bluuebunny/crossref_metadata_2025 huggingface dataset:
Angiotensin II Stimulates Spinally Projecting Paraventricular Neurons through Presynaptic Disinhibition
Authors: Li De-Pei , Chen Shao-Rui , Pan Hui-Lin
Published: April 2018

Paraventricular nucleus (PVN) neurons that project to the spinal cord are important in the control of sympathetic outflow. Angiotensin II (Ang II) can stimulate PVN neurons, but its cellular mechanisms are not clear. In this study, we determined the effect of Ang II on the excitatory and inhibitory synaptic inputs to spinally projecting PVN neurons. Whole-cell patch-clamp recordings were performed on PVN neurons labeled by a retrograde fluorescence tracer injected into the thoracic spinal cord of rats. Immunocytochemistry labeling revealed that the immunoreactivity of angiotensin type 1 (AT1) receptors was colocalized with a presynaptic marker, synaptophysin, in the PVN. Application of 0.1–5 μmAng II significantly decreased the amplitude of evoked GABAergic IPSCs in a concentration-dependent manner. Also, Ang II decreased the frequency of miniature IPSCs from 2.56 ± 0.45 to 1.05 ± 0.20 Hz (p< 0.05;n= 12), without affecting the amplitude and the decay time constant. The effect of Ang II on miniature IPSCs was blocked by losartan but not PD123319. However, Ang II had no effect on the evoked glutamatergic EPSCs and did not alter the frequency and amplitude of miniature EPSCs at concentrations that attenuated IPSCs. Furthermore, Ang II increased the firing rate of PVN neurons from 3.75 ± 0.36 to 7.89 ± 0.85 Hz (p< 0.05;n= 9), and such an effect was abolished by losartan. In addition, Ang II failed to excite PVN neurons in the presence of bicuculline. Thus, this study provides substantial new evidence that Ang II excites spinally projecting PVN neurons by attenuation of GABAergic synaptic inputs through activation of presynaptic AT1receptors.
Cooperative Activation of Dopamine D1and D2Receptors Increases Spike Firing of Nucleus Accumbens Neurons via G-Protein βγ Subunits
Authors: Hopf F. Woodward , Cascini Maria Grazia , Gordon Adrienne S. , Diamond Ivan , Bonci Antonello
Published: April 2018

Dopamine in the nucleus accumbens modulates both motivational and addictive behaviors. Dopamine D1and D2receptors are generally considered to exert opposite effects at the cellular level, but many behavioral studies find an apparent cooperative effect of D1and D2receptors in the nucleus accumbens. Here, we show that a dopamine-induced enhancement of spike firing in nucleus accumbens neurons in brain slices required both D1and D2receptors. One intracellular mechanism that might underlie cooperativity of D1and D2receptors is activation of specific subtypes of adenylyl cyclases by G-protein βγ subunits (Gβγ) released from the Gi/o-linked D2receptor in combination with Gαs-like subunits from the D1receptor. In this regard, dopaminergic enhancement of spike firing was prevented by inhibitors of protein kinase A or Gβγ. Furthermore, intracellular perfusion with Gβγenabled D1receptor activation but not D2receptor activation to enhance spike firing. Finally, our data suggest that these pathways may increase spike firing by inhibition of a slow A-type potassium current. These results provide evidence for a novel cellular mechanism through which cooperative action of D1and D2receptors in the nucleus accumbens could mediate dopamine-dependent behaviors.
Changes in Intracellular Calcium and Glutathione in Astrocytes as the Primary Mechanism of Amyloid Neurotoxicity
Authors: Abramov Andrey Y. , Canevari Laura , Duchen Michael R.
Published: April 2018

Although the accumulation of the neurotoxic peptide β amyloid (βA) in the CNS is a hallmark of Alzheimer's disease, the mechanism of βA neurotoxicity remains controversial. In cultures of mixed neurons and astrocytes, we found that both the full-length peptide βA (1–42) and the neurotoxic fragment (25–35) caused sporadic cytoplasmic calcium [intracellular calcium ([Ca2+]c)] signals in astrocytes that continued for hours, whereas adjacent neurons were completely unaffected. Nevertheless, after 24 hr, although astrocyte cell death was marginally increased, ∼50% of the neurons had died. The [Ca2+]csignal was entirely dependent on Ca2+influx and was blocked by zinc and by clioquinol, a heavy-metal chelator that is neuroprotective in models of Alzheimer's disease. Neuronal death was associated with Ca2+-dependent glutathione depletion in both astrocytes and neurons. Thus, astrocytes appear to be the primary target of βA, whereas the neurotoxicity reflects the neuronal dependence on astrocytes for antioxidant support.
γ-Protocadherins Are Targeted to Subsets of Synapses and Intracellular Organelles in Neurons
Authors: Phillips Greg R. , Tanaka Hidekazu , Frank Marcus , Elste Alice , Fidler Lazar , Benson Deanna L. , Colman David R.
Published: April 2018

The clustered protocadherins (Pcdhs) comprise >50 putative synaptic recognition molecules that are related to classical cadherins and highly expressed in the nervous system. Pcdhs are organized into three gene clusters (α, β, and γ). Within the α and γ clusters, three exons encode the cytoplasmic domain for each Pcdh, making these domains identical within a cluster. Using an antibody to the Pcdh-γ constant cytoplasmic domain, we find that all interneurons in cultured hippocampal neurons express high levels of Pcdh-γs in a nonsynaptic distribution. In contrast, only 48% of pyramidal-like cells expressed appreciable levels of these molecules. In these cells, Pcdh-γs were associated with a subset of excitatory synapses in which they may mediate presynaptic to postsynaptic recognition in concert with classical cadherins. Immunogold localization in hippocampal tissue showed Pcdh-γs at some synapses, in nonsynaptic plasma membranes, and in axonal and dendritic tubulovesicular structures, indicating that they may be exchanged among synapses and intracellular compartments. Our results show that although Pcdh-γs can be synaptic molecules, synapses form lacking Pcdh-γs. Thus, Pcdh-γs and their relatives may be late additions to the classical cadherin-based synaptic adhesive scaffold; their presence in intracellular compartments suggests a role in modifying synaptic physiology or stability.
Factors in the Genetic Background Suppress theEngrailed-1Cerebellar Phenotype
Authors: Bilovocky Natalie A. , Romito-DiGiacomo Rita R. , Murcia Crystal L. , Maricich Stephen M. , Herrup Karl
Published: April 2018

The mouse homeodomain protein, Engrailed-1, is generally viewed as an essential player in the early establishment and maintenance of the midbrain/hindbrain region that gives rise to the cerebellum and midbrain. In keeping with this, engineered null mutations at this locus have been reported to lead to perinatal lethality accompanied by near-total absence of cerebellar and caudal midbrain structures. We report here that these cerebellar phenotypes are nearly completely suppressed on a C57BL/6J genetic background. All cell types are present and arranged properly in both the cortex and the deep nuclei, and cell counts reveal no significant absence of cerebellar Purkinje cells. Folial patterns are nearly normal, although an apparent fusion of lobules IV and V is consistently noted. Significantly, no change in theEngrailed-2mutant phenotype occurs after a similar background switch, and whole-mountin situhybridization reveals identicalEn2expression patterns in wild-type C57BL/6J and 129/Sv mice. One likely mechanism for theEn1-/-phenotype suppression is a temporal and/or spatial change in the pattern of Engrailed-2 expression apparent only in the absence of Engrailed-1. In support of this, C57BL/6—En1-/-embryos that are alsoEn2+/-lack a cerebellum and caudal midbrain: a phenotype identical to 129/Sv—En1-/-mice.
Decline of the Critical Period of Visual Plasticity Is Concurrent with the Reduction of NR2B Subunit of the Synaptic NMDA Receptor in Layer 4
Authors: Erisir Alev , Harris Janna L.
Published: April 2018

The specific composition of NMDA receptor subunits is thought to underlie the developmental plasticity of the cortex revealed by unbalanced binocular stimulation. However, evidence that NR2 subunits change in correlation with the critical period at locations that are relevant to visual plasticity has been missing. Using preembedding and postembedding immunostaining, as well as electron microscopy, we quantified the volumetric densities of NR1-, NR2A-, and NR2B-containing synapses in layers 4 and 2/3 of the ferret visual cortex at different postnatal ages. Before eye opening, NR2A is encountered infrequently at postsynaptic sites in layer 4, but it increases sharply by postnatal day 34. In the subsequent weeks, postsynaptic NR2A labeling increases gradually in both layers 4 and 2/3 to become the most prevalent subunit in the adult animal. The NR2B subunit is the more prevalent subunit at the onset of the critical period of cortical plasticity. However, it displays different developmental patterns in layers 4 and 2/3. Although no change occurs in synaptic NR2B density in layer 2/3, in layer 4, NR2B maintains its high levels through the peak of the critical period and then becomes significantly reduced by the end of the peak of the critical period. This low level is maintained throughout adulthood. Our results demonstrate a correlation between the loss of NR2B subunits from layer 4 synaptic sites and the decline of the critical period, suggesting that the presence of NR2B subunits at synaptic sites could be a permissive factor regulating the ocular dominance plasticity of the developing cortex.
Selectively Reduced Expression of Synaptic Plasticity-Related Genes in Amyloid Precursor Protein + Presenilin-1 Transgenic Mice
Authors: Dickey Chad A. , Loring Jeanne F. , Montgomery Julia , Gordon Marcia N. , Eastman P. Scott , Morgan Dave
Published: April 2018

A critical question in Alzheimer's disease (AD) research is the cause of memory loss that leads to dementia. The amyloid precursor protein + presenilin-1 (APP+PS1) transgenic mouse is a model for amyloid deposition, and like AD, the mice develop memory deficits as amyloid deposits accumulate. We profiled gene expression in these transgenic mice by microarray and quantitative RT-PCR (qRT-PCR). At the age when these animals developed cognitive dysfunction, they had reduced mRNA expression of several genes essential for long-term potentiation and memory formation (Arc, Zif268, NR2B, GluR1, Homer-1a, Nur77/TR3). These changes appeared to be related to amyloid deposition, because mRNA expression was unchanged in the regions that did not accumulate amyloid. Transgene expression was similar in both amyloid-containing and amyloid-free regions of the brain. Interestingly, these changes occurred without apparent changes in synaptic structure, because a number of presynaptic marker mRNAs (growth-associated protein-43, synapsin, synaptophysin, synaptopodin, synaptotagmin, syntaxin) remained stable. Additionally, a number of genes related to inflammation were elevated in transgenic mice, primarily in the regions containing amyloid. In AD cortical tissue, the same memory-associated genes were downregulated. However, all synaptic and neuronal transcripts were reduced, implying that the loss of neurons and synapses contributed to these changes. We conclude that reduced expression of selected genes associated with memory consolidation are linked to memory loss in both circumstances. This suggests that the memory loss in APP+PS1 transgenic mice may model the early memory dysfunction in AD before the degeneration of synapses and neurons.
Separation-Induced Receptor Changes in the Hippocampus and Amygdala ofOctodon degus: Influence of Maternal Vocalizations
Authors: Ziabreva Irina , Poeggel Gerd , Schnabel Reinhild , Braun Katharina
Published: April 2018

Relatively little is known about the basic mechanisms that play a role in the vulnerability of the developing brain toward adverse environmental influences. Our study in the South American rodentOctodon degusrevealed that repeated brief separation from the parents and exposure to an unfamiliar environment induces in the hippocampal formation of male and female pups an upregulation of D1and 5-HT1Areceptor density in the stratum radiatum and stratum lacunosum moleculare of the CA1 region. In the CA3 region, only the 5-HT1Areceptors were upregulated; no changes were observed for D1receptors in this region. GABAAreceptor density in the hippocampus and amygdala was downregulated (nonsignificant trend) after parental separation.

The acoustic presence of the mother during parental separation suppressed the D1and 5-HT1Areceptor upregulation in some regions of the hippocampus; no such suppressing influence was observed for the GABAAreceptors. In the basomedial amygdala, the maternal calls enhanced the separation-induced 5-HT1Areceptor upregulation in the male pups, whereas in the female pups the separation-induced receptor densities were not only suppressed by the maternal call but further downregulated, compared with the control group. These results demonstrate that early adverse emotional experience alters aminergic function within the hippocampus and amygdala and that the mother's voice, a powerful emotional signal, can modulate these effects in the developing limbic system.
Self-Organizing Neural Integrator Predicts Interval Times through Climbing Activity
Authors: Durstewitz Daniel
Published: April 2018

Mammals can reliably predict the time of occurrence of an expected event after a predictive stimulus. Climbing activity is a prominent profile of neural activity observed in prefrontal cortex and other brain areas that is related to the anticipation of forthcoming events. Climbing activity might span intervals from hundreds of milliseconds to tens of seconds and has a number of properties that make it a plausible candidate for representing interval time. A biophysical model is presented that produces climbing, temporal integrator-like activity with variable slopes as observed empirically, through a single-cell positive feedback loop between firing rate, spike-driven Ca2+influx, and Ca2+-activated inward currents. It is shown that the fine adjustment of this feedback loop might emerge in a self-organizing manner if the cell can use the variance in intracellular Ca2+fluctuations as a learning signal. This self-organizing process is based on the present observation that the variance of the intracellular Ca2+concentration and the variance of the neural firing rate and of activity-dependent conductances reach a maximum as the biophysical parameters of a cell approach a configuration required for temporal integration. Thus, specific mechanisms are proposed for (1) how neurons might represent interval times of variable length and (2) how neurons could acquire the biophysical properties that enable them to work as timers.
Nogo-A Inhibits Neurite Outgrowth and Cell Spreading with Three Discrete Regions
Authors: Oertle Thomas , van der Haar Marjan E. , Bandtlow Christine E. , Robeva Anna , Burfeind Patricia , Buss Armin , Huber Andrea B. , Simonen Marjo , Schnell Lisa , Brösamle Christian , Kaupmann Klemens , Vallon Rüdiger , Schwab Martin E.
Published: April 2018

Nogo-A is a potent neurite growth inhibitorin vitroand plays a role both in the restriction of axonal regeneration after injury and in structural plasticity in the CNS of higher vertebrates. The regions that mediate inhibition and the topology of the molecule in the plasma membrane have to be defined. Here we demonstrate the presence of three different active sites: (1) an N-terminal region involved in the inhibition of fibroblast spreading, (2) a stretch encoded by the Nogo-A-specific exon that restricts neurite outgrowth and cell spreading and induces growth cone collapse, and (3) a C-terminal region (Nogo-66) with growth cone collapsing function. We show that Nogo-A-specific active fragments bind to the cell surface of responsive cells and to rat brain cortical membranes, suggesting the existence of specific binding partners or receptors. Several antibodies against different epitopes on the Nogo-A-specific part of the protein as well as antisera against the 66 aa loop in the C-terminus stain the cell surface of living cultured oligodendrocytes. Nogo-A is also labeled by nonmembrane-permeable biotin derivatives applied to living oligodendrocyte cultures. Immunofluorescent staining of intracellular, endoplasmic reticulum-associated Nogo-A in cells after selective permeabilization of the plasma membrane reveals that the epitopes of Nogo-A, shown to be accessible at the cell surface, are exposed to the cytoplasm. This suggests that Nogo-A could have a second membrane topology. The two proposed topological variants may have different intracellular as well as extracellular functions.
Glial Reactivity in Ciliary Neurotrophic Factor-Deficient Mice after Optic Nerve Lesion
Authors: Martin Aliki , Hofmann Hans-Dieter , Kirsch Matthias
Published: April 2018

There is evidence that ciliary neurotrophic factor (CNTF), in addition to its neurotrophic activity, positively regulates astrogliosis after CNS injury. CNTF and its receptor, CNTFRα, are strongly upregulated in activated astrocytes. Application of CNTF upregulates GFAP expression in cultured astrocytes and induces various aspects of gliosis in the intact brain. Here we examined whether inactivation of the CNTF gene results in the expected changes in glial reactivity by analyzing gliosis in the superior colliculus (SC) after optic nerve crush.

Basal expression levels of GFAP and vimentin in unlesioned CNTF-deficient mice were reduced by 66 and 37%, respectively. Absolute numbers of astrocytes were found not to be different. Surprisingly, however, lesion induced robust activation of astrocytes in CNTF-deficient mice; the time course of activation was even accelerated as compared with wild-type animals. At later time points, activation reached the same level. With respect to microglial cells, basal expression of microglial markers was unaltered in CNTF–knock-out animals. Lesion-induced upregulation of Iba-1, ICAM-1, and F4/80 in microglial cells was unaffected in CNTF-deficient animals. Differences were observed with respect to the time course of microglial activation, different markers being affected differentially. We further demonstrate that lesion induces upregulation of CNTF-related cytokines (LIF, NNT-1) and, interestingly, a more pronounced upregulation of cytokine receptor components (LIF receptor β, gp130) and TGFβ in CNTF-deficient animals. Our results thus indicate that CNTF is required for the development and maintenance of the mature astrocyte phenotype and provide evidence that CNTF is part of the complex regulatory network modulating lesional glial reactivity after lesion.
The Role of ErbB2 Signaling in the Onset of Terminal Differentiation of OligodendrocytesIn Vivo
Authors: Kim Ju Young , Sun Qin , Oglesbee Michael , Yoon Sung Ok
Published: April 2018

The knock-out analyses of neuregulin and its receptors have indicated that they play essential roles in Schwann cell development. However, the role they play in oligodendrocyte developmentin vivohas remained unclear, because such knock-out animals die before CNS myelination begins. We examined the role of neuregulin signaling in the CNS by generating transgenic mice that express a dominant-negative mutant of the ErbB2 receptor among oligodendrocytes, using an MBP promoter. The transgenic mice exhibited widespread hypomyelination, resulting from a reduction in oligodendrocyte differentiation. The number of progenitors was conversely increased in the transgenic mice. We report that a reduction in oligodendrocyte differentiation is attributed in part to apoptosis of oligodendrocyte progenitors as they exit the cell cycle. A significant reduction in the number of p27+oligodendrocyte precursors in the transgenic mice supports this conclusion. Taken together, these data suggest that for oligodendrocyte progenitors, ErbB2 signaling plays a role in governing a properly timed exit from the cell cycle during development into myelinating oligodendrocytes.
Expression of Voltage-Gated Chloride Channels in Human Glioma Cells
Authors: Olsen M. L. , Schade S. , Lyons S. A. , Amaral M. D. , Sontheimer H.
Published: April 2018

Voltage-gated chloride channels have recently been implicated as being important for cell proliferation and invasive cell migration of primary brain tumors cells. In the present study we provide several lines of evidence that glioma Cl–currents are primarily mediated by ClC-2 and ClC-3, two genes that belong to the ClC superfamily. Transcripts for ClC-2 thru ClC-7 were detected in a human glioma cell line by PCR, whereas only ClC-2, ClC-3, and ClC-5 protein could be identified by Western blot. Prominent ClC-2, -3, and -5 channel expression was also detected in acute patient biopsies from low- and high-grade malignant gliomas. Immunogold electron microscopic studies as well as digital confocal imaging localized a portion of these ClC channels to the plasma membrane. Whole-cell patch-clamp recordings show the presence of two pharmacologically and biophysically distinct Cl–currents that could be specifically reduced by 48 hr exposure of cells to channel-specific antisense oligonucleotides. ClC-3 antisense selectively and significantly reduced the expression of outwardly rectifying current with pronounced voltage-dependent inactivation. Such currents were sensitive to DIDS (200–500 μm) and 5-nitro-2-(3-phenylpropylamino) benzoic acid (165 μm). ClC-2 antisense significantly reduced expression of inwardly rectifying currents, which were potentiated by hyperpolarizing prepulses and inhibited by Cd2+(200–500 μm). Currents that were mediated by ClC-5 could not be demonstrated. We suggest that ClC-2 and ClC-3 channels are specifically upregulated in glioma membranes and endow glioma cells with an enhanced ability to transport Cl–. This may in turn facilitate rapid changes in cell size and shape as cells divide or invade through tortuous extracellular brain spaces.
Caspase-Independent Photoreceptor Apoptosis in Mouse Models of Retinal Degeneration
Authors: Doonan Francesca , Donovan Maryanne , Cotter Thomas G.
Published: April 2018

Apoptosis is the mode of cell death in retinitis pigmentosa, a group of retinal degenerative disorders primarily affecting rod photoreceptors. Although caspases have been demonstrated to play a central role in many incidences of apoptosis, accumulating evidence suggests that they may not be required for all forms of apoptotic cell death. The present study examined the mechanism of cell death in twoin vivomodels of photoreceptor apoptosis: the retinal degeneration (rd) mouse, a naturally occurring mutant model, andN-methyl-N-nitrosourea-induced retinal degeneration. Specifically, we examined the activation status of caspase-9, -8, -7, -3, and -2 and determined the caspase requirements for cytochromecrelease, DNA fragmentation, and apoptosis-associated proteolysis of specific caspase substrates. We show that apoptosis in bothin vivomodels is independent of caspase-9, -8, -7, -3, and -2 activation. DNA fragmentation occurs in the absence of caspase-mediated ICAD (inhibitor of caspase-activated DNase) proteolysis, suggesting that an alternative endonuclease is responsible for DNA cleavage in these models. Importantly, we show that apoptosome activation is prevented because of an absence of mitochondrial cytochromecrelease. Experiments performed using a cell-free system indicate that cytochromec-dependent proteolysis and activation of caspase-9 can be restored in a neonatal cell-free system. However, we found that cytochromec-dependent proteolysis and activation of caspase-9 could not be restored in an adult cell-free system because of an age-related decrease in the expression of Apaf-1 in the normal developing mouse retina. In the rd mouse, however, this age-related downregulation of apoptotic proteins was not observed, highlighting a critical feature of this model and the prevention of cytochromecrelease as an apical event in caspase-independent apoptosis in this system.
Metabolic Mapping of Mouse Brain Activity after Extinction of a Conditioned Emotional Response
Authors: Barrett Douglas , Shumake Jason , Jones Dirk , Gonzalez-Lima F.
Published: April 2018

Metabolic mapping with fluorodeoxyglucose (FDG), a radiolabeled glucose analog, was used to assess regional activity changes in the mouse brain that result from extinction of a conditioned emotional response (CER). In the extinction group, Pavlovian tone–foot shock conditioning, followed by repeated tone-alone presentations, resulted in the reduction of the CER (freezing behavior). A second group underwent CER acquisition alone (nonextinction group), and a third group showed no CER after pseudorandom training. Then mice were injected with FDG, and tone-evoked brain activity was mapped. In the auditory system, increased activity resulted from the associative effects of acquisition training. Effects common to extinction and nonextinction groups, presumably reflecting the tone–foot shock association independently of CER expression, were found in the medial geniculate, hippocampus, and subiculum. In the extinction group, a major finding was the elevated activity in prefrontal cortex regions. In addition, brain–behavior correlations between FDG uptake and freezing behavior confirmed that subjects with higher prefrontal activity were more successful at inhibiting the CER. Interregional activity correlations showed extensive functional coupling across large-scale networks in the extinction group. The increased activity of the prefrontal cortex and its negative interactions with other regions within the extinction group suggest a functional network inhibiting the CER composed of prefrontal cortex, medial thalamus, auditory, and hippocampal regions. This is the first time that such a functional network resulting from Pavlovian extinction has been demonstrated, and it supports Pavlov's original hypothesis of extinction as the formation of cortical inhibitory circuits, rather than unlearning or reversal of the acquisition process.
Barentsz, a New Component of the Staufen-Containing Ribonucleoprotein Particles in Mammalian Cells, Interacts with Staufen in an RNA-Dependent Manner
Authors: Macchi Paolo , Kroening Sven , Palacios Isabel M. , Baldassa Simona , Grunewald Barbara , Ambrosino Concetta , Goetze Bernhard , Lupas Andrei , St. Johnston Daniel , Kiebler Michael
Published: April 2018

Staufen1, the mammalian homolog ofDrosophilaStaufen, assembles into ribonucleoprotein particles (RNPs), which are thought to transport and localize RNA into dendrites of mature hippocampal neurons. We therefore investigated whether additional components of the RNA localization complex besides Staufen are conserved. One candidate is the mammalian homolog ofDrosophilaBarentsz (Btz), which is essential for the localization ofoskarmRNA to the posterior pole of theDrosophilaoocyte and is a component of theoskarRNA localization complex along with Staufen. In this study, we report the characterization of mammalian Btz, which behaves like a nucleocytoplasmic shuttling protein. When expressed in theDrosophilaegg chamber, mammalian Btz is still able to interact withDrosophilaStaufen and reach the posterior pole in the wild-type oocyte, but does not rescue thebtzmutant phenotype. Most interestingly, we show by immunoprecipitation assays that Btz interacts with mammalian Staufen in an RNA-dependent manner through a conserved domain, which encompasses the region of homology to theDrosophilaBtz protein and contains a novel conserved motif. One candidate for an RNA that mediates this interaction is the dendritically localized brain cytoplasmic 1 transcript. In addition, Btz and Staufen1 colocalize within particles in the cell body and, to a more variable extent, in dendrites of mature hippocampal neurons. Together, our data suggest that the mRNA transport machinery is conserved during evolution, and that mammalian Btz is an additional component of the dendritic RNPs in hippocampal neurons.
NMDA and β1-Adrenergic Receptors Differentially Signal Phosphorylation of Glutamate Receptor Type 1 in Area CA1 of Hippocampus
Authors: Vanhoose Amanda M. , Winder Danny G.
Published: April 2018

Glutamatergic synaptic transmission is mediated primarily through the AMPA-type glutamate receptor (AMPAR); the regulation of this receptor underlies many forms of synaptic plasticity. In particular, phosphorylation of GluR1, an AMPAR subunit, by PKA at serine 845 (S845) increases peak open channel probability and is permissive for both the synaptic expression of the receptor and NMDA-receptor (NMDAR)-dependent long-term potentiation (LTP). Robust NMDAR activation activates PKA as well as other signaling enzymes; however, we find that maximal NMDAR activation dephosphorylates GluR1 at the PKA site S845. Coincident inhibition of phosphatases blocks NMDAR-induced dephosphorylation of S845, but surprisingly does not promote PKA phosphorylation at this site. However, we find that phosphorylation of S845 is increased by the activation of a Gs-coupled receptor, the β1-adrenergic receptor. Interestingly, this divergent signaling occurs despite a more robust coupling of the NMDAR to cAMP generation. In addition, NMDAR activation plays a dominant role in S845 regulation, because activation of β1AR after NMDAR activation has no detectable effect on S845 phosphorylation. These data (1) demonstrate highly specific coupling between these receptors and this substrate, (2) provide an example of a substrate critical in NMDAR-dependent LTP that is incompletely regulated by the NMDAR, and (3) highlight the importance of identifying the physiological signals that regulate these critical synaptic substrates.
Alivin 1, a Novel Neuronal Activity-Dependent Gene, Inhibits Apoptosis and Promotes Survival of Cerebellar Granule Neurons
Authors: Ono Tomio , Sekino-Suzuki Naoko , Kikkawa Yoshiaki , Yonekawa Hiromichi , Kawashima Seiichi
Published: April 2018

Neurons require Ca2+-dependent gene transcription for their activity-dependent survival, the mechanisms of which have not been fully elucidated yet. Here, we demonstrate that a novel primary response gene,alivin 1(ali1), is an activity-dependent gene and promotes survival of neurons. Sequence analyses reveal that rat, mouse, and human Ali1 proteins contain seven leucine-rich repeats, one IgC2-like loop and a transmembrane domain, and display homology to Kek and Trk families. Expression ofali1mRNA in cultured cerebellar granule neurons is rigidly regulated by KCl and/or NMDA concentrations in the culture medium and tightly correlated to depolarization-dependent survival and/or NMDA-dependent survival of the granule neuron.ali1mRNA expression was regulated at the transcriptional step by the Ca2+influx through voltage-dependent L-type Ca2+channels when the cells were stimulated by 25 mmKCl. Expression ofali1mRNA in cultured cortical neurons was inhibited when their spontaneous electrical activity was blocked by tetrodotoxin. Thus, the expression is neuronal activity dependent. Overexpression of Ali1 in cerebellar granule neurons inhibited apoptosis that was induced by the medium containing 5 mmKCl. The addition of anti-Ali1 antiserum or the soluble putative extracellular Ali1 domain to the 25 mmKCl-supported culture inhibited the survival of the granule neuron. These results suggest that expression ofali1promotes depolarization-dependent survival of the granule neuron. Mouseali1was mapped to a locus ∼55.3 cM from the centromere on chromosome 15 that is syntenic to positional candidate loci for familial Alzheimer's disease type 5 and Parkinson's disease 8 on human chromosome 12.
Presynaptic Impairment of Synaptic Transmission inDrosophilaEmbryos Lacking Gsα
Authors: Hou Dongmei , Suzuki Kazuhiro , Wolfgang William J. , Clay Catherine , Forte Michael , Kidokoro Yoshiaki
Published: April 2018

Gsα is a subunit of the heterotrimeric G-protein complex, expressed ubiquitously in all types of cells, including neurons.Drosophilalarvae, which have mutations in the Gsα gene, are lethargic, suggesting an impairment of neuronal functions. In this study, we examined synaptic transmission at the neuromuscular synapse in Gsα-null (dgsR60) embryos shortly before they hatched. At low-frequency nerve stimulation, synaptic transmission in mutant embryos was not very different from that in controls. In contrast, facilitation during tetanic stimulation was minimal indgsR60, and no post-tetanic potentiation was observed. Miniature synaptic currents (mSCs) were slightly smaller in amplitude and less frequent indgsR60embryos in normal-K+saline. In high-K+saline, mSCs with distinctly large amplitude occurred frequently in controls at late embryonic stages, whereas those mSCs were rarely observed indgsR60embryos, suggesting a developmental defect in the mutant. Using theGal4-UASexpression system, we found that these phenotypes indgsR60were caused predominantly by lack of Gsα in presynaptic neurons and not in postsynaptic muscles. To test whether Gsα couples presynaptic modulator receptors to adenylyl cyclase (AC), we examined the responses of two known G-protein-coupled receptors indgsR60embryos. Both metabotropic glutamate and octopamine receptor responses were indistinguishable from those of controls, indicating that these receptors are not linked to AC by Gsα. We therefore suggest that synaptic transmission is compromised indgsR60embryos because of presynaptic defects in two distinct processes; one is uncoupling between the yet-to-be-known modulator receptor and AC activation, and the other is a defect in synapse formation.
Priming of Excitatory Synapses by α1Adrenoceptor-Mediated Inhibition of Group III Metabotropic Glutamate Receptors
Authors: Gordon Grant R. J. , Bains Jaideep S.
Published: April 2018

Adaptive responses mediated by the hypothalamus require sustained activation until homeostasis is achieved. Increases in excitatory drive to the magnocellular neuroendocrine cells that mediate these responses, however, result in the activation of a presynaptic metabotropic glutamate receptor (mGluR) that curtails synaptic excitability. Recent evidence that group III mGluRs can be inhibited by protein kinase C prompted us to test the hypothesis that activation of PKC by noradrenaline (NA) inhibits group III mGluRs and increases excitatory synaptic input to these cells. To examine the effects of NA on miniature EPSCs (mEPSCs), we obtained whole-cell recordings from magnocellular vasopressin and oxytocin neurons in the paraventricular nucleus of the hypothalamus. All of the neurons tested in the current study displayed an α1adrenoceptor-mediated increase in mEPSC frequency in response to NA (1–200 μm). The excitatory effects of NA were mimicked by the phorbol ester PMA and blocked by the PKC inhibitor calphostin C. The activation of PKC inhibits the efficacy of group III mGluRs, resulting in an increase in mEPSC frequency in response to a subsequent exposure to NA. By removing feedback inhibition, this mechanism effectively primes the synapses such that subsequent activation is more efficacious. The novel form of synaptic rescaling afforded by this cross-talk between distinct metabotropic receptors provides a means by which ascending catecholamine inputs can facilitate the control of homeostasis by hypothalamic networks.
Tenascin-R as a Repellent Guidance Molecule for Developing Optic Axons in Zebrafish
Authors: Becker Catherina G. , Schweitzer Jörn , Feldner Julia , Becker Thomas , Schachner Melitta
Published: April 2018

To investigate the role of tenascin-R in nervous system development, we studied axon pathfinding in the developing optic system of zebrafish. Zebrafish tenascin-R has the same domain structure as tenascin-R in amniotes. Amino acid sequence identity with human tenascin-R is 60%. In 3-d-old larvae, tenascin-R mRNA is expressed in scattered cells throughout the periventricular cell layer of the diencephalon and tectum. Tenascin-R immunoreactivity is not detectable in the optic nerve, optic tract, or tectal optic neuropil but immediately borders the optic tract caudally. Reducing expression of tenascin-R in 3-d-old larvaein vivoby injecting morpholinos into fertilized eggs led to excessive branching of the optic tract in 86% of all injected larvae compared with 20–37% in controls. Branches were almost exclusively caudal, where tenascin-R immunoreactivity normally borders the optic tract, suggesting a role for tenascin-R in guiding optic axons in the ventral diencephalon by a contact-repellent mechanism.
Altered Anxiety-Related Responses in Mutant Mice Lacking the β4 Subunit of the Nicotinic Receptor
Authors: Salas Ramiro , Pieri Fredalina , Fung Beryl , Dani John A. , De Biasi Mariella
Published: April 2018

Nicotine, acting at nicotinic acetylcholine receptors (nAChRs), is the primary addictive component of tobacco. Smokers often report an anxiolytic effect of cigarettes. This relief of anxiety, attributed to nicotine, is an important contributor to relapse when smokers try to quit. Hence, the study of the anxiolytic effects of nicotine is important for understanding the mechanisms underlying nicotine addiction. Mammalian nAChRs are pentameric ion channels usually composed ofα andβ subunits. Taking advantage ofβ4-homozygous-null mice (β4-/-), we examined the role of the nAChR β4 subunit in anxiety-related behaviors. The β4-/- mice behaved as though they were less anxious than wild-type littermates on the elevated-plus and staircase mazes, tests that measure anxiety-related behaviors. To obtain an independent, physiological indication of the stress produced by several tests, we measured changes in heart rate using telemetry. Consistently with the behavioral phenotype, β4-/- mice had a smaller heart rate increase in the elevated-plus maze than did wild-type littermates. In contrast, during social isolation, a separate test for anxiety,β4-/- mice exhibited a greater increase in heart rate than did wild-type littermates. Finally, β4-/- mice were indistinguishable from their wild-type littermates in the open field, the light/dark box, and the mirrored chamber. The overall results demonstrate that β4-containing (β4*) nAChRs influence behavioral responses during anxiety-related tests, and that this effect depends on the type of anxiety-provoking experience. Through their influence on anxiety-related behavior, β4* nAChRs might influence both tobacco consumption and smoking relapse.
Does cAMP Response Element-Binding Protein Have a Pivotal Role in Hippocampal Synaptic Plasticity and Hippocampus-Dependent Memory?
Authors: Balschun Detlef , Wolfer David P. , Gass Peter , Mantamadiotis Theo , Welzl Hans , Schütz Günther , Frey Julietta U. , Lipp Hans-Peter
Published: April 2018

Previous studies addressing the role of the transcription factor cAMP response element-binding protein (CREB) in mammalian long-term synaptic plasticity and memory by gene targeting were compromised by incomplete deletion of the CREB isoforms. Therefore, we generated conditional knock-out strains with a marked reduction or complete deletion of all CREB isoforms in the hippocampus. In these strains, no deficits could be detected in lasting forms of hippocampal long-term potentiation (LTP) and long-term depression (LTD). When tested for hippocampus-dependent learning, mutants showed normal context-dependent fear conditioning. Water maze learning was impaired during the early stages, but many mutants showed satisfactory scores in probe trials thought to measure hippocampus-dependent spatial memory. However, conditioned taste aversion learning, a putatively hippocampus-independent memory test, was markedly impaired. Our data indicate that in the adult mouse brain, loss of CREB neither prevents learning nor substantially affects performance in some hippocampus-dependent tasks. Furthermore, it spares LTP and LTD in paradigms that are sensitive enough to detect deficits in other mutants. This implies either a species-specific or regionally restricted role of CREB in the brain and/or a compensatory upregulation of the cAMP response element modulator (CREM) and other as yet unidentified transcription factors.
Inhibition of Dendritic Spine Morphogenesis and Synaptic Transmission by Activity-Inducible Protein Homer1a
Authors: Sala Carlo , Futai Kensuke , Yamamoto Kenji , Worley Paul F. , Hayashi Yasunori , Sheng Morgan
Published: April 2018

The postsynaptic density (PSD) proteins Shank and Homer cooperate to induce the maturation and enlargement of dendritic spines (Sala et al., 2001). Homer1a is an activity-inducible short-splice variant of Homer that lacks dimerization capacity. Here, we show that Homer1a reduces the density and size of dendritic spines in cultured hippocampal neurons in correlation with an inhibition of Shank targeting to synapses. Expression of Homer1a also decreases the size of PSD-95 clusters, the number of NMDA receptor clusters, and the level of surface AMPA receptors, implying a negative effect on the growth of synapses. In parallel with the morphological effects on synapses, Homer1a-expressing neurons show diminished AMPA and NMDA receptor postsynaptic currents. All of these outcomes required the integrity of the Ena/VASP Homology 1 domain of Homer1a that mediates binding to the PPXXF motif in Shank and other binding partners. Overexpression of the C-terminal region of Shank containing the Homer binding site causes effects similar to those of Homer1a. These data indicate that an association between Shank and the constitutively expressed long-splice variants of Homer (e.g., Homer1b/c) is important for maintaining dendritic-spine structure and synaptic function. Because Homer1a expression is induced by synaptic activity, our results suggest that this splice variant of Homer operates in a negative feedback loop to regulate the structure and function of synapses in an activity-dependent manner.
Endogenous Interleukin-1 Receptor Antagonist Mediates Anti-Inflammatory and Neuroprotective Actions of Cannabinoids in Neurons and Glia
Authors: Molina-Holgado Francisco , Pinteaux Emmanuel , Moore Jonathan D. , Molina-Holgado Eduardo , Guaza Carmen , Gibson Rosemary M. , Rothwell Nancy J.
Published: April 2018

Interleukin-1 receptor antagonist (IL-1ra) is an important anti-inflammatory cytokine that blocks all known actions of IL-1 and markedly protects against experimentally induced ischemic, excitotoxic, and traumatic brain insults. Cannabinoids (CBs) also exert potent anti-inflammatory and neuroprotective effects, but the mechanisms of their actions are unknown. Here we tested the hypothesis that the actions of CBs are mediated by endogenous IL-1ra. We report for the first time that both CB1and CB2receptors modulate release of endogenous IL-1ra from primary cultured glial cells. Activation of CB1or CB2receptors increased lipopolysaccharide-induced IL-1ra release, and specific CB1or CB2antagonists blocked lipopolysaccharide-induced production of IL-1ra from glial cells. Comparison of neuronal cultures from wild-type mice and mice lacking IL-1ra (knock-out) indicates that endogenous IL-1ra is essential for the neuro-protective effects of CBs against excessive activation of glutamate receptors (excitotoxicity) in response to S-AMPA or NMDA. Similarly, analysis of mixed glial cultures from IL-1ra knock-out mice indicates that endogenous IL-1ra is required for the CB-induced inhibition of nitric oxide production in response to bacterial lipopolysaccharide. These data suggest a novel neuroprotective mechanism of action for CBs in response to inflammatory or excitotoxic insults that is mediated by both CB1and CB2receptor-dependent pathways.
A New Role for the Cell Adhesion Molecule L1 in Neural Precursor Cell Proliferation, Differentiation, and Transmitter-Specific Subtype Generation
Authors: Dihné Marcel , Bernreuther Christian , Sibbe Mirjam , Paulus Werner , Schachner Melitta
Published: April 2018

Adhesion molecules play important roles in the development and regeneration of the CNS and PNS. We found that the immunoglobulin superfamily recognition molecule L1 influences proliferation and differentiation of neural precursor cells. Substrate-coated L1 reduced proliferation of precursor cells in a dose-dependent manner and increased neuronal and decreased astrocytic differentiation when compared with poly-l-lysine or laminin substrates. Enhancement of neuronal differentiation was more effective if L1 was offered via the cell surface of transfected fibroblasts compared with substrate-coated purified L1. Furthermore, L1 decreased cholinergic-subtype differentiation and accelerated GABAergic differentiation of precursor cell-derived neurons in comparison with poly-l-lysine or laminin. Generation of dopaminergic neurons was not influenced by L1. Experiments with precursor cells generated from L1-deficient mice indicate that L1 acts via heterophilic interaction on proliferation and differentiation of L1-negative precursor cells and via a homophilic or L1 coreceptor-mediated interaction on maturation of precursor cell-derived L1-positive neurons. Clonal analysis revealed that L1 equally inhibits proliferation of monopotential, bipotential, and multipotential precursor cells, but selectively enhances neuronal differentiation of multipotential and bipotential neuron-astrocyte precursors. Our observations support a new role for L1 or L1 ligands in neural precursor cell proliferation and differentiation.
A Two-Stage Unsupervised Learning Algorithm Reproduces Multisensory Enhancement in a Neural Network Model of the Corticotectal System
Authors: Anastasio Thomas J. , Patton Paul E.
Published: April 2018

Multisensory enhancement (MSE) is the augmentation of the response to sensory stimulation of one modality by stimulation of a different modality. It has been described for multisensory neurons in the deep superior colliculus (DSC) of mammals, which function to detect, and direct orienting movements toward, the sources of stimulation (targets). MSE would seem to improve the ability of DSC neurons to detect targets, but many mammalian DSC neurons are unimodal. MSE requires descending input to DSC from certain regions of parietal cortex. Paradoxically, the descending projections necessary for MSE originate from unimodal cortical neurons. MSE, and the puzzling findings associated with it, can be simulated using a model of the corticotectal system. In the model, a network of DSC units receives primary sensory input that can be augmented by modulatory cortical input. Connection weights from primary and modulatory inputs are trained in stages one (Hebb) and two (Hebb-anti-Hebb), respectively, of an unsupervised two-stage algorithm. Two-stage training causes DSC units to extract information concerning simulated targets from their inputs. It also causes the DSC to develop a mixture of unimodal and multisensory units. The percentage of DSC multisensory units is determined by the proportion of cross-modal targets and by primary input ambiguity. Multisensory DSC units develop MSE, which depends on unimodal modulatory connections. Removal of the modulatory influence greatly reduces MSE but has little effect on DSC unit responses to stimuli of a single modality. The correspondence between model and data suggests that two-stage training captures important features of self-organization in the real corticotectal system.