bluuebunny/crossref_metadata_2025 huggingface dataset:
Deficiency of Complement Defense Protein CD59 May Contribute to Neurodegeneration in Alzheimer's Disease
Authors: Yang Li-Bang , Li Rena , Meri Seppo , Rogers Joseph , Shen Yong
Published: April 2018

Complement defense 59 (CD59) is a cell surface glycophosphoinositol (GPI)-anchored protein that prevents complement membrane attack complex (MAC) assembly. Here, we present evidence from ELISA assays that CD59 protein levels are significantly decreased in the frontal cortex and hippocampus of Alzheimer's disease (AD) compared with nondemented elderly (ND) patients, whereas complement component 9, a final component to form MAC, is significantly increased. To further confirm the CD59 deficit, PI-specific phospholipase C (PIPLC) was used to cleave the CD59 GPI anchor at the cell surface in intact slices from AD and ND cortex. CD59 released by PIPLC cleavage was significantly reduced in AD compared with ND samples. By the use of a ribonuclease protection technique, amyloid β-peptide was found to downregulate CD59 expression at the mRNA level, suggesting a partial explanation of CD59 deficits in the AD brain. To evaluate the pathophysiological significance of CD59 alterations in neurons, we exposed cultured NT2 cells, which normally underexpress CD59, and NT2 cells transfected to overexpress CD59 to homologous human serum. Lactic acid dehydrogenase assays revealed significant complement-induced cell lysis in CD59-underexpressing NT2 cells and significant protection from such lysis in CD59-overexpressing NT2 cells. Moreover, cells expressing normal levels of CD59 showed no evidence of MAC assembly or damage after exposure to homologous serum, whereas pretreatment of these cells with a CD59-neutralizing antibody resulted in MAC assembly at the cell surface and morphological damage. Taken together, these data suggest that CD59 deficits may play a role in the neuritic losses characteristic of AD.
Akt-Mediated Survival of Oligodendrocytes Induced by Neuregulins
Authors: Flores Ana I. , Mallon Barbara S. , Matsui Takashi , Ogawa Wataru , Rosenzweig Anthony , Okamoto Takashi , Macklin Wendy B.
Published: April 2018

Neuregulins have been implicated in a number of events in cells in the oligodendrocyte lineage, including enhanced survival, mitosis, migration, and differentiation. At least two signaling pathways have been shown to be involved in neuregulin signaling: the phosphatidylinositol (PI)-3 kinase and the mitogen-activated protein kinase pathways. In the present studies, we examined the signaling pathway involved in the survival function of heregulin, focusing on heregulin-induced changes in Akt activity in cultured glial cells, and the consequences of Akt activation in cells in the oligodendrocyte lineage. Heregulin binds erbB receptors, and in our studies, primary cultures of both oligodendrocyte progenitor cells and differentiating oligodendrocytes expressed erbB2, erbB3, and erbB4 receptors. In C6 glioma cells and primary cultures of oligodendrocytes, heregulin induced time- and dose-dependent Akt phosphorylation at Ser473in a wortmannin-sensitive manner. To investigate further the signaling pathway for heregulin in glial cells, BAD was overexpressed in C6 glioma cells. In these cells, heregulin induced phosphorylation of BAD at Ser136. Apoptosis of oligodendrocyte progenitor cells induced by growth factor deprivation was effectively blocked by heregulin in a wortmannin-sensitive manner. Overexpression of dominant negative Akt but not of wild-type Akt by adenoviral gene transfer in primary cultures of both oligodendrocytes and their progenitors induced significant apoptosis through activation of the caspase cascade. The present data suggest that the survival function of heregulin is mediated through the PI-3 kinase/Akt pathway in cells in the oligodendrocyte lineage and that the Akt pathway may be quite important for survival of cells in this lineage.
Coincident Activation of NMDA and Dopamine D1Receptors within the Nucleus Accumbens Core Is Required for Appetitive Instrumental Learning
Authors: Smith-Roe Stephanie L. , Kelley Ann E.
Published: April 2018

The nucleus accumbens, a brain structure ideally situated to act as an interface between corticolimbic information-processing regions and motor output systems, is well known to subserve behaviors governed by natural reinforcers. In the accumbens core, glutamatergic input from its corticolimbic afferents and dopaminergic input from the ventral tegmental area converge onto common dendrites of the medium spiny neurons that populate the accumbens. We have previously found that blockade of NMDA receptors in the core with the antagonist 2-amino-5-phosphonopentanoic acid (AP-5; 5 nmol) abolishes acquisition but not performance of an appetitive instrumental learning task (Kelley et al., 1997). Because it is currently hypothesized that concurrent dopamine D1and glutamate receptor activation is required for long-term changes associated with plasticity, we wished to examine whether the dopamine system in the accumbens core modulates learning via NMDA receptors. Co-infusion of low doses of the D1receptor antagonist SCH-23390 (0.3 nmol) and AP-5 (0.5 nmol) into the accumbens core strongly impaired acquisition of instrumental learning (lever pressing for food), whereas when infused separately, these low doses had no effect. Infusion of the combined low doses had no effect on indices of feeding and motor activity, suggesting a specific effect on learning. We hypothesize that co-activation of NMDA and D1receptors in the nucleus accumbens core is a key process for acquisition of appetitive instrumental learning. Such an interaction is likely to promote intracellular events and gene regulation necessary for synaptic plasticity and is supported by a number of cellular models.
A Common Signaling Pathway for Striatal NMDA and Adenosine A2aReceptors: Implications for the Treatment of Parkinson's Disease
Authors: Nash Joanne E. , Brotchie Jonathan M.
Published: April 2018

The striatum is the major input region of the basal ganglia, playing a pivotal role in the selection, initiation, and coordination of movement both physiologically and in pathophysiological situations such as Parkinson's disease. In the present study, we characterize interactions between NMDA receptors, adenosine receptors, and cAMP signaling within the striatum. Both NMDA (100 μm) and the adenosine A2areceptor agonist CPCA (3 μm) increased cAMP levels (218.9 ± 19.9% and 395.7 ± 67.2%, respectively; cf. basal). The NMDA-induced increase in cAMP was completely blocked when slices were preincubated with either the NMDA receptor antagonist 7-chlorokynurenate or the adenosine A2receptor antagonist DMPX (100 μm), suggesting that striatal NMDA receptors increase cAMP indirectly via stimulation of adenosine A2areceptors. Thus, NMDA receptors and adenosine A2areceptors might share a common signaling pathway within the striatum. In striatal slices prepared from the 6-hydroxydopamine-lesioned rat model of Parkinson's disease, NMDA receptor-mediated increases in cAMP were greater on the lesioned side compared with the unlesioned side (349.6 ± 40.2% compared with 200.9 ± 21.9% of basal levels, respectively). This finding substantiates previous evidence implicating overactivity of striatal NMDA receptors in parkinsonism and suggests that a common NMDA receptor–adenosine A2areceptor–cAMP signaling cascade might be an important mechanism responsible for mediating parkinsonian symptoms.
Sensory Modification of Leech Swimming: Rhythmic Activity of Ventral Stretch Receptors Can Change Intersegmental Phase Relationships
Authors: Cang Jianhua , Friesen W. Otto
Published: April 2018

For segmented animals to generate optimal locomotory movements, appropriate phase relationships between segmental oscillators are crucial. Using swimming leeches, we have investigated the role of sensory input in establishing such relationships. We found that the stretch receptors associated with ventral longitudinal muscles encode the information of muscle contraction during swimming via membrane potential oscillations, with amplitudes of up to 10 mV at our recording site. We subsequently modified the activity of ventral stretch receptors (VSRs) by injecting rhythmic current at different phases of the swim cycle and determined intersegmental phase lags by comparing the delay between the discharges of serially homologous motoneurons in three adjacent segments of isolated nerve cords. When no current was injected, the phase lag between neighboring segments was 8.6 ± 0.8° (mean ± SEM;n= 20), with large phase variations from cycle to cycle, between different episodes, and between different preparations. When the phase of stretch receptor activity was set to 90–150° by current injection, the phase of the motoneuron activity in the ganglion was consistently retarded by ∼5°. It was advanced by ∼5° when the VSR phase was set to 240–300°. Therefore, the rhythmic activity of the ventral stretch receptor generated during swimming can change intersegmental phase lags of leech ganglia in a phase-dependent manner. These stretch receptors may set the optimal intersegmental phases during swimming movement in intact leeches.
A Glia-Derived Signal Regulating Neuronal Differentiation
Authors: Blondel Olivier , Collin Carlos , McCarran William J. , Zhu Shiaoping , Zamostiano Rachel , Gozes Illana , Brenneman Douglas E. , McKay Ronald D. G.
Published: April 2018

Astrocytes are present in large numbers in the nervous system, are associated with synapses, and propagate ionic signals. Astrocytes influence neuronal physiology by responding to and releasing neurotransmitters, but the mechanisms that establish the close interaction between these cells are not defined. Here we use hippocampal neurons in culture to demonstrate that vasoactive intestinal polypeptide (VIP) promotes neuronal differentiation through activity-dependent neurotrophic factor (ADNF), a protein secreted by VIP-stimulated astroglia. ADNF is produced by glial cells and acts directly on neurons to promote glutamate responses and morphological development. ADNF causes secretion of neurotrophin 3 (NT-3), and both proteins regulate NMDA receptor subunit 2A (NR2A) and NR2B. These data suggest that the VIP–ADNF–NT-3 neuronal–glial pathway regulates glutamate responses from an early stage in the synaptic development of excitatory neurons and may also contribute to the known effects of VIP on learning and behavior in the adult nervous system.
Activity-Dependent Patterning of Retinogeniculate Axons Proceeds with a Constant Contribution from AMPA and NMDA Receptors
Authors: Hohnke Carsten D. , Oray Serkan , Sur Mriganka
Published: April 2018

Neural activity is critical for the refinement of neural circuitry during development, although the mechanisms involved in stabilizing appropriate connectivity remain unclear. It has been proposed that the insertion of AMPA receptors at synapses with only NMDA receptors (“silent synapses”) mediates this stabilization, leading to an increasing contribution from AMPA receptors as development proceeds. Here we show in a mammalian system known to undergo activity-dependent development [the segregation of retinal afferents into ON/OFF sublaminae in the ferret lateral geniculate nucleus (LGN)] that the refinement of the neural circuitry occurs in the presence of a constant functional contribution from AMPA and NMDA receptors. Although we detected a small number of silent synapses on LGN cells, their proportion did not decrease with age. The size and kinetics of NMDA-mediated spontaneous EPSCs (sEPSCs) were also stable over this period. Together with previous results reporting the stability of unitary AMPA-mediated EPSCs, the constancy of NMDA-mediated sEPSCs indicates an unchanging AMPA/NMDA contribution. Additionally, the CNQX-sensitivity did not increase for either sEPSCs or optic tract-evoked EPSCs. Likewise, the anatomical AMPA/NMDA ratio, as assayed by quantifying the colocalized expression of AMPA and NMDA receptor subunits, was fixed throughout ON/OFF sublamination. In particular, the colocalization of AMPA receptor subunits (GluR1 or GluR4) and NMDA receptor subunit NR1 opposite identified retinogeniculate terminals was stable during this period. These results add to the view of the population of retinogeniculate synapses as robustly stable or normalized during a period when retinogeniculate axons are undergoing dramatic activity-dependent refinement.
Intra-Accumbens Amphetamine Increases the Conditioned Incentive Salience of Sucrose Reward: Enhancement of Reward “Wanting” without Enhanced “Liking” or Response Reinforcement
Authors: Wyvell Cindy L. , Berridge Kent C.
Published: April 2018

Amphetamine microinjection into the nucleus accumbens shell enhanced the ability of a Pavlovian reward cue to trigger increased instrumental performance for sucrose reward in a pure conditioned incentive paradigm. Rats were first trained to press one of two levers to obtain sucrose pellets. They were separately conditioned to associate a Pavlovian cue (30 sec light) with free sucrose pellets. On test days, the rats received bilateral microinjection of intra-accumbens vehicle or amphetamine (0.0, 2.0, 10.0, or 20.0 μg/0.5 μl), and lever pressing was tested in the absence of any reinforcement contingency, while the Pavlovian cue alone was freely presented at intervals throughout the session. Amphetamine microinjection selectively potentiated the cue-elicited increase in sucrose-associated lever pressing, although instrumental responding was not reinforced by either sucrose or the cue during the test. Intra-accumbens amphetamine can therefore potentiate cue-triggered incentive motivation for reward in the absence of primary or secondary reinforcement. Using the taste reactivity measure of hedonic impact, it was shown that intra-accumbens amphetamine failed to increase positive hedonic reaction patterns elicited by sucrose (i.e., sucrose “liking”) at doses that effectively increase sucrose “wanting.” We conclude that nucleus accumbens dopamine specifically mediates the ability of reward cues to trigger “wanting” (incentive salience) for their associated rewards, independent of both hedonic impact and response reinforcement.
Using Fos Imaging in the Rat to Reveal the Anatomical Extent of the Disruptive Effects of Fornix Lesions
Authors: Vann Seralynne D. , Brown Malcolm W. , Erichsen Jonathan T. , Aggleton John P.
Published: April 2018

Activity of the immediate early gene c-foswas compared across hemispheres in rats with unilateral fornix lesions. To engage Fos production, rats first performed a radial arm maze task that is severely disrupted by bilateral fornix lesions. Using immunohistochemical techniques, Fos-positive cells were visualized and counted in 39 sites in both hemispheres. Fornix lesions led to a significant reduction in Fos in all ipsilateral hippocampal subfields, as well as the entorhinal cortex and most of the subicular complex. Other sites that showed reduced activity included the ipsilateral retrosplenial, anterior cingulate, and postrhinal cortices. Subcortical regions showing significant Fos decreases included the anterior thalamic nuclei, supramammillary nucleus, diagonal band of Broca, and lateral septum. Thus, the effects of fornix lesions extended beyond the hippocampal formation and included sites not directly innervated by the tract. These changes were nevertheless selective, as shown by the lack of hemispheric difference in any of the preselected control sites, the perirhinal cortex, or nucleus accumbens. Furthermore, there were no hemispheric differences in an additional group of animals with unilateral fornix lesions that were killed directly from the home cage. The location of Fos changes closely corresponded to those brain regions that when lesioned disrupt spatial working memory. Moreover, there was a correspondence between those brain regions that show increased Fos production in normal animals performing the radial arm maze task and those affected by fornix lesions. These results show that fornix transection has widespread, but selective, effects on a network of structures normally activated by spatial memory processes, with these effects extending beyond the hippocampal formation.
Postsynaptic Signaling via the μ-Opioid Receptor: Responses of Dorsal Horn Neurons to Exogenous Opioids and Noxious Stimulation
Authors: Trafton Jodie A. , Abbadie Catherine , Marek Kurt , Basbaum Allan I.
Published: April 2018

Although both pre- and postsynaptic mechanisms have been implicated in the analgesia produced by μ-opioids at the spinal cord, it is not known under what conditions these different controls come into play. Because the μ-opioid receptor (MOR) can be visualized in individual lamina II excitatory interneurons and internalizes into endosomes on ligand binding, we tested whether MOR internalization could be monitored and used to measure postsynaptic MOR signaling. To test whether endogenous opioids modulate these lamina II interneurons during noxious stimulation, we next assessed the magnitude of postsynaptic MOR internalization under a variety of nociceptive conditions.

As observed in other systems, we show that MOR internalization in dorsal horn interneurons is demonstrated readily in response to opioid ligands. The MOR internalization is dose-dependent, with a similar dose–response to that observed for opioid-induced increases in potassium conductance. We demonstrate that MOR internalization in lamina II neurons correlates precisely with the extent of analgesia produced by intrathecal DAMGO. These results suggest that MOR internalization provides a good marker of MOR signaling in the spinal cord and that postsynaptic MORs on lamina II interneurons likely participate in the analgesia that is produced by exogenous opioids. We found, however, that noxious stimuli, under normal or inflammatory conditions, did not induce MOR internalization. Thus, endogenous enkephalins and endomorphins, thought to be released during noxious peripheral stimuli, do not modulate nociceptive messages via postsynaptic MORs on lamina II interneurons. We suggest that any endogenous opioids that are released by noxious stimuli target presynaptic MORs or δ-opioid receptors.
Induction of Interleukin-6 by Depolarization of Neurons
Authors: Sallmann Svea , Jüttler Eric , Prinz Simone , Petersen Nicole , Knopf Udo , Weiser Thomas , Schwaninger Markus
Published: April 2018

Interleukin-6 (IL-6) has neuromodulatory and neuroprotective effectsin vivo. It is expressed in glial cells and neurons both under physiological conditions and in various neurological diseases. Although the expression of IL-6 in glia has been intensely investigated, little is known about the regulation of IL-6 production by neurons. Therefore, we investigated the regulation of IL-6 expression in neurons. Membrane depolarization raised IL-6 mRNA accumulation in primary cortical cells and the PC-12 cell line.In vivo, IL-6 mRNA in the brain increased significantly after epileptic seizures. To investigate IL-6 gene transcription, PC-12 cells were transfected with reporter gene constructs containing the human IL-6 promoter. Membrane depolarization raised IL-6 transcription twofold to fourfold. This increase could be blocked by lowering extracellular Ca2+levels or by inhibiting L-type Ca2+channels or Ca2+/calmodulin-dependent protein kinases. Internal mutations in various elements of the IL-6 promoter revealed the glucocorticoid response element (GRE) 2 to be a depolarization-responsive element. Although the GRE2 bound the glucocorticoid receptor (GR) and was stimulated by dexamethasone, the GR was not responsible for the effect of membrane depolarization because a consensus GRE did not mediate stimulation by membrane depolarization. Instead, another yet undefined factor that binds to the IL-6 GRE2 may mediate the response to membrane depolarization. These data demonstrate that the expression of IL-6 in neurons is regulated by membrane depolarization and suggest a novel Ca2+-responsive promoter element. Through this mechanism, IL-6 may function as a neuromodulator induced by neuronal activity.
Localization and Enhanced Current Density of the Kv4.2 Potassium Channel by Interaction with the Actin-Binding Protein Filamin
Authors: Petrecca Kevin , Miller David M. , Shrier Alvin
Published: April 2018

Kv4.2 potassium channels play a critical role in postsynaptic excitability. Immunocytochemical studies reveal a somatodendritic Kv4.2 expression pattern, with the channels concentrated mainly at dendritic spines. The molecular mechanism that underlies the localization of Kv4.2 to this subcellular region is unknown. We used the yeast two-hybrid system to identify the Kv4.2-associated proteins that are involved in channel localization. Here we demonstrate a direct interaction between Kv4.2 and the actin-binding protein, filamin. We show that Kv4.2 and filamin can be coimmunoprecipitated bothin vitroand in brain and that Kv4.2 and filamin share an overlapping expression pattern in the cerebellum and cultured hippocampal neurons. To examine the functional consequences of this interaction, we expressed Kv4.2 in filamin+and filamin−cells and performed immunocytochemical and electrophysiological analyses. Our results indicate that Kv4.2 colocalizes with filamin at filopodial roots in filamin+cells but shows a nonspecific expression pattern in filamin−cells, with no localization to filopodial roots. Furthermore, the magnitude of whole-cell Kv4.2 current density is ∼2.7-fold larger in filamin+cells as compared with these currents in filamin−cells. We propose that filamin may function as a scaffold protein in the postsynaptic density, mediating a direct link between Kv4.2 and the actin cytoskeleton, and that this interaction is essential for the generation of appropriate Kv4.2 current densities.
Disparity in Neurotransmitter Release Probability among Competing Inputs during Neuromuscular Synapse Elimination
Authors: Kopp Diane M. , Perkel David J. , Balice-Gordon Rita J.
Published: April 2018

Competition among the several motor axons transiently innervating neonatal muscle fibers results in an increasing disparity in the quantal content and synaptic territory of each competitor, culminating in the permanent loss of all but one axon from neuromuscular junctions. We asked whether differences in the probability of neurotransmitter release also contribute to the increasing disparity in quantal content among competing inputs, and when in the process of competition changes in release probability become apparent. To address these questions, intracellular recordings were made from dually innervated neonatal mouse soleus muscle fibers, and quantal content and paired-pulse facilitation were evaluated for each input. At short interpulse intervals, paired-pulse facilitation was significantly higher for the weaker input with the smaller quantal content than the stronger input with the larger quantal content. Because neurotransmitter release probability across all release sites is inversely related to the extent of facilitation observed after paired-pulse stimulation, this result suggests that release probability is lower for weak compared with strong inputs innervating the same junction. A disparity in the probability of neurotransmitter release thus contributes to the disparity in quantal content that occurs during synaptic competition. Together, this work suggests that an input incapable of sustaining a high release probability may be at a competitive disadvantage for synaptic maintenance.
Long-Term Nicotine Adaptation inCaenorhabditis elegansInvolves PKC-Dependent Changes in Nicotinic Receptor Abundance
Authors: Waggoner Laura E. , Dickinson Kari A. , Poole Daniel S. , Tabuse Yo , Miwa Johji , Schafer William R.
Published: April 2018

Chronic exposure to nicotine leads to long-term changes in both the abundance and activity of nicotinic acetylcholine receptors, processes thought to contribute to nicotine addiction. We have found that inCaenorhabditis elegans,prolonged nicotine treatment results in a long-lasting decrease in the abundance of nicotinic receptors that control egg-laying. In naive animals, acute exposure to cholinergic agonists led to the efficient stimulation of egg-laying, a response mediated by a nicotinic receptor functionally expressed in the vulval muscle cells. Overnight exposure to nicotine led to a specific and long-lasting change in egg-laying behavior, which rendered the nicotine-adapted animals insensitive to simulation of egg-laying by the nicotinic agonist and was accompanied by a promoter-independent reduction in receptor protein levels. Mutants defective in the genetpa-1, which encodes a homolog of protein kinase C (PKC), failed to undergo adaptation to nicotine; after chronic nicotine exposure they remained sensitive to cholinergic agonists and retained high levels of receptor protein in the vulval muscles. These results suggest that PKC-dependent signaling pathways may promote nicotine adaptation via regulation of nicotinic receptor synthesis or degradation.
NMDA and Glutamate Evoke Excitotoxicity at Distinct Cellular Locations in Rat Cortical NeuronsIn Vitro
Authors: Sinor Jeroo D. , Du Shen , Venneti Sriram , Blitzblau Rachel C. , Leszkiewicz Daniel N. , Rosenberg Paul A. , Aizenman Elias
Published: April 2018

The development of cortical neuronsin vivoandin vitrois accompanied by alterations in NMDA receptor subunit expression and concomitant modifications in the pharmacological profile of NMDA-activated ionic currents. For example, we observed that with decreasing NR2B/NR2A subunit expression ratio, the block of NMDA receptor-mediated whole-cell responses by the NR2B-selective antagonist haloperidol was also decreased. In mature cultures (>22 din vitro), however, NMDA responses obtained from excised nucleated macropatches, which comprised a large portion of the soma, remained strongly antagonized by haloperidol. These results suggest that in more mature neurons NR1/NR2B receptors appear to be preferentially expressed in the cell body. As predicted from the whole-cell recording pharmacological profile, NMDA-induced toxicity was largely unaffected by haloperidol in mature cultures. However, haloperidol effectively blocked glutamate toxicity in the same cultures, suggesting that the neurotoxic actions of this amino acid were mostly due to the activation of somatic NMDA receptors. In experiments in which the potency of glutamate toxicity was increased by the transport inhibitorl-trans-pyrrolidine-2,4-dicarboxylic acid, the neuroprotective effects of haloperidol were significantly diminished. This was likely because of the fact that glutamate, now toxic at much lower concentrations, was able to reach and activate dendritic receptors under these conditions. These results strongly argue that exogenous glutamate and NMDA normally induce excitotoxicity at distinct cellular locations in mature mixed neuronal cultures and that NR1/NR2B receptors remain an important component in the expression of glutamate, but not NMDA-induced excitotoxicity.
Brain-Stimulation Reward Thresholds Raised by an Antisense Oligonucleotide for the M5 Muscarinic Receptor Infused near Dopamine Cells
Authors: Yeomans John S. , Takeuchi Junichi , Baptista Marco , Flynn Donna D. , Lepik Karen , Nobrega Jose , Fulton James , Ralph Martin R.
Published: April 2018

Oligonucleotides targeting M5 muscarinic receptor mRNA were infused for 6 d into the ventral tegmental area of freely behaving rats trained to bar-press for lateral hypothalamic stimulation. The bar-pressing rate was determined at a range of frequencies each day to evaluate the effects of infusions on reward. M5 antisense oligonucleotide (oligo) infusions increased the frequency required for bar pressing by 48% over baseline levels, with the largest increases occurring after 4–6 d of infusion. Two control oligos had only slight effects (means of 5 and 11% for missense and sense oligos, respectively). After the infusion, the required frequency shifted back to baseline levels gradually over 1–5 d. Antisense oligo infusions decreased M5 receptors on the ipsilateral, but not the contralateral, side of the ventral tegmentum, as compared with a missense oligo. Therefore, M5 muscarinic receptors associated with mesolimbic dopamine neurons seem to be important in brain-stimulation reward.
Reliability of a Fly Motion-Sensitive Neuron Depends on Stimulus Parameters
Authors: Warzecha Anne-Kathrin , Kretzberg Jutta , Egelhaaf Martin
Published: April 2018

The variability of responses of sensory neurons constrains how reliably animals can respond to stimuli in the outside world. We show for a motion-sensitive visual interneuron of the fly that the variability of spike trains depends on the properties of the motion stimulus, although differently for different stimulus parameters. (1) The spike count variances of responses to constant and to dynamic stimuli lie in the same range. (2) With increasing stimulus size, the variance may slightly decrease. (3) Increasing pattern contrast reduces the variance considerably. For all stimulus conditions, the spike count variance is much smaller than the mean spike count and does not depend much on the mean activity apart from very low activities. Using a model of spike generation, we analyzed how the spike count variance depends on the membrane potential noise and the deterministic membrane potential fluctuations at the spike initiation zone of the neuron. In a physiologically plausible range, the variance is affected only weakly by changes in the dynamics or the amplitude of the deterministic membrane potential fluctuations. In contrast, the amplitude and dynamics of the membrane potential noise strongly influence the spike count variance. The membrane potential noise underlying the variability of the spike responses in the motion-sensitive neuron is concluded to be affected considerably by the contrast of the stimulus but by neither its dynamics nor its size.
Learning of Visuomotor Transformations for Vectorial Planning of Reaching Trajectories
Authors: Krakauer John W. , Pine Zachary M. , Ghilardi Maria-Felice , Ghez Claude
Published: April 2018

The planning of visually guided reaches is accomplished by independent specification of extent and direction. We investigated whether this separation of extent and direction planning for well practiced movements could be explained by differences in the adaptation to extent and directional errors during motor learning. We compared the time course and generalization of adaptation with two types of screen cursor transformation that altered the relationship between hand space and screen space. The first was a gain change that induced extent errors and required subjects to learn a new scaling factor. The second was a screen cursor rotation that induced directional errors and required subjects to learn new reference axes. Subjects learned a new scaling factor at the same rate when training with one or multiple target distances, whereas learning new reference axes took longer and was less complete when training with multiple compared with one target direction. After training to a single target, subjects were able to transfer learning of a new scaling factor to previously unvisited distances and directions. In contrast, generalization of rotation adaptation was incomplete; there was transfer across distances and arm configurations but not across directions. Learning a rotated reference frame only occurred after multiple target directions were sampled during training. These results suggest the separate processing of extent and directional errors by the brain and support the idea that reaching movements are planned as a hand-centered vector whose extent and direction are established via learning a scaling factor and reference axes.
Projection Neurons with Shared Cotransmitters Elicit Different Motor Patterns from the Same Neural Circuit
Authors: Wood Debra E. , Stein Wolfgang , Nusbaum Michael P.
Published: April 2018

Specificity in the actions of different modulatory neurons is often attributed to their having distinct cotransmitter complements. We are assessing the validity of this hypothesis with the stomatogastric nervous system of the crabCancer borealis.In this nervous system, the stomatogastric ganglion (STG) contains a multifunctional network that generates the gastric mill and pyloric rhythms. Two identified projection neurons [modulatory proctolin neuron (MPN) and modulatory commissural neuron 1 (MCN1)] that innervate the STG and modulate these rhythms contain GABA and the pentapeptide proctolin, but only MCN1 containsCancer borealistachykinin-related peptide (CabTRP Ia). Selective activation of each projection neuron elicits different rhythms from the STG. MPN elicits only a pyloric rhythm, whereas MCN1 elicits a distinct pyloric rhythm as well as a gastric mill rhythm. We tested the degree to which CabTRP Ia distinguishes the actions of MCN1 and MPN. To this end, we used the tachykinin receptor antagonist Spantide I to eliminate the actions of CabTRP Ia. With Spantide I present, MCN1 no longer elicited the gastric mill rhythm and the resulting pyloric rhythm was changed. Although this rhythm was more similar to the MPN-elicited pyloric rhythm, these rhythms remained different. Thus, CabTRP Ia partially confers the differences in rhythm generation resulting from MPN versus MCN1 activation. This result suggests that different projection neurons may use the same cotransmitters differently to elicit distinct pyloric rhythms. It also supports the hypothesis that different projection neurons use a combination of strategies, including using distinct cotransmitter complements, to elicit different outputs from the same neuronal network.
Involvement of the Secretory Pathway for AMPA Receptors in NMDA-Induced Potentiation in Hippocampus
Authors: Broutman Greg , Baudry Michel
Published: April 2018

A chemical form of synaptic potentiation was produced with a brief bath application of NMDA to rat hippocampal slices. Two methods were used to assess changes in membrane-bound AMPA receptors. Traditional subcellular fractionation was used to isolate synaptic membranes; alternatively, membrane receptors were cross-linked with the membrane-impermeable reagent bis(sulfosuccinimidyl) suberate, and levels of nonmembrane receptors were determined. In both cases, Western blots were used to determine the content of receptor subunits in various subcellular fractions. NMDA-induced potentiation was associated with increased levels of glutamate receptor 1 (GluR1) and GluR2/3 subunits of AMPA receptors in synaptic membrane preparations, whereas no change was observed in whole homogenates. Both KN-62, an inhibitor of calcium/calmodulin kinase, and calpain inhibitor III, a calpain inhibitor, inhibited NMDA-induced potentiation and changes in GluR1 and GluR2/3 subunits of AMPA receptors. Brefeldin A (BFA) inhibits protein trafficking between the Golgi apparatus and cell membranes. Pretreatment of hippocampal slices with BFA significantly decreased NMDA-induced potentiation and completely prevented an NMDA-induced increase in GluR1 levels in membrane fractions. Thus, the levels of GluR1 and GluR2/3 subunits of AMPA receptors are rapidly upregulated in synaptic membranes under conditions associated with potentiation of synaptic responses, and this upregulation requires a functional secretory pathway.
Structure and Dynamics of the GABA Binding Pocket: A Narrowing Cleft that Constricts during Activation
Authors: Wagner David A. , Czajkowski Cynthia
Published: April 2018

Photo-affinity labeling and mutagenesis studies have identified several amino acids that may contribute to the ligand binding domains of ligand-gated ion channels. These types of studies, however, only generate a one-dimensional, static description of binding site structure. In this study, we used the substituted cysteine accessibility method not only to identify binding pocket residues but also to elicit information about binding site dynamics and structure. Residues surrounding the putative loop C ligand binding domain of the GABAAreceptor (β2V199 to β2S209) were individually mutated to cysteine, and the mutant subunits were coexpressed with wild-type α1subunits inXenopusoocytes.N-biotinylaminoethyl methanethiosulfonate (MTSEA-biotin) reacts with cysteines introduced at positions G203, S204, Y205, P206, R207, and S209. This accessibility pattern is not consistent with either an α-helix or β-strand. Instead, G203–S209 seems to form a water-accessible extended coil, whereas V199–T202 appears to buried in the protein or membrane. Coapplication of either GABA or the competitive antagonist SR-95531 significantly slows MTSEA-biotin modification of cysteines introduced at positions S204, Y205, R207, and S209, demonstrating that these residues line and face into the GABA binding pocket. MTSEA-biotin reaction rates reveal a steep accessibility gradient from G203–S209 and suggests that the binding pocket is a deep narrowing cleft. Pentobarbital activation of the receptor significantly slows MTSEA-biotin modification of cysteines at S204, R207, and S209, suggesting that the binding site may constrict during gating.
Vitamin D Hormone Confers Neuroprotection in Parallel with Downregulation of L-Type Calcium Channel Expression in Hippocampal Neurons
Authors: Brewer Lawrence D. , Thibault Veronique , Chen Kuey-Chu , Langub Moises C. , Landfield Philip W. , Porter Nada M.
Published: April 2018

Although vitamin D hormone (VDH; 1,25-dihydroxyvitamin D3), the active metabolite of vitamin D, is the major Ca2+-regulatory steroid hormone in the periphery, it is not known whether it also modulates Ca2+homeostasis in brain neurons. Recently, chronic treatment with VDH was reported to protect brain neurons in both aging and animal models of stroke. However, it is unclear whether those actions were attributable to direct effects on brain cells or indirect effects mediated via peripheral pathways. VDH modulates L-type voltage-sensitive Ca2+channels (L-VSCCs) in peripheral tissues, and an increase in L-VSCCs appears linked to both brain aging and neuronal vulnerability. Therefore, we tested the hypothesis that VDH has direct neuroprotective actions and, in parallel, targets L-VSCCs in hippocampal neurons.

Primary rat hippocampal cultures, treated for several days with VDH, exhibited a U-shaped concentration–response curve for neuroprotection against excitotoxic insults: lower concentrations of VDH (1–100 nm) were protective, but higher, nonphysiological concentrations (500–1000 nm) were not. Parallel studies using patch-clamp techniques found a similar U-shaped curve in which L-VSCC current was reduced at lower VDH concentrations and increased at higher (500 nm) concentrations. Real-time PCR studies demonstrated that VDH monotonically downregulated mRNA expression for the α1Cand α1Dpore-forming subunits of L-VSCCs. However, 500 nmVDH also nonspecifically reduced a range of other mRNA species. Thus, these studies provide the first evidence of (1) direct neuroprotective actions of VDH at relatively low concentrations, and (2) selective downregulation of L-VSCC expression in brain neurons at the same, lower concentrations.
Heterogeneity of Hippocampal GABAAReceptors: Regulation by Corticosterone
Authors: Orchinik Miles , Carroll Steven S. , Li Yi-Huey , McEwen Bruce S. , Weiland Nancy G.
Published: April 2018

Chronic stressors produce changes in hippocampal neurochemistry, neuronal morphology, and hippocampal-dependent learning and memory processes. In rats, stress-induced changes in CA3 apical dendritic structure are mediated by corticosterone (CORT) acting, in part, on excitatory amino acid neurotransmission. CORT also alters GABA-mediated inhibitory neurotransmission, so the GABAAreceptor system may also contribute to dendritic remodeling and other stress-related changes in hippocampal function. A previous study indicated that chronic CORT treatment produces complex changes in GABAAreceptor subunit mRNA levels, so we hypothesized that CORT alters the pharmacological properties of hippocampal GABAAreceptors. To test this, adult male rats were treated with CORT or vehicle pellets for 10 d, after which we quantified [35S]t-butylbicyclophosphorothionate ([35S]TBPS) and [3H]flunitrazepam binding to GABAAreceptors usingin vitroreceptor autoradiography. Pharmacological properties of receptors were assessed by examining the allosteric regulation of binding at both sites by GABA and 5α-pregnane-3α,21-diol-20-one (THDOC), an endogenous anxiolytic steroid. We found striking regional differences in the modulation of [35S]TBPS binding, particularly between strata radiatum and strata oriens, suggesting a functional heterogeneity among hippocampal GABAAreceptors even within the apical versus basal dendrites of pyramidal neurons. Furthermore, we found that CORT treatment decreased the negative modulation of hippocampal [35S]TBPS binding by both GABA and THDOC and increased the enhancement of [3H]flunitrazepam binding by GABA and THDOC in the dentate gyrus. Together, these data suggest that prolonged exposure to stress levels of corticosteroids may alter hippocampal inhibitory tone by regulating the pharmacological properties of GABAAreceptors in discrete dendritic subfields.
Three Pairs of Cysteine Residues Mediate Both Redox and Zn2+Modulation of the NMDA Receptor
Authors: Choi Yun-Beom , Chen Huei-Sheng Vincent , Lipton Stuart A.
Published: April 2018

NMDA receptor activity is modulated by various compounds, including sulfhydryl redox agents and Zn2+. In addition to a slow and persistent component of redox modulation common to all NMDA receptors, NR1/NR2A receptors uniquely have a rapid and reversible component that has been variously attributed to redox or Zn2+effects. Here we show that this rapid modulatory effect can be described by two time constants with relatively fast (∼6 sec) and intermediate (60 sec) half lives, and it is likely to be attributable to both redox agents and Zn2+. Using site-directed mutagenesis, we identified three pairs of cysteine residues that underlie the various kinetic components of redox modulation of NMDA-evoked currents inXenopusoocytes expressing NR1/NR2A receptors: (1) Cys 87 and Cys 320 in NR2A underlie the fast component, (2) Cys 79 and Cys 308 in NR1 underlie the intermediate component, and (3) Cys 744 and Cys 798 in NR1 underlie the persistent component. Mutation of these redox-sensitive cysteine residues also affects high-affinity, voltage-independent Zn2+inhibition that is specific to NR1/NR2A receptors. Exposure to methanethiosulfonate agents that modify cysteine residues did not block the Zn2+inhibition. Thus, these cysteine residues do not appear to coordinate Zn2+directly. Instead, the redox status of these cysteine residues may modulate the sensitivity of the receptor to Zn2+.
Quantitative Relationship between Transmitter Release and Calcium Current at the Calyx of Held Synapse
Authors: Sakaba Takeshi , Neher Erwin
Published: April 2018

A newly developed deconvolution method (Neher and Sakaba, 2001) allowed us to resolve the time course of neurotransmitter release at the calyx of Held synapse and to quantify some basic aspects of transmitter release. First, we identified a readily releasable pool (RRP) of synaptic vesicles. We found that the size of the RRP, when tested with trains of strong stimuli, was constant regardless of the exact stimulus patterns, if stimuli were confined to a time interval of ∼60 msec. For longer-lasting stimulus patterns, recruitment of new vesicles to the RRP made a substantial contribution to the total release. Second, the cooperativity of transmitter release as a function of Ca2+current was estimated to be 3–4, which confirmed previous results (Borst and Sakmann, 1999; Wu et al., 1999). Third, an initial small Ca2+influx increased the efficiency of Ca2+currents in subsequent transmitter release. This type of facilitation was blocked by a high concentration of EGTA (0.5 mm). Fourth, the release rates of synaptic vesicles at this synapse turned out to be heterogeneous: once a highly Ca2+-sensitive population of vesicles was consumed, the remaining vesicles released at lower rates. These components of release were more clearly separated in the presence of 0.5 mmEGTA, which prevented the buildup of residual Ca2+. Conversely, raising the extracellular Ca2+concentration facilitated the slower population such that its release characteristics became more similar to those of the faster population under standard conditions. Heterogeneous release probabilities are expected to support the maintenance of synaptic transmission during high-frequency stimulation.
Expression of the Kv3.1 Potassium Channel in the Avian Auditory Brainstem
Authors: Parameshwaran Suchitra , Carr Catherine E. , Perney Teresa M.
Published: April 2018

The Shaw-like potassium channel Kv3.1, a delayed rectifier with a high threshold of activation, is expressed in the time coding nuclei of the bird auditory brainstem. In both barn owls and chickens, Kv3.1 mRNA was expressed in the cochlear nucleus magnocellularis (NM) and the nucleus laminaris (NL). Western blot analysis showed that an antibody raised against the synthetic peptide sequence of rat Kv3.1 (rKv3.1) specifically recognized the same 92 kDa protein bands in both rat and chicken synaptosomal preparations. Immunohistochemical analyses using this anti-rKv3.1 antibody revealed a prominent gradient in Kv3.1 immunoreactivity along the tonotopic axis of the barn owl NM and NL and a less prominent gradient in the chicken. The precise localization of the Kv3.1 immunoproduct was resolved by electron microscopy. In both the owl and the chicken, Kv3.1 was targeted postsynaptically in NM and NL. The major difference in localization of Kv3.1 protein between the two birds was the expression of Kv3.1 in the NM axons and terminals in the region of the barn owl NL. This location of Kv3.1 channels supports its postulated function in reducing the width of action potentials as they invade the presynaptic terminal. The presynaptic localization may be a specialization for enabling neurons in owl NM to transmit high-frequency temporal information with little jitter.
Abnormalities of Male-Specific FRU Protein and Serotonin Expression in the CNS offruitlessMutants inDrosophila
Authors: Lee Gyunghee , Hall Jeffrey C.
Published: April 2018

Thefruitlessgene inDrosophilaproduces male-specific protein (FRUM) involved in the control of courtship. FRUMspatial and temporal patterns were examined infrumutants that exhibit aberrant male courtship. Chromosome breakpoints at the locus eliminated FRUM. Homozygous viable mutants exhibited an intriguing array of defects. Infru1males, there were absences of FRUM-expressing neuronal clusters or stained cells within certain clusters, reductions of signal intensities in others, and ectopic FRUMexpression in novel cells.fru2males exhibited an overall decrement of FRUMexpression in all neurons normally expressing the gene.fru4andfrusatmutants only produced FRUMin small numbers of neurons at extremely low levels, and no FRUMsignals were detected infru3males. This array of abnormalities was inferred to correlate with the varying behavioral defects exhibited by these mutants. Such abnormalities include courtship among males, which has been hypothesized to involve anomalies of serotonin (5-HT) function in the brain. However, double-labeling uncovered no coexpression of FRUMand 5-HT in brain neurons. Yet, a newly identified set of sexually dimorphic FRUM/5-HT-positive neurons was identified in the abdominal ganglion of adult males. These sexually dimorphic neurons (s-Abg) project toward regions of the abdomen involved in male reproduction. The s-Abg neurons and the proximal extents of their axons were unstained or absent in wild-type females and exhibited subnormal or no 5-HT immunoreactivity in certainfru-mutant males, indicating thatfruitlesscontrols the formation of these cells or 5-HT production in them.