bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential Presynaptic Localization of Metabotropic Glutamate Receptor Subtypes in the Rat Hippocampus
Authors: Shigemoto Ryuichi , Kinoshita Ayae , Wada Eiki , Nomura Sakashi , Ohishi Hitoshi , Takada Masahiko , Flor Peter J. , Neki Akio , Abe Takaaki , Nakanishi Shigetada , Mizuno Noboru
Published: April 2018

Neurotransmission in the hippocampus is modulated variously through presynaptic metabotropic glutamate receptors (mGluRs). To establish the precise localization of presynaptic mGluRs in the rat hippocampus, we used subtype-specific antibodies for eight mGluRs (mGluR1–mGluR8) for immunohistochemistry combined with lesioning of the three major hippocampal pathways: the perforant path, mossy fiber, and Schaffer collateral. Immunoreactivity for group II (mGluR2) and group III (mGluR4a, mGluR7a, mGluR7b, and mGluR8) mGluRs was predominantly localized to presynaptic elements, whereas that for group I mGluRs (mGluR1 and mGluR5) was localized to postsynaptic elements. The medial perforant path was strongly immunoreactive for mGluR2 and mGluR7a throughout the hippocampus, and the lateral perforant path was prominently immunoreactive for mGluR8 in the dentate gyrus and CA3 area. The mossy fiber was labeled for mGluR2, mGluR7a, and mGluR7b, whereas the Schaffer collateral was labeled only for mGluR7a. Electron microscopy further revealed the spatial segregation of group II and group III mGluRs within presynaptic elements. Immunolabeling for the group III receptors was predominantly observed in presynaptic active zones of asymmetrical and symmetrical synapses, whereas that for the group II receptor (mGluR2) was found in preterminal rather than terminal portions of axons. Target cell-specific segregation of receptors, first reported for mGluR7a (Shigemoto et al., 1996), was also apparent for the other group III mGluRs, suggesting that transmitter release is differentially regulated by 2-amino-4-phosphonobutyrate-sensitive mGluRs in individual synapses on single axons according to the identity of postsynaptic neurons.
Instantaneous Perturbation of Dentate Interneuronal Networks by a Pressure Wave-Transient Delivered to the Neocortex
Authors: Toth Zsolt , Hollrigel Greg S. , Gorcs Tamas , Soltesz Ivan
Published: April 2018

Whole-cell patch-clamp recordings and immunocytochemical experiments were performed to determine the short- and long-term effects of lateral fluid percussion head injury on the perisomatic inhibitory control of dentate granule cells in the adult rat, with special reference to the development of trauma-induced hyperexcitability. One week after the delivery of a single, moderate (2.0–2.2 atm) mechanical pressure wave to the neocortex, the feed-forward inhibitory control of dentate granule cell discharges was compromised, and the frequency of miniature IPSCs was decreased. Consistent with the electrophysiological data, the number of hilar parvalbumin (PV)- and cholecystokinin (CCK)-positive dentate interneurons supplying the inhibitory innervation of the perisomatic region of granule cells was decreased weeks and months after head injury. The initial injury to the hilar neurons took place instantaneously after the impact and did not require the recruitment of active physiological processes. Furthermore, the decrease in the number of PV- and CCK-positive hilar interneurons was similar to the decrease in the number of the AMPA-type glutamate receptor subunit 2/3-immunoreactive mossy cells, indicating that the pressure wave-transient causes injurious physical stretching and bending of most cells that are large and not tightly packed in a cell layer.

These results reveal for the first time that moderate pressure wave-transients, triggered by traumatic head injury episodes, impact the dentate neuronal network in a unique temporal and spatial pattern, resulting in a net decrease in the perisomatic control of granule cell discharges.
Origin and Route of Tangentially Migrating Neurons in the Developing Neocortical Intermediate Zone
Authors: Tamamaki Nobuaki , Fujimori Kazuhiro E. , Takauji Rumiko
Published: April 2018

Neuroblasts produced in the ventricular zone of the neocortex migrate radially and form the cortical plate, settling in an inside-out order. It is also well known that the tangential cell migration is not negligible in the embryonic neocortex. To have a better understanding of the tangential cell migration in the cortex, we disturbed the migration by making a cut in the neocortex, and we labeled the migrating cells with 1,1′-dioctodecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (DiI)in vivoandin vitro. We also determined the birth dates of the cells.

Disturbance of tangential cell migration caused an accumulation and disappearance of microtubule-associated protein 2 immunoreactive (MAP2-IR) cells on the ventral and dorsal side of the cut, respectively, which indicated that most of the MAP2-IR cells in the intermediate zone (IZ) were migrating toward the dorsal cortex. The DiI injection studyin vivoconfirmed the tendency of the direction of cell migration and suggested the origin of the cells to be in the lateral ganglionic eminence (LGE). DiI injection into the LGEin vitroconfirmed that the LGE cells cross the corticostriatal boundary and enter the IZ of the neocortex. The migrating cells acquired multipolar shape in the IZ of the dorsal cortex and seemed to reside there. A 5-bromo-deoxyuridine incorporation study revealed that the migrating MAP2-IR cells in the IZ were early-generated neurons. We concluded that the majority of tangentially migrating cells were generated in the LGE and identified as a distinct population that was assumed not to have joined the cortical plate.
Synaptic Communication among Hippocampal Interneurons: Properties of Spontaneous IPSCs in Morphologically Identified Cells
Authors: Hájos Norbert , Mody Istvan
Published: April 2018

The properties of spontaneous IPSCs (sIPSCs) recorded with whole-cell patch-clamp techniques were investigated in various anatomically identified hippocampal CA1 interneurons and were compared with those recorded in pyramidal cells. Neurons labeled with biocytin or neurobiotin were classified on the basis of their dendritic and axonal arborizations, leading to the identification of previously unknown interneuron types projecting to the dendritic region of pyramidal cells. In most interneurons, the average sIPSCs decayed slower than did those observed in pyramidal cells. The properties of sIPSCs were homogeneous within a given morphologically identified neuron type. Many interneurons had comparable somatic size, location, and dendritic arbor but displayed extremely different axonal projections paralleled by distinct sIPSC properties. Thus, physiological comparisons are only meaningful after the complete morphological identification of the recorded cells. The decay of sIPSCs matched for amplitudes and rise times could vary over 10-fold in a given interneuron, consistent with electrotonic filtering and possibly with different GABAAreceptor subunit assemblies present at distinct synapses. Our findings demonstrate an extensive connectivity among hippocampal interneurons through GABAAsynapses of various properties that may underlie complex network oscillations at different frequencies.
cAMP Response Element-Binding Protein in the Amygdala Is Required for Long- but not Short-Term Conditioned Taste Aversion Memory
Authors: Lamprecht Raphael , Hazvi Shoshi , Dudai Yadin
Published: April 2018

In conditioned taste aversion (CTA) organisms learn to avoid a taste if the first encounter with that taste is followed by transient poisoning. The neural mechanisms that subserve this robust and long-lasting association of taste and malaise have not yet been elucidated, but several brain areas have been implicated in the process, including the amygdala. In this study we investigated the role of amygdala in general, and the cAMP response element-binding protein (CREB) in the amygdala in particular, in CTA learning and memory. Toward that end, we combined antisense technologyin vivowith behavioral, molecular, and histochemical analysis. Local microinjection of phosphorothioate-modified oligodeoxynucleotides (ODNs) antisense to CREB into the rat amygdala several hours before CTA training transiently reduced the level of CREB protein during training and impaired CTA memory when tested 3–5 d later. In comparison, sense ODNs had no effect on memory. The effect of antisense was not attributable to differential tissue damage and was site-specific. CREB antisense in the amygdala had no effect on retrieval of CTA memory once it had been formed, and did not affect short-term CTA memory. We propose that the amygdala, specifically the central nucleus, is required for the establishment of long-term CTA memory in the behaving rat; that the process involves long-term changes, subserved by CRE-regulated gene expression, in amygdala neurons; and that the amygdala may retain some CTA-relevant information over time rather than merely modulating the gustatory trace during acquisition of CTA.
Nerve Growth Factor Treatment Increases Brain-Derived Neurotrophic Factor Selectively in TrkA-Expressing Dorsal Root Ganglion Cells and in Their Central Terminations within the Spinal Cord
Authors: Michael G. J. , Averill S. , Nitkunan A. , Rattray M. , Bennett D. L. H. , Yan Q. , Priestley J. V.
Published: April 2018

Using immunocytochemistry andin situhybridization, we have examined the expression of brain-derived neurotrophic factor (BDNF) and of neurotrophin receptors in dorsal root ganglion cells. In the adult rat, BDNF mRNA and protein were found mainly in the subpopulation of cells that express the nerve growth factor (NGF) receptor trkA and the neuropeptide calcitonin gene-related peptide (CGRP). NGF increased BDNF within the trkA/CGRP cells to the extent that almost 90% of trkA cells contained BDNF mRNA after intrathecal NGF treatment, and 80–90% of BDNF-expressing cells contained trkA. Non-trkA cells that expressed BDNF included some trkC cells and some small cells that labeled with the lectinGriffonia simplicifoliaIB4, a marker for cells that do not express trks. However, very few trkB cells expressed either BDNF mRNA or protein, and NGF did not increase BDNF expression in non-trkA cells. BDNF protein was anterogradely transported both peripherally and centrally. The central transport resulted in BDNF immunoreactivity in CGRP containing terminal arbors in the dorsal horn of the spinal cord, and this immunoreactivity was increased by NGF treatment. Electron microscopic analysis revealed that the BDNF immunoreactivity was present in finely myelinated and unmyelinated axons and in axon terminals, where it was most concentrated over dense-cored vesicles.

Our data do not support an autocrine or paracrine role for BDNF within normal dorsal root ganglia, but indicate that BDNF may act as an anterograde trophic messenger. NGF levels in the periphery could influence dorsal horn neurons via release of BDNF from primary afferents.
Persistent Structural Modifications in Nucleus Accumbens and Prefrontal Cortex Neurons Produced by Previous Experience with Amphetamine
Authors: Robinson Terry E. , Kolb Bryan
Published: April 2018

Experience-dependent changes in behavior are thought to involve structural modifications in the nervous system, especially alterations in patterns of synaptic connectivity. Repeated experience with drugs of abuse can result in very long-lasting changes in behavior, including a persistent hypersensitivity (sensitization) to their psychomotor activating and rewarding effects. It was hypothesized, therefore, that repeated treatment with the psychomotor stimulant drug amphetamine, which produces robust sensitization, would produce structural adaptations in brain regions that mediate its psychomotor activating and rewarding effects. Consistent with this hypothesis, it was found that amphetamine treatment altered the morphology of neurons in the nucleus accumbens and prefrontal cortex. Exposure to amphetamine produced a long-lasting (>1 month) increase in the length of dendrites, in the density of dendritic spines, and in the number of branched spines on the major output cells of the nucleus accumbens, the medium spiny neurons, as indicated by analysis of Golgi-stained material. Amphetamine treatment produced similar effects on the apical (but not basilar) dendrites of layer III pyramidal neurons in the prefrontal cortex. The ability of amphetamine to alter patterns of synaptic connectivity in these structures may contribute to some of the long-term behavioral consequences of repeated amphetamine use, including amphetamine psychosis and addiction.
Neuronal Activity in Monkey Superior Colliculus Related to the Initiation of Saccadic Eye Movements
Authors: Dorris Michael C. , Paré Martin , Munoz Douglas P.
Published: April 2018

The introduction of a temporal gap between the disappearance of an initially fixated target and the appearance of an eccentric saccadic target results in a general reduction of saccadic reaction times (SRTs)—thegap effect—and often in the production ofexpresssaccades, the latencies of which approach the conduction time of the shortest neural pathways from the retina to the eye muscles. We investigated saccade initiation by recording neuronal activity in the superior colliculus in monkeys performing the gap paradigm. Fixation-related neurons reduced their discharge rate during the gap period, regardless of the SRT. This reduction in activity is consistent with the hypothesized release of ocular fixation that facilitates premotor processes and may contribute to the gap effect. In addition to saccade-related discharges, many saccade-related neurons displayed phasic target-related responses and/or low-frequency preparatory activity during the gap period. The level of this preparatory activity correlated with both SRT and express saccade occurrence when the saccade was made into the response field of the neuron. Evidence indicates that advanced motor preparation is required for express saccade generation, which may be subserved by specific increases in the preparatory activity of saccade-related neurons. Increased preparatory activity may allow the target-related responses to trigger short-latency express saccades directly. This study provides insights into the functional mechanism of saccade initiation and may be relevant to the generation of all voluntary motor responses.
Status Epilepticus-Induced Alterations in Metabotropic Glutamate Receptor Expression in Young and Adult Rats
Authors: Aronica Eleonora M. , Gorter Jan A. , Paupard Marie-Christine , Grooms Sonja Y. , Bennett Michael V. L. , Zukin R. Suzanne
Published: April 2018

In adult rats, kainic acid induces status epilepticus and delayed, selective cell loss of pyramidal neurons in the hippocampal CA3. In pup rats, kainate induces status epilepticus but not the accompanying neuronal cell death. The precise mechanisms underlying this age-dependent vulnerability to seizure-induced cell death are not understood. Metabotropic glutamate receptors (mGluRs) are developmentally and spatially regulated throughout the hippocampus and are implicated in seizure-induced damage. In the present study we usedin situhybridization to examine possible changes in mGluR expression at the level of the hippocampus after status epilepticus in postnatal day 10 (P10) pup and adult (P40) rats. Status epilepticus did not alter expression of mGluR1, mGluR3, or mGluR5 mRNAs. In pup and adult rats, status epilepticus induced a reduction in expression of mGluR2 mRNA in granule cells of the dentate gyrus. This change could lead to augmented glutamate release at mossy fiber synapses on CA3 pyramidal cells and thereby promote hyperexcitation. In pup but not adult rats, mGluR4 mRNA expression was enhanced in CA3 pyramidal neurons. Upregulation of presynaptic mGluR4 in pup CA3 neurons could lead to reduced transmitter release from CA3 axons, including recurrent collaterals, thereby reducing vulnerability of neonatal CA3 neurons to seizure-induced damage. These findings indicate that status epilepticus affects mGluR expression in a gene- and cell-specific manner, and that these changes vary with the developmental stage.
Medial Geniculate Lesions Block Amygdalar and Cingulothalamic Learning-Related Neuronal Activity
Authors: Poremba Amy , Gabriel Michael
Published: April 2018

This study assessed the role of the thalamic medial geniculate (MG) nucleus in discriminative avoidance learning, wherein rabbits acquire a locomotory response to a tone [conditioned stimulus (CS)+] to avoid a foot shock, and they learn to ignore a different tone (CS−) not predictive of foot shock. Limbic (anterior and medial dorsal) thalamic, cingulate cortical, or amygdalar lesions severely impair acquisition, and neurons in these areas develop training-induced activity (TIA): more firing to the CS+ than to the CS−. MG neurons exhibit TIA during learning and project to the amygdala. The MG neurons may supply afferents essential for amygdalar and cingulothalamic TIA and for avoidance learning. To test this hypothesis, bilateral electrolytic or excitotoxic ibotenic acid MG nuclear lesions were induced, and multiunit recording electrodes were chronically implanted into the anterior and posterior cingulate cortex, the anterior-ventral and medial-dorsal thalamic nuclei, and the basolateral nucleus of the amygdala before training. Learning was severely impaired and TIA was abolished in all areas in rabbits with lesions. Thus learning and TIA require the integrity of the MG nucleus. Only damage in the medial MG division was significantly correlated with the learning deficit. The lesions abolished the sensory response of amygdalar neurons, and they attenuated (but did not eliminate) the sensory response of cingulothalamic neurons, suggesting the existence of extra geniculate sources of auditory transmission to the cingulothalamic areas.
The Mechanism of cAMP-Mediated Enhancement at a Cerebellar Synapse
Authors: Chen Chinfei , Regehr Wade G.
Published: April 2018

Increases in cAMP have been shown previously to enhance the strength of the granule cell to Purkinje cell synapse. We have examined the mechanisms underlying this enhancement in rat cerebellar brain slices. Elevation of cAMP levels by forskolin increased synaptic currents in a dose-dependent manner. Fluorometric calcium measurements revealed that forskolin did not affect presynaptic calcium influx or resting calcium levels. The waveform of the presynaptic volley was also unaltered, indicating that changes in the presynaptic action potential did not contribute to synaptic enhancement. However, forskolin enhanced the frequency but not the size of spontaneous miniature EPSCs. There was a one-to-one correspondence between increases of spontaneous and evoked neurotransmitter release. These results suggest that forskolin increases release at this synapse via presynaptic mechanisms that do not alter calcium influx. The effect of forskolin on paired-pulse facilitation was examined to assess the relative contributions of changes in the probability of release (p) and changes in the number of functional release sites (n) to this form of enhancement. These experiments suggest that although small changes inncannot be excluded, most of the enhancement arises from increases inp.
Excitotoxicity in the Enteric Nervous System
Authors: Kirchgessner Annette L. , Liu Min-Tsai , Alcantara Frederick
Published: April 2018

Glutamate, the major excitatory neurotransmitter in the CNS, is also an excitatory neurotransmitter in the enteric nervous system (ENS). We tested the hypothesis that excessive exposure to glutamate, or related agonists, produces neurotoxicity in enteric neurons. Prolonged stimulation of enteric ganglia by glutamate caused necrosis and apoptosis in enteric neurons. Acute and delayed cell deaths were observed. Glutamate neurotoxicity was mimicked by NMDA and blocked by the NMDA antagonistd-2-amino-5-phosphonopentanoate. Excitotoxicity was more pronounced in cultured enteric ganglia than in intact preparations of bowel, presumably because of a reduction in glutamate uptake. Glutamate-immunoreactive neurons were found in cultured myenteric ganglia, and a subset of enteric neurons expressed NMDA (NR1, NR2A/B), AMPA (GluR1, GluR2/3), and kainate (GluR5/6/7) receptor subunits. Glutamate receptors were clustered on enteric neurites. Stimulation of cultured enteric neurons by kainic acid led to the swelling of somas and the growth of varicosities (“blebs”) on neurites. Blebs formed close to neurite intersections and were enriched in mitochondria, as revealed by rhodamine 123 staining. Kainic acid also produced a loss of mitochondrial membrane potential in cultured enteric neurons at sites where blebs tended to form. These observations demonstrate, for the first time, excitotoxicity in the ENS and suggest that overactivation of enteric glutamate receptors may contribute to the intestinal damage produced by anoxia, ischemia, and excitotoxins present in food.
Functional Properties of Perigeniculate Inhibition of Dorsal Lateral Geniculate Nucleus Thalamocortical NeuronsIn Vitro
Authors: Sanchez-Vives Maria V. , McCormick David A.
Published: April 2018

The properties of the inhibitory influence of neurons in the perigeniculate (PGN) nucleus on thalamocortical cells were examined with intracellular recordings in the ferret geniculate slice maintainedin vitro. Activation of PGN neurons with the local application of glutamate caused IPSPs in thalamocortical neurons that were mediated by both GABAAand GABABreceptors, as well as the activation of spindle waves.

With low intensity stimulation of the PGN, local application of bicuculline to the dorsal lateral geniculate nucleus (LGNd) strongly inhibited evoked and spindle-associated IPSPs, indicating that these are largely mediated by GABAAreceptors. The generation of GABABreceptor-mediated IPSPs in thalamocortical cells that were large enough to generate rebound low threshold Ca2+spikes required substantially increased activation of the PGN with glutamate.

The activation of synchronous bicuculline-induced slowed oscillations in thalamocortical neurons required the block of GABAAreceptors in the LGNd as well as in the PGN. These results indicate that bursts of action potentials in PGN neurons can result in the activation of both GABAAand GABABreceptors in thalamocortical neurons, with the strong activation of GABABreceptors requiring an intense, simultaneous discharge of a number of PGN neurons. Functionally, these results suggest that PGN neurons inhibit thalamocortical cells preferentially through the activation of GABAAreceptors, although the strong activation of GABABreceptors may occur under pathological conditions and contribute to the generation of abnormal, synchronous slow oscillations.
Knock-Out Mice Reveal a Critical Antiepileptic Role for Neuropeptide Y
Authors: Baraban Scott C. , Hollopeter Gunther , Erickson Jay C. , Schwartzkroin Philip A. , Palmiter Richard D.
Published: April 2018

Neuropeptide Y (NPY) inhibits excitatory synaptic transmission in the hippocampus and is implicated in control of limbic seizures. In the present study, we examined hippocampal function and the response to pharmacologically induced seizures in mutant mice lacking this peptide. In slice electrophysiology studies, no change in normal hippocampal function was observed in NPY-deficient mice compared with normal wild-type littermates. Kainic acid (KA) produced limbic seizures at a comparable latency and concentration in NPY-deficient mice compared with littermates. However, KA-induced seizures progressed uncontrollably and ultimately produced death in 93% of NPY-deficient mice, whereas death was rarely observed in wild-type littermates. Intracerebroventricular NPY infusion, before KA administration, prevented death in NPY-deficient mice. These results suggest a critical role for endogenous NPY in seizure control.
Dendroaxonal Transcytosis of Transferrin in Cultured Hippocampal and Sympathetic Neurons
Authors: Hémar Agnès , Olivo Jean-Christophe , Williamson Edward , Saffrich Rainer , Dotti Carlos G.
Published: April 2018

Previous studies using overexpressed polymeric immunoglobulin receptor in cultured neurons have suggested that these cells may use a dendroaxonal transcytotic pathway (Ikonen et al., 1993; de Hoop et al., 1995). By using a combination of semiquantitative light microscopy, video microscopy, and a biochemical assay, we show that this pathway is used by the endogenous ligand transferrin (Tf) and its receptor. Labeled Tf added to fully mature hippocampal neurons changes the intracellular distribution of its receptor from preferentially dendritic shortly after addition to dendritic and axonal at longer times. Incubation of living neurons with (caged)FITC-Tf followed by uncaging in the dendrites results in the later appearance of fluorescence in the axon of the same cell. In “chambered” sympathetic neurons in culture,125I-Tf or iron as55Fe-Tf added to the cell body/dendrite chamber is recovered in the axonal chamber, showing that internalized ligand from the cell body–dendrite area is released at the axonal end. Finally, we show that excitatory neurotransmitters increase Tf receptor transcytosis, whereas inhibitory neurotransmitters reduce it. The dendritic uptake, transcytotic transport, and axonal release of physiologically active Tf demonstrated here could be envisioned for other trophic factors and therefore have important consequences for neuronal anterograde target maturation. Moreover, the changes in transcytosis after neurotransmitter addition may be important in the cellular responses that follow electrical activation.
Mutation Causing Autosomal Dominant Nocturnal Frontal Lobe Epilepsy Alters Ca2+Permeability, Conductance, and Gating of Human α4β2 Nicotinic Acetylcholine Receptors
Authors: Kuryatov Alexander , Gerzanich Volodymyr , Nelson Mark , Olale Felix , Lindstrom Jon
Published: April 2018

A mutation (S247F) in the channel-lining domain (M2) of the α4 nicotinic acetylcholine receptor (AChR) subunit has previously been linked genetically to autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE).

To better understand the functional significance of this mutation, we characterized the properties of mutant and wild-type human α4β2 AChRs expressed inXenopusoocytes. Both had similar expression levels and EC50values for ACh and nicotine. Substantial use-dependent functional upregulation was found for mutant α4β2 AChRs, but not for wild type. Mutant AChR responses showed faster desensitization, slower recovery from desensitization, less inward rectification, and virtually no Ca2+permeability as compared with wild-type α4β2 AChRs. Addition of the α5 subunit restored Ca2+permeability to the mutant α4β2α5 AChRs. At −80 mV, wild-type α4β2 AChR single channel currents exhibited two conductances, each with two mean open times (γ1= 17 pS, τ1= 3.7 msec, and τ2= 23.4 msec; γ2= 28 pS, τ1= 1.9 msec, and τ2= 8.1 msec). In contrast, mutant AChRs exhibited only one conductance of 11 pS, with τ1= 1.9 msec and τ2= 4.1 msec.

The net effect of the mutation is to reduce AChR function. This could result in the hyperexcitability characteristic of epilepsy if the mutant AChRs were part of an inhibitory circuit, e.g., presynaptically regulating the release of GABA. In the minority of AChRs containing the α5 subunit, the overall functionality of these AChRs could be maintained despite the mutation in the α4 subunit.
Pyruvate Protects Neurons against Hydrogen Peroxide-Induced Toxicity
Authors: Desagher Solange , Glowinski Jacques , Prémont Joël
Published: April 2018

Hydrogen peroxide (H2O2) is suspected to be involved in numerous brain pathologies such as neurodegenerative diseases or in acute injury such as ischemia or trauma. In this study, we examined the ability of pyruvate to improve the survival of cultured striatal neurons exposed for 30 min to H2O2, as estimated 24 hr later by the 3-[4,5-dimethylthiazol-2-yl]−2,5-diphenyltetrazoliumbromide assay. Pyruvate strongly protected neurons against both H2O2added to the external medium and H2O2endogenously produced through the redox cycling of the experimental quinone menadione. The neuroprotective effect of pyruvate appeared to result rather from the ability of α-ketoacids to undergo nonenzymatic decarboxylation in the presence of H2O2than from an improvement of energy metabolism. Indeed, several other α-ketoacids, including α-ketobutyrate, which is not an energy substrate, reproduced the neuroprotective effect of pyruvate. In contrast, lactate, a neuronal energy substrate, did not protect neurons from H2O2. Optimal neuroprotection was achieved with relatively low concentrations of pyruvate (≤1 mm), whereas at high concentration (10 mm) pyruvate was ineffective. This paradox could result from the cytosolic acidification induced by the cotransport of pyruvate and protons into neurons. Indeed, cytosolic acidification both enhanced the H2O2-induced neurotoxicity and decreased the rate of pyruvate decarboxylation by H2O2. Together, these results indicate that pyruvate efficiently protects neurons against both exogenous and endogenous H2O2. Its low toxicity and its capacity to cross the blood–brain barrier open a new therapeutic perspective in brain pathologies in which H2O2is involved.
Estradiol Enhances Prostaglandin E2Receptor Gene Expression in Luteinizing Hormone-Releasing Hormone (LHRH) Neurons and Facilitates the LHRH Response to PGE2by Activating a Glia-to-Neuron Signaling Pathway
Authors: Rage Florence , Lee Byung Ju , Ma Ying J. , Ojeda Sergio R.
Published: April 2018

Prostaglandin E2(PGE2) mediates the stimulatory effect of norepinephrine (NE) on the secretion of luteinizing hormone-releasing hormone (LHRH), the neuropeptide controlling reproductive function. In rodents, this facilitatory effect requires previous exposure to estradiol, suggesting that the steroid affects downstream components in the cascade that leads to PGE2-induced LHRH release. Because astroglia are the predominant cell type contacting LHRH-secreting nerve terminals, we investigated the involvement of hypothalamic astrocytes in the estradiol facilitation of PGE2-induced LHRH release. A subpopulation of LHRH neurons was found to express the mRNA encoding the PGE2receptor subtype EP1-R, which is coupled to calcium mobilization. The LHRH-producing cell line GT1–1 also contains EP1-R mRNA and, to a lesser extent, the three alternatively spliced forms of EP3-R mRNA (α, β, and γ) that encode receptors linked to inhibition and stimulation of cAMP formation. Hypothalamic astrocytes treated with estradiol produced a conditioned medium that when applied to GT1–1 cells resulted in a selective upregulation of EP1-R and EP3γ-R mRNAs. The conditioned medium also enhanced the LHRH response to EP1-R and EP3-R agonists and the cAMP response to EP3-R activation. Thus, one mechanism by which estradiol facilitates the effect of neurotransmitters acting via PGE2to stimulate LHRH release is by enhancing the glial production of substances that upregulate PGE2receptors on LHRH neurons. The existence of such a mechanism underscores the emerging importance of glial–neuronal communication in the control of brain neurosecretory activity.
Delayed Reduction of Ischemic Brain Injury and Neurological Deficits in Mice Lacking the Inducible Nitric Oxide Synthase Gene
Authors: Iadecola Costantino , Zhang Fangyi , Casey Robyn , Nagayama Masao , Ross M. Elizabeth
Published: April 2018

Inducible nitric oxide synthase (iNOS), an enzyme that produces toxic amounts of nitric oxide, is expressed in a number of brain pathologies, including cerebral ischemia. We used mice with a null mutation of the iNOS gene to study the role of iNOS in ischemic brain damage. Focal cerebral ischemia was produced by occlusion of the middle cerebral artery (MCA). In wild-type mice, iNOS mRNA expression in the post-ischemic brain begun between 24 and 48 hr peaked at 96 hr and subsided 7 d after MCA occlusion. iNOS mRNA induction was associated with expression of iNOS protein and enzymatic activity. In contrast, mice lacking the iNOS gene did not express iNOS message or protein after MCA occlusion. The infarct and the motor deficits produced by MCA occlusion were smaller in iNOS knockouts than in wild-type mice (p< 0.05). Such reduction in ischemic damage and neurological deficits was observed 96 hr after ischemia but not at 24 hr, when iNOS is not yet expressed in wild-type mice. The decreased susceptibility to cerebral ischemia in iNOS knockouts could not be attributed to differences in the degree of ischemia or vascular reactivity between wild-type and knockout mice. These findings indicate that iNOS expression is one of the factors contributing to the expansion of the brain damage that occurs in the post-ischemic period. iNOS inhibition may provide a novel therapeutic strategy targeted specifically at the secondary progression of ischemic brain injury.
Glutamate Transporter GLAST Is Expressed in the Radial Glia–Astrocyte Lineage of Developing Mouse Spinal Cord
Authors: Shibata Takashi , Yamada Keiko , Watanabe Masahiko , Ikenaka Kazuhiro , Wada Keiji , Tanaka Kohichi , Inoue Yoshiro
Published: April 2018

The glutamate transporter GLAST is localized on the cell membrane of mature astrocytes and is also expressed in the ventricular zone of developing brains. To characterize and follow the GLAST-expressing cells during development, we examined the mouse spinal cord byin situhybridization and immunohistochemistry. At embryonic day (E) 11 and E13, cells expressing GLAST mRNA were present only in the ventricular zone, where GLAST immunoreactivity was associated with most of the cell bodies of neuroepithelial cells. In addition, GLAST immunoreactivity was detected in radial processes running through the mantle and marginal zones. From this characteristic cytology, GLAST-expressing cells at early stages were judged to be radial glia cells. At E15, cells expressing GLAST mRNA first appeared in the mantle zone, and GLAST-immunopositive punctate or reticular protrusions were formed along the radial processes. From E18 to postnatal day (P) 7, GLAST mRNA or its immunoreactivity gradually decreased from the ventricular zone and disappeared from radial processes, whereas cells with GLAST mRNA spread all over the mantle zone and GLAST-immunopositive punctate/reticular protrusions predominated in the neuropils. At P7, GLAST-expressing cells were immunopositive for glial fibrillary acidic protein, an intermediate filament specific to astrocytes. Therefore, the glutamate transporter GLAST is expressed from radial glia through astrocytes during spinal cord development. Furthermore, the distinct changes in the cell position and morphology suggest that both the migration and transformation of radial glia cells begin in the spinal cord between E13 and E15, when the active stage of neuronal migration is over.
Differential Effects of Abnormal Tactile Experience on Shaping Representation Patterns in Developing and Adult Motor Cortex
Authors: Huntley George W.
Published: April 2018

This study investigates the influence of early somatosensory experience on shaping movement representation patterns in motor cortex. Electrical microstimulation was used to map bilaterally the motor cortices of adult rats subjected to altered tactile experience by unilateral vibrissa trimming from birth (birth-trimmed group) or for comparable periods that began in adulthood (adult-trimmed group). Findings demonstrated that (1) vibrissa trimming from birth, but not when initiated in adulthood, led to a significantly smaller-sized primary motor cortex (M1) vibrissa representation in the hemisphere contralateral to the trimmed vibrissae, with no evidence for concomitant changes in size of the adjacent forelimb representation or the representation of the intact vibrissae in the opposite (ipsilateral) hemisphere; (2) in the contralateral hemispheres of the birth-trimmed group, an abnormal pattern of evoked vibrissa movement was evident in which bilateral or ipsilateral (intact) vibrissa movement predominated; (3) in both hemispheres of the birth-trimmed group, current thresholds for eliciting movement of the trimmed vibrissa were significantly lower than normal; and (4) in the adult-trimmed group, but not in the birth-trimmed group, there was a decrease bilaterally in the relative frequency of dual forelimb–vibrissa sites that form the common border between these representations. These results show that sensory experience early in life exerts a significant influence in sculpting motor representation patterns in M1. The mature motor cortex is more resistant to the type and magnitude of influence that tactile experience has on developing M1, which may indicate that such an influence is constrained by a developmentally regulated critical period.
Subcortical Input to the Smooth and Saccadic Eye Movement Subregions of the Frontal Eye Field inCebusMonkey
Authors: Tian Jun-ru , Lynch James C.
Published: April 2018

We have recently identified two functional subregions in the frontal eye field (FEF) of theCebusmonkey, a smooth eye movement subregion (FEFsem) and a saccadic subregion (FEFsac). The thalamic input to these two subregions was studied and quantified to gain more information about the influence of the cerebellum and basal ganglia on the oculomotor control mechanisms of the cerebral cortex. A recent study using transneuronal transport of virus demonstrated that there are neurons in the basal ganglia and cerebellum that project to the FEFsac with only a single intervening synapse (Lynch et al., 1994). In the present study, we concentrated on the thalamic input to the FEFsem to define possible basal ganglia–thalamus–cortex and cerebellum–thalamus–cortex channels of information flow to the FEFsem. We localized the functional subregions using low threshold microstimulation, and retrogradely transported fluorescent tracers were then placed into the FEFsem and FEFsac.

The neurons that project to the FEFsem are distributed in (1) the rostral portion of the ventral lateral nucleus, pars caudalis, (2) the caudal portion of the ventral lateral nucleus, pars caudalis, (3) the mediodorsal nucleus, (4) the ventral anterior nucleus, pars parvocellularis, and (5) the ventral anterior nucleus, pars magnocellularis. In contrast, the large majority of neurons that project to the FEFsac are located in the paralaminar region of the mediodorsal nucleus. The FEFsac and FEFsem thus each receive neural input frombothbasal ganglia-receiving and cerebellar-receiving cell groups in the thalamus, but each receives input from a unique combination of thalamic nuclei.
Selective Synaptic Distribution of Kainate Receptor Subunits in the Two Plexiform Layers of the Rat Retina
Authors: Brandstätter Johann Helmut , Koulen Peter , Wässle Heinz
Published: April 2018

The synaptic localization of the kainate receptor subunits GluR6/7 and KA2 and of the ionotropic glutamate receptor subunits δ1/2 was studied in the rat retina using receptor-specific antisera. GluR6/7 and KA2 were present in both synaptic layers of the retina: the inner plexiform layer (IPL) and the outer plexiform layer (OPL). The localization of δ1/2 was restricted to the IPL. Detailed ultrastructural examination showed that in the OPL GluR6/7 was localized in horizontal cell processes postsynaptic to both rod spherules and cone pedicles. It was always only one of the two invaginating horizontal cell processes at the photoreceptor synapses labeled for GluR6/7. KA2 in the OPL was found only postsynaptic to cone pedicles and never postsynaptic to rod spherules. The KA2-labeled processes made flat contacts with the cone pedicles, suggesting they are the dendrites of OFF bipolar cells. In the IPL the different receptor subunits were localized postsynaptically to ribbon synapses of both rod and cone bipolar cells. As a rule, only one of the two postsynaptic elements at the bipolar cell dyad was stained for each of the receptor subunits examined. The selective and heterogeneous distribution of these receptors at the ribbon synapses of the OPL and IPL suggests a high degree of differential processing of the glutamatergic signals.
Endogenous Monocarboxylates Sustain Hippocampal Synaptic Function and Morphological Integrity during Energy Deprivation
Authors: Izumi Yukitoshi , Benz Ann M. , Katsuki Hiroshi , Zorumski Charles F.
Published: April 2018

The ability to fuel neurons via glycogenolysis is believed to be an important function of glia. Indeed, the slow, rather than immediate, depression of synaptic transmission in hippocampal slices during exogenous glucose deprivation suggests that intrinsic energy reservoirs help to sustain neurotransmission. It is believed that glia fuel neighboring neurons via diffusible monocarboxylates such as pyruvate and lactate, although a role for glucose has been proposed also. Using α-cyano-4-hydroxycinnamate (4-CIN) to inhibit monocarboxylate transport and cytochalasin B (CCB) to inhibit glucose transport, we examined the role of glucose and monocarboxylates in supporting the functional and morphological integrity of hippocampal neurons during glucose deprivation. Although 200 μm4-CIN failed to depress EPSPs supported by 10 mmglucose, pretreatment with 4-CIN accelerated the depression of EPSPs during glucose deprivation. 4-CIN also accelerated the decline in glucose-supported EPSPs after administration of 50 μmCCB, whereas CCB failed to alter the slow decay of pyruvate-supported EPSPs during pyruvate deprivation. 4-CIN did not alter the morphology of pyramidal neurons in the presence of 10 mmglucose but produced significant damage during glucose deprivation or CCB administration. These results suggest that endogenous monocarboxylates rather than glucose maintain neuronal integrity during energy deprivation. Furthermore, EPSPs supported by 2–3.3 mmglucose were sensitive to 4-CIN, suggesting that endogenous monocarboxylates are involved in maintaining neuronal function even under conditions of mild glucose deprivation.
Activity-Dependent Dendritic Targeting of BDNF and TrkB mRNAs in Hippocampal Neurons
Authors: Tongiorgi Enrico , Righi Massimo , Cattaneo Antonino
Published: April 2018

The mechanisms underlying the subcellular localization of neurotrophins and their receptors are poorly understood. We show that in cultured hippocampal neurons, the mRNAs for BDNF and TrkB have a somatodendritic localization, and we quantify the extent of their dendritic mRNA localization. In the dendrites the labeling covers on average the proximal 30% of the total dendritic length. On high potassium depolarization, the labeling of BDNF and TrkB mRNA extends on average to 68% of the dendritic length. This increase does not depend on new RNA synthesis, is inhibited by the Na+channel blocker tetrodotoxin, and involves the activation of glutamate receptors. Extracellular Ca2+, partly flowing through L-type Ca2+channels, is absolutely required for this process to occur. At the protein level, a brief stimulation of hippocampal neurons with 10 mmKCl leads to a marked increase of BDNF and TrkB immunofluorescence density in the distal portion of dendrites, which also occurs, even if at lower levels, when transport is inhibited by nocodazole. The protein synthesis inhibitor cycloheximide abolishes this increase. The activity-dependent modulation of mRNA targeting and protein accumulation in the dendrites may provide a mechanism for achieving a selective local regulation of the activity of neurotrophins and their receptors, close to their sites of action.
Myosin VIIA Is Required for Aminoglycoside Accumulation in Cochlear Hair Cells
Authors: Richardson G. P. , Forge A. , Kros C. J. , Fleming J. , Brown S. D. M. , Steel K. P.
Published: April 2018

Myosin VIIA is expressed by sensory hair cells and has a primary structure predicting a role in membrane trafficking and turnover, processes that may underlie the susceptibility of hair cells to aminoglycoside antibiotics. [3H]Gentamicin accumulation and the effects of aminoglycosides were therefore examined in cochlear cultures of mice with different missense mutations in the myosin VIIA gene,Myo7a, to see whether myosin VIIA plays a role in aminoglycoside ototoxicity. Hair cells from homozygous mutantMyo7ash1mice, with a mutation in a nonconserved region of the myosin VIIA head, respond rapidly to aminoglycoside treatment and accumulate high levels of gentamicin. Hair cells from homozygous mutantMyo7a6Jmice, with a mutation at a highly conserved residue close to the ATP binding site of the myosin VIIA head, do not accumulate [3H]gentamicin and are protected from aminoglycoside ototoxicity. Hair cells from heterozygotes of both alleles accumulate [3H]gentamicin and respond to aminoglycosides.

Although aminoglycoside uptake is thought to be via apical surface-associated endocytosis, coated pit numbers on the apical membrane of heterozygous and homozygousMyo7a6Jhair cells are similar. Pulse–chase experiments with cationic ferritin confirm that the apical endocytotic pathway is functional in homozygousMyo7a6Jhair cells. Transduction currents can be recorded from both heterozygous and homozygousMyo7a6Jhair cells, suggesting it is unlikely that the drug enters via diffusion through the mechanotransducer channel. The results show that myosin VIIA is required for aminoglycoside accumulation in hair cells. Myosin VIIA may transport a putative aminoglycoside receptor to the hair cell surface, indirectly translocate it to sites of membrane retrieval, or retain it in the endocytotic pathway.
Impaired Parallel Fiber→Purkinje Cell Synapse Stabilization during Cerebellar Development of Mutant Mice Lacking the Glutamate Receptor δ2 Subunit
Authors: Kurihara Hideo , Hashimoto Kouichi , Kano Masanobu , Takayama Chitoshi , Sakimura Kenji , Mishina Masayoshi , Inoue Yoshiro , Watanabe Masahiko
Published: April 2018

The glutamate receptor δ2 subunit (GluRδ2) is specifically expressed in cerebellar Purkinje cells (PCs) from early developmental stages and is selectively localized at dendritic spines forming synapses with parallel fibers (PFs). Targeted disruption of the GluRδ2 gene leads to a significant reduction of PF→PC synapses. To address its role in the synaptogenesis, the morphology and electrophysiology of PF→PC synapses were comparatively examined in developing GluRδ2 mutant and wild-type cerebella. PCs in GluRδ2 mutant mice were normally produced, migrated, and formed spines, as did those in wild-type mice. At the end of the first postnatal week, 74–78% of PC spines in both mice formed immature synapses, which were characterized by small synaptic contact, few synaptic vesicles, and incomplete surrounding by astroglial processes, eliciting little electrophysiological response. During the second and third postnatal weeks when spines and terminals are actively generated, the percentage of PC spines forming synapses attained 98–99% in wild type but remained as low as 55–60% in mutants, and the rest were unattached to any nerve terminals. As a result, the number of PF synapses per single-mutant PCs was reduced to nearly a half-level of wild-type PCs. Parallelly, PF stimulation less effectively elicited EPSCs in mutant PCs than in wild-type PCs during and after the second postnatal week. These results suggest that the GluRδ2 is involved in the stabilization and strengthening of synaptic connectivity between PFs and PCs, leading to the association of all PC spines with PF terminals to form functionally mature synapses.