissural connection between cochlear nuclei provides a pathway by which binaural input can influence the processing of acoustic information through the ventral cochlear nucleus. Despite anatomical evidence to suggest the existence of such a pathway, its nature and behavior have not been investigated previously. Thisin vivointracellular electrophysiological study provides direct evidence of monosynaptic (mean latency, 1.43 msec), inhibitory commissural input to T stellate cells. This inhibition is fast acting (duration, <10 msec), occurring with little synaptic delay (∼0.3 msec). Electrical stimulation also revealed the initiation of antidromic responses in the onset chopper population, signifying D stellate neurons as a source of commissural inputs. Activation of the commissural connection was most evident in response to broadband stimuli. These results provide the first compelling evidence of a fast, monosynaptic commissural pathway arising from contralateral D stellate neurons providing broadband inhibitory input to T stellate cells.