bluuebunny/crossref_metadata_2025 huggingface dataset:
Protein 4.1N Binding to Nuclear Mitotic Apparatus Protein in PC12 Cells Mediates the Antiproliferative Actions of Nerve Growth Factor
Authors: Ye Keqiang , Compton Duane A. , Lai Michael M. , Walensky Loren D. , Snyder Solomon H.
Published: April 2018

Protein 4.1N is a neuronal selective isoform of the erythrocyte membrane cytoskeleton protein 4.1R. In the present study, we demonstrate an interaction between 4.1N and nuclear mitotic apparatus protein (NuMA), a nuclear protein required for mitosis. The binding involves the C-terminal domain of 4.1N. In PC12 cells treatment with nerve growth factor (NGF) elicits translocation of 4.1N to the nucleus and promotes its association with NuMA. Specific targeting of 4.1N to the nucleus arrests PC12 cells at the G1 phase and produces an aberrant nuclear morphology. Inhibition of 4.1N nuclear translocation prevents the NGF-mediated arrest of cell division, which can be reversed by overexpression of 4.1N. Thus, nuclear 4.1N appears to mediate the antiproliferative actions of NGF by antagonizing the role of NuMA in mitosis.
Neuregulin Induces GABAAReceptor Subunit Expression and Neurite Outgrowth in Cerebellar Granule Cells
Authors: Rieff Heather I. , Raetzman Lori T. , Sapp Douglas W. , Yeh Hermes H. , Siegel Ruth E. , Corfas Gabriel
Published: April 2018

Neuregulin (NRG), a growth and differentiation factor that signals via erbB receptor tyrosine kinases, has been shown to have biological effects in both the CNS and the peripheral nervous system. We report here that erbB4 is expressed in mature cerebellar granule cells, where it appears to be concentrated at the granule cell postsynaptic terminals. We also show that one form of NRG, Ig-NRG, plays a crucial role in aspects of cerebellar granule cell developmentin vitro. First, Ig-NRG treatment of granule cells in culture selectively induces the expression of the GABAAreceptor β2 subunit. This increase in subunit expression is paralleled by an increase in functional GABAAreceptors. In contrast to its effects on GABAAreceptor subunit expression, Ig-NRG does not upregulate NMDA receptor N2B and N2C subunit expression. Second, we demonstrate that Ig-NRG also enhances neurite outgrowth from cultured granule cells. Ig-NRG does not, however, act as a survival factor for the granule cells. We have compared the effect of Ig-NRG with the effects of brain-derived neurotrophic factor (BDNF), a neurotrophin that exerts specific effects on granule cells in culture, and found that BDNF does not mimic the effects of Ig-NRG on GABAAreceptor subunit expression. Our results show that Ig-NRG has specific effects on granule cell development and maturation and may regulate these processesin vivo.
The Chondroitin Sulfate Proteoglycans Neurocan and Phosphacan Are Expressed by Reactive Astrocytes in the Chronic CNS Glial Scar
Authors: McKeon Robert J. , Jurynec Michael J. , Buck Charles R.
Published: April 2018

Chondroitin sulfate proteoglycans (CS-PGs) expressed by reactive astrocytes may contribute to the axon growth-inhibitory environment of the injured CNS. The specific potentially inhibitory CS-PGs present in areas of reactive gliosis, however, have yet to be thoroughly examined. In this study, we used immunohistochemistry, combined immunohistochemistry–in situhybridization, immunoblot analysis, and reverse transcription-PCR to examine the expression of specific CS-PGs by reactive astrocytes in anin vivomodel of reactive gliosis: that is, the glial scar, after cortical injury. Neurocan and phosphacan can be localized to reactive astrocytes 30 d after CNS injury, whereas brevican and versican are not expressed in the chronic glial scar. Neurocan is also expressed by astrocytes in primary cell culture. Relative to the amount present in cultured astrocytes or uninjured cortex, neurocan expression increases significantly in the glial scar resulting from cortical injury, including the re-expression of the neonatal isoform of neurocan. In contrast, phosphacan protein levels are decreased in the glial scar compared with the uninjured brain. Because these CS-PGs are capable of inhibiting neurite outgrowthin vitro, our data suggest that phosphacan and neurocan in areas of reactive gliosis may contribute to axonal regenerative failure after CNS injury.
Cloning of Components of a Novel Subthreshold-Activating K+Channel with a Unique Pattern of Expression in the Cerebral Cortex
Authors: Saganich M. J. , de Miera E. Vega-Saenz , Nadal M. S. , Baker H. , Coetzee W. A. , Rudy B.
Published: April 2018

Potassium channels that are open at very negative membrane potentials govern the subthreshold behavior of neurons. These channels contribute to the resting potential and help regulate the degree of excitability of a neuron by affecting the impact of synaptic inputs and the threshold for action potential generation. They can have large influences on cell behavior even when present at low concentrations because few conductances are active at these voltages. We report the identification of a new K+channel pore-forming subunit of the ether-à-go-go (Eag) family, named Eag2, that expresses voltage-gated K+channels that have significant activation at voltages around −100 mV. Eag2 expresses outward-rectifying,non-inactivatingvoltage-dependent K+currents resembling those of Eag1, including a strong dependence of activation kinetics on prepulse potential. However, Eag2 currents start activating at subthreshold potentials that are 40–50 mV more negative than those reported for Eag1. Because they activate at such negative voltages and do not inactivate, Eag2 channels will contribute sustained outward currents down to the most negative membrane potentials known in neurons. Although Eag2 mRNA levels in whole brain appear to be low, they are highly concentrated in a few neuronal populations, most prominently in layer IV of the cerebral cortex. This highly restricted pattern of cortical expression is unlike that of any other potassium channel cloned to date and may indicate specific roles for this channel in cortical processing. Layer IV neurons are the main recipient of the thalamocortical input. Given their functional properties and specific distribution, Eag2 channels may play roles in the regulation of the behavioral state-dependent entry of sensory information to the cerebral cortex.
Gap Junctional Coupling and Patterns of Connexin Expression among Neonatal Rat Lumbar Spinal Motor Neurons
Authors: Chang Qiang , Gonzalez Michael , Pinter Martin J. , Balice-Gordon Rita J.
Published: April 2018

Interneuronal gap junctional coupling is a hallmark of neural development whose functional significance is poorly understood. We have characterized the extent of electrical coupling and dye coupling and patterns of gap junction protein expression in lumbar spinal motor neurons of neonatal rats. Intracellular recordings showed that neonatal motor neurons are transiently electrically coupled and that electrical coupling is reversibly abolished by halothane, a gap junction blocker. Iontophoretic injection of Neurobiotin, a low molecular weight compound that passes across most gap junctions, into single motor neurons resulted in clusters of many labeled motor neurons at postnatal day 0 (P0)–P2, and single labeled motor neurons after P7. The compact distribution of dye-labeled motor neurons suggested that, after birth, gap junctional coupling is spatially restricted. RT-PCR,in situhybridization, and immunostaining showed that motor neurons express five connexins, Cx36, Cx37, Cx40, Cx43, and Cx45, a repertoire distinct from that expressed by other neurons or glia. Although all five connexins are widely expressed among motor neurons in embryonic and neonatal life, Cx36, Cx37, and Cx43 continue to be expressed in many adult motor neurons, and expression of Cx45, and in particular Cx40, decreases after birth. The disappearance of electrical and dye coupling despite the persistent expression of several gap junction proteins suggests that gap junctional communication among motor neurons may be modulated by mechanisms that affect gap junction assembly, permeability, or open state.
Thrombin-Induced Growth Cone Collapse: Involvement of Phospholipase A2and Eicosanoid Generation
Authors: de la Houssaye Becky A. , Mikule Keith , Nikolic Dejan , Pfenninger Karl H.
Published: April 2018

The studies presented here explore intracellular signals resulting from the action of repellents on growth cones. Growth cone challenge with thrombin or thrombin receptor-activating peptide (TRAP) triggers collapse via a receptor-mediated process. The results indicate that this involves activation of cytosolic phospholipase A2(PLA2) and eicosanoid synthesis. The collapse response to repellents targets at least two functional units of the growth cone, the actin cytoskeleton and substratum adhesion sites. We show in a cell-free assay that thrombin and TRAP cause the detachment of isolated growth cones from laminin. Biochemical analyses of isolated growth cones reveal that thrombin and TRAP stimulate cytosolic PLA2but not phospholipase C. In addition, thrombin stimulates synthesis of 12- and 15-hydroxyeicosatetraenoic acid (HETE) from the released arachidonic acid via a lipoxygenase (LO) pathway. A selective LO inhibitor blocks 12/15-HETE synthesis in growth cones and inhibits thrombin-induced growth cone collapse. Exogenously applied 12(S)-HETE mimics the thrombin effect and induces growth cone collapse in culture. These observations indicate that thrombin-induced growth cone collapse occurs by a mechanism that involves the activation of cytosolic PLA2and the generation of 12/15-HETE.
Involvement of Cajal-Retzius Neurons in Spontaneous Correlated Activity of Embryonic and Postnatal Layer 1 from Wild-Type and Reeler Mice
Authors: Aguiló Agustı́ , Schwartz Theodore H. , Kumar Vikram S. , Peterlin Zita A. , Tsiola Areti , Soriano Eduardo , Yuste Rafael
Published: April 2018

Cajal-Retzius (CR) cells are a transient population of neurons in developing cortical layer 1 that secrete reelin, a protein necessary for cortical lamination. Combining calcium imaging of cortical hemispheres and cross-correlation analysis, we previously found spontaneous correlated activity among non-CR neurons in postnatal rat layer 1. This correlated activity was blocked by GABAergic and glutamatergic antagonists, and we postulated that it was controlled by CR cells. We now investigate the correlated activity of embryonic and postnatal layer 1 in wild-type and reeler mice, mutant in the production of reelin. We find that mouse layer 1 also sustains patterned spontaneous activity and that CR cells participate in correlated networks. These networks are present in embryonic marginal zone and are blocked by GABAergic and glutamatergic antagonists. Surprisingly, network activity in reeler mice displays similar characteristics and pharmacological profile as in wild-type mice, although small differences are detected. Our results demonstrate that the embryonic marginal zone has correlated spontaneous activity that could serve as the scaffold for the development of intracortical connections. Our data also suggest that reelin does not have a major impact in the development of specific synaptic circuits in layer 1.
Neurochemical and Cellular Reorganization of the Spinal Cord in a Murine Model of Bone Cancer Pain
Authors: Schwei Matthew J. , Honore Prisca , Rogers Scott D. , Salak-Johnson Janeen L. , Finke Matthew P. , Ramnaraine Margaret L. , Clohisy Denis R. , Mantyh Patrick W.
Published: April 2018

The cancer-related event that is most disruptive to the cancer patient's quality of life is pain. To begin to define the mechanisms that give rise to cancer pain, we examined the neurochemical changes that occur in the spinal cord and associated dorsal root ganglia in a murine model of bone cancer. Twenty-one days after intramedullary injection of osteolytic sarcoma cells into the femur, there was extensive bone destruction and invasion of the tumor into the periosteum, similar to that found in patients with osteolytic bone cancer. In the spinal cord, ipsilateral to the cancerous bone, there was a massive astrocyte hypertrophy without neuronal loss, an expression of dynorphin and c-Fos protein in neurons in the deep laminae of the dorsal horn. Additionally, normally non-noxious palpation of the bone with cancer induced behaviors indicative of pain, the internalization of the substance P receptor, and c-Fos expression in lamina I neurons. The alterations in the neurochemistry of the spinal cord and the sensitization of primary afferents were positively correlated with the extent of bone destruction and the growth of the tumor. This “neurochemical signature” of bone cancer pain appears unique when compared to changes that occur in persistent inflammatory or neuropathic pain states. Understanding the mechanisms by which the cancer cells induce this neurochemical reorganization may provide insight into peripheral factors that drive spinal cord plasticity and in the development of more effective treatments for cancer pain.
Corticostriatal Projections from Rat Barrel Cortex Have an Anisotropic Organization that Correlates with Vibrissal Whisking Behavior
Authors: Alloway Kevin D. , Crist Jennifer , Mutic Joshua J. , Roy Stephane A.
Published: April 2018

To elucidate the detailed organization of corticostriatal projections from rodent somatosensory cortex, the anterograde tracers biotinylated dextran amine (BDA) and fluoro-ruby (FR) were injected into separate parts of the whisker “barrel” representation. In one group of rats, the two tracers were injected into different barrel columns residing in the same row; in the other group of rats, the tracers were deposited into barrel columns residing in different rows. Reconstructions of labeled axonal varicosities in the neostriatum and ventrobasal thalamus were analyzed quantitatively to compare the extent of overlapping projections to these subcortical structures. For both groups of animals, corticostriatal projections terminated in densely packed clusters that occupied curved lamellar-shaped regions along the dorsolateral edge of the neostriatum. When the tracers were injected into different whisker barrel rows, the distribution of BDA- and FR-labeled terminals in the neostriatum followed a crude somatotopic organization in which the amount of overlap was approximately the same as in the ventrobasal thalamus. When both tracers were injected into the same whisker barrel row, however, the amount of corticostriatal overlap was significantly higher than the amount of overlap observed in the ventrobasal thalamus. These results indicate that corticostriatal projections from whisker barrel cortex have an anisotropic organization that correlates with the pattern of vibrissal movements during whisking behavior.
Saccadic Dysmetria and Adaptation after Lesions of the Cerebellar Cortex
Authors: Barash Shabtai , Melikyan Armenuhi , Sivakov Alexey , Zhang Mingsha , Glickstein Mitchell , Thier Peter
Published: April 2018

We studied the effects of small lesions of the oculomotor vermis of the cerebellar cortex on the ability of monkeys to execute and adapt saccadic eye movements. For saccades in one horizontal direction, the lesions led to an initial gross hypometria and a permanent abolition of the capacity for rapid adaptation. Mean saccade amplitude recovered from the initial hypometria, although variability remained high. A series of hundreds of repetitive saccades in the same direction resulted in gradual decrement of amplitude. Saccades in other directions were less strongly affected by the lesions. We suggest the following. (1) The cerebellar cortex is constantly recalibrating the saccadic system, thus compensating for rapid biomechanical changes such as might be caused by muscle fatigue. (2) A mechanism capable of slow recovery from dysmetria is revealed despite the permanent absence of rapid adaptation.
Proprioceptive Control of Extensor Activity during Fictive Scratching and Weight Support Compared to Fictive Locomotion
Authors: Perreault Marie-Claude , Enriquez-Denton Manuel , Hultborn Hans
Published: April 2018

At rest, extensor group I afferents produce oligosynaptic inhibition of extensor motoneurons. During locomotor activity, however, such inhibition is replaced by oligosynaptic excitation. Oligosynaptic excitation from extensor group I afferents plays a crucial role in the regulation of extensor activity during walking. In this study we investigate the possibility that this mechanism also regulates extensor muscle activity during other motor tasks.

We show that the reflex pathways responsible for extensor group I oligosynaptic excitation during fictive locomotion can be activated during both fictive scratching and fictive weight support (tonic motor activity induced by contralateral scratching). These observations suggest that the excitatory group I oligosynaptic reflex pathways are open for transmission during several forms of motor activities. We also show that extensor group I input during fictive scratching can affect the amplitude and the timing of extensor activity in a pattern similar to that observed during locomotion. Most likely these effects involve the activation of the excitatory group I oligosynaptic reflex pathways. Accordingly, it is suggested that extensor group I oligosynaptic excitation during motor activities other than locomotion is also used to regulate extensor muscle activity. Furthermore, the similarity of effects from extensor group I input on the rhythmicity during scratching and locomotion supports the hypothesis that both rhythms are generated by a common network.
Norepinephrine-Deficient Mice Have Increased Susceptibility to Seizure-Inducing Stimuli
Authors: Szot Patricia , Weinshenker David , White Sylvia S. , Robbins Carol A. , Rust Nicole C. , Schwartzkroin Philip A. , Palmiter Richard D.
Published: April 2018

Several lines of evidence suggest that norepinephrine (NE) can modulate seizure activity. However, the experimental methods used in the past cannot exclude the possible role of other neurotransmitters coreleased with NE from noradrenergic terminals. We have assessed the seizure susceptibility of genetically engineered mice that lack NE. Seizure susceptibility was determined in the dopamine β-hydroxylase null mutant (Dbh−/−) mouse using four different convulsant stimuli: 2,2,2-trifluroethyl ether (flurothyl), pentylenetetrazol (PTZ), kainic acid, and high-decibel sound.Dbh−/− mice demonstrated enhanced susceptibility (i.e., lower threshold) compared with littermate heterozygous (Dbh+/−) controls to flurothyl, PTZ, kainic acid, and audiogenic seizures and enhanced sensitivity (i.e., seizure severity and mortality) to flurothyl, PTZ, and kainic acid. c-Fos mRNA expression in the cortex, hippocampus (CA1 and CA3), and amygdala was increased inDbh−/− mice in association with flurothyl-induced seizures. Enhanced seizure susceptibility to flurothyl and increased seizure-induced c-fos mRNA expression were reversed by pretreatment withl-threo-3,4-dihydroxyphenylserine, which partially restores the NE content inDbh−/− mice. These genetically engineered mice confirm unambiguously the potent effects of the noradrenergic system in modulating epileptogenicity and illustrate the unique opportunity offered byDbh−/− mice for elucidating the pathways through which NE can regulate seizure activity.
Role of Adenosine A2 Receptors in Brain Stimulation Reward under Baseline Conditions and during Cocaine Withdrawal in Rats
Authors: Baldo Brian A. , Koob George F. , Markou Athina
Published: April 2018

The present experiments tested the hypothesis that adenosine A2 receptors are involved in central reward function. Adenosine receptor agonists or antagonists were administered to animals that had been trained to self-stimulate in a rate-free brain stimulation reward (BSR) task that provides current thresholds as a measure of reward. The adenosine A2Areceptor-selective agonists 2-p-(2-carboxyethyl)phenethylamino-5′-N-ethylcarboxamido adenosine hydrochloride (CGS 21680) (0.1–1.0 mg/kg) and 2-[(2-aminoethylamino)carbonylethyl phenylethylamino]-5′-N-ethylcarboxamido adenosine (APEC) (0.003–0.03 mg/kg) elevated reward thresholds without increasing response latencies, a measure of performance. Specifically, CGS 21680 had no effect on response latency, whereas APEC shortened latencies. Bilateral infusion of CGS 21680 (3, 10, and 30 ng/side), directly into the nucleus accumbens, elevated thresholds but shortened latencies. The highly selective A2Aantagonist 8-(3-chlorostyryl)caffeine (0.01–10.0 mg/kg) and the A2-preferring antagonist 3,7-dimethyl-1-propargylxanthine (DMPX) (0.3–10.0 mg/kg) did not alter thresholds or latencies, but DMPX (1.0, 10.0 mg/kg) blocked the threshold-elevating effect of APEC (0.03 mg/kg). In another study, repeated administration of cocaine (eight cocaine injections of 15 mg/kg, i.p., administered over 9 hr) produced elevations in thresholds at 4, 8, and 12 hr after cocaine. DMPX (3 and 10 mg/kg), administered before both the 8 and 12 hr post-cocaine self-stimulation tests, reversed the threshold elevation produced by cocaine withdrawal. These results indicate that stimulating adenosine A2Areceptors diminishes BSR without producing performance deficits, whereas blocking adenosine receptors reverses the reward impairment produced by cocaine withdrawal or by an A2Aagonist. These findings indicate that adenosine, via A2Areceptors, may inhibit central reward processes, particularly during the neuroadaptations associated with chronic drug-induced neuronal activation.
Thalamic–Cortical–Striatal Circuitry Subserves Working Memory during Delayed Responding on a Radial Arm Maze
Authors: Floresco Stan B. , Braaksma Deanna N. , Phillips Anthony G.
Published: April 2018

The medial dorsal nuclei of the thalamus (MDNt), the prefrontal cortex, and the ventral striatum form an interconnected neural circuit that may subserve certain types of working memory. The present series of experiments investigated functional interactions between these brain regions in rats during the performance of delayed and nondelayed spatially cued radial-arm maze tasks. In Experiment 1, transient inactivation of the MDNt by a bilateral injection of lidocaine selectively disrupted performance on a delayed task but not on a nondelayed random foraging version of the radial arm maze task. In Experiment 2, asymmetrical lidocaine injections into the MDNt on one side of the brain and the prefrontal cortex on the other transiently disconnected these two brain regions and significantly impaired foraging during the delayed task. Similarly, disconnections between the prefrontal cortex and the nucleus accumbens also disrupted foraging on this task, whereas disconnections between the MDNt and the nucleus accumbens had no effect. These data suggest that serial transmission of information among the MDNt, the prefrontal cortex, and the nucleus accumbens is required when trial-unique, short-term spatial memory is used to guide prospective search behavior. The results are discussed with respect to a distributed neural network linking limbic, thalamic, cortical, and striatal regions, which mediates executive functions of working memory.
P2Y Purinoceptors Inhibit Exocytosis in Adrenal Chromaffin Cells via Modulation of Voltage-Operated Calcium Channels
Authors: Powell Andrew D. , Teschemacher Anja G. , Seward Elizabeth P.
Published: April 2018

We have used combined membrane capacitance measurements (Cm) and voltage-clamp recordings to examine the mechanisms underlying modulation of stimulus–secretion coupling by a Gi/o-coupled purinoceptor (P2Y) in adrenal chromaffin cells. P2Y purinoceptors respond to extracellular ATP and are thought to provide an important inhibitory feedback regulation of catecholamine release from central and sympathetic neurons. Inhibition of neurosecretion by other Gi/o-protein-coupled receptors may occur by either inhibition of voltage-operated Ca2+channels or modulation of the exocytotic machinery itself. In this study, we show that the P2Y purinoceptor agonist 2-methylthio ATP (2-MeSATP) significantly inhibits Ca2+entry and changes inCmevoked by single 200 msec depolarizations or a train of 20 msec depolarizations (2.5 Hz). We found that P2Y modulation of secretion declines during a train such that only ∼50% of the modulatory effect remains at the end of a train. The inhibition of both Ca2+entry and ΔCmare also attenuated by large depolarizing prepulses and treatment with pertussis toxin. Inhibition of N-type, and to lesser extent P/Q-type, Ca2+channels contribute to the modulation of exocytosis by 2-MeSATP. The Ca2+-dependence of exocytosis triggered by either single pulses or trains of depolarizations was unaffected by 2-MeSATP. When Ca2+channels were bypassed and exocytosis was evoked by flash photolysis of caged Ca2+, the inhibitory effect of 2-MeSATP was not observed. Collectively, these data suggest that inhibition of exocytosis by Gi/o-coupled P2Y purinoceptors results from inhibition of Ca2+channels and the Ca2+signal controlling exocytosis rather than a direct effect on the secretory machinery.
Switching Off and On of Synaptic Sites atAplysiaSensorimotor Synapses
Authors: Royer Sebastien , Coulson Rosalind L. , Klein Marc
Published: April 2018

Using the highly plastic synapses between mechanoreceptor sensory neurons and siphon motor neurons ofAplysiaas a model, we have investigated whether switching off and on of individual synaptic release sites is a strategy that is used by neurons in forms of short-term synaptic modulation with a time course of minutes to hours. We have modified some of the techniques of classical quantal analysis and examined the kinetics of synaptic depression under different stimulation protocols to answer this question. Our analysis shows that both synaptic depression caused by homosynaptic activity and synaptic facilitation induced by an endogenous facilitatory transmitter occur by means of the shutting off and turning on, respectively, of synaptic sites, without intermediate changes in the probability of release. Our findings imply that other forms of plasticity at these synapses, such as post-tetanic potentiation, long-term facilitation, and long-term potentiation, are also expressed by all-or-none changes in activity at individual sites. We thus show that in addition to the mechanisms of synaptic integration that are known to operate in single cells and networks, neurons can exercise a further layer of fine control, at the level of individual release sites.
Identification and Characterization of proSAAS, a Granin-Like Neuroendocrine Peptide Precursor that Inhibits Prohormone Processing
Authors: Fricker Lloyd D. , McKinzie Audra A. , Sun Jilin , Curran Eileen , Qian Yimei , Yan Lin , Patterson Scott D. , Courchesne Paul L. , Richards Bill , Levin Nancy , Mzhavia Nino , Devi Lakshmi A. , Douglass James
Published: April 2018

Five novel peptides were identified in the brains of mice lacking active carboxypeptidase E, a neuropeptide-processing enzyme. These peptides are produced from a single precursor, termed proSAAS, which is present in human, mouse, and rat. ProSAAS mRNA is expressed primarily in brain and other neuroendocrine tissues (pituitary, adrenal, pancreas); within brain, the mRNA is broadly distributed among neurons. When expressed in AtT-20 cells, proSAAS is secreted via the regulated pathway and is also processed at paired-basic cleavage sites into smaller peptides. Overexpression of proSAAS in the AtT-20 cells substantially reduces the rate of processing of the endogenous prohormone proopiomelanocortin. Purified proSAAS inhibits prohormone convertase 1 activity with an IC50of 590 nmbut does not inhibit prohormone convertase 2. Taken together, proSAAS may represent an endogenous inhibitor of prohormone convertase 1.
Restricted Expression of G86R Cu/Zn Superoxide Dismutase in Astrocytes Results in Astrocytosis But Does Not Cause Motoneuron Degeneration
Authors: Gong Yun H. , Parsadanian Alexander S. , Andreeva Albina , Snider William D. , Elliott Jeffrey L.
Published: April 2018

Evidence garnered from both human autopsy studies and genetic animal models has suggested a potential role for astrocytes in the pathogenesis of amyotrophic lateral sclerosis (ALS). Currently, mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1) represent the only known cause of motoneuron loss in the disease, producing 21q linked familial ALS (FALS). To determine whether astrocytic dysfunction has a primary role in familial ALS, we have generated multiple lines of transgenic mice expressing G86R mutant SOD1 restricted to astrocytes. In GFAP-m SOD1 mice, astrocytes exhibit significant hypertrophy and increased GFAP reactivity as the animals mature. However, GFAP-mutant SOD1 transgenic mice develop normally and do not experience spontaneous motor deficits with increasing age. Histological examination of spinal cord in aged GFAP-mSOD1 mice reveals normal motoneuron and microglial morphology. These results indicate that 21q linked FALS is not a primary disorder of astrocytes, and that expression of mutant SOD1 restricted to astrocytes is not sufficient to cause motoneuron degenerationin vivo. Expression of mutant SOD1 in other cell types, most likely neurons, is critical for the initiation of disease.
Aging Affects Hemispheric Asymmetry in the Neural Representation of Speech Sounds
Authors: Bellis Teri James , Nicol Trent , Kraus Nina
Published: April 2018

Hemispheric asymmetries in the processing of elemental speech sounds appear to be critical for normal speech perception. This study investigated the effects of age on hemispheric asymmetry observed in the neurophysiological responses to speech stimuli in three groups of normal hearing, right-handed subjects: children (ages, 8–11 years), young adults (ages, 20–25 years), and older adults (ages > 55 years). Peak-to-peak response amplitudes of the auditory cortical P1–N1 complex obtained over right and left temporal lobes were examined to determine the degree of left/right asymmetry in the neurophysiological responses elicited by synthetic speech syllables in each of the three subject groups. In addition, mismatch negativity (MMN) responses, which are elicited by acoustic change, were obtained. Whereas children and young adults demonstrated larger P1–N1-evoked response amplitudes over the left temporal lobe than over the right, responses from elderly subjects were symmetrical. In contrast, MMN responses, which reflect an echoic memory process, were symmetrical in all subject groups. The differences observed in the neurophysiological responses were accompanied by a finding of significantly poorer ability to discriminate speech syllables involving rapid spectrotemporal changes in the older adult group. This study demonstrates a biological, age-related change in the neural representation of basic speech sounds and suggests one possible underlying mechanism for the speech perception difficulties exhibited by aging adults. Furthermore, results of this study support previous findings suggesting a dissociation between neural mechanisms underlying those processes that reflect the basic representation of sound structure and those that represent auditory echoic memory and stimulus change.
Calcium Transients in the Rhabdomeres of Dark- and Light-Adapted Fly Photoreceptor Cells
Authors: Oberwinkler Johannes , Stavenga Doekele G.
Published: April 2018

The light response of fly photoreceptor cells is modulated by changes in free Ca2+concentration. Fly phototransduction and most processes regulating it take place in or very close to the rhabdomere. We therefore measured the kinetics and the absolute values of the free Ca2+concentration in the rhabdomere of fly photoreceptor cellsin vivoby making use of the natural optics of the fly's eye. We show that Ca2+flowing into the rhabdomere after light stimulation of dark-adapted cells causes fast Ca2+transients that reach peak values higher than 200 μmin <20 msec. Approximately 500 msec later, the free Ca2+concentration has declined again to ∼20 μm. The duration of the Ca2+transients becomes still shorter, and their size reduced, when the photoreceptor cell is light-adapted. This reduction in duration and size of the Ca2+transients is graded with the intensity of the adapting light. The kinetics and absolute values of the free calcium concentration found to occur in the rhabdomere are suitable to mediate the fast feedback signals known to act on the fly phototransduction cascade.
Reciprocal Inhibitory Connections Regulate the Spatiotemporal Properties of Intrathalamic Oscillations
Authors: Sohal Vikaas S. , Huntsman Molly M. , Huguenard John R.
Published: April 2018

Mice with an inactivated GABAAreceptor β3subunit gene have features of Angelman syndrome, including absence-like seizures. This suggests the occurrence of abnormal hypersynchrony in the thalamocortical system. Within the thalamus, the efficacy of inhibitory synapses between thalamic reticular (RE) neurons is selectively compromised, and thalamic oscillationsin vitroare prolonged and lack spatial phase gradients (Huntsman et al., 1999). Here we used computational models to examine how intra-RE inhibition regulates intrathalamic oscillations. A major effect is an abbreviation of network responses, which is caused by long-lasting intra-RE inhibition that shunts recurrent excitatory input. In addition, differential activation of RE cells desynchronizes network activity. Near the slice center, where many cells are initially activated, there is a resultant high level of intra-RE inhibition. This leads to RE cell burst truncation in the central region and a gradient in the timing of thalamocortical cell activity similar to that observedin vitro. Although RE cell burst durations were shortened by this mechanism, there was very little effect on the times at which RE cells began to burst. The above results depended on widespread stimuli that activated RE cells in regions larger than the diameter of intra-RE connections. By contrast, more focal stimuli could elicit oscillations that lasted several cycles and remained confined to a small region. These results suggest that intra-RE inhibition restricts intrathalamic activity to particular spatiotemporal patterns to allow focal recurrent activity that may be relevant for normal thalamocortical function while preventing widespread synchronization as occurs in seizures.
Properties of Horizontal and Vertical Inputs to Pyramidal Cells in the Superficial Layers of the Cat Visual Cortex
Authors: Yoshimura Yumiko , Sato Hiromichi , Imamura Kazuyuki , Watanabe Yasuyoshi
Published: April 2018

The purpose of this study is to elucidate the integrative input mechanisms of pyramidal cells receiving horizontally projecting axon collaterals (horizontal projection) and vertical input from layer IV. We performed whole-cell recordings from pyramidal cells in layer II/III and focally activated other single pyramidal cells monosynaptically connected via long-distance horizontal (LH) projections (the distance between presynaptic and postsynaptic cells was 350–1200 μm) in slice preparations of the kitten primary visual cortex. In addition, presynaptic single fibers in layer IV (vertical input) and/or short-distance horizontal (SH) inputs from neighboring single pyramidal cells (distance within 100 μm) in layer II/III were activated. Unitary EPSPs evoked by the activation of LH and SH connections had smaller amplitude and larger coefficient of variation than those evoked by stimulating the vertical input. Paired-pulse stimulation of the LH and SH inputs caused the depression of the second EPSP, whereas that of vertical inputs caused either facilitation or depression of the second EPSP. The EPSPs evoked by simultaneous activation of LH and vertical inputs summated linearly at the resting membrane potential. However, the EPSPs evoked by stimulation of the two inputs were nonlinearly (supralinearly) summated when the postsynaptic membrane was depolarized to a certain level. Similar EPSP interaction was observed in response to simultaneous activation of the LH and SH inputs.
Interspike Intervals, Receptive Fields, and Information Encoding in Primary Visual Cortex
Authors: Reich Daniel S. , Mechler Ferenc , Purpura Keith P. , Victor Jonathan D.
Published: April 2018

In the primate primary visual cortex (V1), the significance of individual action potentials has been difficult to determine, particularly in light of the considerable trial-to-trial variability of responses to visual stimuli. We show here that the information conveyed by an action potential depends on the duration of the immediately preceding interspike interval (ISI). The interspike intervals can be grouped into several different classes on the basis of reproducible features in the interspike interval histograms. Spikes in different classes bear different relationships to the visual stimulus, both qualitatively (in terms of the average stimulus preceding each spike) and quantitatively (in terms of the amount of information encoded per spike and per second). Spikes preceded by very short intervals (3 msec or less) convey information most efficiently and contribute disproportionately to the overall receptive-field properties of the neuron. Overall, V1 neurons can transmit between 5 and 30 bits of information per second in response to rapidly varying, pseudorandom stimuli, with an efficiency of ∼25%. Although some (but not all) of our results would be expected from neurons that use a firing-rate code to transmit information, the evidence suggests that visual neurons are well equipped to decode stimulus-related information on the basis of relative spike timing and ISI duration.
Laminin Degradation by Plasmin Regulates Long-Term Potentiation
Authors: Nakagami Yasuhiro , Abe Kazuho , Nishiyama Nobuyoshi , Matsuki Norio
Published: April 2018

Plasmin is converted from its zymogen plasminogen by tissue type or urokinase type plasminogen activator (PA) and degrades many components of the extracellular matrix (ECM). To explore the possibility that the PA–plasmin system regulates synaptic plasticity, we investigated the effect of plasmin on degradation of ECM and synaptic plasticity by using organotypic hippocampal cultures. High-frequency stimulation produced long-term potentiation (LTP) in control slices, whereas the potentiation was induced but not maintained in slices pretreated with 100 nmplasmin for 6 hr. The baseline synaptic responses were not affected by pretreatment with plasmin. The impairment of LTP maintenance was not observed in slices pretreated with 100 nmplasmin for 6 hr, washed, and then cultured for 24–48 hr in the absence of plasmin. To identify substrates of plasmin, the expression of three major components of ECM, laminin, fibronectin, and type IV collagen, was investigated by immunofluorescence imaging. The three ECM components were widely distributed in the hippocampus, and only laminin was degraded by plasmin pretreatment. The expression level of laminin returned to normal levels when the slices were cultured for 24–48 hr after washout of plasmin. Furthermore, preincubation with anti-laminin antibodies prevented both the degradation of laminin and the impairment of LTP maintenance by plasmin. These results suggest that the laminin-mediated cell–ECM interaction may be necessary for the maintenance of LTP.
Modulation of Presynaptic Action Potential Kinetics Underlies Synaptic Facilitation of Type B Photoreceptors after Associative Conditioning inHermissenda
Authors: Gandhi Chetan C. , Matzel Louis D.
Published: April 2018

Descriptions of conditioned response generation inHermissendastipulate that the synaptic interaction between type B and A photoreceptors should be enhanced after associative pairings of light and rotation. Although evidence from several laboratories has confirmed this assumption, the mechanism underlying this synaptic facilitation has not been elucidated. Here we report thatin vitroconditioning (i.e., light paired with stimulation of vestibular hair cells) modifies the kinetics of presynaptic action potentials in the B photoreceptor in a manner sufficient to account for this synaptic facilitation. After paired training, we observed an increase in the duration of evoked action potentials and a decrease in the amplitude of the spike afterhyperpolarization in the B-cell. As previously reported, paired training also enhanced the excitability (i.e., input resistance and evoked spike rate) of the B photoreceptor. In a second experiment, simultaneous recordings were made in type B and A photoreceptors, and paired training was found to produce an increase in the amplitude of the IPSP in the A photoreceptor in response to an evoked spike in the B-cell. Importantly, there was no change in the initial slope of the postsynaptic IPSP in the A photoreceptor, suggesting that spike duration-independent mechanisms of neurotransmitter exocytosis or postsynaptic receptor sensitivity did not contribute to the observed synaptic facilitation. Perfusion of 4-aminopyridine (4-AP) mimicked a known effect of behavioral conditioning in that it specifically reduced the amplitude of the transient voltage-dependent K+current (IA) in the B-cell, but in addition, produced action potential broadening and synaptic facilitation that was analogous to that observed afterin vitroconditioning. Finally, the effect of 4-AP on B-cell action potentials and on the postsynaptic IPSP in the A-cell was occluded by previous paired (but not unpaired) training, suggesting that the prolongation of the B-cell action potential by a reduction ofIAwas sufficient to account for the observed synaptic facilitation. The occlusion of the effects of 4-AP by paired training was not attributable to a saturation of the capacity of the B-cell for transmitter exocytosis, because it was observed that tetraethylammonium (TEA)-induced inhibition of the delayed voltage-dependent K+current induced both spike broadening and synaptic facilitation regardless of training history. Collectively, these results demonstrate that training-induced facilitation at B-cell synapses is attributable to the effects of a reduction of a presynaptic K+conductance on action potential kinetics and suggest another critical similarity between the cellular basis for learning inHermissendaand other invertebrate systems.
Role of Glycogen Synthase Kinase-3β in Neuronal Apoptosis Induced by Trophic Withdrawal
Authors: Hetman Michal , Cavanaugh Jane E. , Kimelman David , Xia Zhengui
Published: April 2018

Glycogen synthase kinase-3β (GSK3β) activity is negatively regulated by several signal transduction cascades that protect neurons against apoptosis, including the phosphatidylinositol-3 kinase (PI-3 kinase) pathway. This suggests the interesting possibility that activation of GSK3β may contribute to neuronal apoptosis. Consequently, we evaluated the role of GSK3β in apoptosis in cultured cortical neurons induced by trophic factor withdrawal or by PI-3 kinase inhibition. Neurons were subjected to several apoptotic paradigms, including serum deprivation, serum deprivation combined with exposure to NMDA receptor antagonists, or treatment with PI-3 kinase inhibitors. These treatments all led to stimulation of GSK3β activity in cortical neurons, which preceded the induction of apoptosis. Expression of an inhibitory GSK3β binding protein or a dominant interfering form of GSK3β reduced neuronal apoptosis, suggesting that GSK3β contributes to trophic factor withdrawal-induced apoptosis. Furthermore, overexpression of GSK3β in neurons increased apoptosis, indicating that activation of this enzyme is sufficient to trigger programmed cell death. Although destabilization of β-catenin is an important physiological effect of GSK3β activation, expression of a mutant β-catenin that is not destabilized by GSK3β did not protect against apoptosis. We conclude that inhibition of GSK3β is one of the mechanisms by which PI-3 kinase activation protects neurons from programmed cell death.
A Novel Particulate Form of Ca2+/CaMKII-Dependent Protein Kinase II in Neurons
Authors: Dosemeci Ayse , Reese Thomas S. , Petersen Jennifer , Tao-Cheng Jung-Hwa
Published: April 2018

Cytoskeletal and postsynaptic density (PSD) fractions from forebrain contain discrete spherical structures that are immunopositive for Ca2+/calmodulin-dependent protein kinase II (CaMKII). Spherical structures viewed by rotary shadow electron microscopy have an average diameter of ∼100 nm and, in distinction to postsynaptic densities, do not immunolabel for PSD-95. These structures were purified to near homogeneity by extraction with the detergentN-lauryl sarcosinate. Biochemical analysis revealed that CaMKII accounts for virtually all of the protein in the purified preparation, suggesting that spherical structures are clusters of self-associated CaMKII. Exposure of cultured hippocampal neurons to a mitochondrial uncoupler in glucose-free medium promotes the formation of numerous CaMKII-immunopositive structures identical in size and shape to the CaMKII clusters observed in subcellular fractions. Clustering of CaMKII would reduce its kinase function by preventing its access to fixed substrates. On the other hand, clustering would not affect the ability of the large cellular pool of CaMKII to act as a calmodulin sink, as demonstrated by the Ca2+-dependent binding of gold-conjugated calmodulin to CaMKII clusters. We propose that the observed clustering of CaMKII into spherical structures is a protective mechanism preventing excessive protein phosphorylation upon loss of Ca2+homeostasis, without compromising calmodulin regulation.
Activation of Group II Metabotropic Glutamate Receptors Inhibits Synaptic Excitation of the Substantia Nigra Pars Reticulata
Authors: Bradley Stefania Risso , Marino Michael J. , Wittmann Marion , Rouse Susan T. , Awad Hazar , Levey Allan I. , Conn P. Jeffrey
Published: April 2018

Loss of nigrostriatal dopaminergic neurons in Parkinson's disease (PD) leads to increased activity of glutamatergic neurons in the subthalamic nucleus (STN). Recent studies reveal that the resultant increase in STN-induced excitation of basal ganglia output nuclei is responsible for the disabling motor impairment characteristic of PD. On the basis of this, it is possible that any manipulation that reduces activity at excitatory STN synapses onto basal ganglia output nuclei could be useful in the treatment of PD. We now report that group II metabotropic glutamate receptors (mGluRs) are presynaptically localized on STN terminals and that activation of these receptors inhibits excitatory transmission at STN synapses. In agreement with the hypothesis that this could provide a therapeutic benefit in PD, a selective agonist of group II mGluRs induces a dramatic reversal of catalepsy in a rat model of PD. These results raise the exciting possibility that selective agonists of group II mGluRs could provide an entirely new approach to the treatment of PD. These novel therapeutic agents would provide a noninvasive pharmacological treatment that does not involve the manipulation of dopaminergic systems, thus avoiding the problems associated with current therapies.