bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic Modulation of Kv4-Mediated A-Current by Arachidonic Acid Is Dependent on Potassium Channel Interacting Proteins
Authors: Holmqvist Mats H. , Cao Jie , Knoppers Maria H. , Jurman Mark E. , Distefano Peter S. , Rhodes Kenneth J. , Xie Yu , An W. Frank
Published: April 2018

The Kv4 subfamily of voltage-gated potassium channels is responsible for the transient A-type potassium current that operates at subthreshold membrane potentials to control membrane excitability. Arachidonic acid was shown recently to modulate both the peak amplitude and kinetics of the hippocampal A-current. However, inXenopusoocytes, arachidonic acid only inhibited the peak amplitude of Kv4 current without modifying its kinetics. These results suggest the existence of Kv4 auxiliary subunit(s) in native cells. We report here a K-channel interacting protein (KChIP)-dependent kinetic modulation of Kv4.2 current in Chinese hamster ovary cells and Kv4.2 and Kv4.3 currents inXenopusoocytes by arachidonic acid at physiological concentrations. This concentration-dependent effect of arachidonic acid resembled that observed in cerebellar granule neurons and was fully reversible. Other fatty acids, including a nonhydrolyzable inhibitor of both lipooxygenase and cyclooxygenase, 5,8,11,14-eicosatetraynoic acid (ETYA), also mimicked arachidonic acid in modulating Kv4.3 and Kv4.3/KChIP1 currents. Compared with another transient potassium current formed by Kv1.1/Kvβ1, Kv4.3/KChIP1 current was much more sensitive to arachidonic acid. Association between KChIP1 and Kv4.2 or Kv4.3 was not altered in the presence of 10 μmETYA as measured by immunoprecipitation and association-dependent growth in yeast. Our data suggest that the KChIP proteins represent a molecular entity for the observed difference between arachidonic acid effects on A-current kinetics in heterologous cells and in native cells and are consistent with the notion that KChIP proteins modulate the subthreshold A-current in neurons.
Channel-Lining Residues of the AMPA Receptor M2 Segment: Structural Environment of the Q/R Site and Identification of the Selectivity Filter
Authors: Kuner Thomas , Beck Christine , Sakmann Bert , Seeburg Peter H.
Published: April 2018

In AMPA receptor channels, a single amino acid residue (Q/R site) of the M2 segment controls permeation of calcium ions, single-channel conductance, blockade by intracellular polyamines, and permeation of anions. The structural environment of the Q/R site and its positioning with regard to a narrow constriction were probed with the accessibility of substituted cysteines to positively and negatively charged methanethiosulfonate reagents, applied from the extracellular and cytoplasmic sides of the channel. The accessibility patterns confirm that the M2 segment forms a pore loop with the Q/R site positioned at the tip of the loop (position 0) facing the extracellular vestibule. Cytoplasmically accessible residues on the N- and C-terminal sides of position 0 form the ascending α-helical (−8 to −1) and descending random coil (+1 to +6) components of the loop, respectively. Substitution of a glycine residue at position +2 with alanine strongly decreased the permeability of organic cations, indicating that position +2 contributes to the narrow constriction. The anionic 2-sulfonatoethyl-methanethiosufonate reacted with a cysteine at position 0 only from the external side and with cysteines at positions +1 to +4 only from the cytoplasmic side. These results suggest that charge selectivity occurs external to the constriction (+2) and possibly involves interactions of ions with the negative electrostatic potential created by the dipole of the α-helix formed by the ascending limb of the loop.
Increased Lipid Peroxidation Precedes Amyloid Plaque Formation in an Animal Model of Alzheimer Amyloidosis
Authors: Praticò Domenico , Uryu Kunihiro , Leight Susan , Trojanoswki John Q. , Lee Virginia M.-Y.
Published: April 2018

Oxidative stress is a key feature in the Alzheimer's disease (AD) brain and manifests as lipid peroxidation (LPO). Isoprostanes (iPs) are specific and sensitive markers ofin vivoLPO. To determine whether amyloid β (Aβ) depositionin vivois associated with increased LPO, we examined iP levels in a transgenic mouse model (Tg2576) of AD amyloidosis. Urine, plasma, and brain tissues were collected from Tg2576 and littermate wild-type (WT) animals at different time points starting at 4 months of age and continuing until 18 months of age. Levels of urinary 8,12-iso-iPF2α-VI were higher in Tg2576 than in WT animals as early as 8 months of age and remained this high for the rest of the study. A similar pattern was observed for plasma levels of 8,12-iso-iPF2α-VI. Homogenates from the cerebral cortex and hippocampus of Tg2576 mice had higher levels of 8,12-iso-iPF2α-VI than those from WT mice starting at 8 months of age. In contrast, a surge of Aβ 1–40 and 1–42 levels as well as Aβ deposits in Tg2576 mouse brains occurred later, at 12 months of age. A direct correlation was observed between brain 8,12-iso-iPF2α-VI and Aβ 1–40 and 1–42. Because LPO precedes amyloid plaque formation in Tg2576 mice, this suggests that brain oxidative damage contributes to AD pathogenesis before Aβ accumulation in the AD brain.
NMDA Receptor-Mediated Na+Signals in Spines and Dendrites
Authors: Rose Christine R. , Konnerth Arthur
Published: April 2018

Spines and dendrites of central neurons represent an important site of synaptic signaling and integration. Here we identify a new, synaptically mediated spine signal with unique properties. Using two-photon Na+imaging, we show that suprathreshold synaptic stimulation leads to transient increases in Na+concentration in postsynaptic spines and their adjacent dendrites. This local signal is restricted to a dendritic domain near the site of synaptic input. In presumed active spines within this domain, the Na+level increases by 30–40 mmeven during short bursts of synaptic stimulation. During a long-term potentiation induction protocol (100 Hz, 1 sec), the Na+level in the active spines reaches peak amplitudes of ∼100 mm. We find that the Na+transients are mainly mediated by Na+entry through NMDA receptor channels and are detected during the coincident occurrence of synaptic potentials and backpropagating action potentials. The large amplitudes of the Na+transients and their location on dendritic spines suggest that this signal is an important determinant of electrical and biochemical spine characteristics.
Drosophilaα- and β-Spectrin Mutations Disrupt Presynaptic Neurotransmitter Release
Authors: Featherstone David E. , Davis Warren S. , Dubreuil Ronald R. , Broadie Kendal
Published: April 2018

Spectrins are plasma membrane-associated cytoskeletal proteins implicated in several aspects of synaptic development and function, including presynaptic vesicle tethering and postsynaptic receptor aggregation. To test these hypotheses, we characterizedDrosophilamutants lacking either α- or β-spectrin. TheDrosophilagenome contains only one α-spectrinand one conventional β-spectringene, making it an ideal system to genetically manipulate spectrin levels and examine the resulting synaptic alterations. Both spectrin proteins are strongly expressed in theDrosophilaneuromusculature and highly enriched at the glutamatergic neuromuscular junction. Protein null α- and β-spectrin mutants are embryonic lethal and display severely disrupted neurotransmission without altered morphological synaptogenesis. Contrary to current models, the absence of spectrins does not alter postsynaptic glutamate receptor field function or the ultrastructural localization of presynaptic vesicles. However, the subcellular localization of numerous synaptic proteins is disrupted, suggesting that the defects in presynaptic neurotransmitter release may be attributable to inappropriate assembly, transport, or localization of proteins required for synaptic function.
AMPA/Kainate Receptor Activation Mediates Hypoxic Oligodendrocyte Death and Axonal Injury in Cerebral White Matter
Authors: Tekkök Selva Baltan , Goldberg Mark P.
Published: April 2018

We developed anin situmodel to investigate the hypothesis that AMPA/kainate (AMPA/KA) receptor activation contributes to hypoxic–ischemic white matter injury in the adult brain. Acute coronal brain slices, including corpus callosum, were prepared from adult mice. After exposure to transient oxygen and glucose deprivation (OGD), white matter injury was assessed by electrophysiology and immunofluorescence for oligodendrocytes and axonal neurofilaments. White matter cellular components and the stimulus-evoked compound action potential (CAP) remained stable for 12 hr after preparation. OGD for 30 min resulted in an irreversible loss of the CAP as well as structural disruption of axons and subsequent loss of neurofilament immunofluorescence. OGD also caused widespread oligodendrocyte death, demonstrated by the loss of APC labeling and the gain of pyknotic nuclear morphology and propidium iodide labeling. Blockade of AMPA/KA receptors with 30 μmNBQX or the AMPA-selective antagonist 30 μmGYKI 52466 prevented OGD-induced oligodendrocyte death. Oligodendrocytes also were preserved by the removal of Ca2+, but not by a blockade of voltage-gated Na+channels. The protective action of NBQX was still present in isolated corpus callosum slices. CAP areas and axonal structure were preserved by Ca2+removal and partially protected by a blockade of voltage-gated Na+channels. NBQX prevented OGD-induced CAP loss and preserved axonal structure. These observations highlight convergent pathways leading to hypoxic–ischemic damage of cerebral white matter. In accordance with previous suggestions, the activation of voltage-gated Na+channels contributes to axonal damage. Overactivation of glial AMPA/KA receptors leads to oligodendrocyte death and also plays an important role in structural and functional disruption of axons.
Suppression of Cortical NMDA Receptor Function Prevents Development of Orientation Selectivity in the Primary Visual Cortex
Authors: Ramoa Ary S. , Mower Amanda F. , Liao David , Jafri Syed I. A.
Published: April 2018

Selectivity to visual stimulus orientation is a basic cortical functional property believed to be crucial for normal vision. Maturation of this neuronal property requires neural activity. Still, it is unclear what might be the molecular basis for such activity-dependent processes and whether activity has an instructive or permissive role in development of orientation selectivity. There is strong evidence that the NMDA subtype of the glutamate receptor regulates activity-dependent mechanisms of ocular dominance plasticity during cortical development. For this reason, we have hypothesized that the NMDA receptor participates in activity-dependent mechanisms that sculpt orientation selectivity of cortical neurons. We used chronicin vivoinfusion of antisense oligodeoxynucleotides (ODNs) to suppress NMDA receptor function in primary visual cortex during the period when orientation selectivity develops in ferrets. Chronic suppression of NMDA receptor function prevented the development of orientation and stimulus size selectivity in most cortical cells tested. In contrast, treatment with control sense or missense ODNs did not affect development of orientation selectivity, indicating specificity of effects. Importantly, antisense ODN treatment did not impair visually driven activity, which is required for development to occur. Moreover, orientation selectivity of cortical cells was not disrupted by antisense ODN treatment in mature animals, indicating developmental relevance of the effects. In conclusion, our findings document for the first time that cortical NMDA receptors are essential for the maturation of orientation selectivity. This result supports the notion that activity has an instructive role in sculpting the connections that underlie orientation selectivity in visual cortex.
Unique Functional Properties of On and Off Pathways in the Developing Mammalian Retina
Authors: Wang Guo-Yong , Liets Lauren C. , Chalupa Leo M.
Published: April 2018

In the mature retina, the dendrites of On and Off ganglion cells are segregated into separate sublaminas of the inner plexiform layer, but early in development these processes are multistratified, ramifying more widely within this synaptic layer. The dendritic pattern exhibited by immature ganglion cells suggests that there may be a functional convergence of On and Off pathways in the developing retina, but previous studies have provided evidence against this. Here we demonstrate by patch-clamp recordings and dye filling that ganglion cells with multistratified dendrites respond to the onset, as well as the offset, of light. We further show that, in the dark-adapted retina, the glutamate analog 2-amino-4-phosphonobutric acid abolishes On and Off discharges in ganglion cells with multistratified dendrites. In contrast, in cells with stratified dendrites, this drug selectively blocks On responses. These findings provide evidence for unique functional attributes of On and Off pathways in the developing retina. The properties of immature ganglion cells documented here have important implications for the roles ascribed to neuronal activity in refining connections during the early development of the visual system.
Sonic Hedgehog Facilitates Dopamine Differentiation in the Presence of a Mesencephalic Glial Cell Line
Authors: Matsuura Nobuki , Lie D. Chichung , Hoshimaru Minoru , Asahi Minoru , Hojo Masato , Ishizaki Ryuji , Hashimoto Nobuo , Noji Sumihare , Ohuchi Hideyo , Yoshioka Hidefumi , Gage Fred H.
Published: April 2018

The aim of this study was to establish a cellular system to investigate the requirement for cell surface and diffusible molecules in the differentiation of fetal mesencephalic cells toward the dopamine lineage. Toward this end, we immortalized rat embryonic day 14 (E14) mesencephalon with a regulatable retroviral vector encoding v-myc. The stably transduced cells were pooled and designated as VME14 cells. VME14 cells proliferated rapidly, stopped proliferating, extended processes, and expressed GFAP after suppression of the v-mycexpression with tetracycline, suggesting that VME14 cells differentiated into glial cells. Dissociated cells derived from the E11 rat mesencephalon gave rise to only a small number of tyrosine hydroxylase (TH)-positive neurons. However, when grown on a monolayer of the differentiated VME14 cells, a significantly higher number of cells differentiated into TH-positive neurons. VME14 cells were transduced with the secreted N-terminal cleavage product of the Sonic hedgehog gene (SHH-N), an inducer of mesencephalic dopaminergic neurons. This monoclonal, SHH-N-overexpressing cell line further enhanced dopaminergic differentiation of E11 rat mesencephalon cells. Thus, SHH-N and signals derived from fetal mesencephalic glia act cooperatively to facilitate dopaminergic differentiation. These fetal mesencephalon-derived cell lines will provide tools for the study of signals involved in dopaminergic differentiation.
Mice Lacking tPA, uPA, or Plasminogen Genes Showed Delayed Functional Recovery after Sciatic Nerve Crush
Authors: Siconolfi Lisa B. , Seeds Nicholas W.
Published: April 2018

Axonal outgrowth during peripheral nerve regeneration relies on the ability of growth cones to traverse through an environment that has been altered structurally and along a basal lamina sheath to reinnervate synaptic targets. To promote migration, growth cones secrete proteases that are thought to dissolve cell–cell and cell–matrix adhesions. These proteases include the plasminogen activators (PAs), tissue PA (tPA) and urokinase PA (uPA), and their substrate, plasminogen. PA expression and secretion are upregulated in regenerating mammalian sensory neurons in culture. After sciatic nerve crush in mice, there was an induction of PA mRNAs in the sensory neurons contributing to the crushed nerve and an upregulation of PA-dependent activity in crushed nerve compared with sham counterparts during nerve regeneration. To further assess the role of the PA system during peripheral nerve regeneration, PA-dependent activity as well as recovery of sensory and motor function in the injured hindlimb were assessed in wild-type, tPA, uPA, and plasminogen knock-out mice. Protease activity visualized by gel zymography showed that after nerve crush, the upregulation of PA activity in the tPA and uPA knock-out mice was delayed compared with wild-type mice. Recovery of sensory function was assessed by toe pinch, footpad prick, and the toe-spreading reflex. All knock-out mice demonstrated a significant delay in hindlimb response to these sensory stimuli compared with wild-type mice. For each modality tested, the uPA knock-out mice were the most dramatically affected, showing the longest delay to initiate a response. These studies clearly showed that PAs were necessary for timely functional recovery by regenerating peripheral nerves.
Neuronal Expression of Synaptotagmin-Related Gene 1 Is Regulated by Thyroid Hormone during Cerebellar Development
Authors: Potter Gregory B. , Facchinetti Fabrizio , Beaudoin Gerard M. J. , Thompson Catherine C.
Published: April 2018

Thyroid hormone (TH) is essential for proper brain development, acting through nuclear receptors that modulate the expression of specific genes in response to hormone binding. In a screen for genes regulated by TH in the rat cerebellum, we recently identified a novel gene, synaptotagmin-related gene 1 (Srg1). The Srg1 protein is structurally similar to synaptotagmins, a family of proteins involved in regulating neurotransmission. To elucidate a potential role of Srg1 in brain development, we have investigated the developmental and TH-regulated expression of Srg1 in the neonatal rat brain. We show that expression of both Srg1 RNA and protein is detected only in the brain and specifically in neurons. Srg1 mRNA and protein levels increase postnatally, nearing adult levels after the third postnatal week. Neonatal TH deficiency results in a significant reduction and delay in expression of both Srg1 RNA and protein. Using immunohistochemistry, we were able to detect Srg1 protein in numerous brain regions. In the cerebellum, Srg1 protein is localized to the molecular layer, indicating that it is highly expressed in granule cell axons. To further examine Srg1 expression in cerebellar granule cells (CGCs), we used anin vitrocell culture model. In primary cultures of CGCs, Srg1 expression is significantly reduced in the absence of TH. Srg1 mRNA is rapidly upregulated in cultured CGCs, suggesting a direct response to TH. Neuronal and TH-regulated expression of Srg1, together with its localization to neurites, implicates Srg1 as an important component of the program of gene expression induced by TH in the developing brain.
Maturation of Extinction Behavior in Infant Rats: Large-Scale Regional Interactions with Medial Prefrontal Cortex, Orbitofrontal Cortex, and Anterior Cingulate Cortex
Authors: Nair Hemanth P. , Berndt Jason D. , Barrett Douglas , Gonzalez-Lima F.
Published: April 2018

The ability to express a behavior during the postnatal period may be related to developmental changes in the recruitment of particular neural systems. Here, we show that developmental changes in the functional interactions involving three cortical regions (the medial prefrontal cortex, orbitofrontal cortex, and anterior cingulate cortex) are associated with maturation of extinction behavior in infant rats. Postnatal day 17 (P17) and P12 pups were trained in a straight-alley runway on an alternating schedule of reward and nonreward [patterned single alternation (PSA)] or on a pseudorandom schedule of partial reinforcement (PRF); the pups were then injected with fluorodeoxyglucose (FDG) and shifted to continuous nonreward (extinction). Handled control groups exposed to the same training environment but not trained on a particular schedule were included. Among P17 pups, extinction proceeded faster in PSA pups relative to PRF pups. No differences were found between P12 groups. FDG uptake, an index of acute changes in functional activity, was quantified in the three cortical regions and 27 other brain regions of interest. A multivariate covariance analysis, seed partial least squares, revealed that functional relationships involving the three cortical regions and large-scale systems of regions throughout the rostrocaudal extent of the brain changed with training in P17 pups. The cortical regions were primarily uncoupled in the younger group. The data suggest that functional maturation of the frontal cortical regions and their interactions with other brain systems are related to the maturational shift in behavior.
Auditory Space-Time Receptive Field Dynamics Revealed by Spherical White-Noise Analysis
Authors: Jenison Rick L. , Schnupp Jan W. H. , Reale Richard A. , Brugge John F.
Published: April 2018

Numerous studies have investigated the spatial sensitivity of cat auditory cortical neurons, but possible dynamic properties of the spatial receptive fields have been largely ignored. Given the considerable amount of evidence that implicates the primary auditory field in the neural pathways responsible for the perception of sound source location, a logical extension to earlier observations of spectrotemporal receptive fields, which characterize the dynamics of frequency tuning, is a description that uses sound source direction, rather than sound frequency, to examine the evolution of spatial tuning over time. The object of this study was to describe auditory space-time receptive field dynamics using a new method based on cross-correlational techniques and white-noise analysis in spherical auditory space. This resulted in a characterization of auditory receptive fields in two spherical dimensions of space (azimuth and elevation) plus a third dimension of time. Further analysis has revealed that spatial receptive fields of neurons in auditory cortex, like those in the visual system, are not static but can exhibit marked temporal dynamics. This might result, for example, in a neuron becoming selective for the direction and speed of moving auditory sound sources. Our results show that ∼14% of AI neurons evidence significant space-time interaction (inseparability).
Forced Limb-Use Effects on the Behavioral and Neurochemical Effects of 6-Hydroxydopamine
Authors: Tillerson Jennifer L. , Cohen Ann D. , Philhower Jennifer , Miller Gary W. , Zigmond Michael J. , Schallert Timothy
Published: April 2018

Rats with unilateral depletion of striatal dopamine (DA) show marked preferential use of the ipsilateral forelimb. Previous studies have shown that implementation of motor therapy after stroke improves functional outcome (Taub et al., 1999). Thus, we have examined the impact of forced use of the impaired forelimb during or soon after unilateral exposure to the DA neurotoxin 6-hydroxydopamine (6-OHDA). In one group of animals, the nonimpaired forelimb was immobilized using a cast, which forced exclusive use of the impaired limb for the first 7 d after infusion. The animals that received a cast displayed no detectable impairment or asymmetry of limb use, could use the contralateral (impaired) forelimb independently for vertical and lateral weight shifting, and showed no contralateral turning to apomorphine. The behavioral effects were maintained throughout the 60 d of observation. In addition to the behavioral sparing, these animals showed remarkable sparing of striatal DA, its metabolites, and the expression of the vesicular monoamine transporter, suggesting a decrease in the extent of DA neuron degeneration. Behavioral and neurochemical sparing appeared to be complete when the 7 d period of immobilization was initiated immediately after 6-OHDA infusion, only partial sparing was evident when immobilization was initiated 3 d postoperatively, and no sparing was detected when immobilization was initiated 7 d after 6-OHDA treatment. These results suggest that physical therapy may be beneficial in Parkinson's disease.
Endomorphin-1: Induction of Motor Behavior and Lack of Receptor Desensitization
Authors: Mehta Arpesh , Bot George , Reisine Terry , Chesselet Marie-Françoise
Published: April 2018

The endomorphins are recently discovered endogenous agonists for the μ-opioid receptor (Zadina et al., 1997). Endomorphins produce analgesia; however, their role in other brain functions has not been elucidated. We have investigated the behavioral effects of endomorphin-1 in the globus pallidus, a brain region that is rich in μ-opioid receptors and involved in motor control. Bilateral administration of endomorphin-1 in the globus pallidus of rats induced orofacial dyskinesia. This effect was dose-dependent and at the highest dose tested (18 pmol per side) was sustained during the 60 min of observation, indicating that endomorphin-1 does not induce rapid desensitization of this motor response. In agreement with a lack of desensitization of μ-opioid receptors, 3 hr of continuous exposure of the cloned μ receptor to endomorphin-1 did not diminish the subsequent ability of the agonist to inhibit adenylate cyclase activity in cells expressing the cloned μ-opioid receptor. Confirming the involvement of μ-opioid receptors, the behavioral effect of endomorphin-1 in the globus pallidus was blocked by the opioid antagonist naloxone and the μ-selective peptide antagonist Cys2-Tyr3-Orn5-Pen7amide (CTOP). Furthermore, the selective μ receptor agonist [d-Ala2-N-Me-Phe4-Glycol5]-enkephalin (DAMGO) also stimulated orofacial dyskinesia when infused into the globus pallidus, albeit transiently. Our findings suggest that endogenous μ agonists may play a role in hyperkinetic movement disorders by inducing sustained activation of pallidal opioid receptors.
Brain-Derived Neurotrophic Factor Is Released in the Dorsal Horn by Distinctive Patterns of Afferent Fiber Stimulation
Authors: Lever Isobel J. , Bradbury Elizabeth J. , Cunningham Joanna R. , Adelson David W. , Jones Martyn G. , McMahon Stephen B. , Marvizón Juan Carlos G. , Malcangio Marzia
Published: April 2018

Brain-derived neurotrophic factor (BDNF) is synthesized by small neuron cell bodies in the dorsal root ganglia (DRG) and is anterogradely transported to primary afferent terminals in the dorsal horn where it is involved in the modulation of painful stimuli. Here we show that BDNF is released in the rat isolated dorsal horn after chemical stimulation by capsaicin or electrical stimulation of dorsal roots. Capsaicin superfusion (1–100 μm) induced a dose-dependent release of BDNF, measured using ELISA. The highest dose of capsaicin also induced a depletion of BDNF protein in the dorsal horn. BDNF release was also seen after electrical stimulation of the dorsal roots at C-fiber strength. This release was encoded by specific patterns of afferent fiber stimulation. Neither continuous low-frequency (480 pulses, 1 Hz) nor tetanic high-frequency (300 pulses in 3 trains, 100 Hz) stimulation evoked release of BDNF, although substance P (SP) release was observed under both of these conditions. However, BDNF was released after short bursts of high-frequency stimulation (300 pulses in 75 trains, 100 Hz) along with SP and glutamate. The NMDA antagonistd-AP-5 inhibited electrically evoked BDNF release. BDNF release was also measured after systemic or intrathecal NGF treatment. This upregulated BDNF content in the DRG and increased the capsaicin-evoked release of BDNF. Similarly, the amount of BDNF released by burst stimulation was increased after NGF treatment. This activity-dependent release continued to be encoded solely by this stimulation pattern. These experiments demonstrate that BDNF release in the dorsal horn is encoded by specific patterns of afferent fiber stimulation and is mediated by NMDA receptor activation.
Normalization Models Applied to Orientation Masking in the Human Infant
Authors: Candy T. Rowan , Skoczenski Ann M. , Norcia Anthony M.
Published: April 2018

Human infants can discriminate the orientation of lines within the first week after birth (Atkinson et al., 1988; Slater et al., 1988) but have immature orientation-selective pattern masking until after 6 months of age (Morrone and Burr, 1986). Here the development of orientation processing is further examined using a visual-evoked potential paradigm and normalization models of pattern masking. Contrast response functions were measured for 1 cycle per degree (cpd) gratings, counterphase-reversed in contrast at either 3.3 or 5.5 Hz. A second 1 cpd, 20% contrast, 8.3 Hz grating of either the same or orthogonal orientation was added as a mask. Evoked responses associated with the test grating, the mask, and intermodulation between the two were individually extracted using spectral analysis of the scalp-recorded EEG. Adults exhibited orientation selectivity in the masking of their test component responses and in nonlinear intermodulation between the test and mask stimuli. Infants <5 months old, however, demonstrated nonselective masking or a reversed selectivity in their responses to the test component, with adult-like orientation selectivity in their intermodulation responses. Within the context of a normalization model of pattern masking, the results are consistent with the existence of oriented filters early in life the responses of which are normalized immaturely until ∼5 months of age.
Kainate Receptors Expressed by a Subpopulation of Developing Nociceptors Rapidly Switch from High to Low Ca2+Permeability
Authors: Lee C. Justin , Kong Haeyoung , Manzini M. Chiara , Albuquerque Cristóvão , Chao Moses V. , MacDermott Amy B.
Published: April 2018

Dorsal root ganglion (DRG) neurons first express kainate receptor subunits, predominantly GluR5, during embryonic development. In the DRG and throughout the nervous system, substantial editing of GluR5 mRNA occurs with developmental maturation (Bernard et al., 1999). The accompanying change in Ca2+permeability of functional kainate receptors that is the predicted outcome of this developmental regulation of mRNA editing has not been investigated. Here we report that kainate receptors on DRG neurons from late embryonic and newborn rats are predominantly Ca2+permeable but then become fully Ca2+impermeable later in the first postnatal week. Using multiple markers for nociceptor subpopulations, we show that this switch in Ca2+permeability is not caused by the appearance of a new subpopulation of nociceptors with different receptor properties. Instead, the change in Ca2+permeability matches the time course of post-transcriptional RNA editing of GluR5 at the Q/R site within the pore of the channel, indicating that the change is probably caused by developmentally regulated RNA editing. We also report that, on the basis of the strong correlation of receptor expression with expression of the surface markers LA4, isolectin B4, and LD2, kainate receptors are present on C-fiber-type neurons projecting to lamina II of spinal cord dorsal horn. These results raise the possibility that kainate receptors in their Ca2+-permeable form serve a developmental role in synapse formation between this population of C-fibers and their targets in the spinal cord dorsal horn. Thereafter, the receptors may serve a new function that does not require Ca2+permeability.
Enhanced Spontaneous Transmitter Release Is the Earliest Consequence of Neocortical Hypoxia That Can Explain the Disruption of Normal Circuit Function
Authors: Fleidervish Ilya A. , Gebhardt Christine , Astman Nadav , Gutnick Michael J. , Heinemann Uwe
Published: April 2018

After the onset of an acute episode of arrested circulation to the brain and consequent cerebral hypoxia, EEG changes and modifications of consciousness ensue within seconds. This in part reflects the rapid effect of hypoxia on the neocortex, where oxygen deprivation leads to impaired neuronal excitability and abnormal synaptic transmission. To identify the cellular mechanisms responsible for the earliest changes in neocortical function and to determine their time course, we have used patch-in-slice recording techniques to investigate the effects of acute hypoxia on the synaptic and intrinsic properties of layer 5 neurons. Coronal slices of mouse somatosensory cortex were maintained at 37°C and challenged with episodes of hypoxia (3–4 min of exposure to 95% N2, 5% CO2). In recordings with cell-attached patch electrodes, activation of ATP-sensitive potassium channels first became detectable 211 ± 11 sec (range, 185–240 sec;n= 6 patches) after the onset of hypoxia. Similar recording techniques revealed no alterations in the properties of Na+currents in the first 4 min after the onset of hypoxia. The earliest hypoxia-induced disturbance was a marked increase in the frequency of spontaneous EPSCs and IPSCs, which began within 15–30 sec of the removal of oxygen. This rapid synaptic effect was not sensitive to TTX and was present in Ca2+-free perfusate, indicating that the hypoxia had a direct influence on the vesicular release mechanisms. The incoherent, massive increase in miniature PSCs would be expected to deplete the readily releasable pool of vesicles in cortical terminals, and to thereby markedly distort the neuronal interactions that underlie normal circuit function.
Caspase-Activated DNase/DNA Fragmentation Factor 40 Mediates Apoptotic DNA Fragmentation in Transient Cerebral Ischemia and in Neuronal Cultures
Authors: Cao Guodong , Pei Wei , Lan Jing , Stetler R. Anne , Luo Yumin , Nagayama Tetsuya , Graham Steven H. , Yin Xiao-Ming , Simon Roger P. , Chen Jun
Published: April 2018

Nuclear changes, including internucleosomal DNA fragmentation, are characteristic features of neuronal apoptosis resulting from transient cerebral ischemia and related brain insults for which the molecular mechanism has not been elucidated. Recent studies suggest that a caspase-3-mediated mechanism may be involved in the process of nuclear degradation in ischemic neurons. In this study, we cloned from rat brain a homolog cDNA encoding caspase-activated deoxyribonuclease (CAD)/DNA fragmentation factor 40 (DFF40), a 40 kDa nuclear enzyme that is activated by caspase-3 and promotes apoptotic DNA degradation. Subsequently, we investigated the role of CAD/DFF40 in the induction of internucleosomal DNA fragmentation in the hippocampus in a rat model of transient global ischemia and in primary neuronal cultures under ischemia-like conditions. At 8–72 hr after ischemia, CAD/DFF40 mRNA and protein were induced in the degenerating hippocampal CA1 neurons. CAD/DFF40 formed a heterodimeric complex in the nucleus with its natural inhibitor CAD (ICAD) and was activated after ischemia in a delayed manner (>24 hr) by caspase-3, which translocated into the nucleus and cleaved ICAD. Furthermore, an induced CAD/DFF40 activity was detected in nuclear extracts in bothin vivoandin vitromodels, and the DNA degradation activity of CAD/DFF40 was inhibited by purified ICAD protein. These results strongly suggest that CAD/DFF40 is the endogenous endonuclease that mediates caspase-3-dependent internucleosomal DNA degradation and related nuclear alterations in ischemic neurons.
Intact Aggrecan and Fragments Generated by Both Aggrecanse and Metalloproteinase-Like Activities Are Present in the Developing and Adult Rat Spinal Cord and Their Relative Abundance Is Altered by Injury
Authors: Lemons Michele L. , Sandy John D. , Anderson Douglas K. , Howland Dena R.
Published: April 2018

Aggrecan is a large proteoglycan (PG) that has been grouped with different PG families on the basis of its physical characteristics. These families include the chondroitin sulfate PGs, which appear to inhibit the migration of cells and axons during development. Although aggrecan has been studied primarily in cartilage, in the present study, tissue samples from developing, mature, and injured-adult rat spinal cords were used to determine whether aggrecan is present in the mammalian spinal cord. By the use of Western blot analysis, tissues were probed with aggrecan-specific antibodies (ATEGQV, TYKHRL, and LEC-7) and aggrecan-specific neoepitope antibodies (NITEGE, FVDIPEN, and TFKEEE) to identify full-length aggrecan and several fragments. Unlike many other aggrecan gene family members, aggrecan species were similar in embryonic day 14, postnatal day 1, and adult spinal cords. Spinal cord injury caused significant decreases in aggrecan. Partial recovery in some aggrecan species was evident by 2 weeks after injury. The presence of specific aggrecan neoepitopes suggested that aggrecan is cleaved in the spinal cord by both a disintegrin and metalloproteinase thrombospondin (also known as aggrecanase) and metalloproteinase-like activities. Many aggrecan species found in the spinal cord were similar to species in cartilage. Additional antibodies were used to identify two other aggrecan gene family members, neurocan and brevican, in the adult spinal cord. These studies present novel information on the aggrecan core protein species and enzymes involved in aggrecan cleavagein vivoin the rat spinal cord throughout development and after injury. They also provide the basis for investigating the function of aggrecan in the spinal cord.
Neuronal Hypertrophy in the Neocortex of Patients with Temporal Lobe Epilepsy
Authors: Bothwell Sarah , Meredith Gloria E. , Phillips Jack , Staunton Hugh , Doherty Colin , Grigorenko Elena , Glazier Steven , Deadwyler Sam A. , O'Donovan Cormac A. , Farrell Michael
Published: April 2018

The underlying cause of neocortical involvement in temporal lobe epilepsy (TLE) remains a fundamental and unanswered question. Magnetic resonance imaging has shown a significant loss in temporal lobe volume, and it has been proposed that neocortical circuits are disturbed functionally because neurons are lost. The present study used design-based stereology to estimate the volume and cell number of Brodmann's area 38, a region commonly resected in anterior temporal lobectomy. Studies were conducted on the neocortex of patients with or without hippocampal sclerosis (HS). Results provide the surprising finding that TLE patients have significant atrophy of neocortical gray matter but no loss of neurons. Neurons are also significantly larger, dendritic trees appear sparser, and spine density is noticeably reduced in TLE specimens compared with controls. The increase in neuronal density we found in TLE patients is therefore attributable to large neurons occupying a much smaller volume than in normal brain. Neurons in the underlying white matter are also increased in size but, in contrast to other reports, are not significantly elevated in number or density. Neuronal hypertrophy affects HS and non-HS brains similarly. The reduction in neuropil and its associated elements therefore appears to be a primary feature of TLE, which is not secondary to cell loss. In both gray and white matter, neuronal hypertrophy means more perikaryal surface area is exposed for synaptic contacts and emerges as a hallmark of this disease.
Psychological Stress Increases Hippocampal Mineralocorticoid Receptor Levels: Involvement of Corticotropin-Releasing Hormone
Authors: Gesing Angela , Bilang-Bleuel Alicia , Droste Susanne K. , Linthorst Astrid C. E. , Holsboer Florian , Reul Johannes M. H. M.
Published: April 2018

We investigated whether acute stressors regulate functional properties of the hippocampal mineralocorticoid receptor (MR), which acts inhibitory on hypothalamic-pituitary-adrenocortical activity. Exposure of rats to forced swimming or novelty evoked a significant rise in density of MR immunoreactivity in all hippocampal subfields after 24 hr, whereas exposure to a cold environment was ineffective. Time course analysis revealed that the effect of forced swimming on MR peaked at 24 hr and returned to control levels between 24 and 48 hr. In pyramidal neurons of CA2 and CA3, marked rises were already observed after 8 hr. Radioligand binding assays showed that corticotropin-releasing hormone (CRH) injected intracerebroventricularly into adrenalectomized rats also produced a rise in hippocampal MR levels; an effect for which the presence of corticosterone, but not dexamethasone, at the time of injection was a prerequisite. Moreover, pretreatment with the CRH receptor antagonist (d-Phe12,Nle21,38,α-Me-Leu37)-CRH12–41blocked the effect of forced swimming on hippocampal MR levels. To investigate whether the rise in MR levels had any functional consequences for HPA regulation, 24 hr after forced swimming, a challenge test with the MR antagonist RU 28318 was conducted. The forced swimming exposed rats showed an enhanced MR-mediated inhibition of HPA activity.

This study identifies CRH as an important regulator of MR, a pathway with marked consequence for HPA axis regulation. We conclude that the interaction between CRH and MR presents a novel mechanism involved in the adaptation of the brain to psychologically stressful events.
Tuning to Interaural Time Differences across Frequency
Authors: Fitzpatrick Douglas C. , Kuwada Shigeyuki
Published: April 2018

Interaural time differences (ITDs) are an important cue for azimuthal sound localization. Sensitivity to this cue depends on temporal synchrony to the waveform (i.e., phase locking) that begins in the hair cells and is relayed to the neural comparators. The synchrony function is low-pass. Therefore, it is expected that neural tuning to ITDs will become narrower with frequency according to a 1/frequency function. To test this, we measured ITD tuning across frequency in neurons from the superior olivary complex, the dorsal nucleus of the lateral lemniscus, the inferior colliculus, the auditory thalamus, and the auditory cortex. For some neurons in each nucleus, the ITD tuning width did become systematically narrower by the expected 1/frequency relationship. However, in other neurons the ITD tuning width was nearly constant across frequency. Constant ITD tuning width was infrequently observed in neurons of the superior olivary complex but was common in neurons in structures above the superior olivary complex. The nearly constant ITD tuning was caused both by sharper ITD tuning at low frequencies and broader tuning at higher frequencies within the low-frequency band. Neurons with nearly constant tuning to ITDs may be the mechanism underlying the perception of ITDs in humans in which just-noticeable differences to changes in ITD decrease by less than the 1/frequency prediction.
Dissociation between Light-Induced Phase Shift of the Circadian Rhythm and Clock Gene Expression in Mice Lacking the Pituitary Adenylate Cyclase Activating Polypeptide Type 1 Receptor
Authors: Hannibal Jens , Jamen Francoise , Nielsen Harriette S. , Journot Laurant , Brabet Philippe , Fahrenkrug Jan
Published: April 2018

The circadian clock located in the suprachiasmatic nucleus (SCN) organizes autonomic and behavioral rhythms into a near 24 hr time that is adjusted daily to the solar cycle via a direct projection from the retina, the retinohypothalamic tract (RHT). This neuronal pathway costores the neurotransmitters PACAP and glutamate, which seem to be important for light-induced resetting of the clock. At the molecular level the clock genesmPer1andmPer2are believed to be target for the light signaling to the clock. In this study, we investigated the possible role of PACAP-type 1 receptor signaling in light-induced resetting of the behavioral rhythm and light-induced clock gene expression in the SCN. Light stimulation at early night resulted in larger phase delays in PACAP-type 1 receptor-deficient mice (PAC1−/−) compared with wild-type mice accompanied by a marked reduction in light-inducedmPer1,mPer2,and c-fosgene expression. Light stimulation at late night inducedmPer1and c-fosgene expression in the SCN to the same levels in both wild type andPAC1−/−mice. However, in contrast to the phase advance seen in wild-type mice,PAC1−/−mice responded with phase delays after photic stimulation. These data indicate thatPAC1receptor signaling participates in the gating control of photic sensitivity of the clock and suggest thatmPer1,mPer2,and c-fosare of less importance for light-induced phase shifts at night.
Distribution of Gustatory Sensitivities in Rat Taste Cells: Whole-Cell Responses to Apical Chemical Stimulation
Authors: Gilbertson Timothy A. , Boughter John D. , Zhang Huai , Smith David V.
Published: April 2018

Several taste transduction mechanisms have been demonstrated in mammals, but little is known about their distribution within and across receptor cells. We recorded whole-cell responses of 120 taste cells of the rat fungiform papillae and soft palate maintained within the intact epithelium in a modified Ussing chamber, which allowed us to flow tastants across the apical membrane while monitoring the activity of the cell with a patch pipette. Taste stimuli were: 0.1msucrose, KCl, and NH4Cl, 0.032mNaCl, and 3.2 mmHCl and quinine hydrochloride (QHCl). When cells were held at their resting potentials, taste stimulation resulted in conductance changes; reversible currents >5 pA were considered reliable responses. Sucrose and QHCl produced a decrease in outward current and membrane conductance, whereas NaCl, KCl, NH4Cl, and HCl elicited inward currents accompanied by increased conductance. Combinations of responses to pairs of the four basic stimuli (sucrose, NaCl, HCl, and QHCl) across the 71–84 cells tested with each pair were predictable from the probabilities of responses to individual stimuli, indicating an independent distribution of sensitivities. Of 62 cells tested with all four basic stimuli, 59 responded to at least one of the stimuli; 16 of these (27.1%) responded to only one, 20 (33.9%) to two, 15 (25.4%) to three, and 8 (13.6%) to all of the basic stimuli. Cells with both inward (Na+) and outward (K+) voltage-activated currents were significantly more broadly tuned to gustatory stimuli than those with only inward currents.
Functional Analysis of Capsaicin Receptor (Vanilloid Receptor Subtype 1) Multimerization and Agonist Responsiveness Using a Dominant Negative Mutation
Authors: Kuzhikandathil Eldo V. , Wang Haibin , Szabo Tamas , Morozova Natasha , Blumberg Peter M. , Oxford Gerry S.
Published: April 2018

The recently cloned vanilloid receptor subtype 1 (VR1) is a ligand-gated channel that is activated by capsaicin, protons, and heat. We have attempted to develop a dominant negative isoform by targeting several mutations of VR1 at highly conserved amino acids or at residues of potential functional importance and expressing the mutants in Chinese hamster ovary cells. Mutation of three highly conserved amino acid residues in the putative sixth transmembrane domain disrupts activation of the VR1 receptor by both capsaicin and resiniferatoxin. The vanilloid binding site in this mutant is intact, although the affinity for [3H]resiniferatoxin (RTX) is diminished by nearly 40-fold. Interestingly, this mutant retains a significant but diminished response to protons, supporting the existence of multiple gating mechanisms for different stimuli. The mutant appears to function by interfering with the gating induced by vanilloids rather than the expression level or permeability of the receptor. In addition, this mutant was found to function as a strong dominant negative mutation when coexpressed with wild-type VR1, providing functional evidence that the VR1 receptor forms a multimeric complex. Analysis of both current density and [3H]RTX affinity in cells cotransfected with different ratios of wild-type and mutant VR1 is consistent with tetrameric stoichiometry for the native capsaicin receptor.