bluuebunny/crossref_metadata_2025_split huggingface dataset:
Selective attention to sound location or pitch studied with event‐related brain potentials and magnetic fields
Authors: Degerman Alexander , Rinne Teemu , Särkkä Anna‐Kaisa , Salmi Juha , Alho Kimmo 
Published: June 2008

AbstractEvent‐related brain potentials (ERPs) and magnetic fields (ERFs) were used to compare brain activity associated with selective attention to sound location or pitch in humans. Sixteen healthy adults participated in the ERP experiment, and 11 adults in the ERF experiment. In different conditions, the participants focused their attention on a designated sound location or pitch, or pictures presented on a screen, in order to detect target sounds or pictures among the attended stimuli. In the Attend Location condition, the location of sounds varied randomly (left or right), while their pitch (high or low) was kept constant. In the Attend Pitch condition, sounds of varying pitch (high or low) were presented at a constant location (left or right). Consistent with previous ERP results, selective attention to either sound feature produced a negative difference (Nd) between ERPs to attended and unattended sounds. In addition, ERPs showed a more posterior scalp distribution for the location‐related Nd than for the pitch‐related Nd, suggesting partially different generators for these Nds. The ERF source analyses found no source distribution differences between the pitch‐related Ndm (the magnetic counterpart of the Nd) and location‐related Ndm in the superior temporal cortex (STC), where the main sources of the Ndm effects are thought to be located. Thus, the ERP scalp distribution differences between the location‐related and pitch‐related Nd effects may have been caused by activity of areas outside the STC, perhaps in the inferior parietal regions.
Impaired GABAergic transmission disrupts normal homeostatic plasticity in rat cortical networks
Authors: Le Roux N. , Amar M. , Moreau A. , Baux G. , Fossier P. 
Published: June 2008

AbstractIn the cortex, homeostatic plasticity appears to be a key process for maintaining neuronal network activity in a functional range. This phenomenon depends on close interactions between excitatory and inhibitory circuits. We previously showed that application of a high frequency of stimulation (HFS) protocol in layer 2/3 induces parallel potentiation of excitatory and inhibitory inputs on layer 5 pyramidal neurons, leading to an unchanged excitation/inhibition (E/I) balance. These coordinated long‐term potentiations of excitation and inhibition correspond to homeostatic plasticity of the neuronal networks. We showed here, on the rat visual cortex, that blockade (with gabazine) or overactivation (with 4,5,6,7‐tetrahydroisoxazolo[5,4‐c]pyridin‐3‐ol) of GABAA receptors enhanced the E/I balance and prevented the potentiation of excitatory and inhibitory inputs after an HFS protocol. These impairements of the GABAergic transmission led to a long‐term depression‐like effect after an HFS protocol. We also observed that the blockade of inhibition reduced excitation (by 60%), and conversely, the blockade of excitation decreased inhibition (by 90%). These results support the idea that inhibitory interneurons are critical for recurrent interactions underlying homeostatic plasticity in cortical networks.
Population coding of song element sequence in the Bengalese finch HVC
Authors: Nishikawa Jun , Okada Masato , Okanoya Kazuo 
Published: June 2008

AbstractBirdsong is a complex vocalization composed of various song elements organized according to sequential rules. Two alternative views exist that explain the neural representation of song element sequences in the songbird brain. The finding of sequential selective neurons supports the idea that the song element sequence is encoded in a chain of rigid selective neurons. Alternatively, song structure could be encoded in an ensemble of relatively broad selective neurons arranged in a distributed manner. Here we attempted to determine which neural representation actually occurs in the song system by recording neural responses to various stimuli and performing information‐theoretic analysis on the data obtained. We recorded the neural responses to all possible element pairs of stimuli in the Bengalese finch brain nucleus high vocal centre (HVC). Our results showed that each neuron has broad but differential response properties to element sequences beyond the structure of self‐generated song. To quantify the transmitted information by such a broadly tuned neural population, we calculated the time course of mutual information between auditory stimuli and neural activities. Confounded information, which represents the relationship between present and previous elements, increased significantly immediately after stimulus presentation. These results indicate that the song element sequence is encoded in a neural ensemble in the HVC via population coding. These findings give us a new encoding scheme for the song element sequence using a distributed neural representation rather than the chain model of rigid selective neurons.
Dynamic coupling of excitatory and inhibitory responses in the medial nucleus of the trapezoid body
Authors: Tolnai Sandra , Englitz Bernhard , Kopp‐Scheinpflug Cornelia , Dehmel Susanne , Jost Jürgen , Rübsamen Rudolf 
Published: June 2008

AbstractThe neuronal representation of acoustic amplitude modulations is an important prerequisite for understanding the processing of natural sounds. We investigated this representation in the medial nucleus of the trapezoid body (MNTB) of the Mongolian gerbil using sinusoidal amplitude modulations (SAM). Depending on the SAM’s carrier frequency (fC) MNTB cells either increase or decrease their discharge rates, indicating underlying excitatory and inhibitory/suppressive mechanisms. As natural sounds typically are composed of multiple spectral components we investigated how stimuli containing two spectral components are represented in the MNTB, especially when they have opposing effects on the discharge rate. Three conditions were compared: SAM stimuli (1) with rate‐increasing fC, (2) with rate‐increasing fC and an additional unmodulated rate‐decreasing pure tone, and (3) with rate‐decreasing fC and an unmodulated, rate‐increasing pure tone. We found that responses under all three conditions showed comparable strength of phase‐locking. Adding a rate‐decreasing tone to a rate‐increasing SAM increased phase‐locking for modulation frequencies (fAM) of ≤ 600 Hz. A comparison of two possible coding strategies – phase‐locking vs. envelope reproduction – indicates that both strategies are realized to different degrees depending on the fAM. We measured latencies for following modulations in rate‐increasing and rate‐decreasing SAMs using a modified reverse correlation approach. Although latencies varied between 2.5 and 5 ms between cells, a decrease in rate consistently followed an increase in rate with a delay of about 0.2 ms in each cell. These results suggest a temporally precise representation of rate‐increasing and rate‐decreasing stimuli at the level of the MNTB during dynamic stimulation.
N‐ethylmaleimide‐sensitive fusion protein (NSF) is involved in central sensitization in the spinal cord through GluR2 subunit composition switch after inflammation
Authors: Katano Tayo , Furue Hidemasa , Okuda‐Ashitaka Emiko , Tagaya Mitsuo , Watanabe Masahiko , Yoshimura Megumu , Ito Seiji 
Published: June 2008

AbstractCentral sensitization, similar to long‐term potentiation in the hippocampus, refers to the increased synaptic efficacy established in somatosensory neurons in the dorsal horn of the spinal cord following tissue injury or nerve damage. In the course of inflammation, many proteins including glutamate receptors are assumed to be dynamically reorganized in the postsynaptic density (PSD) and involved in persistent pain. Mechanical hyperalgesia induced by intraplantar injection of complete Freund’s adjuvant (CFA) was inhibited at 4 h, but not at 24 h, by indomethacin, an inhibitor of prostanoid synthesis. To elucidate the nature of the molecule(s) involved in the late phase of inflammatory pain, we analysed the PSD fraction prepared from the lumbar spinal cord of rats before and 24 h after CFA injection by conducting two‐dimensional differential gel electrophoresis. N‐ethylmaleimide‐sensitive fusion protein (NSF) was identified as a downregulated protein in the PSD by MALDI‐TOF MS and immunoblotting. Concomitant with the decrease in NSF, GluR2 and GluR3 were decreased and GluR1 was conversely increased in the PSD fraction 24 h after CFA injection. In vivo patch‐clamp recordings of rats 24 h after CFA injection showed that excitatory postsynaptic currents of dorsal horn neurons evoked by pinch stimuli to inflamed skin were inwardly rectified and inhibited by 60% by philanthotoxin‐433, a selective inhibitor of the Ca2+ ‐permeable α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptor. These results suggest that peripheral inflammation gives rise to central sensitization in the spinal cord through subunit composition switch of AMPA receptors in the late phase.
Dual modulation of synaptic transmission in the nucleus tractus solitarius by prostaglandin E2 synthesized downstream of IL‐1β
Authors: Marty Vincent , El Hachmane Mickaël , Amédée Thierry 
Published: June 2008

AbstractThe activation of the innate immune system induces the production of blood‐borne proinflammatory cytokines like interleukin‐1β (IL‐1β), which in turn triggers brain‐mediated adaptative responses referred to as sickness behaviour. These responses involve the modulation of neural networks in key regions of the brain. The nucleus tractus solitarius (NTS) of the brainstem is a key nucleus for immune‐to‐brain signalling. It is the main site of termination of vagal afferents and is adjacent to the area postrema, a circumventricular organ allowing blood‐borne action of circulating IL‐1β. Although it is well described that IL‐1β activates cerebral endothelial and glial cells, it is still unknown if and how IL‐1β or downstream‐synthesized molecules impact NTS synaptic function. In this study we report that IL‐1β did not modulate NTS synaptic transmissionper se, whereas prostaglandin E2(PGE2), which is produced downstream of IL‐1β, produced opposite effects on spontaneous and evoked release. On the one hand, PGE2facilitated glutamatergic transmission between local NTS neurons by enhancing the frequency of spontaneous excitatory postsynaptic currents through a presynaptic receptor different from the classical EP1–4 subtypes. On the other hand, PGE2also depressed evoked excitatory input from vagal afferent terminals through presynaptic EP3 receptors coupled to G‐proteins linked to adenylyl cyclase and protein kinase A activity. Our data show that IL‐1β‐induced PGE2can modulate evoked and spontaneous release in the NTS differentially through different mechanisms. These data unravel some molecular mechanisms by which innate immune stimuli could signal to, and be integrated within, the brainstem to produce central adaptative responses.
A novel role for MNTB neuron dendrites in regulating action potential amplitude and cell excitability during repetitive firing
Authors: Leão Richardson N. , Leão Ricardo M. , Da Costa Luciano F. , Rock Levinson S. , Walmsley Bruce 
Published: June 2008

AbstractPrincipal cells of the medial nucleus of the trapezoid body (MNTB) are simple round neurons that receive a large excitatory synapse (the calyx of Held) and many small inhibitory synapses on the soma. Strangely, these neurons also possess one or two short tufted dendrites, whose function is unknown. Here we assess the role of these MNTB cell dendrites using patch‐clamp recordings, imaging and immunohistochemistry techniques. Using outside‐out patches and immunohistochemistry, we demonstrate the presence of dendritic Na+ channels. Current‐clamp recordings show that tetrodotoxin applied onto dendrites impairs action potential (AP) firing. Using Na+ imaging, we show that the dendrite may serve to maintain AP amplitudes during high‐frequency firing, as Na+ clearance in dendritic compartments is faster than axonal compartments. Prolonged high‐frequency firing can diminish Na+ gradients in the axon while the dendritic gradient remains closer to resting conditions; therefore, the dendrite can provide additional inward current during prolonged firing. Using electron microscopy, we demonstrate that there are small excitatory synaptic boutons on dendrites. Multi‐compartment MNTB cell simulations show that, with an active dendrite, dendritic excitatory postsynaptic currents (EPSCs) elicit delayed APs compared with calyceal EPSCs. Together with high‐ and low‐threshold voltage‐gated K+ currents, we suggest that the function of the MNTB dendrite is to improve high‐fidelity firing, and our modelling results indicate that an active dendrite could contribute to a ‘dual’ firing mode for MNTB cells (an instantaneous response to calyceal inputs and a delayed response to non‐calyceal dendritic excitatory postsynaptic potentials).
A role for alpha‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid GluR1 phosphorylation in the modulatory effects of appetitive reward cues on goal‐directed behavior
Authors: Crombag Hans S. , Sutton Jeffrey M. , Takamiya Kogo , Holland Peter C. , Gallagher Michela , Huganir Richard L. 
Published: June 2008

AbstractAlpha‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA) receptor regulation has been shown to be critically involved in synaptic plasticity underlying learning and memory. This regulation occurs through trafficking of the receptor and modulation of the receptor’s channel properties, both of which depend on protein phosphorylation. Using homologous recombination (knock‐in) techniques we targeted two phosphorylation sites on the AMPA‐GluR1 receptor: the Ser831 site, phosphorylated by calcium calmodulin‐dependent protein kinase II/protein kinase C, and the Ser845 site, phosphorylated by protein kinase A. Mice with mutations that prevented phosphorylation at one or both of these sites were tested on a single‐outcome Pavlovian‐instrumental transfer task often used to assess the acquisition of incentive motivation by cues for food reinforcement. Mice were separately trained to associate a Pavlovian cue with food and to perform an instrumental lever‐press response to earn that same reward. During a transfer test, the cue was presented while the mice were lever‐pressing under extinction conditions. Whereas wild‐type control mice showed substantial enhancement of lever‐pressing when the cue was presented (i.e. showed Pavlovian‐instrumental transfer), mice with mutations at both of these phosphorylation sites showed no evidence of such transfer. By contrast, mice with either serine site mutated alone showed normal transfer. These results suggest critical roles for GluR1 phosphorylation pathways in a form of incentive learning that can play an important part in regulating normal motivated behavior as well as maladaptive behaviors such as addiction and eating disorders.
Cysteine string protein‐α is essential for the high calcium sensitivity of exocytosis in a vertebrate synapse
Authors: Ruiz R. , Casañas J. J. , Südhof T. C. , Tabares L. 
Published: June 2008

AbstractCysteine string protein (CSPα) is a synaptic vesicle protein present in most central and peripheral nervous system synapses. Previous studies demonstrated that the deletion of CSPα results in postnatal sensorial and motor impairment and premature lethality. To understand the participation of CSPα in neural function in vertebrates, we have studied the properties of synaptic transmission of motor terminals in wild‐type and CSPα knockout mice. Our results demonstrate that, in the absence of CSPα, fast Ca2+‐triggered release was not affected at postnatal day (P)14 but was dramatically reduced at P18 and P30 without a change in release kinetics. Although mutant terminals also exhibited a reduction in functional vesicle pool size by P30, further analysis showed that neurotransmission could be ‘rescued’ by high extracellular [Ca2+] or by the presence of a phorbol ester, suggesting that an impairment in the fusion machinery, or in vesicle recycling, was not the primary cause of the dysfunction of this synapse. The specific shift to the right of the Ca2+ dependence of synchronous release, and the lineal dependence of secretion on extracellular [Ca2+] in mutant terminals after P18, suggests that CSPα is indispensable for a normal Ca2+ sensitivity of exocytosis in vertebrate mature synapses.
Environmental enrichment ameliorates a motor coordination deficit in a mouse model of Rett syndrome –Mecp2gene dosage effects and BDNF expression
Authors: Kondo Mari , Gray Laura J. , Pelka Gregory J. , Christodoulou John , Tam Patrick P. L. , Hannan Anthony J. 
Published: June 2008

AbstractRett syndrome, commonly associated with mutations of the methyl CpG‐binding protein 2 (MECP2) gene, is characterised by an apparently normal early postnatal development followed by deterioration of acquired cognitive and motor coordination skills in early childhood. To evaluate whether environmental factors may influence the disease outcome of Rett syndrome, we tested the effect of environmental enrichment from 4 weeks of age on the behavioural competence of mutant mice harboring aMecp2 tm1Tam‐null allele. Our findings show that enrichment improves motor coordination in heterozygousMecp2 +/−females but notMecp2 −/ymales. Standard‐housedMecp2 +/−mice had an initial motor coordination deficit on the accelerating rotarod, which improved with training then deteriorated in subsequent weeks. Enrichment resulted in a significant reduction in this coordination deficit inMecp2 +/−mice, returning the performance to wild‐type levels. Brain‐derived neurotrophic factor (BDNF) protein levels were 75 and 85% of wild‐type controls in standard‐housed and environmentally enrichedMecp2 +/−cerebellum, respectively.Mecp2 −/ymice showed identical deficits of cerebellar BDNF (67% of wild‐type controls) irrespective of their housing environment. Our findings demonstrate a positive impact of environmental enrichment in a Rett syndrome model; this impact may be dependent on the existence of one functional copy ofMecp2.
Age‐related changes in dopamine transporters and accumulation of 3‐nitrotyrosine in rhesus monkey midbrain dopamine neurons: Relevance in selective neuronal vulnerability to degeneration
Authors: Kanaan N. M. , Kordower J. H. , Collier T. J. 
Published: June 2008

AbstractAging is the strongest risk factor for developing Parkinson’s disease (PD). There is a preferential loss of dopamine (DA) neurons in the ventral tier of the substantia nigra (vtSN) compared to the dorsal tier and ventral tegmental area (VTA) in PD. Examining age‐related and region‐specific differences in DA neurons represents a means of identifying factors potentially involved in vulnerability or resistance to degeneration. Nitrative stress is among the factors potentially underlying DA neuron degeneration. We studied the relationship between 3‐nitrotyrosine (3NT; a marker of nitrative damage) and DA transporters [DA transporter (DAT) and vesicular monoamine transporter‐2 (VMAT)] during aging in DA subregions of rhesus monkeys. The percentage of DA neurons containing 3NT increased significantly only in the vtSN with advancing age, and the vtSN had a greater percentage of 3NT‐positive neurons when compared to the VTA. The relationship between 3NT and DA transporters was determined by measuring fluorescence intensity of 3NT, DAT and VMAT staining. 3NT intensity increased with advancing age in the vtSN. Increased DAT, VMAT and DAT/VMAT ratios were associated with increased 3NT in individual DA neurons. These results suggest nitrative damage accumulates in midbrain DA neurons with advancing age, an effect exacerbated in the vulnerable vtSN. The capacity of a DA neuron to accumulate more cytosolic DA, as inferred from DA transporter expression, is related to accumulation of nitrative damage. These findings are consistent with a role for aging‐related accrual of nitrative damage in the selective vulnerability of vtSN neurons to degeneration in PD.
Enhanced Ras activity preserves dendritic size and extension as well as synaptic contacts of neurons after functional deprivation in synRas mice
Authors: Alpár A. , Naumann N. , Härtig W. , Arendt T. , Gärtner U. 
Published: June 2008

AbstractThe monomeric GTP‐binding protein p21Ras has been repeatedly implicated in neuronal stability and plastic changes of the adult nervous system. Recently, we have shown that expression of constitutively active Ras protein in transgenic synRas mice results in a significant increase in the dendritic size and complexity of differentiated pyramidal neurons as well as in increased synaptic connectivity. In the present study, we examined the organization of the vibrissae‐barrel cortex in synRas mice and the effects of enhanced Ras activity on deprivation‐induced dendritic reorganization after vibrissectomy. The results demonstrate a significant increase in vibrissae‐barrel sizes and proportional spacing between barrels in synRas mice, suggesting that the neuronal target specificity of thalamocortical terminals is preserved. Accordingly, the arrangement of double bouquet cells at the borders of barrel columns ensuring functional distinctness is unchanged. Partial vibrissectomy is followed by significant dendritic regression of corresponding pyramidal neurons in the barrel cortex of wild‐type mice, which, however, could not be observed in synRas mice. The results provide the first evidence for a role of Ras in preserving neuronal structure after functional deprivation in vivo.
The shape of an ecological trade‐off varies with environment
Authors: Jessup Christine M. , Bohannan Brendan J. M. 
Published: June 2008

AbstractCentral to most theories that explain the diversity of life is the concept that organisms face trade‐offs. Theoretical work has shown that the precise shape of a trade‐off relationship affects evolutionary predictions. One common trade‐off is that between competitive ability and resistance to predators, parasitoids, pathogens or herbivores. We used a microbial experimental system to elucidate the shape of the relationship between parasitoid resistance and competitive ability. For each of 86 bacteriophage‐resistant isolates of the bacteriumEscherichia coliB, we measured the degree of resistance to bacteriophage T2 (a viral parasitoid) and relative competitive ability in both the resource environment in which strains were isolated and in two alternate environments. We observed that environmental change can alter trade‐off shape, and that different physiological mechanisms can lead to different trade‐off shapes and different sensitivities to environmental change. These results highlight the important interaction between environment and trade‐off shape in affecting ecological and evolutionary dynamics.
Phylogenetic analysis of Porphyromonas species isolated from the oral cavity of Australian marsupials
Authors: Mikkelsen Deirdre , Milinovich Gabriel J. , Burrell Paul C. , Huynh Sharnan C. , Pettett Lyndall M. , Blackall Linda L. , Trott Darren J. , Bird Philip S. 
Published: June 2008

Summary Porphyromonas species are frequently isolated from the oral cavity and are associated with periodontal disease in both animals and humans. Black, pigmented Porphyromonas spp. isolated from the gingival margins of selected wild and captive Australian marsupials with varying degrees of periodontal disease (brushtail possums, koalas and macropods) were compared phylogenetically to Porphyromonas strains from non‐marsupials (bear, wolf, coyote, cats and dogs) and Porphyromonas gingivalis strains from humans using 16S rRNA gene sequence analysis. The results of the phylogenetic analysis identified three distinct groups of strains. A monophyletic P. gingivalis group (Group 1) contained only strains isolated from humans and a Porphyromonas gulae group (Group 2) was divided into three distinct subclades, each containing both marsupial and non‐marsupial strains. Group 3, which contained only marsupial strains, including all six strains isolated from captive koalas, was genetically distinct from P. gulae and may constitute a new Porphyromonas species.