bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid Regulation of Brain-Derived Neurotrophic Factor mRNA within Eye-Specific Circuits during Ocular Dominance Column Formation
Authors: Lein Edward S. , Shatz Carla J.
Published: April 2018

The neurotrophin brain-derived neurotrophic factor (BDNF) has emerged as a candidate retrograde signaling molecule for geniculocortical axons during the formation of ocular dominance columns. Here we examined whether neuronal activity can regulate BDNF mRNA in eye-specific circuits in the developing cat visual system. Dark-rearing throughout the critical period for ocular dominance column formation decreases levels of BDNF mRNA within primary visual cortex, whereas short-term (2 d) binocular blockade of retinal activity with tetrodotoxin (TTX) downregulates BDNF mRNA within the lateral geniculate nucleus (LGN) and visual cortical areas. Brief (6 hr to 2 d) monocular TTX blockade during the critical period and also in adulthood causes downregulation in appropriate eye-specific laminae in the LGN and ocular dominance columns within primary visual cortex. Monocular TTX blockade at postnatal day 23 also downregulates BDNF mRNA in a periodic fashion, consistent with recent observations that ocular dominance columns can be detected at these early ages by physiological methods. In contrast, 10 d monocular TTX during the critical period does not cause a lasting decrease in BDNF mRNA expression in columns pertaining to the treated eye, consistent with the nearly complete shift in physiological response properties of cortical neurons in favor of the unmanipulated eye known to result from long-term monocular deprivation. These observations demonstrate that BDNF mRNA levels can provide an accurate “molecular readout” of the activity levels of cortical neurons and are consistent with a highly local action of BDNF in strengthening and maintaining active synapses during ocular dominance column formation.
Gap Junctions Linking the Dendritic Network of GABAergic Interneurons in the Hippocampus
Authors: Fukuda Takaichi , Kosaka Toshio
Published: April 2018

The network of GABAergic interneurons connected by chemical synapses is a candidate for the generator of synchronized oscillations in the hippocampus. We present evidence that parvalbumin (PV)-containing GABAergic neurons in the rat hippocampal CA1 region, known to form a network by mutual synaptic contacts, also form another network connected by dendrodendritic gap junctions. Distal dendrites of PV neurons run parallel to the alveus (hippocampal white matter) and establish multiple contacts with one another at the border between the stratum oriens and the alveus. In electron microscopic serial section analysis, gap junctions could be identified clearly at 24% of these contact sites. A dendrodendritic chemical synapse and a mixed synapse also were found between PV-immunoreactive dendrites. Three-dimensional reconstruction of the dendritic arborization revealed that both PV neurons of the well known vertical type (presumptive basket cells and axoaxonic cells) and those of another horizontal type constitute the dendritic network at the light microscopic level. The extent of dendritic fields of single PV neurons in the lateral direction was 538 ± 201 μm (n= 5) in the vertical type and 838 ± 159 μm (n= 6) in the horizontal type. Our previous and present observations indicate that PV-containing GABAergic neurons in the hippocampus form the dual networks connected by chemical and electrical synapses located at axosomatic and dendrodendritic contact sites, respectively. Gap junctions linking the dendritic network may mediate coherent synaptic inputs to distant interneurons and thereby facilitate the synchronization of oscillatory activities generated in the interneuron network.
Implications of All-or-None Synaptic Transmission and Short-Term Depression beyond Vesicle Depletion: A Computational Study
Authors: Matveev Victor , Wang Xiao-Jing
Published: April 2018

The all-or-none character of transmission at central synapses is commonly viewed as evidence that only one vesicle can be released per action potential at a single release site. This interpretation is still a matter of debate; its resolution is important for our understanding of the nature of quantal response. In this work we explore observable consequences of the univesicular release hypothesis by studying a stochastic model of synaptic transmission. We investigated several alternative mechanisms for the all-or-none response: (1) the univesicular release constraint realized through lateral inhibition across presynaptic membrane, (2) the constraint of a single releasable vesicle per active zone, and (3) the postsynaptic receptor saturation.

We show that both the univesicular release constraint and the postsynaptic receptor saturation lead to a limited amount of depression by vesicle depletion, so that depletion alone cannot account for the strong paired-pulse depression observed at some cortical synapses. Although depression can be rapid if there is only one releasable vesicle per active zone, this scenario leads to a limit on the transmission probability. We evaluate additional mechanisms beyond vesicle depletion, and our results suggest that the strong paired-pulse depression may be a result of activity-dependent inactivation of the exocytosis machinery.

Furthermore, we found that the statistical analysis of release events, in response to a long stimulus train, might allow one to distinguish experimentally between univesicular and multivesicular release scenarios. We show that without the univesicular release constraint, the temporal correlation between release events is always negative, whereas it is typically positive with such a constraint if the vesicle fusion probability is sufficiently large.
Neural Sensitivity to Interaural Time Differences: Beyond the Jeffress Model
Authors: Fitzpatrick Douglas C. , Kuwada Shigeyuki , Batra Ranjan
Published: April 2018

Interaural time differences (ITDs) are a major cue for localizing the azimuthal position of sounds. The dominant models for processing ITDs are based on the Jeffress model and predict neurons that fire maximally at a common ITD across their responsive frequency range. Such neurons are indeed found in the binaural pathways and are referred to as “peak-type.” However, other neurons discharge minimally at a common ITD (trough-type), and others do not display a common ITD at the maxima or minima (intermediate-type). From recordings of neurons in the auditory cortex of the unanesthetized rabbit to low-frequency tones and envelopes of high-frequency sounds, we show that the different response types combine to form a continuous axis of best ITD. This axis extends to ITDs well beyond that allowed by the head width. In Jeffress-type models, sensitivity to large ITDs would require neural delay lines with large differences in path lengths between the two ears. Our results suggest instead that sensitivity to large ITDs is created with short delay lines, using neurons that display intermediate- and trough-type responses. We demonstrate that a neuron's best ITD can be predicted from (1) its characteristic delay, a rough measure of the delay line, (2) its characteristic phase, which defines the response type, and (3) its best frequency for ITD sensitivity. The intermediate- and trough-type neurons that have large best ITDs are predicted to be most active when sounds at the two ears are decorrelated and may transmit information about auditory space other than sound localization.
NMDA-Dependent Modulation of Hippocampal Kainate Receptors by Calcineurin and Ca2+/Calmodulin-Dependent Protein Kinase
Authors: Ghetti Andrea , Heinemann Stephen F.
Published: April 2018

Neurotransmitter receptor function can be influenced by the phosphorylation state of the receptor or of associated proteins. Here we show that kainate receptors expressed in cultured hippocampal neurons can be modulated by Ca2+/calmodulin-dependent phosphatase (calcineurin) and Ca2+/calmodulin-dependent kinase (CaMK). Ca2+influx through NMDA receptor or voltage-sensitive calcium channels resulted in a transient depression of the kainate receptor current. This calcium-induced depression of the kainate receptor current depended on the activation of the phosphatase calcineurin. The amplitude of the kainate receptor currents returned to the baseline level in ∼9 sec (τ = 3.6 sec), and the recovery of the current amplitude depended on CaMK activity. The effect on kainate receptor currents was dependent on the frequency of NMDA receptor activation. Although low-frequency (0.1 Hz) NMDA application induced depression followed by recovery of the kainate receptor currents, higher frequency (1 Hz) NMDA applications induced a more prolonged depression. Kainate receptors have been shown to modulate synaptic transmission by both presynaptic and postsynaptic mechanisms. Our results suggest that synaptic activity mediated by NMDA receptors, or other routes of Ca2+influx, may, in turn, modulate the function of kainate receptors.
Do Phosphatidylinositides Modulate Vertebrate Phototransduction?
Authors: Womack Kyle B. , Gordon Sharona E. , He Feng , Wensel Theodore G. , Lu Chin-Chi , Hilgemann Donald W.
Published: April 2018

Mammalian rod cyclic nucleotide gated (CNG) channels (i.e., α plus β subunits) are strongly inhibited by phosphatidylinositol 4,5-bisphosphate (PIP2) when they are expressed inXenopusoocytes and studied in giant membrane patches. Cytoplasmic Mg-ATP inhibits CNG currents similarly, and monoclonal antibodies to PIP2reverse the effect and hyperactivate currents. When α subunits are expressed alone, PIP2inhibition is less strong; olfactory CNG channels are not inhibited. In giant patches from rod outer segments, inhibition by PIP2is intermediate. Other anionic lipids (e.g., phosphatidyl serine and phosphatidic acid), a phosphatidylinositol-specific phospholipase C, and full-length diacylglycerol have stimulatory effects. Although ATP also potently inhibits cGMP-activated currents in rod patches, the following findings indicate that ATP is used to transphosphorylate GMP, generated from cGMP, to GTP. First, a phosphodiesterase (PDE) inhibitor, Zaprinast, blocks inhibition by ATP. Second, inhibition can be rapidly reversed by exogenous regulator of G-protein signaling 9, suggesting G-protein activation by ATP. Third, the reversal of ATP effects is greatly slowed when cyclic inosine 5′-monophosphate is used to activate currents, as expected for slow inosine 5′ triphosphate hydrolysis by G-proteins. Still, other results remain suggestive of regulatory roles for PIP2. First, the cGMP concentration producing half-maximal CNG channel activity (K1/2) is decreased by PIP2antibody in the presence of PDE inhibitors. Second, the activation of PDE activity by several nucleotides, monitored electrophysiologically and biochemically, is reversed by PIP2antibody. Third, exogenous PIP2can enhance PDE activation by nucleotides.
The Cytosolic Antioxidant Copper/Zinc-Superoxide Dismutase Prevents the Early Release of Mitochondrial Cytochrome c in Ischemic Brain after Transient Focal Cerebral Ischemia in Mice
Authors: Fujimura Miki , Morita-Fujimura Yuiko , Noshita Nobuo , Sugawara Taku , Kawase Makoto , Chan Pak H.
Published: April 2018

Release of mitochondrial cytochrome c into the cytosol is a critical step in apoptosis. We have reported that early release of cytochrome cin vivooccurs after permanent focal cerebral ischemia (FCI) and is mediated by the mitochondrial antioxidant manganese superoxide dismutase (SOD). However, the role of reactive oxygen species produced after ischemia–reperfusion in the mitochondrial apoptosis process is still unknown, although overexpression of copper/zinc-SOD (SOD1), a cytosolic isoenzyme, protects against ischemia–reperfusion. We now hypothesize that the overexpression of SOD1 also prevents apoptosis after FCI. To address this issue, we examined the subcellular distribution of the cytochrome c protein in both wild-type mice and in SOD1 transgenic (Tg) mice after transient FCI. Cytosolic cytochrome c was detected as early as 2 hr after reperfusion, and correspondingly, mitochondrial cytochrome c was significantly reduced after FCI. Cytosolic cytochrome c was significantly lower in the SOD1 Tg mice compared with wild types 2 (p< 0.0001) and 4 (p< 0.05) hr after FCI. Apaf-1, which interacts with cytochrome c and activates caspases, was constitutively expressed in both groups of animals, with no alteration after FCI. Double staining with cytochrome c immunohistochemistry and terminal deoxynucleotidyl transferase-mediated uridine 5′-triphosphate-biotin nick end labeling showed a spatial relationship between cytosolic cytochrome c expression and DNA fragmentation. A significant amount of DNA laddering was detected 24 hr after ischemia and was reduced in SOD1 Tg mice. These data suggest that SOD1 blocks cytosolic release of cytochrome c and could thereby reduce apoptosis after transient FCI.
Geranylgeranyl-Pyrophosphate, an Isoprenoid of Mevalonate Cascade, Is a Critical Compound for Rat Primary Cultured Cortical Neurons to Protect the Cell Death Induced by 3-Hydroxy-3-Methylglutaryl-CoA Reductase Inhibition
Authors: Tanaka Tomoaki , Tatsuno Ichiro , Uchida Daigaku , Moroo Iku , Morio Hiroshi , Nakamura Susumu , Noguchi Yoshihiko , Yasuda Tatsuji , Kitagawa Masatoshi , Saito Yasushi , Hirai Aizan
Published: April 2018

We investigated the role of the intrinsic mevalonate cascade in the neuronal cell death (NCD) induced by the inhibition of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase in rat primary cortical neurons cultured from the brains of 17-d-old fetal SD rats. HMG-CoA reductase inhibitors induced NCD [HMG-CoA reductase inhibitor-induced NCD (H-NCD)] in time- and dose-dependent manners. The apoptotic characteristics were revealed by the formation of the DNA ladder and by the electron microscopical observation. During the progression of H-NCD, p53 was induced followed by the expression of Bax. Although the mevalonate completely inhibited H-NCD, the cholesterol did not. Thus, we examined two major metabolites of mevalonate, geranylgeranyl-pyrophosphate (GGPP) and farnesyl-pyrophosphate (FPP), using a novel liposome system for uptake into the cells. GGPP, not FPP, prohibited H-NCD with inhibition of the induction of p53 and Bax. The inhibition of HMG-CoA reductase decreased the amount of membrane-associated Rho small GTPase families, but not Ras small GTPase, and GGPP restored the blockage by HMG-CoA reductase inhibitor in the translocation or redistribution of Rho small GTPase families to membrane. These data indicated that (1) the inhibition of the intrinsic mevalonate cascade induces the apoptotic NCD with the induction of p53 followed by that of Bax, (2) the inhibition of HMG-CoA reductase concomitantly causes blockage of the translocation or redistribution of Rho small GTPase families, not Ras small GTPase, to membrane, and (3) GGPP, not FPP, is one of the essential metabolites in the mevalonate cascade for protecting neurons from H-NCD.
Calmodulin-Binding Peptide PEP-19 Modulates Activation of Calmodulin Kinase IIIn Situ
Authors: Johanson Roy A. , Sarau Henry M. , Foley James J. , Slemmon J. Randall
Published: April 2018

PEP-19 is a 6 kDa polypeptide that is highly expressed in select populations of neurons that sometimes demonstrate resistance to degeneration. These include the granule cells of the hippocampus and the Purkinje cells of the cerebellum. Its only identified activity to date is that of binding apo-calmodulin. As a consequence, it has been demonstrated to act as an inhibitor of calmodulin-dependent neuronal nitric oxide synthasein vitro, although PEP-19 regulation of calmodulin-dependent enzymes has never been characterized in intact cells. The activation of the calmodulin-dependent enzyme calmodulin kinase II (CaM kinase II) was studied in PC12 cells that had been transfected so as to express physiological levels of PEP-19. The expression of PEP-19 yielded a stable phenotype that failed to activate CaM kinase II upon depolarization in high K+. However, CaM kinase II could be fully activated when calcium influx was achieved with ATP. The effect of PEP-19 on CaM kinase II activation was not attributable to changes in the cellular expression of calmodulin. The cellular permeability of the transfected cells to calcium ions also appeared essentially unchanged. The results of this study demonstrated that PEP-19 can regulate CaM kinase IIin situin a manner that was dependent on the stimulus used to mobilize calcium. The selective nature of the regulation by PEP-19 suggests that its function is not to globally suppress calmodulin activity but rather change the manner in which different stimuli can access this activity.
Heteromeric Assembly of GABABR1 and GABABR2 Receptor Subunits Inhibits Ca2+Current in Sympathetic Neurons
Authors: Filippov Alexander K. , Couve Andrés , Pangalos Menelas N. , Walsh Frank S. , Brown David A. , Moss Stephen J.
Published: April 2018

Neuronal GABABreceptors regulate calcium and potassium currents via G-protein-coupled mechanisms and play a critical role in long-term inhibition of synaptic transmission in the CNS. Recent studies have demonstrated that assembly of GABABreceptor GABABR1 and GABABR2 subunits into functional heterodimers is required for coupling to potassium channels in heterologous systems. However whether heterodimerization is required for the coupling of GABABreceptors to effector systems in neurons remains to be established. To address this issue, we have studied the coupling of recombinant GABABreceptors to endogenous Ca2+channels in superior cervical ganglion (SCG) neurons using nuclear microinjection to introduce both sense and antisense expression constructs. Patch-clamp recording from neurons injected with both GABABR1a/1b and GABABR2 cDNAs or with GABABR2 alone produced marked baclofen-mediated inhibition of Ca2+channel currents via apertussistoxin-sensitive mechanism. The actions of baclofen were blocked by CGP62349, a specific GABABantagonist, and were voltage dependent. Interestingly, SCGs were found to express abundantly GABABR1 but not GABABR2 at the protein level. To determine whether heterodimerization of GABABR1 and GABABR2 subunits was required for Ca2+inhibition, the GABABR2 expression construct was microinjected with a GABABR1 antisense construct. This resulted in a dramatic decrease in the levels of the endogenous GABABR1 protein and a marked reduction in the inhibitory effects of baclofen on Ca2+currents. Therefore our results suggest that in neurons heteromeric assemblies of GABABR1 and GABABR2 are essential to mediate GABAergic inhibition of Ca2+channel currents.
Trk C Signaling Is Required for Retinal Progenitor Cell Proliferation
Authors: Das Indranil , Sparrow Janet R. , Lin Michelle I. , Shih Evangeline , Mikawa Takashi , Hempstead Barbara L.
Published: April 2018

Although neurotrophin actions in the survival of specific retinal cell types have been identified, the biological functions for neurotrophin-3 (NT-3) in early retinal development remain unclear. Having localized NT-3 and trk C expression at early developmental stages when retinal neuroepithelial progenitor cells predominate, we sought to modulate NT-3 signaling in these cells by overexpressing a truncated isoform of the NT-3 receptor, trk C. We have demonstrated that this non-catalytic receptor can inhibit NT-3 signaling when coexpressed with the full-length kinase-active trk C receptor. Using a replication-deficient retrovirus to ectopically express the truncated trk C receptor to limited numbers of progenitor cellsin ovo, we examined the effects of disrupted trk C signaling on the proliferation or differentiation of retinal cells. Clones expressing truncated trk C exhibited a 70% reduction in clone size, compared with clones infected with a control virus, indicating that inhibition of trk C signaling decreased the clonal expansion of cells derived from a single retinal progenitor cell. Additionally, impaired NT-3 signaling resulted in a reduction of all retinal cell types, suggesting that NT-3 targets retinal precursor cells rather than differentiated cell types. BrdU labeling studies performed at E6 indicate that this reduction in cell number occurs through a decrease in cell proliferation. These studies suggest that NT-3 is an important mitogen early in retinal development and serves to establish the size of the progenitor pool from which all future differentiated cells arise.
GABAergic Inhibition in Nucleus Magnocellularis: Implications for Phase Locking in the Avian Auditory Brainstem
Authors: Monsivais Pablo , Yang Lichuan , Rubel Edwin W
Published: April 2018

In the avian auditory brainstem, nucleus magnocellularis (NM) functions to relay phase-locked signals to nucleus laminaris for binaural coincidence detection. Although many studies have revealed that NM neurons exhibit intrinsic physiological and anatomical specializations for this purpose, the role of inhibition has not been fully explored. The present study characterizes the organization of GABAergic feedback to NM. Anterograde and retrograde labeling methods showed that NM receives a prominent projection from the ipsilateral superior olivary nucleus (SON). The functional features of this projection were explored in a brain slice preparation. Stimulating fibers from the SON evoked long-lasting, depolarizing responses in NM neurons that were blockable by bicuculline, a GABAAreceptor antagonist. The slow time course of these responses allowed them to undergo temporal summation during repetitive stimulation. The summed GABAergic response was capable of blocking spikes generated in NM neurons by suprathreshold current injection. This inhibitory effect was attributable to a large reduction in input resistance caused by a combination of the opening of a GABAergic Cl−conductance and the recruitment of a low-voltage activated K+conductance. This large reduction of input resistance increased the amount of current necessary to drive NM neurons to threshold. The results lead us to propose that GABAergic inhibition enhances phase-locking fidelity of NM neurons, which is essential to binaural coincidence detection in nucleus laminaris.
Neural Activity Relating to Generation and Representation of Galvanic Skin Conductance Responses: A Functional Magnetic Resonance Imaging Study
Authors: Critchley Hugo D. , Elliott Rebecca , Mathias Christopher J. , Dolan Raymond J.
Published: April 2018

Central feedback of peripheral states of arousal influences motivational behavior and decision making. The sympathetic skin conductance response (SCR) is one index of autonomic arousal. The precise functional neuroanatomy underlying generation and representation of SCR during motivational behavior is undetermined, although it is impaired by discrete brain lesions to ventromedial prefrontal cortex, anterior cingulate, and parietal lobe. We used functional magnetic resonance imaging to study brain activity associated with spontaneous fluctuations in amplitude of SCR, and activity corresponding to generation and afferent representation of discrete SCR events. Regions that covaried with increased SCR included right orbitofrontal cortex, right anterior insula, left lingual gyrus, right fusiform gyrus, and left cerebellum. At a less stringent level of significance, predicted areas in bilateral medial prefrontal cortex and right inferior parietal lobule covaried with SCR. Generation of discrete SCR events was associated with significant activity in left medial prefrontal cortex, bilateral extrastriate visual cortices, and cerebellum. Activity in right medial prefrontal cortex related to afferent representation of SCR events. Activity in bilateral medial prefrontal lobe, right orbitofrontal cortex, and bilateral extrastriate visual cortices was common to both generation and afferent representation of discrete SCR events identified in a conjunction analysis. Our results suggest that areas implicated in emotion and attention are differentially involved in generation and representation of peripheral SCR responses. We propose that this functional arrangement enables integration of adaptive bodily responses with ongoing emotional and attentional states of the organism.
Enhanced Inhibition of Synaptic Transmission by Dopamine in the Nucleus Accumbens during Behavioral Sensitization to Cocaine
Authors: Beurrier Corinne , Malenka Robert C.
Published: April 2018

Neural adaptations in the nucleus accumbens (NAc), a key component of the mesolimbic dopamine (DA) system, are thought to mediate several of the long-term behavioral sequelas of chronicin vivoexposure to drugs of abuse. Here, we examine whether the modulation of excitatory synaptic transmission by DA in the NAc shell is modified after chronic cocaine exposure that induced behavioral sensitization. The DA-induced inhibition of AMPA receptor-mediated synaptic responses was enhanced in cocaine-treated mice, an effect that was caused by activation of D1-like receptors. DA did not enhance NMDA receptor-mediated synaptic responses in saline- and cocaine-treated mice or in the dorsal striatum of control mice. We hypothesize that the enhanced inhibitory effects of DA on synaptic transmission in the NAc are one of a number of adaptations that contribute to a decrease in excitatory drive to NAc after exposure to drugs of abuse.
Limbic Seizures Induce P-Glycoprotein in Rodent Brain: Functional Implications for Pharmacoresistance
Authors: Rizzi Massimo , Caccia Silvio , Guiso Giovanna , Richichi Cristina , Gorter Jan A. , Aronica Eleonora , Aliprandi Marisa , Bagnati Renzo , Fanelli Roberto , D'Incalci Maurizio , Samanin Rosario , Vezzani Annamaria
Published: April 2018

The causes and mechanisms underlying multidrug resistance (MDR) in epilepsy are still elusive and may depend on inadequate drug concentration in crucial brain areas. We studied whether limbic seizures or anticonvulsant drug treatments in rodents enhance the brain expression of the MDR gene (mdr) encoding a permeability glycoprotein (P-gp) involved in MDR to various cancer chemotherapeutic agents. We also investigated whether changes in P-gp levels affect anticonvulsant drug concentrations in the brain.MdrmRNA measured by RT-PCR increased by 85% on average in the mouse hippocampus 3–24 hr after kainic acid-induced limbic seizures, returning to control levels by 72 hr. Treatment with therapeutic doses of phenytoin or carbamazepine for 7 d did not changemdrmRNA expression in the mouse hippocampus 1–72 hr after the last drug administration. Six hours after seizures, the brain/plasma ratio of phenytoin was reduced by 30% and its extracellular concentration estimated by microdialysis was increased by twofold compared with control mice. Knock-out mice (mdr1a/b −/−) lacking P-gp protein showed a 46% increase in phenytoin concentrations in the hippocampus 1 and 4 hr after injection compared with wild-type mice. A significant 23% increase was found in the cerebellum at 1 hr and in the cortex at 4 hr. Carbamazepine concentrations were measurable in the hippocampus at 3 hr inmdr1a/b −/− mice, whereas they were undetectable at the same time interval in wild-type mice. In rats having spontaneous seizures 3 months after electrically induced status epilepticus,mdr1mRNA levels were enhanced by 1.8-fold and fivefold on average in the hippocampus and entorhinal cortex, respectively. Thus, changes in P-gp mRNA levels occur in limbic areas after both acute and chronic epileptic activity. P-gp alterations significantly affect antiepileptic drugs concentrations in the brain, suggesting that seizure-inducedmdrmRNA expression contributes to MDR in epilepsy.
Neurofilament-M Interacts with the D1Dopamine Receptor to Regulate Cell Surface Expression and Desensitization
Authors: Kim Ok-Jin , Ariano Marjorie A. , Lazzarini Robert A. , Levine Michael S. , Sibley David R.
Published: April 2018

We used the yeast two-hybrid assay to identify novel proteins that interact with the D1dopamine receptor. The third cytoplasmic loop (residues 217–273) of the rat D1receptor was used as bait to identify clones encoding interacting proteins from a rat brain cDNA library. This identified two clones encoding the C terminus of rat neurofilament-M (NF-M) (residues 782–846). The NF-M clone did not interact with the third cytoplasmic loops of the rat D2, D3, or D4receptors, but showed weak interaction with that of the D5receptor. Coexpression of full-length NF-M with the D1receptor in HEK-293 cells resulted in >50% reduction of receptor binding accompanied by a reduction in D1receptor-mediated cAMP accumulation. NF-M had no effect on the expression of other dopamine receptor subtypes. Using a D1receptor-green fluorescent protein chimera and confocal fluorescence microscopy, we found that NF-M reduced D1receptor expression at the cell surface and promoted accumulation of the receptor in the cytosol. Interestingly, the D1receptors that were expressed at the cell surface in the presence of NF-M were resistant to agonist-induced desensitization. Cellular colocalization of NF-M and the D1receptor in the rat brain was examined by epifluorescence microscopy. These experiments showed that ∼50% of medium-sized striatal neurons expressed both proteins. Colocalization was also observed in pyramidal cells and interneurons within the frontal cortex. Similar immunohistochemical analyses using NF-M-deficient mice showed decrements in D1receptor expression compared with control mice. These results suggest that NF-M interacts with the D1receptorin vivoand may modify its expression and regulation.
Synchronous Neuronal Activity Is a Signal for Axonal Sprouting after Cortical Lesions in the Adult
Authors: Carmichael S. Thomas , Chesselet Marie-Françoise
Published: April 2018

The ability of the adult brain to form new connections in areas denervated by a lesion (axonal sprouting) is more widespread than previously thought, but mechanisms remain unknown. We have previously demonstrated an unexpected, robust axonal sprouting of contralateral corticostriatal neurons into the denervated striatum after ischemic cortical lesions. We now take advantage of marked differences in the degree of axonal sprouting from contralateral homotypic cortex after two types of cortical lesions to define the role of neuronal activity in this response. Thermal–ischemic lesions (TCL) of sensorimotor cortex, which induce axonal sprouting, produced two sequential patterns of low-frequency, synchronized neuronal activity that are not seen after similarly sized aspiration lesions, which do not induce axonal sprouting. An early rhythm of synchronous neuronal activity occurred in perilesion cortex on day 1 after lesion, with a frequency range of 0.2–2 Hz. A later pattern of activity occurred on days 2 and 3 after lesion, with a frequency range of 0.1–0.4 Hz. This second rhythm synchronized neuronal activity across widespread areas, including the cortical areas that contain the cell bodies of the sprouting axons. TTX was used to block this patterned neuronal activity and determine whether axonal sprouting was prevented. Chronic TTX infusion into the lesion site blocked the synchronous neuronal activity after TCL as well as axonal sprouting. Thus, both after different types of lesions and in the blockade experiments axonal sprouting was strongly correlated with synchronous neuronal activity, suggesting a role for this activity in anatomical reorganization after brain lesion in the adult.
Purified Adult Ensheathing Glia Fail to Myelinate Axons under Culture Conditions that Enable Schwann Cells to Form Myelin
Authors: Plant Giles W. , Currier Paul F. , Cuervo Ernesto P. , Bates Margaret L. , Pressman Yelena , Bunge Mary Bartlett , Wood Patrick M.
Published: April 2018

Several studies have suggested that olfactory ensheathing glia (EG) can form Schwann cell (SC)-like myelin. Because of possible misinterpretation attributable to contaminating SCs, the capacity of EG to produce myelin needs to be explored further. Therefore, we compared the abilities of adult EG, purified by immunopanning with p75 antibody, and adult SCs to produce myelin when cocultured with purified dorsal root ganglion neurons (DRGNs) in serum-free and serum-containing media. In both media formulations, the number of myelin sheaths in SC/DRGN cultures was far higher than in EG/DRGN cultures; the number of sheaths in EG/DRGN cultures was equal to that in purified DRGN cultures without added cells. The latter result demonstrates that myelination by a few SCs remaining in purified DRGN cultures may occur, suggesting that myelin in EG/DRGN cultures could be SC myelin. Striking differences in the relationship of EG and SC processes to axons were observed. Whereas SCs displayed relatively short, thick processes that engulfed axons in small bundles or in individual cytoplasmic furrows and segregated larger axons into one-to-one relationships, EG extended flattened sheets that partitioned or only partially encircled fascicles of axons, sometimes spanning the entire culture. SCs exhibited behavior typical of SCs in peripheral nerves, whereas EG exhibited characteristics resembling those of EG in olfactory nerves. In sum, p75-selected EG from adult animals did not exhibit an SC-like relationship to axons and did not form myelin.
Dendroarchitecture of Relay Cells in Thalamic Barreloids: A Substrate for Cross-Whisker Modulation
Authors: Varga Caroline , Sı́k Attila , Lavallée Philippe , Deschênes Martin
Published: April 2018

A double-labeling protocol was used to determine how the dendroarchitecture of relay cells relates to the three-dimensional structure of barreloids in the ventral posterior medial nucleus of the rat thalamus. Single barreloids were retrogradely labeled by injecting Fluoro-Gold in identified barrel columns, and single relay cells activated by the same whisker, or by an adjacent whisker located on the same arc, were juxtacellularly labeled with biotinylated dextran. Results show that the dendritic field of relay cells is asymmetric, variously oriented with respect to the geometry of the barreloids, and that all cells extend dendrites in surrounding barreloids. Extrabarreloid dendrites are of small size (<1.5 μm) and represent up to 54% (range, 11–54%) of the total dendritic length. In contrast, the thick proximal dendrites remain confined to the home barreloid of the cell, being directed toward its center or along its margin. There is a trend for cells located dorsally in barreloids to form more elaborate trees with a larger proportion of extrabarreloid dendrites. Electron microscopic examination of labeled cells shows that extrabarreloid dendrites are exclusively contacted by synaptic terminals of cortical and reticular thalamic origin, whereas intrabarreloid dendrites also receive contacts from lemniscal terminals. Because corticothalamic and reticular thalamic cells establish point-to-point connections with homotopic barreloids, it is proposed that the spatial arrangement of dendrites determines the combination of whisker deflection that best modulates cell firing. Because relay cell responses are direction sensitive, maximal modulation would occur if dendritic field orientation relates to the direction selectivity of responses.
Resolution of Sensory Ambiguities for Gaze Stabilization Requires a Second Neural Integrator
Authors: Green Andrea M. , Angelaki Dora E.
Published: April 2018

The ability to simultaneously move in the world and maintain stable visual perception depends critically on the contribution of vestibulo-ocular reflexes (VORs) to gaze stabilization. It is traditionally believed that semicircular canal signals drive compensatory responses to rotational head disturbances (rotational VOR), whereas otolith signals compensate for translational movements [translational VOR (TVOR)]. However, a sensory ambiguity exists because otolith afferents are activated similarly during head translations and reorientations relative to gravity (i.e., tilts). Extra-otolith cues are, therefore, necessary to ensure that dynamic head tilts do not elicit a TVOR. To investigate how extra-otolith signals contribute, we characterized the temporal and viewing distance-dependent properties of a TVOR elicited in the absence of a lateral acceleration stimulus to the otoliths during combined translational/rotational motion. We show that, in addition to otolith signals, angular head position signals derived by integrating sensory canal information drive the TVOR. A physiological basis for these results is proposed in a model with two distinct integration steps. Upstream of the well known oculomotor velocity-to-position neural integrator, the model incorporates a separate integration element that could represent the “velocity storage integrator,” whose functional role in the oculomotor system has so far remained controversial. We propose that a key functional purpose of the velocity storage network is to temporally integrate semicircular canal signals, so that they may be used to extract translation information from ambiguous otolith afferent signals in the natural and functionally relevant bandwidth of head movements.
Suppression of Adult Neurogenesis Impairs Olfactory Learning and Memory in an Adult Insect
Authors: Scotto-Lomassese Sophie , Strambi Colette , Strambi Alain , Aouane Aïcha , Augier Roger , Rougon Geneviève , Cayre Myriam
Published: April 2018

Although adult neurogenesis has now been demonstrated in many different species, the functional role of newborn neurons still remains unclear. In the house cricket, a cluster of neuroblasts, located in the main associative center of the insect brain, keeps producing new interneurons throughout the animal's life. Here we address the functional significance of adult neurogenesis by specific suppression of neuroblast proliferation using γ irradiation of the insect's head and by examining the impact on the insect's learning ability. Forty gray irradiation performed on the first day of adult life massively suppressed neuroblasts and their progeny without inducing any noticeable side effect. We developed a new operant conditioning paradigm especially designed for crickets: the “escape paradigm.” Using olfactory cues, visual cues, or both, crickets had to choose between two holes, one allowing them to escape and the other leading to a trap. Crickets lacking adult neurogenesis exhibited delayed learning when olfactory cues alone were used. Furthermore, retention 24 hr after conditioning was strongly impaired in irradiated crickets. By contrast, when visual cues instead of olfactory ones were provided, performance of irradiated insects was only slightly affected; when both olfactory and visual cues were present, their performance was not different from that of controls. From these results, it can be postulated that newborn neurons participate in the processing of olfactory information required for complex operant conditioning.
Altered Neuronal Excitability in Cerebellar Granule Cells of Mice Lacking Calretinin
Authors: Gall David , Roussel Céline , Susa Isabella , D'Angelo Egidio , Rossi Paola , Bearzatto Bertrand , Galas Marie Christine , Blum David , Schurmans Stéphane , Schiffmann Serge N.
Published: April 2018

Calcium-binding proteins such as calretinin are abundantly expressed in distinctive patterns in the CNS, but their physiological function remains poorly understood. Calretinin is expressed in cerebellar granule cells, which provide the major excitatory input to Purkinje cells through parallel fibers. Calretinin-deficient mice exhibit dramatic alterations in motor coordination and Purkinje cell firing recordedin vivothrough unknown mechanisms. In the present study, we used patch-clamp recording techniques in acute slice preparation to investigate the effect of a null mutation of the calretinin gene on the intrinsic electroresponsiveness of cerebellar granule cells at a mature developmental stage. Calretinin-deficient granule cells exhibit faster action potentials and generate repetitive spike discharge showing an enhanced frequency increase with injected currents. These alterations disappear when 0.15 mmof the exogenous fast-calcium buffer BAPTA is infused in the cytosol to restore the calcium-buffering capacity. A proposed mathematical model demonstrates that the observed alterations of granule cell excitability can be explained by a decreased cytosolic calcium-buffering capacity resulting from the absence of calretinin. This result suggests that calcium-binding proteins modulate intrinsic neuronal excitability and may therefore play a role in information processing in the CNS.
Activity-Dependent Plasticity of Transmitter Release from Nerve Terminals in Rat Fast and Slow Muscles
Authors: Reid Brian , Martinov Vladimir N. , Njå Arild , Lømo Terje , Bewick Guy S.
Published: April 2018

Neuromuscular junctions (NMJs) on fast and slow muscle fibers display different transmitter release characteristics that appear well adapted to the different patterns of nerve impulses that they transmitin vivo. Here, we ask whether the release properties of such NMJs, termed fast and slow, can be transformed by chronic nerve stimulation. In young adult rats, nerve impulse conduction in the sciatic nerve was blocked by TTX, and the nerve to the fast extensor digitorum longus (EDL) or the slow soleus (SOL) muscle stimulated directly below the block with slow (20 Hz for 10 sec every 30 sec) or fast (150 Hz for 1 sec every 60 sec) stimulus patterns, respectively. After 3-4 weeks, originally fast EDL-NMJs and slow SOL-NMJs had become almost fully transformed to slow and fast NMJs, respectively, with respect to maintenance of transmitter release during tonic 20 Hz stimulationin vitroand ratio of quantal content to vesicle pool size. TTX block alone had no such transforming effect. Vesicle recycle time was unaffected by the stimulation, whereas initial quantal content and vesicle pool size were reduced (by 49% and 57% in EDL and 33% and 67% in SOL). Muscle fiber diameter also declined (by 49% in EDL and 33% in SOL vs 46% in unstimulated SOL; unstimulated EDL was not examined). We conclude that fast and slow NMJs display marked plasticity by being able to adapt important release characteristics to the impulse patterns imposed on them.
ZNRF Proteins Constitute a Family of Presynaptic E3 Ubiquitin Ligases
Authors: Araki Toshiyuki , Milbrandt Jeffrey
Published: April 2018

Protein ubiquitination has been implicated recently in neural development, plasticity, and degeneration. We previously identified ZNRF1/nin283, a protein with a unique, evolutionarily conserved C-terminal domain containing a juxtaposed zinc finger/RING finger combination. Here we describe the identification of a closely related protein, ZNRF2, thus defining a novel family of ZNRF E3 ubiquitin ligases. Both ZNRF1 and ZNRF2 have E3 ubiquitin ligase activity and are highly expressed in the nervous system, particularly during development. In neurons, ZNRF proteins are located in different compartments within the presynaptic terminal: ZNRF1 is associated with synaptic vesicle membranes, whereas ZNRF2 is present in presynaptic plasma membranes. Mutant ZNRF proteins with a disrupted RING finger, a domain necessary for their E3 function, can each inhibit Ca2+-dependent exocytosis in PC12 cells. These data suggest that ZNRF proteins play a role in the establishment and maintenance of neuronal transmission and plasticity via their ubiquitin ligase activity.
Forebrain-Specific Neuronal Inhibition of Nuclear Factor-κB Activity Leads to Loss of Neuroprotection
Authors: Fridmacher Valérie , Kaltschmidt Barbara , Goudeau Bertrand , Ndiaye Delphine , Rossi Francesco Mattia , Pfeiffer Julia , Kaltschmidt Christian , Israël Alain , Mémet Sylvie
Published: April 2018

The transcription factor Rel/nuclear factor (NF)-κB is known for its fundamental role in regulating immune and inflammatory responses. In the brain, constitutive NF-κB activity has been detected exclusively in neurons, and a large diversity of stimuli have been reported to induce NF-κB activity. Yet the function of this transcription factor in the nervous system remains unclear, and its role in neuroprotection or neurodegeneration is open to debate. Recently it was suggested that κB-driven gene expression in neurons is controlled by Sp1-like factors. To clarify such controversy, we have characterized here a novel mouse model in which the entire NF-κB-dependent transcriptional response is abolished in the forebrain. Calcium-calmodulin-dependent kinase II α promoter-driven tetracycline transactivator was used for regulated expression of a transdominant negative mutant of inhibitor κBα (super-repressor) together with a green fluorescent protein tracer. Inhibition of expression of a κB-dependentlacZtransgene was shown in triple transgenic mice, which correlated with the loss of κB-specific DNA binding. In transgenic organotypic hippocampal slice cultures, expression of the super-repressor led to strong cell death after neurotoxic insults. These data demonstrate for the first time that neuron-restricted ablation of NF-κB-driven gene expression increases neurodegeneration. This might lead to the path for new treatments of neurodegenerative diseases.
A Region on Chromosome 15 Controls Intersession Habituation in Mice
Authors: Bolivar Valerie , Flaherty Lorraine
Published: April 2018

Habituation to a novel environment, as measured by a change in exploratory activity over time, can be measured both within (intrasession) and across (intersession) sessions. The role of genetics in intrasession habituation has been investigated previously in quantitative trait loci studies, but little attention has been focused on the role of genetics on intersession habituation. We reported recently that inbred strains respond differently in an intersession habituation test. By testing a total of 25 BXD recombinant inbred lines, we were able to map a chromosomal region that strongly influences the way in which mice habituate. This region located on chromosome 15 appears to the major one affecting habituation and accounts for 80% of the genetic variance. We subsequently confirmed this map position by testing (C57BL/6J × DBA/2J) F2mice.
Planar and Vertical Signals Control Cellular Differentiation and Patterning in the Mammalian Cochlea
Authors: Montcouquiol Mireille , Kelley Matthew W.
Published: April 2018

The sensory epithelium of the mammalian cochlea is composed of a regular mosaic of sensory hair cells and nonsensory supporting cells. During development, differentiation occurs in a gradient that progresses along the axis of the cochlea from base to apex. To begin to identify some of the factors that regulate this developmental process, the potential roles of planar and vertical signals were examined during early stages of cochlear development. We demonstrate roles for both underlying mesenchymal cells and adjacent epithelial cells in the differentiation and patterning of the sensory epithelium, and in particular in the development of mechanosensory hair cells. As development proceeds, the requirements for both planar and vertical signals decrease, and development of the sensory epithelium becomes essentially independent from these cues. Finally, we demonstrate that the temporal gradient of cellular differentiation is not dependent on planar signals within the developing sensory epithelium.
Touring Religion, Touring Ritual
Authors: Erdely Jennifer L.
Published: April 2018

Although tourism is considered leisure, tours can serve other means for the tour-participant. Tours can prompt memories of the past, and offer a framework for understanding our pasts. This essay uses touring as a metaphor and a mechanism of exploring our pasts to better understand our presence/present. Through autoethnographic methods, this essay examines tourism as ritual and explores rituals as a resource for making sense of painful pasts. Painful memories can pervade individuals’ minds, altering their perspective and understanding of events, interactions, and relationships. This essay demonstrates how tourism can help people overcoming the memories of sexual assault to find healing.