bluuebunny/crossref_metadata_2025 huggingface dataset:
Voila, a NewDrosophilaCourtship Variant that Affects the Nervous System: Behavioral, Neural, and Genetic Characterization
Authors: Balakireva Maria , Stocker Reinhard F. , Gendre Nanaë , Ferveur Jean-François
Published: April 2018

InDrosophila melanogaster, a specificPGAL4transposon induces theVoila1genetic variant and produces multiple phenotypes. HomozygousVoila1/1flies rarely reach adulthood, whereas heterozygousVoila1/+adult males show strong bisexual behavior. Males with a single copy ofVoila1driving the feminizing transgeneUAS-transformershow very reduced sexual activity but no overall effect on their behavior.Voila1is specifically expressed in the nervous system. In the CNS, it is expressed mainly in the mushroom bodies and, to a lesser extent, in the antennal lobes. In the peripheral nervous system, GAL4 expression is almost entirely restricted to the gustatory sensilla. Using chromosomal deficiencies, the behavioral alteration was genetically mapped to the same location as thePGAL4element (86E1–2). The multiple behavioral effects of theVoilagenetic variant are discussed in light of its expression in the nervous system and its genetic basis.
Induction of Caspase-3-Like Protease May Mediate Delayed Neuronal Death in the Hippocampus after Transient Cerebral Ischemia
Authors: Chen Jun , Nagayama Tetsuya , Jin Kunlin , Stetler R. Anne , Zhu Raymond L. , Graham Steven H. , Simon Roger P.
Published: April 2018

Delayed neuronal death after transient cerebral ischemia may be mediated, in part, by the induction of apoptosis-regulatory gene products. Caspase-3 is a newly characterized mammalian cysteine protease that promotes cell death during brain development, in neuronal cultures, and in other cell types under many different conditions. To determine whether caspase-3 serves to regulate neuronal death after cerebral ischemia, we have (1) cloned a cDNA encoding the rat brain caspase-3; (2) examined caspase-3 mRNA and protein expression in the brain usingin situhybridization, Northern and Western blot analyses, and double-labeled immunohistochemistry; (3) determined caspase-3-like activity in brain cell extracts; and (4) studied the effect of caspase-3 inhibition on cell survival and DNA fragmentation in the hippocampus in a rat model of transient global ischemia. At 8–72 hr after ischemia, caspase-3 mRNA and protein were induced in the hippocampus and caudate-putamen (CPu), accompanied by increased caspase-3-like protease activity. In the hippocampus, caspase-3 mRNA and protein were predominantly increased in degenerating CA1 pyramidal neurons. Proteolytic activation of the caspase-3 precursor was detected in hippocampus and CPu but not in cortex at 4–72 hr after ischemia. Double-label experiments detected DNA fragmentation in the majority of CA1 neurons and selective CPu neurons that overexpressed caspase-3. Furthermore, ventricular infusion of Z-DEVD-FMK, a caspase-3 inhibitor, decreased caspase-3 activity in the hippocampus and significantly reduced cell death and DNA fragmentation in the CA1 sector up to 7 d after ischemia. These data strongly suggest that caspase-3 activity contributes to delayed neuronal death after transient ischemia.
Axon Withdrawal during Synapse Elimination at the Neuromuscular Junction Is Accompanied by Disassembly of the Postsynaptic Specialization and Withdrawal of Schwann Cell Processes
Authors: Culican Susan M. , Nelson Carla C. , Lichtman Jeff W.
Published: April 2018

Nerve terminal withdrawal is accompanied by a loss of acetylcholine receptors (AChRs) at corresponding postsynaptic sites during the process of synapse elimination at developing (Balice-Gordon and Lichtman, 1993) and reinnervated adult (Rich and Lichtman, 1989a) neuromuscular junctions. Aside from AChR and nerve terminal loss, however, the molecular and cellular alterations that occur at sites of elimination are unknown. To gain a better understanding of the cascade of events that leads to the disassembly of synaptic sites during the synapse elimination process, we surveyed the distribution of molecular elements of the postsynaptic specialization, the basal lamina, and supporting Schwann cells during the process of synapse elimination that occurs after reinnervation. In addition, quantitative techniques were used to determine the temporal order of disappearance of molecules that were lost relative to the loss of postsynaptic AChRs. We found that the dismantling of the postsynaptic specialization was inhomogeneous, with evidence of rapid dissolution of some aspects of the postsynaptic apparatus and slower loss of others. We also observed a loss of Schwann cell processes from sites of synapse elimination, with a time course similar to that seen for nerve terminal retraction. In contrast, all of the extracellular markers that we examined were lost slowly from sites of synapse loss. We therefore conclude that the synapse elimination process is synapse-wide, removing not only nerve terminals but also Schwann cells and many aspects of the postsynaptic apparatus. The disassembly occurs in a stereotyped sequence with some synaptic elements appearing much more stable than others.
Activity-Dependent Development of Calcium Regulation in Growing Motor Axons
Authors: Lnenicka Gregory A. , Arcaro Kathleen F. , Calabro John M.
Published: April 2018

In cultured nerve cord explants from the crayfish (Procambarus clarkii), the normal impulse activity levels of growing motor axons determine their response to Ca2+influx. During depolarization or Ca2+ionophore application, normally active tonic motor axons continue to grow, whereas inactive phasic motor axons retract and often degenerate. To determine the role of Ca2+regulation in this difference, we measured the intracellular free Ca2+concentration ([Ca2+]i) with fura-2. Growth cones from tonic axons normally had a higher [Ca2+]ithan those from phasic axons. When depolarized with 60 mmK+, growth cones and neurites from phasic axons had a [Ca2+]ithree to four times higher than did those from tonic axons. This difference in Ca2+regulation includes greater Ca2+-handling capacity for growing tonic axons; the increase in [Ca2+]iproduced by the Ca2+ionophore 4-bromo-A23187 (0.25 μm) is four to five times greater in phasic than in tonic axons, and the decline in [Ca2+]iat the end of a depolarizing pulse is three to four times faster in tonic axons than phasic ones. Blocking impulses in growing tonic axons for 2–3 d with tetrodotoxin reduces their capacity to regulate [Ca2+]i. Thus, growing tonic and phasic axons have differences in Ca2+regulation that develop as a result of their different activity levels. These activity-dependent differences in Ca2+regulation influence axon growth and degeneration and probably influence other neuronal processes that are mediated by changes in [Ca2+]i.
Differential Withdrawal of Retinal Axons Induced by a Secreted Factor
Authors: Ichijo Hiroyuki , Bonhoeffer Friedrich
Published: April 2018

To understand the development of the topographic map in the chick retinotectal projection, we studied the long-term interactions between retinal axons and tectal cell processes using a novel coculture system, theryomenchamber. Both nasal and temporal retinal axons initially grew equally well on a substrate consisting of posterior tectal cell processes; however, subsequently most temporal axons withdrew from this surface, whereas most nasal axons did not. Experiments using conditioned media indicate that posterior tectal cells induced withdrawal of the temporal axons by secreting a soluble factor. This withdrawal seems to be distinct from the immediate repulsive effect of ephrin-A2 (ELF-1) and ephrin-A5 (RAGS) seen in the stripe assay because (1) the withdrawal-inducing factor was diffusible, whereas ephrin-A2 and -A5 are membrane-bound, and (2) the withdrawal-inducing factor appeared later in development than ephrin-A2 and -A5. Furthermore, sensitivity to the withdrawal-inducing factor decreased continuously from the temporal to nasal retina. These results suggest that target cell-induced axonal withdrawal may be involved during a late stage of the development of the retinotectal map.
The Role of Parietal Cortex in Verbal Working Memory
Authors: Jonides John , Schumacher Eric H. , Smith Edward E. , Koeppe Robert A. , Awh Edward , Reuter-Lorenz Patricia A. , Marshuetz Christy , Willis Christopher R.
Published: April 2018

Neuroimaging studies of normal subjects and studies of patients with focal lesions implicate regions of parietal cortex in verbal working memory (VWM), yet the precise role of parietal cortex in VWM remains unclear. Some evidence (Paulesu et al., 1993; Awh et al., 1996) suggests that the parietal cortex mediates the storage of verbal information, but these studies and most previous ones included encoding and retrieval processes as well as storage and rehearsal of verbal information. A recent positron emission tomography (PET) study by Fiez et al. (1996) isolated storage and rehearsal from other VWM processes and did not find reliable activation in parietal cortex. This result suggests that parietal cortex may not be involved in VWM storage, contrary to previous proposals. However, we report two behavioral studies indicating that some of the verbal material used by Fiez et al. (1996) may not have required phonological representations in VWM. In addition, we report a PET study that isolated VWM encoding, retrieval, and storage and rehearsal processes in different PET scans and used material likely to require phonological codes in VWM. After subtraction of appropriate controls, the encoding condition revealed no reliable activations; the retrieval condition revealed reliable activations in dorsolateral prefrontal, anterior cingulate, posterior parietal, and extrastriate cortices, and the storage condition revealed reliable activations in dorsolateral prefrontal, inferior frontal, premotor, and posterior parietal cortices, as well as cerebellum. These results suggest that parietal regions are part of a network of brain areas that mediate the short-term storage and retrieval of phonologically coded verbal material.
Lasting N-Terminal Phosphorylation of c-Jun and Activation of c-Jun N-Terminal Kinases after Neuronal Injury
Authors: Herdegen Thomas , Claret Francois-Xavier , Kallunki Tuula , Martin-Villalba Ana , Winter Christine , Hunter Tony , Karin Michael
Published: April 2018

Transcription factor c-Jun is proposed to control neuronal cell death and survival, but its activation by N-terminal phosphorylation and the underlying activity of the c-Jun N-terminal kinases (JNKs) remain to be elucidated in the adult mammalian brain. We generated a polyclonal antiserum that specifically recognizes c-Jun phosphorylated at its serine 73 (S73) residue after UV irradiation of 3T3 cells. Disruption of thec-junlocus in 3T3 cells abolished this reaction, and retransfection of the humanc-junat thec-jun−/−background restored it.

The phospho-c-Jun antiserum was used to visualize N-terminally phosphorylated c-Jun in the adult rat brain with cellular resolution. Prolonged c-Jun S73 phosphorylation was detected in affected neurons up to 5 d after transient occlusion of medial cerebral artery or up to 50 d after transection of central nerve fiber tracts. After cerebral ischemia–reperfusion, phosphorylation of c-Jun was linked with induced expression of Fas-ligand (APO-1, CD95-ligand), whose gene is a putative c-Jun/AP-1 target, and with terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (TUNEL) reactivity, a marker for apoptosis. After nerve fiber transection, however, lasting c-Jun phosphorylation occurred in axotomized neurons negative for Fas-ligand or TUNEL and regardless of degeneration or survival. In contrast to these lasting phosphorylation patterns, transient seizure activity by pentylenetetrazole provoked only a brief c-Jun phosphorylation and JNK activation.

In extracts from ischemic or axotomized brain compartments, c-Jun phosphorylation correlated with enhanced long-term JNK activity, and in-gel kinase assays visualized proteins with sizes corresponding to JNK isoforms as the only c-Jun N-terminally phosphorylating enzymes.

These results demonstrate that lasting c-Jun S73 phosphorylation and JNK activity are part of neuronal stress response after neurodegenerative disorders in the adult mammalian brain with Fas-ligand as a putative apoptotic effector.
Neuronal Matrix Metalloproteinase-2 Degrades and Inactivates a Neurite-Inhibiting Chondroitin Sulfate Proteoglycan
Authors: Zuo Jian , Ferguson Toby A. , Hernandez Yosbani J. , Stetler-Stevenson William G. , Muir David
Published: April 2018

Chondroitin sulfate proteoglycans (CSPGs) are implicated in the regulation of axonal growth. We previously reported that the neurite-promoting activity of laminin is inhibited by association with a Schwann cell-derived CSPG and that endoneurial laminin may be inhibited by this CSPG as well [Zuo J, Hernandez YJ, Muir D (1998) Chondroitin sulfate proteoglycan with neurite-inhibiting activity is upregulated after peripheral nerve injury. J Neurobiol 34:41–54]. Mechanisms regulating axonal growth were studied by using anin vitrobioassay in which regenerating embryonic dorsal root ganglionic neurons (DRGn) were grown on sections of normal adult nerve. DRGn achieved slow neuritic growth on sections of normal nerve, which was reduced significantly by treatment with metalloproteinase inhibitors. Similar results were obtained on a synthetic substratum composed of laminin and inhibitory CSPG. DRGn expressed the matrix metalloproteinase, MMP-2, which was transported to the growth cone. Recombinant MMP-2 inactivated the neurite-inhibiting CSPG without hindering the neurite-promoting potential of laminin. Similarly, neuritic growth by DRGn cultured on normal nerve sections was increased markedly by first treating the nerve sections with MMP-2. The proteolytic deinhibition by MMP-2 was equivalent to and nonadditive with that achieved by chondroitinase, suggesting that both enzymes inactivated inhibitory CSPG. Additionally, the increases in neuritic growth resulting from treating nerve sections with MMP-2 or chondroitinase were blocked by anti-laminin antibodies. From these results we conclude that MMP-2 provides a mechanism for the deinhibition of laminin in the endoneurial basal lamina and may play an important role in the regeneration of peripheral nerve.
G-Protein-Dependent Facilitation of Neuronal α1A, α1B, and α1ECa Channels
Authors: Meza Ulises , Adams Brett
Published: April 2018

Modulation of neuronal voltage-gated Ca channels has important implications for synaptic function. To investigate the mechanisms of Ca channel modulation, we compared the G-protein-dependent facilitation of three neuronal Ca channels. α1A, α1B, or α1Esubunits were transiently coexpressed with α2–δband β3subunits in HEK293 cells, and whole-cell currents were recorded. After intracellular dialysis with GTPγS, strongly depolarized conditioning pulses facilitated currents mediated by each Ca channel type. The magnitude of facilitation depended on current density, with low-density currents being most strongly facilitated and high-density currents often lacking facilitation. Facilitating depolarizations speeded channel activation ∼1.7-fold for α1Aand α1Band increased current amplitudes by the same proportion, demonstrating equivalent facilitation of G-protein-inhibited α1Aand α1Bchannels. Inactivation typically obscured facilitation of α1Ecurrent amplitudes, but the activation kinetics of α1Ecurrents showed consistent and pronounced G-protein-dependent facilitation. The onset and decay of facilitation had the same kinetics for α1A, α1B, and α1E, suggesting that Gβγ dimers dissociate from and reassociate with these Ca channels at very similar rates. To investigate the structural basis for N-type Ca channel modulation, we expressed a mutant of α1Bmissing large segments of the II–III loop and C terminus. This deletion mutant exhibited undiminished G-protein-dependent facilitation, demonstrating that a Gβγ interaction site recently identified within the C terminus of α1Eis not required for modulation of α1B.
Regulated Expression of the Cell Adhesion Glycoprotein F3 in Adult Hypothalamic Magnocellular Neurons
Authors: Pierre Karin , Rougon Geneviève , Allard Michèle , Bonhomme Renée , Gennarini Gianfranco , Poulain Dominique A. , Theodosis Dionysia. T.
Published: April 2018

F3, a glycoprotein of the immunoglobulin superfamily implicated in axonal growth, occurs in oxytocin (OT)-secreting and vasopressin (AVP)-secreting neurons of the adult hypothalamo-neurohypophysial system (HNS) whose axons undergo morphological changes in response to stimulation. Immunocytochemistry and immunoblot analysis showed that during basal conditions of HNS secretion, there are higher levels of this glycosylphosphatidyl inositol-anchored protein in the neurohypophysis, where their axons terminate, than in the hypothalamic nuclei containing their somata. Physiological stimulation (lactation, osmotic challenge) reversed this pattern and resulted in upregulation of F3 expression, paralleling that of OT and AVP under these conditions.In situhybridization revealed that F3 expression in the hypothalamus is restricted to its magnocellular neurons and demonstrated a more than threefold increase in F3 mRNA levels in response to stimulation. Confocal and electron microscopy localized F3 in secretory granules in all neuronal compartments, a localization confirmed by detection of F3 immunoreactivity in granule-enriched fractions obtained by sucrose density gradient fractionation of rat neurohypophyses. F3 was not visible on any cell surface in the magnocellular nuclei. In contrast, in the neurohypophysis, it was present not only in secretory granules but also on the surface of axon terminals and glia and in extracellular spaces.

Taken together, our observations reveal that the cell adhesion glycoprotein F3 is colocalized with neurohypophysial peptides in secretory granules. It follows, therefore, the regulated pathway of secretion in HNS neurons to be released by exocytosis at their axon terminals in the neurohypophysis, where it may intervene in activity-dependent structural axonal plasticity.
Monocular Core Zones and Binocular Border Strips in Primate Striate Cortex Revealed by the Contrasting Effects of Enucleation, Eyelid Suture, and Retinal Laser Lesions on Cytochrome Oxidase Activity
Authors: Horton Jonathan C. , Hocking Davina R.
Published: April 2018

In primate striate cortex, geniculocortical afferents in layer IVc terminate in parallel stripes called ocular dominance columns. We propose that this segregation of ocular inputs generates a related but distinct columnar system of monocular core zones alternating with binocular border strips. Evidence for this functional parcellation was obtained by comparing the effects of enucleation, eyelid suture, and retinal laser lesions on cytochrome oxidase (CO) activity in eight macaques. Enucleation produced a high-contrast pattern of dark and light columns in layer IVc, corresponding precisely to the ocular dominance columns, whereas eyelid suture produced a low-contrast pattern of thin dark columns alternating with wide pale columns. [3H]Proline eye injection showed that the thin dark columns corresponded to the core zones of the open eye’s ocular dominance columns. The wide pale columns resulted from loss of CO activity in the sutured eye’s core zones and within both eyes’ border strips. Loss of CO activity within both eyes’ border strips suggested that these regions are binocular. To confirm our findings, we compared different CO patterns in the same cortex by making retinal laser lesions in four animals. They produced a CO pattern tantamount to “focal” enucleation, although contrast was low when laser damage was confined to the outer retina. CO levels in cortical scotomas remained severely depressed for months after retinal lesions, even when the other eye was enucleated. This observation provided little anatomical support for the notion of topographic plasticity after visual deafferentation. In a single human subject with macular degeneration, CO revealed a low-contrast pattern of ocular dominance columns, resembling the pattern in monkeys with laser-induced photoreceptor damage.
Anterograde Signaling by Nitric Oxide: Characterization andIn VitroReconstitution of an Identified Nitrergic Synapse
Authors: Park Ji-Ho , Straub Volko A. , O’Shea Michael
Published: April 2018

Nitric oxide (NO) is recognized as a signaling molecule in the CNS where it is a candidate retrograde neurotransmitter. Here we provide direct evidence that NO mediates slow excitatory anterograde transmission between the NO synthase (NOS)-expressing B2 neuron and an NO-responsive follower neuron named B7nor. Both are motoneurons located in the buccal ganglia of the snailLymnaea stagnaliswhere they participate in feeding behavior. Transmission between B2 and B7nor is blocked by inhibiting NOS and is suppressed by extracellular scavenging of NO. Furthermore, focal application of NO to the cell body of the B7nor neuron causes a depolarization that mimics the effect of B2 activity. The slow interaction between the B2 and B7nor neurons can be re-established when the two neurons are cocultured, and it shows the same susceptibility to NOS inhibition and NO scavenging. In cell culture we have also examined spatial aspects of NO signaling. We show that before the formation of an anatomical connection, the presynaptic neuron can cause depolarizing potentials in the follower neuron at distances up to 50 μm. The strength of the interaction increases when the distance between the cells is reduced. Our results suggest that NO can function as both a synaptic and a nonsynaptic signaling molecule.
Glutamate Receptor Targeting to Synaptic Populations on Purkinje Cells Is Developmentally Regulated
Authors: Zhao Hui-Min , Wenthold Robert J. , Petralia Ronald S.
Published: April 2018

Selective targeting of neurotransmitter receptors to specific synapse populations occurs in adult neurons, but little is known about the development of these receptor distribution patterns. In this study, we demonstrate that a specific developmental switch occurs in the targeting of a receptor to an identified synapse population. Localization of delta and AMPA glutamate receptors at parallel and climbing fiber synapses on the developing Purkinje cells was studied using postembedding immunogold. Delta receptors were found to be abundant on postsynaptic membranes at parallel fiber synapses from postnatal day 10 (P10) to adult. In contrast, delta receptors were found to be high at climbing fiber synapses only at P10 and P14. Thus, a major finding of this paper is that high levels of delta receptors are transiently expressed in climbing fiber synapses in the second postnatal week. Labeling of synapses with anti-delta receptor antibody at P10 was limited to the postsynaptic membrane of excitatory synapses and was absent from GABAergic synapses. Unlike delta receptor immunolabeling, AMPA receptor immunolabeling (GluR2/3 and GluR2 antibodies) was high in the postsynaptic membranes of synapses at early postnatal ages (P2 and P5) and was higher in climbing fiber synapses than in parallel fiber synapses from P10 to adult. The present study shows that synapse-specific targeting of glutamate receptors in Purkinje cells is developmentally regulated, with the postsynaptic receptor composition established during synapse maturation. This composition is not dependent on the nature of the initial establishment of synaptic connections.
The Role of Corticotropin-Releasing Factor and Corticosterone in Stress- and Cocaine-Induced Relapse to Cocaine Seeking in Rats
Authors: Erb Suzanne , Shaham Yavin , Stewart Jane
Published: April 2018

We have shown previously that footshock stress and priming injections of cocaine reinstate cocaine seeking in rats after prolonged drug-free periods (Erb et al., 1996). Here we examined the role of brain corticotropin-releasing factor (CRF) and the adrenal hormone corticosterone in stress- and cocaine-induced reinstatement of cocaine seeking in rats. The ability of footshock stress and priming injections of cocaine to induce relapse to cocaine seeking was studied after intracerebroventricular infusions of the CRF receptor antagonistd-Phe CRF12–41, after adrenalectomy, and after adrenalectomy with corticosterone replacement. Rats were allowed to self-administer cocaine (1.0 mg/kg/infusion, i.v) for 3 hr daily for 10–14 d and were then placed on an extinction schedule during which saline was substituted for cocaine. Tests for reinstatement were given after intermittent footshock (10 min; 0.5 mA) and after priming injections of saline and cocaine (20 mg/kg, i.p.). Footshock reinstated cocaine seeking in both intact animals and animals with corticosterone replacement but not in adrenalectomized animals. The CRF receptor antagonistd-Phe CRF12–41blocked footshock-induced reinstatement at all doses tested in both intact animals and animals with corticosterone replacement. Reinstatement by priming injections of cocaine was only minimally attenuated by adrenalectomy and by pretreatment withd-Phe CRF12–41. These data suggest that brain CRF plays a critical role in stress-induced, but only a modulatory role in cocaine-induced, reinstatement of cocaine seeking. Furthermore, the data show that although reinstatement of cocaine seeking by footshock stress requires minimal, basal, levels of corticosterone, stress-induced increases in corticosterone do not play a role in this effect.
Cloning and Functional Expression of anAplysia5-HT Receptor Negatively Coupled to Adenylate Cyclase
Authors: Angers Annie , Storozhuk Maksim V. , Duchaı̂ne Thomas , Castellucci Vincent F. , DesGroseillers Luc
Published: April 2018

Serotonin (5-HT) is involved in the control of various behaviors inAplysia californica, including reproduction, feeding, locomotion, circadian rhythm, synaptic plasticity, and synaptic growth. The large variety of functions of 5-HT is mediated by different receptor subtypes that are coupled to different second-messenger systems. Here, we report the cloning of a cDNA coding for anAplysiaG-protein-coupled 5-HT receptor (5-HTap1). Its deduced amino acid sequence resembles those of the 5-HT1receptor subfamily. When expressed in stable cell lines, 5-HTap1exhibits high-affinity binding for the serotonergic radioligand [N-methyl-3H]lysergic acid diethylamide. This binding is competed by several 5-HT agonists and antagonists, and the pharmacological profile of inhibition has some similarities with those of 5-HT1and 5-HT7receptors. Application of 5-HT or its agonists 5-carboxamidotryptamine maleate and (±)-8-hydroxy-2-(di-n-propyl-amino) tetralin hydrobromide on cells transformed with 5-HTap1produced a dose-dependent inhibition of forskolin-stimulated cAMP accumulation. 5-HTap1is thus negatively coupled to adenylate cyclase. The production of antiserum against the 5-HTap1receptor allowed us to examine its expression in animal tissues. The receptor protein is detected in every tissue examined, although it seems only weakly expressed in some samples. The receptor is also found in every ganglia of the nervous system, both in the sheath and in the neurons. 5-HTap1mRNA is absent from the sheath, indicating that the protein observed there is probably located on the nerve terminals.
The K+Channel GeneEther a Go-GoIs Required for the Transduction of a Subset of Odorants in AdultDrosophila melanogaster
Authors: Dubin Adrienne E. , Liles Margaret M. , Harris Greg L.
Published: April 2018

The functional identity of an olfactory receptor neuron is determined in part by its repertoire of responses to odorants. As an approach toward understanding the contributions of particular conductances to olfactory neuron excitability and odor discrimination, we have investigated the role of the putative cyclic nucleotide-modulated K+channel subunit encoded by theether a go-go(eag) gene in odorant responsiveness inDrosophila melanogaster. Four independent mutanteagalleles exhibited reduced antennal sensitivity to a subset of nine odorants, all having short aliphatic side chains: ethyl butyrate (EB), propionic acid, 2-butanone, and ethyl acetate. Significantly fewereagantennal neurons responded to EB compared with control neurons; the proportion sensitive to 2-heptanone was similar to controls. Two aspects of the character of EB-induced excitability were affected by mutations ineag. First, fewer EB-induced inhibitory responses were observed ineagmutants, and second, fewer excitatory odorant responses dependent on extracellular Ca2+were observed. Furthermore, modulation of neuronal excitability by membrane-permeant cyclic nucleotide analogs was largelyeagdependent. Focal application of high K+saline to sensillae altered the excitability of the majority of neurons from wild-type but noteagantennae, suggesting that Eag may have a dendritic localization.
Contrast-Invariant Orientation Tuning in Cat Visual Cortex: Thalamocortical Input Tuning and Correlation-Based Intracortical Connectivity
Authors: Troyer Todd W. , Krukowski Anton E. , Priebe Nicholas J. , Miller Kenneth D.
Published: April 2018

The origin of orientation selectivity in visual cortical responses is a central problem for understanding cerebral cortical circuitry. In cats, many experiments suggest that orientation selectivity arises from the arrangement of lateral geniculate nucleus (LGN) afferents to layer 4 simple cells. However, this explanation is not sufficient to account for the contrast invariance of orientation tuning.

To understand contrast invariance, we first characterize the input to cat simple cells generated by the oriented arrangement of LGN afferents. We demonstrate that it has two components: a spatial-phase-specific component (i.e., one that depends on receptive field spatial phase), which is tuned for orientation, and a phase-nonspecific component, which is untuned. Both components grow with contrast.

Second, we show that a correlation-based intracortical circuit, in which connectivity between cell pairs is determined by the correlation of their LGN inputs, is sufficient to achieve well tuned, contrast-invariant orientation tuning. This circuit generates both spatially opponent, “antiphase” inhibition (“push–pull”), and spatially matched, “same-phase” excitation. The inhibition, if sufficiently strong, suppresses the untuned input component and sharpens responses to the tuned component at all contrasts. The excitation amplifies tuned responses. This circuit agrees with experimental evidence showing spatial opponency between, and similar orientation tuning of, the excitatory and inhibitory inputs received by a simple cell. Orientation tuning is primarily input driven, accounting for the observed invariance of tuning width after removal of intracortical synaptic input, as well as for the dependence of orientation tuning on stimulus spatial frequency.

The model differs from previous push–pull models in requiring dominant rather than balanced inhibition and in predicting that a population of layer 4 inhibitory neurons should respond in a contrast-dependent manner to stimuli of all orientations, although their tuning width may be similar to that of excitatory neurons. The model demonstrates that fundamental response properties of cortical layer 4 can be explained by circuitry expected to develop under correlation-based rules of synaptic plasticity, and shows how such circuitry allows the cortex to distinguish stimulus intensity from stimulus form.
Cellular Correlates of Long-Term Sensitization inAplysia
Authors: Cleary Leonard J. , Lee Wai L. , Byrne John H.
Published: April 2018

Althoughin vitroanalyses of long-term changes in the sensorimotor connection ofAplysiahave been used extensively to understand long-term sensitization, relatively little is known about the ways in which the connection is modified by learningin vivo. Moreover, sites other than the sensory neurons might be modified as well. In this paper, several different biophysical properties of sensory neurons, motor neurons, and LPl17, an identified interneuron, were examined. Membrane properties of sensory neurons, which were expressed as increased excitability and increased spike afterdepolarization, were affected by the training. The biophysical properties of motor neurons also were affected by training, resulting in hyperpolarization of the resting membrane potential and a decrease in spike threshold. These results suggest that motor neurons are potential loci for storage of the memory in sensitization. The strength of the connection between sensory and motor neurons was affected by the training, although the connection between LPl17 and the motor neuron was unaffected. Biophysical properties of LPl17 were unaffected by training. The results emphasize the importance of plasticity at sensory–motor synapses and are consistent with the idea that there are multiple sites of plasticity distributed throughout the nervous system.
Anion Currents and Predicted Glutamate Flux through a Neuronal Glutamate Transporter
Authors: Otis Thomas S. , Jahr Craig E.
Published: April 2018

Kinetic properties of a native, neuronal glutamate transporter were studied by using rapid applications of glutamate to outside-out patches excised from Purkinje neurons. Pulses of glutamate activated anion currents associated with the transporter that were weakly antagonized by the transporter antagonist kainate. In addition, kainate blocked a resting anion conductance observed in the absence of glutamate. Transporter currents in response to glutamate concentration jumps under a variety of conditions were used to construct a cyclic kinetic model of the transporter. The model simulates both the anion conductance and the glutamate flux through the transporter, thereby permitting several predictions regarding the dynamics of glutamate transport at the synapse. For example, the concentration-dependent binding rate of glutamate to the transporter is high, similar to binding rates suggested for ligand-gated glutamate receptors. At saturating glutamate concentrations, transporters cycle at a steady-state rate of 13/sec. Transporters are predicted to have a high efficiency; once bound, a glutamate molecule is more likely to be transported than to unbind. Physiological concentrations of internal sodium and glutamate significantly slow net transport. Finally, a fixed proportion of anion and glutamate flux is expected over a wide range of circumstances, providing theoretical support for using net charge flux to estimate the amount and time course of glutamate transport.
Imaging Spreading Depression and Associated Intracellular Calcium Waves in Brain Slices
Authors: Basarsky Trent A. , Duffy Steven N. , Andrew R. David , MacVicar Brian A.
Published: April 2018

Spreading depression (SD) was analyzed in hippocampal and neocortical brain slices by imaging intrinsic optical signals in combination with either simultaneous electrophysiological recordings or imaging of intracellular calcium dynamics. The goal was to determine the roles of intracellular calcium (Ca2+int) waves in the generation and propagation of SD. Imaging of intrinsic optical signals in the hippocampus showed that ouabain consistently induced SD, which characteristically started in the CA1 region, propagated at 15–35 μm/sec, and traversed across the hippocampal fissure to the dentate gyrus. In the dendritic regions of both CA1 and the dentate gyrus, SD caused a transient increase in light transmittance, characterized by both a rapid onset and a rapid recovery. In contrast, in the cell body regions the transmittance increase was prolonged. Simultaneous imaging of intracellular calcium and intrinsic optical signals revealed that a slow Ca2+intincrease preceded any change in transmittance. Additionally, a wave of increased Ca2+inttypically propagated many seconds ahead of the change in transmittance. These calcium increases were also observed in individual astrocytes injected with calcium orange, indicating that Ca2+intwaves were normally associated with SD. However, when hippocampal slices were incubated in calcium-free/EGTA external solutions, SD was still observed, although Ca2+intwaves were completely abolished. Under these conditions SD had a comparable peak increase in transmittance but a slower onset and a faster recovery. These results demonstrate that although there are calcium dynamics associated with SD, these increases are not necessary for the initiation or propagation of spreading depression.
Embryonic Expression of the Myelin Basic Protein Gene: Identification of a Promoter Region That Targets Transgene Expression to Pioneer Neurons
Authors: Landry Charles F. , Pribyl Thomas M. , Ellison Julie A. , Givogri M. Irene , Kampf Kathy , Campagnoni Celia W. , Campagnoni Anthony T.
Published: April 2018

The myelin basic protein (MBP) gene produces two families of structurally related proteins from three different promoters—the golli products, generated from the most upstream promoter, and the MBPs, produced from the two downstream promoters. In this report we describe the expression of golli proteins within some of the earliest neuronal populations of the brain, including Cajal–Retzius cells and preplate neurons of the forebrain, representing a new marker for these cells. To identify elements responsible for neuronal expression of the golli products, we generated transgenic animals from constructs containing different portions of the upstream promoter. A construct containing 1.1 kb immediately upstream of the golli transcription start site targeted expression of β-galactosidase to preplate neurons and a subset of Cajal–Retzius cells in transgenic mice—the first reported genetic element to target expression to these pioneer cortical populations. Although expression in Cajal–Retzius cells declined with embryonic development, preplate cells continued to express the transgene after arriving at their final destination in the subplate. Interestingly, expression persisted in subplate neurons found within a distinct layer between the white matter and cortical layer VI well into postnatal life. Birth dating studies with bromodeoxyuridine indicated that these neurons were born between E10.5 and E12.5. Thus, the transgene marked subplate neurons from their birth, providing a fate marker for these cells. This work suggests a role for the MBP gene in the early developing brain long before myelination and especially in the pioneer cortical neurons important in the formation of the cortical layers.
TrkB and TrkC Signaling Are Required for Maturation and Synaptogenesis of Hippocampal Connections
Authors: Martı́nez Albert , Alcántara Soledad , Borrell Vı́ctor , Del Rı́o José A. , Blasi Joan , Otal Raquel , Campos Narciso , Boronat Albert , Barbacid Mariano , Silos-Santiago Inmaculada , Soriano Eduardo
Published: April 2018

Recent studies have suggested a role for neurotrophins in the growth and refinement of neural connections, in dendritic growth, and in activity-dependent adult plasticity. To unravel the role of endogenous neurotrophins in the development of neural connections in the CNS, we studied the ontogeny of hippocampal afferents intrkB (−/−) andtrkC (−/−) mice. Injections of lipophilic tracers in the entorhinal cortex and hippocampus of newborn mutant mice showed that the ingrowth of entorhinal and commissural/associational afferents to the hippocampus was not affected by these mutations. Similarly, injections of biocytin in postnatal mutant mice (P10–P16) did not reveal major differences in the topographic patterns of hippocampal connections.

In contrast, quantification of biocytin-filled axons showed that commissural and entorhinal afferents have a reduced number of axon collaterals (21–49%) and decreased densities of axonal varicosities (8–17%) in bothtrkB (−/−) andtrkC (−/−) mice. In addition, electron microscopic analyses showed thattrkB (−/−) andtrkC (−/−) mice have lower densities of synaptic contacts and important structural alterations of presynaptic boutons, such as decreased density of synaptic vesicles. Finally, immunocytochemical studies revealed a reduced expression of the synaptic-associated proteins responsible for synaptic vesicle exocytosis and neurotransmitter release (v-SNAREs and t-SNAREs), especially intrkB (−/−) mice. We conclude that neithertrkB nortrkC genes are essential for the ingrowth or layer-specific targeting of hippocampal connections, although the lack of these receptors results in reduced axonal arborization and synaptic density, which indicates a role for TrkB and TrkC receptors in the developmental regulation of synaptic inputs in the CNSin vivo. The data also suggest that the genes encoding for synaptic proteins may be targets of TrkB and TrkC signaling pathways.
A Statistical Paradigm for Neural Spike Train Decoding Applied to Position Prediction from Ensemble Firing Patterns of Rat Hippocampal Place Cells
Authors: Brown Emery N. , Frank Loren M. , Tang Dengda , Quirk Michael C. , Wilson Matthew A.
Published: April 2018

The problem of predicting the position of a freely foraging rat based on the ensemble firing patterns of place cells recorded from the CA1 region of its hippocampus is used to develop a two-stage statistical paradigm for neural spike train decoding. In the first, or encoding stage, place cell spiking activity is modeled as an inhomogeneous Poisson process whose instantaneous rate is a function of the animal’s position in space and phase of its theta rhythm. The animal’s path is modeled as a Gaussian random walk. In the second, or decoding stage, a Bayesian statistical paradigm is used to derive a nonlinear recursive causal filter algorithm for predicting the position of the animal from the place cell ensemble firing patterns. The algebra of the decoding algorithm defines an explicit map of the discrete spike trains into the position prediction. The confidence regions for the position predictions quantify spike train information in terms of the most probable locations of the animal given the ensemble firing pattern. Under our inhomogeneous Poisson model position was a three to five times stronger modulator of the place cell spiking activity than theta phase in an open circular environment. For animal 1 (2) the median decoding error based on 34 (33) place cells recorded during 10 min of foraging was 8.0 (7.7) cm. Our statistical paradigm provides a reliable approach for quantifying the spatial information in the ensemble place cell firing patterns and defines a generally applicable framework for studying information encoding in neural systems.
Low Doses of Ethanol Reduce Evidence for Nonlinear Structure in Brain Activity
Authors: Ehlers Cindy L. , Havstad James , Prichard Dean , Theiler James
Published: April 2018

Recent theories of the effects of ethanol on the brain have focused on its direct actions on neuronal membrane proteins. However, neuromolecular mechanisms whereby ethanol produces its CNS effects in low doses typically used by social drinkers (e.g., 2–3 drinks, 10–25 mm, 0.05–0.125 gm/dl) remain less well understood. We propose the hypothesis that ethanol may act by introducing a level of randomness or “noise” in brain electrical activity. We investigated the hypothesis by applying a battery of tests originally developed for nonlinear time series analysis and chaos theory to EEG data collected from 32 men who had participated in an ethanol/placebo challenge protocol. Because nonlinearity is a prerequisite for chaos and because we can detect nonlinearity more reliably than chaos, we concentrated on a series of measures that quantitated different aspects of nonlinearity. For each of these measures the method of surrogate data was used to assess the significance of evidence for nonlinear structure. Significant nonlinear structure was found in the EEG as evidenced by the measures of time asymmetry, determinism, and redundancy. In addition, the evidence for nonlinear structure in the placebo condition was found to be significantly greater than that for ethanol. Nonlinear measures, but not spectral measures, were found to correlate with a subject’s overall feeling of intoxication. These findings are consistent with the notion that ethanol may act by introducing a level of randomness in neuronal processing as assessed by EEG nonlinear structure.
Postnatal Development of Type I and Type II Hair Cells in the Mouse Utricle: Acquisition of Voltage-Gated Conductances and Differentiated Morphology
Authors: Rüsch Alfons , Lysakowski Anna , Eatock Ruth Anne
Published: April 2018

The type I and type II hair cells of mature amniote vestibular organs have been classified according to their afferent nerve terminals: calyx and bouton, respectively. Mature type I and type II cells also have different complements of voltage-gated channels. Type I cells alone express a delayed rectifier, gK,L, that is activated at resting potential. We report that in mouse utricles this electrophysiological differentiation occurs during the first postnatal week. Whole-cell currents were recorded from hair cells in denervated organotypic cultures and in acutely excised epithelia. From postnatal day 1 (P1) to P3, most hair cells expressed a delayed rectifier that activated positive to resting potential and a fast inward rectifier, gK1. Between P4 and P8, many cells acquired the type I-specific conductance gK,Land/or a slow inward rectifier, gh. By P8, the percentages of cells expressing gK,Land ghwere at mature levels.

To investigate whether the electrophysiological differentiation correlated with morphological changes, we fixed utricles at different times between P0 and P28. Ultrastructural criteria were developed to classify cells when calyces were not present, as in cultures and neonatal organs. The morphological and electrophysiological differentiation followed different time courses, converging by P28. At P0, when no hair cells expressed gK,L, 33% were classified as type I by ultrastructural criteria. By P28, ∼60% of hair cells in acute preparations received calyx terminals and expressed gK,L. Data from the denervated cultures showed that neither electrophysiological nor morphological differentiation depended on ongoing innervation.
Center–Surround Antagonism Based on Disparity in Primate Area MT
Authors: Bradley David C. , Andersen Richard A.
Published: April 2018

Most neurons in primate visual area MT have a large, modulatory region surrounding their classically defined receptive field, or center. The velocity tuning of this “surround” is generally antagonistic to the center, making it potentially useful for detecting image discontinuities on the basis of differential motion. Because classical MT receptive fields are also disparity-selective, one might expect to find disparity-based surround antagonism as well; this would provide additional information about image discontinuities. However, the effects of disparity in the MT surround have not been studied previously. We measured single-neuron responses to variable-disparity moving patterns in the MT surround while holding a central moving pattern at a fixed disparity. Of the 130 neurons tested, 84% exhibited a modulatory surround, and in 52% of these, responses were significantly affected by disparity in the surround. In most cases, disparity effects in the surround were antagonistic to the center; that is, neurons were generally suppressed when center and surround stimuli had the same disparity, with decreasing suppression as the center and surround stimuli became separated in depth. Also, the effects of disparity and direction were mainly additive; i.e., disparity effects were generally independent of direction, and vice versa. These results suggest that the MT center–surround apparatus provides information about image discontinuities, not only on the basis of velocity differences but on the basis of depth differences as well. This supports the hypothesis that MT surrounds have a role in image segmentation.