bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibrissa Resonance as a Transduction Mechanism for Tactile Encoding
Authors: Neimark Maria A. , Andermann Mark L. , Hopfield John J. , Moore Christopher I.
Published: April 2018

We present evidence that resonance properties of rat vibrissae differentially amplify high-frequency and complex tactile signals. Consistent with a model of vibrissa mechanics, optical measurements of vibrissae revealed that their first mechanical resonance frequencies systematically varied from low (60-100 Hz) in longer, posterior vibrissae to high (∼750 Hz) in shorter, anterior vibrissae. Resonance amplification of tactile input was observedin vivoandex vivo, and in a variety of boundary conditions that are likely to occur during perception, including stimulation of the vibrissa with moving complex natural stimuli such as sandpaper. Vibrissae were underdamped, allowing for sharp tuning to resonance frequencies. Vibrissa resonance constitutes a potentially useful mechanism for perception of high-frequency and complex tactile signals. Amplification of small amplitude signals by resonance could facilitate detection of stimuli that would otherwise fail to drive neural activity. The systematic map of frequency sensitivity across the face could facilitate texture discrimination through somatotopic encoding of frequency content. These findings suggest strong parallels between vibrissa tactile processing and auditory encoding, in which the cochlea also uses resonance to amplify low-amplitude signals and to generate a spatial map of frequency sensitivity.
Functional Connectivity of the Medial Temporal Lobe Relates to Learning and Awareness
Authors: McIntosh Anthony Randal , Rajah M. Natasha , Lobaugh Nancy J.
Published: April 2018

Learning with awareness is believed to require the involvement of the medial temporal lobe (MTL). In this study, the hypothesis tested was that this involvement is best appreciated by the pattern of MTL functional connectivity with other brain areas. In a sensory learning paradigm, human subjects were classified as AWARE or UNAWARE, on the basis of whether they noted that one of two tones predicted a visual event. Only AWARE subjects acquired and reversed a differential response to the tones. However, learned facilitation was evident in both groups. MTL activity, indexed by blood flow changes measured with positron emission tomography, was correlated with facilitation in both groups but in opposite directions (greater MTL activity was related to less facilitation in AWARE subjects but more facilitation in UNAWARE subjects). Discrimination and reversal in AWARE subjects involved anterior medial, inferior prefrontal, and lateral occipital cortices. Furthermore, unique regional patterns of MTL functional connectivity were observed: AWARE subjects engaged dorsolateral prefrontal and lateral occipital cortices, whereas UNAWARE subjects showed a more spatially restricted network involving contralateral MTL regions and the thalamus. In the AWARE group, the MTL functional connectivity pattern overlapped with regions associated with facilitation and discrimination, but in UNAWARE subjects, the MTL pattern was related only to facilitation. These results suggest that the MTL and functional connected regions, including dorsolateral and medial prefrontal cortex, acted to link facilitation and discrimination patterns in AWARE subjects. Thus, the contribution of the MTL to learning and awareness is shaped by the pattern of interregional interactions, the neural context.
N- and C-Terminal Domains of β-Catenin, Respectively, Are Required to Initiate and Shape Axon Arbors of Retinal Ganglion CellsIn Vivo
Authors: Elul Tamira M. , Kimes Nikole E. , Kohwi Minoree , Reichardt Louis F.
Published: April 2018

We used deletion mutants to study β-catenin function in axon arborization of retinal ganglion cells (RGCs) in liveXenopus laevistadpoles. A deletion mutant βcatΔARM consists of the N- and C-terminal domains of wild-type β-catenin that contain, respectively, α-catenin and postsynaptic density-95 (PSD-95)/discs large (Dlg)/zona occludens-1 (ZO-1) (PDZ) binding sites but lacks the central armadillo repeat region that binds cadherins and other proteins. Expression of ΔARM in RGCs of live tadpoles perturbed axon arborization in two distinct ways: some RGC axons did not form arbors, whereas the remaining RGC axons formed arbors with abnormally long and tangled branches. Expression of the N- and C-terminal domains of β-catenin separately in RGCs resulted in segregation of these two phenotypes. The axons of RGCs overexpressing the N-terminal domain of β-catenin developed no or very few branches, whereas axons of RGCs overexpressing the C-terminal domain of β-catenin formed arbors with long, tangled branches. Additional analysis revealed that the axons of RGCs that did not form arbors after overexpression of ΔARM or the N-terminal domain of β-catenin were frequently mistargeted within the tectum. These results suggest that interactions of the N-terminal domain of β-catenin with α-catenin and of the C-terminal domain with PDZ domain-containing proteins are required, respectively, to initiate and shape axon arbors of RGCsin vivo.
Functional Connectivity between the Superficial and Deeper Layers of the Superior Colliculus: An Anatomical Substrate for Sensorimotor Integration
Authors: Doubell Timothy P. , Skaliora Irini , Baron Jérôme , King Andrew J.
Published: April 2018

The superior colliculus (SC) transforms both visual and nonvisual sensory signals into motor commands that control orienting behavior. Although the afferent and efferent connections of this midbrain nucleus have been well characterized, little is know about the intrinsic circuitry involved in sensorimotor integration. Transmission of visual signals from the superficial (sSC) to the deeper layers (dSC) of the SC has been implicated in both the triggering of orienting movements and the activity-dependent processes that align maps of different sensory modalities during development. However, evidence for the synaptic connectivity appropriate for these functions is lacking. In this study, we used a variety of anatomical and physiological methods to examine the functional organization of the sSC-dSC pathway in juvenile and adult ferrets. Axonal tracing in adult ferrets showed that, as in other species, sSC neurons project topographically to the dSC, providing a route for the transmission of visual signals to the multisensory output layers of the SC. We found that sSC axons terminate on dSC neurons that stain prominently for the NR1 subunit of the NMDA receptor, a subpopulation of which were identified as tectoreticulospinal projection neurons. We also show that the sSC-dSC pathway is topographically organized and mediated by monosynaptic excitatory synapses even before eye opening in young ferrets, suggesting that visual signals routed via the sSC may influence the activity of dSC neurons before the emergence of their multisensory response properties. These findings indicate that superficial- to deep-layer projections provide spatially ordered visual signals, both during development and into adulthood, directly to SC neurons that are involved in coordinating sensory inputs with motor outputs.
Multiple Trafficking Signals Regulate Kainate Receptor KA2 Subunit Surface Expression
Authors: Ren Zhao , Riley Nathan J. , Garcia Elizabeth P. , Sanders James M. , Swanson Geoffrey T. , Marshall John
Published: April 2018

The kainate receptor subunit KA2 does not form functional homomeric channels despite its structural similarity to the functional glutamate receptor 5-7subunits and high agonist binding affinity inin vitroassays. In this study, we first demonstrate that homomeric KA2 receptors fail to reach the plasma membrane and then identify the molecular mechanisms preventing surface expression. Specifically, we show that KA2 subunits form homooligomeric receptors that are confined to the endoplasmic reticulum (ER). We then demonstrate that, in both heterologous expression systems and primary neurons, the intracellular retention of KA2 is not caused by subunit misfolding but, rather, is mediated through discrete protein trafficking signals, including an arginine-rich ER retention/retrieval motif and a di-leucine endocytic sequence in the C terminus of the KA2 subunit. Disruption of these motifs results in ER exit and surface expression of KA2 homomeric receptors that remain nonfunctional. Furthermore, our data suggest that the ER retention/retrieval signal in KA2 is sterically shielded during heteromeric assembly, allowing delivery of functional heteromeric receptors to the plasma membrane. Taken together, our results illustrate novel regulatory mechanisms that control the intracellular trafficking and surface expression of kainate receptors.
AppGene Dosage Modulates Endosomal Abnormalities of Alzheimer's Disease in a Segmental Trisomy 16 Mouse Model of Down Syndrome
Authors: Cataldo Anne M. , Petanceska Suzana , Peterhoff Corrinne M. , Terio Nicole B. , Epstein Charles J. , Villar Angela , Carlson Elaine J. , Staufenbiel Matthias , Nixon Ralph A.
Published: April 2018

Altered neuronal endocytosis is the earliest known pathology in sporadic Alzheimer's disease (AD) and Down syndrome (DS) brain and has been linked to increased Aβ production. Here, we show that a genetic model of DS (trisomy 21), the segmental trisomy 16 mouse Ts65Dn, develops enlarged neuronal early endosomes, increased immunoreactivity for markers of endosome fusion (rab5, early endosomal antigen 1, and rabaptin5), and endosome recycling (rab4) similar to those in AD and DS individuals. These abnormalities are most prominent in neurons of the basal forebrain, which later develop aging-related atrophy and degenerative changes, as in AD and DS. We also show thatApp, one of the triplicated genes in Ts65Dn mice and human DS, is critical to the development of these endocytic abnormalities. Selectively deleting one copy ofAppor a small portion of the chromosome 16 segment containingAppfrom Ts65Dn mice eliminated the endosomal phenotype. OverexpressingAppat high levels in mice did not alter early endosomes, implying that one or more additional genes on the triplicated segment of chromosome 16 are also required for the Ts65Dn endosomal phenotype. These results identify an essential role forAppgene triplication in causing AD-related endosomal abnormalities and further establish the pathogenic significance of endosomal dysfunction in AD.
Brain-Derived Neurotrophic Factor Is Required for the Maintenance of Cortical Dendrites
Authors: Gorski Jessica A. , Zeiler Steven R. , Tamowski Susan , Jones Kevin R.
Published: April 2018

Brain-derived neurotrophic factor (BDNF) is thought to be involved in neuronal survival, migration, morphological and biochemical differentiation, and modulation of synaptic function in the CNS. In the rodent cortex, postnatal BDNF expression is initially low but subsequently increases to reach maximal levels around weaning. Thus, BDNF expression peaks at a time when both structural and functional maturation of cortical circuitry occurs. Although the function of BDNF has been probed using many approaches, its requirements during this phase of life have not previously been examined genetically. To test thein vivorequirements for BDNF during this important phase of development we generated early-onset forebrain-specificBDNFmutant mice. Although these mice undergo forebrain-restricted deletion ofBDNFby Cre-mediated recombination during embryogenesis, they are healthy, and we did not detect the loss of specific cortical excitatory or inhibitory neurons. However, the neocortex of 5-week-old mice was thinner, attributable at least partly to neuronal shrinkage. Importantly, although visual cortical layer 2/3 neurons in the mutants initially developed normal dendrite structure, dendritic retraction became apparent by 3 weeks of age. Thus, our observations suggest that cortically expressed BDNF functions to support the maintenance of cortical neuron size and dendrite structure rather than the initial development of these features. This is consistent with a role for BDNF in stabilizing the “survival” of circuitry during the phase of activity-dependent reorganization of cortical connectivity.
Development and Subunit Composition of Synaptic NMDA Receptors in the Amygdala: NR2B Synapses in the Adult Central Amygdala
Authors: Lopez de Armentia Mikel , Sah Pankaj
Published: April 2018

NMDA receptors are well known to play an important role in synaptic development and plasticity. Functional NMDA receptors are heteromultimers thought to contain two NR1 subunits and two or three NR2 subunits. In central neurons, NMDA receptors at immature glutamatergic synapses contain NR2B subunits and are largely replaced by NR2A subunits with development. At mature synapses, NMDA receptors are thought to be multimers that contain either NR1/NR2A or NR1/NR2A/NR2B subunits, whereas receptors that contain only NR1/NR2B subunits are extrasynaptic. Here, we have studied the properties of NMDA receptors at glutamatergic synapses in the lateral and central amygdala. We find that NMDA receptor-mediated synaptic currents in the central amygdala in both immature and mature synapses have slow kinetics and are substantially blocked by the NR2B-selective antagonists (1S, 2S)-1-(4-hydroxyphenyl)-2-(4-hydroxy-4-phenylpiperidino)-1-propano and ifenprodil, indicating that there is no developmental change in subunit composition. In contrast, at synapses on pyramidal neurons in the lateral amygdala, whereas NMDA EPSCs at immature synapses are slow and blocked by NR2B-selective antagonists, at mature synapses their kinetics are faster and markedly less sensitive to NR2B-selective antagonists, consistent with a change from NR2B to NR2A subunits. Using real-time PCR and Western blotting, we show that in adults the ratio of levels of NR2B to NR2A subunits is greater in the central amygdala than in the lateral amygdala. These results show that the subunit composition synaptic NMDA receptors in the lateral and central amygdala undergo distinct developmental changes.
Olfactory Bulb Mitral-Tufted Cell Plasticity: Odorant-Specific Tuning Reflects Previous Odorant Exposure
Authors: Fletcher Max L. , Wilson Donald A.
Published: April 2018

Olfactory system second-order neurons, mitral-tufted cells, have odorant receptive fields (ORFs) (molecular receptive ranges in odorant space for carbon chain length in organic odorant molecules). This study quantified several dimensions of these excitatory odorant receptive fields to novel odorants in rats and then examined the effects of passive odorant exposure on the shape of the ORF-tuning curve. ORFs for carbon chain length of novel ethyl esters (pure odorants that the animals had not been exposed to previously) were determined before and after a 50 sec prolonged exposure to one of the odorants. In response to novel odorants, quantitative analysis of mitral-tufted cell excitatory ORFs revealed that the median ORF width spanned 3-4 carbons, generally with a single-most excitatory odorant. Exposure to either the most excitatory odorant (ON-PEAK) or an odorant that was two carbons longer (OFF-PEAK) for 50 sec produced whole ORF suppression immediately after the end of the prolonged exposure, with the ON-PEAK exposure producing the greatest suppression. These results are consistent with a feature-detecting function for mitral-tufted cells. Redetermination of the ORF 15 and 60 min after the exposure revealed that OFF-PEAK exposure produced a reduction in responsiveness to the best odorant and an increase in responsiveness to the exposed odorant. In contrast, exposure to the ON-PEAK odorant or no odorant did not affect ORFs. Given that mitral-tufted cells receive exclusive excitatory input from olfactory receptor neurons expressing identical receptor proteins, it is hypothesized that experience-induced mitral-tufted cell ORF changes reflect modulation of lateral and centrifugal olfactory bulb circuits.
Lack of Huntingtin-Associated Protein-1 Causes Neuronal Death Resembling Hypothalamic Degeneration in Huntington's Disease
Authors: Li Shi-Hua , Yu Zhao-Xue , Li Cui-Lin , Nguyen Huu-Phuc , Zhou Yong-Xing , Deng Chuxia , Li Xiao-Jiang
Published: April 2018

Huntington's disease (HD) is caused by a polyglutamine expansion in the disease protein huntingtin. The polyglutamine expansion causes huntingtin to interact abnormally with a number of proteins. However, it is unclear whether, and how, huntingtin-associated proteins are involved in the neurodegeneration in HD. Here, we show that huntingtin-associated protein-1 (HAP1), which is involved in intracellular trafficking of epidermal growth factor receptor (EGFR), is highly expressed in the hypothalamus. Mice lacking HAP1 die after birth because of depressed feeding activity. Terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling staining and electron microscopic examination revealed the degeneration in hypothalamic regions that control feeding behavior. Hypothalamic degeneration was also observed in HD transgenic mice that have a significant loss of body weight. Inhibition of HAP1 expression decreases EGFR signaling and cell viability, whereas overexpression of HAP1 enhances this signaling activity and inhibits mutant huntingtin-mediated cytotoxicity. These results suggest that the effect of mutant huntingtin on HAP1 and EGFR signaling may contribute to the hypothalamic neurodegeneration and loss of body weight in HD.
Sensitivity of Neurons to Weak Electric Fields
Authors: Francis Joseph T. , Gluckman Bruce J. , Schiff Steven J.
Published: April 2018

Weak electric fields modulate neuronal activity, and knowledge of the interaction threshold is important in the understanding of neuronal synchronization, in neural prosthetic design, and in the public health assessment of environmental extremely low frequency fields. Previous experimental measurements have placed the threshold between 1 and 5 mV/mm, although theory predicts that elongated neurons should have submillivolt per millimeter sensitivity near 100 μV/mm. We here provide the first experimental confirmation that neuronal networks are detectably sensitive to submillivolt per millimeter electrical fields [Gaussian pulses 26 msec full width at half-maximal, 140 μV/mm root mean square (rms), 295 μV/mm peak amplitude], an order of magnitude below previous findings, and further demonstrate that these networks are more sensitive than the average single neuron threshold (185 μV/mm rms, 394 μV/mm peak amplitude) to field modulation.
Glutamate Triggers Rapid Glucose Transport Stimulation in Astrocytes as Evidenced by Real-Time Confocal Microscopy
Authors: Loaiza Anitsi , Porras Omar H. , Barros Luis Felipe
Published: April 2018

Glutamate stimulates glycolysis in astrocytes, a phenomenon that couples astrocytic metabolism with neuronal activity. However, it is not known whether glutamate also affects glucose transporter-1 (GLUT1), the transporter responsible for glucose entry into astrocytes. To address this question, two different real-time single-cell hexose uptake assays were applied to cultured hippocampal astrocytes using confocal epifluorescence microscopy. Glutamate caused a twofold to threefold increase in the zero-trans uptake rates of the fluorescent hexoses 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose (2-NBDG) and 6-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-6-deoxyglucose (6-NBDG). Galactose uptake, determined by the calcein volumetric assay, was stimulated to a similar extent, confirming the fluorescent hexose data, and also demonstrating that glutamate stimulation is aVmaxeffect. Remarkably, glucose transport stimulation developed fully inside 10 sec, which is 100 times faster than acute stimulations of glucose transport in other cell types. Glutamate did not significantly affect the rate of 6-NBDG uptake by GLUT1-expressing epithelial Clone 9 cells, suggesting that an astrocyte-specific factor is required for transport stimulation. We conclude that glucose transport stimulation occurs early during astrocytic activation by glutamate, which provides a novel regulatory node to current models of brain energy metabolism. This mechanism should also be considered for the interpretation of functional imaging data based on hexoses.
Lateralization of Circadian Pacemaker Output: Activation of Left- and Right-Sided Luteinizing Hormone-Releasing Hormone Neurons Involves a Neural Rather Than a Humoral Pathway
Authors: de la Iglesia Horacio O. , Meyer Jennifer , Schwartz William J.
Published: April 2018

Locomotor activity and luteinizing hormone (LH) secretion in golden hamsters share a common circadian pacemaker in the suprachiasmatic nucleus (SCN), but the rhythms do not seem to share a common output pathway from the SCN. Locomotion is believed to be driven by humoral factor(s), whereas LH secretion may depend on specific ipsilateral neural efferents from the SCN to LH releasing hormone (LHRH)-containing neurons in the preoptic area. In this paper we provide the first functional evidence for such efferents in neurologically intact hamsters by exploiting a phenomenon known as “splitting” in constant light, in which circa-12 hr (approximately 12 hr) locomotor activity bouts reflect an antiphase oscillation of the left and right sides of the bilaterally paired SCN. In ovariectomized, estrogen-treated (OVX + E2) female hamsters, splitting is also known to include circa-12 hr LH secretory surges. Here we show that behaviorally “split” OVX + E2females exhibit a marked left-right asymmetry in immunoreactive c-Fos expression in both SCN and activated LHRH neurons, with the percentage of LHRH+/c-Fos+double-labeled cells approximately fivefold higher on the side corresponding to the side of the SCN with higher c-Fos immunoreactivity. Our results suggest that splitting involves alternating left- and right-sided stimulation of LHRH neurons; under such circumstances, the functional activity of the neuroendocrine hypothalamus mirrors intrinsic side-to-side differences in SCN gene expression. The circadian regulation of reproductive activity depends on lateralized, point-to-point axonal projections rather than on diffusible factors.
Freud-1: A Neuronal Calcium-Regulated Repressor of the 5-HT1A Receptor Gene
Authors: Ou Xiao-Ming , Lemonde Sylvie , Jafar-Nejad Hamed , Bown Christopher D. , Goto Aya , Rogaeva Anastasia , Albert Paul R.
Published: April 2018

Altered regulation of 5-HT1A receptors is implicated in mood disorders such as anxiety and major depression. To provide insight into its transcriptional regulation, we previously identified a novel DNA element [14 bp 5′-repressor element (FRE)] of the 5-HT1A receptor gene that mediates repression in neuronal and non-neuronal cells (Ou et al., 2000). We have now cloned a novel DNA binding protein [five′ repressor element under dual repression binding protein-1 (Freud-1)] that binds to FRE to mediate repression of the 5-HT1A receptor or heterologous promoters. Freud-1 is evolutionarily conserved and contains two DM-14 basic repeats, a predicted helix-loop-helix DNA binding domain, and a protein kinase C conserved region 2 (C2)/calcium-dependent lipid binding (CalB) calcium/phospholipid binding domain. An intact CalB domain was required for Freud-1-mediated repression. In serotonergic raphe cells, overexpression of Freud-1 repressed the 5-HT1A promoter and decreased 5-HT1A receptor protein levels, whereas transfection of antisense to Freud-1 derepressed the 5-HT1A gene and increased 5-HT1A receptor protein expression. Calcium-dependent signaling blocked Freud-1-FRE binding and derepressed the 5-HT1A promoter. Treatment with inhibitors of calmodulin or CAM-dependent protein kinase reversed calcium-mediated inhibition of Freud-1. Freud-1 RNA and protein were present in raphe nuclei, hippocampus, cortex, and hypothalamus, and Freud-1 protein was colocalized with 5-HT1A receptors, suggesting its importance in regulating 5-HT1A receptorsin vivo. Thus, Freud-1 represents a novel calcium-regulated repressor that negatively regulates basal 5-HT1A receptor expression in neurons and may play a role in the altered regulation of 5-HT1A receptors associated with anxiety or major depression.
ATP Modulation of Excitatory Synapses onto Interneurons
Authors: Khakh Baljit S. , Gittermann Daniel , Cockayne Debra A. , Jones Alison
Published: April 2018

Inhibitory interneurons play important roles in neuronal circuits, but the synaptic mechanisms that regulate excitatory input onto interneurons remain to be fully understood. We show that ATP-gated presynaptic P2X2 channels facilitate excitatory transmission onto stratum radiatum interneurons but not onto CA1 pyramidal neurons. ATP released endogenously during carbachol-induced oscillations facilitates excitatory synapses onto interneurons. Overall, these data provide evidence for the molecular identity, synaptic function, and interneuron synapse specificity of a presynaptic neurotransmitter-gated cation channel. The findings highlight a novel form of presynaptic facilitation for hippocampal interneurons and suggest a role for extracellular ATP in neuronal networks.
Human α4β2 Acetylcholine Receptors Formed from Linked Subunits
Authors: Zhou Yan , Nelson Mark E. , Kuryatov Alexander , Choi Catherine , Cooper John , Lindstrom Jon
Published: April 2018

We prepared concatamers of α4 and β2 subunits for human nicotinic acetylcholine receptors (AChRs), in which the C terminus of α4 was linked to the N terminus of β2, or vice versa, via a tripeptide sequence repeated 6 or 12 times, and expressed them inXenopusoocytes. Linkage did not substantially alter channel amplitude or channel open-duration. Linkage at the C terminus of α4 prevented AChR potentiation by 17-β-estradiol by disruption of its binding site. Assembly of AChRs from concatamers was less efficient, but function was much more efficient than that of unlinked subunits. With both linked and free subunits, greater ACh-induced currents per surface AChR were observed with the (α4)3(β2)2stoichiometry than with the (α4)2(β2)3stoichiometry. The (α4)3(β2)2stoichiometry exhibited much lower ACh sensitivity. When concatamers were expressed alone, dipentameric AChRs were formed in which the (α4)2(β2)3pentamer was linked to the (α4)3(β2)2pentamer. Dipentamers were selectively expressed on the cell surface, whereas most monopentamers with dangling subunits were retained intracellularly. Coexpression of concatamers with monomeric β2, β4, or α4 subunits resulted in monopentamers, the stoichiometry of which was determined by the free subunit added. Linkage between the C terminus of β2 and the N terminus of α4 favored formation of ACh-binding sites within the concatamer, whereas linkage between the C terminus of α4 and the N terminus of β2 favored formation of ACh-binding sites between concatamers. These protein-engineering studies provide insight into the structure and function of α4β2 AChRs, emphasizing the functional differences between α4β2 AChRs of different stoichiometries.
Improvement in Fear Memory by Histamine-Elicited ERK2 Activation in Hippocampal CA3 Cells
Authors: Giovannini Maria Grazia , Efoudebe Marcel , Passani Maria Beatrice , Baldi Elisabetta , Bucherelli Corrado , Giachi Filippo , Corradetti Renato , Blandina Patrizio
Published: April 2018

Consolidation of associative memories appears to require extracellular signal-related kinase2 (ERK2) activation, which is modulated by several factors, including neurotransmitter receptor stimulation. Here we show thatin vitrostimulation of either H2or H3histaminergic receptors activates ERK2 in hippocampal CA3 pyramidal cells. In behaving animals, bilateral posttraining injections into the dorsal hippocampus of histamine H2or H3receptor agonists improve memory consolidation after contextual fear conditioning. Local administration of U0126, a selective inhibitor of ERK kinase, prevents memory improvements exerted by the agonists, without causing any behavioral effect per se. This is the first evidence of a positive correlation between ERK phosphorylation and memory improvement. Moreover, we demonstrate that the brain histaminergic system regulates hippocampal ERK cascade. Finally, our data indicate that early ERK2 hippocampal activation is not required for the expression of long-term fear memories.
Mechanisms of Mitochondria-Neurofilament Interactions
Authors: Wagner O. I. , Lifshitz J. , Janmey P. A. , Linden M. , McIntosh T. K. , Leterrier J.-F.
Published: April 2018

Mitochondria are localized to regions of the cell where ATP consumption is high and are dispersed according to changes in local energy needs. In addition to motion directed by molecular motors, mitochondrial distribution in neuronal cells appears to depend on the docking of mitochondria to microtubules and neurofilaments. We examined interactions between mitochondria and neurofilaments using fluorescence microscopy, dynamic light scattering, atomic force microscopy, and sedimentation assays. Mitochondria-neurofilament interactions depend on mitochondrial membrane potential, as revealed by staining with a membrane potential sensitive dye (JC-1) in the presence of substrates/ADP or uncouplers (valinomycin/carbonyl cyanidep-(trifluoromethoxy)phenylhydrazone) and are affected by the phosphorylation status of neurofilaments and neurofilament sidearms. Antibodies against the neurofilament heavy subunit disrupt binding between mitochondria and neurofilaments, and isolated neurofilament sidearms alone interact with mitochondria, suggesting that they mediate the interactions between the two structures. These data suggest that specific and regulated mitochondrial-neurofilament interactions occurin situand may contribute to the dynamic distribution of these organelles within the cytoplasm of neurons.
Impaired Long-Term Memory and NR2A-Type NMDA Receptor-Dependent Synaptic Plasticity in Mice Lacking c-Fos in the CNS
Authors: Fleischmann Alexander , Hvalby Oivind , Jensen Vidar , Strekalova Tatyana , Zacher Christiane , Layer Liliana E. , Kvello Ane , Reschke Markus , Spanagel Rainer , Sprengel Rolf , Wagner Erwin F. , Gass Peter
Published: April 2018

The immediate early gene c-fosis part of the activator protein-1 transcription factor and has been postulated to participate in the molecular mechanisms of learning and memory. To test this hypothesisin vivo, we generated mice with a nervous system-specific c-fosknock-out using the Cre-loxP system. Adult mice lacking c-Fos in the CNS (c-fosΔCNS) showed normal general and emotional behavior but were specifically impaired in hippocampus-dependent spatial and associative learning tasks. These learning deficits correlated with a reduction of long-term potentiation (LTP) in hippocampal CA3-CA1 synapses. The magnitude of LTP was restored by a repeated tetanization procedure, suggesting impaired LTP induction in c-fosΔCNSmice. This rescue was blocked by a selective inhibitor of NR2B-type NMDA receptors. This blockade was compensated in wild-type mice by NR2A-type NMDA receptor-activated signaling pathways, thus indicating that these pathways are compromised in c-fosΔCNSmice. In summary, our data suggest a role for c-Fos in hippocampus-dependent learning and memory as well as in NMDA receptor-dependent LTP formation.
Neuroprotective Activities of Sodium Valproate in a Murine Model of Human Immunodeficiency Virus-1 Encephalitis
Authors: Dou Huanyu , Birusingh Kevin , Faraci Jill , Gorantla Santhi , Poluektova Larisa Y. , Maggirwar Sanjay B. , Dewhurst Stephen , Gelbard Harris A. , Gendelman Howard E.
Published: April 2018

Human immunodeficiency virus-1 (HIV-1) infection of the nervous system can result in neuroinflammatory events leading first to neuronal dysfunction then to cognitive and behavioral impairments in infected people. The multifaceted nature of the disease process, commonly called HIV-1-associated dementia (HAD), provides a number of adjunctive therapeutic opportunities. One proposed adjunctive therapy is sodium valproate (VPA), an anticonvulsant known to promote neurite outgrowth and increase β-catenin through inhibiting glycogen synthase kinase 3β activity and tau phosphorylation. We now show that VPA treatment of rat cortical neurons exposed to HIV-1 gp120 prevents resultant neurotoxic activities. This includes the induction of significant neurite outgrowth and microtubule-associated protein 2 (MAP-2) and neuron-specific nuclear protein (NeuN) antigens in affected neuronal cell bodies and processes. Similarly, VPA protects severe combined immunodeficient (SCID) mice against the neurodegeneration of HIV-1ADAinfected monocyte-derived macrophages (MDMs). In SCID mice with HIV-1 MDM-induced encephalitis, VPA treatment significantly reduced neuronal phosphorylatedβ-catenin and tau without affecting HIV-1 replication or glial activation. We conclude that VPA protects neurons against HIV-1 infected MDM neurotoxicity, possibly through its effects on the phosphorylation of tau and β-catenin. The use of VPA as an adjuvant in treatment of human HAD is being pursued.
Decreased Temporal Precision of Auditory Signaling inKcna1-Null Mice: An Electrophysiological StudyIn Vivo
Authors: Kopp-Scheinpflug Cornelia , Fuchs Katja , Lippe William R. , Tempel Bruce L. , Rübsamen Rudolf
Published: April 2018

The voltage-gated potassium (Kv) channel subunit Kv1.1, encoded by theKcna1gene, is expressed strongly in the ventral cochlear nucleus (VCN) and the medial nucleus of the trapezoid body (MNTB) of the auditory pathway. To examine the contribution of the Kv1.1 subunit to the processing of auditory information,in vivosingle-unit recordings were made from VCN neurons (bushy cells), axonal endings of bushy cells at MNTB cells (calyces of Held), and MNTB neurons ofKcna1-null (-/-) mice and littermate control (+/+) mice. Thresholds and spontaneous firing rates of VCN and MNTB neurons were not different between genotypes. At higher sound intensities, however, evoked firing rates of VCN and MNTB neurons were significantly lower in -/- mice than +/+ mice. The SD of the first-spike latency (jitter) was increased in VCN neurons, calyces, and MNTB neurons of -/- mice compared with +/+ controls. Comparison along the ascending pathway suggests that the increased jitter found in -/- MNTB responses arises mostly in the axons of VCN bushy cells and/or their calyceal terminals rather than in the MNTB neurons themselves. At high rates of sinusoidal amplitude modulations, -/- MNTB neurons maintained high vector strength values but discharged on significantly fewer cycles of the amplitude-modulated stimulus than +/+ MNTB neurons. These results indicate that inKcna1-null mice the absence of the Kv1.1 subunit results in a loss of temporal fidelity (increased jitter) and the failure to follow high-frequency amplitude-modulated sound stimulationin vivo.
Signaling at the Gliovascular Interface
Authors: Simard Marie , Arcuino Gregory , Takano Takahiro , Liu Qing Song , Nedergaard Maiken
Published: April 2018

Advances in fluorescent calcium indicating dyes over the past decade have identified calcium signaling as the tool by which astrocytes communicate among themselves and with neighboring neurons. Studies of astrocyte-neuron interactions have shown that calcium signaling is a potent modulator of the strength of both excitatory and inhibitory synapses. The concept that astrocytes possess a mechanism for rapid cell communication has not been incorporated, however, into the supportive functions of astrocytes. Because many of the classical tasks of astrocytes are linked to the blood-brain barrier, we have here examined the expression of proteins required for calcium signaling in their vascular end-foot processes. The gap junction protein, Cx43, was expressed intensively around the vessels interconnecting astrocytic end-foot processes. These gap junctions permitted diffusion of Lucifer yellow, specifically along the path of glial end feet apposed to the vessel wall. The purinergic receptors, P2Y(2) and P2Y(4), were also strongly expressed at the gliovascular interface and colocalized with GFAP around larger vessels in cortex. Multiphoton imaging of freshly prepared brain slices loaded with Fluo-4/AM revealed that ATP mobilized cytosolic calcium in astrocytic end feet, whereas electrical stimulation triggered calcium waves propagating along the vessel wall. Brain endothelial cells and pericytes were physically separated from astrocytes by the basal lamina and responded only weakly to ATP. These observations identify astrocytic end-foot processes plastered at the vessel wall as a center for purinergic signaling. It is speculated that calcium signaling may play a role in astrocytic functions related to the blood-brain barrier, including blood flow regulation, metabolic trafficking, and water homeostasis.
The Role of Microtubule-Associated Protein 2c in the Reorganization of Microtubules and Lamellipodia during Neurite Initiation
Authors: Dehmelt Leif , Smart Fiona M. , Ozer Rachel S. , Halpain Shelley
Published: April 2018

During neurite initiation, cells surrounded by a flattened, actin-rich lamellipodium transform to produce thin, microtubule-filled neurite shafts tipped by actin-rich growth cones, but little is known about this transformation. Our detailed time-lapse analyses of cultured hippocampal neurons, a widely used model system for neuronal development, revealed that neurites emerge from segmented lamellipodia, which then gradually extend from the cell body to become nascent growth cones. This suggests that actin- and microtubule-rich structures are reorganized in a coordinated manner. We hypothesized that proteins such as microtubule-associated protein 2 (MAP2), which can interact with both cytoskeletal components, might be critically involved in neurite initiation. Live-cell video and fluorescence microscopy in Neuro-2a cells showed that expression of MAP2c triggers neurite formation via rapid accumulation and bundling of stable, MAP2c-bound microtubules, concurrent with a gradual transformation of lamellipodia into nascent growth cones. The microtubule-stabilizing agent Taxol did not mimic this effect, suggesting that the ability of MAP2c to stabilize microtubules is not sufficient for neurite initiation. However, combination of Taxol treatment with actin disruption induced robust process formation, suggesting that inhibitory effects of F-actin need to be overcome as well. Neurite initiation by MAP2c required its microtubule-binding domain and was enhanced by its binding domain for cAMP-dependent protein kinase (PKA). MAP2c mutants defective in both PKA and microtubule binding acted as dominant negative inhibitors of neurite initiation in neuroblastoma cells and primary hippocampal neurons. Together, these data suggest that MAP2c bears functions that both stabilize microtubules and directly or indirectly alter actin organization during neurite initiation.
Synchronization of a Nonlinear Oscillator: Processing the Cf Component of the Echo-Response Signal in the Cochlea of the Mustached Bat
Authors: Russell Ian J. , Drexl Markus , Foeller Elisabeth , Vater Marianne , Kössl Manfred
Published: April 2018

Cochlear microphonic potential (CM) was recorded from the CF2 region and the sparsely innervated zone (the mustached bat's cochlea fovea) that is specialized for analyzing the Doppler-shifted echoes of the first-harmonic (∼61 kHz) of the constant-frequency component of the echolocation call. Temporal analysis of the CM, which is tuned sharply to the 61 kHz cochlear resonance, revealed that at the resonance frequency, and within 1 msec of tone onset, CM is broadly tuned with linear magnitude level functions. CM measured during the ongoing tone and in the ringing after tone offset is 50 dB more sensitive, is sharply tuned, has compressive level functions, and the phase leads onset CM by 90°: an indication that cochlear responses are amplified during maximum basilar membrane velocity. For high-level tones above the resonance frequency, CM appears at tone onset and after tone offset. Measurements indicate that the two oscillators responsible for the cochlear resonance, presumably the basilar and tectorial membranes, move together in phase during the ongoing tone, thereby minimizing net shear between them and hair cell excitation. For tones within 2 kHz of the cochlear resonance the frequency of CM measured within 2 msec of tone onset is not that of the stimulus but is proportional to it. For tones just below the cochlear resonance region CM frequency is a constant amount below that of the stimulus depending on CM measurement delay from tone onset. The frequency responses of the CM recorded from the cochlear fovea can be accounted for through synchronization between the nonlinear oscillators responsible for the cochlear resonance and the stimulus tone.
Caspase-Dependent and Caspase-Independent Oligodendrocyte Death Mediated by AMPA and Kainate Receptors
Authors: Sánchez-Gómez María Victoria , Alberdi Elena , Ibarretxe Gaskon , Torre Iratxe , Matute Carlos
Published: April 2018

Oligodendrocytes are vulnerable to excitotoxic signals mediated by AMPA receptors and by high- and low-affinity kainate receptors. Here we investigated the nature of the cell death triggered by activation of these receptors in primary cultures of oligodendrocytes from the rat optic nerve. Activation of AMPA receptors at both submaximal and maximal concentrations of the agonist induced massive calcium entry, mitochondrial depolarization, and a rise in the level of reactive oxygen species that correlated with a decrease in the levels of reduced glutathione. In addition, excitotoxicity initiated by submaximal, but not maximal, activation of AMPA receptors was prevented by caspase-3 blockade and by the concomitant blockade of caspases 8 and 9. In turn, maximal activation of high- or low-affinity kainate receptors induced mitochondrial events and toxicity levels similar to those observed with submaximal activation of AMPA receptors. In contrast to AMPA receptor-mediated insults, calcineurin inhibition or caspase-9 blockade was sufficient to prevent cell death triggered by both types of kainate receptors. Consistent with these results, prolonged glutamate receptor activation in freshly isolated optic nerves caused selective activation of caspase-3 and chromatin condensation in oligodendrocytes. Overall, the evidence presented here indicates that oligodendrocyte death by excitotoxicity is mediated by caspase-dependent and -independent mechanisms.
Rapid Signaling of Estrogen in Hypothalamic Neurons Involves a Novel G-Protein-Coupled Estrogen Receptor that Activates Protein Kinase C
Authors: Qiu Jian , Bosch Martha A. , Tobias Sandra C. , Grandy David K. , Scanlan Thomas S. , Rønnekleiv Oline K. , Kelly Martin J.
Published: April 2018

Classically, 17β-estradiol (E2) is thought to control homeostatic functions such as reproduction, stress responses, feeding, sleep cycles, temperature regulation, and motivated behaviors through transcriptional events. Although it is increasingly evident that E2can also rapidly activate kinase pathways to have multiple downstream actions in CNS neurons, the receptor(s) and the signal transduction pathways involved have not been identified. We discovered that E2can alter μ-opioid and GABA neurotransmission rapidly through nontranscriptional events in hypothalamic GABA, proopiomelanocortin (POMC), and dopamine neurons. Therefore, we examined the effects of E2in these neurons using whole-cell recording techniques in ovariectomized female guinea pigs. E2reduced rapidly the potency of the GABABreceptor agonist baclofen to activate G-protein-coupled, inwardly rectifying K+channels in hypothalamic neurons. These effects were mimicked by the membrane impermeant E2-BSA and selective estrogen receptor modulators, including a new diphenylacrylamide compound, STX, that does not bind to intracellular estrogen receptors α or β, suggesting that E2acts through a unique membrane receptor. We characterized the coupling of this estrogen receptor to a Gαq-mediated activation of phospholipase C, leading to the upregulation of protein kinase Cδ and protein kinase A activity in these neurons. Moreover, using single-cell reverse transcription-PCR, we identified the critical transcripts, PKCδ and its downstream target adenylyl cyclase VII, for rapid, novel signaling of E2in GABA, POMC, and dopamine neurons. Therefore, this unique Gq-coupled estrogen receptor may be involved in rapid signaling in hypothalamic neurons that are critical for normal homeostatic functions.
Ontogeny of the Pre-Bötzinger Complex in Perinatal Rats
Authors: Pagliardini Silvia , Ren Jun , Greer John J.
Published: April 2018

The aim of this study was to provide a systematic examination of the ontogenesis of the mammalian respiratory rhythm generating center, the pre-Bötzinger complex (pre-BötC). A combination of immunohistochemical markers and electrophysiological recordings was used to determine the time of inception of the pre-BötC and the developmental changes during the perinatal period in rats spanning from embryonic day 15 (E15) to postnatal day 7. The first clear indication of neurons immunopositive for neurokinin-1 receptors (NK1Rs) and somatostatin expression, two proposed markers for pre-BötC neurons, was at ∼E17. Birth dating of neurons in the ventrolateral medulla using 5-bromo-2′-deoxyuridine demonstrated that NK1R-positive neurons populating the area of the pre-BötC during late E16-E18 are born at E12.5-E13.5, ∼2 d later than adjacent NK1R-positive neurons in the ventrolateral medulla. Extracellular recordings of neuronal populations within the pre-BötC of perinatal medullary slice preparations demonstrated that the onset of rhythmical respiratory discharge commences at ∼E17. Application of substance P, a ligand for NK1R receptors, to the media bathing E17 medullary slice and brainstem-spinal cord preparations resulted in a marked increase in respiratory frequency. These data provide insights into the ontogeny of the pre-BötC, giving fundamental information on the genesis, settlement, and inception of rhythmic activity within the group of neurons proposed to be responsible for the respiratory rhythm generation. Furthermore, this provides the foundation for further analyses of cell lineage, the transcriptional control of respiratory neuronal development, and electrophysiological and pharmacological properties of the pre-BötC during the prenatal period.
GLR-1, a Non-NMDA Glutamate Receptor Homolog, Is Critical for Long-Term Memory inCaenorhabditis elegans
Authors: Rose Jacqueline K. , Kaun Karla R. , Chen Sylvia H. , Rankin Catharine H.
Published: April 2018

Long-term memory for habituation to tap inCaenorhabditis elegansdepends onglr-1, a homolog of mammalian non-NMDA glutamate receptors; mutations inglr-1blocked long-term memory formation. Green fluorescent protein (GFP) constructs were used to visualizeglr-1expression in the interneurons of the mechanosensory circuit and synaptobrevin in the tap sensory neurons of trained and untrained worms. Trained animals had less GLR-1::GFP expression than untrained animals; there was no difference in the vesicle marker synaptobrevin. Heat shock during training blocked both the behavioral expression of long-term memory and the change in GLR-1::GFP expression. Thus, long-term memory inC. elegansis dependent onglr-1and likely involves changes in the expression or localization of glutamate receptors.