bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence That Gz-Proteins Couple to Hypothalamic 5-HT1AReceptorsIn Vivo
Authors: Serres F. , Li Q. , Garcia F. , Raap D. K. , Battaglia G. , Muma N. A. , Van de Kar L. D.
Published: April 2018

Usingin situhybridization and immunoblot analysis, the present studies identified GzmRNA and Gz-protein in the hypothalamic paraventricular nucleus. The role of Gz-proteins in hypothalamic 5-HT1Areceptor signaling was examinedin vivo. Activation of 5-HT1Areceptors increases the secretion of oxytocin and ACTH, but not prolactin. Intracerebroventricular infusion (3–4 d) of Gzantisense oligodeoxynucleotides, with different sequences and different phosphorothioate modification patterns, reduced the levels of Gz-protein in the hypothalamic paraventricular nucleus, whereas missense oligodeoxynucleotides had no effect. Neither antisense nor missense oligodeoxynucleotide treatment altered basal plasma levels of ACTH, oxytocin, or prolactin, when compared with untreated controls. An antisense-induced decrease in hypothalamic Gz-protein levels was paralleled by a significant decrease in the oxytocin and ACTH responses to the 5-HT1Aagonist 8-hydroxy-dipropylamino-tetralin (8-OH-DPAT). In contrast, the prolactin response to 8-OH-DPAT (which cannot be blocked by 5-HT1Aantagonists) was not inhibited by Gzantisense oligodeoxynucleotides. Gz-proteins are the only members of the Gi/Go-protein family that are not inactivated by pertussis toxin. In a control experiment, pertussis toxin treatment (1μg/5 μl, i.c.v.; 48 hr before the 8-OH-DPAT challenge) did not inhibit the ACTH response, potentiated the oxytocin response, and eliminated the prolactin response to 8-OH-DPAT. Thus, pertussis toxin-sensitive Gi/Go-proteins do not mediate the 5-HT1Areceptor-mediated increase in ACTH and oxytocin secretion. Combined, these studies provide the firstin vivoevidence for a key role of Gz-proteins in coupling hypothalamic 5-HT1Areceptors to effector mechanisms.
Reluctant Gating of Single N-Type Calcium Channels during Neurotransmitter-Induced Inhibition in Bullfrog Sympathetic Neurons
Authors: Lee Hye Kyung , Elmslie Keith S.
Published: April 2018

Whole-cell recordings have been used to extensively characterize the voltage-dependent inhibition of N-type calcium current induced by various neurotransmitters. Results from these studies have yielded several predictions on the effect of inhibition on N-channel gating, namely delayed channel opening and inhibition-induced reluctant openings. Previous single N-channel studies observed delayed channel opening but failed to find reluctant openings. However, strong depolarizations may be necessary to see reluctant openings, but this was not tested. We have examined N-channel gating at voltages depolarized to those used previously and found a neurotransmitter-induced open state that has properties predicted for the reluctant open state. The openings had lower open probability (Po) and brief open times compared to the dominant gating state observed in control (highPo). These reluctant events were reduced after strong depolarizing pulses used to reverse inhibition. The threshold voltage for activation of reluctant events was ∼30 mV depolarized to that of the normal gating state (highPo). However, an action potential will provide sufficient depolarization to open reluctant N-channels.
Plasma Membrane Calcium Pump Isoform 1 Gene Expression Is Repressed by Corticosterone and Stress in Rat Hippocampus
Authors: Bhargava Aditi , Meijer Onno C. , Dallman Mary F. , Pearce David
Published: April 2018

Glucocorticoids (GCs) are critical to learning and memory, in large part because of their actions in the hippocampus. Chronic high levels of GCs have profound effects on hippocampal structure and function and can even result in irreversible neurodegeneration. Hippocampal GC actions are mediated by intracellular receptors that modulate the transcription of specific target genes. In a screen for genes repressed by GCs in rat hippocampus, we identified plasma membrane calcium pump isoform 1 (PMCA1), a plasma membrane calcium ATPase. In Northern blots, PMCA1 was repressed ∼33% after a high, but not a low dose of the GC, corticosterone (B), suggesting glucocorticoid (but not mineralocorticoid) receptor-mediated repression. Furthermore,in situhybridization demonstrated that B significantly downregulated PMCA1 mRNA in all brain regions examined. Repression of PMCA1 was also observed in cultured hippocampal neurons, but only when the cells were in the differentiated state. Stress also repressed PMCA1 expression in hippocampus of adrenal-intact animals, and a clear inverse correlation between B level and PMCA1 mRNA could be discerned. However, other non-B-dependent factors appeared to be involved in the response of PMCA1 to stress because, unlike exogenous B, cold stress did not repress PMCA1 in brain regions other than hippocampus. Moreover, in the presence of constant B (B-replaced, adrenalectomized animals), cold stress led to increased hippocampal PMCA1 expression. These observations suggest that repression of PMCA1 represents one molecular mechanism by which corticosteroids regulate Ca2+homeostasis and hence influence neuronal activity. Moreover, other stress-related neurohumoral factors appear to counter the repressive effects of B. Defects in the balance between GC-mediated and non-GC-mediated effects on PMCA1 expression may have adverse effects on neuronal function and ultimately result in irreversible neuronal damage.
Zinc-Induced Cortical Neuronal Death: Contribution of Energy Failure Attributable to Loss of NAD+and Inhibition of Glycolysis
Authors: Sheline Christian T. , Behrens M. Margarita , Choi Dennis W.
Published: April 2018

Excessive zinc influx may contribute to neuronal death after certain insults, including transient global ischemia. In light of evidence that levels of intracellular free Zn2+associated with neurotoxicity may be sufficient to inhibit glyceraldehyde-3-phosphate dehydrogenase (GAPDH), experiments were performed looking for reduced glycolysis and energy failure in cultured mouse cortical neurons subjected to lethal Zn2+exposure. As predicted, cultures exposed for 3–22 hr to 40 μmZn2+developed an early increase in levels of dihydroxy-acetone phosphate (DHAP) and fructose 1,6-bisphosphate (FBP) and a progressive loss of ATP levels, followed by neuronal cell death; furthermore, addition of the downstream glycolytic substrate pyruvate to the bathing medium attenuated the fall in ATP and neuronal death.

However, an alternative to direct Zn2+inhibition of GAPDH was raised by the observation that Zn2+exposure also induced an early decrease in nicotinamide-adenine dinucleotide (NAD+) levels, an event itself capable of inhibiting GAPDH. Favoring this indirect mechanism of GAPDH inhibition, the neuroprotective effects of pyruvate addition were associated with normalization of cellular levels of NAD+, DHAP, and FBP. Zn2+-induced neuronal death was also attenuated by addition of the energy substrate oxaloacetate, the activator of pyruvate dehydrogenase, dichloroacetate, or the inhibitors of NAD+catabolism, niacinamide or benzamide. Acetyl carnitine, α-keto butyrate, lactate, and β-hydroxy-butyrate did not attenuate Zn2+-induced neurotoxicity, perhaps because they could not regenerate NAD+or be used for energy production in the presence of glucose.
Ethanol-Associated Behaviors of Mice Lacking Norepinephrine
Authors: Weinshenker David , Rust Nicole C. , Miller Nicole S. , Palmiter Richard D.
Published: April 2018

Although norepinephrine (NE) has been implicated in animal models of ethanol consumption for many years, the exact nature of its influence is not clear. Lesioning and pharmacological studies examining the role of NE in ethanol consumption have yielded conflicting results. We took a genetic approach to determine the effect of NE depletion on ethanol-mediated behaviors by using dopamine β-hydroxylase knockout (Dbh−/−) mice that specifically lack the ability to synthesize NE.Dbh−/− males have reduced ethanol preference in a two-bottle choice paradigm and show a delay in extinguishing an ethanol-conditioned taste aversion, suggesting that they drink less ethanol in part because they find its effects more aversive. Both male and femaleDbh−/− mice are hypersensitive to the sedative and hypothermic effects of systemic ethanol administration, and the sedation phenotype can be rescued pharmacologically by acute replacement of central NE. Neither the decreased body temperature nor changes in ethanol metabolism can explain the differences in consumption and sedation. These results demonstrate a significant role for NE in modulating ethanol-related behaviors and physiological responses.
Glial Cell Line-Derived Neurotrophic Factor Is Essential for Postnatal Survival of Midbrain Dopamine Neurons
Authors: Granholm Ann-Charlotte , Reyland Mary , Albeck David , Sanders Linda , Gerhardt Greg , Hoernig George , Shen Liya , Westphal Heiner , Hoffer Barry
Published: April 2018

Glial cell line-derived neurotrophic factor (GDNF) is one of the most potent trophic factors that have been identified for midbrain dopamine (DA) neurons. Null mutations for trophic factor genes have been used frequently for studies of the role of these important proteins in brain development. One problem with these studies has been that often only prenatal development can be studied because many of the knockout strains, such as those with GDNF null mutations, will die shortly after birth. In this study, we looked at the continued fate of specific neuronal phenotypes from trophic factor knockout mice beyond the time that these animals die. By transplanting fetal neural tissues from GDNF −/−, GDNF +/−, and wild-type (WT) mice into the brain of adult wild-type mice, we demonstrate that the continued postnatal development of ventral midbrain dopamine neurons is severely disturbed as a result of the GDNF null mutation. Ventral midbrain grafts from −/− fetuses have markedly reduced DA neuron numbers and fiber outgrowth. Moreover, DA neurons in such transplants can be “rescued” by immersion in GDNF before grafting. These findings suggest that postnatal survival and/or phenotypic expression of ventral mesencephalic DA neurons is dependent on GDNF. In addition, we present here a strategy for studies of maturation and even aging of tissues from trophic factor and other knockout animals that do not survive past birth.
Intrinsic Bias and Lineage Restriction in the Phenotype Determination of Dopamine and Neuropeptide Y Amacrine Cells
Authors: Moody Sally A. , Chow Ida , Huang Sen
Published: April 2018

Blastomere lineages are differentially biased to produce different neurotransmitter subtypes of amacrine cells (Huang and Moody, 1995,1997). To elucidate when this bias is acquired, we examined amacrine lineages at different early developmental times. Our experiments demonstrate that the bias to express dopamine and neuropeptide Y amacrine fates involves several steps before the formation of the definitive optic cup. At cleavage stages, a retinal progenitor that contributes large numbers of cells is already biased to produce its normal repertoire of dopamine amacrine cells, as revealed by transplantation to a new location, whereas the amacrine fate of a progenitor that contributes fewer cells is modified by its new position. At neural plate stages, not all retinal progenitors are multipotent. Nearly one-half populate only the inner nuclear layer and are enriched in amacrine cells. During early optic vesicle stages, an appropriate mitotic tree is required for dopamine and neuropeptide Y, but not serotonin, amacrine cell clusters to form. Thus, the acquisition of amacrine fate bias involves intrinsic maternal factors at cleavage, fate restriction in the neural plate, and specified mitotic patterns in the optic vesicle. At each of these steps only a subset of the embryonic retinal progenitors contributing to amacrine subtypes is biased; the remaining progenitors maintain multipotency. Thus, from the earliest embryonic stages, progenitors of the retina are a dynamic mosaic. This is the first experimental demonstration of amacrine fate decisions that occur during early embryonic periods in advance of the events described in the later, committed retina.
A Spatiotemporal Wave of Turnover and Functional Maturation of Olfactory Receptor Neurons in the Spiny LobsterPanulirus argus
Authors: Steullet Pascal , Cate Holly S. , Derby Charles D.
Published: April 2018

Olfactory receptor neurons (ORNs) of crustaceans are housed in aesthetasc sensilla that are located on the lateral flagellum of the antennule. We used young adult spiny lobsters to examine turnover of aesthetascs and functional maturation of their ORNs after molting. The proliferation zone for new aesthetascs is located in the proximal part of the aesthetasc-bearing region and progressively moves along a distoproximal axis. Older aesthetascs are lost in the distal part of the aesthetasc-bearing region. As a result, an aesthetasc may be shed three to six molts after it differentiates. Taurine-like immunoreactivity is elevated in ORNs of aesthetascs that have yet to emerge on the cuticular surface and thereafter decreases gradually and asynchronously. ORNs from the distalmost-developing aesthetascs lose taurine-like immunoreactivity immediately before sensillar emergence, whereas ORNs from the most proximal and lateral new aesthetascs retain taurine-like immunoreactivity throughout the intermolt stage after sensillar emergence. Furthermore, taurine-like immunoreactivity is inversely correlated with odor responsiveness. These results suggest that taurine-like immunoreactivity reveals immature ORNs and that their functional maturation is not synchronized with molting and may not be completed until many weeks after sensillar emergence. Our data suggest successive spatiotemporal waves of birth, differentiation and functional maturation, and death of ORNs.
Ectopic Expression of the Neuropeptide Pigment-Dispersing Factor Alters Behavioral Rhythms inDrosophila melanogaster
Authors: Helfrich-Förster Charlotte , Täuber Marcus , Park Jae H. , Mühlig-Versen Max , Schneuwly Stephan , Hofbauer Alois
Published: April 2018

To study the function of the neuropeptide pigment-dispersing factor (PDF) in the circadian system ofDrosophila, we misexpressed thepdfgene from the grasshopperRomaleain the CNS ofDrosophilaand investigated the effect of this on behavioral rhythmicity.pdfwas either ectopically expressed in different numbers of neurons in the brain or the thoracical nervous system or overexpressed in the pacemaker neurons alone. We found severe alterations in the activity and eclosion rhythm of several but not all lines with ectopicpdfexpression. Only ectopicpdfexpression in neurons that projected into the dorsal central brain severely influenced activity rhythms. Therefore, we conclude that PDF acts as a neuromodulator in the dorsal central brain that is involved in the rhythmic control of behavior. Overexpression ofpdfin the pacemaker neurons alone or in the other neurons that express the clock genesperiod(per) andtimeless(tim) did not disturb the activity rhythm. Such flies still showed a rhythm in PDF accumulation in the central brain terminals. This rhythm was absent in the terminals of neurons that expressed PDF ectopically. Probably, PDF is rhythmically processed, transported, or secreted in neurons expressingperandtim, and additional PDF expression in these cells does not influence this rhythmic process. In neurons lackingperandtim, PDF appears to be continuously processed, leading to a constant PDF secretion at their nerve terminals. This may lead to conflicting signals in the rhythmic output pathway and result in a severely altered rhythmic behavior.
Novel Hippocampal Interneuronal Subtypes Identified Using Transgenic Mice That Express Green Fluorescent Protein in GABAergic Interneurons
Authors: Oliva Anthony A. , Jiang Minghui , Lam Trang , Smith Karen L. , Swann John W.
Published: April 2018

The chief inhibitory neurons of the mammalian brain, GABAergic neurons, are comprised of a myriad of diverse neuronal subtypes. To facilitate the study of these neurons, transgenic mice were generated that express enhanced green fluorescent protein (EGFP) in subpopulations of GABAergic neurons. In one of the resulting transgenic lines, called GIN (GFP-expressingInhibitoryNeurons), EGFP was found to be expressed in a subpopulation of somatostatin-containing GABAergic interneurons in the hippocampus and neocortex. In both live and fixed brain preparations from these mice, detailed microanatomical features of EGFP-expressing interneurons were readily observed. In stratum oriens of the hippocampus, EGFP-expressing interneurons were comprised almost exclusively of oriens/alveus interneurons with lacunosum-moleculare axon arborization (O-LM cells). In the neocortex, the somata of EGFP-expressing interneurons were largely restricted to layers II-IV and upper layer V.

In hippocampal area CA1, two previously uncharacterized subtypes of interneurons were identified using the GIN mice: stratum pyramidale interneurons with lacunosum-moleculare axon arborization (P-LM cells) and stratum radiatum interneurons with lacunosum-moleculare axon arborization (R-LM cells). These newly identified interneuronal subtypes appeared to be closely related to O-LM cell, as they selectively innervate stratum lacunosum-moleculare. Whole-cell patch-clamp recordings revealed that these cells were fast-spiking and showed virtually no spike frequency accommodation. The microanatomical features of these cells suggest that they function primarily as “input-biasing” neurons, in that synaptic volleys in stratum radiatum would lead to their activation, which in turn would result in selective suppression of excitatory input from the entorhinal cortex onto CA1 pyramidal cells.
The Genetic VariantVoila1Causes Gustatory Defects duringDrosophilaDevelopment
Authors: Balakireva Maria , Gendre Nanaë , Stocker Reinhard F. , Ferveur Jean-François
Published: April 2018

Voila1, an enhancer-trap strain inDrosophila melanogaster, expresses GAL4 in most gustatory neurons, both before and after metamorphosis.Voila1expression starts at embryonic stage 10. In the periphery, it labels larval gustatory sensilla in the antennomaxillary complex as well as in the pharynx. GAL4 is also expressed in the CNS in a manner that prefigures expression in adult flies. MostVoila1/1homozygotes die between second larval instar and early adulthood. Moreover, escapingVoila1/1larvae do not show gustatory responses to NaCl and sucrose. The simultaneous rescue of normal larval gustation together with adult viability after removal of the transposable PGAL4 element suggests that both these phenotypes are caused by the same inserted element.
Extraretinal Control of Saccadic Suppression
Authors: Diamond Mark R. , Ross John , Morrone M. C.
Published: April 2018

We measured the time course of saccadic suppression and tested whether suppression results entirely from retinal image motion or has an extraretinal source. We measured contrast thresholds for low-frequency gratings modulated either in luminance, at 17 cd/m2and 0.17 cd/m2, or color at 17 cd/m2. Gratings were flashed on a uniform background before, during, or after voluntary 12° saccades and, additionally in the case of luminance modulated gratings, saccades simulated by mirror motion.

A 10-fold decrease in contrast sensitivity was found for luminance-modulated gratings with saccades, but little suppression was found with simulated saccades. Adding high-contrast noise to the display increased the magnitude and the duration of the suppression during simulated saccades but had little effect on suppression produced by real saccades.

Suppression anticipates saccades by 50 msec, is maximal at the moment of saccadic onset, and outlasts saccades by ∼50 msec. At lower luminance, suppression is reduced, and its course is shallower than at higher luminance.

Simulated saccades produce shallower suppression over a longer time course at both luminances. No suppression was found for chromatically modulated gratings.

Differences between real and simulated saccades in the magnitude and time course of sensitivity loss suggest that saccadic suppression has an extraretinal component.

We model the effects of saccades by adding a signal to the visual input, so as to saturate the nonlinear stage of visual processing and make detection of a test stimulus more difficult.
The Regulatory Connection between the Activity of Granule Cell NMDA Receptors and Dendritic Differentiation of Cerebellar Purkinje Cells
Authors: Hirai Hirokazu , Launey Thomas
Published: April 2018

It is known that cerebellar granule cells are powerful inducers for the differentiation of Purkinje cells. However, the detailed mechanism of this regulation has not yet been clarified. Here, using cerebellar neuronal culture, we show that the activation of NMDA receptors expressed by granule cells triggers the signaling pathway for the dendritic differentiation of Purkinje cells. This signal has been shown to promote the granule cell survival through BDNF-mediated TrkB activation, leading to Purkinje cell differentiation by increasing the granule–Purkinje cell interaction. Among the possible signal molecules provided to the dendrites of Purkinje cells from granule cells, nitric oxide was found to have no effect on the dendritic outgrowth and branching, but electrical activity and the subsequent intracellular Ca2+increase were thought to play an important role in the branching and thickening of the dendrites, because blockade of both non-NMDA and metabotropic glutamate receptors caused a significant decrease in the number of branch points and the diameter of Purkinje dendrites without apparently affecting the dendrite extension and spine formation. Collectively, these results suggest that Purkinje cell differentiation is regulated by two successive steps. The first step is initiated by the NMDA receptor-mediated signal in granule cells, which acts as a trophic factor for granule cells. The second step involves the activation of granule–Purkinje synapses, providing neurotrophic substances and electrical activity essential for Purkinje cell differentiation.
Molecular and Functional Heterogeneity of Hyperpolarization-Activated Pacemaker Channels in the Mouse CNS
Authors: Santoro Bina , Chen Shan , Lüthi Anita , Pavlidis Paul , Shumyatsky Gleb P. , Tibbs Gareth R. , Siegelbaum Steven A.
Published: April 2018

The hyperpolarization-activated cation current (termedIh,Iq, orIf) was recently shown to be encoded by a new family of genes, named HCN forhyperpolarization-activatedcyclicnucleotide-sensitivecationnonselective. When expressed in heterologous cells, each HCN isoform generates channels with distinct activation kinetics, mirroring the range of biophysical properties of nativeIhcurrents recorded in different classes of neurons. To determine whether the functional diversity ofIhcurrents is attributable to different patterns of HCN gene expression, we determined the mRNA distribution across different regions of the mouse CNS of the three mouse HCN genes that are prominently expressed there (mHCN1, 2 and 4). We observe distinct patterns of distribution for each of the three genes. Whereas mHCN2 shows a widespread expression throughout the CNS, the expression of mHCN1 and mHCN4 is more limited, and generally complementary. mHCN1 is primarily expressed within neurons of the neocortex, hippocampus, and cerebellar cortex, but also in selected nuclei of the brainstem. mHCN4 is most highly expressed within neurons of the medial habenula, thalamus, and olfactory bulb, but also in distinct neuronal populations of the basal ganglia. Based on a comparison of mRNA expression with an electrophysiological characterization of nativeIhcurrents in hippocampal and thalamic neurons, our data support the idea that the functional heterogeneity ofIhchannels is attributable, in part, to differential isoform expression. Moreover, in some neurons, specific functional roles can be proposed forIhchannels with defined subunit composition.
VMAT-Mediated Changes in Quantal Size and Vesicular Volume
Authors: Colliver T. L. , Pyott S. J. , Achalabun M. , Ewing Andrew G.
Published: April 2018

It has been well established that the volume of secretory vesicles can be modulated. However, we present the first data demonstrating that the amount of transmitter in a vesicle can regulate its volume. Amperometry and transmission electron microscopy have been used to determine thatl-3,4-dihydroxyphenylalanine and reserpine increase and decrease, respectively, the volume of single pheochromocytoma cell vesicles as well as their catecholamine content. Because changes in vesicular catecholamine content are tracked by changes in vesicle volume, our results indicate that when quantal size is altered via the vesicular monoamine transporter the concentration of catecholamines within the vesicles remains relatively constant. This previously unidentified cellular response provides new insight into how catecholamines can be packaged in and released from secretory vesicles.
Neuroprotection by Encephalomyelitis: Rescue of Mechanically Injured Neurons and Neurotrophin Production by CNS-Infiltrating T and Natural Killer Cells
Authors: Hammarberg H. , Lidman O. , Lundberg C. , Eltayeb S. Y. , Gielen A. W. , Muhallab S. , Svenningsson A. , Lindå H. , van der Meide P. H. , Cullheim S. , Olsson T. , Piehl F.
Published: April 2018

In experimental autoimmune encephalomyelitis (EAE), CD4+self-reactive T cells target myelin components of the CNS. However, the consequences of an autoaggressive T cell response against myelin for neurons are currently unknown. We herein demonstrate that EAE induced by active immunization with an encephalitogenic myelin basic protein peptide dramatically reduces the loss of spinal motoneurons after ventral root avulsion in rats. Both brain-derived neurotophic factor (BDNF)- and neurotrophin-3 (NT-3)-like immunoreactivities were detected in mainly T and natural killer (NK) cells in the spinal cord. In addition, very high levels of BDNF, NT-3, and glial cell line-derived neurotrophic factor mRNAs were present in T and NK cell populations infiltrating the CNS. Interestingly, bystander recruited NK and T cells displayed similar or higher neurotrophic factor levels compared with the EAE disease-driving encephalitogenic T cell population. High levels of tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) mRNAs were also detected, and both these cytokines can be harmful to several types of CNS cells, including neurons. However, treatment of embryonic motoneuron cultures with TNF-α or IFN-γ only had a deleterious effect in cultures deprived of neurotrophic factors. These results suggest that the potentially neurodamaging consequences of severe CNS inflammation are curbed by the production of several potent neurotrophic factors in leukocytes.
Modulation of Interleukin-1β and Tumor Necrosis Factor α Signaling by P2 Purinergic Receptors in Human Fetal Astrocytes
Authors: Liu Judy S. H. , John Gareth R. , Sikora Andrew , Lee Sunhee C. , Brosnan Celia F.
Published: April 2018

In human astrocytes, interleukin-1β (IL-1β) is a potent inducer of genes associated with inflammation. In this study, we tested the hypothesis that in primary cultures of human fetal astrocytes signaling by the P2 purinergic nucleotide receptor pathway contributes to, or modulates, cytokine-mediated signal transduction. Calcium imaging studies indicated that most cells in culture responded to ATP, whereas only a subpopulation responded to UTP. Pretreatment of astrocytes with P2 receptor antagonists, including suramin and periodate oxidized ATP (oATP), resulted in a significant downregulation of IL-1β-stimulated expression of nitric oxide, tumor necrosis factor (TNFα), and IL-6 at both the protein and mRNA levels, without affecting cell viability. In cells transiently transfected with reporter constructs, IL-1β demonstrated more potent activation of the transcription factors nuclear factor -κB (NF-κB) and activator protein-1 (AP-1) than TNFα. However, pretreatment with oATP downregulated activation of NF-κB and AP-1 by IL-1β or TNFα. Electromobility shift assays using oligonucleotides containing specific NF-κB binding sequences confirmed that pretreatment with oATP or apyrase attenuated cytokine-mediated induction of this transcription factor. From these data, we conclude that P2 receptor-mediated signaling intersects with that of IL-1β and TNFα to regulate responses to cytokines in the CNS. Because inflammation, trauma, and stress all lead to the release of high levels of extracellular nucleotides, such as ATP and UTP, signaling via P2 receptors may provide a mechanism whereby cells can sense and respond to events occurring in the extracellular environment and can fine tune the transcription of genes involved in the inflammatory response.
BaxInactivation in Lurcher Mutants Rescues Cerebellar Granule Cells But Not Purkinje Cells or Inferior Olivary Neurons
Authors: Selimi Fekrije , Vogel Michael W. , Mariani Jean
Published: April 2018

Lurcher is a gain-of-function mutation in the δ2 glutamate receptor gene (Grid2) that turns the receptor into a leaky ion channel. The expression of the Lurcher gene in heterozygous (Grid2Lc/+) mutants induces the death of almost all Purkinje cells starting from the second postnatal week. Ninety percent of the granule cells and 60–75% of the inferior olivary neurons die because of the loss of their target neurons, the Purkinje cells. The apoptotic nature of the neurodegeneration has been demonstrated previously by the presence of activated caspase-3 and DNA fragmentation.Bax, a pro-apoptotic gene of the Bcl-2 family, has been shown to be involved in developmental neuronal death. To study the role ofBaxinGrid2Lc/+neurodegeneration, double mutants withGrid2Lc/+ mice andBaxknock-out mice (Bax−/−) were generated.Baxdeletion had no effect on the death of Purkinje cells and inferior olivary neurons, although a temporary rescue of some Purkinje cells could be detected in P15Grid2Lc/+;Bax−/− animals. From postnatal day 15 (P15) to P60, the number of granule cells inGrid2Lc/+;Bax−/−mice did not significantly change and was significantly increased compared with the number found inGrid2Lc/+;Bax+/+ mice. Granule cell number in P60Grid2Lc/+;Bax−/− mice corresponded to 70% of the number found in wild-type mice. Our results show thatBaxinactivation inGrid2Lc/+mice does not rescue intrinsic Purkinje cell death or the target-related cell death of olivary neurons, butBaxinactivation does inhibit persistently target-related cell death in cerebellar granule cells.
The “Waiting Period” of Sensory and Motor Axons in Early Chick Hindlimb: Its Role in Axon Pathfinding and Neuronal Maturation
Authors: Wang Guoying , Scott Sheryl A.
Published: April 2018

During embryonic development motor axons in the chick hindlimb grow out slightly before sensory axons and wait in the plexus region at the base of the limb for ∼24 hr before invading the limb itself (Tosney and Landmesser, 1985a). We have investigated the role of this waiting period by asking, Is the arrest of growth cones in the plexus region a general property of both sensory and motor axons? Why do axons wait? Does eliminating the waiting period affect the further development of motor and sensory neurons?

Here we show that sensory axons, like motor axons, pause in the plexus region and that neither sensory nor motor axons require cues from the other population to wait in or exit from the plexus region. By transplanting older or younger donor limbs to host embryos, we show that host axons innervate donor limbs on a schedule consistent with the age of the grafted limbs. Thus, axons wait in the plexus region for maturational changes to occur in the limb rather than in the neurons themselves. Both sensory and motor axons innervate their appropriate peripheral targets when the waiting period is eliminated by grafting older donor limbs. Therefore, axons do not require a prolonged period in the plexus region to sort out and project appropriately. Eliminating the waiting period does, however, accelerate the onset of naturally occurring cell death, but it does not enhance the development of central projections or the biochemical maturation of sensory neurons.
TrkB Receptor Ligands Promote Activity-Dependent Inhibitory Synaptogenesis
Authors: Seil Fredrick J. , Drake-Baumann Rosemarie
Published: April 2018

Organotypic cerebellar cultures derived from newborn mice were simultaneously exposed to activity-blocking agents and neurotrophins for 2 weeks. Activity-blocked explants treated with the TrkB receptor ligands BDNF and neurotrophin-4 (NT-4) developed a full complement of Purkinje cell inhibitory axosomatic synapses, as defined ultrastructurally, and displayed control spontaneous cortical discharge rates after recovery from activity blockade. Otherwise untreated activity-blocked cultures and activity-blocked cultures exposed to the TrkC receptor ligand NT-3 had reduced inhibitory synapse development and persistent cortical hyperactivity after recovery. The added TrkB receptor ligands did not induce axonal sprouting to account for increased inhibitory synaptogenesis. Addition of neurotrophins to untreated cerebellar cultures did not increase the complement of Purkinje cell axosomatic synapses. Exposure of cerebellar cultures to a combination of antibodies to BDNF and NT-4 resulted in reduced inhibitory synapse formation, similar to the effects of activity blockade, indicating the necessity for endogenous neurotrophins for development of the full complement of inhibitory synapses in the presence of neuronal activity. Application of antibodies to BDNF and NT-4 to cerebellar explants exposed to picrotoxin to increase neuronal activity prevented the hyperinnervation of Purkinje cell somata by inhibitory terminals characteristic of cultures exposed to picrotoxin alone. These results are consistent with the concept that TrkB receptor ligands promote inhibitory synaptogenesis. The ability of neurotrophins to substitute for neuronal activity in encouraging development of inhibitory synapses may have therapeutic implications.
Interaction between Metabotropic and Ionotropic Glutamate Receptors Regulates Neuronal Network Activity
Authors: Krieger Patrik , Hellgren-Kotaleski Jeanette , Kettunen Petronella , El Manira Abdel Jabbar
Published: April 2018

Experimental and computational techniques have been used to investigate the group I metabotropic glutamate receptor (mGluR)-mediated increase in the frequency of spinal cord network activity underlying locomotion in the lamprey. Group I mGluR activation potentiated the amplitude of NMDA-induced currents in identified motoneurons and crossed caudally projecting network interneurons. Group I mGluRs also potentiated NMDA-induced calcium responses. This effect was blocked by a group I mGluR-specific antagonist, but not by blockers of protein kinase A, C, or G. The effect of group I mGluRs activation was also tested on NMDA-induced oscillations known to occur during fictive locomotion. Activation of these receptors increased the duration of the plateau phase and decreased the duration of the hyperpolarizing phase. These effects were blocked by a group I mGluR antagonist. To determine its role in the modulation of NMDA-induced oscillations and the locomotor burst frequency, the potentiation of NMDA receptors by mGluRs was simulated using computational techniques. Simulating the interaction between these receptors reproduced the modulation of the plateau and hyperpolarized phases of NMDA-induced oscillations, and the increase in the frequency of the locomotor rhythm.

Our results thus show a postsynaptic interaction between group I mGluRs and NMDA receptors in lamprey spinal cord neurons, which can account for the regulation of the locomotor network output by mGluRs.
Increased Excitability of Aged Rabbit CA1 Neurons after Trace Eyeblink Conditioning
Authors: Moyer James R. , Power John M. , Thompson Lucien T. , Disterhoft John F.
Published: April 2018

Cellular properties of CA1 neurons were studied in hippocampal slices 24 hr after acquisition of trace eyeblink conditioning in young adult and aging rabbits. Aging rabbits required significantly more trials than young rabbits to reach a behavioral criterion of 60% conditioned responses in an 80 trial session. Intracellular recordings revealed that CA1 neurons from aging control rabbits had significantly larger, longer lasting postburst afterhyperpolarizations (AHPs) and greater spike frequency adaptation (accommodation) relative to those from young adult control rabbits. After learning, both young and aging CA1 neurons exhibited increased postsynaptic excitability compared with their respective age-matched control rabbits (naive and rabbits that failed to learn). Thus, after learning, CA1 neurons from both age groups had reduced postburst AHPs and reduced accommodation. No learning-related differences were seen in resting membrane potential, membrane time constant, neuron input resistance, or action potential characteristics. Furthermore, comparisons between CA1 neurons from trace-conditioned aging and trace-conditioned young adult rabbits revealed no statistically significant differences in postburst AHPs or accommodation, indicating that similar levels of postsynaptic excitability were attained during successful acquisition of trace eyeblink conditioning, regardless of rabbit age. These data represent the firstin vitrodemonstration of learning-related excitability changes in aging rabbit CA1 neurons and provide additional evidence for involvement of changes in postsynaptic excitability of CA1 neurons in both aging and learning.
Gastrin-Releasing Peptide Phase-Shifts Suprachiasmatic Nuclei Neuronal RhythmsIn Vitro
Authors: McArthur Angela J. , Coogan Andrew N. , Ajpru Supaporn , Sugden David , Biello Stephany M. , Piggins Hugh D.
Published: April 2018

The main mammalian circadian pacemaker is located in the suprachiasmatic nuclei (SCN) of the hypothalamus. Gastrin-releasing peptide (GRP) and its receptor (BB2) are synthesized by rodent SCN neurons, but the role of GRP in circadian rhythm processes is unknown. In this study, we examined the phase-resetting actions of GRP on the electrical activity rhythms of hamster and rat SCN neuronsin vitro. In both rat and hamster SCN slices, GRP treatment during the day did not alter the time of peak SCN firing. In contrast, GRP application early in the subjective night phase-delayed, whereas similar treatment later in the subjective night phase-advanced the firing rate rhythm in rat and hamster SCN slices. These phase shifts were completely blocked by the selective BB2receptor antagonist, [d-Phe6, Des-Met14]-bombesin 6–14 ethylamide. We also investigated the temporal changes in the expression of genes for the BB1and BB2receptors in the rat SCN using a quantitative competitive RT-PCR protocol. The expression of the genes for both receptors was easily detected, but their expression did not vary over the diurnal cycle. These data show that GRP phase-dependently phase resets the rodent SCN circadian pacemakerin vitroapparently via the BB2receptor. Because this pattern of phase shifting resembles that of light on rodent behavioral rhythms, these results support the contention that GRP participates in the photic entrainment of the rodent SCN circadian pacemaker.
Granulocyte-Macrophage Colony-Stimulating Factor Modulates Rapid Eye Movement (REM) Sleep and Non-REM Sleep in Rats
Authors: Kimura Mayumi , Kodama Tohru , Aguila M. Cecilia , Zhang Shi-Qing , Inoué Shojiro
Published: April 2018

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a hematopoietic cytokine that may affect various functions of the CNS because the molecule and its receptors are expressed in the brain. The present study examines the effects of GM-CSF on sleep using rats and the secretion of three neurotransmitters/hormones that are involved in sleep regulation. When infused intracerebroventricularly at doses as low as 10 pmol for 10 hr during the dark period, GM-CSF promoted predominantly rapid eye movement (REM) sleep and moderate amounts of non-REM sleep without eliciting fever. An injection of GM-CSF (3.0 pmol) into the arcuate nucleus increased the release of nitric oxide (NO) from the hypothalamus but did not alter plasma levels of growth hormone. The release of somatostatin (SRIF) from the medial basal hypothalamus was stimulated by 1 × 10−11M GM-CSF. These findings indicated that centrally administered GM-CSF stimulates SRIF release through activation of the NO system in the hypothalamus. Because SRIF promotes REM sleep, it may also mediate the effects of GM-CSF on REM sleep. The present study indicates a novel central effect of GM-CSF that modulates sleep, supporting the notion that hematopoietic cytokines also play roles in the CNS.
Visual Responses of Neurons in the Middle Temporal Area of New World Monkeys after Lesions of Striate Cortex
Authors: Rosa Marcello G. P. , Tweedale Rowan , Elston Guy N.
Published: April 2018

In primates, lesions of striate cortex (V1) result in scotomas in which only rudimentary visual abilities remain. These aspects of vision that survive V1 lesions have been attributed to direct thalamic pathways to extrastriate areas, including the middle temporal area (MT). However, studies in New World monkeys and humans have questioned this interpretation, suggesting that remnants of V1 are responsible for both the activation of MT and residual vision. We studied the visual responses of neurons in area MT in New World marmoset monkeys in the weeks after lesions of V1. The extent of the scotoma in each case was estimated by mapping the receptive fields of cells located near the lesion border and by histological reconstruction. Two response types were observed among the cells located in the part of MT that corresponds, in visuotopic coordinates, to the lesioned part of V1. Many neurons (62%) had receptive fields that were displaced relative to their expected location, so that they represented the visual field immediately surrounding the scotoma. This may be a consequence of a process analogous to the reorganization of the V1 map after retinal lesions. However, another 20% of the cells had receptive fields centered inside the scotoma. Most of these neurons were strongly direction-selective, similar to normal MT cells. These results show that MT cells differ in their responses to lesioning of V1 and that only a subpopulation of MT neurons can be reasonably linked to residual vision and blindsight.
Mutants of a Temperature-Sensitive Two-P Domain Potassium Channel
Authors: Kunkel Maya T. , Johnstone Duncan B. , Thomas James H. , Salkoff Lawrence
Published: April 2018

Within theCaenorhabditis elegansgenome there exist at least 42 genes encoding TWK (two-P domain K+) channels, potassium channel subunits that contain two pore regions and four transmembrane domains. We now report the first functional characterization of a TWK channel fromC. elegans. Although potassium channels have been reported to be activated by a variety of factors, TWK-18 currents increase dramatically with increases in temperature. Two mutant alleles of thetwk-18gene confer uncoordinated movement and paralysis inC. elegans. Expression of wild-type and mutant TWK-18 channels inXenopusoocytes showed that mutant channels express much larger potassium currents than wild-type channels. Promoter–green fluorescent protein fusion experiments indicate that TWK-18 is expressed in body wall muscle. Our genetic and physiological data suggest that the movement defects observed in mutanttwk-18animals may be explained by an increased activity of the mutant TWK-18 channels.
Two NoveldoubletimeMutants Alter Circadian Properties and Eliminate the Delay between RNA and Protein inDrosophila
Authors: Suri Vipin , Hall Jeffery C. , Rosbash Michael
Published: April 2018

Phosphorylation is an important feature of pacemaker organization inDrosophila. Genetic and biochemical evidence suggests involvement of the casein kinase I homologdoubletime(dbt) in theDrosophilacircadian pacemaker. We have characterized two noveldbtmutants. Both cause a lengthening of behavioral period and profoundly alterperiod(per) andtimeless(tim) transcript and protein profiles. The PER profile shows a major difference from the wild-type program only during the morning hours, consistent with a prominent role for DBT during the PER monomer degradation phase. The transcript profiles are delayed, but there is little effect on the protein accumulation profiles, resulting in the elimination of the characteristic lag between the mRNA and protein profiles. These results and others indicate that light and post-transcriptional regulation play major roles in defining the temporal properties of the protein curves and suggest that this lag is unnecessary for the feedback regulation ofperandtimprotein onperandtimtranscription.
NF-κB Signaling Promotes Both Cell Survival and Neurite Process Formation in Nerve Growth Factor-Stimulated PC12 Cells
Authors: Foehr Erik D. , Lin Xin , O'Mahony Alison , Geleziunas Romas , Bradshaw Ralph A. , Greene Warner C.
Published: April 2018

Nerve growth factor binds to the TrkA and p75NTR(p75) and generates signals leading to neuronal cell survival, differentiation, and programmed cell death. Here we describe a series of experiments involving selective activation of either TrkA or p75 in which distinct cell-signaling intermediates promote different cellular consequences. We analyzed pheochromocytoma 12 (PC12) cells stably expressing chimeras consisting of the extracellular domain of PDGF receptor (PDGFR) fused to the transmembrane and cytoplasmic segments of p75 or TrkA. Because PC12 cells lack endogenous PDGFR, addition of PDGF to these cell lines permits selective activation of the p75 or TrkA responses without stimulating endogenous receptors. Although both p75 and TrkA activated nuclear factor-κB (NF-κB), we show that distinct proximal-signaling intermediates are used by each receptor. A dominant-negative mutant of TRAF6 blocked p75- but not TrkA-mediated induction of NF-κB. Conversely a dominant-negative mutant of Shc inhibited TrkA but not p75 activation of NF-κB. Both of these distinct signaling pathways subsequently converge, leading to activation of the IκB kinase complex. Moreover, the activation of NF-κB by these distinct pathways after stimulation of either TrkA or p75 leads to different physiological consequences. Blocking p75-mediated activation of NF-κB by ecdysone-inducible expression of a nondegradable mutant of IκBα significantly enhanced apoptosis. In contrast, blocking NF-κB induction via TrkA significantly inhibited neurite process formation in PC12 cells. Together these findings indicate that, although both of these receptors lead to the activation of NF-κB, they proceed via distinct proximal-signaling intermediates and contribute to different cellular outcomes.