bluuebunny/crossref_metadata_2025 huggingface dataset:
Synchronizing Retinal Activity in Both Eyes Disrupts Binocular Map Development in the Optic Tectum
Authors: Brickley Stephen G. , Dawes Elizabeth A. , Keating Michael J. , Grant Simon
Published: April 2018

Spatiotemporal correlations in the pattern of spontaneous and evoked retinal ganglion cell (RGC) activity are believed to influence the topographic organization of connections throughout the developing visual system. We have tested this hypothesis by examining the effects of interfering with these potential activity cues during development on the functional organization of binocular maps in theXenopusfrog optic tectum. Paired recordings combined with cross-correlation analyses demonstrated that exposing normal frogs to a continuous 1 Hz of stroboscopic illumination synchronized the firing of all three classes of RGC projecting to the tectum and induced similar patterns of temporally correlated activity across both lobes of the nucleus. Embryonic and eye-rotated larval animals were reared until early adulthood under equivalent stroboscopic conditions. The maps formed by each RGC class in the contralateral tectum showed normal topography and stratification after strobe rearing, but with consistently enlarged multiunit receptive fields. Maps of the ipsilateral eye, formed by crossed isthmotectal axons, showed significant disorder and misalignment with direct visual input from the retina, and in the eye-rotated animals complete compensatory reorientation of these maps usually induced by this procedure failed to occur. These findings suggest that refinement of retinal arbors in the tectum and the ability of crossed isthmotectal arbors to establish binocular convergence with these retinal afferents are disrupted when they all fire together. Our data thus provide direct experimental evidence that spatiotemporal activity patterns within and between the two eyes regulate the precision of their developing connections.
Pointing to Kinesthetic Targets in Space
Authors: Baud-Bovy Gabriel , Viviani Paolo
Published: April 2018

An experiment investigated in human adults the sensorimotor transformation involved in pointing to a spatial target identified previously by kinesthetic cues. In the “locating phase,” a computer-controlled mechanical arm guided the left [condition LR (left–right)] or right [condition RR (right–right)] finger of the blindfolded participant to one of 27 target positions. In the subsequent “pointing phase,” the participant tried to reach the same position with the right finger. The final finger position and the posture of the arm were measured in both conditions. Constant errors were large but consistent and remarkably similar across conditions, suggesting that, whatever the locating hand, target position is coded in an extrinsic frame of reference (target position hypothesis). The main difference between the same-hand (RR) and different-hand (LR) conditions was a symmetric shift of the pattern of endpoints with respect to the midsagittal plane. This effect was modeled accurately by assuming a systematic bias in the perception of the postural angles of the locating arm. The analysis of the variable errors indicated that target position is represented internally in a spherical coordinate system centered on the shoulder of the pointing arm and that the main source of variability is within the planning stage of the pointing movement. Locating and pointing postures depended systematically on target position. We tested qualitatively the hypothesis that the selection of both postures (inverse kinematic problem) is constrained by a minimum-distance principle. In condition RR, pointing posture depended also on the locating posture, implying the presence of a memory trace of the previous movement. A scheme is suggested to accommodate the results within an extended version of the target position hypothesis.
Quantitative Analysis of a Directed Behavior in the Medicinal Leech: Implications for Organizing Motor Output
Authors: Lewis John E. , Kristan William B.
Published: April 2018

The local bend is a directed behavior produced by the leech,Hirudo medicinalis, in response to a light touch. Contraction of longitudinal muscles near the touched location results in a bend directed away from the stimulus. We quantify the relationship between the location of touch around the body perimeter and the behavioral output by using video analysis, muscle tension measurements, and electromyography. On average, the direction of the behavioral output differed from the touch location by <8% of the total body perimeter. We discuss our results in the context of two contrasting behavioral strategies: aContinuousstrategy, in which the local bend is directed exactly opposite to stimulus location, and aCategoricalstrategy, in which there are four distinct bend directions, each elicited by stimuli given in a single quadrant of the body perimeter. To distinguish between these strategies, we delivered two competing stimuli simultaneously. The resulting behavioral output is best described by an average of the effects of each stimulus given alone and thus provides support for the Continuous strategy. We also use a simple model, based on anatomical and physiological data, to predict the responses of the known motor neurons to different stimulus locations. The model shows that the activation of two of the motor neurons (D and V) is inconsistent with a Categorical strategy. However, these neurons are known to be active during the local bend behavior. This result, along with our experimental observations, suggests that the local bend network uses a Continuous strategy to encode stimulus location and produce directed behavioral output.
D1Receptor Modulation of Hippocampal–Prefrontal Cortical Circuits Integrating Spatial Memory with Executive Functions in the Rat
Authors: Seamans Jeremy K. , Floresco Stan B. , Phillips Anthony G.
Published: April 2018

Dopamine (DA) within the prefrontal cortex (PFC) plays an important role in modulating the short-term retention of information during working memory tasks. In contrast, little is known about the role of DA in modulating other executive aspects of working memory such as the use of short-term memory to guide action. The present study examined the effects of D1and D2receptor blockade in the PFC on foraging by rats on a radial arm maze under two task conditions: (1) a delayed task in which spatial information acquired during a training phase was used 30 min later to guide prospective responses, and (2) a nondelayed task that was identical to the test phase of the delayed task but lacked a training phase, thereby depriving rats of previous information about the location of food on the maze. In experiment 1, microinjections of the D1antagonist SCH-23390 (0.05, 0.5, or 5 μg/μl), but not the D2anatagonist sulpiride (0.05, 0.5, or 5 μg/μl), into the prelimbic region of the PFC before the test phase disrupted performance of the delayed task without affecting response latencies. In contrast, neither drug affected performance of the nondelayed task. In the present study, we also investigated the role of D1receptors in modulating activity in hippocampal–PFC circuits during delayed responding. Unilateral injections of SCH-23390 into the PFC in the hemisphere contralateral to a microinjection of lidocaine into the hippocampus severely disrupted performance of the delayed task. Thus, the ability to use previously acquired spatial information to guide responding 30 min later on a radial arm maze requires D1receptor activation in the PFC and D1receptor modulation of hippocampal inputs to the PFC. These data suggest that D1receptors in the PFC are involved in working memory processes other than just the short-term active retention of information and also provide direct evidence for DA modulation of limbic–PFC circuits during behavior.
Fornix Lesions Can Facilitate Acquisition of the Transverse Patterning Task: A Challenge for “Configural” Theories of Hippocampal Function
Authors: Bussey Timothy J. , Clea Warburton E. , Aggleton John P. , Muir Janice L.
Published: April 2018

Configural theories of hippocampal function predict that hippocampal dysfunction should impair acquisition of the transverse patterning task, which involves the concurrent solution of three discrimination problems: A+ versus B−; B+ versus C−; and C+ versus A−. The present study tested this prediction in rats using computer-graphic stimuli presented on a touchscreen. Experiment 1 assessed the effects of fornix lesions when the three problems were introduced sequentially (phase 1: A+ vs B−; phase 2: A+ vs B−, B+ vs C−; phase 3: A+ vs B−, B+ vs C−, C+ vs A−). Fornix lesions significantlyfacilitatedacquisition of the complete transverse patterning task (phase 3) but had no effect on the number of sessions or errors required to attain criterion during phase 1 or phase 2. In experiment 2, in which all three problems were presented concurrently from the outset of training, fornix-lesioned animals outperformed control animals during the seventh block of acquisition trials and were not impaired during any stage of acquisition. Importantly, these same animals were significantly impaired on two allocentric spatial tasks: T-maze alternation (experiments 1 and 2) and the Morris Swim Task (experiment 1). These results contradict the predictions of configural theories of hippocampal function and cast doubt on the popular notion that spatial learning is a special case of configural learning.
Bidirectional Synaptic Plasticity in the Rat Basolateral Amygdala: Characterization of an Activity-Dependent Switch Sensitive to the Presynaptic Metabotropic Glutamate Receptor Antagonist 2S-α-Ethylglutamic Acid
Authors: Li He , Weiss Susan R. B. , Chuang De-Maw , Post Robert M. , Rogawski Michael A.
Published: April 2018

This study examines forms of activity-dependent synaptic plasticity in the basolateral amygdalain vitroand demonstrates that a brief high frequency stimulus (HFS) train can induce a switch in the direction of the enduring change in synaptic strength induced by subsequent low-frequency stimulation (LFS). LFS (1 Hz, 15 min) of the external capsule (EC) induced a persistent 1.7-fold enhancement in the amplitude of synaptic potentials recorded intracellularly in basolateral amygdala neurons. The enhancement occurred gradually during the stimulation and was maintained for >30 min after termination of the stimulus train. LFS-induced enduring synaptic facilitation was not affected by the NMDA receptor antagonistd(−)-2-amino-5-phosphonopentanoate (APV; 100 μm). Brief high-frequency EC stimulation (HFS; 100 Hz, 1 sec) induced APV-sensitive short-term potentiation (2.5-fold) that generally decayed within 10 min. When LFS was applied after recovery from the short-term potentiating effect of HFS (HFS/LFS), there was an initial transient (<10 min) enhancement of the synaptic response followed by persistent synaptic depression (synaptic potential amplitude reduced by 22% at 30 min). This represents the first demonstration of stimulus-dependent long-lasting synaptic depression in the amygdala. Application of the presynaptic (group II) metabotropic glutamate receptor antagonist 2S-α-ethylglutamic acid (EGLU; 50 μm) prevented the HFS-dependent switch from synaptic facilitation to depression. Thus, LFS in thein vitroamygdala slice can induce either enduring synaptic potentiation or depression, depending on whether a priming HFS train has been applied. This experience-dependent switch, a novel form of metaplasticity, is not dependent on NMDA receptors but may require group II metabotropic glutamate receptors. In the amygdala, experiential modification of activity-dependent long-term synaptic plasticity adds flexibility to the ways in which synaptic strength can be modified and could play a role in diverse amygdala-dependent processes, including the formation, storage, and extinction of emotional memory and the regulation of epileptogenesis.
Intrastriatal Mesencephalic Grafts Affect Neuronal Activity in Basal Ganglia Nuclei and Their Target Structures in a Rat Model of Parkinson’s Disease
Authors: Nakao Naoyuki , Ogura Mitsuhiro , Nakai Kunio , Itakura Toru
Published: April 2018

Nigrostriatal dopamine (DA) lesions lead to changes of neuronal activity in basal ganglia nuclei such as the globus pallidus (GP, the rodent homolog of lateral globus pallidus), entopeduncular nucleus (EP, the rodent homolog of medial globus pallidus), substantia nigra pars reticulata (SNR), and subthalamic nucleus (STN). We investigated in rats whether embryonic mesencephalic DA neurons grafted in the striatum may affect the lesion-induced alterations of neuronal activity in these structures. Regional neuronal activity was determined by use of quantitative cytochrome oxidase histochemistry. It was also examined in lesioned rats whether the grafts may regulate the expression of c-Fos after systemic administration of apomorphine in the basal ganglia nuclei as well as their target structures, including the ventromedial thalamic nucleus (VM), superior colliculus (SC), and pedunculopontine nucleus (PPN). Lesioned rats exhibited an increased activity of CO in the GP, EP, SNR, and STN ipsilateral to the lesion. Intrastriatal nigral grafts reversed the increases in the CO activity in the EP and SNR, whereas the grafts failed to affect the enzyme activity in the GP or STN. Apomorphine induced an increased expression of c-Fos in the GP, STN, VM, SC, and PPN on the lesioned side. The enhanced expression of this protein in all the structures except for the STN was attenuated by nigral grafts. The present results indicate that intrastriatal DA neuron grafts can normalize the lesion-induced changes of neuronal activity in the output nuclei of the basal ganglia as well as their target structures.
Activation of Serotonergic Neurons in the Raphe Magnus Is Not Necessary for Morphine Analgesia
Authors: Gao Keming , Chen David O. , Genzen Jonathan R. , Mason Peggy
Published: April 2018

A wealth of pharmacological and behavioral data suggests that spinally projecting serotonergic cells mediate opioid analgesia. A population of medullary neurons, located within raphe magnus (RM) and the neighboring reticular nuclei, contains serotonin and is the source of serotonin in the spinal dorsal horn. To test whether serotonergic neurons mediate opioid analgesia, morphine was administered during recordings from medullary cells that were physiologically characterized as serotonergic (5HTp) by their slow and steady discharge pattern in the lightly anesthetized rat. Selected 5HTpcells (n= 14) were intracellularly labeled, and all contained serotonin immunoreactivity. The discharge of most 5HTpcells was not affected by an analgesic dose of systemic morphine. In a minority of cases, 5HTpcells either increased or decreased their discharge after morphine administration. However, morphine altered the discharge of some 5HTpcells in the absence of producing analgesia and conversely did not alter the discharge of most 5HTpcells in cases in which analgesia occurred. RM cells with irregular discharge patterns and excitatory or inhibitory responses to noxious tail heat were classified asonandoffcells, respectively. Allonandoffcells that were intracellularly labeled (n= 9) lacked serotonin immunoreactivity. Alloncells were inhibited, and mostoffcells were excited by systemic morphine. Because 5HTpcells do not consistently change their discharge during morphine analgesia, they are unlikely to mediate the analgesic effects of morphine. Instead, nonserotonergic cells are likely to mediate morphine analgesia in the anesthetized rat. In light of the sensitivity of morphine analgesia to manipulations of serotonin, serotonin release, although neither necessary nor sufficient for opioid analgesia, is proposed to facilitate the analgesic effects of nonserotonergic RM terminals in the spinal cord.
Vasopressin Regularizes the Phasic Firing Pattern of Rat Hypothalamic Magnocellular Vasopressin Neurons
Authors: Gouzènes Laurent , Desarménien Michel G. , Hussy Nicolas , Richard Philippe , Moos Françoise C.
Published: April 2018

Vasopressin (AVP) magnocellular neurons of hypothalamic nuclei express specific phasic firing (successive periods of activity and silence), which conditions the mode of neurohypophyseal vasopression release. In situations favoring plasmatic secretion of AVP, the hormone is also released at the somatodendritic level, at which it is believed to modulate the activity of AVP neurons. We investigated the nature of this autocontrol by testing the effects of juxtamembrane applications of AVP on the extracellular activity of presumed AVP neurons in paraventricular and supraoptic nuclei of anesthetized rats. AVP had three effects depending on the initial firing pattern: (1) excitation of faintly active neurons (periods of activity of <10 sec), which acquired or reinforced their phasic pattern; (2) inhibition of quasi-continuously active neurons (periods of silences of <10 sec), which became clearly phasic; and (3) no effect on neurons already showing an intermediate phasic pattern (active and silent periods of 10–30 sec). Consequently, AVP application resulted in a narrower range of activity patterns of the population of AVP neurons, with a Gaussian distribution centered around a mode of 57% of time in activity, indicating a homogenization of the firing pattern. The resulting phasic pattern had characteristics close to those established previously for optimal release of AVP from neurohypophyseal endings. These results suggest a new role for AVP as an optimizing factor that would foster the population of AVP neurons to discharge with a phasic pattern known to be most efficient for hormone release.
Prenatal Stress Enhances Stress- and Corticotropin-Releasing Factor-Induced Stimulation of Hippocampal Acetylcholine Release in Adult Rats
Authors: Day Jamie C. , Koehl Muriel , Deroche Veronique , Le Moal Michel , Maccari Stefania
Published: April 2018

There is growing evidence that stressors occurring during pregnancy can impair biological and behavioral responses to stress in the adult offspring. For instance, prenatal stress enhances emotional reactivity, anxiety, and depressive-like behaviors associated with a prolonged stress-induced corticosterone secretion and a reduction in hippocampal corticosteroid receptors. Among the neurotransmitters involved in these hormonal and behavioral responses, acetylcholine may play a critical role. However, it is unknown whether prenatal stressful events also may influence the development of cholinergic systems. In the present study, hippocampal acetylcholine was measured, byin vivomicrodialysis, in both male and female adult prenatally stressed rats, under basal conditions, after a mild stress (saline injection) or after intracerebroventricular administration of corticotropin-releasing factor (CRF; 0.1 nm). No difference in basal release of acetylcholine was observed between control and prenatally stressed rats of both genders. Mild stress was found to increase hippocampal acetylcholine release to a greater extent in prenatally stressed rats than in controls. In males, the CRF-induced increase in hippocampal acetylcholine release was larger in prenatally stressed rats, as compared with controls, during the first hour after the injection and in females during the third hour after the injection. These data indicate that prenatal stress has long-term effects on the development of forebrain cholinergic systems. The augmented increase in hippocampal acetylcholine release after the mild stress and CRF injection in prenatally stressed rats may be involved in some of the hormonal and behavioral abnormalities found in prenatally stressed rats.
The Cytoplasmic Domain of the Large Myelin-Associated Glycoprotein Isoform Is Needed for Proper CNS But Not Peripheral Nervous System Myelination
Authors: Fujita Nobuya , Kemper April , Dupree Jeffrey , Nakayasu Hiroyuki , Bartsch Udo , Schachner Melitta , Maeda Nobuyo , Suzuki Kinuko , Suzuki Kunihiko , Popko Brian
Published: April 2018

The myelin-associated glycoprotein (MAG) is a member of the immunoglobulin gene superfamily and is thought to play a critical role in the interaction of myelinating glial cells with the axon. Myelin from mutant mice incapable of expressing MAG displays various subtle abnormalities in the CNS and degenerates with age in the peripheral nervous system (PNS). Two distinct isoforms, large MAG (L-MAG) and small MAG (S-MAG), are produced through the alternative splicing of the primary MAG transcript. The cytoplasmic domain of L-MAG contains a unique phosphorylation site and has been shown to associate with the fyn tyrosine kinase. Moreover, L-MAG is expressed abundantly early in the myelination process, possibly indicating an important role in the initial stages of myelination. We have adapted the gene-targeting approach in embryonic stem cells to generate mutant mice that express a truncated form of the L-MAG isoform, eliminating the unique portion of its cytoplasmic domain, but that continue to express S-MAG. Similar to the total MAG knockouts, these animals do not express an overt clinical phenotype. CNS myelin of the L-MAG mutant mice displays most of the pathological abnormalities reported for the total MAG knockouts. In contrast to the null MAG mutants, however, PNS axons and myelin of older L-MAG mutant animals do not degenerate, indicating that S-MAG is sufficient to maintain PNS integrity. These observations demonstrate a differential role of the L-MAG isoform in CNS and PNS myelin.
Dopamine D1Receptors Facilitate GABAASynaptic Currents in the Rat Substantia Nigra Pars Reticulata
Authors: Radnikow Gabriele , Misgeld Ulrich
Published: April 2018

GABA neurons in the substantia nigra pars reticulata receive input from GABAergic fibers originating in the forebrain. The role of dopaminergic D1receptors located on these fibers was investigated using tight-seal whole-cell recordings from visually identified pars reticulata neurons of rat substantia nigra slices. Nondopaminergic pars reticulata neurons were characterized by their electrophysiological properties. Postsynaptic currents evoked by minimal stimulation in the presence of ionotropic glutamate receptor antagonists were blocked by bicuculline, indicating that they were GABAAIPSCs. Evoked GABAAIPSCs were potentiated by D1receptor agonists. After application of D1receptor agonists, miniature IPSCs [recorded in the presence of tetrodotoxin (TTX) and the Ca2+channel blocker Cd2+] increased in frequency but not in amplitude. Effects of D1receptor stimulation were mimicked by forskolin, as expected, if a cAMP-dependent mechanism was involved. The D1antagonist SCH23390 blocked the effects of the agonists, and perfusion with SCH23390 resulted in a reduction of evoked IPSCs. In TTX and Cd2+, which prevented dopamine release, the D1antagonist had no effect on miniature IPSCs. Blocking of monoamine uptake by imipramine increased the amplitude of evoked IPSCs. We conclude that dopamine released from dendrites of dopaminergic neurons enhances GABA release in the pars reticulata of the substantia nigra through D1receptors presumably located on striatonigral afferents. These D1receptors, thereby, can reinforce D1receptor-mediated activation of striatal projection neurons that inhibit the inhibitory output neurons of the basal ganglia in substantia nigra.
Manganese Superoxide Dismutase Protects nNOS Neurons from NMDA and Nitric Oxide-Mediated Neurotoxicity
Authors: Gonzalez-Zulueta Mirella , Ensz Lisa M. , Mukhina Galina , Lebovitz Russell M. , Zwacka Ralf M. , Engelhardt John F. , Oberley Larry W. , Dawson Valina L. , Dawson Ted M.
Published: April 2018

Neuronal nitric oxide synthase (nNOS) neurons kill adjacent neurons through the action of NMDA-glutamate receptor activation, although they remain relatively resistant to the toxic effects of NMDA and NO. The molecular basis of the resistance of nNOS neurons to toxic insults is unknown. To begin to understand the molecular mechanisms of the resistance of nNOS neurons, we developed a pheochromacytoma-derived cell line (PC12) that is resistant to the toxic effects of NO. We found through serial analysis of gene expression (SAGE) that manganese superoxide dismutase (MnSOD) is enriched in the NO-resistant PC12 cell-derived line (PC12-R). Antisense MnSOD renders PC12-R cells sensitive to NO toxicity and increases the sensitivity to NO in the parental, NO-sensitive PC12 line (PC12-S). Adenoviral transfer of MnSOD protects PC12-S cells against NO toxicity. We extended these studies to cortical cultures and showed that MnSOD is enriched in nNOS neurons and that antisense MnSOD renders nNOS neurons susceptible to NMDA neurotoxicity, although it has little effect on the overall susceptibility of cortical neurons to NMDA toxicity. Overexpression of MnSOD provides dramatic protection against NMDA and NO toxicity in cortical cultures, but not against kainate or AMPA neurotoxicity. Furthermore, nNOS neurons from MnSOD−/−mice are markedly sensitive to NMDA toxicity. Adenoviral transfer of MnSOD to MnSOD−/−cultures restores resistance of nNOS neurons to NMDA toxicity. Thus, MnSOD is a major protective protein that appears to be essential for the resistance of nNOS neurons in cortical cultures to NMDA mediated neurotoxicity.
Fibrillar β-Amyloid Induces Microglial Phagocytosis, Expression of Inducible Nitric Oxide Synthase, and Loss of a Select Population of Neurons in the Rat CNSIn Vivo
Authors: Weldon Derik T. , Rogers Scott D. , Ghilardi Joseph R. , Finke Matthew P. , Cleary James P. , O’Hare Eugene , Esler William P. , Maggio John E. , Mantyh Patrick W.
Published: April 2018

To determine the stability of β-amyloid peptide (Aβ) and the glial and neuronal changes induced by Aβ in the CNSin vivo, we made single injections of fibrillar Aβ (fAβ), soluble Aβ (sAβ), or vehicle into the rat striatum. Injected fAβ is stablein vivofor at least 30 d after injection, whereas sAβ is primarily cleared within 1 d. After injection of fAβ, microglia phagocytize fAβ aggregates, whereas nearby astrocytes form a virtual wall between fAβ-containing microglia and the surrounding neuropil. Similar glial changes are not observed after sAβ injection. Microglia and astrocytes near the injected fAβ show a significant increase in inducible nitric oxide synthase (iNOS) expression compared with that seen with sAβ or vehicle injection. Injection of fAβ but not sAβ or vehicle induces a significant loss of parvalbumin- and neuronal nitric oxide synthase-immunoreactive neurons, whereas the number of calbindin-immunoreactive neurons remains unchanged. These data demonstrate that fAβ is remarkably stable in the CNSin vivoand suggest that fAβ neurotoxicity is mediated in large part by factors released from activated microglia and astrocytes, as opposed to direct interaction between Aβ fibrils and neurons.
Refractoriness and Neural Precision
Authors: Berry Michael J. , Meister Markus
Published: April 2018

The response of a spiking neuron to a stimulus is often characterized by its time-varying firing rate, estimated from a histogram of spike times. If the cell’s firing probability in each small time interval depends only on this firing rate, one predicts a highly variable response to repeated trials, whereas many neurons show much greater fidelity. Furthermore, the neuronal membrane is refractory immediately after a spike, so that the firing probability depends not only on the stimulus but also on the preceding spike train. To connect these observations, we investigated the relationship between the refractory period of a neuron and its firing precision. The light response of retinal ganglion cells was modeled as probabilistic firing combined with a refractory period: the instantaneous firing rate is the product of a “free firing rate,” which depends only on the stimulus, and a “recovery function,” which depends only on the time since the last spike. This recovery function vanishes for an absolute refractory period and then gradually increases to unity. In simulations, longer refractory periods were found to make the response more reproducible, eventually matching the precision of measured spike trains. Refractoriness, although often thought to limit the performance of neurons, may in fact benefit neuronal reliability. The underlying free firing rate derived by allowing for the refractory period often exceeded the observed firing rate by an order of magnitude and was found to convey information about the stimulus over a much wider dynamic range. Thus, the free firing rate may be the preferred variable for describing the response of a spiking neuron.
Selective Enhancement of P-Type Calcium Currents by Isoproterenol in the Rat Amygdala
Authors: Huang Chiung-Chun , Wang Su-Jane , Gean Po-Wu
Published: April 2018

We investigated activation of β-adrenergic receptor–adenylyl cyclase–cAMP cascade on the whole-cell voltage-dependent Ca2+currents (ICa) in acutely isolated rat basolateral amygdala neurons. Application of β-receptor agonist isoproterenol (Iso) caused a long-term enhancement ofICa. The effect of Iso was blocked by concurrent application of β-receptor antagonist propranolol. However, delayed application of propranolol after theICaenhancement did not affect Iso-induced potentiation, suggesting that the sustained effect was not caused by a slow washout of Iso. Nimodipine and ω-conotoxin-GVIA reduced theICaby ∼35 and ∼29%, respectively, without reducing enhancement ofICaby Iso significantly. The modulation appeared to involve P-type current, because the enhancement was abolished after pretreatment with ω-agatoxin-IVA. Forskolin, an adenylyl cyclase activator, mimicked the action of Iso in enhancingICa, and this effect was blocked by an inhibitor of cAMP cascade, indicating a cAMP-dependent mechanism. Iso also induced a long-term potentiation (LTP) of synaptic transmission, which could be prevented by P-type Ca2+channel blockers. These results suggest that P-type Ca2+channels were selectively upregulated in the basolateral amygdala neurons, and enhancement of P-type currents could contribute to presynaptic form of LTP.
Mouse Cerebellar Granule Cell Differentiation: Electrical Activity Regulates the GABAAReceptor α6 Subunit Gene
Authors: Mellor J. R. , Merlo D. , Jones A. , Wisden W. , Randall A. D.
Published: April 2018

GABAAreceptor α6 subunit gene expression marks cerebellar granule cell maturation. To study this process, we used the Δα6lacZ mouse line, which has a lacZ reporter inserted into the α6 gene. At early stages of postnatal cerebellar development, α6-lacZ expression is mosaic; expression starts at postnatal day 5 in lobules 9 and 10, and α6-lacZ is switched on inside-out, appearing first in the deepest postmigratory granule cells. We looked for factors regulating this expression in cell culture. Membrane depolarization correlates inversely with α6-lacZ expression: granule cells grown in 25 mm[K+]ofor 11–15 d do not express the α6 gene, whereas cultures grown for the same period in 5 mm[K+]odo. This is influenced by a critical early period: culturing for ≥3 d in 25 mm[K+]ocurtails the ability to induce the α6 gene on transfer to 5 mm[K+]o. If the cells start in 5 mm[K+]o, however, they still express the α6-lacZ gene in 25 mm[K+]o. In contrast to granule cells grown in 5 mm[K+]o, cells cultured in 25 mm[K+]oexhibit no action potentials, mEPSCs, or mIPSCs. In chronic 5 mm[K+]o, factors may therefore be released that induce α6. Blockade of ionotropic and metabotropic GABA and glutamate receptors or L-, N-, and P/Q-type Ca2+channels did not prevent α6-lacZ expression, but inhibition of action potentials with tetrodotoxin blocked expression in a subpopulation of cells.
Episodic Ataxia Mutations in Kv1.1 Alter Potassium Channel Function by Dominant Negative Effects or Haploinsufficiency
Authors: Zerr Patricia , Adelman John P. , Maylie James
Published: April 2018

Subunits of the voltage-gated potassium channel Kv1.1 containing mutations responsible for episodic ataxia (EA), a human inherited neurological disease, were expressed inXenopusoocytes. Five EA subunits formed functional homomeric channels with lower current amplitudes and altered gating properties compared with wild type. Two EA mutations located in the first cytoplasmic loop, R239S and F249I, yielded minimal or no detectable current, and Western blot analysis showed reduced protein levels. Coinjection of equal amounts of EA and wild-type mRNAs, mimicking the heterozygous condition, resulted in current amplitudes and gating properties that were intermediate between wild-type and EA homomeric channels, suggesting that heteromeric channels are formed with a mixed stoichiometry of EA and wild-type subunits. To examine the relative contribution of EA subunits in forming heteromeric EA and wild-type channels, each EA subunit was made insensitive to TEA, TEA-tagged, and coexpressed with wild-type subunits. TEA-tagged R239S and F249I induced the smallest shift in TEA sensitivity compared with homomeric wild-type channels, whereas the other TEA-tagged EA subunits yielded TEA sensitivities similar to coexpression of wild-type and TEA-tagged wild-type subunits. Taken together, these results show that the different mutations in Kv1.1 affect channel function and indicate that both dominant negative effects and haplotype insufficiency may result in the symptoms of EA.
Protein Kinase C Activation Increases Release of Secreted Amyloid Precursor Protein without Decreasing Aβ Production in Human Primary Neuron Cultures.
Authors: LeBlanc Andréa C. , Koutroumanis Maria , Goodyer Cynthia G.
Published: April 2018

Overexpression and altered metabolism of amyloid precursor protein (APP) resulting in increased 4 kDa amyloid β peptide (Aβ) production are believed to play a major role in Alzheimer’s disease (AD). Therefore, reducing Aβ production in the brain is a possible therapy for AD. Because AD pathology is fairly restricted to the CNS of humans, we have established human cerebral primary neuron cultures to investigate the metabolism of APP. In many cell lines and rodent primary neuron cultures, phorbol ester activation of protein kinase C (PKC) increases the release of the secreted large N-terminal fragment of amyloid precursor protein (sAPP) and decreases Aβ release (Buxbaum et al., 1993; Gadzuba et al., 1993; Hung et al., 1993). In contrast, we find that PKC activation in human primary neurons increases the rate of sAPP release and the production of APP C-terminal fragments and 4 kDa Aβ. Our results indicate species- and cell type-specific regulation of APP metabolism. Therefore, our results curtail the use of PKC activators in controlling human brain Aβ levels.
Phosphatidylinositol 3-Kinase and Akt Protein Kinase Are Necessary and Sufficient for the Survival of Nerve Growth Factor-Dependent Sympathetic Neurons
Authors: Crowder Robert J. , Freeman Robert S.
Published: April 2018

Recent studies have suggested a role for phosphatidylinositol (PI) 3-kinase in cell survival, including the survival of neurons. We used rat sympathetic neurons maintainedin vitroto characterize the potential survival signals mediated by PI 3-kinase and to test whether the Akt protein kinase, a putative effector of PI 3-kinase, functions during nerve growth factor (NGF)-mediated survival. Two PI 3-kinase inhibitors, LY294002 and wortmannin, block NGF-mediated survival of sympathetic neurons. Cell death caused by LY294002 resembles death caused by NGF deprivation in that it is blocked by a caspase inhibitor or a cAMP analog and that it is accompanied by the induction ofc-jun,c-fos, andcyclin D1mRNAs. Treatment of neurons with NGF activates endogenous Akt protein kinase, and LY294002 or wortmannin blocks this activation. Expression of constitutively active Akt or PI 3-kinase in neurons efficiently prevents death after NGF withdrawal. Conversely, expression of dominant negative forms of PI 3-kinase or Akt induces apoptosis in the presence of NGF. These results demonstrate that PI 3-kinase and Akt are both necessary and sufficient for the survival of NGF-dependent sympathetic neurons.
A Distinct Subgroup of Small DRG Cells Express GDNF Receptor Components and GDNF Is Protective for These Neurons after Nerve Injury
Authors: Bennett David L. H. , Michael Gregory J. , Ramachandran Navin , Munson John B. , Averill Sharon , Yan Qiao , McMahon Stephen B. , Priestley John V.
Published: April 2018

Several lines of evidence suggest that neurotrophin administration may be of some therapeutic benefit in the treatment of peripheral neuropathy. However, a third of sensory neurons do not express receptors for the neurotrophins. These neurons are of small diameter and can be identified by the binding of the lectin IB4 and the expression of the enzyme thiamine monophosphatase (TMP). Here we show that these neurons express the receptor components for glial-derived neurotrophic factor (GDNF) signaling (RET, GFRα-1, and GFRα-2). In lumbar dorsal root ganglia, virtually all IB4-labeled cells express RET mRNA, and the majority of these cells (79%) also express GFRα-1, GFRα-2, or GFRα-1 plus GFRα-2.

GDNF, but not nerve growth factor (NGF), can prevent several axotomy-induced changes in these neurons, including the downregulation of IB4 binding, TMP activity, and somatostatin expression. GDNF also prevents the slowing of conduction velocity that normally occurs after axotomy in a population of small diameter DRG cells and the A-fiber sprouting into lamina II of the dorsal horn. GDNF therefore may be useful in the treatment of peripheral neuropathies and may protect peripheral neurons that are refractory to neurotrophin treatment.
Disruption of Mitochondrial Respiration Inhibits Volume-Regulated Anion Channels and Provokes Neuronal Cell Swelling
Authors: Patel Amanda J. , Lauritzen Inger , Lazdunski Michel , Honoré Eric
Published: April 2018

Hypoxia and inhibitors of mitochondrial respiration impair the regulatory volume decrease (RVD) of cerebellar granule neurons after hypotonic swelling. RVD is linked to the opening of volume-regulated anion channels (VRACs). VRACs are outwardly rectifying, inactivate slowly during maintained depolarization, and are permeable to the cellular organic osmolyte taurine. Channel activation requires nonhydrolytic ATP binding and is not modulated by intracellular ADP. VRAC opening is reversibly depressed by hypoxia and by mitochondrial inhibitors such as oligomycin, rotenone, and antimycin A. These results demonstrate that neuronal VRAC activation and swelling are both tightly linked to cellular energy. Moreover, the findings reported in this work may have a particular significance for inherited mitochondrial human diseases, such as mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), which cause brain swelling and edema.
G-Protein-Coupled Modulation of Presynaptic Calcium Currents and Transmitter Release by a GABABReceptor
Authors: Takahashi Tomoyuki , Kajikawa Yoshinao , Tsujimoto Tetsuhiro
Published: April 2018

Presynaptic GABABreceptors play a regulatory role in central synaptic transmission. To elucidate their underlying mechanism of action, we have made whole-cell recordings of calcium and potassium currents from a giant presynaptic terminal, the calyx of Held, and EPSCs from its postsynaptic target in the medial nucleus of the trapezoid body of rat brainstem slices. The GABABreceptor agonist baclofen suppressed EPSCs and presynaptic calcium currents but had no effect on voltage-dependent potassium currents. The calcium current–EPSC relationship measured during baclofen application was similar to that observed on reducing [Ca2+]o, suggesting that the presynaptic inhibition generated by baclofen is caused largely by the suppression of presynaptic calcium influx. Presynaptic loading of the GDP analog guanosine-5′-O-(2-thiodiphosphate) (GDPβS) abolished the effect of baclofen on both presynaptic calcium currents and EPSCs. The nonhydrolyzable GTP analog guanosine 5′-O-(3-thiotriphosphate) (GTPγS) suppressed presynaptic calcium currents and occluded the effect of baclofen on presynaptic calcium currents and EPSCs. Photoactivation of GTPγS induced an inward rectifying potassium current at the calyx of Held, whereas baclofen had no such effect. We conclude that presynaptic GABABreceptors suppress transmitter release through G-protein-coupled inhibition of calcium currents.
Extrasynaptic Glutamate Diffusion in the Hippocampus: Ultrastructural Constraints, Uptake, and Receptor Activation
Authors: Rusakov Dmitri A. , Kullmann Dimitri M.
Published: April 2018

Fast excitatory synapses are generally thought to act as private communication channels between presynaptic and postsynaptic neurons. Some recent findings, however, suggest that glutamate may diffuse out of the synaptic cleft and bind to several subtypes of receptors, either in the perisynaptic membrane or at neighboring synapses. It is not known whether activation of these receptors can occur in response to the release of a single vesicle of glutamate. Here we estimate the spatiotemporal profile of glutamate in the extrasynaptic space after vesicle exocytosis, guided by detailed ultrastructural measurements of the CA1 neuropil in the adult rat. We argue that the vicinity of the synapse can be treated as an isotropic porous medium, in which diffusion is determined by the extracellular volume fraction and the tortuosity factor, and develop novel stereological methods to estimate these parameters. We also estimate the spatial separation between synapses, to ask whether glutamate released at one synapse can activate NMDA and other high-affinity receptors at a neighboring synapse. Kinetic simulations of extrasynaptic glutamate uptake show that transporters rapidly reduce the free concentration of transmitter. Exocytosis of a single vesicle is, however, sufficient to bind to high-affinity receptors situated in the immediate perisynaptic space. The distance separating a typical synapse from its nearest neighbor is ∼465 nm. Whether glutamate can reach a sufficient concentration to activate NMDA receptors at this distance depends critically on the diffusion coefficient in the extracellular space. If diffusion is much slower than in free aqueous solution, NMDA receptors could mediate crosstalk between neighboring synapses.
Increased Synaptic Sprouting in Response to Estrogen via an Apolipoprotein E-Dependent Mechanism: Implications for Alzheimer’s Disease
Authors: Stone David J. , Rozovsky Irina , Morgan Todd E. , Anderson Christopher P. , Finch Caleb E.
Published: April 2018

Estrogen replacement therapy appears to delay the onset of Alzheimer’s disease (AD), but the mechanisms for this action are incompletely known. We show how the enhancement of synaptic sprouting by estradiol (E2) in response to an entorhinal cortex (EC) lesion model of AD may operate via an apolipoprotein E (apoE)-dependent mechanism. In wild-type (WT) mice, ovariectomy decreased commissural/associational sprouting to the inner molecular layer of the dentate gyrus, with synaptophysin (SYN) as a marker. E2replacement returned SYN in the inner layer to levels of EC-lesioned, ovary-bearing controls and increased the area of compensatory synaptogenesis in the outer molecular layer. In EC-lesioned apoE-knock-out (KO) mice, however, E2did not enhance sprouting. We also examined apoJ (clusterin) mRNA, which is implicated in AD by its presence in senile plaques, its transport of Aβ across the blood–brain barrier, and its induction by neurodegenerative lesioning. ApoJ mRNA levels were increased by E2replacement in EC-lesioned WT mice but not in apoE-KO mice. These data suggest a mechanism for the protective effects of estrogens on AD and provide a link between two important risk factors in the etiology of AD, the apoE ε4 genotype and an estrogen-deficient state. This is also the first evidence that SYN, a presynaptic protein involved in neurotransmitter release, is regulated by E2in the adult brain, and that apoE is necessary for the induction of apoJ mRNA by E2in brain injury.
Traumatic Spinal Cord Injury Induces Nuclear Factor-κB Activation
Authors: Bethea John R. , Castro Marcia , Keane Robert W. , Lee Thomas T. , Dietrich W. Dalton , Yezierski Robert P.
Published: April 2018

Inflammatory responses are a major component of secondary injury and play a central role in mediating the pathogenesis of acute and chronic spinal cord injury (SCI). The nuclear factor-κB (NF-κB) family of transcription factors is required for the transcriptional activation of a variety of genes regulating inflammatory, proliferative, and cell death responses of cells. In this study we examined the temporal and cellular expression of activated NF-κB after traumatic SCI. We used a contusion model (N.Y.U. Impactor) to initiate the early biochemical and molecular changes that occur after traumatic injury to reproduce the pathological events associated with acute inflammation after SCI. The activation and cellular distribution of activated NF-κB was evaluated by using a monoclonal antibody that selectively recognizes activated p65 in a NF-κB dimer. Immunohistochemical and Western blot analyses demonstrated that NF-κB activation occurred as early as 0.5 hr postinjury and persisted for at least 72 hr. Using electrophoretic mobility shift assays (EMSA), we demonstrate that NF-κB is activated after SCI. In our immunohistochemical, Western, and EMSA experiments there are detectable levels of activated NF-κB in our control animals. Using double-staining protocols, we detected activated NF-κB in macrophages/microglia, endothelial cells, and neurons within the injured spinal cord. Colocalization of activated NF-κB with the NF-κB-dependent gene product, inducible nitric oxide synthase (iNOS), suggests functional implications for this transcription factor in the pathogenesis of acute spinal cord injury. Although there is considerable evidence for the involvement of an inflammatory reaction after traumatic SCI, this is the first evidence for the activation of NF-κB after trauma. Strategies directed at blocking the initiation of this cascade may prove beneficial as a therapeutic approach for the treatment of acute SCI.
Glial Fibrillary Acidic Protein–Apolipoprotein E (apoE) Transgenic Mice: Astrocyte-Specific Expression and Differing Biological Effects of Astrocyte-Secreted apoE3 and apoE4 Lipoproteins
Authors: Sun Yuling , Wu Shan , Bu Guojun , Onifade Moyosore K. , Patel Shilen N. , LaDu Mary Jo , Fagan Anne M. , Holtzman David M.
Published: April 2018

The ε4 allele of apolipoprotein E (apoE) is associated with increased risk for Alzheimer’s disease (AD) and poor outcome after brain injury. In the CNS, apoE is expressed by glia, predominantly astrocytes. To define the potential biological functions of different human apoE isoforms produced within the brain, transgenic mice were generated in which human apoE3 and apoE4 expression is under control of the astrocyte-specific glial fibrillary acidic protein (GFAP) promoter. These animals were then bred back to apoE knock-out mice. Human apoE protein is found within astrocytes and the neuropil throughout development and into the adult period, as assessed by immunocytochemistry and immunoblot analysis in several GFAP-apoE3 and E4 lines. Cultured astrocytes from these mice secrete apoE3 and apoE4 in lipoproteins that are high-density lipoprotein-like in size. When primary hippocampal neurons are grown in the presence of astrocyte monolayers derived from these transgenic mice, there is significantly greater neurite outgrowth from neurons grown in the presence of apoE3-secreting astrocytes compared with apoE4-secreting or apoE knock-out astrocytes. These effects are not dependent on direct astrocyte–neuron contact and appear to require the low-density lipoprotein receptor-related protein. These data suggest that astrocyte-secreted, apoE3-containing lipoproteins have different biological effects than apoE4-containing lipoproteins. In addition to providing information regarding the role of astrocyte-secreted apoE lipoproteins in the normal brain, these animals will also be useful in models of both AD and CNS injury.