bluuebunny/crossref_metadata_2025 huggingface dataset:
Precisely Synchronized Oscillatory Firing Patterns Require Electroencephalographic Activation
Authors: Herculano-Houzel Suzana , Munk Matthias H. J. , Neuenschwander Sergio , Singer Wolf
Published: April 2018

Neuronal response synchronization with millisecond precision has been proposed to serve feature binding in vision and should therefore, like visual experience, depend on central states. Here we test this hypothesis by examining the occurrence and strength of response synchronization in areas 17 and 18 of anesthetized cats as a function of central states. These were assessed from the frequency content of the electroencephalogram, low power in the δ and high power in the γ frequency ranges (here 20–70 Hz) being considered as a signature of activated states. We evaluated both spontaneous state changes and transitions induced by electrical stimulation of the mesencephalic reticular formation. During states of low central activation, visual responses were robust but lacked signs of precise synchronization. At intermediate levels of activation, responses became synchronized and exhibited an oscillatory patterning in the range of 70–105 Hz. At higher levels of activation, a different pattern of response synchronization and oscillatory modulation appeared, oscillation frequency now being in the range of 20–65 Hz. The strength of response synchronization and oscillatory modulation in the 20–65 Hz range increased with further activation and was associated with a decrease in oscillation frequency. We propose that the oscillatory patterning in the 70–105 Hz range is attributable to oscillatory retinothalamic input and that a minimal level of activation is necessary for cortical neurons to follow this oscillatory pattern. In contrast, the synchronization of responses at oscillation frequencies in the 20–65 Hz range appears to result from intracortical synchronizing mechanisms, which become progressively more effective as central activation increases. Surprisingly, enhanced synchronization and oscillatory modulation in the γ frequency range were not associated with consistent increases in response amplitude, excluding a simple relation between central activation and neuronal discharge rate. The fact that intracortical synchronizing mechanisms are particularly effective during states of central activation supports the hypothesis that precise synchronization of responses plays a role in sensory processing.
Functional Micro-Organization of Primary Visual Cortex: Receptive Field Analysis of Nearby Neurons
Authors: DeAngelis Gregory C. , Ghose Geoffrey M. , Ohzawa Izumi , Freeman Ralph D.
Published: April 2018

It is well established that multiple stimulus dimensions (e.g., orientation and spatial frequency) are mapped onto the surface of striate cortex. However, the detailed organization of neurons within a local region of striate cortex remains unclear. Within a vertical column, do all neurons have the same response selectivities? And if not, how do they most commonly differ and why? To address these questions, we recorded from nearby pairs of simple cells and made detailed spatiotemporal maps of their receptive fields. From these maps, we extracted and analyzed a variety of response metrics. Our results provide new insights into the local organization of striate cortex. First, we show that nearby neurons seldom have very similar receptive fields, when these fields are characterized in space and time. Thus, there may be less redundancy within a column than previously thought. Moreover, we show that correlated discharge increases with receptive field similarity; thus, the local dissimilarity between neurons may allow for noise reduction by response pooling. Second, we show that several response variables are clustered within striate cortex, including some that have not received much attention such as response latency and temporal frequency. We also demonstrate that other parameters are not clustered, including the spatial phase (or symmetry) of the receptive field. Third, we show that spatial phase is the single parameter that accounts for most of the difference between receptive fields of nearby neurons. We consider the implications of this local diversity of spatial phase for population coding and construction of higher-order receptive fields.
Dopamine Fluctuations in the Nucleus Accumbens during Maintenance, Extinction, and Reinstatement of Intravenous d-Amphetamine Self-Administration
Authors: Ranaldi Robert , Pocock Dorothy , Zereik Richard , Wise Roy A.
Published: April 2018

Moment-to-moment fluctuations of nucleus accumbens dopamine (DA) were determined in rats self-administering or passively receiving “yoked” intravenous infusions ofd-amphetamine. The initial lever presses of each session caused elevations in DA concentration, usually to an initial peak that was not maintained throughout the rest of the session. As the initial (“loading”) injections were metabolized, DA levels dropped toward baseline but were sustained at elevated plateaus by subsequent lever pressing that was spaced throughout the remainder of the 3 hr sessions. During this period, DA levels fluctuated phasically, time-locked to the cycle of periodic lever pressing. Consistent with the known pharmacological actions and dynamics of amphetamine, peak DA elevations were seen ∼10–15 min after each injection, and the mean DA level was at a low point in the phasic cycle at the time of each new lever press. During extinction periods when saline was substituted for amphetamine, DA levels dropped steadily toward baseline levels despite a dramatic increase in (now-unrewarded) lever pressing. Noncontingent injections during extinction reinstated lever-pressing behavior and increased nucleus accumbens DA concentrations. These data are consistent with the hypothesis that under the conditions of this experiment—during periods of amphetamine intoxication in well-trained animals—the timing of amphetamine self-administration comes primarily under the control of extracellular DA concentrations. The probability of lever pressing during the maintenance phase is highest when DA concentrations fall near a characteristic trigger point, a trigger point that is significantly elevated above baseline, and falls as DA concentrations fall below or increase above that trigger point.
Dopamine Reuptake Inhibition in the Rostral Agranular Insular Cortex Produces Antinociception
Authors: Burkey Adam R. , Carstens Earl , Jasmin Luc
Published: April 2018

We provide evidence for an antinociceptive effect of dopamine in the rat cerebral cortex that is mediated through descending nociceptive inhibition of spinal neurons. Injection of the dopamine reuptake inhibitor GBR-12935 in the rostral agranular insular cortex (RAIC), a cortical area that receives a dense dopaminergic projection and is involved in descending antinociception (Burkey et al., 1996), resulted in dose-dependent inhibition of formalin-induced nociceptive behavior, without any alteration of motor function. Injection of the dopamine reuptake inhibitor in the surrounding cortical areas had no effect on nociceptive behaviors. GBR-12935 also produced a reduction in noxious stimulus-inducedc-fosexpression in nociceptive areas of the spinal dorsal horn, suggesting that dopamine in the RAIC acts in part through descending antinociception. Electrophysiological recording from single wide dynamic range-type spinal dorsal horn neurons confirmed the descending nociceptive inhibitory effect. GBR-12935 in the RAIC significantly reduced neuronal responses evoked by noxious thermal stimulation of the skin, an effect that was reversed by local administration of the selective D1 receptor antagonist SCH-23390. Finally, administration of SCH-23390 alone in the RAIC decreased paw withdrawal latencies from noxious heat, suggesting that dopamine acts tonically in the cortex to inhibit nociception.
The Incorporation of NMDA Receptors with a Distinct Subunit Composition at Nascent Hippocampal SynapsesIn Vitro
Authors: Tovar Kenneth R. , Westbrook Gary L.
Published: April 2018

Activity-dependent synaptic rearrangements during CNS development require NMDA receptor activation. The control of NMDA receptor function by developmentally regulated subunit expression has been proposed as one mechanism for this receptor dependence. We examined the phenotype of synaptic and extrasynaptic NMDA receptors during the development of synaptic load using the NMDA receptor 2B (NR2B)-selective antagonist ifenprodil. In cultured rat hippocampal neurons when relatively few synapses had formed, the ifenprodil block of EPSCs was less than whole-cell currents, the latter of which included both synaptic and extrasynaptic receptors. At the same developmental stage, we found that extrasynaptic receptors outnumbered synaptic receptors by 3:1; thus whole-cell currents were dominated by the extrasynaptic population. We used the macroscopic kinetics of ifenprodil block to distinguish between the receptor populations. The ifenprodil kinetics of whole-cell currents from neurons before and during the development of synaptic load was comparable with that of whole-cell currents in HEK293 cells transfected with NR1 and NR2B cDNA, indicating that extrasynaptic receptors are largely NR1/NR2B heteromers. In contrast, synaptic receptors included both a highly ifenprodil-sensitive (NR1/NR2B) component as well as a second population with lower ifenprodil sensitivity; the reduced ifenprodil block of EPSCs was attributable to synaptic receptors with lower ifenprodil sensitivity rather than to the appearance of ifenprodil-insensitive (NR1/NR2A) receptors. Our data indicate that the synaptic NMDA receptor complement changes quickly after synapse formation. We suggest that synapses containing predominately NR1/NR2B heteromers represent “immature” sites, whereas mature sites express NMDA receptors with a distinct, presumably triheteromeric, subunit composition.
Localization of Type I Inositol 1,4,5-Triphosphate Receptor in the Outer Segments of Mammalian Cones
Authors: Wang Tian-Li , Sterling Peter , Vardi Noga
Published: April 2018

Calcium enters the outer segment of a vertebrate photoreceptor through a cGMP-gated channel and is extruded via a Na/Ca, K exchanger. We have identified another element in mammalian cones that might help to control cytoplasmic calcium. Reverse transcription-PCR performed on isolated photoreceptors identified mRNA for the SII−splice variant of the type I receptor for inositol 1,4,5-triphosphate (IP3), and Western blots showed that the protein also is expressed in outer segments. Immunocytochemistry showed type I IP3receptor to be abundant in red-sensitive and green-sensitive cones of the trichromatic monkey retina, but it was negative or weakly expressed in blue-sensitive cones and rods. Similarly, the green-sensitive cones expressed the receptor in dichromatic retina (cat, rabbit, and rat), but the blue-sensitive cones did not. Immunostain was localized to disk and plasma membranes on the cytoplasmic face. To restore sensitivity after a light flash, cytoplasmic cGMP must rise to its basal level, and this requires cytoplasmic calcium to fall. Cessation of calcium release via the IP3receptor might accelerate this fall and thus explain why the cone recovers much faster than the rod. Furthermore, because its own activity of the IP3receptor depends partly on cytoplasmic calcium, the receptor might control the set point of cytoplasmic calcium and thus affect cone sensitivity.
High Tolerance and Delayed Elastic Response of Cultured Axons to Dynamic Stretch Injury
Authors: Smith Douglas H. , Wolf John A. , Lusardi Theresa A. , Lee Virginia M.-Y. , Meaney David F.
Published: April 2018

Although axonal injury is a common feature of brain trauma, little is known of the immediate morphological responses of individual axons to mechanical injury. Here, we developed anin vitromodel system that selectively stretches axons bridging two populations of human neurons derived from the cell line N-Tera2. We found that these axons demonstrated a remarkably high tolerance to dynamic stretch injury, with no primary axotomy at strains <65%. In addition, the axolemma remained impermeable to small molecules after injury unless axotomy had occurred. We also found that injured axons exhibited the behavior of “delayed elasticity” after injury, going from a straight orientation before injury to developing an undulating course as an immediate response to injury, yet gradually recovering their original orientation. Surprisingly, some portions of the axons were found to be up to 60% longer immediately after injury. Subsequent to returning to their original length, injured axons developed swellings of appearance remarkably similar to that found in brain-injured humans. These findings may offer insight into mechanical-loading conditions leading to traumatic axonal injury and into potential mechanisms of axon reassembly after brain trauma.
c-junIs Dispensable for Developmental Cell Death and Axogenesis in the Retina
Authors: Herzog Karl-Heinz , Chen Shu-Cheng , Morgan James I.
Published: April 2018

Although a number of studies have implicated c-Jun in neuronal death and axonal regeneration, it is unknown whether Jun function is essential for either response. One approach to resolve this issue is to analyze knock-out mice. However, c-jun-null mice die at midgestation, precluding critical investigation. Therefore, a xenograft paradigm was used in which retinas from embryonic day 12.5 (E12.5) c-junnullizygous or wild-type mice were transplanted onto the superior colliculus of newborn rats. The rats were allowed to develop, and the grafts were assayed at various times for cell death and axon growth. Histologically, grafts of both genotypes developed in identical manners and had morphological characteristics of retinas. A functional c-junallele was not essential for axogenesis, because ganglion cells in retinal grafts from c-junnullizygous mice developed axons that projected into the colliculus. Programmed cell death (PCD) was also evident in the age-appropriate regions of the retina in both wild-type and c-jun-null grafts. Furthermore, there were no discernible differences in the number or location of dying cells in the two genotypes. That c-junwas not essential for PCD was supported by two additional findings. First, a c-jun-lacZ reporter gene was expressed in many cells in developing and grafted retinas, although only a few of these cells were destined to die. Second, in E12.5 c-jun-null embryos there were normal levels of PCD in the trigeminal ganglion. Together, these data indicate that c-Jun is not essential for axon growth in the retina or for PCD in the retina and trigeminal ganglion.
Role of Phosphorylation of Alzheimer’s Amyloid Precursor Protein during Neuronal Differentiation
Authors: Ando Kanae , Oishi Masaki , Takeda Shizu , Iijima Ko-ichi , Isohara Toshio , Nairn Angus C. , Kirino Yutaka , Greengard Paul , Suzuki Toshiharu
Published: April 2018

Alzheimer’s amyloid precursor protein (APP), the precursor of β-amyloid (Aβ), is an integral membrane protein with a receptor-like structure. We recently demonstrated that the mature APP (mAPP; N- and O-glycosylated form) is phosphorylated at Thr668 (numbering for APP695 isoform), specifically in neurons. Phosphorylation of mAPP appears to occur during, and after, neuronal differentiation. Here we report that the phosphorylation of mAPP begins 48–72 hr after treatment of PC12 cells with NGF and that this correlates with the timing of neurite outgrowth. The phosphorylated form of APP is distributed in neurites and mostly in the growth cones of differentiating PC12 cells. PC12 cells stably expressing APP with Thr668Glu substitution showed remarkably reduced neurite extension after treatment with NGF. These observations suggest that the phosphorylated form of APP may play an important role in neurite outgrowth of differentiating neurons.
Adult Mammalian Forebrain Ependymal and Subependymal Cells Demonstrate Proliferative Potential, but only Subependymal Cells Have Neural Stem Cell Characteristics
Authors: Chiasson Bernard J. , Tropepe Vincent , Morshead Cindi M. , van der Kooy Derek
Published: April 2018

The adult derivatives of the embryonic forebrain germinal zones consist of two morphologically distinct cell layers surrounding the lateral ventricles: the ependyma and the subependyma. Cell cycle analyses have revealed that at least two proliferating populations exist in this region, one that is constitutively proliferating and one that is relatively quiescent and thought to include the endogenous adult neural stem cells. Earlier studies demonstrated that specific dissection of the region surrounding the lateral ventricles was necessary for thein vitroisolation of multipotent, self-renewing neural stem cells. However, in these studies, the ependymal layer was not physically separated from the subependymal layer to identify the specific adult laminar localization of the neural stem cells around the lateral ventricles. To determine which cellular compartment in the adult forebrain contained the neural stem cells, we isolated and cultured the ependyma separately from the subependyma and tested for the presence of neural stem cells using thein vitroneurosphere assay. We demonstrate that the ependymal cells can proliferatein vitroto form sphere-like structures. However, the ependymal cells generating spheres do not have the ability to self-renew (proliferate to form secondary spheres after dissociation) nor to produce neurons, but rather only seem to generate glial fibrillary acidic protein-positive ependymal cells when plated under differentiation conditions in culture. On the other hand, a subpopulation of subependymal cells do possess the self-renewing and multipotential characteristics of neural stem cells. Therefore, the adult forebrain neural stem cell resides within the subependymal compartment.
Contributions of Tutor and Bird’s Own Song Experience to Neural Selectivity in the Songbird Anterior Forebrain
Authors: Solis Michele M. , Doupe Allison J.
Published: April 2018

Auditory neurons of the anterior forebrain (AF) of zebra finches become selective for song during song learning. In adults, these neurons respond more to the bird’s own song (BOS) than to the songs of other zebra finches (conspecifics) or BOS played in reverse. In contrast, AF neurons from young birds (30 d) respond equally well to all song stimuli. AF selectivity develops rapidly during song learning, appearing in 60-d-old birds. At this age, many neurons also respond equally well to BOS and tutor song. These similar neural responses to BOS and tutor song might reflect contributions from both song experiences to selectivity, because auditory experiences of both BOS and tutor song are essential for normal song learning. Alternatively, they may simply result from acoustic similarities between BOS and tutor song. Understanding which experience shapes selectivity could elucidate the function of song-selective AF neurons.

To minimize acoustic similarity between BOS and tutor song, we induced juvenile birds to produce abnormal song by denervating the syrinx, the avian vocal organ, before song onset. We recorded single neurons extracellularly in the AF at 60 d, after birds had had substantial experience of both the abnormal BOS (tsBOS) and tutor song. Some neurons preferred the unique tsBOS over the tutor song, clearly indicating a role for BOS experience in shaping neural selectivity. In addition, a sizable proportion of neurons responded equally well to tsBOS and tutor song, despite their acoustic dissimilarity. These neurons were not simply immature, because they were selective for tsBOS and tutor song relative to conspecific and reverse song. Furthermore, their similar responses to tsBOS and tutor song could not be attributed to residual acoustic similarities between the two stimuli, as measured by several song analyses. The neural sensitivity to two very different songs suggests that single AF neurons may be shaped by both BOS and tutor song experience.
GABABReceptor Antagonism: Facilitatory Effects on Memory Parallel Those on LTP Induced by TBS but Not HFS
Authors: Stäubli Ursula , Scafidi Joey , Chun Daniel
Published: April 2018

The present experiments used CGP 35348, a selective GABABreceptor antagonist with a significantly higher affinity for post- versus presynaptic receptors, to dissociate the role of antagonist concentration versus stimulation mode in determining whether GABABreceptor blockade facilitates or suppresses long-term potentiation (LTP). The antagonist was applied by pressure ejection to one of two recording sites in area CA1 of hippocampal slices before LTP was induced at both sites with either theta burst or high-frequency stimulation (TBS or HFS). TBS produced a dose-dependent facilitation of potentiation that turned into depression at the highest concentration tested, a result reflecting the dose-dependent balance between the drug’s postsynaptic disinhibitory effect and its action on presynaptic autoreceptors regulating the release of GABA. In contrast, HFS-induced LTP increased monotonically with drug concentration, suggesting that blockade of postsynaptic GABABreceptors is the only factor contributing to HFS-induced LTP. To test the relevance of the two sets of LTP results, we performed behavioral studies examining the effect of different dosages of antagonist on spatial retention and found that memory was enhanced at intermediate dosages but not at very low and high concentrations, reminiscent of the bell-shaped dose–response curve obtained for TBS-induced LTP. These findings are consistent with the notion that LTP induced by electrical stimulation modeled after endogenous theta-modulated activity patterns bears more relevance to behavior than does potentiation induced by arbitrary tetanic trains.
The Dopamine D2, but not D3or D4, Receptor Subtype is Essential for the Disruption of Prepulse Inhibition Produced by Amphetamine in Mice
Authors: Ralph Rebecca J. , Varty Geoffrey B. , Kelly Michele A. , Wang Yan-Min , Caron Marc G. , Rubinstein Marcelo , Grandy David K. , Low Malcolm J. , Geyer Mark A.
Published: April 2018

Brain dopamine (DA) systems are involved in the modulation of the sensorimotor gating phenomenon known as prepulse inhibition (PPI). The class of D2-like receptors, including the D2, D3, and D4 receptor subtypes, have all been implicated in the control of PPI via studies of DA agonists and antagonists in rats. Nevertheless, the functional relevance of each receptor subtype remains unclear because these ligands are not specific. To determine the relevance of each receptor subtype, we used genetically altered strains of “knock-out” mice lacking the DA D2, D3, or D4 receptors. We tested the effects of each knock-out on both the phenotypic expression of PPI and the disruption of PPI produced by the indirect DA agonistd-amphetamine (AMPH). No phenotypic differences in PPI were observed at baseline. AMPH significantly disrupted PPI in the D2 (+/+) mice but had no effect in the D2 (−/−) mice. After AMPH treatment, both DA D3 and D4 receptor (+/+) and (−/−) mice had significant disruptions in PPI. These findings indicate that the AMPH-induced disruption of PPI is mediated via the DA D2 receptor and not the D3 or D4 receptor subtypes. Uncovering the neural mechanisms involved in PPI will further our understanding of the substrates of sensorimotor gating and could lead to better therapeutics to treat gating disorders, such as schizophrenia.
Path Integration Absent in Scent-Tracking Fimbria–Fornix Rats: Evidence for Hippocampal Involvement in “Sense of Direction” and “Sense of Distance” Using Self-Movement Cues
Authors: Whishaw Ian Q. , Gorny Bogdan
Published: April 2018

Allothetic and idiothetic navigation strategies use very different cue constellations and computational processes. Allothetic navigation requires the use of the relationships between relatively stable external (visual, olfactory, auditory) cues, whereas idiothetic navigation requires the integration of cues generated by self-movement and/or efferent copy of movement commands. The flexibility with which animals can switch between these strategies and the neural structures that support these strategies are not well understood. By capitalizing on the proclivity of foraging rats to carry large food pellets back to a refuge for eating, the present study examined the contribution of the hippocampus to the use of allothetic versus idiothetic navigation strategies. Control rats and fimbria–fornix-ablated rats were trained to follow linear, polygonal, and octagonal scent trails that led to a piece of food. The ability of the rats to return to the refuge with the food via the shortest route using allothetic cues (visual cues and/or the odor trail available) or using ideothetic cues (the odor trail removed and the rats blindfolded or tested in infrared light) was examined. Control rats “closed the polygon” by returning directly home in all cue conditions. Fimbria–fornix rats successfully used allothetic cues (closed the polygon using visual cues or tracked back on the string) but were insensitive to the direction and distance of the refuge and were lost when restricted to idiothetic cues. The results support the hypothesis that the hippocampal formation is necessary for navigation requiring the integration of idiothetic cues.
A Furosemide-Sensitive K+–Cl−Cotransporter Counteracts Intracellular Cl−Accumulation and Depletion in Cultured Rat Midbrain Neurons
Authors: Jarolimek Wolfgang , Lewen Andrea , Misgeld Ulrich
Published: April 2018

Efficacy of postsynaptic inhibition through GABAAreceptors in the mammalian brain depends on the maintenance of a Cl−gradient for hyperpolarizing Cl−currents. We have taken advantage of the reduced complexity under which Cl−regulation can be investigated in cultured neurons as opposed to neurons in otherin vitropreparations of the mammalian brain. Tightseal whole-cell recording of spontaneous GABAAreceptor-mediated postsynaptic currents suggested that an outward Cl−transport reduced dendritic [Cl−]iif the somata of cells were loaded with Cl−via the patch pipette. We determined dendritic and somatic reversal potentials of Cl−currents induced by focally applied GABA to calculate [Cl−]iduring variation of [K+]oand [Cl−] in the patch pipette. [Cl−]iand [K+]owere tightly coupled by a furosemide-sensitive K+–Cl−cotransport. Thermodynamic considerations excluded the significant contribution of a Na+–K+–Cl−cotransporter to the net Cl−transport. We conclude that under conditions of normal [K+]othe K+–Cl−cotransporter helps to maintain [Cl−]iat low levels, whereas under pathological conditions, under which [K+]oremains elevated because of neuronal hyperactivity, the cotransporter accumulates Cl−in neurons, thereby further enhancing neuronal excitability.
Activation and Inactivation of the Voltage-Gated Sodium Channel: Role of Segment S5 Revealed by a Novel Hyperkalaemic Periodic Paralysis Mutation
Authors: Bendahhou Saı̈d , Cummins Theodore R. , Tawil Rabi , Waxman Stephen G. , Ptácek Louis J.
Published: April 2018

Hyperkalaemic periodic paralysis, paramyotonia congenita, and potassium-aggravated myotonia are three autosomal dominant skeletal muscle disorders linked to theSCN4Agene encoding the α-subunit of the human voltage-sensitive sodium channel. To date, ∼20 point mutations causing these disorders have been described. We have identified a new point mutation, in theSCN4Agene, in a family with a hyperkalaemic periodic paralysis phenotype. This mutation predicts an isoleucine-to-phenylalanine substitution at position 1495 located in the transmembrane segment S5 in the fourth homologous domain of the human α-subunit sodium channel. Introduction of the I1495F mutation into the wild-type channels disrupted the macroscopic current inactivation decay and shifted both steady-state activation and inactivation to the hyperpolarizing direction. The recovery from fast inactivation was slowed, and there was no effect on channel deactivation. Additionally, a significant enhancement of slow inactivation was observed in the I1495F mutation. In contrast, the T704M mutation, a hyperkalaemic periodic paralysis mutation located in the cytoplasmic interface of the S5 segment of the second domain, also shifted activation in the hyperpolarizing direction but had little effect on fast inactivation and dramatically impaired slow inactivation. These results, showing that the I1495F and T704M hyperkalaemic periodic paralysis mutations both have profound effects on channel activation and fast–slow inactivation, suggest that the S5 segment maybe in a location where fast and slow inactivation converge.
Activity-Dependent Modulation of Rod Photoreceptor Cyclic Nucleotide-Gated Channels Mediated by Phosphorylation of a Specific Tyrosine Residue
Authors: Molokanova Elena , Maddox Floyd , Luetje Charles W. , Kramer Richard H.
Published: April 2018

Cyclic nucleotide-gated (CNG) channels are crucial for phototransduction in vertebrate rod photoreceptors. The cGMP sensitivity of these channels is modulated by diffusible intracellular messengers, including Ca2+/calmodulin, contributing to negative feedback during sensory adaptation. Membrane-associated protein tyrosine kinases and phosphatases also modulate rod CNG channels, but whether this results from direct changes in the phosphorylation state of the channel protein has been unclear. Here, we show that bovine rod CNG channel α-subunits (bRET) contain a tyrosine phosphorylation site crucial for modulation. bRET channels expressed inXenopusoocytes exhibit modulation, whereas rat olfactory CNG channels (rOLF) do not. Chimeric channels reveal that differences in the C terminus, containing the cyclic nucleotide-binding domain, account for this difference. One specific tyrosine in bRET (Y498) appears to be crucial; replacement of this tyrosine in bRET curtails modulation, whereas installation into rOLF confers modulability. As the channel becomes dephosphorylated, there is an increase in the rate of spontaneous openings in the absence of ligand, indicating that changes in the phosphorylation state affect the allosteric gating equilibrium. Moreover, we find that dephosphorylation, which favors channel opening, requires open channels, whereas phosphorylation, which promotes channel closing, requires closed channels. Hence, modulation by changes in tyrosine phosphorylation is activity-dependent and may constitute a positive feedback mechanism, contrasting with negative feedback systems underlying adaptation.
Nerve Growth Factor Signaling through p75 Induces Apoptosis in Schwann Cells via a Bcl-2-Independent Pathway
Authors: Soilu-Hänninen Merja , Ekert Paul , Bucci Tamara , Syroid Daniel , Bartlett Perry F. , Kilpatrick Trevor J.
Published: April 2018

Apoptosis is involved in the regulation of Schwann cell numbers during normal development and after axonal damage, but the molecular regulation of Schwann cell death remains unknown. We have used stably transfected rat Schwann cell lines to study the potential roles of nerve growth factor (NGF), the antiapoptotic protein Bcl-2 and the cytokine response modifier A (CrmA) in modulating Schwann cell deathin vitro. Bcl-2 inhibited Schwann cell apoptosis induced by survival factor withdrawal, whereas CrmA did not. In contrast, Bcl-2-transfected Schwann cells were susceptible to apoptosis in response to exogenous NGF, whereas CrmA-expressing cell lines were resistant. Demonstration of high levels of the low-affinity neurotrophin receptor p75 but not the high-affinity TrkA receptor on the Bcl-2-transfected cell lines suggested that the NGF-induced killing was mediated by p75. This was confirmed by resistance of Schwann cells isolated from p75 knockout mice to the NGF-induced cell death. Nerve growth factor also promoted the death of wild-type mouse and rat Schwann cells in the absence of survival factor withdrawal. Endogenous Bcl-2 mRNA was expressed by wild-type Schwann cells in all conditions that promoted survival but was downregulated to undetectable levels after survival factor withdrawal. In conclusion, our results demonstrate the existence of two separate pathways that expedite apoptosis in Schwann cells: a Bcl-2-blockable pathway initiated on loss of trophic support, and a Bcl-2-independent, CrmA-blockable pathway mediated via the p75 receptor.
A Single Growth Cone is Capable of Integrating Simultaneously Presented and Functionally Distinct Molecular Cues during Target Recognition
Authors: Rose Demian , Chiba Akira
Published: April 2018

A variety of cell recognition pathways affect neuronal target recognition. However, whether such pathways can converge at the level of a single growth cone is not well known. The RP3 motoneuron inDrosophilahas previously been shown to respond to the muscle cell surface molecules TOLL and fasciclin III (FAS3), which are normally encountered during RP3 pathfinding in a sequential manner. TOLL and FAS3, putative “negative” and “positive” recognition molecules, respectively, affect RP3 antagonistically. Under normal conditions, TOLL and FAS3 together improve the accuracy of its target recognition. Here, we show that, when presented with concurrent TOLL and FAS3 expression, RP3 responds to both, integrating their effects. This was demonstrated most succinctly by single cell visualization methods. When a balance in relative expression levels between the two antagonistic cues is achieved, the RP3 growth cone exhibits a phenotype virtually identical to that seen when neither TOLL nor FAS3 is misexpressed. Thus, growth cones are capable of quantitatively evaluating distinct recognition cues and integrating them to attain a net result, in effect responding to the “balance of power” between positive and negative influences. We suggest that the ability to integrate multiple recognition pathways in real-time is one important way in which an individual growth cone interprets and navigates complex molecular environments.
Ephrin-A Binding and EphA Receptor Expression Delineate the Matrix Compartment of the Striatum
Authors: Janis L. Scott , Cassidy Robert M. , Kromer Lawrence F.
Published: April 2018

The striatum integrates limbic and neocortical inputs to regulate sensorimotor and psychomotor behaviors. This function is dependent on the segregation of striatal projection neurons into anatomical and functional components, such as the striosome and matrix compartments. In the present study the association of ephrin-A cell surface ligands and EphA receptor tyrosine kinases (RTKs) with the organization of these compartments was determined in postnatal rats. Ephrin-A1 and ephrin-A4 selectively bind to EphA receptors on neurons restricted to the matrix compartment. Binding is absent from the striosomes, which were identified by μ-opioid receptor immunostaining. In contrast, ephrin-A2, ephrin-A3, and ephrin-A5 exhibit a different mosaic binding pattern that appears to define a subset of matrix neurons.In situhybridization for EphA RTKs reveals that the two different ligand binding patterns strictly match the mRNA expression patterns of EphA4 and EphA7. Ligand–receptor binding assays indicate that ephrin-A1 and ephrin-A4 selectively bind EphA4 but not EphA7 in the lysates of striatal tissue. Conversely, ephrin-A2, ephrin-A3, and ephrin-A5 bind EphA7 but not EphA4. These observations implicate selective interactions between ephrin-A molecules and EphA RTKs as potential mechanisms for regulating the compartmental organization of the striatum.
Propagating Activation during Oscillations and Evoked Responses in Neocortical Slices
Authors: Wu Jian-young , Guan Li , Tsau Yang
Published: April 2018

Population activity in the cortex is poorly understood. In this report we use voltage-sensitive dye imaging to examine the spatiotemporal patterns of a 7–10 Hz oscillation in neocortical slices from rat somatosensory areas. This oscillation appeared as a component of spontaneous epochs when the preparation was bathed in low [Mg] artificial CSF (ACSF) (Silva et al., 1991). Each epoch started with a synchronized spike, and 3–200 cycles of oscillation emerged afterward. Voltage-sensitive dye imaging revealed that the oscillations in the local field potential recordings were actually caused by a propagating population activation. This activation propagated in a relatively uniform size (not expanding). We call this confined, propagating activation a “dynamic ensemble.” During each oscillation cycle, one (occasionally two) dynamic ensemble(s) appeared in the slice and was sustained for 60–200 msec. Dynamic ensembles propagated at ∼30 mm/sec; the activity could propagate in both directions in cortical slices. The propagation consisted in part of “jumps,” the locations of which were not fixed. Dynamic ensembles were distinguishable from the epileptiform spikes that occurred in low [Mg] ACSF. Population events similar to dynamic ensembles were also evoked under conditions of unaltered excitability (slice in normal ACSF) by electrical stimulation that activated a low density of neurons in a large area. Our data suggest that self-sustained, spatially confined, and propagating dynamic ensembles might be related to the epoch oscillations in somatosensory cortex seenin vivo(Nicolelis et al., 1995) and thus resemble one form of population activation in the neocortex.
Modulation of Learning and Anxiety by Corticotropin-Releasing Factor (CRF) and Stress: Differential Roles of CRF Receptors 1 and 2
Authors: Radulovic Jelena , Rühmann Andreas , Liepold Thomas , Spiess Joachim
Published: April 2018

The differential modulation of learning and anxiety by corticotropin-releasing factor (CRF) through CRF receptor subtypes 1 (CRFR1) and 2 (CRFR2) is demonstrated. As learning paradigm, context- and tone-dependent fear conditioning of the mouse was used. Injection of CRF into the dorsal hippocampus before training enhanced learning through CRFR1 as demonstrated by the finding that this effect was prevented by the local injection of the unselective CRFR antagonist astressin, but not by the CRFR2-specific antagonist antisauvagine-30 (anti-Svg-30). In contrast, injection of CRF into the lateral intermediate septum impaired learning through CRFR2, as demonstrated by the ability of antisauvagine-30 to block this effect. When antisauvagine-30 was injected alone into the lateral intermediate septum, learning was enhanced. Such tonic control of learning was not observed when astressin or antisauvagine-30 was injected into the dorsal hippocampus. Injection of CRF after the training into the dorsal hippocampus and the lateral intermediate septum also enhanced and impaired learning, respectively. Thus, it was indicated that CRF acted on memory consolidation. It was concluded that the observed effects reflected changes of associative learning and not arousal, attention, or motivation. Although a dose of 20 pmol human/rat CRF was sufficient to affect learning significantly, a fivefold higher dose was required to induce anxiety by injection into the septum. Immobilization for 1 hr generated a stress response that included the induction of anxiety through septal CRFR2 and the subsequent enhancement of learning through hippocampal CRFR1. The involvement of either receptor subtype was demonstrated by region-specific injections of astressin and antisauvagine-30.
Substrate Turnover by Transporters Curtails Synaptic Glutamate Transients
Authors: Mennerick Steven , Shen Weixing , Xu Wanyan , Benz Ann , Tanaka Kohichi , Shimamoto Keiko , Isenberg Keith E. , Krause James E. , Zorumski Charles F.
Published: April 2018

Although inhibitors of glutamate transport prolong synaptic currents at many glutamate synapses, the cause of the current prolongation is unclear. Transport inhibitors may prolong synaptic currents by simply interfering with synaptic glutamate binding to transporters, by inhibiting substrate translocation, or by promoting accumulation of ambient glutamate, which may act cooperatively at receptors with synaptic glutamate. We show that reversal of the membrane potential of astrocytes surrounding the synapse prolongs synaptic currents but does not decrease the apparent affinity of transporters or significantly alter glutamate-dependent kinetics of macroscopic transporter currents in excised membrane patches. Positive membrane potentials do not affect binding of a nontransported glutamate analog, nor do positive membrane potentials alter the number of transporters available to bind analog. We also test the hypothesis that glutamate accumulation during uptake inhibition by transporter substrates is the direct cause of synaptic current prolongations. Transporter substrates elevate ambient glutamate near synapses by fostering reverse transport of endogenous glutamate. However, increases in ambient glutamate cannot account for the prolongations of synaptic currents, because a nonsubstrate transport inhibitor does not foster reverse uptake yet it prolongs synaptic currents. Moreover, exogenous glutamate does not mimic synaptic current prolongations induced by substrate inhibitors. These results provide strong support for a major role of substrate translocation in determining the time course of the glutamate concentration transient at excitatory synapses.
Mitochondria Regulate the Ca2+–Exocytosis Relationship of Bovine Adrenal Chromaffin Cells
Authors: Giovannucci David R. , Hlubek Michael D. , Stuenkel Edward L.
Published: April 2018

The present study expands the contemporary view of mitochondria as important participants in cellular Ca2+dynamics and provides evidence that mitochondria regulate the supply of release-competent secretory granules. Using pharmacological probes to inhibit mitochondrial Ca2+import, the ability of mitochondria to modulate secretory activity in single, patch-clamped bovine chromaffin cells was examined by simultaneously monitoring rapid changes in membrane surface area (ΔCm) and cytosolic Ca2+levels ([Ca2+]c). Repetitive step depolarizations or action potential waveforms were found to raise the [Ca2+]cof chromaffin cells into the 1 μmto tens of micromolar range. Inhibiting mitochondria by treatment with carbonyl cyanidep-(trifuoro-methoxy)phenylhydrazone, antimycin–oligomycin, or ruthenium red revealed that mitochondria are a prominent component for the clearance of Ca2+that entered via voltage-activated Ca2+channels. Disruption of cellular Ca2+homeostasis by poisoning mitochondria enhanced the secretory responsiveness of chromaffin cells by increasing the amplitude of the transient rise and the time course of recovery to baseline of the evoked Δ[Ca2+]c. The enhancement of the secretory response was represented by significant deviation of the Ca2+–exocytosis relationship from a standard relationship that equates Ca2+influx and ΔCm. Thus, mitochondria would play a critical role in the control of secretory activity in chromaffin cells that undergo tonic or repetitive depolarizing activity, likely by limiting the Ca2+-dependent activation of specific proteins that recruit or prime secretory granules for exocytosis.
Analysis of the Retrograde Transport of Glial Cell Line-Derived Neurotrophic Factor (GDNF), Neurturin, and Persephin Suggests ThatIn VivoSignaling for the GDNF Family is GFRα Coreceptor-Specific
Authors: Leitner Melanie L. , Molliver Derek C. , Osborne Patricia A. , Vejsada Richard , Golden Judy P. , Lampe Patricia A. , Kato Ann C. , Milbrandt Jeffrey , Johnson Eugene M.
Published: April 2018

Neurturin (NRTN) and glial cell line-derived neurotrophic factor (GDNF) are members of a family of trophic factors with similar actionsin vitroon certain neuronal classes. Retrograde transport of GDNF and NRTN was compared in peripheral sensory, sympathetic, and motor neurons to determine whetherin vivothese factors are transported selectively by different neuronal populations. After sciatic nerve injections, NRTN was transported by sensory neurons of the dorsal root ganglion (DRG). Competition studies demonstrated only limited cross-competition between NRTN and GDNF, indicating selective receptor-mediated transport of these factors. By using immunohistochemistry, we identified two populations of NRTN-transporting DRG neurons: a major population of small, RET-positive, IB4-positive, non-TrkA-expressing neurons that also show the ability to transport GDNF and a minor population of calretinin-expressing neurons that fail to transport GDNF. Spinal motor neurons in the adult showed relatively less ability to transport NRTN than to transport GDNF, although NRTN prevented the cell death of neonatal motor neurons in a manner very similar to GDNF (Yan et al., 1995) and persephin (PSPN) (Milbrandt et al., 1998). Last, NRTN, like GDNF, was not transported to sympathetic neurons of the adult superior cervical ganglion (SCG) after injection into the anterior eye chamber. These data reveal a high degree of functional selectivity of GDNF family receptor-α (GFRα) coreceptor subtypes for NRTN and GDNFin vivo.
Unilateral GluR2(B) Hippocampal Knockdown: A Novel Partial Seizure Model in the Developing Rat
Authors: Friedman Linda K. , Koudinov Alexei R.
Published: April 2018

Kainic acid (KA) induces status epilepticus in both adult and young rats but with different consequences on pathology and gene expression. In adults, GluR2(B) AMPA subunit expression is markedly reduced in CA3 neurons before neurodegeneration. In pups, the GluR2(B) subunit is sustained, possibly contributing to neuronal survival. Mechanisms underlying the reduced vulnerability of developing neurons to seizures was investigated by examining the effects of unilateral microinfusions of GluR2(B) antisense oligodeoxynucleotides (AS-ODNs) into the hippocampus of young rats in the presence or absence of a subconvulsive dose of KA. GluR2(B) AS-ODN infusions resulted in spontaneous seizure-like behavior, high stimulus intensity population spikes in the absence of long-term potentiation, and neurodegeneration of CA3 neurons lateral to the infusion site. Electroencephalography revealed paroxysmal activity and high-frequency high-amplitude discharges associated with vigorous and continuous scratching, wild running, or bilateral jerking movements. Pups lacking phenotypic behavior exhibited high-rhythmic oscillations and status epilepticus by the dose of KA used. Radiolabeled AS-ODNs accumulated throughout the ipsilateral dorsal hippocampus. GluR2(B) but not GluR1(A) receptor protein was markedly reduced after GluR2(B) knockdown. In contrast, GluR1(A) knockdown reduced GluR1(A) but not GluR2(B) protein without change in behavior or morphology. Therefore, unilateral downregulation of hippocampal GluR2(B) but not GluR1(A) protein reduces the seizure threshold and survival of CA3 neurons in the immature hippocampus, possibly providing a novel partial seizure model in the developing rat.
The Neural Cell Adhesion Molecules L1 and NCAM-180 Act in Different Steps of Neurite Outgrowth
Authors: Takei Kohtaro , Chan Timothy A. , Wang Feng-Song , Deng Haiyan , Rutishauser Urs , Jay Daniel G.
Published: April 2018

The formation of neurocircuitry depends on the control of neurite outgrowth that, in turn, can be divided into two processes: nerve growth cone protrusion and neurite extension. It has long been known that the neural cell adhesion molecules L1 and NCAM-180 promote neurite outgrowth, but how they function in growth cones is unclear. We addressed the roles of L1 and NCAM-180 in neurite outgrowth by using microscale chromophore-assisted laser inactivation (micro-CALI) of these proteins to perturb their functions at precise times in single growth cones of embryonic chick dorsal root ganglion neurons grown in culture. Micro-CALI of L1 causes neurite retraction after a 10 min lag period but does not affect growth cone protrusion. In contrast, micro-CALI of NCAM-180 causes rapid growth cone retraction but does not affect neurite extension. The simultaneous inactivation of both these molecules resulted in both distinct effects that were segregated in time. The behavior of growth cones after these micro-CALI treatments resemble the drug-induced perturbation of microtubules for L1 and F-actin for NCAM-180. These findings suggest distinct roles in the growth cone for L1 and NCAM-180 in different steps of neurite outgrowth: L1 functions in neurite extension,whereas NCAM-180 functions in growth cone protrusion.