bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction between the Postsubiculum and Anterior Thalamus in the Generation of Head Direction Cell Activity
Authors: Goodridge Jeremy P. , Taube Jeffrey S.
Published: April 2018

Previous research has identified neurons in the postsubiculum (PoS) and anterior dorsal thalamic nucleus (AD) of the rat that discharge as a function of the animal’s head direction. In addition, anatomical studies have shown that the AD and PoS are reciprocally connected with one another. The current study examined whether head direction (HD) cells in each of the two areas is dependent on input from the other structure. After both electrolytic or neurotoxic lesions of the AD, no cells were identified with direction-specific discharge in the PoS. In contrast, AD HD cell activity was still present after neurotoxic lesions to the PoS. However, AD HD cells in PoS-lesioned rats exhibited three important differences compared with AD HD cells in intact animals: (1) their directional firing range was significantly larger, (2) their firing predicted the animal’s future head direction by a larger amount, and (3) their preferred firing direction was substantially less influenced by a prominent visual landmark within the recording environment. These results indicate that information critical for HD cell activity is conveyed in both directions between the AD and the PoS; whereas the AD is necessary for the presence of HD cell activity in the PoS, the PoS appears important in allowing visual landmarks to exert control over the preferred firing direction of AD HD cells. These findings have implications for several computational models that propose to account for the generation of the HD cell signal.
The β-Amyloid Precursor Protein of Alzheimer’s Disease Enhances Neuron Viability and Modulates Neuronal Polarity
Authors: Perez Ruth G. , Zheng Hui , Van der Ploeg Lex H. T. , Koo Edward H.
Published: April 2018

β-Amyloid precursor protein (βPP) can reside at neuron and glial cell surfaces or undergo proteolytic processing into secreted fragments. Although βPP has been studied extensively, its precise physiological role is unknown. A line of transgenic knock-out mice selectively deficient in βPP survive and breed but exhibit motor dysfunction and brain gliosis, consistent with a physiological role for βPP in neuron development. To elucidate these functions, we cultured hippocampal neurons from wild-type and βPP-deficient mice and compared their ability to attach, survive, and develop neurites. We found that hippocampal neurons from βPP-deficient mice had diminished viability and retarded neurite development. We also compared the effects of βPP secretory products, released from wild-type astrocytes, on process outgrowth from wild-type and βPP-deficient hippocampal neurons. Outgrowth was enhanced at 1 d in the presence of wild-type astrocytes, as compared with βPP-deficient astrocytes. However, by 3 d, neurons had shorter axons but more minor processes with more branching when cocultured with wild-type astrocytes, as compared with βPP-deficient astrocytes. Our data demonstrate that cell-associated neuronal βPP contributes to neuron viability, axonogenesis, and arborization and that βPP secretory products modulate axon growth, dendrite branching, and dendrite numbers.
Importance of Polysynaptic Inputs and Horizontal Connectivity in the Generation of Tetanus-Induced Long-Term Potentiation in the Rat Auditory Cortex
Authors: Kudoh Masaharu , Shibuki Katsuei
Published: April 2018

Supragranular pyramidal neurons in the adult rat auditory cortex (AC) show marked long-term potentiation (LTP) of population spikes after tetanic white matter stimulation (TS). For determination of whether this marked LTP is specific to AC, LTP in rat AC slices was compared with LTP in slices of the visual cortex (VC). The amplitude of TS-induced LTP in AC was twice that in VC. LTP of EPSPs was also studied with perforated patch or whole-cell recording. Although the amplitude of TS-induced LTP of EPSPs in AC was larger that in VC, no cortical difference was found in LTP elicited by low-frequency stimulation paired with current injection. Neocortical LTP is dependent on the activation of NMDA receptors, and induction of LTP requires postsynaptic depolarization for removal of Mg2+blockade of NMDA receptors. The postsynaptic depolarization elicited by TS in supragranular pyramidal neurons in AC was significantly larger than that in VC. Cutting of supragranular horizontal connections resulted in a decrease in the depolarization amplitude in AC but an increase in the depolarization amplitude in VC. The cortical difference in TS-induced LTP was diminished in the slices in which horizontal connections in supragranular layers were cut. The estimated density of horizontal axon collaterals of supragranular pyramidal neurons in AC was approximately twice that in VC. These results strongly suggest that the marked polysynaptic and postsynaptic depolarization during TS and the resulting marked LTP in AC are attributed to well developed horizontal axon collaterals of supragranular pyramidal neurons in AC.
Measurement of Intracellular Free Zinc in Living Cortical Neurons: Routes of Entry
Authors: Sensi Stefano L. , Canzoniero Lorella M. T. , Yu Shan Ping , Ying Howard S. , Koh Jae-Young , Kerchner Geoffrey A. , Choi Dennis W.
Published: April 2018

We used the ratioable fluorescent dye mag-fura-5 to measure intracellular free Zn2+([Zn2+]i) in cultured neocortical neurons exposed to neurotoxic concentrations of Zn2+in concert with depolarization or glutamate receptor activation and identified four routes of Zn2+entry. Neurons exposed to extracellular Zn2+plus high K+responded with a peak cell body signal corresponding to a [Zn2+]iof 35–45 nm. This increase in [Zn2+]iwas attenuated by concurrent addition of Gd3+, verapamil, ω-conotoxin GVIA, or nimodipine, consistent with Zn2+entry through voltage-gated Ca2+channels. Furthermore, under conditions favoring reverse operation of the Na+–Ca2+exchanger, Zn2+application induced a slow increase in [Zn2+]iand outward whole-cell current sensitive to benzamil–amiloride. Thus, a second route of Zn2+entry into neurons may be via transporter-mediated exchange with intracellular Na+. Both NMDA and kainate also induced rapid increases in neuronal [Zn2+]i. The NMDA-induced increase was only partly sensitive to Gd3+or to removal of extracellular Na+, consistent with a third route of entry directly through NMDA receptor-gated channels. The kainate-induced increase was highly sensitive to Gd3+or Na+removal in most neurons but insensitive in a minority subpopulation (“cobalt-positive cells”), suggesting that a fourth route of neuronal Zn2+entry is through the Ca2+-permeable channels gated by certain subtypes of AMPA or kainate receptors.
Nerve Growth Factor Modulates Synaptic Transmission between Sympathetic Neurons and Cardiac Myocytes
Authors: Lockhart Sybil T. , Turrigiano Gina G. , Birren Susan J.
Published: April 2018

Regulation of heart rate by the sympathetic nervous system involves the release of norepinephrine (NE) from nerve terminals onto heart tissue, resulting in an elevation in beat rate. Nerve growth factor (NGF) is a neurotrophin produced by the heart that supports the survival and differentiation of sympathetic neurons. Here we report that NGF also functions as a modulator of sympathetic synaptic transmission. We determined the effect of NGF on the strength of synaptic transmission in co-cultures of neonatal rat cardiac myocytes and sympathetic neurons from the superior cervical ganglion (SCG). Synaptic transmission was assayed functionally, as an increase in the beat rate of a cardiac myocyte during stimulation of a connected neuron. Application of NGF produced a pronounced, reversible enhancement of synaptic strength. We found that TrkA, the receptor tyrosine kinase that mediates many NGF responses, is expressed primarily by neurons in these cultures, suggesting a presynaptic mechanism for the effects of NGF. A presynaptic model is further supported by the finding that NGF did not alter the response of myocytes to application of NE. In addition to the acute modulatory effects of NGF, we found that the concentration of NGF in the growth medium affects the level of synaptic transmission in cultures of sympathetic neurons and cardiac myocytes. These results indicate that in addition to its role as a survival factor, NGF plays both acute and long-term roles in the regulation of developing sympathetic synapses in the cardiac system.
Motoneuron Apoptosis Is Blocked by CEP-1347 (KT 7515), a Novel Inhibitor of the JNK Signaling Pathway
Authors: Maroney Anna C. , Glicksman Marcie A. , Basma Alie N. , Walton Kevin M. , Knight Ernest , Murphy Carol A. , Bartlett Becky A. , Finn James P. , Angeles Thelma , Matsuda Yuzuru , Neff Nicola T. , Dionne Craig A.
Published: April 2018

Neurons undergoing apoptosis can be rescued by trophic factors that simultaneously increase the activity of extracellular signal-regulated kinase (ERK) and decrease c-Jun N-terminal kinase (JNK) and p38. We identified a molecule, CEP-1347 (KT7515), that rescues motoneurons undergoing apoptosis and investigated its effect on ERK1 and JNK1 activity. Cultured rat embryonic motoneurons, in the absence of trophic factor, began to die 24–48 hr after plating. During the first 24 hr ERK1 activity was unchanged, whereas JNK1 activity increased fourfold. CEP-1347 completely rescued motoneurons for at least 72 hr with an EC50of 20 ± 2 nm. CEP-1347 did not alter ERK1 activity but rapidly inhibited JNK1 activation. The IC50of CEP-1347 for JNK1 activation was the same as the EC50for motoneuron survival. Inhibition of JNK1 activation by CEP-1347 was not selective to motoneurons. CEP-1347 also inhibited JNK1 activity in Cos7 cells under conditions of ultraviolet irradiation, osmotic shock, and inhibition of glycosylation. Inhibition by CEP-1347 of the JNK1 signaling pathway appeared to be selective, because CEP-1347 did not inhibit p38-regulated mitogen-activated protein kinase-activated protein kinase-2 (MAPKAP2) activity in Cos7 cells subjected to osmotic shock. The direct molecular target of CEP-1347 was not JNK1, because CEP-1347 did not inhibit JNK1 activity in Cos7 cells cotransfected with MEKK1 and JNK1 cDNA constructs. This is the first demonstration of a small organic molecule that promotes motoneuron survival and that simultaneously inhibits the JNK1 signaling cascade.
The Mitogen-Activated Protein Kinase p38-2 Is Necessary for the Inhibition of N-Type Calcium Current by Bradykinin
Authors: Wilk-Blaszczak Malgorzata A. , Stein Bernd , Xu Shuichan , Barbosa Miguel S. , Cobb Melanie H. , Belardetti Francesco
Published: April 2018

Calcium influx via voltage-dependent calcium channels (ICa,V) links depolarization of excitable cells to critical cellular processes, such as secretion, contraction, and gene transcription. Fast regulation of ICa,V(<1 sec) by G-protein-coupled receptors is a relatively well-defined mechanism, whereas slow (30–60 sec) actions of transmitters and hormones on the same current remain poorly understood. In NG108-15 cells, the kinetically slow inhibition of N-type ICa,Vby bradykinin (BK) requires the sequential activation of two G-proteins, heterotrimeric G13and monomeric Rac1/Cdc42. We have now defined a role in this pathway for the relatively fast-acting p38 mitogen-activated protein kinase (MAPK). The slow inhibition of ICa,Vby BK was suppressed specifically by SB203580, a compound that inhibits the p38 family of MAPKs. BK potently and selectively activated a newly discovered p38 family member, p38-2. These data provide the first evidence that a MAPK is involved in the regulation of ICa,Vby a receptor-mediated process.
In VivoExpression and Regulation of Elk-1, a Target of the Extracellular-Regulated Kinase Signaling Pathway, in the Adult Rat Brain
Authors: Sgambato Véronique , Vanhoutte Peter , Pagès Christiane , Rogard Monique , Hipskind Robert , Besson Marie-Jo , Caboche Jocelyne
Published: April 2018

The transcription factor Elk-1, a nuclear target of extracellular-regulated kinases (ERKs), plays a pivotal role in immediate early gene induction by external stimuli. Notably, the degree of phosphorylation of Elk-1 is tightly correlated with the level of activation of transcription of c-fosby proliferative signals. No data yet indicate the role of Elk-1 in the adult brainin vivo. To address this question, we have analyzed in the present work (1) Elk-1 mRNA and protein expression in the adult rat brain, and (2) the regulation of Elk-1 (i.e., its phosphorylation state) in anin vivomodel of immediate early gene (IEG) induction: an electrical stimulation of the cerebral cortex leading to c-fosandzif268mRNA induction in the striatum. Usingin situhybridization, we show that Elk-1 mRNA is expressed in various brain structures of adult rat, and that this expression is exclusively neuronal. We demonstrate by immunocytochemistry using various specific Elk-1 antisera that the protein is not only nuclear (as shown previously in transiently transfected cell lines) but is also present in soma, dendrites, and axon terminals. On electrical stimulation of the glutamatergic corticostriatal pathway, we show a strict spatiotemporal correspondence among ERK activation, Elk-1 phosphorylation, and IEG mRNA induction. Furthermore, both activated proteins, analyzed by immunocytochemistry, are found in cytosolic and nuclear comparments of neuronal cells in the activated area. Our data suggest that the ERK signaling pathway plays an important role in regulating genes controlled by serum response element sites via phosphorylation of Elk-1in vivo.
Organization and Transmitter Specificity of Medullary Neurons Activated by Sustained Hypertension: Implications for Understanding Baroreceptor Reflex Circuitry
Authors: Chan Raymond K. W. , Sawchenko Paul E.
Published: April 2018

In situexpression ofc-fosobserved in response to phenylephrine (PE)-induced hypertension provided a basis for characterizing the organization and neurotransmitter specificity of neurons at nodal points of medullary baroreflex circuitry. Sustained hypertension induced by a moderate dose of PE provoked patterns ofc-fosmRNA and protein expression that conformed in the nucleus of the solitary tract (NTS) to the termination patterns of primary baroreceptor afferents and in the caudal ventrolateral medulla (CVLM) to a physiologically defined depressor region. A majority of barosensitive CVLM neurons concurrently displayed markers for the GABAergic phenotype; few were glycinergic. Phenylephrine-sensitive GABAergic neurons that were retrogradely labeled after tracer deposits in pressor sites of the rostral ventrolateral medulla (RVLM) occupied a zone extending ∼1.4 mm rostrally from the level of the calamus scriptorius, intermingled partly with catecholaminergic neurons of the A1 and C1 cell groups. By contrast, barosensitive neurons of the NTS were found to be phenotypically complex, with very few projecting directly to the RVLM. Extensive colocalization of PE-induced Fos-IR and markers for the nitric oxide phenotype were seen in a circumscribed, rostral, portion of the baroreceptor afferent zone of the NTS, whereas only a small proportion of PE-sensitive neurons in the NTS were found to be GABAergic. PE treatment parameters have been identified that provide a basis for defining and characterizing populations of neurons at the first station in the central processing of primary baroreceptor input and at a key inhibitory relay in the CVLM.
A Model That Accounts for Activity in Primate Frontal Cortex during a Delayed Matching-to-Sample Task
Authors: Moody Sohie Lee , Wise Steven P. , di Pellegrino Giuseppe , Zipser David
Published: April 2018

A fully recurrent neural network model was optimized to perform a spatial delayed matching-to-sample task (DMS). In DMS, a stimulus is presented at a sample location, and a match is reported when a subsequent stimulus appears at that location. Stimuli elsewhere are ignored. Computationally, a DMS system could consist of memory and comparison components. The model, although not constrained to do so, worked by using two corresponding classes of neurons in the hidden layer: storage and comparator units. Storage units form a dynamical system with one fixed point attractor for each sample location. Comparator units constitute a system receiving input from these storage units as well as from current input stimuli. Both unit types were tuned directionally. These two sources of information combine to create unique patterns of activity that determine whether a match has occurred. In networks with abundant hidden units, the storage and comparator functions were distributed so that individual units took part in both. We compared the model with single-neuron recordings from premotor (PM) and prefrontal (PF) cortex. As shown previously, many PM and PF neurons behaved like storage units. In addition, both regions contain neurons that behave like the comparator units of the model and appear to have dual functionality similar to that observed in the model units. No neuron in either area had properties identical to those of the match output neuron of the model. However, four PF neurons and one PM neuron resembled the output signal more closely than any of the hidden units of the model.
Masked Presentations of Emotional Facial Expressions Modulate Amygdala Activity without Explicit Knowledge
Authors: Whalen Paul J. , Rauch Scott L. , Etcoff Nancy L. , McInerney Sean C. , Lee Michael B. , Jenike Michael A.
Published: April 2018

Functional magnetic resonance imaging (fMRI) of the human brain was used to study whether the amygdala is activated in response to emotional stimuli, even in the absence of explicit knowledge that such stimuli were presented. Pictures of human faces bearing fearful or happy expressions were presented to 10 normal, healthy subjects by using a backward masking procedure that resulted in 8 of 10 subjects reporting that they had not seen these facial expressions. The backward masking procedure consisted of 33 msec presentations of fearful or happy facial expressions, their offset coincident with the onset of 167 msec presentations of neutral facial expressions. Although subjects reported seeing only neutral faces, blood oxygen level-dependent (BOLD) fMRI signal in the amygdala was significantly higher during viewing of masked fearful faces than during the viewing of masked happy faces. This difference was composed of significant signal increases in the amygdala to masked fearful faces as well as significant signal decreases to masked happy faces, consistent with the notion that the level of amygdala activation is affected differentially by the emotional valence of external stimuli. In addition, these facial expressions activated the sublenticular substantia innominata (SI), where signal increases were observed to both fearful and happy faces—suggesting a spatial dissociation of territories that respond to emotional valence versus salience or arousal value. This study, using fMRI in conjunction with masked stimulus presentations, represents an initial step toward determining the role of the amygdala in nonconscious processing.
Leptin Receptor Immunoreactivity in Chemically Defined Target Neurons of the Hypothalamus
Authors: Håkansson Marie-Louise , Brown Hilary , Ghilardi Nico , Skoda Radek C. , Meister Björn
Published: April 2018

The adipose tissue-derived hormone leptin regulates body weight homeostasis by decreasing food intake and increasing energy expenditure. The weight-reducing action of leptin is thought to be mediated primarily by signal transduction through the leptin receptor (LR) in the hypothalamus. We have used immunohistochemistry to localize LR-immunoreactive (LR-IR) cells in the rat brain using an antiserum against a portion of the intracellular domain of LR that is common to all LR isoforms. The antiserum recognized the short and long isoforms of LR in transfected hematopoietic BaF3 cells. To examine the chemical nature of target cells for leptin, direct double-labeling immunofluorescence histochemistry was applied. The results show extensive distribution of LR-like immunoreactivity (LR-LI) in the brain with positively stained cells present, e.g., in the choroid plexus, cerebral cortex, hippocampus, thalamus, and hypothalamus. In the hypothalamus, strongly LR-IR neurons were present in the supraoptic nucleus (SON) and paraventricular nucleus (PVN), periventricular nucleus, arcuate nucleus, and lateral hypothalamus. Weaker LR-IR neurons were also demonstrated in the lateral and medial preoptic nuclei, suprachiasmatic nucleus, ventromedial and dorsomedial nuclei, and tuberomammillary nucleus. Confocal laser scanning microscopy showed LR-LI in the periphery of individual cells. In magnocellular neurons of the SON and PVN, LR-LI was demonstrated in vasopressin- and oxytocin-containing neurons. In parvocellular neurons of the PVN, LR-LI was demonstrated in many corticotropin-releasing hormone-containing neurons. LR-IR neurons were mainly seen in the ventromedial aspect of the arcuate nucleus, where LR-LI co-localized with neuropeptide Y. In the ventrolateral part of the arcuate nucleus, LR-LI was present in many large adrenocorticotropic hormone-IR proopiomelanocortin-containing neurons and in a few galanin-, neurotensin-, and growth hormone-releasing hormone-containing neurons. In the dorsomedial arcuate nucleus, few tyrosine hydroxylase (dopamine)-containing neurons were seen to have LR-LI. Melanin-concentrating hormone-containing neurons in the lateral hypothalamus had LR-LI. Based on the immunohistochemical results, possible interactions of leptin with brain mechanisms are discussed.
Growth Factor Receptor Tyrosine Kinases Acutely Regulate Neuronal Sodium Channels through the Src Signaling Pathway
Authors: Hilborn Michael D. , Vaillancourt Richard R. , Rane Stanley G.
Published: April 2018

Growth factor receptor tyrosine kinase (RTK)-activated signaling pathways are well established regulators of neuronal growth and development, but whether these signals provide mechanisms for acute modulation of neuronal activity is just beginning to be addressed. We show in pheochromocytoma (PC12) cells that acute application of ligands for both endogenous RTKs [trkA, basic FGF (bFGF) receptor, and epidermal growth factor (EGF) receptor] and ectopically expressed platelet-derived growth factor (PDGF) receptors rapidly inhibits whole-cell sodium channel currents, coincident with a hyperpolarizing shift in the voltage dependence of inactivation. Sodium channel inhibition by trkA and PDGF receptors is mutually occlusive, suggestive of a common signal transduction mechanism. Furthermore, specific inhibitors for trkA and PDGF RTK activities abrogate sodium channel inhibition in response to NGF and PDGF, respectively, showing that the intrinsic RTK activity of these receptors is necessary for sodium channel inhibition. Use of PDGF receptor mutants deficient for specific signaling activities demonstrated that this inhibition is dependent on RTK interaction with Src but not with other RTK-associated signaling molecules. Inhibition was also compromised in cells expressing dominant-negative Ras. These results suggest a possible mechanism for acute physiological actions of RTKs, and they indicate regulatory functions for Ras and Src that may complement the roles of these signaling proteins in long-term neuronal regulation.
Assembly of Proteins to Postsynaptic Densities after Transient Cerebral Ischemia
Authors: Hu Bing-Ren , Park Minkyu , Martone Maryann E. , Fischer Wolfgang H. , Ellisman Mark H. , Zivin Justin A.
Published: April 2018

Transient ischemia leads to changes in synaptic efficacy and results in selective neuronal damage during the postischemic phase, although the mechanisms are not fully understood. The protein composition and ultrastructure of postsynaptic densities (PSDs) were studied by using a rat transient ischemic model. We found that a brief ischemic episode induced a marked accumulation in PSDs of the protein assembly ATPases,N-ethylmaleimide-sensitive fusion protein, and heat–shock cognate protein-70 as well as the BDNF receptor (trkB) and protein kinases, as determined by protein microsequencing. The changes in PSD composition were accompanied by a 2.5-fold increase in the yield of PSD protein relative to controls. Biochemical modification of PSDs correlated well with an increase in PSD thickness observedin vivoby electron microscopy. We conclude that a brief ischemic episode modifies the molecular composition and ultrastructure of synapses by assembly of proteins to the postsynaptic density, which may underlie observed changes in synaptic function and selective neuronal damage.
Fetal Spinal Cord Transplants Support the Development of Target Reaching and Coordinated Postural Adjustments after Neonatal Cervical Spinal Cord Injury
Authors: Diener Pamela S. , Bregman Barbara S.
Published: April 2018

Neonatal midthoracic spinal cord injury disrupts the development of postural reflexes and hindlimb locomotion. The recovery of rhythmical alternating movements, such as locomotion, is enhanced in injured animals receiving fetal spinal cord transplants. Neonatal cervical spinal cord injury disrupts not only locomotion but also skilled forelimb movement. The aims of this study were to determine the consequences of cervical spinal cord injury on forelimb motor function and to determine whether transplants of fetal spinal cord support normal development of skilled forelimb use after this injury. Three-day-old rats received a cervical spinal cord lesion at C3, with or without a transplant of fetal cervical spinal cord (embryonic day 14); unoperated pups served as controls. Animals were examined daily during the first month of life using a behavioral protocol that assessed reflexes, postural reactions, and forelimb motor skills. They also were trained and tested as adults to assess performance in goal-directed reaching tasks. The onset of postural reflexes was delayed in the lesion-only group, and goal-directed reaching and associated postural adjustments failed to develop. The transplant group developed reflex responses and skilled forelimb activity that resembled normal movement patterns. Transplant animals developed both target reaching and accompanying postural adjustments. Target reaching requires integration of segmental, intersegmental, and supraspinal input to propriospinal and motor neurons over many spinal cord levels. Transplants may support the reestablishment of input onto these neurons, permitting the development of skilled forelimb activity after neonatal cervical spinal cord injury. The neuroanatomical reorganization of descending and propriospinal input was examined in the companion paper (Diener and Bregman, 1998).
Transport and Turnover of Microtubules in Frog Neurons Depend on the Pattern of Axonal Growth
Authors: Chang Sunghoe , Rodionov Vladimir I. , Borisy Gary G. , Popov Sergey V.
Published: April 2018

The transport of axonal microtubules in growing neurites has been a controversial issue because of clear but conflicting results obtained with fluorescence-marking techniques. We have attempted to resolve the discordance via analysis of the relationship between apparent microtubule translocation and cell adhesion. Neuronal cultures were prepared fromXenopusembryos 1 d after injection of Cy3-conjugated tubulin into one of the blastomeres of two-cell-stage embryos. Anterograde translocation of axonal microtubules was observed in neurons cultured on a laminin-coated surface, in agreement with previously published data forXenopusembryonic neurons. However, when neuronal cultures were prepared on a concanavalin A-treated surface, the axonal microtubules were stationary, as reported for all other neurons investigated previously. Neuronal cultures prepared on laminin- and concanavalin A-coated surfaces also demonstrated dramatic differences in the pattern of axonal growth, dynamics of axonal microtubules, and response to brefeldin A treatment. Our findings suggest that transport and dynamics of axonal microtubules may be directly affected by the mechanical tension produced by growth cone activity.
The Ca2+Channel β3Subunit Differentially Modulates G-Protein Sensitivity of α1Aand α1BCa2+Channels
Authors: Roche John P. , Treistman Steven N.
Published: April 2018

We have shown previously that the Ca2+channel β3subunit is capable of modulating tonic G-protein inhibition of α1Aand α1BCa2+channels expressed in oocytes. Here we determine the modulatory effect of the Ca2+channel β3subunit on M2muscarinic receptor-activated G-protein inhibition and whether the β3subunit modulates the G-protein sensitivity of α1Aand α1Bcurrents equivalently. To compare the relative inhibition by muscarinic activation, we have used successive ACh applications to remove the large tonic inhibition of these channels. We show that the resulting rebound potentiation results entirely from the loss of tonic G-protein inhibition; although the currents are temporarily relieved of tonic inhibition, they are still capable of undergoing inhibition through the muscarinic pathway. Using this rebound protocol, we demonstrate that the inhibition of peak current amplitude produced by M2receptor activation is similar for α1Aand α1Bcalcium currents. However, the contribution of the voltage-dependent component of inhibition, characterized by reduced inhibition at very depolarized voltage steps and the relief of inhibition by depolarizing prepulses, was slightly greater for the α1Bcurrent than for the α1Acurrent. After co-expression of the β3subunit, the sensitivity to M2receptor-induced G-protein inhibition was reduced for both α1Aand α1Bcurrents; however, the reduction was significantly greater for α1Acurrents. Additionally, the difference in the voltage dependence of inhibition of α1Aand α1Bcurrents was heightened after co-expression of the Ca2+channel β3subunit. Such differential modulation of sensitivity to G-protein modulation may be important for fine tuning release in neurons that contain both of these Ca2+channels.
RGS4 Inhibits Signaling by Group I Metabotropic Glutamate Receptors
Authors: Saugstad Julie A. , Marino Michael J. , Folk Julie A. , Hepler John R. , Conn P. Jeffrey
Published: April 2018

Metabotropic glutamate receptors (mGluRs) couple to heterotrimeric G-proteins and regulate cell excitability and synaptic transmission in the CNS. Considerable effort has been focused on understanding the cellular and biochemical mechanisms that underlie regulation of signaling by G-proteins and their linked receptors, including the mGluRs. Recent findings demonstrate that regulators of G-protein signaling (RGS) proteins act as effector antagonists and GTPase-activating proteins for Gαsubunits to inhibit cellular responses by G-protein-coupled receptors. RGS4 blocks Gqactivation of phospholipase Cβ and is expressed broadly in rat brain. The group I mGluRs (mGluRs 1 and 5) couple to Gqpathways to regulate several effectors in the CNS. We examined the capacity of RGS4 to regulate group I mGluR responses. InXenopusoocytes, purified RGS4 virtually abolishes the mGluR1a- and mGluR5a-mediated but not the inositol trisphospate-mediated activation of a calcium-dependent chloride current. Additionally, RGS4 markedly attenuates the mGluR5-mediated inhibition of potassium currents in hippocampal CA1 neurons. This inhibition is dose-dependent and occurs at concentrations that are virtually identical to those required for inhibition of phospholipase C activity in NG108–15 membranes and reconstituted systems using purified proteins. These findings demonstrate that RGS4 can modulate mGluR responses in neurons, and they highlight a previously unknown mechanism for regulation of G-protein-coupled receptor signaling in the CNS.
Interaction of Presenilins with the Filamin Family of Actin-Binding Proteins
Authors: Zhang Wanjiang , Han Sang Woo , McKeel Daniel W. , Goate Alison , Wu Jane Y.
Published: April 2018

Mutations in presenilin genes PS1 and PS2 account for ∼50% of early-onset familial Alzheimer’s disease (FAD). The PS1 and PS2 genes encode highly homologous transmembrane proteins related to theCaenorhabditis eleganssel-12 and spe-4 gene products. A hydrophilic loop region facing the cytoplasmic compartment is likely to be functionally important because at least 14 mutations in FAD patients have been identified in this region. We report here that the loop regions of PS1 and PS2 interact with nonmuscle filamin (actin-binding protein 280, ABP280) and a structurally related protein (filamin homolog 1, Fh1). Overexpression of PS1 appears to modify the distribution of ABP280 and Fh1 proteins in cultured cells. A monoclonal antibody recognizing ABP280 and Fh1 binds to blood vessels, astrocytes, neurofibrillary tangles, neuropil threads, and dystrophic neurites in the AD brain. Detection of ABP280/Fh1 proteins in these structures suggests that these presenilin-interacting proteins may be involved in the development of AD and that interactions between presenilins and ABP280/Fh1 may be functionally significant. The ABP280 gene is located on the human X chromosome, whereas the newly identified Fh1 gene maps to human chromosome 3. These results provide a new basis for understanding the function of presenilin proteins and further implicate cytoskeletal elements in AD pathogenesis.
Single Neuron Mosaics of theDrosophila gigasMutant Project beyond Normal Targets and Modify Behavior
Authors: Canal Inmaculada , Acebes Angel , Ferrús Alberto
Published: April 2018

gigasis a lethal mutant that differentiates enlarged cells, including the nucleus. This trait manifests only after the completion of the mitotic program. We have taken advantage of this phenotype to testin vivothe capacity of normal target cells to arrest the growth of mutant sensory axons. Single neuron connectivity changes have been analyzed in mosaics after horseradish peroxidase retrograde tracings. A mutant mechanoreceptor neuron, growing over a genetically normal substrate, contacts its normal target, and in addition projects to novel areas of the CNS. The mutant axon does terminate its growth eventually, and the new additional targets that are reached correspond to mechanoreceptor domains in other ganglia, indicating that this territorial constraint is operational in the mutant.gigasneurons maintain their stereotyped profile and represent an expanded version of the normal branching pattern. The ultrastructure of the invading projections does not reveal gliotic or necrotic reactions from the new cell contacts. The functional consequences of the connectivity changes produced by the mutant mechanoreceptors have been studied in grooming behavior. Mosaic flies carrying a singlegigasmechanoreceptor show modified, albeit context-coherent, grooming responses after stimulation of the mutant bristle, whereas the response from neighboring normal sensory neurons remains unchanged. All of these experiments indicate that target recognition and growth arrest are two dissectible processes of neural development, and they highlight the autonomous features of the growth cone during pathfinding.
Primary Neural Precursors and Intermitotic Nuclear Migration in the Ventricular Zone of Adult Canaries
Authors: Alvarez-Buylla Arturo , Garcı́a-Verdugo Jose Manuel , Mateo Adria S. , Merchant-Larios Horacio
Published: April 2018

New neurons continue to be born in the ventricular zone (VZ) of the lateral ventricles in the brain of adult birds. On the basis of serial section reconstruction and electron microscopy, we determined that the VZ of the adult canary brain is composed of three main cell types (A, B, and E). Type A cells were never found in contact with the ventricle and had microtubule-rich processes typical of young migrating neurons. Type B cells were organized as a pseudostratified epithelium, all contacted the ventricle, and most had a characteristic single cilium. Type E cells, also in contact with ventricle, were ultrastructurally similar to the mammalian multiciliated ependymal cells. After six injections of [3H]-thymidine (1 every 12 hr), Types A and B cells were found labeled. Type E cells were never [3H]-thymidine labeled. One to two hours after a single injection of [3H]-thymidine, all labeled cells corresponded to Type B cells. At survivals of 5, 24, and 74 hr after [3H]-thymidine injection, the proportion of labeled Type B cells decreased and that of Type A cells increased, indicating that Type B cells were the primary precursors. Most [3H]-labeled nuclei at 1–2 hr after [3H]-thymidine injection were separated from the ventricular cavity, but most of the mitotic cells were adjacent to the ventricle. This observation and measurements of the distance between labeled nuclei and the ventricular surface at 1, 5, 7, and 11 hr after [3H]-thymidine injection indicate that Type B cell nuclei move toward the ventricle to divide. This work reveals the architecture of the VZ in an adult vertebrate brain, identifies the primary precursor of new neurons, and describes nuclear translocation of these precursors during the cell cycle.
Mitogen-Activated Protein and Tyrosine Kinases in the Activation of Astrocyte Volume-Activated Chloride Current
Authors: Crépel Valérie , Panenka William , Kelly Melanie E. M. , MacVicar Brian A.
Published: April 2018

Astrocytes swell during neuronal activity as they accumulate K+to buffer the increase in external K+released from neurons. This swelling activates volume-sensitive Cl−channels, which are thought to be important in regulatory volume decrease and in the response of the CNS to trauma and excitotoxicity. Mitogen-activated protein (MAP) kinases also are activated by cell volume changes, but their roles in volume regulation are unknown. We have investigated the role of tyrosine and MAP kinases in the activation of volume-activated Cl−channels in cultured astrocytes, using whole-cell patch-clamp recording and Western immunoblots. As previously described, hypo-osmotic solution induced an outwardly rectifying Cl−current, which was blocked by NPPB and SITS. This Cl−current did not depend on [Ca2+]ibecause it was still observed when 20 mmBAPTA was included in the pipette, but it did exhibit rundown when ATP was omitted. Inhibition of tyrosine kinases with genistein or tyrphostin A23 (but not the inactive agents daidzein and tyrphostin A1) blocked the Cl−current. The MAP kinase kinase (MEK) inhibitor PD 98059 reversibly inhibited activation of the Cl−current by hypo-osmotic solution. Western immunoblots showed that genistein or PD 98059 blocked activation of Erk-1 and Erk-2 by hypo-osmotic solution in astrocytes. Therefore, activation of tyrosine and MAP kinases by swelling is a critical step in the opening of volume-sensitive Cl−channels.
Long-Term Potentiation of Synaptic Transmission in the Avian Hippocampus
Authors: Margrie Troy W. , Rostas John A. P. , Sah Pankaj
Published: April 2018

The avian hippocampus plays a pivotal role in memory required for spatial navigation and food storing. Here we have examined synaptic transmission and plasticity within the hippocampal formation of the domestic chicken using anin vitroslice preparation. With the use of sharp microelectrodes we have shown that excitatory synaptic inputs in this structure are glutamatergic and activate both NMDA- and AMPA-type receptors on the postsynaptic membrane. In response to tetanic stimulation, the EPSP displayed a robust long-term potentiation (LTP) lasting >1 hr. This LTP was unaffected by blockade of NMDA receptors or chelation of postsynaptic calcium. Application of forskolin increased the EPSP and reduced paired-pulse facilitation (PPF), indicating an increase in release probability. In contrast, LTP was not associated with a change in the PPF ratio. Induction of LTP did not occlude the effects of forskolin. Thus, in contrast to NMDA receptor-independent LTP in the mammalian brain, LTP in the chicken hippocampus is not attributable to a change in the probability of transmitter release and does not require activation of adenylyl cyclase. These findings indicate that a novel form of synaptic plasticity might underlie learning in the avian hippocampus.
Bax Involvement in p53-Mediated Neuronal Cell Death
Authors: Xiang Hong , Kinoshita Yoshito , Knudson C. Michael , Korsmeyer Stanley J. , Schwartzkroin Philip A. , Morrison Richard S.
Published: April 2018

The tumor suppressor gene p53 has been implicated in the loss of neuronal viability, but the signaling events associated with p53-mediated cell death in cortical and hippocampal neurons are not understood. Previous work has shown that adenovirus-mediated delivery of the p53 gene causes cortical and hippocampal neuronal cell death with some features typical of apoptosis. In the present study we determined whether p53-initiated changes in neuronal viability were dependent on members of the Bcl-2 family of cell death regulators. Primary cultures of cortical neurons were derived from animals containing Bax (+/+ and +/−) or those deficient in Bax (−/−). Cell damage was assessed by direct cell counting and by measurements of MTT activity. Neurons containing at least one copy of the Bax gene were damaged severely by exposure to excitotoxins or by the induction of DNA damage. In contrast, Bax-deficient neurons (−/−) exhibited significant protection from both types of injury. Bax protein expression was elevated significantly by glutamate exposure, but not by camptothecin-induced DNA damage in wild-type neurons. The glutamate-induced increase in Bax protein was dependent on the presence of the p53 gene. However, increased p53 expression, using adenovirus-mediated transduction, was not sufficient by itself to elevate Bax protein levels. These results demonstrate that Bax is required for neuronal cell death in response to some forms of cytotoxic injury and further support the key role for p53 activation in response to excitotoxic and genotoxic injury.
Coordination of Neuronal Activity in Developing Visual Cortex by Gap Junction-Mediated Biochemical Communication
Authors: Kandler Karl , Katz Lawrence C.
Published: April 2018

During brain development, endogenously generated coordinated neuronal activity regulates the precision of developing synaptic circuits (Shatz and Stryker, 1988; Weliky and Katz, 1997). In the neonatal neocortex, a form of endogenous coordinated activity is present as locally restricted intercellular calcium waves that are mediated by gap junctions (Yuste et al., 1992). As in other neuronal and non-neuronal systems, these coordinated calcium fluctuations may form the basis of functional cell assemblies (for review, see Warner, 1992; Peinado et al., 1993b). In the present study, we investigated the cellular mechanisms that mediate the activation of neuronal domains and the propagation of intercellular calcium waves in slices from neonatal rat neocortex. The occurrence of neuronal domains did not depend on intercellular propagation of regenerative electrical signals because domains persisted after blockade of sodium and calcium-dependent action potentials. Neuronal domains were elicited by intracellular infusion of inositol trisphosphate (IP3) but not of calcium, indicating the involvement of IP3-related second-messenger systems. Pharmacological stimulation of metabotropic glutamate receptors, which are linked to the production of IP3, elicited similarly coordinated calcium increases, whereas pharmacological blockade of metabotropic glutamate receptors dramatically reduced the number of neuronal domains. Therefore, the propagating cellular signal that causes the occurrence of neuronal domains seems to be inositol trisphosphate but not calcium. Because coordination of neuronal calcium changes by gap junctions is independent of electrical signals, the function of gap junctions between neocortical neurons is probably to synchronize biochemical rather than electrical activity.
The Differential Expression of Low-Threshold Sustained Potassium Current Contributes to the Distinct Firing Patterns in Embryonic Central Vestibular Neurons
Authors: Gamkrelidze Georgi , Giaume Christian , Peusner Kenna D.
Published: April 2018

The principal cells of the chick tangential nucleus are second-order sensory neurons that participate in the three-neuron vestibulo-ocular and vestibulocollic reflexes. In postnatal animals, second-order vestibular neurons fire repetitively on depolarization. Previous studies have shown that, although this is an important feature for normal reflex function, it is only acquired gradually during embryonic development. Whereas at 13 embryonic days (E13) the principal cells accommodate after firing a single spike, at E16 a few principal cells repetitively can fire multiple action potentials on depolarization. Finally, in the hatchling, the vast majority of principal cells is capable of nonaccommodating firing on depolarization. As a first step in understanding the mechanisms underlying developmental change in excitability of these second-order vestibular neurons, we analyzed the outward potassium currents and their role in accommodation, using brainstem slices at E16. The principal cells exhibited transient and sustained potassium currents, with both of these containing calcium-dependent components. Further, both high- and low-threshold sustained potassium currents have been distinguished. The low-threshold dendrotoxin-sensitive sustained potassium current (IDS) is associated with principal cells that accommodate and is not expressed in those that fire repetitively. Finally, blocking ofIDStransforms accommodating cells into neurons capable of firing trains of action potentials on depolarization. These findings indicate that suppression ofIDSduring development is sufficient to transform accommodating principal cells into nonaccommodating firing neurons and suggests that developmental regulation of this current is necessary for the establishment of normal vestibular function.
Organization and Reorganization of Neuromuscular Junctions in Mice Lacking Neural Cell Adhesion Molecule, Tenascin-C, or Fibroblast Growth Factor-5
Authors: Moscoso Lisa M. , Cremer Harold , Sanes Joshua R.
Published: April 2018

Many proteins have been hypothesized to mediate intercellular interactions that regulate the formation, maturation, and maintenance of the skeletal neuromuscular junction. Three of the best characterized of these are a membrane-associated adhesion molecule, neural cell adhesion molecule (N-CAM), an extracellular matrix component, tenascin-C, and a soluble growth factor, fibroblast growth factor-5 (FGF-5). To assess the roles of these molecules in synaptogenesisin vivo, we examined neuromuscular junctions in homozygous mutant mice lacking N-CAM, tenascin-C, FGF-5, or both N-CAM and tenascin-C. End plates were 14% smaller in N-CAM-deficient mice than in controls, and formation of junctional folds was delayed in this mutant. In all other respects tested, however, the structure and molecular architecture of neuromuscular junctions were normal in all three single mutants and in the double mutant. We also tested the abilities of damaged motor axons to reinnervate mutant muscle after axotomy and of intact motor axons to sprout after partial denervation. Again, no significant differences among genotypes were observed. Together, these results demonstrate that N-CAM, tenascin-C, and FGF-5 are dispensable for major aspects of synaptic development and regeneration.