bluuebunny/crossref_metadata_2025 huggingface dataset:
Ca2+Influx Inhibits Dynamin and Arrests Synaptic Vesicle Endocytosis at the Active Zone
Authors: Cousin Michael A. , Robinson Phillip J.
Published: April 2018

Ca2+entry into nerve terminals through clusters of voltage-dependent Ca2+channels (VDCCs) at active zones creates a microdomain of elevated intracellular free Ca2+concentration ([Ca2+]i) that stimulates exocytosis. We show that this VDCC-mediated [Ca2+]ielevation has no specific role in stimulating endocytosis but can inhibit endocytosis evoked by three different methods in isolated mammalian nerve terminals. The inhibition can be relieved by using either VDCC antagonists or fast, but not slow, binding intracellular Ca2+chelators. The Ca2+-dependent inhibition of endocytosis is mimickedin vitroby a low-affinity inhibition of dynamin I vesiculation of phospholipids. Increased [Ca2+]ialso inhibits dynamin II GTPase activity and receptor-mediated endocytosis in non-neuronal cells. VDCC-meditated Ca2+entry inhibits dynamin-mediated endocytosis at the active zone and provides neurons with a mechanism to clear recycling vesicles to nonactive zone regions during periods of high activity.
Target-Related and Intrinsic Neuronal Death in Lurcher Mutant Mice Are Both Mediated by Caspase-3 Activation
Authors: Selimi Fekrije , Doughty Martin , Delhaye-Bouchaud Nicole , Mariani Jean
Published: April 2018

The Lurcher (Lc) mutation in the δ2 glutamate receptor gene leads to the presence of a constitutive inward current in the cerebellar Purkinje cells of Lurcher heterozygous mice and to the postnatal degeneration of these neurons. In addition, cerebellar granule cells and olivary neurons ofLc/+ mice die as an indirect effect of the mutation after the loss of their target Purkinje cells. The apoptotic nature ofLc/+ Purkinje cell death remains controversial. To address this question, we studied the involvement of caspase-3, a key effector of apoptosis, in the neurodegenerative processes occurring inLc/+cerebellum. Several antibodies recognizing different regions of caspase-3 were used in immunoblotting and immunohistochemical experiments. We demonstrate that pro-caspase-3 is specifically upregulated in the dying Lc/+ Purkinje cells, but not in granule cells and olivary neurons, suggesting that different death-inducing signals trigger variant apoptotic pathways in the CNS. The subcellular localization of pro-caspase-3 was shown to be cytoplasmic and mitochondrial. Active caspase-3 as well as DNA fragmentation was found in numerous granule cells and some Purkinje cells of theLc/+cerebellum. Thus, caspase-3 activation is involved in both the direct and indirect neuronal death induced by the Lurcher mutation, strongly supporting the idea that theLc/+ Purkinje cell dies by apoptosis.
Identification of the Kainate Receptor Subunits Underlying Modulation of Excitatory Synaptic Transmission in the CA3 Region of the Hippocampus
Authors: Contractor Anis , Swanson Geoffrey T. , Sailer Andreas , O'Gorman Stephen , Heinemann Stephen F.
Published: April 2018

To understand the physiological role of kainate receptors and their participation in seizure induction in animal models of epilepsy, it will be necessary to develop a comprehensive description of their action in the CA3 region of the hippocampus. Activation of presynaptic kainate receptors depresses excitatory synaptic transmission at mossy fiber and associational-commissural inputs to CA3 pyramidal neurons (Vignes et al., 1998; Bortolotto et al., 1999; Kamiya and Ozawa, 2000). In this study, we use gene-targeted mice lacking glutamate receptor 5 (GluR5) or GluR6 kainate receptor subunits to identify the receptor subunits that comprise the kainate receptors responsible for presynaptic modulation of CA3 transmission. We found that bath application of kainate (3 μm) profoundly reduced EPSCs at mossy fiber and collateral synapses in neurons from wild-type and GluR5−/−mice but had no effect on EPSCs in neurons from GluR6−/−mice. These results therefore contrast with previous studies that supported a role for GluR5-containing receptors at mossy fiber and associational-commissural synapses (Vignes et al., 1998; Bortolotto et al., 1999). Surprisingly, at perforant path synapses kainate receptor activation enhanced transmission; this potentiation was abolished in both GluR5 and GluR6 knock-out mice. Kainate receptors thus play multiple and complex roles to modulate excitatory synaptic transmission in the CA3 region of the hippocampus.
Two Independent Pathways Mediated by cAMP and Protein Kinase A Enhance Spontaneous Transmitter Release atDrosophilaNeuromuscular Junctions
Authors: Yoshihara Motojiro , Suzuki Kazuhiro , Kidokoro Yoshiaki
Published: April 2018

cAMP is thought to be involved in learning process and known to enhance transmitter release in various systems. Previously we reported that cAMP enhances spontaneous transmitter release in the absence of extracellular Ca2+and that the synaptic vesicle protein neuronal-synaptobrevin (n-syb), is required in this enhancement (n-syb-dependent; Yoshihara et al., 1999). In the present study, we examined the cAMP-induced enhancement of transmitter release in the presence of external Ca2+. We raised the intracellular concentration of cAMP by application of either forskolin, an activator of adenylyl cyclase, or by 4-chlorophenylthio-(CPT)-cAMP, a membrane-permeable analog of cAMP, in the presence of external Ca2+, while recording miniature synaptic currents (mSCs) at the neuromuscular junction inn-sybnull mutant embryos. The frequency of mSCs increased in response to elevation of cAMP, and this effect of cAMP was completely blocked by Co2+(n-syb-independent pathway). In contrast, in wild-type embryos the cAMP-induced mSC frequency increase was partially blocked by Co2+. In a mutant,DC0, defective in protein kinase A (PKA), nerve-evoked synaptic currents were indistinguishable from the control, but mSCs were less frequent. In this mutant the enhancement by cAMP of both nerve-evoked and spontaneous transmitter release was completely absent, even in the presence of external Ca2+. Taken together, these results suggest that cAMP enhances spontaneous transmitter release by increasing Ca2+influx (n-syb-independent) as well as by modulating the release mechanism without Ca2+influx (n-syb-dependent) in wild-type embryos, and these two effects are mediated by PKA encoded by theDC0gene.
Mismatched Appositions of Presynaptic and Postsynaptic Components in Isolated Hippocampal Neurons
Authors: Rao Anuradha , Cha Eric M. , Craig Ann Marie
Published: April 2018

To determine whether presynaptic input is necessary for postsynaptic differentiation, we isolated hippocampal neurons in microisland culture and thus deprived pyramidal cells of GABA input and GABAergic neurons of glutamate input. We find that glutamate input is necessary for clustering the AMPA-type glutamate receptor but not for clustering the NMDA receptor or the associated PSD-95 family scaffold in GABAergic cells; GABA input is not necessary for clustering the GABAAreceptor or gephyrin in pyramidal cells. Isolated neurons showed a surprising mismatch of presynaptic and postsynaptic components. For example, in isolated pyramidal neurons, although GABAAreceptor clusters covered <4% of the dendritic surface and presynaptic boutons covered <12%, a full two-thirds of the GABAAreceptor clusters were localized inappropriately opposite the non-GABAergic, presumed glutamatergic, terminals. Furthermore, inhibitory and excitatory postsynaptic components were segregated into separate clusters in isolated cells and apposed to separate boutons of a single axon. Thus, GABAAreceptors were clustered opposite some terminals, whereas NMDA receptors were clustered opposite other terminals of a single axon. These results suggest the involvement of a synaptogenic signal common to glutamate and GABA synapses that permits experimentally induced mismatching of presynaptic and postsynaptic components in isolated neurons, as well as a second specificity-conferring signal that mediates appropriate matching in mixed cultures.
Neurotensin-Induced Bursting of Cholinergic Basal Forebrain Neurons Promotes γ and θ Cortical Activity Together with Waking and Paradoxical Sleep
Authors: Cape Edmund G. , Manns Ian D. , Alonso Angel , Beaudet Alain , Jones Barbara E.
Published: April 2018

Cholinergic basal forebrain neurons have long been thought to play an important role in cortical activation and behavioral state, yet the precise way in which they influence these processes has yet to be fully understood. Here, we have examined the effects on the electroencephalogram (EEG) and sleep–wake state of basal forebrain administration of neurotensin (NT), a neuropeptide that has been shownin vitroto potently and selectively modulate the cholinergic cells. Microinjection of (0.1–3.0 mm) NT into the basal forebrain of freely moving, naturally waking-sleeping rats produced a dose-dependent decrease in δ (∼1–4 Hz) and increase in both θ (∼4–9 Hz) and high-frequency γ activity (30–60 Hz) across cortical, areas with no increase in the electromyogram. These EEG changes were accompanied by concomitant decreases in slow wave sleep (SWS) and transitional SWS (tSWS), increases in wake, and most remarkably, increases in paradoxical sleep (PS) and transitional PS (tPS), despite the virtual absence of SWS. The effects were attributed to direct action on cholinergic neurons as evidenced by selective internalization of a fluorescent ligand, Fluo-NT, in choline acetyltransferase (ChAT)-immunoreactive cells and stimulation by NT of bursting discharge in juxtacellularly recorded, Neurobiotin-labeled, ChAT-immunoreactive neurons. We conclude that NT-induced rhythmic bursting of cholinergic basal forebrain neurons stimulates rhythmic θ oscillations and γ across the cerebral cortex. With the selective action of NT on the cholinergic cells, their bursting discharge promotes θ and γ independent of motor activity and thereby also stimulates and enhances PS.
Origins and Distribution of Cholinergically Induced β Rhythms in Hippocampal Slices
Authors: Shimono Ken , Brucher Fernando , Granger Richard , Lynch Gary , Taketani Makoto
Published: April 2018

Regional variations and substrates of high-frequency rhythmic activity induced by cholinergic stimulation were studied in hippocampal slices with 64-electrode recording arrays. (1) Carbachol triggered β waves (17.6 ± 5.7 Hz) in pyramidal regions of 75% of the slices. (2) The waves had phase shifts across the cell body layers and were substantially larger in the apical dendrites than in cell body layers or basal dendrites. (3) Continuous, two-dimensional current source density analyses indicated apical sinks associated with basal sources, lasting ∼10 msec, followed by apical sources and basal sinks, lasting ∼20 msec, in a repeating pattern with a period in the range of 15–25 Hz. (4) Carbachol-induced β waves in the hippocampus were accompanied by 40 Hz (γ) oscillations in deep layers of the entorhinal cortex. (5) Cholinergically elicited β and γ rhythms were eliminated by antagonists of either AMPA or GABA receptors. Benzodiazepines markedly enhanced β activity and sometimes introduced a distinct γ frequency peak. (6) Twenty Hertz activity after orthodromic activation of field CA3 was distributed in the same manner as carbachol-induced β waves and was generated by a current source in the apical dendrites of CA3. This source was eliminated by high concentrations of GABAAreceptor blockers. It is concluded that cholinergically driven β rhythms arise independently in hippocampal subfields from oscillatory circuits involving (1) bursts of pyramidal cell discharges, (2) activation of a subset of feedback interneurons that project apically, and (3) production of a GABAA-mediated hyperpolarization in the outer portions of the apical dendrites of pyramidal neurons.
Distributed and Partially Separate Pools of Neurons Are Correlated with Two Different Components of the Gill-Withdrawal Reflex inAplysia
Authors: Zochowski Michal , Cohen Lawrence B. , Fuhrmann Galit , Kleinfeld David
Published: April 2018

We compared the spike activity of individual neurons in theAplysiaabdominal ganglion with the movement of the gill during the gill-withdrawal reflex. We discriminated four populations that collectively encompass approximately half of the active neurons in the ganglion: (1) second-order sensory neurons that respond to the onset and offset of stimulation of the gill and are active before the movement starts; (2) neurons whose activity is correlated with the position of the gill and typically have a tonic output during gill withdrawal; (3) neurons whose activity is correlated with the velocity of the movement and typically fire in a phasic manner; and (4) neurons whose activity is correlated with both position and velocity. A reliable prediction of the position of the gill is achieved only with the combined output of 15–20 neurons, whereas a reliable prediction of the velocity depends on the combined output of 40 or more cells.
Intrinsic Membrane Properties Underlying Spontaneous Tonic Firing in Neostriatal Cholinergic Interneurons
Authors: Bennett Ben D. , Callaway Joseph C. , Wilson Charles J.
Published: April 2018

Neostriatal cholinergic interneurons produce spontaneous tonic firing in the absence of synaptic input. Perforated patch recording and whole-cell recording combined with calcium imaging were usedin vitroto identify the intrinsic membrane properties underlying endogenous excitability. Spontaneous firing was driven by the combined action of a sodium current and the hyperpolarization-activated cation current (Ih), which together ensured that there was no zero current point in the subthreshold voltage range. Blockade of sodium channels orIhestablished a stable subthreshold resting membrane potential. A tetrodotoxin-sensitive region of negative slope conductance was observed between approximately −60 mV and threshold (approximately −50 mV) and the h-current was activated at all subthreshold voltages.

Calcium imaging experiments revealed that there was minimal calcium influx at subthreshold membrane potentials but that action potentials produced elevations of calcium in both the soma and dendrites. Spike-triggered calcium entry shaped the falling phase of the action potential waveform and activated calcium-dependent potassium channels. Blockade of big-conductance channels caused spike broadening. Application of apamin, which blocks small-conductance channels, abolished the slow spike afterhyperpolarization (AHP) and caused a transition to burst firing.

In the absence of synaptic input, a range of tonic firing patterns are observed, suggesting that the characteristic spike sequences described for tonically active cholinergic neurons (TANs) recordedin vivoare intrinsic in origin. The pivotal role of the AHP in regulating spike patterning indicates that burst firing of TANsin vivocould arise from direct or indirect modulation of the AHP without requiring phasic synaptic input.
Requirement of Translation But Not Transcription for the Maintenance of Long-Term Depression in the CA1 Region of Freely Moving Rats
Authors: Manahan-Vaughan Denise , Kulla Alexander , Frey J. Uwe
Published: April 2018

Hippocampal long-term depression (LTD) comprises a persistent reduction in synaptic strength that can be induced in the CA1 region by repeated low-frequency stimulation (LFS). Previous studies have demonstrated that hippocampal long-term potentiation requiresde novoprotein synthesis. Whether hippocampal LTD is also protein synthesis-dependent is not known. In this study, we investigated if the previous administration of translation inhibitors (anisomycin or emetine) or a transcription inhibitor (actinomycin-D) influenced the profile of LTD in freely moving adult Wistar rats. Seven- to 8-week-old animals underwent chronic implantation of a recording electrode in the CA1 stratum radiatum and a stimulation electrode in the Schaffer collateral/commissural fiber pathway. A cannula was implanted in the ipsilateral cerebral ventricle to enable drug administration. Experiments were commenced 10 d after the implantation procedure. Immediately after application of LFS (1 Hz, 900 pulses) robust LTD was seen that persisted for >8 hr in control animals. Application of anisomycin (240 μg/5 μl) emetine (240 μg/5 μl) before LFS prevented the expression of LTD or ∼4.5 hr after LFS. Previous administration of actinomycin D (72 μg/12 μl) had no effect on the expression of LTD. None of the compounds elicited significant effects on basal synaptic transmission when administered in the absence of LFS. These data suggest that LTD in the CA1 regionin vivois protein synthesis-dependent. Furthermore, persistent LTD can be established through the translation of existing mRNA, whereasde novomRNA transcription does not appear to be necessary.
Avoidance Task Training Potentiates Phasic Pontine-Wave Density in the Rat: A Mechanism for Sleep-Dependent Plasticity
Authors: Datta Subimal
Published: April 2018

Behavioral studies of learning and memory in both humans and animals support a role for sleep in the consolidation and integration of memories. The present study explored possible physiological mechanisms of sleep-dependent behavioral plasticity by examining the relationship between learning and state-dependent phasic signs of rapid eye movement (REM) sleep. Cortical electroencephalogram, electromyogram, eye movement, hippocampal θ-wave, and pontine-wave (P-wave) measures were recorded simultaneously in freely moving rats after a session of conditioned avoidance learning or a control session. After learning trials, rats spent 25.5% more time in REM sleep and 180.6% more time in a transitional state between slow-wave sleep and REM sleep (tS-R) compared with that in control trials. Both REM sleep and tS-R behavioral states are characterized by the presence of P-waves. P-wave density was significantly greater in the first four episodes of REM sleep after the learning session compared with the control session. Furthermore, the P-wave density change between the first and third REM sleep episodes was proportional to the improvement of task performance between the initial training session and the postsleep retest session. These findings show that the increase in P-wave density during the post-training REM sleep episodes is correlated with the effective consolidation and retention of avoidance task learning.
Key Role for the Epsilon Isoform of Protein Kinase C in Painful Alcoholic Neuropathy in the Rat
Authors: Dina Olayinka A. , Barletta Justine , Chen Xiaojie , Mutero Annick , Martin Annick , Messing Robert O. , Levine Jon D.
Published: April 2018

Chronic alcohol consumption produces a painful peripheral neuropathy for which there is no reliably successful therapy, attributable to, in great part, a lack of understanding of the underlying mechanisms. We tested the hypothesis that neuropathic pain associated with chronic alcohol consumption is a result of abnormal peripheral nociceptor function. In rats maintained on a diet to simulate chronic alcohol consumption in humans, mechanical hyperalgesia was present by the fourth week and maximal at 10 weeks. Thermal hyperalgesia and mechanical allodynia were also present. Mechanical threshold of C-fibers in ethanol fed rats was lowered, and the number of action potentials during sustained stimulation increased. The hyperalgesia was acutely attenuated by intradermal injection of nonselective protein kinase C (PKC) or selective PKCε inhibitors injected at the site of nociceptive testing. Western immunoblot analysis indicated a higher level of PKCε in dorsal root ganglia from alcohol-fed rats, supporting a role for enhanced PKCε second-messenger signaling in nociceptors contributing to alcohol-induced hyperalgesia.
Hypothalamic Arousal Regions Are Activated during Modafinil-Induced Wakefulness
Authors: Scammell Thomas E. , Estabrooke Ivy V. , McCarthy Marie T. , Chemelli Richard M. , Yanagisawa Masashi , Miller Matthew S. , Saper Clifford B.
Published: April 2018

Modafinil is an increasingly popular wake-promoting drug used for the treatment of narcolepsy, but its precise mechanism of action is unknown. To determine potential pathways via which modafinil acts, we administered a range of doses of modafinil to rats, recorded sleep/wake activity, and studied the pattern of neuronal activation using Fos immunohistochemistry. To contrast modafinil-induced wakefulness with spontaneous wakefulness, we administered modafinil at midnight, during the normal waking period of rats. To determine the influence of circadian phase or ambient light, we also injected modafinil at noon on a normal light/dark cycle or in constant darkness. We found that 75 mg/kg modafinil increased Fos immunoreactivity in the tuberomammillary nucleus (TMN) and in orexin (hypocretin) neurons of the perifornical area, two cell groups implicated in the regulation of wakefulness. This low dose of modafinil also increased the number of Fos-immunoreactive (Fos-IR) neurons in the lateral subdivision of the central nucleus of the amygdala. Higher doses increased the number of Fos-IR neurons in the striatum and cingulate cortex. In contrast to previous studies, modafinil did not produce statistically significant increases in Fos expression in either the suprachiasmatic nucleus or the anterior hypothalamic area. These observations suggest that modafinil may promote waking via activation of TMN and orexin neurons, two regions implicated in the promotion of normal wakefulness. Selective pharmacological activation of these hypothalamic regions may represent a novel approach to inducing wakefulness.
Inhibition of Krebs Cycle Enzymes by Hydrogen Peroxide: A Key Role of α-Ketoglutarate Dehydrogenase in Limiting NADH Production under Oxidative Stress
Authors: Tretter Laszlo , Adam-Vizi Vera
Published: April 2018

In this study we addressed the function of the Krebs cycle to determine which enzyme(s) limits the availability of reduced nicotinamide adenine dinucleotide (NADH) for the respiratory chain under H2O2-induced oxidative stress, in intact isolated nerve terminals. The enzyme that was most vulnerable to inhibition by H2O2proved to be aconitase, being completely blocked at 50 μmH2O2. α-Ketoglutarate dehydrogenase (α-KGDH) was also inhibited but only at higher H2O2concentrations (≥100 μm), and only partial inactivation was achieved. The rotenone-induced increase in reduced nicotinamide adenine dinucleotide (phosphate) [NAD(P)H] fluorescence reflecting the amount of NADH available for the respiratory chain was also diminished by H2O2, and the effect exerted at small concentrations (≤50 μm) of the oxidant was completely prevented by 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), an inhibitor of glutathione reductase. BCNU-insensitive decline by H2O2in the rotenone-induced NAD(P)H fluorescence correlated with inhibition of α-ketoglutarate dehydrogenase. Decrease in the glutamate content of nerve terminals was induced by H2O2at concentrations inhibiting aconitase. It is concluded that (1) aconitase is the most sensitive enzyme in the Krebs cycle to inhibition by H2O2, (2) at small H2O2concentrations (≤50 μm) when aconitase is inactivated, glutamate fuels the Krebs cycle and NADH generation is unaltered, (3) at higher H2O2concentrations (≥100 μm) inhibition of α-ketoglutarate dehydrogenase limits the amount of NADH available for the respiratory chain, and (4) increased consumption of NADPH makes a contribution to the H2O2-induced decrease in the amount of reduced pyridine nucleotides. These results emphasize the importance of α-KGDH in impaired mitochondrial function under oxidative stress, with implications for neurodegenerative diseases and cell damage induced by ischemia/reperfusion.
Agrin Controls Synaptic Differentiation in Hippocampal Neurons
Authors: Böse Christian M. , Qiu Dike , Bergamaschi Andrea , Gravante Biagio , Bossi Mario , Villa Antonello , Rupp Fabio , Malgaroli Antonio
Published: April 2018

Agrin controls the formation of the neuromuscular junction. Whether it regulates the differentiation of other types of synapses remains unclear. Therefore, we have studied the role of agrin in cultured hippocampal neurons. Synaptogenesis was severely compromised when agrin expression or function was suppressed by antisense oligonucleotides and specific antibodies. The effects of antisense oligonucleotides were found to be highly specific because they were reversed by adding recombinant agrin and could not be detected in cultures from agrin-deficient animals. Interestingly, the few synapses formed in reduced agrin conditions displayed diminished vesicular turnover, despite a normal appearance at the EM level. Thus, our results demonstrate the necessity of agrin for synaptogenesis in hippocampal neurons.
Chronic Antidepressant Treatment Increases Neurogenesis in Adult Rat Hippocampus
Authors: Malberg Jessica E. , Eisch Amelia J. , Nestler Eric J. , Duman Ronald S.
Published: April 2018

Recent studies suggest that stress-induced atrophy and loss of hippocampal neurons may contribute to the pathophysiology of depression. The aim of this study was to investigate the effect of antidepressants on hippocampal neurogenesis in the adult rat, using the thymidine analog bromodeoxyuridine (BrdU) as a marker for dividing cells. Our studies demonstrate that chronic antidepressant treatment significantly increases the number of BrdU-labeled cells in the dentate gyrus and hilus of the hippocampus. Administration of several different classes of antidepressant, but not non-antidepressant, agents was found to increase BrdU-labeled cell number, indicating that this is a common and selective action of antidepressants. In addition, upregulation of the number of BrdU-labeled cells is observed after chronic, but not acute, treatment, consistent with the time course for the therapeutic action of antidepressants. Additional studies demonstrated that antidepressant treatment increases the proliferation of hippocampal cells and that these new cells mature and become neurons, as determined by triple labeling for BrdU and neuronal- or glial-specific markers. These findings raise the possibility that increased cell proliferation and increased neuronal number may be a mechanism by which antidepressant treatment overcomes the stress-induced atrophy and loss of hippocampal neurons and may contribute to the therapeutic actions of antidepressant treatment.
Protection by Synergistic Effects of Adenovirus-Mediated X-Chromosome-Linked Inhibitor of Apoptosis and Glial Cell Line-Derived Neurotrophic Factor Gene Transfer in the 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Model of Parkinson's Disease
Authors: Eberhardt Olaf , Coelln Rainer V. , Kügler Sebastian , Lindenau Jörg , Rathke-Hartlieb Silvia , Gerhardt Ellen , Haid Sibylle , Isenmann Stefan , Gravel Claude , Srinivasan Anu , Bähr Mathias , Weller Michael , Dichgans Johannes , Schulz Jörg B.
Published: April 2018

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produces clinical, biochemical, and neuropathological changes reminiscent of those occurring in idiopathic Parkinson's disease (PD). Here we show that a peptide caspase inhibitor,N-benzyloxy-carbonyl-val-ala-asp-fluoromethyl ketone, or adenoviral gene transfer (AdV) of a protein caspase inhibitor, X-chromosome-linked inhibitor of apoptosis (XIAP), prevent cell death of dopaminergic substantia nigra pars compacta (SNpc) neurons induced by MPTP or its active metabolite 1-methyl-4-phenylpyridiniumin vitroandin vivo. Because the MPTP-induced decrease in striatal concentrations of dopamine and its metabolites does not differ between AdV-XIAP- and control vector-treated mice, this protection is not associated with a preservation of nigrostriatal terminals. In contrast, the combination of adenoviral gene transfer of XIAP and of the glial cell line-derived neurotrophic factor to the striatum provides synergistic effects, rescuing dopaminergic SNpc neurons from cell death and maintaining their nigrostriatal terminals. These data suggest that a combination of a caspase inhibitor, which blocks death, and a neurotrophic factor, which promotes the specific function of the rescued neurons, may be a promising strategy for the treatment of PD.
Reduced Rearing Temperature Augments Responses in Sympathetic Outflow to Brown Adipose Tissue
Authors: Morrison Shaun F. , Ramamurthy Sheela , Young James B.
Published: April 2018

Sympathetic outflow to brown adipose tissue (BAT) contributes to both thermoregulation and energy expenditure in rats through regulation of BAT thermogenesis. Acute cold exposure in mature animals augments BAT thermogenesis; however, the enhanced BAT thermogenic response returns to normal shortly after cessation of the cold exposure. In this study, we sought to determine whether cold exposure in early neonatal life could induce enhanced responses in the sympathetic outflow to BAT and whether this altered sympathetic regulation would be sustained after the cold stimulus was removed. BAT sympathetic nerve activity (SNA) was recorded in urethane–chloralose-anesthetized, artificially ventilated rats that were raised from birth in either 18 or 30°C environments and then, at 8 weeks of age, were maintained in 23°C for at least 4 weeks. An acute hypothermic stimulus, disinhibition of a brainstem thermogenic network in the raphe pallidus, or electrical stimulation in this raphe site produced increases in BAT SNA that were twice as great in rats reared at 18°C as in those reared at 30°C. The norepinephrine content of the interscapular BAT (IBAT) and the number of sympathetic ganglion cells projecting to interscapular BAT were 70% greater in the 18°C-reared rats. We conclude that neonatal exposure to a cold environment induces a permanent developmental alteration in the capacity for sympathetic stimulation of BAT thermogenesis that may be mediated, in part, by a greater number of sympathetic ganglion cells innervating BAT in cold-reared animals.
Modeling of Membrane Excitability in Gonadotropin-Releasing Hormone-Secreting Hypothalamic Neurons Regulated by Ca2+-Mobilizing and Adenylyl Cyclase-Coupled Receptors
Authors: LeBeau Andrew P. , Van Goor Fredrick , Stojilkovic Stanko S. , Sherman Arthur
Published: April 2018

Gonadotropin-releasing hormone (GnRH) secretion from native and immortalized hypothalamic neurons is regulated by endogenous Ca2+-mobilizing and adenylyl cyclase (AC)-coupled receptors. Activation of both receptor types leads to an increase in action potential firing frequency and a rise in the intracellular Ca2+concentration ([Ca2+]i) and neuropeptide secretion. The stimulatory action of Ca2+-mobilizing agonists on voltage-gated Ca2+influx is determined by depletion of the intracellular Ca2+pool, whereas AC agonist-stimulated Ca2+influx occurs independently of stored Ca2+and is controlled by cAMP, possibly through cyclic nucleotide-gated channels. Here, experimental records from immortalized GnRH-secreting neurons are simulated with a mathematical model to determine the requirements for generating complex membrane potential (Vm) and [Ca2+]iresponses to Ca2+-mobilizing and AC agonists. Included in the model are three pacemaker currents: a store-operated Ca2+current (ISOC), an SK-type Ca2+-activated K+current (ISK), and an inward current that is modulated by cAMP and [Ca2+]i(Id). Spontaneous electrical activity and Ca2+signaling in the model are predominantly controlled byId, which is activated by cAMP and inhibited by high [Ca2+]i. Depletion of the intracellular Ca2+pool mimics the receptor-induced activation ofISOCandISK, leading to an increase in the firing frequency and Ca2+influx after a transient cessation of electrical activity. However, increasing the activity ofIdsimulates the experimental response to forskolin-induced activation of AC. Analysis of the behaviors ofISOC,Id, andISKin the model reveals the complexity in the interplay of these currents that is necessary to fully account for the experimental results.
A Common Mechanism Underlies Vertebrate Calcium Signaling andDrosophilaPhototransduction
Authors: Chorna-Ornan Irit , Joel-Almagor Tamar , Ben-Ami Hagit Cohen , Frechter Shahar , Gillo Boaz , Selinger Zvi , Gill Donald L. , Minke Baruch
Published: April 2018

Drosophilaphototransduction is an important model system for studies of inositol lipid signaling. Light excitation inDrosophilaphotoreceptors depends on phospholipase C, because null mutants of this enzyme do not respond to light. Surprisingly, genetic elimination of the apparently single inositol trisphosphate receptor (InsP3R) ofDrosophilahas no effect on phototransduction. This led to the proposal thatDrosophilaphotoreceptors do not use the InsP3branch of phospholipase C (PLC)-mediated signaling for phototransduction, unlike most other inositol lipid-signaling systems. To examine this hypothesis we applied the membrane-permeant InsP3R antagonist 2-aminoethoxydiphenyl borate (2-APB), which has proved to be an important probe for assessing InsP3R involvement in various signaling systems. We first examined the effects of 2-APB onXenopusoocytes. We found that 2-APB is efficient at reversibly blocking the robust InsP3-mediated Ca2+release and store-operated Ca2+entry inXenopusoocytes at a stage operating after production of InsP3but before the opening of the surface membrane Cl−channels by Ca2+. We next demonstrated that 2-APB is effective at reversibly blocking the response to light ofDrosophilaphotoreceptors in a light-dependent manner at a concentration range similar to that effective inXenopusoocytes and other cells. We show furthermore that 2-APB does not directly block the light-sensitive channels, indicating that it operates upstream in the activation of these channels. The results indicate an important link in the coupling mechanism of vertebrate store-operated channels andDrosophilaTRP channels, which involves the InsP3branch of the inositol lipid-signaling pathway.
Two-Tiered Inhibition of Axon Regeneration at the Dorsal Root Entry Zone
Authors: Ramer Matt S. , Duraisingam Ishwari , Priestley John V. , McMahon Stephen B.
Published: April 2018

Glial-derived inhibitory molecules and a weak cell-body response prevent sensory axon regeneration into the spinal cord after dorsal root injury. Neurotrophic factors, particularly neurotrophin-3 (NT-3), may increase the regenerative capacity of sensory neurons after dorsal rhizotomy, allowing regeneration across the dorsal root entry zone (DREZ). Intrathecal NT-3, delivered at the time of injury, promoted an upregulation of the growth-associated protein GAP-43 primarily in large-diameter sensory profiles (which did not occur after rhizotomy alone), as well as regeneration of cholera toxin B-labeled sensory axons across the DREZ and deep into the dorsal horn. However, delaying treatment for 1 week compromised regeneration: although axons still penetrated the DREZ, growth within white matter was qualitatively and quantitatively restricted. This was not associated with an impaired cell-body response (GAP-43 upregulation was equivalent for both immediate and delayed treatments), or with astrogliosis at the DREZ, which begins almost immediately after rhizotomy, but with the delayed appearance of mature ED1-expressing phagocytes in the dorsal white matter between 1 and 2 weeks after lesion, marking the beginning of myelin breakdown. After rhizotomy with immediate NT-3 treatment, regeneration continues beyond 2 weeks, but in the dorsal gray matter rather than in the degenerating dorsal columns. The ability of NT-3 to promote regeneration across the DREZ, but not after the beginning of degeneration after delayed treatment reveals a hierarchy of inhibitory influences: the astrogliotic, but not the degenerative barrier is surmountable by NT-3 treatment.
Patterns of Neural Circuit Activation and Behavior during Dominance Hierarchy Formation in Freely Behaving Crayfish
Authors: Herberholz Jens , Issa Fadi A. , Edwards Donald H.
Published: April 2018

Creation of a dominance hierarchy within a population of animals typically involves a period of agonistic activity in which winning and losing decide relative positions in the hierarchy. Among crayfish, fighting between size-matched animals leads to an abrupt change of behavior as the new subordinate retreats and escapes from the attacks and approaches of the dominant (Issa et al., 1999). We used high-speed videography and electrical recordings of aquarium field potentials to monitor the release of aggressive and defensive behavior, including the activation of neural circuits for four different tail-flip behaviors. We found that the sequence of tail-flip circuit excitation traced the development of their dominance hierarchy. Offensive tail flipping, attacks, and approaches by both animals were followed by a sharp rise in the frequency of nongiant and medial giant escape tail flips and a fall in the frequency of offensive tail flips of the new subordinate. These changes suggest that sudden, coordinated changes in the excitability of a set of neural circuits in one animal produce the changes in behavior that mark its transition to subordinate status.
Regulation of Serotonin Release in the Lateral Septum and Striatum by Corticotropin-Releasing Factor
Authors: Price Michelle L. , Lucki Irwin
Published: April 2018

The serotonergic dorsal raphé nucleus (DRN) is innervated by corticotropin-releasing factor (CRF)-immunoreactive fibers and contains CRF receptor-binding sites, suggesting that endogenous CRF regulates this system. The present study examined the possibility that CRF in the DRN regulates the release of serotonin (5-HT) in forebrain terminal regions. Intracerebroventricular administration of CRF produced a bimodal effect on extracellular levels of 5-HT in the lateral septum. Doses of 0.3 and 1.0 μg decreased extracellular 5-HT levels, whereas both a higher (3.0 μg) and a lower (0.1 μg) dose had no effect. The reduction of extracellular 5-HT in the lateral septum by CRF (0.3 μg, i.c.v.) was blocked by pretreatment with the CRF receptor antagonistd-PheCRF12–41(3.0 μg, i.c.v.). Direct administration of CRF (30 ng) into the DRN reduced extracellular 5-HT levels in the lateral septum and the striatum. Furthermore, injection ofd-PheCRF12–41(10 ng) into the DRN before ventricular administration of CRF (0.3 μg, i.c.v.) blocked the decrease in extracellular 5-HT in both the lateral septum and striatum. Taken together, these data support the hypothesis that CRF may modulate 5-HT release in terminal regions via its effects at the level of the DRN. This modulation supports a potential interaction between CRF and 5-HT in stress-related psychiatric disorders in which both systems have been implicated.
Distinct Molecular Determinants Govern Syntaxin 1A-Mediated Inactivation and G-Protein Inhibition of N-Type Calcium Channels
Authors: Jarvis Scott E. , Zamponi Gerald W.
Published: April 2018

We have reported recently that syntaxin 1A mediates two effects on N-type channels transiently expressed in tsA-201 cells: a hyperpolarizing shift in the steady-state inactivation curve as well as a tonic inhibition of the channel by G-protein βγ subunits (Jarvis et al., 2000). Here we have examined some of the molecular determinants and factors that modulate the action of syntaxin 1A on N-type calcium channels. With the additional coexpression of SNAP25, the syntaxin 1A-induced G-protein modulation of the channel became reduced in magnitude by ∼50% but nonetheless remained significantly higher than the low levels of background inhibition seen with N-type channels alone. In contrast, coexpression of nSec-1 did not reduce the syntaxin 1A-mediated G-protein inhibition; however, interestingly, nSec-1 was able to induce tonic G-protein inhibition even in the absence of syntaxin 1A. Both SNAP25 and nSec-1 blocked the negative shift in half-inactivation potential that was induced by syntaxin 1A. Activation of protein kinase C via phorbol esters or site-directed mutagenesis of three putative PKC consensus sites in the syntaxin 1A binding region of the channel (S802, S896, S898) to glutamic acid (to mimic a permanently phosphorylated state) did not affect the syntaxin 1A-mediated G-protein modulation of the channel. However, in the S896E and S898E mutants, or after PKC-dependent phosphorylation of the wild-type channels, the susceptibility of the channel to undergo shifts in half-inactivation potential was removed. Thus, separate molecular determinants govern the ability of syntaxin 1A to affect N-type channel gating and its modulation by G-proteins.
Syntaxin 1A Supports Voltage-Dependent Inhibition of α1BCa2+Channels by Gβγ in Chick Sensory Neurons
Authors: Lü Qiang , AtKisson M. S. , Jarvis Scott E. , Feng Zhong-Ping , Zamponi Gerald W. , Dunlap Kathleen
Published: April 2018

N-type Ca2+channels are modulated by a variety of G-protein-coupled pathways. Some pathways produce a transient, voltage-dependent (VD) inhibition of N channel function and involve direct binding of G-protein subunits; others require the activation of intermediate enzymes and produce a longer-lasting, voltage-independent (VI) form of inhibition. The ratio of VD:VI inhibition differs significantly among cell types, suggesting that the two forms of inhibition play unique physiological roles in the nervous system. In this study, we explored mechanisms capable of altering the balance of VD and VI inhibition in chick dorsal root ganglion neurons. We report that (1) VD:VI inhibition is critically dependent on the Gβγ concentration, with VI inhibition dominant at low Gβγ concentrations, and (2) syntaxin-1A (but not syntaxin-1B) shifts the ratio in favor of VD inhibition by potentiating the VD effects of Gβγ. Variations in expression levels of G-proteins and/or syntaxin provide the means to alter over a wide range both the extent and the rate of Ca2+influx through N channels.
Protein Kinase C-Mediated Inhibition of μ-Opioid Receptor Internalization and Its Involvement in the Development of Acute Tolerance to Peripheral μ-Agonist Analgesia
Authors: Ueda Hiroshi , Inoue Makoto , Matsumoto Takayuki
Published: April 2018

We investigated the role of protein kinase C (PKC) in cell μ-opioid receptor (MOR) internalization and MOR-mediated acute tolerancein vivo. When Chinese hamster ovary cells expressing MOR were exposed to [D-Ala2,MePhe4,Gly-ol5]-enkephalin (DAMGO), receptor internalization was observed at 30 min. Incubation with morphine failed to induce receptor internalization. When calphostin C, a PKC inhibitor, was added, receptor internalization was observed as early as 10 min after morphine stimulation. The MOR internalization induced by DAMGO or morphine in the presence of calphostin C was dynamin dependent, because it was abolished 2 d after pretreatment with recombinant adenovirus to express a dominant interfering dynamin mutant (K44A/dynamin adenovirus). On the other hand, in a peripheral nociception test in mice, the nociceptive flexor response after intraplantar injection (i.pl.) of bradykinin was markedly inhibited by DAMGO (i.pl.). DAMGO analgesia was not affected by 2 hr prior injection (i.pl.) of DAMGO. Marked acute tolerance was observed after pretreatment with dynamin antisense oligodeoxynucleotide or K44A/dynamin adenovirus. The DAMGO-induced acute tolerance under such pretreatments was inhibited by calphostin C. Together, these findings suggest that PKC desensitizes MOR or has a role in the development of acute tolerance through MOR by inhibiting internalization mechanisms as a resensitization process.
Kainate Receptors Regulate Unitary IPSCs Elicited in Pyramidal Cells by Fast-Spiking Interneurons in the Neocortex
Authors: Ali Afia B. , Rossier Jean , Staiger Jochen F. , Audinat Etienne
Published: April 2018

Unitary IPSCs elicited by fast-spiking (FS) interneurons in layer V pyramidal cells of the neocortex were studied by means of dual whole-cell recordings in acute slices. FS to pyramidal cell unitary IPSCs were depressed by (RS)-S-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl) (ATPA), a kainate (KA) receptor agonist, and by the endogenous agonistl-glutamate in the presence of AMPA, NMDA, mGluR, and GABABreceptor antagonists. This effect was accompanied by an increase in failure rate of synaptic transmission, in the coefficient of variation, and in the paired pulse ratio, indicating a presynaptic origin of the IPSC depression. Pairing the activation of the presynaptic neuron with a depolarization of the postsynaptic cell mimicked the decrease of unitary IPSCs, and this effect persisted when postsynaptic sodium action potentials were blocked with the local anesthetic QX314. The effects of ATPA, glutamate, and of the pairing protocol were almost totally blocked by CNQX. These data suggest that KA receptors located on presynaptic FS cell terminals decrease the release of GABA and can be activated by glutamate released from the somatodendritic compartment of the postsynaptic pyramidal cells.
Representation of Acoustic Communication Signals by Insect Auditory Receptor Neurons
Authors: Machens Christian K. , Stemmler Martin B. , Prinz Petra , Krahe Rüdiger , Ronacher Bernhard , Herz Andreas V. M.
Published: April 2018

Despite their simple auditory systems, some insect species recognize certain temporal aspects of acoustic stimuli with an acuity equal to that of vertebrates; however, the underlying neural mechanisms and coding schemes are only partially understood. In this study, we analyze the response characteristics of the peripheral auditory system of grasshoppers with special emphasis on the representation of species-specific communication signals. We use both natural calling songs and artificial random stimuli designed to focus on two low-order statistical properties of the songs: their typical time scales and the distribution of their modulation amplitudes.

Based on stimulus reconstruction techniques and quantified within an information-theoretic framework, our data show that artificial stimuli with typical time scales of >40 msec can be read from single spike trains with high accuracy. Faster stimulus variations can be reconstructed only for behaviorally relevant amplitude distributions. The highest rates of information transmission (180 bits/sec) and the highest coding efficiencies (40%) are obtained for stimuli that capture both the time scales and amplitude distributions of natural songs.

Use of multiple spike trains significantly improves the reconstruction of stimuli that vary on time scales <40 msec or feature amplitude distributions as occur when several grasshopper songs overlap. Signal-to-noise ratios obtained from the reconstructions of natural songs do not exceed those obtained from artificial stimuli with the same low-order statistical properties. We conclude that auditory receptor neurons are optimized to extract both the time scales and the amplitude distribution of natural songs. They are not optimized, however, to extract higher-order statistical properties of the song-specific rhythmic patterns.