bluuebunny/crossref_metadata_2025 huggingface dataset:
Interneurons of the Dentate–Hilus Border of the Rat Dentate Gyrus: Morphological and Electrophysiological Heterogeneity
Authors: Mott David D. , Turner Dennis A. , Okazaki Maxine M. , Lewis Darrell V.
Published: April 2018

Interneurons located near the border of the dentate granule cell layer and the hilus were studied in hippocampal slices using whole-cell current clamp and biocytin staining. Because these interneurons exhibit both morphological and electrophysiological diversity, we asked whether passive electrotonic parameters or repetitive firing behavior correlated with axonal distribution. Each interneuron was distinguished by a preferred axonal distribution in the molecular layer or granule cell layer, and four groups could be discerned, the axons of which arborized in (1) the granule cell layer, (2) the inner molecular layer, (3) the outer molecular layer, and (4) diffusely in the molecular layer. In our sample, interneurons with axons arborizing diffusely in the molecular layer were most frequent, and those with axons restricted to the granule cell layer were least frequent. Resting potential, input resistance, time constant, electrotonic length, and spike frequency adaptation (SFA) were not significantly different among the four groups, and the variability in SFA between cells with similar axonal distributions was striking. Clear differences in action potential morphology and afterhyperpolarizations, however, emerged when nonadapting interneurons were compared with those exhibiting SFA. Interneurons exhibiting SFA had characteristically broader spikes, progressive slowing of action potential repolarization during repetitive firing, and slow afterhyperpolarizations that distinguished them from nonadapting interneurons. We propose that the variability in repetitive firing behavior and morphology exhibited by each of these interneurons makes each interneuron unique and may provide a high level of fine tuning of inhibitory control critical to information processing in the dentate.
A Novel Basal Promoter Element Is Required for Expression of the Rat Tyrosine Hydroxylase Gene
Authors: Patankar Swati , Lazaroff Meredith , Yoon Sung Ok , Chikaraishi Dona M.
Published: April 2018

Transcription of the rat tyrosine hydroxylase (TH) gene is controlled by enhancer sequences in its 5′ flanking region; these enhancers include the AP1, dyad, and cAMP response element (CRE) motifs. We show that a novel basal promoter element (−17 GCCTGCCTGGCGA −5) positioned between the TATA box and +1 works in conjunction with the upstream AP1-dyad and CRE enhancers but cannot support transcription by itself. A mutation of this element, termed partial dyad, reduces basal expression of a reporter gene in TH-positive cell lines and TH-negative lines but has no effect on cAMP- or KCl-induced expression. A double mutant at positions −17 and −11 of the partial dyad reduces transcriptional activation by 80%. Conversely, insertion of this element into a heterologous promoter restores basal expression to levels mediated by the native TH promoter. The partial dyad is a novel activational element that is required for full expression of the TH gene and may assist in the function of the AP1, dyad, and CRE motifs and also other enhancers further upstream. Hence, the rat TH gene is unusual in that its enhancers will not function with a heterologous promoter but require a specific TH promoter sequence for full activation.
Neuritic Outgrowth Associated with Astroglial Phenotypic Changes Induced by Antisense Glial Fibrillary Acidic Protein (GFAP) mRNA in Injured Neuron–Astrocyte Cocultures
Authors: Lefrançois Thierry , Fages Christiane , Peschanski Marc , Tardy Marcienne
Published: April 2018

In the adult CNS, axons fail to regenerate after injury. Among the cell interactions that lead to this failure are those developed with astrocytes. In an effort to elucidate the mechanisms underlying these negative interactions, we have used astrocytes treated with antisense glial fibrillary acidic protein (GFAP) mRNA to inhibit the formation of gliofilaments, indispensable for the astroglial morphological response to injury, and have studied their permissivity for neuritic outgrowth. In a neuron–astrocyte coculture, a mechanical lesion led to hypertrophy of astrocytes neighboring the lesion. Neuronal cell bodies and neurites were absent both from the area of lesion and from its surroundings. Reactive astrocytes appeared, therefore, to be a nonpermissive substrate. Transfection that used antisense GFAP mRNA blocked astroglial morphological changes and was characterized by both a persistence of neuronal cell bodies in the vicinity of the lesion site and a growth of neurites into the same region. These morphological differences were associated with a 46% decrease in the GFAP translation capacity and a 50% increase in the concentration of GAP-43 in the treated cultures. Neurons were associated mainly with an extracellular laminin network, which was predominant at the lesion site in treated cocultures. In contrast, those astrocytes highly laminin-immunoreactive appeared to be a nonpermissive substrate for neurons. These results show that inhibition in GFAP synthesis, leading to a reduction of astroglial hypertrophy, relieves the blockade of neuritic outgrowth that normally is observed after a lesion. The mechanisms may involve changes in the secretion of extracellular matrix molecules by astrocytes.
Calcium Entry through Cyclic Nucleotide-Gated Channels in Individual Cilia of Olfactory Receptor Cells: Spatiotemporal Dynamics
Authors: Leinders-Zufall Trese , Rand Mark N. , Shepherd Gordon M. , Greer Charles A. , Zufall Frank
Published: April 2018

Transient elevations of intracellular Ca2+play an important role in regulating the sensitivity of olfactory transduction, but such elevations have not been demonstrated in the olfactory cilia, which are the site of primary odor transduction. To begin to understand Ca2+signaling in olfactory cilia, we used high-resolution imaging techniques to study the Ca2+transients that occur in salamander olfactory receptor neurons (ORNs) as a result of cyclic nucleotide-gated (CNG) channel activation. To visualize ciliary Ca2+signals, we loaded ORNs with the Ca2+indicator dye Fluo-3 AM and measured fluorescence with a laser scanning confocal microscope. Application of the phosphodiesterase inhibitor IBMX increased fluorescence in the cilia and other neuronal compartments; the ciliary signal occurred first and was more transient. This signal could be abolished by lowering external Ca2+or by applying LY83583, a potent blocker of CNG channels, indicating that Ca2+entry through CNG channels was the primary source of fluorescence increases. Direct activation of CNG channels with low levels of 8-Br-cGMP (1 μm) led to tonic Ca2+signals that were restricted locally to the cilia and the dendritic knob. Elevated external K+, which depolarizes cell membranes, increased fluorescence signals in the cell body and dendrite but failed to increase ciliary Ca2+fluorescence. The results demonstrate the existence and spatiotemporal properties of Ca2+transients in individual olfactory cilia and implicate CNG channels as a major pathway for Ca2+entry into ORN cilia during odor transduction.
Slow-Channel Transgenic Mice: A Model of Postsynaptic Organellar Degeneration at the Neuromuscular Junction
Authors: Gomez Christopher M. , Maselli Ricardo , Gundeck Jo Ellen , Chao Mary , Day John W. , Tamamizu Shiori , Lasalde Jose A. , McNamee Mark , Wollmann Robert L.
Published: April 2018

The slow-channel congenital myasthenic syndrome (SCCMS) is a dominantly inherited disorder of neuromuscular transmission characterized by delayed closure of the skeletal muscle acetylcholine receptor (AChR) ion channel and degeneration of the neuromuscular junction. The identification of a series of AChR subunit mutations in the SCCMS supports the hypothesis that the altered kinetics of the endplate currents in this disease are attributable to inherited abnormalities of the AChR. To investigate the role of these mutant AChR subunits in the development of the synaptic degeneration seen in the SCCMS, we have studied the properties of the AChR mutation, εL269F, found in a family with SCCMS, using bothin vitroandin vivoexpression systems. The mutation causes a sixfold increase in the open time of AChRs expressedin vitro, similar to the phenotype of other reported mutants. Transgenic mice expressing this mutant develop a syndrome that is highly reminiscent of the SCCMS. Mice have fatigability of limb muscles, electrophysiological evidence of slow AChR ion channels, and defective neuromuscular transmission. Pathologically, the motor endplates show focal accumulation of calcium and striking ultrastructural changes, including enlargement and degeneration of the subsynaptic mitochondria and nuclei. These findings clearly demonstrate the role of this mutation in the spectrum of abnormalities associated with the SCCMS and point to the subsynaptic organelles as principal targets in this disease. These transgenic mice provide a useful model for the study of excitotoxic synaptic degeneration.
Transient Changes in Flocculonodular Lobe Protein Kinase C Expression during Vestibular Compensation
Authors: Goto Mark M. , Romero Guillermo G. , Balaban Carey D.
Published: April 2018

Protein kinase C (PKC) is a family of intracellular signal transduction enzymes, comprising isoforms that vary in sensitivity to calcium, arachidonic acid, and diacylglycerol. PKC isoforms α, γ, and δ are expressed by cerebellar Purkinje cells and neurons in the cerebellar nuclei and vestibular nuclei of the Long–Evans rat. In control rats, these PKCs are distributed symmetrically in the flocculonodular-lobe Purkinje cells. Behavioral recovery from vestibular dysfunction produced by unilateral labyrinthectomy (UL) is accompanied by asymmetric expression of PKC isoforms in these regions within 6 hr after UL. These expression changes were localized within parasagittal regions of the flocculus and nodulus. The distribution of PKCα, -γ, and -δ were identical, suggesting that they are coregulated in cerebellar Purkinje cells during this early compensatory period. The pattern of Purkinje cell PKC expression returned to the control, symmetric distribution within 24 hr after UL. It is hypothesized that these regional changes in Purkinje cell PKC expression are an early intracellular signal contributing to vestibular compensation. In particular, regulation of PKC expression may contribute to changes in the efficacy of cerebellar synaptic plasticity during the acute post-UL period.
Metabotropic Glutamate Agonist-Induced Rotation: A Pharmacological, FOS Immunohistochemical, and [14C]-2-Deoxyglucose Autoradiographic Study
Authors: Kearney Jennifer A. Feeley , Frey Kirk A. , Albin Roger L.
Published: April 2018

Metabotropic glutamate receptors (mGluRs) are a major class of excitatory amino acid receptors. Eight mGluR subtypes, coupled to a variety of effector systems, have been cloned. These receptors have been classified into three groups based on amino acid sequence homology, effector systems, and pharmacological profile. Group I mGluRs increase phosphoinositide turnover, whereas groups II and III mGluRs are negatively coupled to adenylyl cyclase. The striatum possesses a high density of mGluR binding sites, and several mGluR mRNAs and proteins are expressed by striatal neurons. In rats, unilateral striatal injection of the nonsubtype selective mGluR agonist 1-aminocyclopentane-1S,3R-dicarboxylic acid (1S,3R-ACPD) results in contralateral rotation with delayed onset, thought to be secondary to an increase in dopamine release. We sought to determine the mGluR subtype(s) involved, the modulation of the rotation by other basal ganglia neurotransmitter systems, and the functional anatomy underlying the rotational behavior. The group I mGluR agonist 3,5-dihydroxyphenylglycine (DHPG) induced contralateral rotation in a dose-dependent manner, whereas group II and group III agonists were ineffective. Rotation induced by DHPG or 1S,3R-ACPD was attenuated by group I antagonists, but not by group II or group III antagonists. This suggests that the rotation is mediated by group I mGluRs. Rotation induced by DHPG or 1S,3R-ACPD was attenuated by pretreatment with antagonists at muscarinic cholinergic, adenosine A2, dopamine D2, or dopamine D1receptors. Examination of FOS-like immunoreactivity after group I and group II mGluR agonist administration suggests increased activity in the striatopallidal pathway. However, [14C]-2-deoxyglucose uptake studies indicate increased activity in nuclei of the striatopallidal (indirect) pathway, particularly in the subthalamic nucleus, only after group I mGluR activation.
Long-Term Intracerebroventricular Infusion of Corticotropin-Releasing Hormone Alters Neuroendocrine, Neurochemical, Autonomic, Behavioral, and Cytokine Responses to a Systemic Inflammatory Challenge
Authors: Linthorst Astrid C. E. , Flachskamm Cornelia , Hopkins Stephen J. , Hoadley Margaret E. , Labeur Marta S. , Holsboer Florian , Reul Johannes M. H. M.
Published: April 2018

Corticotropin-releasing hormone (CRH) was infused intracerebroventricularly into rats for 7 d via a miniosmotic pump (1 μg · μl−1 · hr−1). Body temperature and locomotor activity were recorded during the treatment using biotelemetry, whereas hippocampal serotonergic neurotransmission and free corticosterone levels were monitored usingin vivomicrodialysis on day 7 of CRH treatment. During the microdialysis experiment, behavioral activity was scored by assessing the time during which rats were active (locomotion, grooming, eating, drinking). Continuous intracerebroventricular infusion of CRH produced a transient increase in body temperature and locomotion. Moreover, intracerebroventricularly CRH-treated rats showed elevated free corticosterone levels with no apparent diurnal rhythm.

Intraperitoneal administration of bacterial endotoxin [lipopolysaccharide (LPS); 100 μg/kg body weight] on day 7 of CRH/vehicle treatment produced a marked fever response in control animals, which was significantly blunted in intracerebroventricularly CRH-treated rats. Although free corticosterone levels reached similar peak concentrations in both intracerebroventricularly vehicle- and CRH-infused groups after LPS, this response was delayed significantly by ∼1 hr in the intracerebroventricularly CRH-treated animals. Microdialysis experiments showed no changes in basal extracellular levels of serotonin and 5-hydroxyindoleacetic acid in intracerebroventricularly CRH-infused animals. Injection of LPS in intracerebroventricularly CRH-treated rats produced a blunted 5-HT response and a delayed onset of behavioral inhibition and other signs of sickness behavior. Assessment of the endotoxin-induced cytokine responses showed significantly enhanced plasma interleukin-1 (IL-1) and IL-6 bioactivities in the intracerebroventricularly CRH-infused animals 3 hr after injection of LPS, whereas tumor necrosis factor bioactivity responses were not different.

Our data demonstrate that chronically elevated brain CRH levels produce marked changes in basal (largely CRH regulated) physiological and behavioral processes accompanied by aberrant responses to an acute challenge. The present study provides evidence that chronic CRH hypersecretion is an important factor in the etiology of stress-related disorders.
A Slow Outward Current Activated by FMRFamide in Heart Interneurons of the Medicinal Leech
Authors: Nadim Farzan , Calabrese Ronald L.
Published: April 2018

The endogenous neuropeptide FMRFamide (Phe-Met-Arg-Phe-NH2) can accelerate the oscillation of reciprocally inhibitory pairs of interneurons that pace heartbeat in the medicinal leech. A model based on all available biophysical data of a two-cell heart interneuron oscillator provides a theoretical basis for understanding this modulation. Previously observed modulation of K+currents by FMRFamide cannot account for this acceleratory effect in the model. This observation prompted the present reexamination of K+currents in heart interneurons. We devised better methods for separation of the various components of K+current and more accurately measured their activation and deactivation kinetics. Moreover, we demonstrated that FMRFamide activates a previously undetected K+current (IKF), which has very slow activation and deactivation kinetics. Addition of physiologically measured amounts ofIKFto the model two-cell oscillator can account for the acceleratory effect of FMRFamide.
Postnatal Development of Serotonergic Innervation, 5-HT1AReceptor Expression, and 5-HT Responses in Rat Motoneurons
Authors: Talley Edmund M. , Sadr Negar N. , Bayliss Douglas A.
Published: April 2018

We compared the electrophysiological responses to serotonin (5-HT) of neonatal and juvenile rat hypoglossal motoneurons (HMs) by using intracellular recording techniques in a brainstem slice preparation. In neonatal HMs (≤P8), 5-HT caused a substantial decrease in the amplitude of spike afterhyperpolarization (AHP) that was associated with an increase in the minimal repetitive firing frequency (Fmin). Previous work has shown that this effect of 5-HT was mediated by the 5-HT1Areceptor and may be secondary to inhibition of N- and P/Q-type calcium channels. In contrast to results from neonates, we found that 5-HT did not inhibit the AHP in juvenile HMs (≥ P20). Application of a cocktail of calcium channel toxins (ω-Conotoxin-GVIA and ω-Agatoxin-IVA) to juvenile HMs substantially inhibited the AHP, indicating that calcium entry through N- and P/Q-type channels supports the AHP in juvenile HMs, as it does in neonates. In addition, intracellular injection of the long-lasting GTP analog GTPγS induced an agonist-independent increase inFminsimilar to that seen in neonates in the presence of 5-HT. Together, these results suggested that intracellular mechanisms downstream of the 5-HT1Areceptor capable of inhibiting the AHP were intact in juvenile HMs. Therefore, we investigated the possibility that age-related changes in effects of 5-HT on the AHP resulted from altered expression of the 5-HT1Areceptor. To this end, we performed ligand-binding autoradiography using [3H]8-OH-DPAT, a 5-HT1Aagonist, andin situhybridization using radiolabeled oligonucleotide probes specific for the 5-HT1Areceptor. The two approaches gave remarkably similar results. The highest levels of 5-HT1Areceptor expression were found in neonatal HMs, with maximal binding and hybridization at approximately postnatal day 7 (P7) and only low levels of receptor expression by P28. Finally, immunohistochemistry for 5-HT revealed that these developmental changes in 5-HT1Areceptor expression occurred coincident with a postnatal increase in serotonergic innervation of the hypoglossal nucleus (nXII). Together, these findings indicate that developmental changes occur in the serotonergic innervation of nXII and in the expression of 5-HT1Areceptors in HMs during the early postnatal period, resulting in markedly different effects of 5-HT on firing behavior in neonatal and juvenile HMs.
Visual and Somatosensory Information about Object Shape Control Manipulative Fingertip Forces
Authors: Jenmalm Per , Johansson Roland S.
Published: April 2018

We investigated the importance of visual versus somatosensory information for the adaptation of the fingertip forces to object shape when humans used the tips of the right index finger and thumb to lift a test object. The angle of the two flat grip surfaces in relation to the vertical plane was changed between trials from −40 to 30°. At 0° the two surfaces were parallel, and at positive and negative angles the object tapered upward and downward, respectively. Subjects automatically adapted the balance between the horizontal grip force and the vertical lift force to the object shape and thereby maintained a rather constant safety margin against frictional slips, despite the huge variation in finger force requirements. Subjects used visual cues to adapt force to object shape parametrically in anticipation of the force requirements imposed once the object was contacted. In the absence of somatosensory information from the digits, sighted subjects still adapted the force coordination to object shape, but without vision and somatosensory inputs the performance was severely impaired. With normal digital sensibility, subjects adapted the force coordination to object shape even without vision. Shape cues obtained by somatosensory mechanisms were expressed in the motor output about 0.1 sec after contact. Before this point in time, memory of force coordination used in the previous trial controlled the force output. We conclude that both visual and somatosensory inputs can be used in conjunction with sensorimotor memories to adapt the force output to object shape automatically for grasp stability.
Slow-Channel Myasthenic Syndrome Caused By Enhanced Activation, Desensitization, and Agonist Binding Affinity Attributable to Mutation in the M2 Domain of the Acetylcholine Receptor α Subunit
Authors: Milone Margherita , Wang Hai-Long , Ohno Kinji , Fukudome Takayasu , Pruitt J. Ned , Bren Nina , Sine Steven M. , Engel Andrew G.
Published: April 2018

We describe a novel genetic and kinetic defect in a slow-channel congenital myasthenic syndrome. The severely disabled propositus has advanced endplate myopathy, prolonged and biexponentially decaying endplate currents, and prolonged acetylcholine receptor (AChR) channel openings. Genetic analysis reveals the heterozygous mutation αV249F in the propositus and mosaicism for αV249F in the asymptomatic father. Unlike mutations described previously in the M2 transmembrane domain, αV249F is located N-terminal to the conserved leucines and is not predicted to face the channel lumen. Expression of the αV249F AChR in HEK fibroblasts demonstrates increased channel openings in the absence of ACh, prolonged openings in its presence, enhanced steady-state desensitization, and nanomolar rather than micromolar affinity of one of the two binding sites in the resting activatable state. Thus, neuromuscular transmission is compromised because cationic overloading leads to degenerating junctional folds and loss of AChR, because an increased fraction of AChR is desensitized in the resting state, and because physiological rates of stimulation elicit additional desensitization and depolarization block of transmission.
Quantal Neurotransmitter Secretion Rate Exhibits Fractal Behavior
Authors: Lowen Steven B. , Cash Sydney S. , Poo Mu-ming , Teich Malvin C.
Published: April 2018

The rate of exocytic events from both neurons and non-neuronal cells exhibits fluctuations consistent with fractal (self-similar) behavior in time, as evidenced by a number of statistical measures. We explicitly demonstrate this for neurotransmitter secretion atXenopusneuromuscular junctions and for rat hippocampal synapses in culture; the exocytosis of exogenously supplied neurotransmitter from culturedXenopusmyocytes and from rat fibroblasts behaves similarly. The magnitude of the fluctuations of the rate of exocytic events about the mean decreases slowly as the rate is computed over longer and longer time periods, the periodogram decreases in power-law manner with frequency, and the Allan factor (relative variance of the number of exocytic events) increases as a power-law function of the counting time. These features are hallmarks of self-similar behavior. Their description requires models that exhibit long-range correlation (memory) in event occurrences. We have developed a physiologically plausible model that accords with all of the statistical measures that we have examined. The appearance of fractal behavior at synapses, as well as in systems comprising collections of synapses, indicates that such behavior is ubiquitous in neural signaling.
Selective Destruction of Stable Microtubules and Axons by Inhibitors of Protein Serine/Threonine Phosphatases in Cultured Human Neurons (NT2N Cells)
Authors: Merrick Sandra E. , Trojanowski John Q. , Lee Virginia M.-Y.
Published: April 2018

Paired helical filaments (PHFs) in the neurofibrillary tangles (NFTs) in Alzheimer’s disease (AD) brains are composed of highly phosphorylated isoforms of tau (PHFtau) that fail to bind microtubules (MTs), and the levels of MT-binding competent tau are decreased in AD brains with abundant PHFtau. Because this loss of MT binding could compromise the viability of tangle-bearing AD neurons by destabilizing MTs, we asked whether these events could be initiated by inhibiting protein phosphatase 1 (PP1) and PP2A in cultured human neurons (NT2N cells) using okadaic acid (OK) and calyculin-A (CL-A). The treatment of NT2N cells with OK and CL-A increased tau phosphorylation, decreased the binding of tau to MTs, and selectively depolymerized the more stable detyrosinated MTs but not the more labile tyrosinated MTs. Significantly, this led to the rapid degeneration of axons, which are enriched in the more stable detyrosinated MTs, and PP2A was implicated in the initiation of this cascade of events because PP2A but not PP1 was closely associated with MTs in the NT2N cells. These studies imply that inactivation of PP2A in vulnerable neurons of the AD brain may play a mechanistic role in the conversion of normal tau into PHFtau, in the depolymerization of stable MTs, and in the degeneration of axons emanating from tangle-bearing neurons.
Differential Autoreceptor Control of Somatodendritic and Axon Terminal Dopamine Release in Substantia Nigra, Ventral Tegmental Area, and Striatum
Authors: Cragg Stephanie J. , Greenfield Susan A.
Published: April 2018

Dopamine (DA) is released from somatodendritic sites of neurons in the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA), where it has neuromodulatory effects. The aim of this study was to evaluate the role of D2autoreceptor inhibition in the regulation of this somatodendritic release in each region. Fast cyclic voltammetry at carbon fiber microelectrodes was used to measure electrically evoked DA releasein vitro. Furthermore, we compared D2regulation of somatodendritic release with the more familiar axon terminal release in caudate putamen (CPu) and nucleus accumbens (NAc). Evoked DA release was TTX-sensitive at all sites. There was significant D2autoinhibition of DA release in SNc; however, this mechanism was two- to threefold less powerful, as compared with axon terminal release in CPu. In contrast to SNc, somatodendritic release in VTA was not under significant D2receptor control, whereas release in the respective axon terminal region (NAc) was controlled strongly by autoinhibition. Thus, these data indicate that, first, autoinhibition via D2receptors consistently plays a less significant role in the control of somatodendritic than axon terminal DA release, and, second, even at the level of somatodendrites themselves, D2autoinhibition displays marked regional variation. In the light of previous data indicating that DA uptake processes are also less active in somatodendritic than in terminal regions, these results are interpreted as indicating that DA transmission is regulated differently in somatodendritic zones, as compared with axon terminals, and thus may have different functional consequences.
Influence of Subunit Composition on Desensitization of Neuronal Acetylcholine Receptors at Low Concentrations of Nicotine
Authors: Fenster Catherine P. , Rains M. Felicia , Noerager Brett , Quick Michael W. , Lester Robin A. J.
Published: April 2018

The influence of α and β subunits on the properties of nicotine-induced activation and desensitization of neuronal nicotinic acetylcholine receptors (nAChRs) expressed inXenopusoocytes was examined. Receptors containing α4 subunits were more sensitive to activation by nicotine than α3-containing receptors. At low concentrations of nicotine, nAChRs containing β2 subunits reached near-maximal desensitization more rapidly than β4-containing receptors. The concentration of nicotine producing half-maximal desensitization was influenced by the particular α subunit expressed; similar to results for activation, α4-containing receptors were more sensitive to desensitizing levels of nicotine than α3-containing receptors. The α subunit also influenced the rate of recovery from desensitization; this rate was approximately inversely proportional to the apparent nicotine affinity for the desensitized state. The homomeric α7 receptor showed the lowest sensitivity to nicotine for both activation and desensitization; α7 nAChRs also demonstrated the fastest desensitization kinetics. These subunit-dependent properties remained in the presence of external calcium, although subtle, receptor subtype-specific effects on both the apparent affinities for activation and desensitization and the desensitization kinetics were noted. These data imply that the subunit composition of various nAChRs determines the degree to which receptors are desensitized and/or activated by tobacco-related levels of nicotine. The subtype-specific balance between receptor activation and desensitization should be considered important when the cellular and behavioral actions of nicotine are interpreted.
Muscarinic Modulation of Spike Backpropagation in the Apical Dendrites of Hippocampal CA1 Pyramidal Neurons
Authors: Tsubokawa Hiroshi , Ross William N.
Published: April 2018

In pyramidal neurons from the CA1 region of the rat hippocampus, Na+-dependent action potentials backpropagate over the dendrites in an activity-dependent manner. Consequently, later spikes in a train have smaller amplitudes when recorded in the apical arbors. We studied the effect of the cholinergic agonist carbachol (CCh) on this pattern of activity when spikes were evoked synaptically or antidromically in the transverse slice preparation. Concentrations as low as 1 μmwere effective in reversing the modulation, making the amplitude of all spikes in a train equal and independent of the frequency of spike firing. CCh did not change the propagation of the first spike in a train. These effects of CCh were blocked by 1 μmatropine, showing that only muscarinic receptors were involved. The effects of CCh on the pattern of spike propagation were observed in the proximal and middle dendrites, but recordings in the distal dendrites (>300 μm from the soma) showed that CCh did not boost the amplitude in this region. Intracellular BAPTA (10 mm) or EGTA (10 mm) had no effect on activity-dependent backpropagation but blocked the effect of CCh. Backpropagating spikes caused increases in [Ca2+]iat all dendritic locations. In the middle and distal dendrites these increases normally peaked at the time of the first few large action potentials. In association with the enhancement of spike backpropagation, CCh increased the amplitude and duration of the train-evoked [Ca2+]ichanges. These effects of CCh on dendritic spike potentials and associated [Ca2+]ichanges may be important in modulating synaptic integration and plasticity in these neurons.
Sonic Hedgehog Promotes the Survival of Specific CNS Neuron Populations and Protects These Cells from Toxic InsultIn Vitro
Authors: Miao Ningning , Wang Monica , Ott Jennifer A. , D’Alessandro Josephine S. , Woolf Tod M. , Bumcrot David A. , Mahanthappa Nagesh K. , Pang Kevin
Published: April 2018

Sonic hedgehog (Shh), an axis-determining secreted protein, is expressed during early vertebrate embryogenesis in the notochord and ventral neural tube. In this site it plays a role in the phenotypic specification of ventral neurons along the length of the CNS. For example, Shh induces the differentiation of motor neurons in the spinal cord and dopaminergic neurons in the midbrain. Shh expression, however, persists beyond this induction period, and we have asked whether the protein shows novel activities beyond phenotype specification. Using cultures derived from embryonic day 14.5 (E14.5) rat ventral mesencephalon, we show that Shh is also trophic for dopaminergic neurons. Interestingly, Shh not only promotes dopaminergic neuron survival, but also promotes the survival of midbrain GABA-immunoreactive (GABA-ir) neurons. In cultures derived from the E15–16 striatum, Shh promotes the survival of GABA-ir interneurons to the exclusion of any other cell type. Cultures derived from E15–16 ventral spinal cord reveal that Shh is again trophic for interneurons, many of which are GABA-ir and some of which express the Lim-1/2 nuclear marker, but it does not appear to support motorneuron survival. Shh does not support the survival of sympathetic or dorsal root ganglion neurons. Finally, using the midbrain cultures, we show that in the presence of MPP+, a highly specific neurotoxin, Shh prevents dopaminergic neuron death that normally would have occurred. Thus Shh may have therapeutic value as a protective agent in neurodegenerative disease.
AMPA Receptor Facilitation Accelerates Fear Learning without Altering the Level of Conditioned Fear Acquired
Authors: Rogan Michael T. , Stäubli Ursula V. , LeDoux Joseph E.
Published: April 2018

Rats treated with the AMPA receptor-facilitating drug 1-(quinoxolin-6-ylcarbonyl)piperidine (BDP-12) during training acquired fear conditioning to a tone faster than vehicle-treated controls. The effect on acquisition was dependent on the dose given. BDP-12-treated rats and vehicle-treated controls reached the same level of conditioned fear and extinguished at the same rate. The dissociation of learning rate from these other normally covariant measures suggests that the drug had a specific and isolated effect on acquisition. Controls for drug effects on stimulus sensitivity, locomotor activity, generalized fearfulness, and other performance factors support this interpretation. The known action of BDP-12 on receptor dynamics suggests that its effect on acquisition may be attributed to specific modulation of an AMPA and NMDA receptor-dependent plasticity mechanism. The finding that the drug accelerates acquisition but does not affect the level of conditioned fear acquired parallels the effect of the drug on long-term potentiation (LTP) (increasing the rate but not the ceiling of potentiation) and suggests that common mechanisms may underlie fear conditioning and LTP.
Lesions of the Medial Geniculate Nuclei Specifically Block Corticosterone Release and Induction of c-fosmRNA in the Forebrain Associated with Audiogenic Stress in Rats
Authors: Campeau Serge , Akil Huda , Watson Stanley J.
Published: April 2018

Audiogenic stress is known to activate the hypothalamo-pituitary-adrenocortical (HPA) axis in rats. The goal of the present study was to determine whether the medial geniculate nuclei (including all auditory nuclei of the thalamus), which are obligatory relays in the transmission of auditory information to the forebrain, are critically involved in HPA activation by audiogenic stress. To this end, corticosterone levels and regional brain activity indexed by c-fosmRNA induction, elicited by 30 min of 105 dB white noise, were measured. Compared with unoperated and sham-operated rats, complete medial geniculate nuclei lesions blocked corticosterone release normally induced by loud noise. The effects of the lesions were specific to loud noise insofar as corticosterone release in response to restraint or ether stress was not reduced in lesioned rats.

We have determined previously that audiogenic stress is associated with a specific regional pattern of c-fosmRNA induction. Rats sustaining complete medial geniculate lesions demonstrated a blockade of c-fosmRNA induction in several audiogenic stress responsive regions, also known to directly innervate medial parvocellular neurons of the paraventricular hypothalamic nucleus. Thus, in addition to blockade in the paraventricular hypothalamic nucleus, c-fosmRNA induction in the lesioned animals was abolished in the bed nucleus of the stria terminalis, especially its anterior medial and ventral aspects, the septohypothalamic nucleus, and the anteroventral preoptic area, compared with unoperated and sham-operated rats. Several additional regions in the lesioned rats failed to show reliable c-fosmRNA induction compared with naive rat controls. Nearly all other regions that showed reliable c-fosmRNA induction in the unoperated and sham-operated rats displayed either similar or slightly reduced levels in complete medial geniculate-lesioned rats, suggesting that these regions are not part of a critical HPA activational circuit in response to audiogenic stress. On the basis of these results, putative circuits from the medial geniculate nuclei to the paraventricular nucleus of the hypothalamus involved in activation of the HPA axis by audiogenic stress are discussed.
A Model Neuron with Activity-Dependent Conductances Regulated by Multiple Calcium Sensors
Authors: Liu Zheng , Golowasch Jorge , Marder Eve , Abbott L. F.
Published: April 2018

Membrane channels are subject to a wide variety of regulatory mechanisms that can be affected by activity. We present a model of a stomatogastric ganglion (STG) neuron in which several Ca2+-dependent pathways are used to regulate the maximal conductances of membrane currents in an activity-dependent manner. Unlike previous models of this type, the regulation and modification of maximal conductances by electrical activity is unconstrained. The model has seven voltage-dependent membrane currents and uses three Ca2+sensors acting on different time scales. Starting from random initial conditions over a given range, the model sets the maximal conductances for its active membrane currents to values that produce a predefined target pattern of activity ∼90% of the time. In these models, the same pattern of electrical activity can be produced by a range of maximal conductances, and this range is compared with voltage-clamp data from the lateral pyloric neuron of the STG. If the electrical activity of the model neuron is perturbed, the maximal conductances adjust to restore the original pattern of activity. When the perturbation is removed, the activity pattern is again restored after a transient adjustment period, but the conductances may not return to their initial values. The model suggests that neurons may regulate their conductances to maintain fixed patterns of electrical activity, rather than fixed maximal conductances, and that the regulation process requires feedback systems capable of reacting to changes of electrical activity on a number of different time scales.
A Mutation Affecting Dihydropyridine-Sensitive Current Levels and Activation Kinetics inDrosophilaMuscle and Mammalian Heart Calcium Channels
Authors: Ren Dejian , Xu Hongjian , Eberl Daniel F. , Chopra Maninder , Hall Linda M.
Published: April 2018

TheDmca1Dgene encodes aDrosophilacalcium channel α1subunit. We describe the first functional characterization of a mutation in this gene. This α1subunit mediates the dihydropyridine-sensitive calcium channel current in larval muscle but does not contribute to the amiloride-sensitive current in that tissue. A mutation, which changes a highly conserved Cys to Tyr in transmembrane domain IS1, identifies a residue important for channel function not only inDrosophilamuscle but also in mammalian cardiac channels. In both cases, mutations in this Cys residue slow channel activation and reduce expressed currents. Amino acid substitutions at this Cys position in the cardiac α1subunit show that the size of the side chain, rather than its ability to form disulfide bonds, affects channel activation.
DegenerationIn Vivoof Rat Hippocampal Neurons by Wild-Type Alzheimer Amyloid Precursor Protein Overexpressed by Adenovirus-Mediated Gene Transfer
Authors: Nishimura Isao , Uetsuki Taichi , Dani Sergio U. , Ohsawa Yoshiyuki , Saito Izumu , Okamura Hitoshi , Uchiyama Yasuo , Yoshikawa Kazuaki
Published: April 2018

In an attempt to elucidate the pathological implications of intracellular accumulation of the amyloid precursor protein (APP) in postmitotic neuronsin vivo, we transferred APP695 cDNA into rat hippocampal neurons by using a replication-defective adenovirus vector. We first improved the efficiency of adenovirus-mediated gene transfer into neuronsin vivoby using hypertonic mannitol. When a β-galactosidase-expressing recombinant adenovirus suspended in 1mmannitol was injected into a dorsal hippocampal region, a number of neurons in remote areas were positively stained, presumably owing to increased retrograde transport of the virus. When an APP695-expressing adenovirus was injected into the same site, part of the infected neurons in the hippocampal formation underwent severe degeneration in a few days, whereas astrocytes near the injection site showed no apparent degeneration. These degenerating neurons accumulated different epitopes of APP, and β/A4 protein (Aβ)-immunoreactive materials were undetected in the extracellular space. A small number of degenerating neurons showed nuclear DNA fragmentation. Electron microscopic examinations demonstrated that degenerating neurons had shrunken perikarya along with synaptic abnormalities. Microglial cells/macrophages were often found in close proximity to degenerating neurons, and in some cases they phagocytosed these neurons. These results suggest that intracellular accumulation of wild-type APP695 causes a specific type of neuronal degenerationin vivoin the absence of extracellular Aβ deposition.
Honeybee Blue- and Ultraviolet-Sensitive Opsins: Cloning, Heterologous Expression inDrosophila, and Physiological Characterization
Authors: Townson Steven M. , Chang Belinda S. W. , Salcedo Ernesto , Chadwell Linda V. , Pierce Naomi E. , Britt Steven G.
Published: April 2018

The honeybee (Apis mellifera) visual system contains three classes of retinal photoreceptor cells that are maximally sensitive to light at 440 nm (blue), 350 nm (ultraviolet), and 540 nm (green). We performed a PCR-based screen to identify the genes encoding theApisblue- and ultraviolet (UV)-sensitive opsins. We obtained cDNAs that encode proteins having a high degree of sequence and structural similarity to other invertebrate and vertebrate visual pigments. TheApisblue opsin cDNA encodes a protein of 377 amino acids that is most closely related to other invertebrate visual pigments that are thought to be blue-sensitive. The UV opsin cDNA encodes a protein of 371 amino acids that is most closely related to the UV-sensitiveDrosophilaRh3 and Rh4 opsins. To test whether these novelApisopsin genes encode functional visual pigments and to determine their spectral properties, we expressed them in the R1–6 photoreceptor cells of blindninaEmutantDrosophila, which lack the major opsin of the fly compound eye. We found that the expression of either theApisblue- or UV-sensitive opsin in transgenic flies rescued the visual defect ofninaEmutants, indicating that both genes encode functional visual pigments. Spectral sensitivity measurements of these flies demonstrated that the blue and UV visual pigments are maximally sensitive to light at 439 and 353 nm, respectively. These maxima are in excellent agreement with those determined previously by single-cell recordings fromApisphotoreceptor cells and provide definitive evidence that the genes described here encode visual pigments having blue and UV sensitivity.
Calcium Extrusion from Mammalian Photoreceptor Terminals
Authors: Morgans Catherine W. , El Far Oussama , Berntson Amy , Wässle Heinz , Taylor W. Rowland
Published: April 2018

Ribbon synapses of vertebrate photoreceptors constantly release glutamate in darkness. Transmitter release is maintained by a steady influx of calcium through voltage-dependent calcium channels, implying the presence of a mechanism that is able to extrude calcium at an equal rate. The two predominant mechanisms of intracellular calcium extrusion are the plasma membrane calcium ATPase (PMCA) and the Na+/Ca2+-exchanger. Immunohistochemical staining of retina sections revealed strong immunoreactivity for the PMCA in rod and cone terminals, whereas staining for the Na+/Ca2+-exchanger was very weak. The PMCA was localized to the plasma membrane along the sides of the photoreceptor terminals and was excluded from the base of the terminals where the active zones are located. The amplitude of a calcium-activated chloride current was used to monitor the intracellular calcium concentration. An upper limit for the time required to remove intracellular free calcium is obtained from two time constants measured for the calcium-activated chloride current tail currents: one of 50 msec and a second of 190 msec. Calcium extrusion was inhibited in the absence of intracellular ATP or in the presence of the PMCA inhibitor orthovanadate, but was unaffected by replacement of external Na+with Li+. The data indicate that the PMCA, rather than the Na+/Ca2+-exchanger, is the predominant mechanism for calcium extrusion from photoreceptor synaptic terminals.
Multiple Signaling Pathways Regulate Cell Surface Expression and Activity of the Excitatory Amino Acid Carrier 1 Subtype of Glu Transporter in C6 Glioma
Authors: Davis Karen E. , Straff Dean J. , Weinstein Edward A. , Bannerman Peter G. , Correale Dana M. , Rothstein Jeffrey D. , Robinson Michael B.
Published: April 2018

Neuronal and glial sodium-dependent transporters are crucial for the control of extracellular glutamate levels in the CNS. The regulation of these transporters is relatively unexplored, but the activity of other transporters is regulated by protein kinase C (PKC)- and phosphatidylinositol 3-kinase (PI3K)-mediated trafficking to and from the cell surface. In the present study the C6 glioma cell line was used as a model system that endogenously expresses the excitatory amino acid carrier 1 (EAAC1) subtype of neuronal glutamate transporter. As previously observed, phorbol 12-myristate 13-acetate (PMA) caused an 80% increase in transporter activity within minutes that cannot be attributed to the synthesis of new transporters. This increase in activity correlated with an increase in cell surface expression of EAAC1 as measured by using a membrane-impermeant biotinylation reagent. Both effects of PMA were blocked by the PKC inhibitor bisindolylmaleimide II (Bis II). The putative PI3K inhibitor, wortmannin, decreasedl-[3H]-glutamate uptake activity by >50% within minutes. Wortmannin decreased theVmaxofl-[3H]-glutamate andd-[3H]-aspartate transport, but it did not affect Na+-dependent [3H]-glycine transport. Wortmannin also decreased cell surface expression of EAAC1. Although wortmannin did not block the effects of PMA on activity, it prevented the PMA-induced increase in cell surface expression. This trafficking of EAAC1 also was examined with immunofluorescent confocal microscopy, which supported the biotinylation studies and also revealed a clustering of EAAC1 at cell surface after treatment with PMA. These studies suggest that the trafficking of the neuronal glutamate transporter EAAC1 is regulated by two independent signaling pathways and also may suggest a novel endogenous protective mechanism to limit glutamate-induced excitotoxicity.