bluuebunny/crossref_metadata_2025 huggingface dataset:
Presynaptic Inhibition of Primary Olfactory Afferents Mediated by Different Mechanisms in Lobster and Turtle
Authors: Wachowiak Matt , Cohen Lawrence B.
Published: April 2018

Presynaptic regulation of transmission at the first olfactory synapse was investigated by selectively imaging axon terminals of receptor neurons in the lobster olfactory lobe and turtle olfactory bulb. In both species, action potential propagation into axon terminals after olfactory nerve stimulation was measured using voltage-sensitive dyes. In addition, in the turtle, calcium influx into terminals was measured by selectively labeling receptor neurons with dextran-conjugated calcium indicator dyes. In the lobster, application of the inhibitory transmitters GABA or histamine suppressed action potentials in the terminals. The suppression was blocked by picrotoxin and cimetidine, respective antagonists to lobster GABA and histamine receptors. These results suggest that previously characterized GABA and histaminergic interneurons regulate olfactory input by suppressing action potential propagation into axon terminals of olfactory afferents. In contrast, in the turtle olfactory bulb, neither GABA nor dopamine had any effect on receptor cell action potentials as measured with voltage-sensitive dyes. However, calcium influx into axon terminals was reduced by the GABABagonist baclofen and the dopamine D2agonist quinpirole, and paired-pulse suppression of calcium influx was reduced by the GABABantagonist saclofen. These results indicate that in the turtle, GABA and dopamine mediate presynaptic inhibition not by affecting action potentials directly, as in the lobster, but by reducing calcium influx via GABABand dopamine D2receptors. Thus, although mediated by different cellular mechanisms, presynaptic regulation of olfactory input to the CNS, via dual synaptic pathways, is a feature common to vertebrates and invertebrates. This inhibition may be important in the processing of olfactory information.
Domains Responsible for Constitutive and Ca2+-Dependent Interactions between Calmodulin and Small Conductance Ca2+-Activated Potassium Channels
Authors: Keen John E. , Khawaled Radwan , Farrens David L. , Neelands Torben , Rivard Andre , Bond Chris T. , Janowsky Aaron , Fakler Bernd , Adelman John P. , Maylie James
Published: April 2018

Small conductance Ca2+-activated potassium channels (SK channels) are coassembled complexes of pore-forming SK α subunits and calmodulin. We proposed a model for channel activation in which Ca2+binding to calmodulin induces conformational rearrangements in calmodulin and the α subunits that result in channel gating. We now report fluorescence measurements that indicate conformational changes in the α subunit after calmodulin binding and Ca2+binding to the α subunit–calmodulin complex. Two-hybrid experiments showed that the Ca2+-independent interaction of calmodulin with the α subunits requires only the C-terminal domain of calmodulin and is mediated by two noncontiguous subregions; the ability of the E-F hands to bind Ca2+is not required. Although SK α subunits lack a consensus calmodulin-binding motif, mutagenesis experiments identified two positively charged residues required for Ca2+-independent interactions with calmodulin. Electrophysiological recordings of SK2 channels in membrane patches from oocytes coexpressing mutant calmodulins revealed that channel gating is mediated by Ca2+binding to the first and second E-F hand motifs in the N-terminal domain of calmodulin. Taken together, the results support a calmodulin- and Ca2+-calmodulin-dependent conformational change in the channel α subunits, in which different domains of calmodulin are responsible for Ca2+-dependent and Ca2+-independent interactions. In addition, calmodulin is associated with each α subunit and must bind at least one Ca2+ion for channel gating. Based on these results, a state model for Ca2+gating was developed that simulates alterations in SK channel Ca2+sensitivity and cooperativity associated with mutations in CaM.
TheweaverMousegain-of-functionPhenotype of Dopaminergic Midbrain Neurons Is Determined by Coactivation ofwvGirk2 and K-ATP Channels
Authors: Liss Birgit , Neu Axel , Roeper Jochen
Published: April 2018

The phenotype of substantia nigra (SN) neurons in homozygousweaver(wv/wv) mice was studied by combining patch-clamp and single-cell RT-multiplex PCR techniques in midbrain slices of 14-d-old mice. In contrast to GABAergic SN neurons, which were unaffected in homozygousweavermice (wv/wv), dopaminergic SN neurons possessed a dramatically altered phenotype with a depolarized membrane potential and complete loss of spontaneous pacemaker activity. Thegain-of-functionphenotype was mediated by a large, nonselective membrane conductance exclusively present in (wv/wv) dopaminergic SN neurons. This constitutively activated conductance displayed a sensitivity to external QX-314 (IC50= 10.6 μm) very similar to that of heterologously expressedwvGirk2 channels and was not further activated by G-protein stimulation. Single-cell Girk1–4 expression profiling suggested that homomeric Girk2 channels were present in most dopaminergic SN neurons, whereas Girk2 was always coexpressed with other Girk family members in GABAergic SN neurons. Surprisingly, acute QX-314 inhibition ofwvGirk2 channels did not induce wild-type-like pacemaker activity but instead caused membrane hyperpolarization. Additional application of a blocker of ATP-sensitive potassium channels (100 μmtolbutamide) induced wild-type-like pacemaker activity. We conclude that thegain-of-function weaverphenotype of dopaminergic substantia nigra neurons is mediated by coactivation ofwvGirk2 and SUR1/Kir6.2-mediated ATP-sensitive K+channels. We also show that in contrast to wild-type neurons, all (wv/wv) dopaminergic SN neurons expressed calbindin, a calcium-binding protein that marks dopaminergic SN neurons resistant to neurodegeneration. The identification of two ion channels that in concert determine theweaverphenotype of surviving calbindin-positive dopaminergic SN neurons will help to understand the molecular mechanisms of selective neurodegeneration of dopaminergic SN neurons in theweavermouse and might be important in Parkinson’s disease.
Reorganization and Movement of Microtubules in Axonal Growth Cones and Developing Interstitial Branches
Authors: Dent Erik W. , Callaway John L. , Szebenyi Györgyi , Baas Peter W. , Kalil Katherine
Published: April 2018

Local changes in microtubule organization and distribution are required for the axon to grow and navigate appropriately; however, little is known about how microtubules (MTs) reorganize during directed axon outgrowth. We have used time-lapse digital imaging of developing cortical neurons microinjected with fluorescently labeled tubulin to follow the movements of individual MTs in two regions of the axon where directed growth occurs: the terminal growth cone and the developing interstitial branch. In both regions, transitions from quiescent to growth states were accompanied by reorganization of MTs from looped or bundled arrays to dispersed arrays and fragmentation of long MTs into short MTs. We also found that long-term redistribution of MTs accompanied the withdrawal of some axonal processes and the growth and stabilization of others. Individual MTs moved independently in both anterograde and retrograde directions to explore developing processes. Their velocities were inversely proportional to their lengths. Our results demonstrate directly that MTs move within axonal growth cones and developing interstitial branches. Our findings also provide the first direct evidence that similar reorganization and movement of individual MTs occur in the two regions of the axon where directed outgrowth occurs. These results suggest a model whereby short exploratory MTs could direct axonal growth cones and interstitial branches toward appropriate locations.
Postsynaptic Calcium/Calmodulin-Dependent Protein Kinase II Is Required to Limit Elaboration of Presynaptic and Postsynaptic Neuronal Arbors
Authors: Zou Dong-Jing , Cline Hollis T.
Published: April 2018

Neuronal dendritic and axonal arbors grow to a characteristic size and then stabilize their structures. Activity-dependent stop-growing signals may limit neuronal process elaboration. We tested whether endogenous calcium/calmodulin-dependent protein kinase II (CaMKII) activity in postsynaptic optic tectal cells is required to restrict the elaboration of neuronal processes in theXenopustadpole retinotectal projection. Optic tectal cells were infected with vaccinia viruses that express CaMKII-specific inhibitory peptides.In vivotime-lapse imaging revealed that expression of CaMKII inhibitors blocked the growth restriction that normally occurs during maturation of tectal cell dendritic arbors. Postsynaptic CaMKII inhibition also increased the growth of presynaptic retinotectal axon arbors. The results indicate that endogenous postsynaptic CaMKII activity is required to limit the growth of presynaptic and postsynaptic arbor structuresin vivo.
A Role for HSP27 in Sensory Neuron Survival
Authors: Lewis Susan E. , Mannion Richard J. , White Fletcher A. , Coggeshall Richard E. , Beggs Simon , Costigan Michael , Martin Jody L. , Dillmann Wolfgang H. , Woolf Clifford J.
Published: April 2018

Peripheral nerve injury in neonatal rats results in the death of the majority of the axotomized sensory neurons by 7 d after injury. In adult animals, however, all sensory neurons survive for at least 4 months after axotomy. How sensory neurons acquire the capacity to survive axonal injury is not known. Here we describe how the expression of the small heat shock protein 27 (HSP27) is correlated with neuronal survival after axotomyin vivoand after NGF withdrawalin vitro.The number of HSP27-immunoreactive neurons in the L4 DRG is low at birth and does not change significantly for 21 d after postnatal day 0 (P0) sciatic nerve axotomy. In contrast, in the adult all axotomized neurons begin to express HSP27. One week after P0 sciatic nerve section the total number of neurons in the L4 DRG is dramatically reduced, but all surviving axotomized neurons, as identified by c-jun immunoreactivity, are immunoreactive for HSP27. In addition, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling reveals that very few HSP27-expressing neurons are dying 48 hr after neonatal axotomy.In vitro, a similar correlation exists between HSP27 expression and survival; in P0 DRG cultures, neurons that express HSP27 preferentially survive NGF withdrawal. Finally, overexpression of human HSP27 in neonatal rat sensory and sympathetic neurons significantly increases survival after NGF withdrawal, with nearly twice as many neurons surviving at 48 hr. Together these results suggest that HSP27 in sensory neurons plays a role in promoting survival after axotomy or neurotrophin withdrawal.
Vector Averaging Occurs Downstream from Learning in Smooth Pursuit Eye Movements of Monkeys
Authors: Kahlon Maninder , Lisberger Stephen G.
Published: April 2018

How are sensory-motor transformations organized in a cortical motor system? In general, sensory information is transformed through a variety of signal processing operations in the context of distinct coordinate frameworks. We studied the interaction of two distinct operations in pursuit eye movements, learning and vector-averaging, to gain insight into their underlying coordinate frameworks and their sequence in sensory-motor processing. Learning was induced in the initiation of pursuit eye movements by targets that moved initially at one speed for 100 msec and then increased or decreased to a sustained final speed. Vector averaging was studied by comparing the initial eye acceleration evoked by the simultaneous motion of two targets with that evoked by each target singly. Learning caused specific effects on the direction of the vector-averaged responses to two-target stimuli that included one target moving in the direction used to induce learning. Learned increases or decreases in eye acceleration caused the direction of the responses to two-targets to rotate toward or away from the learning direction. Learning also caused nonspecific changes in the responses to two-target stimuli. After any learning protocol, two-target responses usually became smaller, and their directions rotated away from the axis of the target motion used for learning. Quantitative analysis showed that the specific effects of learning were predicted most closely by a model in which vector averaging occurs downstream from the site(s) of learning. We suggest that the pursuit system creates parallel commands for potential movements to each of the targets in two-target stimuli, and that learning occurs in the coordinates of the potential movements.
Sensory Loss by Selected Whisker Removal Produces Immediate Disinhibition in the Somatosensory Cortex of Behaving Rats
Authors: Kelly M. Kathleen , Carvell George E. , Kodger Judith M. , Simons Daniel J.
Published: April 2018

This study used extracellular unit recordings in behaving animals to evaluate thalamocortical response transformations in the rat whisker–barrel system. Based on previous acute studies using controlled whisker stimulation, we hypothesized that in a cortical barrel adjacent (non-principal) whiskers exert a net inhibitory effect. In contrast, in thalamic barreloid neurons, the effects of neighboring whiskers should be net facilitatory. We evaluated these hypotheses by recording unit activity at 21 sites in17 animals trained to explore a wire mesh screen with their whiskers. In the middle of the recording session, selected vibrissae were clipped close to the skin surface. The absence of whiskers surrounding the principal whisker was associated with a mean 20% increase in cortical activity and, conversely, a 37% decrease in the thalamic activity. Removal of the principal whisker resulted in a 50% decrease in cortical unit firing. Findings are consistent with the idea that, in the behaving animal, each barrel uses multi-whisker thalamic inputs and local inhibitory circuitry to sharpen the receptive field properties of its constituent neurons. Cortical disinhibition as a consequence of selective whisker removal is likely to be an important factor underlying altered receptive field properties in sensory-deprived animals.
Opioid Enhancement of Calcium Oscillations and Burst Events Involving NMDA Receptors and L-Type Calcium Channels in Cultured Hippocampal Neurons
Authors: Przewlocki Rysard , Parsons Kathy L. , Sweeney Dan D. , Trotter Carol , Netzeband Jeffrey G. , Siggins George R. , Gruol Donna L.
Published: April 2018

Opioid receptor agonists are known to alter the activity of membrane ionic conductances and receptor-activated channels in CNS neurons and, via these mechanisms, to modulate neuronal excitability and synaptic transmission. In neuronal-like cell lines opioids also have been reported to induce intracellular Ca2+signals and to alter Ca2+signals evoked by membrane depolarization; these effects on intracellular Ca2+may provide an additional mechanism through which opioids modulate neuronal activity. However, opioid effects on resting or stimulated intracellular Ca2+levels have not been demonstrated in native CNS neurons. Thus, we investigated opioid effects on intracellular Ca2+in cultured rat hippocampal neurons by using fura-2-based microscopic Ca2+imaging. The opioid receptor agonistd-Ala2-N-Me-Phe4,Gly-ol5-enkephalin (DAMGO; 1 μm) dramatically increased the amplitude of spontaneous intracellular Ca2+oscillations in the hippocampal neurons, with synchronization of the Ca2+oscillations across neurons in a given field. The effects of DAMGO were blocked by the opioid receptor antagonist naloxone (1 μm) and were dependent on functional NMDA receptors and L-type Ca2+channels. In parallel whole-cell recordings, DAMGO enhanced spontaneous, synaptically driven NMDA receptor-mediated burst events, depolarizing responses to exogenous NMDA and current-evoked Ca2+spikes. These results show that the activation of opioid receptors can augment several components of neuronal Ca2+signaling pathways significantly and, as a consequence, enhance intracellular Ca2+signals. These results provide evidence of a novel neuronal mechanism of opioid action on CNS neuronal networks that may contribute to both short- and long-term effects of opioids.
Cell Type-Specific Activation of Neuronal Nicotinic Acetylcholine Receptor Subunit Genes by Sox10
Authors: Liu Qun , Melnikova Irena N. , Hu Minjie , Gardner Paul D.
Published: April 2018

The regulatory factor Sox10 is expressed in neural crest derivatives during development as well as in the adult CNS and peripheral nervous system. Mutations of the human Sox10 gene have been identified in patients with Waardenburg-Hirschsprung syndrome that is characterized by defects in neural crest development. Previous studies suggested that Sox10 might function as an important transcriptional regulator of neural crest development. No natural target genes of Sox10 have yet been identified. Although human Sox10 activates a synthetic promoter consisting of a TATA box and multiple Sox consensus sequences, no transcriptional activity of the rat Sox10 homolog has been detected. Here we report that the neuronal nicotinic acetylcholine receptor β4 and α3 subunit gene promoters are transactivated by rat Sox10 in a cell type-specific manner. The α3 and β4 subunits, in combination with the α5 subunit, make up the predominant nicotinic receptor subtype expressed in the peripheral nervous system. Transfections using Sox10 mutants indicate that the C-terminal region is dispensable for its ability to activate the β4 and α3 promoters. Rat Sox10 was originally identified as an accessory protein of the POU domain protein Tst-1/Oct6/SCIP in glial cells. Tst-1/Oct6/SCIP was shown previously to activate the α3 promoter. We now demonstrate that it can transactivate the β4 promoter as well. However, we were unable to detect any synergistic effects of Sox10 and Tst-1/Oct6/SCIP on β4 or α3 promoter activity. Finally, we present data suggesting that recombinant Sox10 protein can directly interact with a previously characterized regulatory region of the β4 gene.
Amphetamine Depresses Excitatory Synaptic Transmission via Serotonin Receptors in the Ventral Tegmental Area
Authors: Jones Susan , Kauer Julie A.
Published: April 2018

The ventral tegmental area (VTA) is the origination zone for dopaminergic neurons involved in reward and addictive properties of a variety of abused substances. A major excitatory projection to VTA neurons originates in the medial prefrontal cortex, and several lines of evidence suggest that glutamatergic synapses on VTA neurons are activated and modified during exposure to psychostimulant drugs. Here, we report for the first time that amphetamine depresses excitatory glutamatergic synaptic transmission onto VTA neurons in the midbrain slice preparation. Unexpectedly, this depression is mediated not by activation of dopamine receptors, but instead by activation of serotonin receptors. Our findings suggest that an acute effect of amphetamine exposure is the release of serotonin in the VTA, which in turn modulates excitation of VTA neurons. This process may be an important early component of permanent changes occurring in the reward pathway that contribute to drug addiction.
Neuronal Death and Blood–Brain Barrier Breakdown after Excitotoxic Injury Are Independent Processes
Authors: Chen Zu-lin , Indyk Justin A. , Bugge Thomas H. , Kombrinck Keith W. , Degen Jay L. , Strickland Sidney
Published: April 2018

Neuronal damage in the CNS after excitotoxic injury is correlated with blood-brain barrier (BBB) breakdown. We have used a glutamate analog injection model and genetically altered mice to investigate the relationship between these two processes in the hippocampus. Our results show that BBB dysfunction occurs too late to initiate neurodegeneration. In addition, plasma infused directly into the hippocampus is not toxic and does not affect excitotoxin-induced neuronal death. To test plasma protein recruitment in neuronal degeneration, we used plasminogen-deficient (plg−/−) mice, which are resistant to excitotoxin-induced degeneration. Plasminogen is produced in the hippocampus and is also present at high levels in plasma, allowing us to determine the contribution of each source to cell death. Intrahippocampal delivery of plasminogen to plg−/−mice restored degeneration to wild-type levels, but intravenous delivery of plasminogen did not. Finally, although the neurons in plg−/−mice do not die after excitotoxin injection, BBB breakdown occurs to a similar extent as in wild-type mice, indicating that neuronal death is not necessary for BBB breakdown. These results indicate that excitotoxin-induced neuronal death and BBB breakdown are separable events in the hippocampus.
Development of P2 Olfactory Glomeruli in P2-Internal Ribosome Entry Site-Tau-LacZ Transgenic Mice
Authors: Royal Stephanie J. , Key Brian
Published: April 2018

Primary olfactory neurons project their axons to the olfactory bulb, where they terminate in discrete loci called glomeruli. All neurons expressing the same odorant receptor appear to terminate in a few glomeruli in each olfactory bulb. In the P2-IRES-tau-LacZ line of transgenic mice, LacZ is expressed in the perikarya and axons of primary olfactory neurons that express the P2 odorant receptor. In the present study, we examined the developmental appearance of P2 neurons, the topographical targeting of P2 axons, as well as the formation of P2 glomeruli in the olfactory bulb. P2 axons were first detected in the olfactory nerve fiber layer at embryonic day 14.5 (E14.5), and by E15.5 these axons terminated in a broad locus in the presumptive glomerular layer. During the next 5 embryonic days, the elongated cluster of axons developed into discrete glomerulus-like structures. In many cases, glomeruli appeared as pairs, which were initially connected by a fascicle of P2 axons. This connection was lost by postnatal day 7.5, and double glomeruli at the same locus were observed in 85% of adult animals. During the early postnatal period, there was considerable mistargeting of P2 axons. In some cases P2 axons entered inappropriate glomeruli or continued to grow past the glomerular layer into the deeper layers of the olfactory bulb. These aberrant axons were not observed in adult animals. These results indicate that olfactory axons exhibit errors while converging onto a specific glomerulus and suggest that guidance cues may be diffusely distributed at target sites in the olfactory bulb.
Cellular and Subcellular Specification of Na,K-ATPase α and β Isoforms in the Postnatal Development of Mouse Retina
Authors: Wetzel Randall K. , Arystarkhova Elena , Sweadner Kathleen J.
Published: April 2018

The Na,K-ATPase is a dominant factor in retinal energy metabolism, and unique combinations of isoforms of its α and β subunits are expressed in different cell types and determine its functional properties. We used isoform-specific antibodies and fluorescence confocal microscopy to determine the expression of Na,K-ATPase α and β subunits in the mouse and rat retina. In the adult retina, α1 was found in Müller and horizontal cells, α2 in some Müller glia, and α3 in photoreceptors and all retinal neurons. β1 was largely restricted to horizontal, amacrine, and ganglion cells; β2 was largely restricted to photoreceptors, bipolar cells, and Müller glia; and β3 was largely restricted to photoreceptors. Photoreceptor inner segments have the highest concentration of Na,K-ATPase in adult retinas. Isoform distribution exhibited marked changes during postnatal development. α3 and β2 were in undifferentiated photoreceptor somas at birth but only later were targeted to inner segments and synaptic terminals. β3, in contrast, was expressed late in photoreceptor differentiation and was immediately targeted to inner segments. A high level of β1 expression in horizontal cells preceded migration, whereas increases in β2 expression in bipolar cells occurred very late, coinciding with synaptogenesis in the inner plexiform layer. Most of the spatial specification of Na,K-ATPase isoform expression was completed before eye opening and the onset of electroretinographic responses on postnatal day 13 (P13), but quantitative increase continued until P22 in parallel with synaptogenesis.
Neuregulins Signaling via a Glial erbB-2–erbB-4 Receptor Complex Contribute to the Neuroendocrine Control of Mammalian Sexual Development
Authors: Ma Ying J. , Hill Diane F. , Creswick Kimberly E. , Costa Maria E. , Cornea Anda , Lioubin Mario N. , Plowman Gregory D. , Ojeda Sergio R.
Published: April 2018

Activation of erbB-1 receptors by glial TGFα has been shown to be a component of the developmental program by which the neuroendocrine brain controls mammalian sexual development. The participation of other members of the erbB family may be required, however, for full signaling capacity. Here, we show that activation of astrocytic erbB-2/erbB-4 receptors plays a significant role in the process by which the hypothalamus controls the advent of mammalian sexual maturation. Hypothalamic astrocytes express both the erbB-2 and erbB-4 genes, but no erbB-3, and respond to neuregulins (NRGs) by releasing prostaglandin E2(PGE2), which acts on neurosecretory neurons to stimulate secretion of luteinizing hormone-releasing hormone (LHRH), the neuropeptide controlling sexual development. The actions of TGFα and NRGs in glia are synergistic and involve recruitment of erbB-2 as a coreceptor, via erbB-1 and erbB-4, respectively. Hypothalamic expression of both erbB-2 and erbB-4 increases first in a gonad-independent manner before the onset of puberty, and then, at the time of puberty, in a sex steroid-dependent manner. Disruption of erbB-2 synthesis in hypothalamic astrocytes by treatment with an antisense oligodeoxynucleotide inhibited the astrocytic response to NRGs and, to a lesser extent, that to TGFα and blocked the erbB-dependent, glia-mediated, stimulation of LHRH release. Intracerebral administration of the oligodeoxynucleotide to developing animals delayed the initiation of puberty. Thus, activation of the erbB-2–erbB-4 receptor complex appears to be a critical component of the signaling process by which astrocytes facilitate the acquisition of female reproductive capacity in mammals.
Brain-Derived Neurotrophic Factor Differentially Regulates Retinal Ganglion Cell Dendritic and Axonal ArborizationIn Vivo
Authors: Lom Barbara , Cohen-Cory Susana
Published: April 2018

Expression of the neurotrophin brain-derived neurotrophic factor (BDNF) and its receptor trkB in the ganglion cell layer of theXenopusretina during retinal ganglion cell (RGC) dendritic arborization indicates that BDNF is spatially and temporally available to influence RGC morphological differentiation (Cohen-Cory and Fraser, 1994; Cohen-Cory et al., 1996). BDNF promotes RGC axon arborizationin vivoby acting as a target-derived trophic factor (Cohen-Cory and Fraser, 1995). To determine whether BDNF also acts locally to regulate RGC dendritic developmentin vivo, we altered retinal neurotrophin levels at the onset of dendritic arborization and assessed the resulting arbor morphologies of RGCs retrogradely labeled with fluorescent dextrans. Injecting neurotrophins or BDNF function-blocking antibodies coupled to microspheres provided local alterations of retinal neurotrophin levels. BDNF significantly decreased RGC dendritic arbor complexity, whereas neutralizing endogenous BDNF levels with function-blocking antibodies significantly increased dendritic arbor complexity. RGCs exposed to other neurotrophins, as well as RGCs in retinae treated with BDNF but in areas not directly exposed to the neurotrophin, developed dendritic arbors that were indistinguishable from controls, indicating that exogenous BDNF acts specifically and locally. In the tectum, where RGC axons arborize, BDNF had opposite effects. BDNF significantly increased RGC axon arbor complexity and anti-BDNF reduced RGC arborization. Thus, BDNF reduces RGC dendritic arborization within the retina and increases axon arborization in the tectum. These results indicate that BDNF can differentially modulate axonal and dendritic arborization within a single neuronal population in opposing manners and raise the possibility that differential modulation by a neurotrophic factor finely tunes the morphological differentiation program of a neuron.
Formation of Cortical Fields on a Reduced Cortical Sheet
Authors: Huffman Kelly J. , Molnár Zoltán , Van Dellen Anton , Kahn Dianna M. , Blakemore Colin , Krubitzer Leah
Published: April 2018

Theories of both cortical field development and cortical evolution propose that thalamocortical projections play a critical role in the differentiation of cortical fields (O'Leary, 1989; Krubitzer, 1995). In the present study, we examined how changing the size of the immature neocortex before the establishment of thalamocortical connections affects the subsequent development and organization of the adult neocortex. This alteration in cortex is consistent with one of the most profound changes made to the mammalian neocortex throughout evolution: cortical size. Removing the caudal one-third to three-fourths of the cortical neuroepithelial sheet unilaterally at an early stage of development in marsupials resulted in normal spatial relationships between visual, somatosensory, and auditory cortical fields on the remaining cortical sheet. Injections of neuroanatomical tracers into the reduced cortex revealed in an altered distribution of thalamocortical axons; this alteration allowed the maintenance of their original anteroposterior distribution. These results demonstrate the capacity of the cortical neuroepithelium to accommodate different cortical fields at early stages of development, although the anteroposterior and mediolateral relationships between cortical fields appear to be invariant. The shifting of afferents and efferents with cortical reduction or expansion at very early stages of development may have occurred naturally in different lineages over time and may be sufficient to explain much of the phenotypic variation in cortical field number and organization in different mammals.
Identification, Isolation, and Promoter-Defined Separation of Mitotic Oligodendrocyte Progenitor Cells from the Adult Human Subcortical White Matter
Authors: Roy Neeta Singh , Wang Su , Harrison-Restelli Catherine , Benraiss Abdellatif , Fraser Richard A. R. , Gravel Michel , Braun Peter E. , Goldman Steven A.
Published: April 2018

Previous studies have suggested the persistence of oligodendrocyte progenitor cells in the adult mammalian subcortical white matter. To identify oligodendrocyte progenitors in the adult human subcortical white matter, we transfected dissociates of capsular white matter with plasmid DNA bearing the gene for green fluorescence protein (hGFP), placed under the control of the human early promoter (P2) for the oligodendrocytic protein cyclic nucleotide phosphodiesterase (P/hCNP2). Within 4 d after transfection with P/hCNP2:hGFP, a discrete population of small, bipolar cells were noted to express GFP. These cells were A2B5-positive (A2B5+), incorporated bromodeoxyuridinein vitro, and constituted <0.5% of all cells. Using fluorescence-activated cell sorting (FACS), the P/hCNP2-driven GFP+cells were then isolated and enriched to near-purity. In the weeks after FACS, most P/hCNP2:hGFP-sorted cells matured as morphologically and antigenically characteristic oligodendrocytes. Thus, the human subcortical white matter harbors mitotically competent progenitor cells, which give rise primarily to oligodendrocytesin vitro. By using fluorescent transgenes of GFP expressed under the control of an early oligodendrocytic promoter, these oligodendrocyte progenitor cells may be extracted and purified from adult human white matter in sufficient numbers for implantation and cell-based therapy.
Selective Inhibition of Spinal Cord Neurite Outgrowth and Cell Survival by the Eph Family Ligand Ephrin-A5
Authors: Yue Yong , Su Jianying , Cerretti Douglas Pat , Fox Gary M. , Jing Shuqian , Zhou Renping
Published: April 2018

The Eph family tyrosine kinase receptors and their ligands, the ephrins, have been shown to play critical roles in cell migration, tissue morphogenesis, and axonal guidance in many different systems. However, their function in the spinal cord has not been examined carefully. We showed in this study that several Eph receptors, including EphA3, Eph A4, and Eph A5, are expressed in the ventral spinal cord in partially overlapping patterns, with EphA5 exhibiting the most widespread transcription in the entire ventral spinal cord during early development. Complementary to the receptor expression, a ligand of these receptors, ephrin-A5, is transcribed in the dorsal half of the spinal cord. Consistent with the spatial location of receptor expression, the ligand selectively inhibits neurite outgrowth and induces cell death of the ventral, but not the dorsal, spinal cord neurons. These observations suggest that interactions between the Eph family receptors and ligands exerts negative influences on ventral spinal cord neurons and thus may play important roles in regulating morphogenesis and axon guidance in the spinal cord.
Null Mutation of c-fos Causes Exacerbation of Methamphetamine-Induced Neurotoxicity
Authors: Deng Xiaolin , Ladenheim Bruce , Tsao Li-I , Cadet Jean Lud
Published: April 2018

Methamphetamine neurotoxicity has been demonstrated in rodents and nonhuman primates. These neurotoxic effects may be associated with mechanisms involved in oxidative stress and the activation of immediate early genes (IEG). It is not clear, however, whether these IEG responses are involved in a methamphetamine-induced toxic cascade or in protective mechanisms against the deleterious effects of the drug. As a first step toward clarifying this issue further, the present study was thus undertaken to assess the toxic effects of methamphetamine in heterozygous and homozygous c-fos knock-out as well as wild-type mice. Administration of methamphetamine caused significant reduction in [125I]RTI-121–labeled dopamine uptake sites, dopamine transporter protein, and tyrosine hydroxylase–like immunohistochemistry in the striata of wild-type mice. These decreases were significantly exacerbated in heterozygous and homozygous c-fos knock-out mice, with the homozygous showing greater loss of striatal dopaminergic markers. Moreover, in comparison with wild-type animals, both genotypes of c-fos knock-out mice showed more DNA fragmentation, measured by the number of terminal deoxynucleotidyl transferase–mediated dUTP nick-end–labeled nondopaminergic cells in their cortices and striata. In contrast, wild-type mice treated with methamphetamine demonstrated a greater number of glial fibrillary acidic protein–positive cells than did c-fos knock-out mice. These data suggest that c-fos induction in response to toxic doses of methamphetamine might be involved in protective mechanisms against this drug-induced neurotoxicity.
Reversible Downregulation of Protein Kinase A during Olfactory Learning Using Antisense Technique Impairs Long-Term Memory Formation in the Honeybee,Apis mellifera
Authors: Fiala André , Müller Uli , Menzel Randolf
Published: April 2018

In this study, we examined the role of cAMP-dependent protein kinase (PKA) in associative olfactory learning of the honeybee,Apis mellifera.In the bee, specific interference with molecules to clarify their role in a certain behavior is difficult, because genetic approaches, such as mutants or transgenic animals, are not feasible at the moment. As a new approach in insectsin vivo, we report the use of short antisense oligonucleotides. We show that phosphorothioate-modified oligodeoxynucleotides complementary to the mRNA of a catalytic subunit of PKA directly injected into the bee brain cause a reversible and specific downregulation of both the amount of the catalytic subunit and of PKA activity by 10–15%. The amounts of the regulatory subunit of PKA, as well as PKC, are not affected. The slight “knockdown” of PKA activity during the training procedure, a classical olfactory conditioning of the proboscis extension reflex, neither affects acquisition nor memory retention 3 or 6 hr after training. However, it causes an impairment of long-term memory retention 24 hr after training. Downregulation of PKA 3 hr after training has no detectable effect on memory formation. We conclude that PKA contributes to the induction of a long-term memory 24 hr after training when activated during learning. Second, we demonstrate that the antisense technique is feasible in honeybeesin vivoand provides a new and powerful tool for the study of the molecular basis of learning and memory formation in insects.
Temporal Characteristics of Response Integration Evoked by Multiple Whisker Stimulations in the Barrel Cortex of Rats
Authors: Shimegi Satoshi , Ichikawa Takehiko , Akasaki Takafumi , Sato Hiromichi
Published: April 2018

We investigated the responses of 114 cells in the barrel cortex of rats to describe the temporal characteristics of excitatory interactions among neurons serving two vibrissae. To examine these interactions, the principal whisker and one adjacent whisker in the same row were stimulated simultaneously or serially at various interstimulus intervals (ISIs). In 37% of the cells tested, combined stimulation of two whiskers exhibited response facilitation; the response to the combined stimulus was larger than the sum of the responses to stimulation of the individual whiskers. The occurrence and magnitude of the facilitation were strongly dependent on the ISI. The ISI capable of producing facilitation for a particular cell was tuned to a narrow range (mean ± SD, 5.3 ± 2.3 msec). The ISI that evoked the maximal facilitation was 1.3 ± 1.3, 3.4 ± 2.3, and 2.8 ± 4.5 msec for neurons in layers II/III, IV, and V/VI, respectively. These ISIs corresponded to the difference in latencies between the responses to the individual stimulations of the principal and adjacent whiskers. A significant response facilitation was observed in the regular-spiking cells but not in the fast-spiking cells. When the ISI was longer than the range that evoked facilitation, a suppression of the response to the second whisker stimulation was observed. Facilitation was observed predominantly in layer II/III cells (69%) and to a lesser extent in cells of layers IV (15%) and V/VI (24%). Our results suggest that, in the barrel cortex, the temporal relationships among tactile stimuli are coded by facilitatory and inhibitory interactions among neurons located in neighboring barrel columns.
Ultrafast Inactivation Causes Inward Rectification in a Voltage-Gated K+Channel fromCaenorhabditis elegans
Authors: Fleischhauer Richard , Davis M. Wayne , Dzhura Igor , Neely Alan , Avery Leon , Joho Rolf H.
Published: April 2018

Theexp-2gene in the nematodeCaenorhabditis elegansinfluences the shape and duration of the action potential of pharyngeal muscle cells. Several loss-of-function mutations inexp-2lead to broadening of the action potential and to a concomitant slowing of the pumping action of the pharynx. In contrast, a gain-of-function mutation leads to narrow action potentials and shallow pumping. We cloned and functionally characterized theexp-2gene. Theexp-2gene is homologous to genes of the family of voltage-gated K+channels (Kv type). TheXenopusoocyte-expressed EXP-2 channel, although structurally closely related to Kv-type channels, is functionally distinct and very similar to the human ether-à-gogo-related gene (HERG) K+channel. In response to depolarization, EXP-2 activates slowly and inactivates very rapidly. On repolarization, recovery from inactivation is also rapid and strongly voltage-dependent. These kinetic properties make the Kv-type EXP-2 channel an inward rectifier that resembles the structurally unrelated HERG channel. Apart from many similarities to HERG, however, the molecular mechanism of fast inactivation appears to be different. Moreover, the single-channel conductance is 5- to 10-fold larger than that of HERG and most Kv-type K+channels. It appears that the inward rectification mechanism by rapid inactivation has evolved independently in two distinct classes of structurally unrelated, voltage-gated K+channels.
Inflammatory Mechanisms in Alzheimer's Disease: Inhibition of β-Amyloid-Stimulated Proinflammatory Responses and Neurotoxicity by PPARγ Agonists
Authors: Combs Colin K. , Johnson Derrick E. , Karlo J. Colleen , Cannady Steven B. , Landreth Gary E.
Published: April 2018

Alzheimer's disease (AD) is characterized by the extracellular deposition of β-amyloid fibrils within the brain and the subsequent association and phenotypic activation of microglial cells associated with the amyloid plaque. The activated microglia mount a complex local proinflammatory response with the secretion of a diverse range of inflammatory products. Nonsteroidal anti-inflammatory drugs (NSAIDs) are efficacious in reducing the incidence and risk of AD and significantly delaying disease progression. A recently appreciated target of NSAIDs is the ligand-activated nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ). PPARγ is a DNA-binding transcription factor whose transcriptional regulatory actions are activated after agonist binding. We report that NSAIDs, drugs of the thiazolidinedione class, and the natural ligand prostaglandin J2 act as agonists for PPARγ and inhibit the β-amyloid-stimulated secretion of proinflammatory products by microglia and monocytes responsible for neurotoxicity and astrocyte activation. The activation of PPARγ also arrested the differentiation of monocytes into activated macrophages. PPARγ agonists were shown to inhibit the β-amyloid-stimulated expression of the cytokine genes interleukin-6 and tumor necrosis factor α. Furthermore, PPARγ agonists inhibited the expression of cyclooxygenase-2. These data provide direct evidence that PPARγ plays a critical role in regulating the inflammatory responses of microglia and monocytes to β-amyloid. We argue that the efficacy of NSAIDs in the treatment of AD may be a consequence of their actions on PPARγ rather than on their canonical targets the cyclooxygenases. Importantly, the efficacy of these agents in inhibiting a broad range of inflammatory responses suggests PPARγ agonists may provide a novel therapeutic approach to AD.
Hebbian Mechanisms Revealed by Electrical Stimulation at Developing Rat Neuromuscular Junctions
Authors: Busetto Giuseppe , Buffelli Mario , Tognana Enrico , Bellico Francesco , Cangiano Alberto
Published: April 2018

Synapse competition and elimination are widespread developmental processes, first demonstrated at neonatal neuromuscular junctions. Action potential activity was long shown to exert a powerful influence, but mechanisms and contribution relative to other factors are still not well understood. Here we show that replacement of natural motoneuronal discharge with synchronous activity suppresses elimination of polyneuronal innervation of myofibers. This requires the simultaneous chronic conduction block (tetrodotoxin) and distal electrical stimulation of motor axons during ectopic synaptogenesis in denervated adult soleus muscle. If in fact chronic stimulation is applied without central block of motor axons, the time course of synapse elimination is as fast as in control muscles undergoing natural activity. Our findings follow the prediction of Hebb's postulate and imply that asynchronous activity drives developmental synapse elimination in muscle. They further suggest that motoneurons could become transiently synchronized during development and regeneration, helping to establish the initial polyneuronal innervation.
Expression of Neurotrophin-3 (NT-3) and Anterograde Axonal Transport of Endogenous NT-3 by Retinal Ganglion Cells in Chick Embryos
Authors: von Bartheld Christopher S. , Butowt Rafal
Published: April 2018

Anterograde axonal transport of neurotrophins has been demonstrated recently, but to date such transport has only been shown for brain-derived neurotrophic factor and no other endogenous neurotrophin. Endogenous neurotrophin-3 (NT-3) protein is present in the ganglion cell layer of the chicken retina, as well as the superficial layers of the optic tectum. NT-3 immunolabel in these tectal layers is largely reduced or abolished after treatment of the eye with colchicine or monensin, demonstrating that endogenous NT-3 is transported to the optic tectum by retinal ganglion cells (RGCs). Reverse transcription-PCR analysis of RGCs purified to 100% shows that RGCs, but not tectal cells, express NT-3 mRNA. Blockade of the intercellular transfer of NT-3 within the retina does not reduce the anterograde transport of endogenous NT-3 to the tectum, indicating that a major fraction of the anterogradely transported NT-3 is produced by RGCs rather than taken up from other retinal cells. Immunolabel for the neurotrophin receptor p75, but not trkB or trkC, in the superficial tectum coincides with the NT-3 label. The p75 label in the neuropil of superficial tectal layers is largely reduced or eliminated by injection of monensin in the eye, indicating that p75 protein is exported along RGC axons to the retinotectal terminals and may act as a neurotrophin carrier. These results show that NT-3 is produced by RGCs and that some of this NT-3 is transported anterogradely along the axons to the superficial layers of the tectum, possibly to regulate the survival, synapse formation, or dendritic growth of tectal neurons.
BDNF Promotes the Regenerative Sprouting, But Not Survival, of Injured Serotonergic Axons in the Adult Rat Brain
Authors: Mamounas Laura A. , Altar C. Anthony , Blue Mary E. , Kaplan David R. , Tessarollo Lino , Lyons W. Ernest
Published: April 2018

Brain-derived neurotrophic factor (BDNF) has trophic effects on serotonergic (5-HT) neurons in the adult brain and can prevent the severe loss of cortical 5-HT axons caused by the neurotoxinp-chloroamphetamine (PCA). However, it has not been determined whether BDNF promotes the survival of 5-HT axons during PCA-insult or facilitates their regenerative sprouting after injury. We show here that BDNF fails to protect most 5-HT axons from PCA-induced degeneration. Instead, chronic BDNF infusions markedly stimulate the sprouting of both intact and PCA-lesioned 5-HT axons, leading to a hyperinnervation at the neocortical infusion site. BDNF treatment promoted the regrowth of 5-HT axons when initiated up to a month after PCA administration. The sprouted axons persisted in cortex for at least 5 weeks after terminating exogenous BDNF delivery. BDNF also encouraged the regrowth of the 5-HT plexus in the hippocampus, but only in those lamina where 5-HT axons normally ramify. In addition, intracortical BDNF infusions induced a sustained local activation of the TrkB receptor. The dose–response profiles for BDNF to stimulate 5-HT sprouting and Trk signaling were remarkably similar, suggesting a physiological link between the two events; both responses were maximal at intermediate doses of BDNF but declined at higher doses (“inverted-U-shaped” dose–response curves). Underlying the downregulation of the Trk signal with excessive BDNF was a decline in full-length TrkB protein, but not truncated TrkB protein or TrkB mRNA levels. Thus, BDNF–TrkB signaling does not protect 5-HT neurons from axonal injury, but has a fundamental role in promoting the structural plasticity of these neurons in the adult brain.