bluuebunny/crossref_metadata_2025 huggingface dataset:
Separate Proliferation Kinetics of Fibroblast Growth Factor-Responsive and Epidermal Growth Factor-Responsive Neural Stem Cells within the Embryonic Forebrain Germinal Zone
Authors: Martens David J. , Tropepe Vincent , van der Kooy Derek
Published: April 2018

The embryonic forebrain germinal zone contains two separate and additive populations of epidermal growth factor (EGF)- and fibroblast growth factor (FGF)-responsive stem cells that both exhibit self-renewal and multipotentiality. Although cumulative S phase labeling studies have investigated the proliferation kinetics of the overall population of precursor cells within the forebrain germinal zone through brain development, little is known about when and how (symmetrically or asymmetrically) the small subpopulations of stem cells are proliferatingin vivo. This has been determined by injecting timed-pregnant mice with high doses of tritiated thymidine (3H-thy) to kill any stem cells proliferating within the striatal germinal zonein vivoand then by assaying for neurosphere formationin vitro. Injections of 0.8 mCi of3H-thy given every 2 hr for 12 hr to timed-pregnant mice at E11, E14, and E17 resulted in significant depletions in the number of neurospheres generated by FGF-responsive stem cells at E11 and by EGF-responsive and FGF-responsive stem cells at E14 and E17. With increasing embryonic age, the depletions observed in the number of neurospheres generatedin vitroin response to FGF2 after exposure to3H-thyin vivodecreased, suggesting there is an increase in the length of the cell cycle of FGF-responsive neural stem cells through embryonic development. The results suggest that the FGF-responsive stem cell population expands between E11 and E14 by dividing symmetrically, but switches to primarily asymmetric division between E14 and E17. The EGF-responsive stem cells arise after E11, and their population expands through symmetric divisions and through asymmetric divisions of FGF-responsive stem cells.
Fast Network Oscillations in the Newborn Rat HippocampusIn Vitro
Authors: Palva J. Matias , Lamsa Karri , Lauri Sari E. , Rauvala Heikki , Kaila Kai , Taira Tomi
Published: April 2018

Spontaneous neural activity is crucial for the formation of the intricate patterns of cortical connectivity during development. In particular, temporal correlations in presynaptic and postsynaptic activity have been hypothesized to be a critical determinant in the selection of neurons that are to become wired together. To date, however, temporally correlated activity in the neonatal brain has been believed to take place with a precision of tens of milliseconds to seconds.

Here we describe a novel type of a fast network oscillation associated with millisecond synchronization of pyramidal cell firing in newborn rat hippocampusin vitro. Individual pyramidal neurons fired mainly at lower gamma frequencies (20–40 Hz) but were synchronized into a high-frequency (100–400 Hz) population oscillation that was reflected in field potential spikes and intracellular AMPA–kainate receptor-mediated currents. The high-frequency population oscillation was patterned by a gamma-frequency modulatory oscillation. The gamma modulation was imposed by GABAergic currents, which exerted an inhibitory action on pyramidal neurons. Patterned activity based on GABAergic inhibition and glutamatergic excitation thus occurs already in newborn hippocampus. The network oscillations described here may be a mechanism for selective coincidence detection with a millisecond range temporal precision to shape the patterns of connectivity within the emerging hippocampal synaptic circuitry.
Enhanced and Impaired Attentional Performance After Infusion of D1 Dopaminergic Receptor Agents into Rat Prefrontal Cortex
Authors: Granon Sylvie , Passetti Filippo , Thomas Kerrie L. , Dalley Jeffrey W. , Everitt Barry J. , Robbins Trevor W.
Published: April 2018

The role in spatial divided and sustained attention of D1 and D2-like dopamine (DA) receptors in the rat prelimbic medial prefrontal cortex (mPFC) was investigated in a five-choice serial reaction time task. Rats were trained to detect brief flashes of light (0.5–0.25 sec) presented randomly in a spatial array of five apertures. When performance stabilized, animals received bilateral microinfusions of either the D1 DA receptor antagonist SCH 23390, the D1 DA receptor agonist SKF 38393, or the D2 DA antagonist sulpiride into the mPFC. Rats were divided into two groups, with low (<75% correct) and high (>75%) baseline levels of accuracy. Infusions of the D2 receptor antagonist sulpiride had no significant effect on any task variable. SCH 23390 (0.3 μg) selectively impaired the accuracy of attentional performance in rats in the high baseline condition. By contrast, SKF 38393 (0.06 μg) enhanced the accuracy of attentional performance in the low baseline condition, a lower dose (0.03 μg) also increasing the speed of making correct responses. Finally, the beneficial effects of SKF-383893 on choice accuracy were antagonized by SCH 23390 (1.0 μg).

The results provide apparently the first demonstration of enhanced cognitive function after local administration of a D1 receptor agonist to the mPFC and suggest dissociable roles of D1 and D2 DA receptors of the mPFC in modulating attentional function.
Backpropagation of Physiological Spike Trains in Neocortical Pyramidal Neurons: Implications for Temporal Coding in Dendrites
Authors: Williams Stephen R. , Stuart Greg J.
Published: April 2018

In vivoneocortical neurons fire apparently random trains of action potentials in response to sensory stimuli. Does this randomness represent a signal or noise around a mean firing rate? Here we use the timing of action potential trains recordedin vivoto explore the dendritic consequences of physiological patterns of action potential firing in neocortical pyramidal neuronsin vitro. We find that action potentials evoked by physiological patterns of firing backpropagate threefold to fourfold more effectively into the distal apical dendrites (>600 μm from the soma) than action potential trains reflecting their mean firing rate. This amplification of backpropagation was maximal during high-frequency components of physiological spike trains (80–300 Hz). The disparity between backpropagation during physiological and mean firing patterns was dramatically reduced by dendritic hyperpolarization. Consistent with this voltage dependence, dendritic depolarization amplified single action potentials by fourfold to sevenfold, with a spatial profile strikingly similar to the amplification of physiological spike trains. Local blockade of distal dendritic sodium channels substantially reduced amplification of physiological spike trains, but did not significantly alter action potential trains reflecting their mean firing rate. Dendritic electrogenesis during physiological spike trains was also reduced by the blockade of calcium channels. We conclude that amplification of backpropagating action potentials during physiological spike trains is mediated by frequency-dependent supralinear temporal summation, generated by the recruitment of distal dendritic sodium and calcium channels. Together these data indicate that the temporal nature of physiological patterns of action potential firing contains a signal that is transmitted effectively throughout the dendritic tree.
Interstitial Carbonic Anhydrase (CA) Activity in Brain Is Attributable to Membrane-Bound CA Type IV
Authors: Tong Chi-Kun , Brion Luc P. , Suarez Carlos , Chesler Mitchell
Published: April 2018

We tested the hypothesis that extracellular membrane-bound carbonic anhydrase (CA) type IV is responsible for the regulation of interstitial pH (pHo) transients in brain. Rat hippocampal slices were incubated in phosphatidylinositol-specific phospholipase C (PI-PLC), which cleaves the link of CA IV to the external face of plasma membranes. Then evoked alkaline pHoshifts were studied in a recording chamber, using pH microelectrodes. Incubation fluid was saved for later analysis. The ability to buffer a rapid alkaline load was reduced markedly in PI-PLC-treated tissue as compared with adjacent, paired control slices. The effect of benzolamide (a poorly permeant CA inhibitor) on evoked pHoshifts was diminished greatly in the PI-PLC-treated tissue, consistent with the washout of interstitial CA. Treatment of the incubation fluid with SDS abolished nearly all of the CA activity in fluid from controls, whereas an SDS-insensitive component remained in the fluid from PI-PLC-treated slices. These data suggested that CA type II (which is blocked by SDS) leaked from injured glial cells in both slice preparations, whereas CA type IV (which is insensitive to SDS) was liberated selectively into the fluid from PI-PLC-treated tissue. Western blot analysis was consistent with this interpretation, demonstrating a predominance of CA IV in the incubation fluid from PI-PLC-treated tissue and variable amounts of CA II in fluid from PI-PLC-treated and control slices. These results demonstrate that interstitial CA activity brain is attributable principally to membrane-bound CA IV.
Associative Long-Term Depression in the Hippocampus Is Dependent on Postsynaptic N-Type Ca2+Channels
Authors: Normann Claus , Peckys Diana , Schulze Christian H. , Walden Jörg , Jonas Peter , Bischofberger Josef
Published: April 2018

Long-term depression (LTD) is a form of synaptic plasticity that can be induced either by low-frequency stimulation of presynaptic fibers or in an associative manner by asynchronous pairing of presynaptic and postsynaptic activity. We investigated the induction mechanisms of associative LTD in CA1 pyramidal neurons of the hippocampus using whole-cell patch-clamp recordings and Ca2+imaging in acute brain slices. Asynchronous pairing of postsynaptic action potentials with EPSPs evoked with a delay of 20 msec induced a robust, long-lasting depression of the EPSP amplitude to 43%. Unlike LTD induced by low-frequency stimulation, associative LTD was resistant to the application ofd-AP-5, indicating that it is independent of NMDA receptors. In contrast, associative LTD was inhibited by (S)-α-methyl-4-carboxyphenyl-glycine, indicating the involvement of metabotropic glutamate receptors. Furthermore, associative LTD is dependent on the activation of voltage-gated Ca2+channels by postsynaptic action potentials. Both nifedipine, an L-type Ca2+channel antagonist, and ω-conotoxin GVIA, a selective N-type channel blocker, abolished the induction of associative LTD. 8-hydroxy-2-dipropylaminotetralin (OH-DPAT), a 5-HT1Areceptor agonist, inhibited postsynaptic Ca2+influx through N-type Ca2+channels, without affecting presynaptic transmitter release. OH-DPAT also inhibited the induction of associative LTD, suggesting that the involvement of N-type channels makes synaptic plasticity accessible to modulation by neurotransmitters. Thus, the modulation of N-type Ca2+channels provides a gain control for synaptic depression in hippocampal pyramidal neurons.
Dopamine and cAMP-Regulated Phosphoprotein 32 kDa Controls Both Striatal Long-Term Depression and Long-Term Potentiation, Opposing Forms of Synaptic Plasticity
Authors: Calabresi Paolo , Gubellini Paolo , Centonze Diego , Picconi Barbara , Bernardi Giorgio , Chergui Karima , Svenningsson Per , Fienberg Allen A. , Greengard Paul
Published: April 2018

A complex chain of intracellular signaling events, critically important in motor control, is activated by the stimulation of D1-like dopamine (DA) receptors in striatal neurons. At corticostriatal synapses on medium spiny neurons, we provide evidence that the D1-like receptor-dependent activation of DA and cyclic adenosine 3′,5′ monophosphate-regulated phosphoprotein 32 kDa is a crucial step for the induction of both long-term depression (LTD) and long-term potentiation (LTP), two opposing forms of synaptic plasticity. In addition, formation of LTD and LTP requires the activation of protein kinase G and protein kinase A, respectively, in striatal projection neurons. These kinases appear to be stimulated by the activation of D1-like receptors in distinct neuronal populations.
Initiating or Blocking Locomotion in Spinal Cats by Applying Noradrenergic Drugs to Restricted Lumbar Spinal Segments
Authors: Marcoux Judith , Rossignol Serge
Published: April 2018

After an acute low thoracic spinal transection (T13), cats can be made to walk with the hindlimbs on a treadmill with clonidine, an α2-noradrenergic agonist. Because previous studies of neonatal rat spinal cordin vitrosuggest that the most important lumbar segments for rhythmogenesis are L1–L2, we investigated the role of various lumbar segments in the initiation of walking movements on a treadmill of adult cats spinalized (T13), 5–6 d earlier. The locomotor activities were evaluated from electromyographic and video recordings. The results show that: (1) localized topical application of clonidine in restricted baths over either the L3–L4 or the L5–L7 segments was sufficient to induce walking movements. Yohimbine, an α2-noradrenergic antagonist, could block this locomotion when applied over L3–L4 or L5–L7; (2) microinjections of clonidine in one or two lumbar segments from L3 to L5 could also induce locomotion; (3) after an intravenous injection of clonidine, locomotion was blocked by microinjections of yohimbine in segments L3, L4, or L5 but not if the injection was in L6; (4) locomotion was also blocked in all cases by additional spinal transections at L3 or L4. These results show that it is possible to initiate walking in the adult spinal cat with a pharmacological stimulation of a restricted number of lumbar segments and also that the integrity of the L3–L4 segments is necessary to sustain the locomotor activity.
Loss of Presynaptic and Postsynaptic Structures Is Accompanied by Compensatory Increase in Action Potential-Dependent Synaptic Input to Layer V Neocortical Pyramidal Neurons in Aged Rats
Authors: Wong Tak Pan , Marchese Giorgio , Casu Maria Antonietta , Ribeiro-da-Silva Alfredo , Cuello A. Claudio , De Koninck Yves
Published: April 2018

Reduction in both presynaptic and postsynaptic structures in the aging neocortex may significantly affect functional synaptic properties in this area. To directly address this issue, we combined whole-cell patch-clamp recording of spontaneously occurring postsynaptic currents (PSCs) with morphological analysis of layer V pyramidal neurons in the parietal cortex of young adult (1- to 2-month-old) and aged (28- to 37-month-old) BNxF344 F1hybrid rats. Analysis of spontaneous PSCs was used to contrast functional properties of basal synaptic input with structural alterations in the dendritic tree of pyramidal neurons and density of terminals in contact with these cells.

We observed significant changes in a number of morphological parameters of pyramidal neurons in aged rats. These include smaller cell body size and fewer basal dendritic branches (but not of oblique dendrites and dendritic tufts) and spines. Ultrastructural analysis also revealed a lower density of presynaptic terminals per unit length of postsynaptic membrane of labeled pyramidal neurons in the aged brain. This reduction in both presynaptic and postsynaptic elements was paralleled by a significant decrease in frequency of tetrodotoxin-insensitive miniature (action potential-independent) PSCs (mPSCs). The frequency of excitatory and inhibitory mPSCs was reduced to the same extent. In contrast, no significant change was observed in the frequency of spontaneous PSCs recorded in absence of tetrodotoxin (sPSCs), indicating an increase in action potential-dependent (frequencysPSCs− frequencymPSCs) input to pyramidal neurons in the aged group. This functional compensation may explain the lack of drastic loss of spontaneous neuronal activity in normal aging.
Neuroprotective Role of Dopamine Against Hippocampal Cell Death
Authors: Bozzi Yuri , Vallone Daniela , Borrelli Emiliana
Published: April 2018

Glutamate excitotoxicity plays a key role in the induction of neuronal cell death occurring in many neuropathologies, including epilepsy. Systemic administration of the glutamatergic agonist kainic acid (KA) is a well characterized model to study epilepsy-induced brain damage. KA-evoked seizures in mice result in hippocampal cell death, with the exception of some strains that are resistant to KA excitotoxicity. Little is known about the factors that prevent epilepsy-related neurodegeneration. Here we show that dopamine has such a function through the activation of the D2 receptor (D2R). D2R gene inactivation confers susceptibility to KA excitotoxicity in two mouse strains known to be resistant to KA-induced neurodegeneration. D2R−/− mice develop seizures when administered KA doses that are not epileptogenic for wild-type (WT) littermates. The spatiotemporal pattern of c-fosand c-junmRNA induction well correlates with the occurrence of seizures in D2R−/− mice. Moreover, KA-induced seizures result in extensive hippocampal cell death in D2R−/− but not WT mice. In KA-treated D2R−/− mice, hippocampal neurons die by apoptosis, as indicated by the presence of fragmented DNA and the induction of the proapoptotic protein BAX. These results reveal a central role of D2Rs in the inhibitory control of glutamate neurotransmission and excitotoxicity.
Induction of Cyclin-Dependent Kinase 5 in the Hippocampus by Chronic Electroconvulsive Seizures: Role of ΔFosB
Authors: Chen Jingshan , Zhang Yajun , Kelz Max B. , Steffen Cathy , Ang Eugenius S. , Zeng Ling , Nestler Eric J.
Published: April 2018

The transcription factor ΔFosB is induced in the hippocampus and other brain regions by repeated electroconvulsive seizures (ECS), an effective antidepressant treatment. The unusually high stability of this protein makes it an attractive candidate to mediate some of the long-lasting changes in the brain caused by ECS treatment. To understand how ΔFosB might alter brain function, we examined the gene expression profiles in the hippocampus of inducible transgenic mice that express ΔFosB in this brain region by the use of cDNA expression arrays that contain 588 genes. Of the 430 genes detected, 20 genes were consistently upregulated, and 14 genes were downregulated, by >50%. One of the upregulated genes is cyclin-dependent kinase 5 (cdk5). On the basis of its purported role in regulating neuronal structure, we studied directly whether cdk5 is a true target for ΔFosB. Upregulation of cdk5 immunoreactivity in the hippocampus was confirmed by Western blotting in the ΔFosB-expressing transgenic mice as well as in rats treated chronically with ECS. Chronic ECS treatment also increased, in the hippocampus, the phosphorylation state of tau, a microtubule-associated protein that is a known substrate for cdk5. A 1.6 kb fragment of the cdk5 promoter was cloned, and activity of the promoter was found to be increased after overexpression of ΔFosB in cell culture. Moreover, mutation of the single consensus activator protein-1 site contained within the cdk5 promoter fragment completely abolished activation of the promoter by ΔFosB. Together, these results suggest that cdk5 is one target by which ΔFosB produces some of its physiological effects in the hippocampus and thereby mediates certain long-term consequences of chronic ECS treatment.
Delaying Caspase Activation by Bcl-2: A Clue to Disease Retardation in a Transgenic Mouse Model of Amyotrophic Lateral Sclerosis
Authors: Vukosavic Slobodanka , Stefanis Leonidas , Jackson-Lewis Vernice , Guégan Christelle , Romero Norma , Chen Caiping , Dubois-Dauphin Michel , Przedborski Serge
Published: April 2018

Molecular mechanisms of apoptosis may participate in motor neuron degeneration produced by mutant copper/zinc superoxide dismutase (mSOD1), the only proven cause of amyotrophic lateral sclerosis (ALS). Consistent with this, herein we show that the spinal cord of transgenic mSOD1 mice is the site of the sequential activation of caspase-1 and caspase-3. Activated caspase-3 and its produced β-actin cleavage fragments are found in apoptotic neurons in the anterior horn of the spinal cord of affected transgenic mSOD1 mice; although such neurons are few, their scarcity should not undermine the potential importance of apoptosis in the overall mSOD1-related neurodegeneration. Overexpression of the anti-apoptotic protein Bcl-2 attenuates neurodegeneration and delays activation of the caspases and fragmentation of β-actin. These data demonstrate that caspase activation occurs in this mouse model of ALS during neurodegeneration. Our study also suggests that modulation of caspase activity may provide protective benefit in the treatment of ALS, a view that is consistent with our recent demonstration of caspase inhibition extending the survival of transgenic mSOD1 mice.
Neurotrophin-4/5 Alters Responses and Blocks the Effect of Monocular Deprivation in Cat Visual Cortex during the Critical Period
Authors: Gillespie Deda C. , Crair Michael C. , Stryker Michael P.
Published: April 2018

The mechanisms underlying changes in neural responses and connections in the visual cortex may be studied by occluding one eye during a critical period in early postnatal life. Under these conditions, neurons in the visual cortex rapidly lose their responses to the deprived eye and ultimately lose many of their inputs from that eye. Cats at the peak of the critical period received infusions of exogenous neurotrophin NT-4/5 into primary visual cortex beginning before a short period of monocular deprivation. Within areas affected by NT-4/5, cortical cells remained responsive to the deprived eye, and maps of ocular dominance were no longer evident using intrinsic-signal optical imaging. Cortical cells also became broadly tuned for stimulus orientation and less responsive to visual stimulation through either eye. These effects required at least 48 hr exposure to the neurotrophin and were specific for trkB, because they were not seen with the trkA or trkC ligands NGF or NT-3. Even after neurons had already lost their responses to the deprived eye, subsequent NT-4/5 infusion could restore them. The NT-4/5 effects were not seen after the critical period. Together, these results suggest that trkB activation during the critical period may promote promiscuous connections independent of correlated activity.
Association of Cocaine- and Amphetamine-Regulated Transcript-Immunoreactive Elements with Thyrotropin-Releasing Hormone-Synthesizing Neurons in the Hypothalamic Paraventricular Nucleus and Its Role in the Regulation of the Hypothalamic–Pituitary–Thyroid Axis during Fasting
Authors: Fekete Csaba , Mihály Emese , Luo Lu-Guang , Kelly Joseph , Clausen Jes Thorn , Mao QuanFu , Rand William M. , Moss Larry Gene , Kuhar Michael , Emerson Charles H. , Jackson Ivor M. D. , Lechan Ronald M.
Published: April 2018

Because cocaine- and amphetamine-regulated transcript (CART) coexists with α-melanocyte stimulating hormone (α-MSH) in the arcuate nucleus neurons and we have recently demonstrated that α-MSH innervates TRH-synthesizing neurons in the hypothalamic paraventricular nucleus (PVN), we raised the possibility that CART may also be contained in fibers that innervate hypophysiotropic thyrotropin-releasing hormone (TRH) neurons and modulate TRH gene expression. Triple-labeling fluorescentin situhybridization and immunofluorescence were performed to reveal the morphological relationships between pro-TRH mRNA-containing neurons and CART- and α-MSH-immunoreactive (IR) axons. CART-IR axons densely innervated the majority of pro-TRH mRNA-containing neurons in all parvocellular subdivisions of the PVN and established asymmetric synaptic specializations with pro-TRH neurons. However, whereas all α-MSH-IR axons in the PVN contained CART-IR, only a portion of CART-IR axons in contact with pro-TRH neurons were immunoreactive for α-MSH. In the medial and periventricular parvocellular subdivisions of the PVN, CART was co-contained in ∼80% of pro-TRH neuronal perikarya, whereas colocalization with pro-TRH was found in <10% of the anterior parvocellular subdivision neurons. In addition, >80% of TRH/CART neurons in the periventricular and medial parvocellular subdivisions accumulated Fluoro-Gold after systemic administration, suggesting that CART may serve as a marker for hypophysiotropic TRH neurons. CART prevented fasting-induced suppression of pro-TRH in the PVN when administered intracerebroventricularly and increased the content of TRH in hypothalamic cell cultures. These studies establish an anatomical association between CART and pro-TRH-producing neurons in the PVN and demonstrate that CART has a stimulatory effect on hypophysiotropic TRH neurons by increasing pro-TRH gene expression and the biosynthesis of TRH.
Calcium-Dependent Inhibition of L, N, and P/Q Ca2+Channels in Chromaffin Cells: Role of Mitochondria
Authors: Hernández-Guijo Jesús M. , Maneu-Flores Victoria E. , Ruiz-Nuño Ana , Villarroya Mercedes , García Antonio G. , Gandía Luis
Published: April 2018

The hypothesis that the buffering of Ca2+by mitochondria could affect the Ca2+-dependent inhibition of voltage-activated Ca2+channels, (ICa), was tested in voltage-clamped bovine adrenal chromaffin cells. The protonophore carbonyl cyanide m-chlorophenyl-hydrazone (CCCP), the blocker of the Ca2+uniporter ruthenium red (RR), and a combination of oligomycin plus rotenone were used to interfere with mitochondrial Ca2+buffering. In cells dialyzed with an EGTA-free solution, peakICagenerated by 20 msec pulses to 0 or +10 mV, applied at 15 sec intervals, from a holding potential of −80 mV, decayed rapidly after superfusion of cells with 2 μmCCCP (τ = 16.7 ± 3 sec;n= 8). In cells dialyzed with 14 mmEGTA, CCCP did not provokeICaloss. Cell dialysis with 4 μmruthenium red or cell superfusion with oligomycin (3 μm) plus rotenone (4 μm) also accelerated the decay ofICa. After treatment with CCCP, decay of N- and P/Q-type Ca2+channel currents occurred faster than that of L-type Ca2+channel currents. These data are compatible with the idea that the elevation of the bulk cytosolic Ca2+concentration, [Ca2+]c, causes the inhibition of L- and N- as well as P/Q-type Ca2+channels expressed by bovine chromaffin cells. This [Ca2+]csignal appears to be tightly regulated by rapid Ca2+uptake into mitochondria. Thus, it is plausible that mitochondria might efficiently regulate the activity of L, N, and P/Q Ca2+channels under physiological stimulation conditions of the cell.
GABA Transaminase Inhibition Induces Spontaneous and Enhances Depolarization-Evoked GABA Efflux via Reversal of the GABA Transporter
Authors: Wu Yuanming , Wang Wengang , Richerson George B.
Published: April 2018

The GABA transporter can reverse with depolarization, causing nonvesicular GABA release. However, this is thought to occur only under pathological conditions. Patch-clamp recordings were made from rat hippocampal neurons in primary cell cultures. Inhibition of GABA transaminase with the anticonvulsant γ-vinyl GABA (vigabatrin; 0.05–100 μm) resulted in a large leak current that was blocked by bicuculline (50 μm). This leak current occurred in the absence of extracellular calcium and was blocked by the GABA transporter antagonist SKF-89976a (5 μm). These results indicate that vigabatrin induces spontaneous GABA efflux from neighboring cells via reversal of GABA transporters, subsequently leading to the stimulation of GABAAreceptors on the recorded neuron. The leak current increased slowly over 4 d of treatment with 100 μmvigabatrin, at which time it reached an equivalent conductance of 9.0 ± 4.9 nS. Blockade of glutamic acid decarboxylase with semicarbazide (2 mm) decreased the leak current that was induced by vigabatrin by 47%. In untreated cells, carrier-mediated GABA efflux did not occur spontaneously but was induced by an increase in [K+]ofrom 3 to as little as 6 mm. Vigabatrin enhanced this depolarization-evoked nonvesicular GABA release and also enhanced the heteroexchange release of GABA induced by nipecotate. Thus, the GABA transporter normally operates near its equilibrium and can be easily induced to reverse by an increase in cytosolic [GABA] or mild depolarization. We propose that this transporter-mediated nonvesicular GABA release plays an important role in neuronal inhibition under both physiological and pathophysiological conditions and is the target of some anticonvulsants.
Rapid Signaling at Inhibitory Synapses in a Dentate Gyrus Interneuron Network
Authors: Bartos Marlene , Vida Imre , Frotscher Michael , Geiger Jörg R. P. , Jonas Peter
Published: April 2018

Mutual synaptic interactions between GABAergic interneurons are thought to be of critical importance for the generation of network oscillations and for temporal encoding of information in the hippocampus. However, the functional properties of synaptic transmission between hippocampal interneurons are largely unknown. We have made paired recordings from basket cells (BCs) in the dentate gyrus of rat hippocampal slices, followed by correlated light and electron microscopical analysis. Unitary GABAAreceptor-mediated IPSCs at BC–BC synapses recorded at the soma showed a fast rise and decay, with a mean decay time constant of 2.5 ± 0.2 msec (32°C). Synaptic transmission at BC–BC synapses showed paired-pulse depression (PPD) (32 ± 5% for 10 msec interpulse intervals) and multiple-pulse depression during repetitive stimulation. Detailed passive cable model simulations based on somatodendritic morphology and localization of synaptic contacts further indicated that the conductance change at the postsynaptic site was even faster, decaying with a mean time constant of 1.8 ± 0.6 msec. Sequential triple recordings revealed that the decay time course of IPSCs at BC–BC synapses was approximately twofold faster than that at BC–granule cell synapses, whereas the extent of PPD was comparable. To examine the consequences of the fast postsynaptic conductance change for the generation of oscillatory activity, we developed a computational model of an interneuron network. The model showed robust oscillations at frequencies >60 Hz if the excitatory drive was sufficiently large. Thus the fast conductance change at interneuron–interneuron synapses may promote the generation of high-frequency oscillations observed in the dentate gyrusin vivo.
Combinatorial Expression Patterns of LIM-Homeodomain and Other Regulatory Genes Parcellate Developing Thalamus
Authors: Nakagawa Yasushi , O'Leary Dennis D. M.
Published: April 2018

The anatomical and functional organization of dorsal thalamus (dTh) and ventral thalamus (vTh), two major regions of the diencephalon, is characterized by their parcellation into distinct cell groups, or nuclei, that can be histologically defined in postnatal animals. However, because of the complexity of dTh and vTh and difficulties in histologically defining nuclei at early developmental stages, our understanding of the mechanisms that control the parcellation of dTh and vTh and the differentiation of nuclei is limited. We have defined a set of regulatory genes, which include five LIM-homeodomain transcription factors (Isl1,Lhx1,Lhx2,Lhx5, andLhx9) and three other genes (Gbx2,Ngn2, andPax6), that are differentially expressed in dTh and vTh of early postnatal mice in distinct but overlapping patterns that mark nuclei or subsets of nuclei. These genes exhibit differential expression patterns in dTh and vTh as early as embryonic day 10.5, when neurogenesis begins; the expression of most of them is detected as progenitor cells exit the cell cycle. Soon thereafter, their expression patterns are very similar to those that we observe postnatally, indicating that unique combinations of these genes mark specific cell groups from the time they are generated to their later differentiation into nuclei. Our findings suggest that these genes act in a combinatorial manner to control the specification of nuclei-specific properties of thalamic cells and the differentiation of nuclei within dTh and vTh. These genes may also influence the pathfinding and targeting of thalamocortical axons through both cell-autonomous and non-autonomous mechanisms.
Ephrin B1 Is Expressed on Neuroepithelial Cells in Correlation with Neocortical Neurogenesis
Authors: Stuckmann Ingo , Weigmann Anja , Shevchenko Andrej , Mann Matthias , Huttner Wieland B.
Published: April 2018

To identify molecules involved in neurogenesis, we have raised monoclonal antibodies against embryonic day 12.5 mouse telencephalon. One antibody, monoclonal antibody 25H11, stains predominantly the ventricular zone of the anterior and lateral telencephalon. Purification of the 25H11 antigen, a 47 kDa integral membrane protein, from ≈2500 mouse telencephali reveals its identity with ephrin B1. Ephrin B1 appears at the onset of neocortical neurogenesis, being first expressed in neuron-generating neuroepithelial cells and rapidly thereafter in virtually all neuroepithelial cells. Expression of ephrin B1 persists through the period of neocortical neurogenesis and is downregulated thereafter. Ephrin B1 is present on the ventricular as well as basolateral plasma membrane of neuroepithelial cells and exhibits an ventricular-high to pial-low gradient across the ventricular zone. Expression of ephrin B1 is also detected on radial glial cells, extending all the way to their pial endfeet, and on neurons in the mantle/intermediate zone but not in the cortical plate. Our results suggest that ephrin B1, presumably via ephrin–Eph receptor signaling, has a role in neurogenesis. Given the ventricular-to-pial gradient of ephrin B1 on the neuroepithelial cell surface and its known role in cell migration in other systems mediated by its repulsive properties, we propose that ephrin B1 may be involved in the migration of newborn neurons out from the ventricular zone toward the neocortex.
Predictability Modulates Human Brain Response to Reward
Authors: Berns Gregory S. , McClure Samuel M. , Pagnoni Giuseppe , Montague P. Read
Published: April 2018

Certain classes of stimuli, such as food and drugs, are highly effective in activating reward regions. We show in humans that activity in these regions can be modulated by the predictability of the sequenced delivery of two mildly pleasurable stimuli, orally delivered fruit juice and water. Using functional magnetic resonance imaging, the activity for rewarding stimuli in both the nucleus accumbens and medial orbitofrontal cortex was greatest when the stimuli were unpredictable. Moreover, the subjects' stated preference for either juice or water was not directly correlated with activity in reward regions but instead was correlated with activity in sensorimotor cortex. For pleasurable stimuli, these findings suggest that predictability modulates the response of human reward regions, and subjective preference can be dissociated from this response.
How Protein Kinase C Activation Protects Nerve Cells from Oxidative Stress-Induced Cell Death
Authors: Maher Pamela
Published: April 2018

Oxidative stress is implicated in the nerve cell death that occurs in a variety of neurological disorders, and the loss of protein kinase C (PKC) activity has been coupled to the severity of the damage. The functional relationship between stress, PKC, and cell death is, however, unknown. Using an immortalized hippocampal cell line that is particularly sensitive to oxidative stress, I show that activation of PKC by the phorbol ester tetradecanoylphorbol acetate (TPA) inhibits cell death via the stimulation of a complex protein phosphorylation pathway. TPA treatment leads to the rapid activation of extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK), the inactivation of p38 mitogen-activated protein kinase (MAPK), and the downregulation of PKCδ. Inhibition of either ERK or JNK activation blocks TPA-mediated protection, whereas p38 MAPK and PKCδ inhibitors block stress-induced nerve cell death. Both p38 MAPK inactivation and JNK activation appear to be downstream of ERK because an agent that blocks ERK activation also blocks the modulation of these other MAP kinase family members by TPA treatment. Thus, the protection from oxidative stress afforded nerve cells by PKC activity requires the combined modulation of multiple enzyme pathways and suggests why the loss of PKC activity contributes to nerve cell death.
A Novel Member of the Ig Superfamily,turtle, is a CNS-Specific Protein Required for Coordinated Motor Control
Authors: Bodily Kale D. , Morrison Clayton M. , Renden Robert B. , Broadie Kendal
Published: April 2018

We describe here the cloning and functional characterization of a neural-specific novel member of the Ig superfamily,turtle(tutl), with a structure of five Ig C2-type domains, two fibronectin type III domains, and one transmembrane region. Alternative splicing of thetutlgene produces at least four Tutl isoforms, including two transmembrane proteins and two secreted proteins, with primary structures closely related to a human brain protein (KIAA1355), the Deleted in Colorectal Cancer/Neogenin/Frazzled receptor family, and the Roundabout/Dutt1 receptor family. An allelic series oftutlgene mutations resulted in recessive lethality to semilethality, indicating that the gene is essential. In contrast to other family members,tutldoes not play a detectable role in axon pathfinding or nervous system morphogenesis. Likewise, basal synaptic transmission and locomotory movement are unaffected. However,tutlmutations cause striking movement defects exhibited in specific types of highly coordinated behavior. Specifically,tutlmutants display an abnormal response to tactile stimulation, the inability to regain an upright position from an inverted position (hence, “turtle”), and the inability to fly in adulthood. These phenotypes demonstrate thattutlplays an essential role in establishing a nervous system capable of executing coordinated motor output in complex behaviors.
Motoneuron Survival Is Enhanced in the Absence of Neuromuscular Junction Formation in Embryos
Authors: Terrado J. , Burgess R. W. , DeChiara T. , Yancopoulos G. , Sanes J. R. , Kato A. C.
Published: April 2018

Approximately half of the motoneurons produced during development die before birth or shortly after birth. Although it is believed that survival depends on a restricted supply of a trophic sustenance produced by the synaptic target tissue (i.e., muscle), it is unclear whether synapse formation per se is involved in motoneuron survival. To address this issue, we counted cranial motoneurons in a set of mutant mice in which formation of neuromuscular junctions is dramatically impaired (i.e., null mutants for agrin, nerve-derived agrin, rapsyn, and MuSK).

We demonstrate that in the absence of synaptogenesis, there is an 18–34% increase in motoneuron survival in the facial, trochlear, trigeminal motor, and hypoglossal nuclei; the highest survival occurred in the MuSK-deficient animals in which synapse formation is most severely compromised. There was no change in the size of the mutant motoneurons as compared with control animals, and the morphology of the mutant motoneurons appeared normal. We postulate that the increased axonal branching observed in these mutants leads to a facilitated “access” of the motoneurons to muscle-derived trophic factors at sites other than synapses or that inactivity increases the production of such factors. Finally, we examined motoneurons in double mutants of CNTFRα−/−(in which there is a partial loss of motoneurons) and MuSK−/−(in which there is an increased survival of motoneurons). The motoneuron numbers in the double mutants parallel those of the single MuSK-deficient mice, indicating that synapse disruption can even overcome the deleterious effect of CNTFRα ablation.
Disruption of Layers 3 and 4 during Development Results in Altered Thalamocortical Projections in Ferret Somatosensory Cortex
Authors: Noctor Stephen C. , Palmer Sidney L. , McLaughlin Debra F. , Juliano Sharon L.
Published: April 2018

The precision of projections from dorsal thalamus to neocortex are key toward understanding overall cortical organization and function. To identify the significance of layer 4 cells in receiving the bulk of thalamic projections in somatosensory cortex, we disrupted layer 4 genesis and studied the effect on thalamic terminations in ferrets. Second, we ascertained the result of layer 4 disruption on functional responses and topographic organization. Methylazoxy methanol (MAM) was injected into pregnant ferrets on embryonic day 33 (E33), when most layer 4 neurons of somatosensory cortex are generated. This treatment resulted in dramatic reduction in the thickness of targeted layer 4. E38 MAM treatment was used as a control, when layer 2–3 neurons are generated. The projections of ventrobasal thalamus into somatosensory cortex were studied using DiI injections. We found only subtle differences between groups (normal, E33, or E38 MAM-treated) in the thalamic afferent pattern on postnatal day 1 (P1) and P7. On P14, thalamic terminations distribute almost equally throughout the remaining cortical layers in the E33 MAM-treated group compared with normal and E38 MAM-treated animals, in which the ventrobasal thalamus projects primarily to central layers. Electrophysiological recordings conducted on mature ferrets treated with MAM on E33 demonstrated that somatotopic organization and receptive field size are normal. These findings emphasize the importance of layer 4 in determining the normal laminar pattern of thalamic termination and suggest that, although its absence is likely to impact on complex neocortical functional responses, topographic organization does not arise from the influence of layer 4.
Fear and Feeding in the Nucleus Accumbens Shell: Rostrocaudal Segregation of GABA-Elicited Defensive Behavior Versus Eating Behavior
Authors: Reynolds Sheila M. , Berridge Kent C.
Published: April 2018

This study examined localization of positive versus negative motivational functions mediated by GABA circuits within the accumbens shell. Microinjections of a GABAAagonist (0, 25, 75, and 225 ng/0.5 μl muscimol) in rostral shell sites elicited appetitive increases in eating behavior. In contrast, microinjections in caudal shell sites elicited defensive burying or paw-treading behavior. Rats whose microinjections landed bilaterally outside of the accumbens shell did not display either behavior. Defensive treading elicited by caudal shell muscimol microinjection appeared to be a negative motivated response to threat (similar in parameters and orientation to normal defensive burying of a threatening electrified shock prod). The nucleus accumbens shell thus appears functionally heterogeneous in coding motivational valence. The demonstration that muscimol elicits positive eating behavior from rostral shell versus negative defensive behavior from caudal shell suggests in particular that GABAergic substrates of positive and negative types of motivated behavior in the nucleus accumbens shell are segregated along a rostrocaudal gradient.
Excitatory Nicotinic and Desensitizing Muscarinic (M2) Effects on C-Nociceptors in Isolated Rat Skin
Authors: Bernardini Nadia , Sauer Susanne K. , Haberberger Rainer , Fischer Michael J. M. , Reeh Peter W.
Published: April 2018

The actions of different cholinergic agonists and antagonists were investigated on nociceptive afferents using the rat skin–saphenous nerve preparation,in vitro. Nicotine was able to weakly excite C-nociceptors and to induce a mild sensitization to heat stimulation (in 77% of tested fibers) in a dose-dependent manner (10−6to 10−5m), but it caused no alteration in mechanical responsiveness tested with von Frey hairs. Muscarine did not induce a significant nociceptor excitation, but almost all fibers exhibited a marked desensitization to mechanical and heat stimuli in a dose-dependent manner (from 10−6to 10−4m). The muscarinic effects could be prevented by the general muscarinic antagonist scopolamine (10−5m), by the M3 antagonist 1,1-dimethyl-4-diphenylacetoxypiperidium oxide (10−6m) co-applied with the M2 antagonist gallamine (10−5m), and by gallamine alone. As positive control we used the relatively M2-selective agonist arecaidine (10−6to 10−5m), obtaining a similar desensitizing effect as with muscarine. Finally, we performed an immunocytochemical study that demonstrated the presence of M2 but not M3 receptors in thin epidermal nerve fibers of the rat hairy skin. Altogether, these data demonstrate opposite effects of nicotinic and muscarinic receptor stimulation on cutaneous nociceptors. M2 receptor-mediated depression of nociceptive responsiveness may convey a therapeutic, i.e., analgesic or antinociceptive, potential.
Gαq-Deficient Mice Lack Metabotropic Glutamate Receptor-Dependent Long-Term Depression But Show Normal Long-Term Potentiation in the Hippocampal CA1 Region
Authors: Kleppisch Thomas , Voigt Viktor , Allmann Rüdiger , Offermanns Stefan
Published: April 2018

Long-term potentiation (LTP) and depression (LTD) are potential cellular mechanisms involved in learning and memory. Group I metabotropic glutamate receptors (mGluR), which are linked to heterotrimeric G-proteins of the Gqfamily (Gqand G11), have been reported to facilitate both hippocampal LTP and LTD. To evaluate their functional role in synaptic plasticity, we studied LTD and LTP in the CA1 region of the hippocampus from wild-type, Gαq(−/−), and Gα11(−/−) mice. Basic parameters of the synaptic transmission were not altered in Gαq(−/−) and Gα11(−/−) mice. Moreover, these mice showed normal LTP in response to a strong tetanus and to a weak tetanus. However, LTD induced either by a group I mGluRs agonist or by paired-pulse low-frequency stimulation (PP-LFS) was absent in Gαq(−/−) mice. Moreover, PP-LFS caused potentiation of the synaptic transmission in these mice that was not affected by the NMDAR antagonist AP-5. These results show that Gqplays a crucial role in the mGluR-dependent LTD, whereas hippocampal LTP is not affected by the lack of a single member of the Gqfamily.
Predominance of Late-Spiking Neurons in Layer VI of Rat Perirhinal Cortex
Authors: McGann John P. , Moyer James R. , Brown Thomas H.
Published: April 2018

Recent work demonstrated the importance of perirhinal cortex (PR) in a variety of behavioral tasks and disease processes. Studies from our laboratory revealed that some layers of PR contain neurons with unusual properties. Here we report a detailed examination of the cellular neurobiology of layer VI of PR, using whole-cell recordings and biocytin cell fills in horizontal rat brain slices. The most striking finding is that an overwhelming majority (∼86%) of neurons are late-spiking (LS) cells, which can delay the onset of their spike trains by several seconds or more relative to the onset of a depolarizing current step. LS neurons previously have been shown to exist only in very small numbers in a limited number of other cortical regions. Anatomical reconstructions have revealed that the LS neurons vary greatly in morphology, including both pyramidal and nonpyramidal cells. Another surprising physiological finding is the fact that single-spiking (SS) neurons are the second most common cell type (∼7%). SS neurons issue only a single action potential even in response to extreme depolarization. They have been seen previously in the amygdala, but never in cortex. A third remarkable finding is that there are almost no regular spiking (RS) neurons, unlike all other cortical regions that have been studied. This unique abundance of LS neurons in layer VI, along with the presence of SS neurons and the absence of RS neurons, demonstrates that layer VI of PR is unlike any other cortical region that has been studied to date.