bluuebunny/crossref_metadata_2025 huggingface dataset:
Dysfunctions in Mice by NMDA Receptor Point Mutations NR1(N598Q) and NR1(N598R)
Authors: Single Frank N. , Rozov Andrei , Burnashev Nail , Zimmermann Frank , Hanley Daniel F. , Forrest Douglas , Curran Tom , Jensen Vidar , Hvalby Øivind , Sprengel Rolf , Seeburg Peter H.
Published: April 2018

NMDA receptors in mice were mutated by gene targeting to substitute asparagine (N) in position 598 of the NR1 subunit to glutamine (Q) or arginine (R). Animals expressing exclusively the mutatedNR1alleles,NR1Q/QandNR1−/Rmice, developed a perinatally lethal phenotype mainly characterized by respiratory failure. The dysfunctions were partially rescued in heterozygous mice by the presence of pure wild-type receptors. Thus,NR1+/Qmice exhibited reduced life expectancy, with females being impaired in nurturing;NR1+/Rmice displayed signs of underdevelopment such as growth retardation and impaired righting reflex, and died before weaning. We analyzed the key properties of NMDA receptors, high Ca2+permeability, and voltage-dependent Mg2+block, in the mutant mice. Comparison of the complex physiological and phenotypical changes observed in the different mutants indicates that properties controlled by NR1 subunit residue N598 are important for autonomic brain functions at birth and during postnatal development. We conclude that disturbed NMDA receptor signaling mediates a variety of neurological phenotypes.
Phenotypic Knockout of Nerve Growth Factor in Adult Transgenic Mice Reveals Severe Deficits in Basal Forebrain Cholinergic Neurons, Cell Death in the Spleen, and Skeletal Muscle Dystrophy
Authors: Ruberti Francesca , Capsoni Simona , Comparini Alessandro , Di Daniel Elena , Franzot Jessica , Gonfloni Stefania , Rossi Gabriella , Berardi Nicoletta , Cattaneo Antonino
Published: April 2018

The disruption of the nerve growth factor (NGF) gene in transgenic mice leads to a lethal phenotype (Crowley et al., 1994) and hinders the study of NGF functions in the adult. In this study the phenotypic knockout of NGF in adult mice was achieved by expressing transgenic anti-NGF antibodies, under the control of the human cytomegalovirus promoter. In adult mice, antibody levels are 2000-fold higher than in newborns. Classical NGF targets, including sympathetic and sensory neurons, are severely affected. In the CNS, basal forebrain and hippocampal cholinergic neurons are not affected in the early postnatal period, whereas they are greatly reduced in the adult (55 and 62% reduction, respectively). Adult mice show a reduced ability in spatial learning behavioral tasks. Adult, but not neonatal, transgenic mice further show a new phenotype at the level of peripheral tissues, such as apoptosis in the spleen and dystrophy of skeletal muscles. The analysis of this novel comprehensive transgenic model settles the controversial issue regarding the NGF dependence of cholinergic neurons in adult animals and reveals new NGF functions in adult non-neuronal tissues. The results demonstrate that the decreased availability of NGF in the adult causes phenotypic effects via processes that are at least partially distinct from early developmental effects of NGF deprivation.
Brief Electrical Stimulation Promotes the Speed and Accuracy of Motor Axonal Regeneration
Authors: Al-Majed Abdulhakeem A. , Neumann Catherine M. , Brushart Thomas M. , Gordon Tessa
Published: April 2018

Functional recovery is often poor despite the capacity for axonal regeneration in the peripheral nervous system and advances in microsurgical technique. Regeneration of axons in mixed nerve into inappropriate pathways is a major contributing factor to this failure. In this study, we use the rat femoral nerve model of transection and surgical repair to evaluate (1) the effect of nerve transection on the speed of regeneration and the generation of motor-sensory specificity, (2) the efficacy of electrical stimulation in accelerating axonal regeneration and promoting the reinnervation of appropriate muscle pathways by femoral motor nerves, and (3) the mechanism of action of electrical stimulation. Using the retrograde neurotracers fluorogold and fluororuby to backlabel motoneurons that regenerate axons into muscle and cutaneous pathways, we found the following. (1) There is a very protracted period (10 weeks) of axonal outgrowth that adds substantially to the delay in axonal regeneration (staggered regeneration). This process of staggered regeneration is associated with preferential motor reinnervation (PMR). (2) One hour to 2 weeks of 20 Hz continuous electrical stimulation of the parent axons proximal to the repair site dramatically reduces this period (to 3 weeks) and accelerates PMR. (3) The positive effect of short-term electrical stimulation is mediated via the cell body, implicating an enhanced growth program. The effectiveness of such a short-period low-frequency electrical stimulation suggests a new therapeutic approach to accelerate nerve regeneration after injury and, in turn, improve functional recovery.
The Transmembrane Protein Semaphorin 6A Repels Embryonic Sympathetic Axons
Authors: Xu Xiao-Mei , Fisher Daniel A. , Zhou Lijuan , White Fletcher A. , Ng Sheldon , Snider William D. , Luo Yuling
Published: April 2018

Semaphorin 6A (Sema6A) (previously named Semaphorin VIa) is the originally described member of the vertebrate semaphorin class 6, a group of transmembrane semaphorins homologous to the insect semaphorin class 1. Although Sema-1a (previously named semaphorin I) has been implicated in axon guidance in insects, the function of Sema6A is currently unknown. We have expressed the extracellular domain of Sema6A in mammalian cells as either a monomeric or a dimeric fusion protein and tested for potential axon guidance effects on two populations of embryonic neurons in growth cone collapse and collagen matrix chemorepulsion assays. Sema6A was observed to induce growth cone collapse of sympathetic neurons with an EC50 of ∼200 pm, although a 10-fold higher (EC50 of ∼2 nm) concentration was necessary to induce growth cone collapse of dorsal root ganglion neurons. The activity of Sema6A is likely to depend on protein dimerization or oligomerization. Although Sema6A mRNA is expressed in complex patterns during embryonic development, it is strikingly absent from sympathetic ganglia. Sema6A is, however, expressed in areas avoided by sympathetic axons and in areas innervated by sympathetics, but before their arrival. Our results demonstrate that transmembrane semaphorins, like the secreted ones, can act as repulsive axon guidance cues. Our findings are consistent with a role for Sema6A in channeling sympathetic axons into the sympathetic chains and controlling the temporal sequence of sympathetic target innervation.
Cortical Processing of Human Somatic and Visceral Sensation
Authors: Aziz Q. , Thompson D. G. , Ng V. W. K. , Hamdy S. , Sarkar S. , Brammer M. J. , Bullmore E. T. , Hobson A. , Tracey I. , Gregory L. , Simmons A. , Williams S. C. R.
Published: April 2018

Somatic sensation can be localized precisely, whereas localization of visceral sensation is vague, possibly reflecting differences in the pattern of somatic and visceral input to the cerebral cortex. We used functional magnetic resonance imaging to study the cortical processing of sensation arising from the proximal (somatic) and distal (visceral) esophagus in six healthy male subjects. Esophageal stimulation was performed by phasic distension of a 2 cm balloon at 0.5 Hz. For each esophageal region, five separate 30 sec periods of nonpainful distension were alternated with five periods of similar duration without distension. Gradient echoplanar images depicting bold contrast were acquired using a 1.5 T GE scanner. Distension of the proximal esophagus was localized precisely to the upper chest and was represented in the trunk region of the left primary somatosensory cortex. In contrast, distension of the distal esophagus was perceived diffusely over the lower chest and was represented bilaterally at the junction of the primary and secondary somatosensory cortices. Different activation patterns were also observed in the anterior cingulate gyrus with the proximal esophagus being represented in the right midanterior cingulate cortex (BA 24) and the distal esophagus in the perigenual area (BA32). Differences in the activation of the dorsolateral prefrontal cortex and cerebellum were also observed for the two esophageal regions. These findings suggest that cortical specialization in the sensory-discriminative, affective, and cognitive areas of the cortex accounts for the perceptual differences observed between the two sensory modalities.
A Positron Emission Tomographic Study of Auditory Localization in the Congenitally Blind
Authors: Weeks Robert , Horwitz Barry , Aziz-Sultan Ali , Tian Biao , Wessinger C. Mark , Cohen Leonardo G. , Hallett Mark , Rauschecker Josef P.
Published: April 2018

We have used positron emission tomography (PET) to measure regional cerebral blood flow (rCBF) in sighted and congenitally blind subjects performing auditory localization tasks. During scanning, the spectral and binaural cues of localized sound were reproduced by a sound system and delivered via headphones. During tasks that required auditory localization both the sighted and blind subjects strongly activated posterior parietal areas. In addition, the blind subjects activated association areas in the right occipital cortex, the foci of which were similar to areas previously identified in visual location and motion detection experiments in sighted subjects. The blind subjects, therefore, demonstrated visual to auditory cross-modal plasticity with auditory localization activating occipital association areas originally intended for dorsal-stream visual processing.

To determine the functional connectivity of pre-selected brain regions in primary and non-primary auditory and posterior parietal cortex in the two cohorts, we performed an inter-regional correlation analysis on the rCBF data set. During auditory localization in the blind subjects, rCBF activity in the right posterior parietal cortex was positively correlated with that in the right occipital region, whereas in sighted subjects correlations were generally negative. There were no significant positive occipital correlations in either cohort when reference regions in temporal or left parietal cortex were chosen. This indicates that in congenitally blind subjects the right occipital cortex participates in a functional network for auditory localization and that occipital activity is more likely to arise from connections with posterior parietal cortex.
Task-Dependent Constraints in Motor Control: Pinhole Goggles Make the Head Move Like an Eye
Authors: Ceylan M. , Henriques D. Y. P. , Tweed D. B. , Crawford J. D.
Published: April 2018

In the 19th century, Donders observed that only one three-dimensional eye orientation is used for each gaze direction. Listing's law further specifies that the full set of eye orientation vectors forms a plane, whereas the equivalent Donders' law for the head, the Fick strategy, specifies a twisted two-dimensional range. Surprisingly, despite considerable research and speculation, the biological reasons for choosing one such range over another remain obscure. In the current study, human subjects performed head-free gaze shifts between visual targets while wearing pinhole goggles. During fixations, the head orientation range still obeyed Donders' law, but in most subjects, it immediately changed from the twisted Fick-like range to a flattened Listing-like range. Further controls showed that this was not attributable to loss of binocular vision or increased range of head motion, nor was it attributable to blocked peripheral vision; when subjects pointed a helmet-mounted laser toward targets (a task with goggle-like motor demands but normal vision), the head followed Listing's law even more closely. Donders' law of the head only broke down (in favor of a “minimum-rotation strategy”) when head motion was dissociated from gaze. These behaviors could not be modeled using current “Donders' operators” but were readily simulated nonholonomically, i.e., by modulating head velocity commands as a function of position and task. We conclude that the gaze control system uses such velocity rules to shape Donders' law on a moment-to-moment basis, not primarily to satisfy perceptual or anatomic demands, but rather for motor optimization; the Fick strategy optimizes the role of the head as a platform for eye movement, whereas Listing's law optimizes rapid control of the eye (or head) as a gaze pointer.
Progressive Postnatal Assembly of Limbic–Autonomic Circuits Revealed by Central Transneuronal Transport of Pseudorabies Virus
Authors: Rinaman Linda , Levitt Pat , Card J. Patrick
Published: April 2018

The development of neuronal projections to a target and the establishment of synaptic connections with that target can be temporally distinct events, which typically are distinguished by functional assessments. We have applied a novel neuroanatomical approach to characterize the development of limbic forebrain synaptic inputs to autonomic neurons in neonatal rats. Transneuronal labeling of preautonomic forebrain neurons was achieved by inoculating the ventral stomach wall with pseudorabies virus (PRV) on postnatal day 1 (P1), P4, or P8. In each age group, PRV-positive neurons were present in autonomic and preautonomic regions of the spinal cord and brainstem 62–64 hr after inoculation. Transneuronal forebrain labeling in rats injected on P8 was similar to the transneuronal labeling reported previously in adult rats and included neurons in the medial and lateral hypothalamus, amygdala, bed nucleus of the stria terminalis, and visceral cortices. However, no cortex labeling and only modest amygdala and bed nucleus labeling were observed in rats injected with PRV on P4, and only medial hypothalamic labeling was observed in rats injected on P1. Additional tracing experiments involving central injections of PRV or cholera toxin β indicated that lateral hypothalamic and telencephalic regions projected to the medullary dorsal vagal complex several days before establishing synaptic connections with gastric-related autonomic neurons. These results demonstrate a novel strategy for evaluating synaptic connectivity in developing neural circuits and show a temporally segregated postnatal emergence of medial hypothalamic, lateral hypothalamic, and telencephalic synaptic inputs to central autonomic neurons.
Axotomized and Intact Muscle Afferents But No Skin Afferents Develop Ongoing Discharges of Dorsal Root Ganglion Origin after Peripheral Nerve Lesion
Authors: Michaelis Martin , Liu Xianguo , Jänig Wilfrid
Published: April 2018

After peripheral nerve lesions, some axotomized afferent neurons develop ongoing discharges that originate in the dorsal root ganglion (DRG). We investigatedin vivowhich functional types of afferent neurons contributed to this ectopic activity. Six to twelve days after the gastrocnemius soleus (GS) nerve supplying skeletal muscle and the sural (SU) nerve supplying skin had been transected (experimental group E1), 20.4% of afferent neurons with myelinated axons projecting into the GS nerve produced ongoing discharges of irregular or bursting pattern. In contrast, all SU neurons were silent. Additional transection of peroneal and tibial nerves (group E2) induced ongoing activity in a similar percentage of GS neurons (22.1%), but their mean discharge frequency was higher (6.0 vs 2.7 Hz), and more of them exhibited bursting discharges (63 vs 17%). When the GS nerve had been left intact while tibial, peroneal, and SU nerve had been transected (group E3), 18.8% of unlesioned GS neurons developed ongoing discharges at a mean frequency of 6.1 Hz; most of them exhibited a bursting pattern. Without a preceding nerve lesion, almost no GS neuron (1.1%) fired spontaneously. Most afferent neurons with ongoing activity had an axonal conduction velocity of 5–30 m/sec indicating that some of these neurons may have had nociceptive function. These findings provide the first evidence that after peripheral nerve injury both axotomized as well as intact afferent neurons supplying skeletal muscle but not skin afferents generate ongoing activity within the DRG, probably because of a yet unknown signal in the DRG triggered by axotomy.
Involvement of Retinoblastoma Family Members and E2F/DP Complexes in the Death of Neurons Evoked by DNA Damage
Authors: Park David S. , Morris Erick J. , Bremner Rod , Keramaris Elizabeth , Padmanabhan Jaya , Rosenbaum Michele , Shelanski Michael L. , Geller Herbert M. , Greene Lloyd A.
Published: April 2018

Neuronal death evoked by DNA damage requires cyclin-dependent kinase 4 (Cdk4) and 6 activity and is accompanied by elevation of cyclin D1-associated kinase activity. Because Cdk4/6 phosphorylates retinoblastoma protein (pRb) family members that then modulate the transcriptional activity of E2F/DP1 complexes, we examined the involvement of these components in DNA damage-evoked neuronal death. Camptothecin induced rapid pRb and p107 phosphorylation at a Cdk4/6 phosphorylation site followed by selective loss of Rb and p107. The CDK inhibitor flavopiridol suppressed pRb and p107 phosphorylation and loss, implicating CDK activity in these events. Moreover, the loss of pRb and p107 appeared to be mediated by caspases because it was blocked by general caspase inhibitors. The role of phosphorylation and pRb and p107 loss in the death pathway was indicated by observations that virally mediated expression of pRb mutated at sites of phosphorylation, including the Cdk4/6 site, inhibited death. Finally, expression of dominant-negative versions of DP1, known to compromise E2F transcriptional activity, protects cortical neurons from death induced by camptothecin and sympathetic neurons from death evoked by UV treatment. Taken together, these results implicate the CDK–pRb/E2F/DP pathway as a required element in the neuronal death evoked by DNA damage.
Brain-Derived Neurotrophic Factor (BDNF) Induces Dendritic Targeting of BDNF and Tyrosine Kinase B mRNAs in Hippocampal Neurons through a Phosphatidylinositol-3 Kinase-Dependent Pathway
Authors: Righi Massimo , Tongiorgi Enrico , Cattaneo Antonino
Published: April 2018

This study aims to understand the mechanisms of dendritic targeting of brain-derived neurotrophic factor (BDNF) and tyrosine kinase B (TrkB) mRNAs. We show that brief depolarizations are sufficient to induce accumulation of BDNF and TrkB mRNAs in dendrites of hippocampal neurons. Endogenous BDNF, secreted during the KCl stimulation, contributes significantly to the dendritic accumulation of BDNF–TrkB mRNAs. In the absence of depolarization, 1 min pulses of exogenous BDNF are sufficient to induce dendritic accumulation of BDNF–TrkB mRNAs. After binding to TrkB, BDNF exerts this action by activating a PI-3 kinase-dependent pathway. The accumulation of dendritic mRNA by BDNF is not mediated by BDNF-induced neurotransmitter release. Because most hippocampal neurons coexpress BDNF and TrkB receptors, these results show that the subcellular distribution of BDNF–TrkB mRNAs is under the control of an autocrine–paracrine BDNF–TrkB-dependent loop.
Protein Aggregation after Transient Cerebral Ischemia
Authors: Hu B. R. , Martone M. E. , Jones Y. Z. , Liu C. L.
Published: April 2018

Protein aggregates containing ubiquitinated proteins are commonly present in neurodegenerative disorders and have been considered to cause neuronal degeneration. Here, we report that transient cerebral ischemia caused severe protein aggregation in hippocampal CA1 neurons. By using ethanolic phosphotungstic acid electron microscopy (EM) and ubiquitin immunogold EM, we found that protein aggregates were accumulated in CA1 neurons destined to die 72 hr after 15 min of cerebral ischemia. Protein aggregates appeared as clumps of electron-dense materials that stained heavily for ubiquitin and were associated with various intracellular membranous structures. The protein aggregates appeared at 4 hr and progressively accumulated at 24 and 48 hr of reperfusion in CA1 dying neurons. However, they were rarely observed in dentate gyrus neurons that were resistant to ischemia. At 4 hr of reperfusion, protein aggregates were mainly associated with intracellular vesicles in the soma and dendrites, and the nuclear membrane. By 24 hr of reperfusion, the aggregates were also associated with mitochondria, the Golgi apparatus, and the dendritic plasmalemma. High-resolution confocal microscopy further demonstrated that protein aggregates containing ubiquitin were persistently and progressively accumulated in all CA1 dying neurons but not in neuronal populations that survive in this model. We conclude that proteins are severely aggregated in hippocampal neurons vulnerable to transient brain ischemia. We hypothesize that the accumulation of protein aggregates cause ischemic neuronal death.
Agonist- and Reflex-Evoked Internalization of Metabotropic Glutamate Receptor 5 in Enteric Neurons
Authors: Liu Min-tsai , Kirchgessner Annette L.
Published: April 2018

We demonstrate that metabotropic glutamate receptor 5 (mGluR5) is present in the guinea pig ileum. A punctate ring-like distribution of immunoreactivity is found on the soma of a subset of neurons, consistent with an association of mGluR5 with the plasma membrane. mGluR5-containing cells in the submucosal plexus are predominantly noncholinergic and contain vasoactive intestinal peptide, a marker of secretomotor neurons. Using immunocytochemistry in conjunction with confocal microscopy, we show that the mGluR5 undergoes agonist- and reflex-evoked internalization that is inhibited by the group I antagonist 1-aminoindan-1,5-dicarboxylic acid. In addition, group I mGluR antagonists reduce the distension-induced phosphorylation of cAMP-responsive element-binding protein in enteric neurons and attenuate both glutamate- and group I agonist-induced depolarizing responses and slow synaptic events in submucosal neurons. These findings support the idea that mGluRs play a role in enteric reflexes and suggest that internalization might be a major mechanism for regulation of mGluR activity.
Synucleins Are Developmentally Expressed, and α-Synuclein Regulates the Size of the Presynaptic Vesicular Pool in Primary Hippocampal Neurons
Authors: Murphy Diane D. , Rueter Susan M. , Trojanowski John Q. , Lee Virginia M.-Y.
Published: April 2018

α-, β-, and γ-Synuclein, a novel family of neuronal proteins, has become the focus of research interest because α-synuclein has been increasingly implicated in the pathogenesis of Parkinson's and Alzheimer's disease. However, the normal functions of the synucleins are still unknown. For this reason, we characterized α-, β-, and γ-synuclein expression in primary hippocampal neuronal cultures and showed that the onset of α- and β-synuclein expression was delayed after synaptic development, suggesting that these synucleins may not be essential for synapse formation. In mature cultured primary neurons, α- and β-synuclein colocalized almost exclusively with synaptophysin in the presynaptic terminal, whereas little γ-synuclein was expressed at all. To assess the function of α-synuclein, we suppressed expression of this protein with antisense oligonucleotide technology. Morphometric ultrastructural analysis of the α-synuclein antisense oligonucleotide-treated cultures revealed a significant reduction in the distal pool of synaptic vesicles. These data suggest that one function of α-synuclein may be to regulate the size of distinct pools of synaptic vesicles in mature neurons.
Brain-Derived Neurotrophic Factor Differentially Regulates Excitatory and Inhibitory Synaptic Transmission in Hippocampal Cultures
Authors: Bolton M. McLean , Pittman Andrew J. , Lo Donald C.
Published: April 2018

Brain-derived neurotrophic factor (BDNF) has been postulated to be a key signaling molecule in regulating synaptic strength and overall circuit activity. In this context, we have found that BDNF dramatically increases the frequency of spontaneously initiated action potentials in hippocampal neurons in dissociated culture. Using analysis of unitary synaptic transmission and immunocytochemical methods, we determined that chronic treatment with BDNF potentiates both excitatory and inhibitory transmission, but that it does so via different mechanisms. BDNF strengthens excitation primarily by augmenting the amplitude of AMPA receptor-mediated miniature EPSCs (mEPSCs) but enhances inhibition by increasing the frequency of mIPSC and increasing the size of GABAergic synaptic terminals. In contrast to observations in other systems, BDNF-mediated increases in AMPA-receptor mediated mEPSC amplitudes did not require activity, because blocking action potentials with tetrodotoxin for the entire duration of BDNF treatment had no effect on the magnitude of this enhancement. These forms of synaptic regulations appear to be a selective action of BDNF because intrinsic excitability, synapse number, and neuronal survival are not affected in these cultures. Thus, although BDNF induces a net increase in overall circuit activity, this results from potentiation of both excitatory and inhibitory synaptic drive through distinct and selective physiological mechanisms.
Laminar Distribution of Neurons in Extrastriate Areas Projecting to Visual Areas V1 and V4 Correlates with the Hierarchical Rank and Indicates the Operation of a Distance Rule
Authors: Barone Pascal , Batardiere Alexandre , Knoblauch Kenneth , Kennedy Henry
Published: April 2018

The directionality of corticocortical projections is classified as feedforward (going from a lower to higher hierarchical levels), feedback (interconnecting descending levels), and lateral (interconnecting equivalent levels). Directionality is determined by the combined criteria of the laminar patterns of the axon terminals as well as the cells of origins and has been used to construct models of the visual system, which reveals a strict hierarchical organization (Felleman and Van Essen, 1991; Hilgetag et al., 1996a). However, these models are indeterminate partly because we have no indication of the distance separating adjacent levels. Here we have attempted to determine a graded parameter describing the anatomical relationship of interconnected areas. We have investigated whether the precise percentage of labeled supragranular layer neurons (SLN%) in each afferent area after injection in either visual areas V1 or V4 determines its hierarchical position in the Felleman and Van Essen (1991) model. This shows that pathway directionality in the Felleman and Van Essen model is characterized by a range of SLN% values. The one exception is the projection of the frontal eye field to area V4, which resembles a feedforward projection. Individual areal differences in SLN% values are highly significant, and the number of hierarchical steps separating a target area from a source area is found to be tightly correlated to SLN%. The present results show that the hierarchical rank of each afferent area is reliably indicated by SLN%, and therefore this constitutes a graded parameter that is related to hierarchical distance.
Activation of Intrinsic Afferent Pathways in Submucosal Ganglia of the Guinea Pig Small Intestine
Authors: Pan Hui , Gershon Michael D.
Published: April 2018

The enteric nervous system contains intrinsic primary afferent neurons that allow mucosal stimulation to initiate reflexes without CNS input. We tested the hypothesis that submucosal primary afferent neurons are activated by 5-hydroxytryptamine (5-HT) released from the stimulated mucosa. Fast and/or slow EPSPs were recorded in submucosal neurons after the delivery of exogenous 5-HT, WAY100325 (a 5-HT1Pagonist), mechanical, or electrical stimuli to the mucosa of myenteric plexus-free preparations (± extrinsic denervation). These events were responses of second-order cells to transmitters released by excited primary afferent neurons. After all stimuli, fast and slow EPSPs were abolished by a 5-HT1Pantagonist,N-acetyl-5-hydroxytryptophyl-5-hydroxytryptophan amide, and by 1.0 μmtropisetron, but not by 5-HT4-selective antagonists (SB204070 and GR113808A) or 5-HT3-selective antagonists (ondansetron and 0.3 μmtropisetron). Fast EPSPs in second-order neurons were blocked by hexamethonium, and most slow EPSPs were blocked by an antagonist of human calcitonin gene-related peptide (hCGRP8–37). hCGRP8–37also inhibited the spread of excitation in the submucosal plexus, assessed by measuring the uptake of FM2-10 and induction ofc-fos. In summary, data are consistent with the hypothesis that 5-HT from enterochromaffin cells in response to mucosal stimuli initiates reflexes by stimulating 5-HT1Preceptors on submucosal primary afferent neurons. Second-order neurons respond to these cholinergic/CGRP-containing cells with nicotinic fast EPSPs and/or CGRP-mediated slow EPSPs. Slow EPSPs are necessary for excitation to spread within the submucosal plexus. Because some second-order neurons contain also CGRP, primary afferent neurons may be multifunctional and also serve as interneurons.
Classical Conditioning of Feeding inAplysia: I. Behavioral Analysis
Authors: Lechner Hilde A. , Baxter Douglas A. , Byrne John H.
Published: April 2018

A training protocol was developed to classically condition feeding behavior inAplysia californicausing tactile stimulation of the lips as the conditional stimulus (CS) and food as the unconditional stimulus (US). Paired training induced a greater increase in the number of bites to the CS than unpaired training or US-only stimulation. Memory for classical conditioning was retained for at least 24 hr. The organization of the reinforcement pathway that supports classical conditioning was analyzed in additional behavioral experiments. No evidence was found for the contribution to appetitive reinforcement of US-mediating pathways originating in the lips of the animals. Bilateral lesions of the anterior branch of the esophageal nerve, which innervates parts of the foregut, however, were found to attenuate classical conditioning. Thus, it appears likely that reinforcement during appetitive classical conditioning of feeding was mediated by afferent pathways that originate in the foregut. The companion paper (Lechner et al., 2000) describes two neurophysiological correlates of the classical conditioning.
Synergistically Interacting Dopamine D1 and NMDA Receptors Mediate Nonvesicular Transporter-Dependent GABA Release from Rat Striatal Medium Spiny Neurons
Authors: Schoffelmeer Anton N. M. , Vanderschuren Louk J. M. J. , De Vries Taco J. , Hogenboom Francois , Wardeh George , Mulder Arie H.
Published: April 2018

Given the complex interactions between dopamine D1 and glutamate NMDA receptors in the striatum, we investigated the role of these receptors in transporter-mediated GABA release from cultured medium spiny neurons of rat striatum. Like NMDA receptor-mediated [3H]-GABA release, that induced by prolonged (20 min) dopamine D1 receptor activation was enhanced on omission of external calcium, was action potential-independent (tetrodotoxin-insensitive), and was diminished by the GABA transporter blocker nipecotic acid, indicating the involvement of transporter-mediated release. Interestingly, lowering the external sodium concentration only reduced the stimulatory effect of NMDA. Blockade of Na+/K+-ATPase by ouabain enhanced NMDA-induced but abolished dopamine-induced release. Moreover, dopamine appeared to potentiate the effect of NMDA on [3H]-GABA release. These effects of dopamine were mimicked by forskolin. μ-Opioid receptor-mediated inhibition of adenylyl cyclase by morphine reduced dopamine- and NMDA-induced release. These results confirm previous studies indicating that NMDA receptor activation causes a slow action potential-independent efflux of GABA by reversal of the sodium-dependent GABA transporter on sodium entry through the NMDA receptor channel. Moreover, our data indicate that activation of G-protein-coupled dopamine D1 receptors also induces a transporter-mediated increase in spontaneous GABA release, but through a different mechanism of action, i.e., through cAMP-dependent inhibition of Na+/K+-ATPase, inducing accumulation of intracellular sodium, reversal of the GABA carrier, and potentiation of NMDA-induced release. These receptor interactions may play a crucial role in the behavioral activating effects of psychostimulant drugs.
Elimination of the Fast Transient in Superior Cervical Ganglion Neurons with Expression of KV4.2W362F: Molecular Dissection ofIA
Authors: Malin Sacha A. , Nerbonne Jeanne M.
Published: April 2018

Electrophysiological and molecular studies have revealed considerable heterogeneity in voltage-gated K+currents and in the subunits that underlie these channels in mammalian neurons. At present, however, the relationship between native K+currents and cloned subunits is poorly understood. In the experiments here, a molecular genetic approach was exploited to define the molecular correlate of the fast transient outward K+current,IAf, in sympathetic neurons and to explore the functional role ofIAfin shaping action potential waveforms and controlling repetitive firing patterns. Using the biolistic gene gun, cDNAs encoding a dominant negative mutant Kv4.2 α-subunit (Kv4.2W362F) and enhanced green fluorescent protein (EGFP) were introduced into rat sympathetic neuronsin vitro. Whole-cell voltage-clamp recordings obtained from EGFP-positive cells revealed thatIAfis selectively eliminated in cells expressing Kv4.2W362F, demonstrating that Kv4 α-subunits underlieIAfin sympathetic neurons. In addition,IAfdensity is increased significantly in cells overexpressing wild-type Kv4.2. In cells expressing Kv4.2W362F, input resistances are increased and (current) thresholds for action potential generation are decreased, demonstrating thatIAfplays a pivotal role in regulating excitability. Expression of Kv4.2W362F and elimination ofIAfalso alters the distribution of repetitive firing patterns observed in response to a prolonged injection of depolarizing current. The wild-type superior cervical ganglion is composed of phasic, adapting, and tonic firing neurons. Elimination ofIAfincreases the percentage of adapting cells by shifting phasic cells to the adapting firing pattern, and increasedIAfdensity reduces the number of adapting cells.
Increased Binding Activity at an Antioxidant-Responsive Element in the Metallothionein-1 Promoter and Rapid Induction of Metallothionein-1 and -2 in Response to Cerebral Ischemia and Reperfusion
Authors: Campagne Menno van Lookeren , Thibodeaux Harold , van Bruggen Nick , Cairns Belinda , Lowe David G.
Published: April 2018

Metallothioneins (MTs) are cysteine-rich metal-binding proteins that are potentially involved in zinc homeostasis and free radical scavenging. The expression pattern of MT-1 and the binding activity of various MT-1 promoter elements were investigated after mild focal cerebral ischemia in the rat. Transient focal ischemia was induced by occluding both common carotid arteries and the right middle cerebral artery for 30 min. By the use of real-time quantitative PCR, a 10-fold increase in MT-1 and -2 mRNA levels was found in the cortex 24 hr after reperfusion.In situhybridization and immunocytochemistry showed a rapid increase in MT-1 and -2 mRNA and MT protein in endothelial cells of microvessels at 6 hr after reperfusion, followed by an increased expression in astrocytes of the infarcted cortex at 24 hr after reperfusion. The early increase in MT expression preceded an increase in cerebral edema measured with T2-weighted magnetic resonance imaging. Gel shift assays were performed on nuclear extracts prepared from cortices before and at 6 and 24 hr after reperfusion. Increased binding activity was found at an antioxidant/electrophilic response element (ARE) sequence in the MT-1 promoter at 6 hr with a lower and variable binding activity at 24 hr after reperfusion. Constitutive binding activity was found for Sp1 and a metal response element in the MT-1 promoter that did not increase after ischemia and reperfusion. This study suggests a role of ARE-binding proteins in inducing cerebral MT-1 expression and implicates MT-1 as one of the early detoxifying genes in an endogenous defense response to cerebral ischemia and reperfusion.
Long-Term Potentiation of Intrinsic Excitability at the Mossy Fiber–Granule Cell Synapse of Rat Cerebellum
Authors: Armano S. , Rossi P. , Taglietti V. , D'Angelo E.
Published: April 2018

Synaptic activity can induce persistent modifications in the way a neuron reacts to subsequent inputs by changing either synaptic efficacy or intrinsic excitability. After high-frequency synaptic stimulation, long-term potentiation (LTP) of synaptic efficacy is commonly observed at hippocampal synapses (Bliss and Collingridge, 1993), and potentiation of intrinsic excitability has recently been reported in cerebellar deep nuclear neurons (Aizenmann and Linden, 2000). However, the potential coexistence of these two aspects of plasticity remained unclear. In this paper we have investigated the effect of high-frequency stimulation on synaptic transmission and intrinsic excitability at the mossy fiber–granule cell relay of the cerebellum. High-frequency stimulation, in addition to increasing synaptic conductance (D'Angelo et al., 1999), increased granule cell input resistance and decreased spike threshold. These changes depended on postsynaptic depolarization and NMDA receptor activation and were prevented by inhibitory synaptic activity. Potentiation of intrinsic excitability was induced by relatively weaker inputs than potentiation of synaptic efficacy, whereas with stronger inputs the two aspect of potentiation combined to enhance EPSPs and spike generation. Potentiation of intrinsic excitability may extend the computational capability of the cerebellar mossy fiber–granule cell relay.
Early Onset of Axonal Degeneration in Double (plp−/−mag−/−) and Hypomyelinosis in Triple (plp−/−mbp−/−mag−/−) Mutant Mice
Authors: Uschkureit Thomas , Spörkel Olaf , Stracke Jens , Büssow Heinrich , Stoffel Wilhelm
Published: April 2018

Double (plp−/−mag−/−) and triple (plp−/−mbp−/−mag−/−) null-allelic mouse lines deficient in proteolipid protein (PLP), myelin-associated glycoprotein (MAG), and myelin basic protein (MBP) were generated and characterized genetically, biochemically, and morphologically including their behavioral capacities. Theplp−/−mag−/− mutant develops a rapidly progressing axon degeneration in CNS with severe cognitive and motor coordinative deficits but has a normal longevity. CNS axons of theplp−/−mbp−/−mag−/− mouse are hypomyelinated and ensheathed by “pseudomyelin” with disturbed protein and complex lipid composition. Theshiverertrait in theplp−/−mbp−/−mag−/− similar to theplp−/−mbp−/− mutant is significantly ameliorated, and its lifespan is considerably prolonged. The longevity of these dysmyelinosis mouse mutants recommends them as suitable models for the long-term evaluation of stem cell therapeutic strategies.
Mice Deficient in the Polysialyltransferase ST8SiaIV/PST-1 Allow Discrimination of the Roles of Neural Cell Adhesion Molecule Protein and Polysialic Acid in Neural Development and Synaptic Plasticity
Authors: Eckhardt Matthias , Bukalo Olena , Chazal Geneviève , Wang Lihua , Goridis Christo , Schachner Melitta , Gerardy-Schahn Rita , Cremer Harold , Dityatev Alexander
Published: April 2018

Functional properties of the neural cell adhesion molecule (NCAM) are strongly influenced by polysialylation. We used gene-targeting to generate mice lacking ST8SiaIV/PST-1, one of the polysialyltransferases responsible for addition of polysialic acid (PSA) to NCAM. Mice homozygous for the null mutation reveal normal development of gross anatomical features. In contrast to NCAM-deficient mice, olfactory precursor cells in the rostral migratory stream express PSA and follow their normal pathway. Furthermore, delamination of mossy fibers in the hippocampal CA3 region, as found in NCAM-deficient mice, does not occur in ST8SiaIV mutants. However, during postnatal development these animals show a decrease of PSA in most brain regions compared to wild-type animals. Loss of PSA in the presence of NCAM protein but in the absence of obvious histological changes allowed us to directly address the role of PSA in synaptic plasticity. Schaffer collateral-CA1 synapses, which express PSA in wild types, showed impaired long-term potentiation (LTP) and long-term depression (LTD) in adult mutants. This impairment was age-dependent, following the time course of developmental disappearance of PSA. Contrary to NCAM mutant mice, LTP in ST8SiaIV mutants was undisturbed at mossy fiber–CA3 synapses, which do not express PSA in wild-type mice. The results demonstrate an essential role for ST8SiaIV in synaptic plasticity in hippocampal CA1 synapses, whereas PSA produced by different polysialyltransferase or polysialyltransferases at early stages of differentiation regulates migration of neural precursor cells and correct lamination of mossy fibers. We suggest that NCAM but not PSA is likely to be important for LTP in the hippocampal CA3 region.
Columnar Organization of Dendrites and Axons of Single and Synaptically Coupled Excitatory Spiny Neurons in Layer 4 of the Rat Barrel Cortex
Authors: Lübke Joachim , Egger Veronica , Sakmann Bert , Feldmeyer Dirk
Published: April 2018

Cortical columns are the functional units of the neocortex that are particularly prominent in the “barrel” field of the somatosensory cortex. Here we describe the morphology of two classes of synaptically coupled excitatory neurons in layer 4 of the barrel cortex, spiny stellate, and star pyramidal cells, respectively. Within a single barrel, their somata tend to be organized in clusters. The dendritic arbors are largely confined to layer 4, except for the distal part of the apical dendrite of star pyramidal neurons that extends into layer 2/3. In contrast, the axon of both types of neurons spans the cortex from layer 1 to layer 6. The most prominent axonal projections are those to layers 4 and 2/3 where they are largely restricted to a single cortical column. In layers 5 and 6, a small fraction of axon collaterals projects also across cortical columns. Consistent with the dense axonal projection to layers 4 and 2/3, the total number and density of boutons per unit axonal length was also highest there. Electron microscopy combined with GABA postimmunogold labeling revealed that most (>90%) of the synaptic contacts were established on dendritic spines and shafts of excitatory neurons in layers 4 and 2/3.

The largely columnar organization of dendrites and axons of both cell types, combined with the preferential and dense projections within cortical layers 4 and 2/3, suggests that spiny stellate and star pyramidal neurons of layer 4 serve to amplify thalamic input and relay excitation vertically within a single cortical column.
Formation of Intermediate Filament Protein Aggregates with Disparate Effects in Two Transgenic Mouse Models Lacking the Neurofilament Light Subunit
Authors: Beaulieu Jean-Martin , Jacomy Hélène , Julien Jean-Pierre
Published: April 2018

Protein aggregates containing intermediate filaments (IFs) are a hallmark of degenerating spinal motor neurons in amyotrophic lateral sclerosis (ALS). Recently, we reported that a deficiency in neurofilament light subunit (NF-L), a phenomenon associated with ALS, promoted the formation of IF inclusions with ensuing motor neuron death in transgenic mice overproducing peripherin, a type III IF protein detected in axonal inclusions of ALS patients. To further assess the role of NF-L in the formation of abnormal IF inclusions, we generated transgenic mice overexpressing human neurofilament heavy subunits (hNF-H) in a context of targeted disruption of the NF-L gene (hH;L−/− mice). The hH;L−/− mice exhibited motor dysfunction, and they developed nonfilamentous protein aggregates containing NF-H and peripherin proteins in the perikarya of spinal motor neurons. However, the perikaryal protein aggregates in the hH;L−/− mice did not provoke motor neuron death, unlike toxic IF inclusions induced by peripherin overexpression in NF-L null mice (Per;L−/− mice). Our results indicate that different types of IF protein aggregates with distinct properties may occur in a context of NF-L deficiency and that an axonal localization of such aggregates may be an important factor of toxicity.
Small GTPases Rac and Rho in the Maintenance of Dendritic Spines and Branches in Hippocampal Pyramidal Neurons
Authors: Nakayama Ann Y. , Harms Matthew B. , Luo Liqun
Published: April 2018

The shape of dendritic trees and the density of dendritic spines can undergo significant changes during the life of a neuron. We report here the function of the small GTPases Rac and Rho in the maintenance of dendritic structures. Maturing pyramidal neurons in rat hippocampal slice culture were biolistically transfected with dominant GTPase mutants. We found that expression of dominant-negative Rac1 results in a progressive elimination of dendritic spines, whereas hyperactivation of RhoA causes a drastic simplification of dendritic branch patterns that is dependent on the activity of a downstream kinase ROCK. Our results suggest that Rac and Rho play distinct functions in regulating dendritic spines and branches and are vital for the maintenance and reorganization of dendritic structures in maturing neurons.
Activity-Dependent Regulation of Substance P Expression and Topographic Map Maintenance by a Cholinergic Pathway
Authors: Tu Shichun , Butt Christopher M. , Pauly James R. , Debski Elizabeth A.
Published: April 2018

We have assessed the role of activity in the adult frog visual system in modulating two aspects of neuronal plasticity: neurotransmitter expression and topographic map maintenance. Chronic treatment of one tectal lobe with the non-NMDA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione decreased the percentage of substance P-like immunoreactive (SP-IR) tectal cells in the untreated lobe while disrupting topographic map formation in the treated one. Treatment with the NMDA receptor antagonistd-(−)-2-amino-5-phosphonovaleric acid (d-AP-5) disrupted the topographic map but had no affect on SP-IR cells. These results indicate that maintenance of the topographic map is dependent on direct input from the glutamatergic retinal ganglion cells, whereas substance P (SP) expression is being regulated by a pathway that relays activity from one tectal lobe to the other. Such a pathway is provided by the cholinergic nucleus isthmi, which is reciprocally connected to the ipsilateral tectum and sends a projection to the contralateral one.

Mecamylamine and atropine, antagonists of nicotinic and muscarinic receptors, respectively, were used together to block all cholinergic activity or alone to block receptor subclass activity. All three treatments decreased SP expression and disrupted the topographic map in the treated tectal lobe. We conclude that both SP expression and topographic map maintenance in the adult optic tectum are activity-dependent processes. Although our results are consistent with the maintenance of the topographic map through an NMDA receptor-based mechanism, they suggest that SP expression is regulated by a cholinergic interaction that depends on retinal ganglion cell input only for its activation.