bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metabotropic Glutamate Receptor Activation in Cerebellar Purkinje Cells as Substrate for Adaptive Timing of the Classically Conditioned Eye-Blink Response
Authors: Fiala John C. , Grossberg Stephen , Bullock Daniel 
Published: April 2018

To understand how the cerebellum adaptively times the classically conditioned nictitating membrane response (NMR), a model of the metabotropic glutamate receptor (mGluR) second messenger system in cerebellar Purkinje cells is constructed. In the model, slow responses, generated postsynaptically by mGluR-mediated phosphoinositide hydrolysis and calcium release from intracellular stores, bridge the interstimulus interval (ISI) between the onset of parallel fiber activity associated with the conditioned stimulus (CS) and climbing fiber activity associated with unconditioned stimulus (US) onset. Temporal correlation of metabotropic responses and climbing fiber signals produces persistent phosphorylation of both AMPA receptors and Ca2+-dependent K+channels. This is responsible for long-term depression (LTD) of AMPA receptors. The phosphorylation of Ca2+-dependent K+channels leads to a reduction in baseline membrane potential and a reduction of Purkinje cell population firing during the CS–US interval. The Purkinje cell firing decrease disinhibits cerebellar nuclear cells, which then produce an excitatory response corresponding to the learned movement. Purkinje cell learning times the response, whereas nuclear cell learning can calibrate it. The model reproduces key features of the conditioned rabbit NMR: Purkinje cell population response is timed properly; delay conditioning occurs for ISIs of up to 4 sec, whereas trace conditioning occurs only at shorter ISIs; mixed training at two different ISIs produces a double-peaked response; and ISIs of 200–400 msec produce maximal responding. Biochemical similarities between timed cerebellar learning and photoreceptor transduction, and circuit similarities between the timed cerebellar circuit and a timed dentate-CA3 hippocampal circuit, are noted.
Visual Stimulation Regulates the Expression of Transcription Factors and Modulates the Composition of AP-1 in Visual Cortexa
Authors: Kaminska Bozena , Kaczmarek Leszek , Chaudhuri Avi 
Published: April 2018

It is believed that long-term changes in neuronal function are orchestrated by transcription factors, such as AP-1 and ZIF 268, which are in turn regulated by synaptic stimulation. To further our understanding of the functional effects of such expression, we have examined the DNA-binding activities of both AP-1 and ZIF 268 by way of electrophoretic mobility shift assays (EMSA) on nuclear extracts from visual cortices of rats treated with selective light exposure. Visual stimulation after dark rearing increased the DNA-binding activities of both AP-1 and ZIF 268 to their highest levels within 2 hr. ZIF 268 thereafter dropped to levels similar to that observed in naive animals, whereas AP-1 DNA-binding activity continued to remain elevated even after 24 hr of stimulation. The components of the AP-1 complex, when assessed by EMSA-supershift analysis, showed considerable variability under different conditions of exposure. FosB and JunD were the major constituents of AP-1 in both naive and dark-reared animals. Brief visual stimulation (2 hr) added c-Fos, c-Jun, and JunB to this complex, whereas prolonged stimulation (6−24 hr) reduced c-Fos and c-Jun levels significantly, leaving only FosB, JunB, and JunD as the major components of AP-1. These results suggest that transcriptional control by AP-1 may be generated by selective combinatorial interactions of different members of the Fos and Jun families and that are guided by activity-dependent processes.
Systemic Administration of a Nerve Growth Factor Conjugate Reverses Age-Related Cognitive Dysfunction and Prevents Cholinergic Neuron Atrophy
Authors: Bäckman Cristina , Rose Gregory M. , Hoffer Barry J. , Henry Michael A. , Bartus Raymond T. , Friden Phillip , Granholm Ann-Charlotte 
Published: April 2018

Intraventricular administration of nerve growth factor (NGF) in rats has been shown to reduce age-related atrophy of central cholinergic neurons and the accompanying memory impairment. Intraventricular administration of NGF is necessary because NGF will not cross the blood–brain barrier (BBB). Here we have used a novel carrier system, consisting of NGF covalently linked to an anti-transferrin receptor antibody (OX-26), to transport biologically active NGF across the BBB. In our experiment, aged (24 months old) Fischer 344 rats received intravenous injections of the OX-26-NGF conjugate or a control solution (a mixture of unconjugated OX-26 and NGF) twice weekly for 6 weeks. The OX-26-NGF injections resulted in a significant improvement in spatial learning in previously impaired rats but disrupted the learning ability of previously unimpaired rats. Neuroanatomical analyses showed that OX-26-NGF conjugate treatment resulted in a significant increase in cholinergic cell size in the medial septal region of rats initially impaired in spatial learning. These results indicate the potential use of the transferrin receptor antibody delivery system for treatment of CNS disorders with neurotrophic proteins.
Trace Eyeblink Conditioning Increases CA1 Excitability in a Transient and Learning-Specific Manner
Authors: Moyer Jr. James R. , Thompson Lucien T. , Disterhoft John F. 
Published: April 2018

Time-dependent, learning-related changes in hippocampal excitability were evaluated by recording from rabbit CA1 pyramidal neurons in slices prepared at various times after acquisition of trace eyeblink conditioning. Increased excitability (reduced postburst afterhyperpolarizations and reduced spike-frequency adaptation) was seen as early as 1 hr after acquisition to behavioral criterion, was maximal in neurons studied 24 hr later, and returned to baseline within 7 d, whereas behavioral performance remained asymptotic for months. Neurons were held at −67 mV to equate voltage-dependent effects. No learning-related effects were observed on input resistance, action-potential amplitude or duration, or resting membrane potential. The excitability changes were learning-specific, because they were not seen in neurons from very slow learning (exhibited <30% conditioned responses after 15 training sessions) or from pseudoconditioned control rabbits. Neurons from rabbits that displayed asymptotic behavioral performance after long-term retention testing (an additional training session 14 d after learning) were also indistinguishable from control neurons. Thus, the increased excitability of CA1 neurons was not performance- or memory-dependent. Rather, the time course of increased excitability may represent a critical window during which learning-specific alterations in postsynaptic excitability of hippocampal neurons are important for consolidation of the learned association elsewhere in the brain.
Mitochondrial Dysfunction Is a Primary Event in Glutamate Neurotoxicity
Authors: Schinder Alejandro F. , Olson Eric C. , Spitzer Nicholas C. , Montal Mauricio 
Published: April 2018

Excitotoxic neuronal death, associated with neurodegenerative disorders and hypoxic insults, results from excessive exposure to excitatory neurotransmitters. Glutamate neurotoxicity is triggered primarily by massive Ca2+influx arising from overstimulation of the NMDA subtype of glutamate receptors. The underlying mechanisms, however, remain elusive. We have tested the hypothesis that mitochondria are primary targets in excitotoxicity by confocal imaging of intracellular Ca2+([Ca2+]i) and mitochondrial membrane potential (ΔΨ) on cultured rat hippocampal neurons. Sustained activation of NMDA receptors (20 min) elicits reversible elevation of [Ca2+]i. Longer activation (50 min) renders elevation of [Ca2+]iirreversible (Ca2+overload). Susceptibility to NMDA-induced Ca2+overload is increased when the 20 min stimuli are applied to neurons pretreated with electron transport chain inhibitors, thereby implicating mitochondria in [Ca2+]ihomeostasis during excitotoxic challenges. Remarkably, ΔΨ exhibits prominent and persistent depolarization in response to NMDA, which closely parallels the incidence of neuronal death. Blockade of the mitochondrial permeability transition pore by cyclosporin A allows complete recovery of ΔΨ and prevents cell death. These results suggest that early mitochondrial damage plays a key role in induction of glutamate neurotoxicity.
Trophic Effects of Androgen: Receptor Expression and the Survival of Laryngeal Motor Neurons after Axotomy
Authors: Pérez Julio , Kelley Darcy B. 
Published: April 2018

To determine whether changes in androgen receptor (AR) expression are associated with trophic actions of androgens, we have examined the laryngeal motor nucleus (N. IX–X) ofXenopus laevis1 and 5 months after section of the laryngeal nerve.In situhybridization was used to recognize cells expressing mRNA for theXenopusAR and bromodeoxyuridine to assess cell proliferation. In addition, the total number of cells was determined in untreated and dihydrotestosterone (DHT)-treated animals after 5 months of axotomy. After 1 month of axotomy, the number of AR mRNA-expressing cells in N. IX–X is 1.8-fold higher than in the intact side. Androgen upregulates expression of AR mRNA in N. IX–X on both the intact and the axotomized sides, suggesting that the increase is independent of contact with muscle. Neither the axotomy- nor the androgen-induced increase in number of cells expressing AR mRNA is attributable to cell proliferation. Five months after axotomy, both the total number of cells and the number of AR mRNA-expressing cells are severely decreased in the axotomized N. IX–X. DHT treatment mitigates the cell loss in N. IX–X induced by prolonged axotomy; the effect includes maintenance of AR mRNA-expressing cells. Gonadally intact males have more cells in the axotomized N. IX–X than castrated animals, suggesting that androgen acts at physiological levels as a trophic hormone. Axotomy-induced upregulation of AR expression may facilitate the trophic actions of androgens.
Aggregation of Sodium Channels Induced by a Postnatally Upregulated Isoform of Agrin
Authors: Sharp Andrew A. , Caldwell John H. 
Published: April 2018

Agrin is involved in signaling the formation of high concentrations of acetylcholine receptors (AChRs) at the neuromuscular junction (NMJ). There are multiple isoforms of agrin attributable to alternative splicing, and these isoforms are differentially expressed during development and between tissues. The ability to cluster AChRs varies among the agrin isoforms. Sodium channels (NaChs) are also concentrated at the NMJ. We have tested various agrin isoforms for their ability to induce formation of clusters of NaChs. We grew cocultures of dissociated adult rat muscle fibers with chinese hamster ovary (CHO) cells that had been transfected with different isoforms of agrin. Using immunocytochemical techniques, we determined that after 1 d in culture, CHO cells synthesizing the neuronally expressed isoform with an eight amino acid insert (Agrin8) were able to form NaCh clusters at sites of contact between the CHO cell and muscle cell. Clusters of NaChs could be formed anywhere along a muscle fiber, but more clusters were detected close to the endplate where the endogenous level of NaChs was higher. None of the other neuronal-specific agrin isoforms was able to cluster NaChs. Because Agrin8 is the only agrin isoform that is upregulated at birth when NaChs begin to cluster at the NMJ, we conclude that Agrin8 expression by motor neurons is a signal for NaCh clustering at the NMJ during normal development.
Conditional Ablation of Cerebellar Astrocytes in Postnatal Transgenic Mice
Authors: Delaney Catherine L. , Brenner Michael , Messing Albee 
Published: April 2018

Astrocytes have been proposed to have multiple roles in the development and maintenance of the vertebrate CNS. To facilitate documentation of these roles, we designed a transgene to enable their ablation at selectable times. The transgene consists of the coding region for the herpes simplex virus-thymidine kinase (HSV-TK) under the control of the human glial fibrillary acidic protein gene promoter. The HSV-TK is innocuous but converts the antiherpetic agent ganciclovir (GCV) to a toxic product that interferes with DNA replication in proliferating cells. In a developmental study, transgenic mice were treated with GCV during the first postnatal week, with evaluation at P19. Treated mice displayed severe ataxia. Histological examination revealed disrupted astrocyte development, particularly in the cerebellum, with marked secondary effects on other cell types. Cerebellar defects included a loss in the numbers of astrocytes and an overall reduction in cerebellar size and disruption of the normally well defined cellular layers. Radial glia were disordered, Purkinje cells were ectopically distributed and displayed abnormal dendritic trees, and granule cells were markedly depleted. These effects were more severe in animals treated on postnatal day 1 versus treatment at day 5. A major factor causing granule cell death was excitotoxicity attributable to activation of NMDA receptors. These results suggest a critical role for astrocytes in cerebellar development.
Molecular Determinants of β1Subunit-Induced Gating Modulation in Voltage-Dependent Na+Channels
Authors: Makita Naomasa , Bennett Paul B. , George Jr. Alfred L. 
Published: April 2018

Recombinant brain, skeletal muscle, and heart voltage-gated Na+channel α subunits differ in their functional responses to an accessory β1subunit when coexpressed inXenopusoocytes. We exploited the distinct β1subunit responses observed for the human heart (hH1) and human skeletal muscle (hSkM1) isoforms to identify determinants of this response. Chimeric α subunits were constructed by exchanging the S5–S6 interhelical loops of each domain between hH1 and hSkM1 and then examined for effects on inactivation induced by coexpressed β1subunit in oocytes. Substitution of single S5–S6 loops in either domain 1 (D1/S5–S6) or domain 4 (D4/S5–S6) of hSkM1 by the corresponding segments of hH1 produced channels that exhibited an attenuated response to coexpressed β1subunit. Substitutions of both D1/S5–S6 and D4/S5–S6 in hSkM1 by the corresponding loops from hH1 completely abolished the effects of the β1subunit on inactivation. The reciprocal chimera in which both D1/S5–S6 and D4/S5–S6 from hSkM1 were transplanted into hH1 exhibited significant β1responsiveness (accelerated inactivation). The region within D4/S5–S6 that conferred β1responsiveness was determined to reside primarily within an extracellular loop between the putative pore-forming segment SS2 and D4/S6. Gating modulation was also demonstrated using a chimeric β subunit consisting of the extracellular domains of β1and the transmembrane and C-terminal domains of the rat brain β2subunit. These results suggest that the D1/S5–S6 and D4/S5–S6 loops in the α subunit and the extracellular domain of the β1subunit are important determinants of the β1subunit-induced gating modulation in Na+channels.
Regulation of Purkinje Cell Alignment by Reelin as Revealed with CR-50 Antibody
Authors: Miyata Takaki , Nakajima Kazunori , Mikoshiba Katsuhiko , Ogawa Masaharu 
Published: April 2018

Cerebellar Purkinje cells are generated in the ventricular zone, migrate outward, and finally form a monolayer in the cortex. Inreelermice, however, most Purkinje cells cluster abnormally in subcortical areas. Reelin, the candidatereelergene product recognized by the CR-50 monoclonal antibody, is concentrated in a cortical zone along which Purkinje cells are aligned linearly, implying that it may regulate their alignment. We used anin vitrosystem and a transplantation approach to analyze the function of Reelin.Explant culture for 7 d of cerebella isolated from wild-type andreelermice at embryonic day 13 (E13) reproduced in a phenotype-dependent manner the two distinct arrangement patterns (linear vs clustered) of Purkinje cells. Extensive CR-50 binding to wild-type explants converted the linear pattern into areeler-like, clustered pattern. On the other hand, whenreelerexplants lacking Reelin were crowned with an artificial layer of Reelin+granule cells, some Reelin molecules were distributed into a superficial zone of thereelerexplants, and Purkinje cells formed a linear pattern along the Reelin-rich overlay. This “rescue” effect was also inhibited by CR-50. Hence, Reelin is involved in the Purkinje cell alignment, and the lack of this activity may explain the malformation inreelercerebella.We further injected Reelin+granule cells into the fourth ventricle of E12–13 mice. Extensive incorporation of the injected Reelin+cells into the ventricular zone, but not of Reelin−cells, forced Purkinje cells of the host cerebella to form an aberrant layer, suggesting that premigratory Purkinje cells may already be responsive to Reelin or Reelin-related signals.
Systemic Morphine-Induced Fos Protein in the Rat Striatum and Nucleus Accumbens Is Regulated by μ Opioid Receptors in the Substantia Nigra and Ventral Tegmental Area
Authors: Bontempi Bruno , Sharp Frank R. 
Published: April 2018

To characterize how systemic morphine induces Fos protein in dorsomedial striatum and nucleus accumbens (NAc), we examined the role of receptors in striatum, substantia nigra (SN), and ventral tegmental area (VTA). Morphine injected into medial SN or into VTA of awake rats induced Fos in neurons in ipsilateral dorsomedial striatum and NAc. Morphine injected into lateral SN induced Fos in dorsolateral striatum and globus pallidus. The morphine infusions produced contralateral turning that was most prominent after lateral SN injections. Intranigral injections of [d-Ala2,N-Me-Phe4, Gly-ol5]-enkephalin (DAMGO), a μ opioid receptor agonist, and of bicuculline, a GABAAreceptor antagonist, induced Fos in ipsilateral striatum. Fos induction in dorsomedial striatum produced by systemic administration of morphine was blocked by (1) SN and VTA injections of the μ1opioid antagonist naloxonazine and (2) striatal injections of either MK 801, an NMDA glutamate receptor antagonist, or SCH 23390, a D1dopamine receptor antagonist.Fos induction in dorsomedial striatum and NAc after systemic administration of morphine seems to be mediated by dopamine neurons in medial SN and VTA that project to medial striatum and NAc, respectively. Systemic morphine is proposed to act on μ opioid receptors located on GABAergic interneurons in medial SN and VTA. Inhibition of these GABA interneurons disinhibits medial SN and VTA dopamine neurons, producing dopamine release in medial striatum and NAc. This activates D1dopamine receptors and coupled with the coactivation of NMDA receptors possibly from cortical glutamate input induces Fos in striatal and NAc neurons. The modulation of target gene expression by Fos could influence addictive behavioral responses to opiates.
Blockade and Recovery of Spontaneous Rhythmic Activity after Application of Neurotransmitter Antagonists to Spinal Networks of the Chick Embryo
Authors: Chub Nikolai , O’Donovan Michael J. 
Published: April 2018

We studied the regulation of spontaneous activity in the embryonic (day 10–11) chick spinal cord. After bath application ofeitheran excitatory amino acid (AP-5 or CNQX) and a nicotinic cholinergic (DHβE or mecamylamine) antagonist,orglycine and GABA receptor (bicuculline, 2-hydroxysaclofen, and strychnine) antagonists, spontaneous activity was blocked for a period (30–90 min) but then reappeared in the presence of the drugs. The efficacy of the antagonists was assessed by their continued ability to block spinal reflex pathways during the reappearance of spontaneous activity. Spontaneous activity ceased over the 4–5 hour monitoring period when both sets of antagonists were applied together.After application of glycine and GABA receptor antagonists, the frequency of occurrence of spontaneous episodes slowed and became highly variable. By contrast, during glutamatergic and nicotinic cholinergic blockade, the frequency of occurrence of spontaneous episodes initially slowed and then recovered to stabilize near the predrug level of activity. Whole-cell recordings made from ventral spinal neurons revealed that this recovery was accompanied by an increase in the amplitude of spontaneously occurring synaptic events.We also measured changes in the apparent equilibrium potential of the rhythmic, synaptic drive of ventral spinal neurons using voltage or discontinuous current clamp. After excitatory blockade, the apparent equilibrium potential of the rhythmic synaptic drive shifted ∼10 mV more negative to approximately −30 mV. In the presence of bicuculline, the apparent equilibrium potential of the synaptic drive shifted toward the glutamate equilibrium potential.Considered with other evidence, these findings suggest that spontaneous rhythmic output is a general property of developing spinal networks, and that GABA and glycinergic networks alter their function to compensate for the blockade of excitatory transmission.
Sodium Current in Rat and Cat Thalamocortical Neurons: Role of a Non-Inactivating Component in Tonic and Burst Firing
Authors: Parri H. Rheinallt , Crunelli Vincenzo 
Published: April 2018

The properties of the Na+current present in thalamocortical neurons of the dorsal lateral geniculate nucleus were investigated in dissociated neonate rat and cat neurons and in neurons from slices of neonate and adult rats using patch and sharp electrode recordings.The steady-state activation and inactivation of the transient Na+current (INa) was well fitted with a Boltzmann curve (voltage of half-maximal activation and inactivation,V1/2, −29.84 mV and −70.04 mV, respectively). Steady-state activation and inactivation curves showed a small region of overlap, indicating the occurrence of aINawindow current.INadecay could be fitted with a single exponential function, consistent with the presence of only one channel type.Voltage ramp and step protocols showed the presence of a noninactivating component of the Na+current (INaP) that activated at potentials more negative (V1/2= −56.93 mV) than those ofINa. The maximal amplitude ofINaPwas ∼2.5% ofINa, thus significantly greater than the calculated contribution (0.2%) of theINawindow component. Comparison of results from dissociated neurons and neurons in slices suggested a dendritic as well as a somatic localization ofINaP. Inclusion of papain in the patch electrode removed the fast inactivation ofINaand induced a current with voltage-dependence (V1/2= −56.92) and activation parameters similar to those ofINaP.Current-clamp recordings with sharp electrodes showed thatINaPcontributed to depolarizations evoked from potentials of approximately −60 mV and unexpectedly to the amplitude and latency of low-threshold Ca2+potentials, suggesting that this noninactivating component of the Na+channel population plays an important role in the integrative properties of thalamocortical neurons during both tonic and burst-firing patterns.