bluuebunny/crossref_metadata_2025 huggingface dataset:
Parkinson-Like Neurodegeneration Induced by Targeted Overexpression of α-Synuclein in the Nigrostriatal System
Authors: Kirik Deniz , Rosenblad Carl , Burger Corinna , Lundberg Cecilia , Johansen Teit E. , Muzyczka Nicholas , Mandel Ronald J. , Björklund Anders
Published: April 2018

Recombinant adeno-associated viral vectors display efficient tropism for transduction of the dopamine neurons of the substantia nigra. Taking advantage of this unique property of recombinant adeno-associated viral vectors, we expressed wild-type and A53T mutated human α-synuclein in the nigrostriatal dopamine neurons of adult rats for up to 6 months. Cellular and axonal pathology, including α-synuclein-positive cytoplasmic inclusions and swollen, dystrophic neurites similar to those seen in brains from patients with Parkinson's disease, developed progressively over time. These pathological alterations occurred preferentially in the nigral dopamine neurons and were not observed in other nondopaminergic neurons transduced by the same vectors. The degenerative changes were accompanied by a loss of 30–80% of the nigral dopamine neurons, a 40–50% reduction of striatal dopamine, and tyrosine hydroxylase levels that was fully developed by 8 weeks. Significant motor impairment developed in those animals in which dopamine neuron cell loss exceeded a critical threshold of 50–60%. At 6 months, signs of cell body and axonal pathology had subsided, suggesting that the surviving neurons had recovered from the initial insult, despite the fact that α-synuclein expression was maintained at a high level. These results show that nigral dopamine neurons are selectively vulnerable to high levels of either wild-type or mutant α-synuclein, pointing to a key role for α-synuclein in the pathogenesis of Parkinson's disease. Targeted overexpression of α-synuclein in the nigrostriatal system may provide a new animal model of Parkinson's disease that reproduces some of the cardinal pathological, neurochemical, and behavioral features of the human disease.
Electrotonically Mediated Oscillatory Patterns in Neuronal Ensembles: AnIn VitroVoltage-Dependent Dye-Imaging Study in the Inferior Olive
Authors: Leznik Elena , Makarenko Vladimir , Llinás Rodolfo
Published: April 2018

Spatiotemporal profiles of ensemble subthreshold neuronal oscillation were studied in brainstem slices using high-speed voltage-sensitive dye imaging. After local electrical stimuli, the overall voltage profile demonstrated coherent oscillatory waves that spread over the inferior olive (IO). These oscillations were also observed in concurrently obtained intracellular recordings from IO neurons. Over the first few seconds after the stimuli, the optically recorded oscillations clustered into coherent groups comprising hundreds of neurons. Statistical analysis of the spatial profiles of these clusters revealed size fluctuation around stable core regions that were surrounded by a rim the diameter of which varied in time during the oscillation period.

The neuronal ensemble oscillations were calcium derived and had an average frequency range of 1–7 Hz. This rhythmic response demonstrated a different spatiotemporal distribution in the presence of picrotoxin, which induced the merging of neuronal clusters into larger areas of coherent activity. The possibility that such clustering is a consequence of intrinsic oscillations in ensembles of coupled neurons was tested using mathematical modeling.
The Physiological Role of 5-HT2AReceptors in Working Memory
Authors: Williams Graham V. , Rao Srinivas G. , Goldman-Rakic Patricia S.
Published: April 2018

Dorsolateral prefrontal cortex has an essential role in the cognitive process of working memory, dysfunction of which is considered to be a core deficit in schizophrenia. Although this cortical region is densely innervated with 5-HT2Areceptors to which atypical antipsychotic drugs bind with high affinity, little is known of the influence of this serotonin receptor subtype on prefrontal function. We addressed this issue by examining the effects of iontophoresis of selective receptor ligands on prefrontal neurons possessing spatially tuned delay activity, or “memory fields,” in monkeys performing a delayed-response task. Memory fields of putative pyramidal cells were attenuated by iontophoresis of 5-HT2Aantagonists, which primarily produced a reduction in delay activity for preferred target locations. Conversely, 5-HT2Astimulation by α-methyl-5-HT or 5-HT itself, accentuated the spatial tuning of these neurons by producing a modest increase in activity for preferred target locations and/or a reduction in activity for nonpreferred locations. The agonist effects could be reversed by the selective antagonist MDL100,907, and were dose-dependent, such that high levels attenuated spatial tuning by profoundly reducing delay activity. A role for feedforward inhibitory circuitry in these effects was supported by the finding that 5-HT2Ablockade also attenuated the memory fields of putative interneurons. We conclude that prefrontal 5-HT2Areceptors have a hitherto unrecognized role in the cognitive function of working memory, which involves actions at both excitatory and inhibitory elements within local circuitry.
Synchronized Neuronal Discharge in the Basal Ganglia of Parkinsonian Patients Is Limited to Oscillatory Activity
Authors: Levy Ron , Hutchison William D. , Lozano Andres M. , Dostrovsky Jonathan O.
Published: April 2018

It has been proposed that an increase in synchronization between neurons in the basal ganglia contributes to the clinical features of Parkinson's disease (PD). To examine this hypothesis, we looked for correlations in the discharge activity of pairs of neurons in the globus pallidus internus (GPi), globus pallidus externus (GPe), and the substantia nigra pars reticulata (SNr). Recordings were performed in PD patients undergoing functional stereotactic mapping for pallidotomy (eight patients) or subthalamic nucleus deep brain stimulation (four patients). A double-microelectrode setup was used to simultaneously record from neurons separated by distances as small as 250 μm. In the five pallidotomy patients without limb tremor during the procedure, none of the 73 GPi pairs and 15 GPe pairs displayed synchronous activity. In the three pallidotomy patients with limb tremor, 6 of 21 GPi pairs and 5 of 29 GPe pairs displayed oscillatory synchronization in the frequency range of the ongoing limb tremor (3–6 Hz) or at higher frequencies (15–30 Hz). Synchronized activity was not observed in the SNr (10 pairs). The findings indicate that oscillatory synchronization between pairs of GPi or GPe neurons is found in patients with limb tremor. These results also suggest that overt neuronal synchronization, which may be attributable to an increase in direct synaptic connections or common collateral afferent inputs, is not present in the basal ganglia of patients with PD.
Cortical Synaptic Arrangements of the Third Visual Pathway in Three Primate Species:Macaca mulatta, Saimiri sciureus, andAotus trivirgatus
Authors: Shostak Yuri , Ding Yuchuan , Mavity-Hudson Julia , Casagrande Vivien A.
Published: April 2018

The koniocellular (K) pathway is one of three pathways from the lateral geniculate nucleus (LGN) to primate visual cortex (V1). K pathway projections to the cytochrome oxidase (CO) blobs of V1 suggest involvement in chromatic processing given reports that the CO blobs in diurnal primates contain cells selective for color. K LGN layers and CO blobs, however, are also well developed in nocturnal primates such as owl monkeys, which are likely to be color blind. Thus, the K pathway plays either different roles in different species or some as yet unidentified common role(s). Because synaptic arrangements underlie functional mechanisms, the purpose of this investigation was to compare the synaptic circuitry related to the K pathway within the CO blobs of two diurnal primates (macaque monkeys and squirrel monkeys) and one nocturnal primate (owl monkey). Presynaptic K axons were labeled with wheat germ agglutinin-HRP, and presynaptic and postsynaptic profiles in CO blobs were identified with post-embedding immunocytochemistry for GABA and glutamate. In all three species, K axon terminals are glutamatergic and larger than local axon terminals, suggesting that they have a greater impact on postsynaptic CO blob targets than signals arriving via layer IV from the P or M pathways. A greater proportion of K axons, however, synapse with larger glutamatergic shafts in the diurnal monkeys than in the nocturnal owl monkey, perhaps reflecting the importance of color within the K pathway of these diurnal species. Alternatively, the loss of color vision in the owl monkey could impact K pathway circuitry earlier in the pathway. The basic similarities between K axon circuitry within the CO blobs of the three primate species examined also could indicate that this pathway plays some common role or roles across species.
Natural Stimulation of the Nonclassical Receptive Field Increases Information Transmission Efficiency in V1
Authors: Vinje William E. , Gallant Jack L.
Published: April 2018

We have investigated how the nonclassical receptive field (nCRF) affects information transmission by V1 neurons during simulated natural vision in awake, behaving macaques. Stimuli were centered over the classical receptive field (CRF) and stimulus size was varied from one to four times the diameter of the CRF. Stimulus movies reproduced the spatial and temporal stimulus dynamics of natural vision while maintaining constant CRF stimulation across all sizes. In individual neurons, stimulation of the nCRF significantly increases the information rate, the information per spike, and the efficiency of information transmission. Furthermore, the population averages of these quantities also increase significantly with nCRF stimulation. These data demonstrate that the nCRF increases the sparseness of the stimulus representation in V1, suggesting that the nCRF tunes V1 neurons to match the highly informative components of the natural world.
Generation of Functional Inhibitory Neurons in the Adult Rat Hippocampus
Authors: Liu ShuHong , Wang Jian , Zhu DongYa , Fu YangPing , Lukowiak Ken , Lu YouMing
Published: April 2018

Several thousand new neurons are produced each day in the adult mammalian hippocampus, among which only excitatory granule cells (GCs) have thus far been identified. In the present study, we used mutant Semliki Forest Virus vectors to express enhanced green fluorescent protein in the hippocampus, and observed that ∼14% of newly generated neurons in the dentate gyrus of adult rats are GABAergic basket cells (BCs). With the use of double whole-cell patch-clamp recordings from BC–GC pairs in hippocampal slices, we demonstrate that newly generated BCs in the dentate gyrus form inhibitory synapses with principal GCs. These data show for the first time that functional inhibitory neurons are recruited in the dentate gyrus of adult rats.
Ca2+Signaling in Mouse Cortical Neurons Studied by Two-Photon Imaging and Photoreleased Inositol Triphosphate
Authors: Stutzmann Grace E. , LaFerla Frank M. , Parker Ian
Published: April 2018

IP3-mediated Ca2+release is a crucial neuronal signaling mechanism that has not been extensively characterized in the mammalian cerebral cortex. We used two-photon, video-rate microscopy to image Ca2+signals evoked by photoreleased IP3in pyramidal neurons of mouse prefrontal cortex. Ca2+responses to photoreleased IP3varied greatly between different neurons; however, within IP3-responsive neurons, the soma invariably showed highest sensitivity, with signals increasing nonlinearly with [IP3]. Responses to paired photorelease displayed inhibition, whereas IP3-evoked Ca2+liberation was potentiated by Ca2+entry during action potentials and vice versa. IP3-mediated Ca2+signals strongly inhibited spike firing through activation of K+membrane conductance. Metabotropic signaling via the phosphoinositide pathway thus serves as a powerful and sustained modulator of excitability in cortical neurons and displays complex reciprocal interactions between electrical and chemical signals.
Accelerated Hippocampal Spreading Depression and Enhanced Locomotory Activity in Mice with Astrocyte-Directed Inactivation of Connexin43
Authors: Theis Martin , Jauch Regina , Zhuo Lang , Speidel Dina , Wallraff Anke , Döring Britta , Frisch Christian , Söhl Goran , Teubner Barbara , Euwens Carsten , Huston Joseph , Steinhäuser Christian , Messing Albee , Heinemann Uwe , Willecke Klaus
Published: April 2018

Using a human glial fibrillary acidic protein (hGFAP) promoter-drivencretransgene, we have achieved efficient inactivation of a floxedconnexin43(Cx43) gene in astrocytes of adult mice. The loss of Cx43 expression was monitored in a cell-autonomous manner via conditional replacement of the Cx43-coding region by alacZreporter gene. In this way, we bypassed the early postnatal lethality previously reported for Cx43 null mice and characterized the phenotypic consequences of Cx43 deficiency in the CNS. Mice lacking Cx43 in astrocytes were viable and showed no evidence of either neurodegeneration or astrogliosis. Spreading depression (SD) is a pathophysiological phenomenon observed in the CNS that is characterized by a propagating wave of depolarization followed by neuronal inactivation. Inhibitors of gap junctional communication have previously been shown to block initiation and propagation of SD. In contrast, we observed an increase in the velocity of hippocampal SD in the stratum radiatum of mice lacking Cx43 in astrocytes. In the same brain subregion, dye-coupling experiments revealed a reduction in overall astrocytic intercellular communication by ∼50%. This strongly suggests separate and different neuronal and glial contributions of gap junctional intercellular communication to SD. Concomitant with increased velocity of spreading depression, we observed enhanced locomotory activity in mice lacking Cx43 in astrocytes.
Surface Expression of GluR-D AMPA Receptor Is Dependent on an Interaction between Its C-Terminal Domain and a 4.1 Protein
Authors: Coleman Sarah K. , Cai Chunlin , Mottershead David G. , Haapalahti Jukka-Pekka , Keinänen Kari
Published: April 2018

Dynamic regulation of the number and activity of AMPA receptors is believed to underlie many forms of synaptic plasticity and is presumably mediated by specific protein–protein interactions involving the C-terminal domain of the receptor. Several proteins interacting with the C-terminal tails of the glutamate receptor (GluR)-A and GluR-B subunits have been identified and implicated in the regulation of endocytosis and exocytosis, clustering, and anchoring of AMPA receptors to the cytoskeleton. In contrast, little is known of the molecular interactions of the GluR-D subunit, or of the mechanisms regulating the traffic of GluR-D-containing AMPA receptors. We analyzed the subcellular localization of homomeric GluR-D receptors carrying C-terminal deletions in transfected human embryonic kidney (HEK) 293 cells and in primary neurons by immunofluorescence microscopy and ELISA. A minimal requirement for a 14-residue cytoplasmic segment for the surface expression of homomeric GluR-D receptors was identified. Previously, a similar region in the GluR-A subunit was implicated in an interaction with 4.1 family proteins. Coimmunoprecipitation demonstrated that GluR-D associated with 4.1 protein(s) in both HEK293 cells and rat brain. Moreover, glutathioneS-transferase pull-down experiments showed that the same 14-residue segment is critical for 4.1 binding to GluR-A and GluR-D. Point mutations within this segment dramatically decreased the surface expression of GluR-D in HEK293 cells, with a concomitant loss of the 4.1 interaction. Our findings demonstrate a novel molecular interaction for the GluR-D subunit and suggest that the association with the 4.1 family protein(s) plays an essential role in the transport to and stabilization of GluR-D-containing AMPA receptors at the cell surface.
Stimulation of the Calcitonin Gene-Related Peptide Enhancer by Mitogen-Activated Protein Kinases and Repression by an Antimigraine Drug in Trigeminal Ganglia Neurons
Authors: Durham Paul L. , Russo Andrew F.
Published: April 2018

Calcitonin gene-related peptide (CGRP) is involved in the underlying pathophysiology of all vascular headaches, including migraines. Elevated levels of CGRP during migraine are restored to normal coincident with headache relief after treatment with the antimigraine drug sumatriptan. We have used primary cultures of trigeminal neurons under conditions simulating migraine pathology and therapy to study the mechanisms controlling the CGRP promoter. Using reporter genes in transient transfection assays, we demonstrate that an 18 bp enhancer containing a helix–loop–helix element is both necessary and sufficient for full promoter activity. NGF treatment and cotransfection with an upstream activator of the extracellular signal-regulated MAP kinases (MAPKs) activated the enhancer. Treatment with sumatriptan repressed NGF- and MAPK-stimulated CGRP promoter activity. Repression was also observed using a synthetic MAPK-responsive reporter gene. Sumatriptan regulation of CGRP gene expression did not couple to a Gi/Gopathway, but rather caused a prolonged increase in intracellular calcium. The importance of the prolonged calcium signal in repression of MAPK activity was demonstrated by using the ionophore ionomycin to mimic sumatriptan action. We propose that activation of MAPK pathways may increase CGRP gene expression during migraine, and that sumatriptan can diametrically oppose that activation via a prolonged elevation of intracellular calcium.
D5 (Not D1) Dopamine Receptors Potentiate Burst-Firing in Neurons of the Subthalamic Nucleus by Modulating an L-Type Calcium Conductance
Authors: Baufreton Jérôme , Garret Maurice , Rivera Alicia , de la Calle Adélaïda , Gonon François , Dufy Bernard , Bioulac Bernard , Taupignon Anne
Published: April 2018

Dopamine is a crucial factor in basal ganglia functioning. In current models of basal ganglia, dopamine is postulated to act on striatal neurons. However, it may also act on the subthalamic nucleus (STN), a key nucleus in the basal ganglia circuit. The data presented here were obtained in brain slices using whole-cell patch clamp. They reveal that D5 dopamine receptors strengthen electrical activity in the subset of subthalamic neurons endowed with burst-firing capacity, resulting in longer discharges of spontaneous or evoked bursts.

To distinguish between D1 and D5 subtypes, the action of agonists in the D1/D5 receptor family was first investigated on rat subthalamic neurons. Single-cell reverse transcription-PCR profiling showed that burst-competent neurons only expressed D5 receptors. Accordingly, receptors localized in postsynaptic membranes within the STN were labeled by a D5-specific antibody. Second, agonists in the D1/D5 family were tested in mouse brain slices. It was found that these agonists were active in D1 receptor knock-out mice in a similar way to wild-type mice or rats. This proved that D5 rather than D1 receptors were involved. Pharmacological tools (dihydropyridines, ω-conotoxins, and calciseptine) were used to identify the target of D5 receptors as an L-type channel. This was reached via G-protein and protein kinase A. The action of dopamine on D5 receptors therefore shapes neuronal activity. It contributes to normal information processing in basal ganglia outside striatum. This finding may be useful in drug therapy for various disorders involving changes in STN activity, such as Parkinson's disease and related disorders.
Involvement of Actin Polymerization in Vesicle Recruitment at the Calyx of Held Synapse
Authors: Sakaba Takeshi , Neher Erwin
Published: April 2018

Depletion and replenishment of pools of synaptic vesicles are important determinants of short-term synaptic plasticity, but the underlying molecular mechanisms are not yet clear. As a first step toward understanding the process of vesicle recruitment, we have applied various specific agents directly to the presynaptic terminal of the calyx of Held synapse. Here we show that the nonhydrolyzable ATP analog ATP-γS retards the recovery from vesicle pool depletion, as does latrunculin A. Phalloidin has no effects on recovery, suggesting that dynamic actin reorganization is not necessary. Unexpectedly, neitherN-ethylmaleimide nor staurosporine affected the recovery, calling into question the role ofN-ethylmaleimide-sensitive factor and protein kinases. The results suggest that intact actin polymerization is involved in vesicle recruitment.
Nonrenewal of Neurons in the Cerebral Neocortex of Adult Macaque Monkeys
Authors: Koketsu Daisuke , Mikami Akichika , Miyamoto Yusei , Hisatsune Tatsuhiro
Published: April 2018

The concept that, after developmental periods, neocortical neurons become numerically stable and are normally nonrenewable has been challenged by a report of continuous neurogenesis in the association areas of the cerebral cortex in the adult Macaque monkey. Therefore, we have reexamined this issue in two different Macaque species using the thymidine analog bromodeoxyuridine (BrdU) as an indicator of DNA replication during cell division. We found several BrdU+/NeuN+ (neuronal nuclei) double-labeled cells, but cortical neurons, distinguished readily by their size and cytological and immunohistochemical properties, were not BrdU positive. We examined in detail the frontal cortex, where it is claimed that the largest daily addition of neurons has been made, but did not see migratory streams or any sign of addition of new neurons. Thus, we concluded that, in the normal condition, cortical neurons of adult primates, similar to other mammalian species, are neither supplemented nor renewable.
Seasonal Plasticity of Peripheral Auditory Frequency Sensitivity
Authors: Sisneros Joseph A. , Bass Andrew H.
Published: April 2018

Female midshipman fish (Porichthys notatus) use the auditory sense to detect and locate vocalizing males during the breeding season. Detection of conspecific vocal signals is essential to their reproductive success and can evoke strong phonotactic responses in gravid females but not in spent females that have released all of their eggs. Here, we test the hypothesis that seasonal variation in reproductive state affects the neurophysiological response properties of the peripheral auditory system in female midshipman fish. Iso-intensity responses of eighth nerve afferents from the sacculus, the main auditory end organ of the inner ear, to individual tones were measured for spike rate and vector strength (VS) of synchronization. Most auditory saccular units in reproductive, summer females showed robust temporal encoding up to 340 Hz, whereas nonreproductive winter females showed comparable encoding only up to 100 Hz. The dramatic upward shift in temporal encoding among summer fish was paralleled by increases in best frequency (BF), maximum evoked spike rate at BF, VS values at BF, and the percentage of units that showed significant VS to iso-intensity tones >140 Hz. Reproductive summer females were best suited to encode the higher harmonic components of male advertisement calls. This first demonstration of a natural cyclicity in peripheral auditory frequency sensitivity among vertebrates may represent, in this case, an adaptive plasticity of the female midshipman's auditory system to enhance the acquisition of auditory information needed for mate identification and localization during the breeding season.
Noise Provides Some New Signals About the Spatial Vision of Amblyopes
Authors: Levi Dennis M. , Klein Stanley A.
Published: April 2018

Amblyopia results in a loss of contrast sensitivity and position acuity. Here we report the results of experiments using noise to try to better understand the nature of the neural losses in amblyopia. In the first experiment, we used noise to derive the template or classification image used to detect a target and to discriminate its position. We found that some amblyopic observers show markedly abnormal templates for the position task and moderately abnormal classification images for the detection task; however, the abnormal template could not fully account for the loss of performance (efficiency). Reduced efficiency in the amblyopic visual system may reflect a poorly matched template, a high fraction of internal to external noise, or both. Comparison of the observers' performance with that of their template suggests that the amblyopes have a high fraction of internal (relative to external) noise. To analyze the internal noise further, we used a “double-pass” technique, in which observers performed the identical experiment twice. The amount of disagreement between the two experiments provides another estimate of the fraction of internal noise. Amblyopes show a much higher fraction of stimulus-dependent internal noise than do normal observers. We conclude that the loss of efficiency in amblyopia is attributable in part to a poorly matched template, but to a greater degree, to a high fraction of internal (relative to external) noise.
Control of Growth Cone Motility and Morphology by LIM Kinase and Slingshot via Phosphorylation and Dephosphorylation of Cofilin
Authors: Endo Mitsuharu , Ohashi Kazumasa , Sasaki Yukio , Goshima Yoshio , Niwa Ryusuke , Uemura Tadashi , Mizuno Kensaku
Published: April 2018

Growth cone motility and morphology are based on actin-filament dynamics. Cofilin plays an essential role for the rapid turnover of actin filaments by severing and depolymerizing them. The activity of cofilin is repressed by phosphorylation at Ser3 by LIM kinase (LIMK, in which LIM is an acronym of the three gene products Lin-11, Isl-1, and Mec-3) and is reactivated by dephosphorylation by phosphatases, termed Slingshot (SSH). We investigated the roles of cofilin, LIMK, and SSH in the growth cone motility and morphology and neurite extension by expressing fluorescence protein-labeled cofilin, LIMK1, SSH1, or their mutants in chick dorsal root ganglion (DRG) neurons and then monitoring live images of growth cones by time-lapse video fluorescence microscopy. The expression of LIMK1 remarkably repressed growth cone motility and neurite extension, whereas the expression of SSH1 or a nonphosphorylatable S3A mutant of cofilin enhanced these events. The fan-like shape of growth cones was disorganized by the expression of any of these proteins. The repressive effects on growth cone behavior by LIMK1 expression were significantly rescued by the coexpression of S3A–cofilin or SSH1. These findings suggest that LIMK1 and SSH1 play critical roles in controlling growth cone motility and morphology and neurite extension by regulating the activity of cofilin and may be involved in signaling pathways that regulate stimulus-induced growth cone guidance. Using various mutants of cofilin, we also obtained evidence that the actin-filament-severing activity of cofilin is critical for growth cone motility and neurite extension.
Contribution of NR2B Subunits to Synaptic Transmission in Amygdaloid Interneurons
Authors: Szinyei Csaba , Stork Oliver , Pape Hans-Christian
Published: April 2018

Synaptic responses of interneurons in the rat lateral amygdala (LA) to electrical microstimulation of putative cortical and thalamic afferents were studied in slice preparationsin situ. The EPSPs at both thalamic and cortical inputs were composed of two major components that were sensitive to 6,7-dinitroxaline-2,3-dione anddl-2-amino-5-phosphonovaleric acid (APV), indicating mediation through AMPA and NMDA receptors. NMDA receptor activation contributed to basal synaptic transmission, as evidenced through a reduction of EPSP amplitudes and integrals by APV. NMDA receptor-mediated postsynaptic currents showed magnesium-regulated voltage dependence, and current–voltage relationships displayed a region of negative slope conductance negative to resting potential. Deactivation of NMDA receptor-mediated currents followed a two exponential time course, with both components being significantly reduced by ifenprodil (10 μm), an antagonist of the NR2B subunit of NMDA receptors. Significant differences were not observed between NMDA currents or ifenprodil effects at thalamic and cortical inputs. Furthermore, recordings from a sample of projection neurons in the LA provided additional evidence for the existence of ifenprodil-sensitive components of thalamically and cortically evoked NMDA receptor-mediated responses. Immunohistochemical double-labeling and combinedin situhybridization/immunohistochemistry demonstrated that GABA-immunoreactive as well as GABA-negative cells express the NR2B subunit. Overall, these results show that GABAergic interneurons in the LA express functional NMDA receptors, which participate in basal synaptic transmission at both thalamic and cortical inputs. The finding that NR2B subunits are critically involved in NMDA receptor-mediated signaling at the two major input pathways to interneurons and projection cells in the LA is particularly interesting in the light of previous observations that NR2B antagonists interfere with plastic changes in the LA related to associative fear conditioning.
Electrophysiological Characterization of Voltage-Gated Currents in Defined Taste Cell Types of Mice
Authors: Medler Kathryn F. , Margolskee Robert F. , Kinnamon Sue C.
Published: April 2018

Despite extensive immunological characterization of the cells within taste buds, little is known about the functional significance of the different cell types. In this study, we use taste cells isolated from mouse vallate and foliate papillae to characterize voltage-gated currents in the three principal elongate types of taste cells: type I, II, and III. Cell types are identified by using antibodies to external epitopes [antigen H for type I cells, antigen A for type II cells, and neural cell adhesion molecule (NCAM) for type III cells]. In addition, we identify the subset of type II cells that contains α-gustducin, a G-protein involved in bitter transduction, by using transgenic mice expressing green fluorescent protein under the control of the gustducin promoter. Our results indicate that antigen H-immunoreactive (-IR) cells and many of the antigen A-IR cells have small voltage-gated inward Na+and outward K+currents but no voltage-gated Ca2+currents. In contrast, a subset of antigen A-IR cells and all NCAM-IR cells have large inward Na+and outward K+currents as well as voltage-gated Ca2+currents. Unexpectedly, all gustducin-expressing cells lacked voltage-gated Ca2+currents, suggesting that these cells use mechanisms other than classical synapses to communicate signals to the brain.
Visualization of Microtubule Growth in Cultured Neurons via the Use of EB3-GFP (End-Binding Protein 3-Green Fluorescent Protein)
Authors: Stepanova Tatiana , Slemmer Jenny , Hoogenraad Casper C. , Lansbergen Gideon , Dortland Bjorn , De Zeeuw Chris I. , Grosveld Frank , van Cappellen Gert , Akhmanova Anna , Galjart Niels
Published: April 2018

Several microtubule binding proteins, including CLIP-170 (cytoplasmic linker protein-170), CLIP-115, and EB1 (end-binding protein 1), have been shown to associate specifically with the ends of growing microtubules in non-neuronal cells, thereby regulating microtubule dynamics and the binding of microtubules to protein complexes, organelles, and membranes. When fused to GFP (green fluorescent protein), these proteins, which collectively are called +TIPs (plus end tracking proteins), also serve as powerful markers for visualizing microtubule growth events. Here we demonstrate that endogenous +TIPs are present at distal ends of microtubules in fixed neurons. Using EB3-GFP as a marker of microtubule growth in live cells, we subsequently analyze microtubule dynamics in neurons. Our results indicate that microtubules grow slower in neurons than in glia and COS-1 cells. The average speed and length of EB3-GFP movements are comparable in cell bodies, dendrites, axons, and growth cones. In the proximal region of differentiated dendrites ∼65% of EB3-GFP movements are directed toward the distal end, whereas 35% are directed toward the cell body. In more distal dendritic regions and in axons most EB3-GFP dots move toward the growth cone. This difference in directionality of EB3-GFP movements in dendrites and axons reflects the highly specific microtubule organization in neurons. Together, these results suggest that local microtubule polymerization contributes to the formation of the microtubule network in all neuronal compartments. We propose that similar mechanisms underlie the specific association of CLIPs and EB1-related proteins with the ends of growing microtubules in non-neuronal and neuronal cells.
Somatodendritic Secretion in Oxytocin Neurons Is Upregulated during the Female Reproductive Cycle
Authors: de Kock Christiaan P. J. , Wierda Keimpe D. B. , Bosman Laurens W. J. , Min Rogier , Koksma Jan-Jurjen , Mansvelder Huibert D. , Verhage Matthijs , Brussaard Arjen B.
Published: April 2018

During the female reproductive cycle, hypothalamic oxytocin (OT) neurons undergo sharp changes in excitability. In lactating mammals, bursts of electrical activity of OT neurons result in the release of large amounts of OT in the bloodstream, which causes milk ejection. One hypothesis is that OT neurons regulate their own firing activity and that of nearby OT neurons by somatodendritic release of OT. In this study, we show that OT neuron activity strongly reduces inhibitory synaptic transmission to these neurons. This effect is blocked by antagonists of both adenosine and OT receptors and is mimicked by OT application. Inhibition of solubleN-ethylmaleimide-sensitive factor attachment protein receptor complex formation by tetanus toxin completely blocked the stimulation-induced reduction in inhibitory input, as did the calcium chelator BAPTA. During lactation, the readily releasable pool of secretory vesicles in OT cell bodies was doubled, and calcium currents were upregulated. This resulted in an increased inhibition of GABAergic synaptic transmission by somatodendritic release during lactation compared with the adult virgin stage. These results demonstrate that somatodendritic release is augmented during lactation, which is a novel form of plasticity to change the strength of synaptic transmission.
TheWldsMutation Delays Robust Loss of Motor and Sensory Axons in a Genetic Model for Myelin-Related Axonopathy
Authors: Samsam Mohtashem , Mi Weiqian , Wessig Carsten , Zielasek Jürgen , Toyka Klaus V. , Coleman Michael P. , Martini Rudolf
Published: April 2018

Mice deficient in the peripheral myelin component P0 mimic severe forms of inherited peripheral neuropathies in humans, with defective myelin formation and consequent axonal loss. We cross-bred these mice with the spontaneous mutant C57BL/Wldstypically showing protection from Wallerian degeneration because of fusion of the ubiquitination factor E4B (Ube4b) and nicotinamide mononucleotide adenylyltransferase (Nmnat) genes. We found that in the double mutants, the robust myelin-related axonal loss is reduced at 6 weeks and 3 months of age. Moreover, retrograde labeling from plantar nerves revealed an increased survival of motor axons. These motor axons appeared functionally active because both the amplitude of compound muscle action potentials and muscle strength were less reduced in the double mutants. At 6 months of age, reduction of axonal loss was no longer detectable in the double mutants when compared with littermates carrying the P0 null mutation only, although theWldsgene was not reduced in its expression at this age. We conclude that myelin-related axonal loss is a process having some features in common with Wallerian degeneration. Introducing theWldsgene would be a promising approach to delaying detrimental axonal loss in myelin disorders.
Resiniferatoxin Induces Paradoxical Changes in Thermal and Mechanical Sensitivities in Rats: Mechanism of Action
Authors: Pan Hui-Lin , Khan Ghous M. , Alloway Kevin D. , Chen Shao-Rui
Published: April 2018

Resiniferatoxin (RTX), an ultrapotent analog of capsaicin, has been used as a tool to study the role of capsaicin-sensitive C fibers in pain. Recently, we found that RTX diminished the thermal sensitivity but unexpectedly increased the sensitivity to tactile stimulation in adult rats. In this study, we explored the potential mechanisms involved in RTX-induced changes in somatosensory function. An intraperitoneal injection of 200 μg/kg RTX, but not its vehicle, rapidly produced an increase in the paw withdrawal latency to a heat stimulus. Also, profound tactile allodynia developed in all the RTX-treated rats in 3 weeks. This paradoxical change in thermal and mechanical sensitivities lasted for at least 6 weeks. Electron microscopic examination of the sciatic nerve revealed a loss of unmyelinated fibers and extensive ultrastructural damage of myelinated fibers in RTX-treated rats. Immunofluorescence labeling showed a diminished vanilloid receptor 1 immunoreactivity in dorsal root ganglia neurons and the spinal dorsal horn of RTX-treated rats. Furthermore, two transganglionic tracers, horseradish peroxidase conjugates of cholera toxin B subunit (CTB) and isolectin-B4ofBandeiraea simplicifolia(IB4), were injected into the opposite sides of the sciatic nerve to trace myelinated and unmyelinated afferent terminations, respectively, in the spinal dorsal horn. In RTX-treated rats, IB4-labeled terminals in the dorsal horn were significantly reduced, and CTB-labeled terminals appeared to sprout into lamina II of the spinal dorsal horn. Thus, this study demonstrates that systemic RTX diminishes the thermal pain sensitivity by depletion of unmyelinated afferent neurons. The delayed tactile allodynia induced by RTX is likely attributable to damage to myelinated afferent fibers and their abnormal sprouting in lamina II of the spinal dorsal horn. These data provide new insights into the potential mechanisms of postherpetic neuralgia.
Emergent Properties of Layer 2/3 Neurons Reflect the Collinear Arrangement of Horizontal Connections in Tree Shrew Visual Cortex
Authors: Chisum Heather J. , Mooser François , Fitzpatrick David
Published: April 2018

The superficial layers of primary visual cortex, unlike layer 4, have an extensive network of long-range horizontal connections linking sites of similar orientation preference. To identify possible functional consequences of this distinct anatomy, we compared the receptive field properties of layers 2/3 and 4 neurons in tree shrew primary visual cortex with electrophysiological recordings. We found that elongated receptive fields, strong orientation tuning, and length summation (properties predicted by the anatomy of the horizontal connections) are present in layer 2/3 neurons, but not in layer 4 neurons. We further characterized the summation fields of layer 2/3 neurons and found axis and orientation-specific facilitation that matched the distribution of horizontal connections. The functional signature of horizontal connections was also evident in the population response of layer 2/3 neurons; the intrinsic signal activation pattern elicited by an array of collinear Gabor elements was significantly stronger than that elicited by a noncollinear array. Furthermore, our results showed that this enhancement of population response was achieved without compromising spatial resolution along the collinear axis, providing stimulus-specific facilitation without filling in between stimuli. Taken together, these results suggest that horizontal connections play a significant role in shaping the visual responses of layer 2/3 neurons.
Switching Memory Systems during Learning: Changes in Patterns of Brain Acetylcholine Release in the Hippocampus and Striatum in Rats
Authors: Chang Qing , Gold Paul E.
Published: April 2018

This experiment measured acetylcholine (ACh) release simultaneously in the hippocampus and striatum while rats were trained in a cross maze. Consistent with past findings, rats initially showed learning on the basis of place (i.e., turning to the correct position relative to the room), but after extensive training, rats shifted to learning on the basis of response (i.e., turning to the right/left to find the food). Profiles of ACh release in the hippocampus and striatum were markedly different during training. In the hippocampus, ACh release increased by ∼60% at the onset of training and remained at that level of release throughout training, even after the rats began to show learning on the basis of turning rather than place. In the striatum, increases in ACh release occurred later, reaching asymptotic increases of 30–40%, coincident with a transition from expressing place learning to expressing response learning. These findings suggest that the hippocampal and striatal systems both participate in learning in this task, but in a manner characterized by differential activation of the neural systems. The hippocampal system is apparently engaged first before the striatum is activated and, to the extent the hippocampus is important for place learning, promotes the use of a place solution to the maze. Later in training, although the hippocampus remains activated, the striatum is also activated in a manner that may enable the use of a response strategy to solve the maze. These findings may offer a neurobiological marker of a transition during skill learning from declarative to procedural learning.
Shape Tuning in Macaque Inferior Temporal Cortex
Authors: Kayaert Greet , Biederman Irving , Vogels Rufin
Published: April 2018

Neurons in the inferior temporal cortex (IT) of the macaque fire more strongly to some shapes than others, but little is known about how to characterize this shape tuning more generally, because most previous studies have used somewhat arbitrary variations in the stimuli with unspecified magnitudes of the changes. The present investigation studied the modulation of IT cells to nonaccidental property (NAP, i.e., invariant to orientations in depth) and metric property (MP, i.e., depth dependent) variations of dimensions of generalized cones (a general formalism for characterizing shapes hypothesized to mediate object recognition). Changes in an NAP resulted in greater neuronal modulation than equally large pixel-wise changes in an MP (including those consisting of a rotation in depth). There was also precise and highly systematic neuronal tuning to the quantitative variations of MPs along specific dimensions to which a neuron was sensitive. The NAP advantage was independent of whether the object was composed of only a single part or had two parts. These findings indicate that qualitative shape changes such as NAPs help explain the surplus amount of IT shape sensitivity that cannot be accounted for on the basis of metric or pixel-based changes alone. This NAP advantage may provide the neural basis for the greater detectability of NAP compared with MP changes in human psychophysics.
Functional Correlations between Neighboring Neurons in the Primate Globus Pallidus Are Weak or Nonexistent
Authors: Bar-Gad Izhar , Heimer Gali , Ritov Ya'acov , Bergman Hagai
Published: April 2018

The anatomical structure of the basal ganglia displays topographical organization and massive funneling of neuronal projections toward the globus pallidus as well as an axonal collateral system within this nucleus. This structure suggests the formation of correlations between the spiking activities of pallidal cells. Nevertheless, previous studies of remote neurons in the pallidum have reported uncorrelated spiking activity. These correlation results may be challenged, because remote pallidal neurons may be located in different pallidal territories. To further test the independence of pallidal activity, we studied the spiking activity of neighboring pairs recorded by the same electrodes. A narrow peak dominated the correlations of all pairs of neurons recorded on the same electrode. This type of peak is classically interpreted as a sign of strong common input. However, recent mathematical analysis shows that such peaks may derive from a technical inability to detect overlapping spikes by spike-sorting techniques. A long-term shallow trough in the correlation of neighboring neurons may also result from the same effect, which we have termed the “shadowing effect.” A comparison of the expected shadowing effect with the actual correlations suggests that no real correlations exist between 93.9% of neighboring pallidal pairs. The remaining 6.1% of the pairs display symmetric long-term positive correlations centered on time 0. Thus, functional interactions between neighboring pallidal neurons do not display any significant differences from the interactions between physically remote neurons in this brain area. Moreover, the combination of anatomical data and current physiological results suggests an active decorrelating process performed in the basal ganglia.
Exploitation of Astrocytes by Glioma Cells to Facilitate Invasiveness: A Mechanism Involving Matrix Metalloproteinase-2 and the Urokinase-Type Plasminogen Activator–Plasmin Cascade
Authors: Le Duc M. , Besson Arnaud , Fogg Darrin K. , Choi Kyu-Sil , Waisman David M. , Goodyer Cynthia G. , Rewcastle Barry , Yong V. Wee
Published: April 2018

The presence of reactive astrocytes around glioma cells in the CNS suggests the possibility that these two cell types could be interacting. We addressed whether glioma cells use the astrocyte environment to modulate matrix metalloproteinase-2 (MMP-2), a proteolytic enzyme implicated in the invasiveness of glioma cells. We found that astrocytes in culture produce significant amounts of the pro-form of MMP-2 but undetectable levels of active MMP-2. However, after coculture with the U251N glioma line, astrocyte pro-MMP-2 was converted to the active form. The mechanism of pro-MMP-2 activation in glioma–astrocyte coculture was investigated and was found to involve the urokinase-type plasminogen activator (uPA)–plasmin cascade whereby uPA bound to uPA receptor (uPAR), leading to the conversion of plasminogen to plasmin. The latter cleaved pro-MMP-2 to generate its active form. Furthermore, key components (i.e., uPAR, uPA, and pro-MMP-2) were contributed principally by astrocytes, whereas the U251N glioma cells provided plasminogen. In correspondence with this biochemical cascade, the transmigration of U251N cells through Boyden invasion chambers coated with an extracellular matrix barrier was increased significantly in the presence of astrocytes, and this was inhibited by agents that disrupted the uPA–plasmin cascade. Finally, using resected human glioblastoma specimens, we found that tumor cells, but not astrocytes, expressed plasminogenin situ. We conclude that glioma cells exploit their astrocyte environment to activate MMP-2 and that this leads to the increased invasiveness of glioma cells.