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Trains
Kinds of Trains Selected AbstractsContinuous Soluble Ziegler-Natta Ethylene Polymerizations in Reactor Trains, 2 , Estimation of Kinetic Parameters from Industrial DataMACROMOLECULAR REACTION ENGINEERING, Issue 2 2008Marcelo Embiruçu Abstract We show that it is possible to estimate kinetic parameters for complex mechanistic polymerization models from available industrial data. A methodology is developed for efficient handling and reconciliation of industrial data and is then applied to allow estimation of kinetic parameters for industrial ethylene polymerizations performed in reactor trains using soluble Ziegler-Natta catalysts. The parameter estimation procedure is formulated as a nonlinear optimization procedure subject to hard and soft model and process constraints. Parameter estimates obtained for the catalyst system allow a very good description of actual industrial data used during the estimation process and also allow very good prediction of process performance when completely new operating conditions are considered. It is concluded that complex phenomenological models can be successfully fitted to actual industrial processes without the need to carry out extensive experimental tests in the laboratory. [source] Continuous Soluble Ziegler-Natta Ethylene Polymerizations in Reactor Trains, 3 , Influence of Operating Conditions upon Process PerformanceMACROMOLECULAR REACTION ENGINEERING, Issue 2 2008Marcelo Embiruçu Abstract The behavior of continuous solution ethylene/but-1-ene polymerizations through Ziegler-Natta catalysts is analyzed, based on a previously developed mathematical model. In order to do that, dynamic simulations are carried out and process responses are analyzed as functions of process operating policies and flowsheet configuration, at conditions that resemble the actual operation of industrial sites. It is shown that system responses are highly nonlinear and very sensitive to disturbances of the operating conditions and that catalyst decay is of fundamental importance for proper understanding of process behavior. Results indicate that mixing conditions inside the reactor vessels exert a significant impact upon the final polymer quality and can be manipulated for in-line control of final resin properties. Finally, it is shown that the development of feed policies, based on the use of lateral feed streams, allows the simultaneous control of melt flow index, stress exponent and polymer density of the final polymer resin. [source] The Effect of Using Variable Frequency Trains During Functional Electrical Stimulation CyclingNEUROMODULATION, Issue 3 2008Simona Ferrante PhD ABSTRACT Objectives., This paper describes an experimental investigation of variable frequency stimulation patterns as a means of increasing torque production and, hence, performance in cycling induced by functional electrical stimulation. Materials and Methods., Experiments were conducted on six able-bodied subjects stimulating both quadriceps during isokinetic trials. Constant-frequency trains (CFT) with 50-msec interpulse intervals and four catchlike-inducing trains (CIT) were tested. The CITs had an initial, brief, high-frequency burst of two pulses at the onset of or within a subtetanic low-frequency stimulation train. Each stimulation train consisted of the same number of pulses. The active torques produced by each train were compared. Parametric main effect ANOVA tests were performed on the active torque-time integral (TTI), on the active torque peaks and on the time needed to reach those peaks (T2P). Results., The electrical stimulation of the quadriceps produced active torques with mean peak values in the range of 1.6,3.5 Nm and a standard error below 0.2 Nm. CITs produced a significant increase of TTI and torque peaks compared with CFTs in all the experimental conditions. In particular, during the postfatigue trials, the CITs with the doublet placed in the middle of the train produced TTIs and torque peaks about 61% and 28% larger than the CFT pattern, respectively. In addition, the CITs showed the lowest reduction of the performance between prefatigue and postfatigue conditions. Conclusions., The use of CITs improves the functional electrical stimulation cycling performance compared with CFT stimulation. This application might have a relevant clinical importance for individuals with stroke where the residual sensation is still present and thus the maximization of the performance without an excessive increase of the stimulation intensity is advisable. Therefore, exercise intensity can be increased yielding a better muscle strength and endurance that may be beneficially for later gait training in individuals with stroke. [source] Length Dependent Potentiation in Electrically Stimulated Human Ankle Dorsiflexor MusclesNEUROMODULATION, Issue 2 2002Petra Mela PhD Abstract The purpose of this study was to investigate the short-term history effect of a decreasing frequency train on force and the influence of joint angle on such effect in human dorsiflexor muscles. Six able-bodied and three spinal cord injured (SCI) subjects took part in the study. Their isometric left dorsiflexor muscles were stimulated with two-second bursts at three ankle joint positions and movements at the ankle were measured. Trains with constant stimulation frequencies (CSF: 50, 25, 20, 16, 12, 8 Hz) and with decreasing stimulation frequencies (DSF1,2) were used. Each DSF tetanus consisted of four 0.5 second bursts of different frequencies (DSF1: 50, 25, 16, 8 Hz; DSF2: 50, 20, 12, 8 Hz). To evaluate the effect of preceding higher stimulation frequencies (DSF), the average moment at corresponding time intervals in the DSF and CSF trials were compared for 25, 20, 16, 12, 8 Hz. Preceding higher stimulation frequencies caused increase of the moment elicited by a given frequency. This was true for all the subjects at dorsiflexed positions, but the effect is highly dependent on joint ankle. At plantar flexed positions moment enhancement was seen only in SCI subjects. We conclude that effects of joint angle as well as individual muscle properties should be taken into account when optimizing muscle force by means of frequency modulation. [source] Sexual Orientation Discrimination after Grant v South-West TrainsTHE MODERN LAW REVIEW, Issue 5 2000Nicholas Bamforth In Grant v South-West Trains [1998] ECR I-621, the European Court of Justice implied that, as a general matter, discrimination against an employee on the ground of sexual orientation did not violate Article 141 EC. This article argues that Grant rests on shaky foundations, in that it is conceptually inconsistent with the Court's earlier decision in P v S and Cornwall County Council [1996] ECR I-2143. Furthermore, the scope of Grant has since been qualified by decisions of the European Court of Human Rights , decisions which may well have undermined the status of the case more broadly. However these difficulties are ultimately resolved, the Court of Justice's treatment of sexual orientation discrimination exposes flaws in its approach as a self-proclaimed constitutional court. [source] Involvement of T-type calcium channels in excitatory junction potentials in rat resistance mesenteric arteriesBRITISH JOURNAL OF PHARMACOLOGY, Issue 6 2002Qi Xi We investigated the role of voltage-operated calcium channels in sympathetic transmission and depolarization-induced contractions in the rat mesenteric artery. In particular, we investigated the role of the T-type voltage-operated calcium channels (T-channels) in mediating excitatory junction potentials (EJPs). EJPs were evoked by electrical field stimulation (trains of five stimuli at 0.9 Hz) in small mesenteric arteries. The average resting membrane potential was ,59.8±0.5 mV (n=65). Trains of stimuli evoked individual EJPs with the peak EJP of 6±0.2 mV (n=34) occurring with the second stimulus. Trains of EJPs were inhibited 90% by tetrodotoxin (0.1 ,M) or by ,-conotoxin GVIA (GVIA, 10 nM) indicating their neural origin. The EJPs were not inhibited by the L-type calcium channel blocker nicardipine at 0.1 ,M, a concentration sufficient to abolish the contraction to potassium depolarization. However, mibefradil (3 ,M), considered a relatively selective T-channel antagonist, inhibited the EJPs by about 50%. This concentration of mibefradil did not inhibit GVIA-sensitive electrically-evoked twitches of the rat vas deferens. Thus the action of mibefradil in reducing EJPs is unlikely to be due to either inhibition of L- or N-type channels but is probably due to inhibition of T-channels. The finding that Ni2+ (300 ,M), an inhibitor of T-type calcium channels, also reduced EJP amplitude by about 80% but did not block electrically-evoked twitches in the rat vas deferens, further supports an important role of T-channels in mediating small depolarizations associated with the EJPs evoked by sympathetic nerve stimulation. British Journal of Pharmacology (2002) 137, 805,812. doi:10.1038/sj.bjp.0704943 [source] Partial reversal of conduction slowing during repetitive stimulation of single sympathetic efferents in human skinACTA PHYSIOLOGICA, Issue 3 2004M. Campero Abstract Aims:, To describe and identify the function of a class of human C fibre with an unusual response to repetitive electrical stimulation. Other C fibres slow progressively at 2 Hz (type 1), reach a latency plateau (type 2) or hardly slow at all (type 3). Methods:, C fibres innervating hairy skin were recorded by microneurography in the superficial peroneal nerves of 19 healthy volunteers. Baseline electrical stimulation of the skin was at 0.25 Hz, and activity-dependent slowing recorded during stimulation at 2 Hz for 3 min and after a 3-min pause in stimulation. Results:, In 41 units, there was a partial recovery of latency during repetitive stimulation. These were classified as ,type-4' units, and identified as sympathetic efferents, since they exhibited spontaneously activity, which was enhanced by manoeuvres that increase sympathetic outflow (15 of 16 cases) and/or suppressed by a proximal anaesthetic block (eight of eight cases). The peak slowing during 2 Hz trains averaged 6.47 ± 2.06% (mean ± SD, n = 41), but after 3 min the slowing had reduced to 4.90 ± 2.20%, which was less than in all type 1 (nociceptor) fibres but similar to that in type 2 (cold) fibres. Compared with cold fibres, type-4 sympathetic fibres slowed more after the first 10 impulses at 2 Hz (2.57 ± 0.45%) and also after a pause in stimulation (1.66 ± 0.51%). Conclusions:, The distinctive activity-dependent slowing profiles of these type-4 sympathetic C units may help identification in vitro, and suggest that hyperpolarization-activated channels have a particularly prominent role in the axonal membrane. [source] Physiological requirement for the glutamate transporter dEAAT1 at the adult Drosophila neuromuscular junctionDEVELOPMENTAL NEUROBIOLOGY, Issue 10 2006Thomas Rival Abstract L -Glutamate is the major excitatory neurotransmitter in the mammalian brain. Specific proteins, the Na+/K+ -dependent high affinity excitatory amino acid transporters (EAATs), are involved in the extracellular clearance and recycling of this amino acid. Type I synapses of the Drosophila neuromuscular junction (NMJ) similarly use L -glutamate as an excitatory transmitter. However, the localization and function of the only high-affinity glutamate reuptake transporter in Drosophila, dEAAT1, at the NMJ was unknown. Using a specific antibody and transgenic strains, we observed that dEAAT1 is present at the adult, but surprisingly not at embryonic and larval NMJ, suggesting a physiological maturation of the junction during metamorphosis. We found that dEAAT1 is not localized in motor neurons but in glial extensions that closely follow motor axons to the adult NMJ. Inactivation of the dEAAT1 gene by RNA interference generated viable adult flies that were able to walk but were flight-defective. Electrophysiological recordings of the thoracic dorso-lateral NMJ were performed in adult dEAAT1-deficient flies. The lack of dEAAT1 prolonged the duration of the individual responses to motor nerve stimulation and this effect was progressively increased during physiological trains of stimulations. Therefore, glutamate reuptake by glial cells is required to ensure normal activity of the Drosophila NMJ, but only in adult flies. © 2006 Wiley Periodicals, Inc. J Neurobiol, 2006 [source] Magnetic motor threshold and response to TMS in major depressive disorderACTA PSYCHIATRICA SCANDINAVICA, Issue 3 2002O. T. Dolberg Dolberg OT, Dannon PN, Schreiber S, Grunhaus L. Magnetic motor threshold and response to TMS in major depressive disorder. Acta Psychiatr Scand 2002: 106: 220,223. © Blackwell Munksgaard 2002. Objective:,The aim of this study was to examine motor threshold (MT) during treatment with transcranial magnetic stimulation (TMS). Method:,The TMS was administered to 46 patients with depression and 13 controls. TMS was performed at 90% power of measured MT. The stimulation frequency was 10 Hz for 6 s, for 20 trains, with 30 s inter-train intervals. The trial included 20 sessions. Patients and controls were assessed on various outcome measures. Results:,The MT values were comparable between patients and controls. Neither demographic nor clinical variables were factors in determining MT. MT was not shown to have any predictive value regarding outcome of treatment. Conclusion:,In this study, MT at baseline or changes in MT during the treatment period were not able to discriminate between patients and controls and were not found to have any predictive value with regard to treatment outcome. [source] Planform dynamics of the Lower Mississippi RiverEARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2006Oliver P. Harmar Abstract This paper presents an analysis of the planform behaviour of the Lower Mississippi River (LMR) using a series of maps and hydrographic surveys covering the period 1765,1975. Data allow analysis at various time and space scales, using fixed and statistically defined reaches, both before and after extensive channel modification. Previous research has interpreted planform change in relation to geomorphological or engineering regime-type analyses of channel length and width for the LMR as a ,single system'. The analysis here is broadly consistent with these approaches, but highlights the importance of meander geometry, in the form of the radius of curvature:width ratio. This neglected factor helps resolve paradoxes relating to observed changes in sediment transport and channel stability. When viewed over smaller time and space scales, analysis of dynamics using fixed reach boundaries reveals a downstream trend in the pattern of planform behaviour, which is closely related to the distribution of valley floor deposits, and which also reflects neotectonic influences. Analysis of changes using statistically determined reach boundaries shows that, over shorter time scales, meander trains are continually formed and modified over a period of approximately 120 years. Zones of more-or-less dynamic behaviour thus move through the LMR. The research also provides a context for 20th century engineering interventions to the river. These have constrained the magnitude of planform adjustment, but also altered the kind of response that is now possible in relation to changes in discharge and sediment load, and as a consequence of internal feedbacks within the LMR system. Copyright © 2006 John Wiley & Sons, Ltd. [source] Semi-empirical model for site effects on acceleration time histories at soft-soil sites.EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 11 2004Part 1: formulation, development Abstract A criterion is developed for the simulation of realistic artificial ground motion histories at soft-soil sites, corresponding to a detailed ground motion record at a reference firm-ground site. A complex transfer function is defined as the Fourier transform of the ground acceleration time history at the soft-soil site divided by the Fourier transform of the acceleration record at the firm-ground site. Working with both the real and the imaginary components of the transfer function, and not only with its modulus, serves to keep the statistical information about the wave phases (and, therefore, about the time variation of amplitudes and frequencies) in the algorithm used to generate the artificial records. Samples of these transfer functions, associated with a given pair of soft-soil and firm-ground sites, are empirically determined from the corresponding pairs of simultaneous records. Each function included in a sample is represented as the superposition of the transfer functions of the responses of a number of oscillators. This formulation is intended to account for the contributions of trains of waves following different patterns in the vicinity of both sites. The properties of the oscillators play the role of parameters of the transfer functions. They vary from one seismic event to another. Part of the variation is systematic, and can be explained in terms of the influence of ground motion intensity on the effective values of stiffness and damping of the artificial oscillators. Another part has random nature; it reflects the random characteristics of the wave propagation patterns associated with the different events. The semi-empirical model proposed recognizes both types of variation. The influence of intensity is estimated by means of a conventional one-dimensional shear wave propagation model. This model is used to derive an intensity-dependent modification of the values of the empirically determined model parameters in those cases when the firm-ground earthquake intensity used to determine these parameters differs from that corresponding to the seismic event for which the simulated records are to be obtained. Copyright © 2004 John Wiley & Sons, Ltd. [source] Efficacy of repetitive transcranial magnetic stimulation in alcohol dependence: a sham-controlled studyADDICTION, Issue 1 2010Biswa R. Mishra ABSTRACT Objective To study the anticraving efficacy of high-frequency repetitive transcranial magnetic stimulation (rTMS) of the right dorsolateral pre-frontal cortex (DLPFC) in patients with alcohol dependence. Methods We performed a prospective, single-blind, sham-controlled study involving 45 patients with alcohol dependence syndrome (according to ICD-10 DCR), with Clinical Institute of Withdrawal Assessment in Alcohol Withdrawal (CIWA-Ar) scores ,10. Patients were allocated to active and sham rTMS in a 2 : 1 ratio, such that 30 patients received active and 15 patients sham rTMS to the right DLPFC (10 Hz frequency, 4.9 seconds per train, inter-train interval of 30 seconds, 20 trains per session, total 10 sessions). The Alcohol Craving Questionnaire (ACQ-NOW) was administered to measure the severity of alcohol craving at baseline, after the last rTMS session and after 1 month of the last rTMS session. Results Two-way repeated-measures analysis of variance (ANOVA) showed significant reduction in the post-rTMS ACQ-NOW total score and factor scores in the group allocated active rTMS compared to the sham stimulation. The effect size for treatment with time interaction was moderate (,2 = 0.401). Conclusions Right dorsolateral pre-frontal high-frequency rTMS was found to have significant anticraving effects in alcohol dependence. The results highlight the potential of rTMS which, combined with other anticraving drugs, can act as an effective strategy in reducing craving and subsequent relapse in alcohol dependence. [source] Label recognition using collinear acoustooptic devices in WDM photonic routerELECTRICAL ENGINEERING IN JAPAN, Issue 3 2007Nobuo Goto Abstract Collinear acoustooptic (AO) switches are investigated for use in label recognition system in photonic routing systems. The optical label discussed in this paper uses optical codes which are encoded in the time domain. Short optical pulse trains representing the codes are processed with integrated AO devices. Proposed device configurations for label recognition are described with the basic operation mechanism. A numerical example for the code recognition is also presented. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(3): 48,55, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20453 [source] The heterogeneous distribution of functional synaptic connections in rat hippocampal dissociated neuron culturesELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 6 2009Suguru N. Kudoh Abstract The dynamics of functional synaptic connections are critical for information processing systems in the brain, such as perception and learning. Using rat hippocampal cells cultured on multielectrode arrays, we investigated the spatiotemporal pattern of spontaneous action potentials. The neurons developed connections and a characteristic high-frequency bursting (HFB) activity was observed transiently. After the period of HFB activity, the distribution of spontaneous activity changed drastically with the appearance of neurons with frequent electrical activity and neurons with little activity in the network. The functional connections of all the combinations of recorded spike trains were estimated and depicted simultaneously in a Connection Map. This map revealed that each culture contained hublike neurons with many functional connections, suggesting that the cultures of dissociated rat hippocampal neurons on multielectrode arrays formed heterogeneous networks of functional connections. In addition, the functional connections were drastically reorganized after the induction of synaptic potentiation, and novel hub neurons emerged. These results indicate that spontaneous activity is enough to construct dynamic assemblies of neurons connected to each other by functional synaptic connections, and that synaptic potentiation can induce reorganization of such assemblies of neurons. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(6): 41,49, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10063 [source] Multiple polypeptide forms observed in two-dimensional gels of Methylococcus capsulatus (Bath) polypeptides are generated during the separation procedureELECTROPHORESIS, Issue 4 2003Frode S. Berven Abstract We have examined two-dimensional electrophoresis (2-DE) gel maps of polypeptides from the Gram-negative bacterium Methylococcus capsulatus (Bath) and found the same widespread trains of spots as often reported in 2-DE gels of polypeptides of other Gram-negative bacteria. Some of the trains of polypeptides, both from the outer membrane and soluble protein fraction, were shown to be generated during the separation procedure of 2-DE, and not by covalent post-translational modifications. The trains were found to be regenerated when rerunning individual polypeptide spots. The polypeptides analysed giving this type of trains were all found to be classified as stable polypeptides according to the instability index of Guruprasad et al. (Protein Eng. 1990, 4, 155,161). The phenomenon most likely reflects conformational equilibria of polypeptides arising from the experimental conditions used, and is a clear drawback of the standard 2-DE procedure, making the gel picture unnecessarily complex to analyse. [source] A performance comparison of individual and combined treatment modules for water recyclingENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 4 2005Stuart Khan Abstract An Advanced Water Recycling Demonstration Plant (AWRDP) was commissioned and constructed by the Queensland State Government in Australia. The AWRDP was used to study the effectiveness of a variety of treatment processes in the upgrading of municipal wastewater for water recycling applications. The AWRDP consists of eight modules, each housing an individual specific treatment process. These processes are flocculation, dissolved air flotation, dual media filtration, ozonation, biological activated carbon adsorption, microfiltration, reverse osmosis, and ultraviolet disinfection. The individual performances of the treatment processes were determined, as well as their interdependence in series. A range of chemical water quality parameters were investigated. The study provides a broad process comparison on the basis of an important catalogue of these key parameters. This will be valuable in the selection and optimization of treatment processes trains in full-scale water recycling applications. © 2005 American Institute of Chemical Engineers Environ Prog, 2005 [source] Kindling Limits the Interictal Neuronal Temporal Response Properties in Cat Primary Auditory CortexEPILEPSIA, Issue 2 2005Pamela A. Valentine Summary:,Purpose: The present study examined the effect of electrical kindling on the interictal temporal response properties of single units recorded from primary auditory cortex (AI) of the adult cat. Methods: Cats were permanently implanted with electrodes in AI, kindled twice daily for 40 sessions, and the contralateral AI was subsequently mapped. Kindling stimulation consisted of 1-s trains of biphasic square-wave pulses applied at a frequency of 60 Hz, 100 ,A above the afterdischarge (AD) threshold. The EEG activity was recorded during each kindling session, and the behavioral manifestation was scored. Subsequent to kindling, multiple single-unit responses were recorded under ketamine anesthesia in response to 1-s-long periodic click trains, with click rates between 2 and 64 Hz. Neuronal responses were characterized according to their ability to respond in time-locked fashion to the clicks. Results: Kindling stimulation resulted in progression of the AD characteristics and seizure behavior, with six of 10 kindled cats reaching a fully generalized state. In the fully kindled cats, the best modulation frequencies and limiting following rates for the single-unit responses were significantly lower compared with those of naive and sham controls. Conclusions: Repeated epileptiform activity interferes with temporal processing in cat auditory cortex in the interictal state. This may have implications for people with epileptic foci in auditory-related areas. [source] Intra- and Intersexual Selection for Multiple Traits in the Peacock (Pavo cristatus)ETHOLOGY, Issue 9 2005Adeline Loyau Animal communication involves a multitude of signals ranging from morphological to behavioural traits. In spite of the diversity of traits used in animal signalling, most studies of sexual selection have focused on single male traits. Moreover, the two forces of sexual selection (male,male competition and female preference) may target different traits and favour the diversification of male signalling. Still, little is known on the combined effects of intra- and intersexual selection on the evolution of multiple signals. The peacock is often cited as one of the best examples of the strength of sexual selection in producing exaggerated traits. Here, we investigated traits under intra- and intersexual selection in a population of free-ranging common peafowl. Peacocks with longer trains and tarsi were more likely to establish a display territory in a central position within the lek and had a higher number of intrusions and agonistic interactions. These traits appeared therefore to be under intrasexual selection. Female selection was assessed as the number of copulations. Mating success was positively correlated with behavioural traits (display activity) and with train ornamentation (number and density of ocelli) suggesting that females use multiple cues during mate selection. Therefore, intra- and intersexual selection seem to operate on different sets of traits. Overall, our results stress the role of multiple receivers on the evolution of multiple signals. [source] Functional electrical stimulation in neurological disordersEUROPEAN JOURNAL OF NEUROLOGY, Issue 5 2008O. K. Sujith Functional electrical stimulation (FES) refers to electrical stimulation of muscles in order to improve the impaired motor function. This is achieved by activating skeletal muscles with constant frequency trains of stimulations. This method has been found useful in various neurological disorders like hemiplegia, foot drop and paraplegia including spinal cord injuries. The first half of this review focuses on the broad clinical applications of functional electrical stimulation, its mechanism of action and the complications of this mode of therapy. Advanced Parkinson's disease (PD) is characterized by marked slowing of gait and frequent freezing episodes. Medical and surgical treatments are often ineffective in managing freezing episodes. The second half of this review discusses briefly the gait abnormalities in PD and the available treatment options. The possible role of FES in improving gait in parkinsonism and the importance of future research in this direction are highlighted. [source] Persistent rhythmic oscillations induced by nicotine on neonatal rat hypoglossal motoneurons in vitroEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2006Nerijus Lamanauskas Abstract Patch-clamp recording from hypoglossal motoneurons in neonatal Wistar rat brainstem slices was used to investigate the electrophysiological effects of bath-applied nicotine (10 µm). While nicotine consistently evoked membrane depolarization (or inward current under voltage clamp), it also induced electrical oscillations (3,13 Hz; lasting for , 8.5 min) on 40% of motoneurons. Oscillations required activation of nicotinic receptors sensitive to dihydro-,-erythroidine (0.5 µm) or methyllycaconitine (5 nm), and were accompanied by enhanced frequency of spontaneous glutamatergic events. The slight voltage dependence of oscillations and their block by the gap junction blocker, carbenoxolone, suggest they originate from electrically coupled neurons. Network nicotinic receptors desensitized more slowly than motoneuron ones, demonstrating that network receptors remained active longer to support heightened release of the endogenous glutamate necessary for enhancing the network excitability. The ionotropic glutamate receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and the group I metabotropic receptor antagonist, (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA), suppressed oscillations, while the NMDA receptor antagonist, d -amino-phosphonovaleriate (APV), produced minimal depression. Nicotine-evoked oscillations constrained spike firing at low rates, although motoneurons could still generate high-frequency trains of action potentials with unchanged gain for input depolarization. This is the first demonstration that persistent activation of nicotinic receptors could cause release of endogenous glutamate to evoke sustained oscillations in the theta frequency range. As this phenomenon likely represented a powerful process to coordinate motor output to tongue muscles, our results outline neuronal nicotinic acetylcholine receptors (nAChRs) as a novel target for pharmacological enhancement of motoneuron output in motor dysfunction. [source] Recovery and refractoriness of auditory evoked fields after gaps in click trainsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2004Alexander Gutschalk Abstract When clicks are presented in a train at a rate above ,5 Hz, they evoke a sustained field in human auditory cortex that can be recorded by magnetoencephalography. In this study we evaluated how this sustained field continues when a click train is interrupted by a silent gap. The stimuli were click trains with interclick intervals of either 12 or 24 ms, which produce pitches of 83.3 or 41.7 Hz, respectively. The click trains were 996 ms in duration with a gap of 12, 24, 48, 96, or 192 ms beginning 504 ms post-stimulus onset. The sustained field for click trains with short gaps was similar to the one evoked by a continuous click train. Subtraction of the response evoked by a solitary click train of 504 ms enabled estimation of the sustained field in the interval after the gap. The comparison revealed that the sustained field amplitude after the gap was larger than that at the onset of the initial click train in the interval from 150 to 350 ms after onset, and the difference decreased with gap duration. In contrast, the transient P1m was refractory for gaps up to 48 ms, but had nearly recovered its initial amplitude for gaps of 192 ms. We discuss how these results might relate to the perception, i.e. if an interrupted click train is perceived as one continuous sound with a transient gap or as two successive events. [source] Xenopus embryonic spinal neurons recorded in situ with patch-clamp electrodes , conditional oscillators after all?EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2003Simon P. Aiken Abstract The central pattern generator for swimming Xenopus embryo is organized as two half-centres linked by reciprocal inhibition. Microelectrode recordings suggest that Xenopus neurons are poorly excitable, necessitating a key role for postinhibitory rebound in the operation of the central pattern generator. However the Xenopus central pattern generator seems unusual in that the component neurons apparently have no intrinsic or conditional rhythmogenic properties. We have re-examined the firing properties of Xenopus embryo spinal neurons by making patch-clamp recordings in situ from intact spinal cord. Recordings made from 99 neurons were divided into three groups. Central pattern generator neurons overwhelmingly (44/51) fired trains of action potentials in response to current injection. Just over half of the sensory interneurons (13/22) also fired trains of action potentials. Neurons that received no synaptic inputs during swimming mostly fired just one or two action potentials (22/26). Thirty-four neurons were identified morphologically. Commissural (8/12) and descending (6/6) interneurons, key components of the spinal central pattern generator, fired repetitive trains of action potentials during current injection. Neurons that were not part of the central pattern generator did not demonstrate this preponderance for repetitive firing. Analysis of the interspike intervals during current injection revealed that the majority of central pattern generators, descending and commissural interneurons, could readily fire at frequencies up to twice that of swimming. We suggest that Xenopus neurons can be considered as conditional oscillators: in the presence of unpatterned excitation they exhibit an ability to fire rhythmically. This property makes the Xenopus embryonic central pattern generator more similar to other model central pattern generators than has hitherto been appreciated. [source] Presynaptic inhibition of Schaffer collateral synapses by stimulation of hippocampal cholinergic afferent fibresEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2003David Fernández de Sevilla Abstract It has been known for decades that muscarinic agonists presynaptically inhibit Schaffer collateral synapses contacting hippocampal CA1 pyramidal neurons. However, a demonstration of the inhibition of Schaffer collateral synapses induced by acetylcholine released by cholinergic hippocampal afferents is lacking. We present original results showing that electrical stimulation at the stratum oriens/alveus with brief stimulus trains inhibited excitatory postsynaptic currents evoked by stimulation of Schaffer collaterals in CA1 pyramidal neurons of rat hippocampal slices. The increased paired-pulse facilitation and the changes in the variance of excitatory postsynaptic current amplitude that paralleled the inhibition suggest that it was mediated presynaptically. The effects of oriens/alveus stimulation were inhibited by atropine, and blocking nicotinic receptors with methyllycaconitine was ineffective, suggesting that the inhibition was mediated via the activation of presynaptic muscarinic receptors. The results provide a novel demonstration of the presynaptic inhibition of glutamatergic neurotransmission by cholinergic fibres in the hippocampus, implying that afferent cholinergic fibres regulate the strength of excitatory synaptic transmission. [source] Modulation by adenosine of both muscarinic M1 -facilitation and M2 -inhibition of [3H]-acetylcholine release from the rat motor nerve terminalsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2002Laura Oliveira Abstract The crosstalk between adenosine and muscarinic autoreceptors regulating evoked [3H]-acetylcholine ([3H]-ACh) release was investigated on rat phrenic nerve-hemidiaphragm preparations. Motor nerve terminals possess facilitatory M1 and inhibitory M2 autoreceptors that can be activated by McN-A-343 (1,30 µm) and oxotremorine (0.3,100 µm), respectively. The muscarinic receptor antagonist, dicyclomine (3 nm,10 µm), caused a biphasic (inhibitory/facilitatory) effect, indicating that M1 -facilitation prevails during 5 Hz stimulation trains. Concomitant activation of AF,DX 116-sensitive M2 receptors was partially attenuated, as pretreatment with M1 antagonists, muscarinic toxin 7 (MT-7, 0.1 nm) and pirenzepine (1 nm), significantly enhanced inhibition by oxotremorine. Activation of A2A -adenosine receptors with CGS 21680C (2 nm) (i) potentiated oxotremorine inhibition, and (ii) shifted McN-A-343-induced facilitation into a small inhibitory effect. Conversely, the A1 -receptor agonist, R- N6 -phenylisopropyl adenosine (R-PIA, 100 nm), attenuated the inhibitory effect of oxotremorine, without changing facilitation by McN-A-343. Synergism between A2A and M2 receptors is regulated by a reciprocal interaction with facilitatory M1 receptors, which may be prevented by pirenzepine (1 nm). During 50 Hz-bursts, facilitation (M1) of [3H]-ACh release by McN-A-343 disappeared, while the inhibitory (M2) effect of oxotremorine became predominant. This muscarinic shift results from the interplay with A2A receptors, as it was precluded by the selective A2A receptor antagonist, ZM 241385 (10 nm). In conclusion, when the muscarinic M1 positive feedback loop is fully operative, negative regulation of ACh release is mediated by adenosine A1 receptors. During high frequency bursts, tonic activation of A2A receptors promotes M2 autoinhibition by braking the M1 receptor operated counteraction. [source] Synaptic plasticity in the basolateral amygdala in transgenic mice expressing dominant-negative cAMP response element-binding protein (CREB) in forebrainEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2000G. Rammes Abstract Electrophysiological and behavioural experiments were performed in transgenic mice expressing a dominant-negative form of cAMP response element-binding protein (CREBA133) in the limbic system. In control littermate in vitro slice preparation, tetanizing the lateral amygdala,basolateral amygdala (BLA) pathway with a single train (100 Hz for 1 s) produced short-term potentiation (STP) in the BLA. Five trains (10-s interstimulus interval) induced long-term potentiation (LTP), which was completely blocked by the N-methyl- d -aspartate (NMDA) receptor antagonist d(,)-2-amino-5-phosphonopentanoic acid (AP5; 50 ,m). When GABAergic (,-aminobutyric acid) inhibition was blocked by picrotoxin (10 ,m), LTP became more pronounced. Low-frequency stimulation (1 Hz for 15 min) induced either long-term depression (LTD) or depotentiation. LTD remained unaffected by AP5 (50 ,m) or by the L- and T-type Ca2+ -channel blockers nifedipine (20 ,m) and Ni2+ (50 ,m), but was prevented by picrotoxin (10 ,m), indicating a GABAergic link in the expression of LTD in the BLA. When conditioned fear was tested, a mild impairment was seen in one of three transgenic lines only. Although high levels of mRNA encoding CREBA133 lead to downregulation of endogenous CREB, expression of LTP and depotentiation were unaltered in BLA of these transgenic animals. These results could suggest that residual CREB activity was still present or that CREB per se is dispensable. Alternatively, other CREB-like proteins were able to compensate for impaired CREB function. [source] Selective Long-Term Electrical Stimulation of Fast Glycolytic Fibres Increases Capillary Supply but not Oxidative Enzyme Activity in Rat Skeletal MusclesEXPERIMENTAL PHYSIOLOGY, Issue 5 2000S. Egginton Glycolytic fibres in rat extensor digitorum longus (EDL) and tibialis anterior (TA) were selectively activated, as demonstrated by glycogen depletion, by indirect electrical stimulation via electrodes implanted in the vicinity of the peroneal nerve using high frequency (40 Hz) trains (250 ms at 1 Hz) and low voltage (threshold of palpable contractions). This regime was applied 10 times per day, each bout being of 15 min duration with 60 min recovery, for 2 weeks. Cryostat sections of muscles were stained for alkaline phosphatase to depict capillaries, succinate dehydrogenase (SDH) to demonstrate oxidative fibres, and periodic acid-Schiff reagent (PAS) to verify glycogen depletion. Specific activity of hexokinase (HK), 6-phosphofructokinase, pyruvate kinase, glycogen phosphorylase and cytochrome c oxidase (COX) were estimated separately in homogenates of the EDL and the predominantly glycolytic cortex and oxidative core of the TA. Stimulation increased the activity of HK but not that of oxidative enzymes in fast muscles. Comparison of changes in oxidative capacity and capillary supply showed a dissociation in the predominantly glycolytic TA cortex. Here, COX was 3.9 ± 0.68 ,M min-1 (g wet wt)-1 in stimulated muscles compared with 3.7 ± 0.52 ,M min-1 (g wet wt)-1 in contralateral muscles (difference not significant), while the percentage of oxidative fibres (those positively stained for SDH) was also similar in stimulated (14.0 ± 2.8%) and contralateral (12.2 ± 1.9%) muscles. In contrast, the capillary to fibre ratio was significantly increased (2.01 ± 0.12 vs. 1.55 ± 0.04, P < 0.01). We conclude that capillary supply can be increased independently of oxidative capacity, possibly due to haemodynamic factors, and serves metabolite removal to a greater extent than substrate delivery. [source] Novel Polymer Electrolyte Membranes for Automotive Applications , Requirements and Benefits,FUEL CELLS, Issue 4 2004C. Wieser Abstract During the past few years, the feasibility of using polymer electrolyte fuel cells in automotive power trains at an impressive performance level has been proven repeatedly. However, current fuel cell stacks are still largely based on decade-old polymer electrolyte membrane technology thus limiting performance, durability, reliability, and cost of the fuel cell systems. The major challenge for membrane R&D constitutes the demand for polymer electrolytes that allow for system operation at higher temperatures and lower water management requirements without increased conduction losses. None the less, demanding automotive requirements will not compromise on other properties such as mechanical and chemical stability and gas permeability. [source] Naturalistic stimulus trains evoke reproducible subicular responses both within and between animals in vivoHIPPOCAMPUS, Issue 2 2010Beth Tunstall Abstract Previous investigation of CA1-evoked subicular responses has used either single low-frequency pulses (LF), paired-pulses (PP), or high-frequency bursts. Here we test for the first time how subiculum responds to naturalistic stimulation trains (NSTs). We recorded CA1-evoked field potentials from dorsal rat subiculum in response to LF, PP, and two NST patterns. The latter were derived from CA1 place cell activity; NST1 contained bursts of stimuli presented in two main episodes, while the burst-patterned stimuli in NST2 were spaced more evenly. NSTs generated significantly greater field responses compared with LF or PP patterns. Response patterns to either NST were significantly correlated across trial repeats in 9 out of 10 rats, supporting a robust postsynaptic encoding of CA1 input by subiculum. Correlations between NST responses were also observed across experiments; however, these were more variable than those within experiments. The relationship between response magnitude and activation history revealed a strong correlation between magnitude and NST instantaneous frequency for NST1 but was weaker for NST2. In addition, the number of stimuli within a prior 500 ms window was a determining factor for response magnitude for both NSTs. Overall, the robust reproducibility in subicular responses within rats suggests that information within NSTs is faithfully transmitted through the CA1-subiculum axis. However, variation in response sequences across rats suggests that encoding patterns to the same input differ across the subiculum. Changes in the ratio of target bursting and regularly spiking neurons along the subicular proximodistal axis may account for this variation. The activation history of this connection also appears to be a strong determining factor for response magnitude. © 2009 Wiley-Liss, Inc. [source] Primary and multisensory cortical activity is correlated with audiovisual perceptsHUMAN BRAIN MAPPING, Issue 4 2010Margo McKenna Benoit Abstract Incongruent auditory and visual stimuli can elicit audiovisual illusions such as the McGurk effect where visual /ka/ and auditory /pa/ fuse into another percept such as/ta/. In the present study, human brain activity was measured with adaptation functional magnetic resonance imaging to investigate which brain areas support such audiovisual illusions. Subjects viewed trains of four movies beginning with three congruent /pa/ stimuli to induce adaptation. The fourth stimulus could be (i) another congruent /pa/, (ii) a congruent /ka/, (iii) an incongruent stimulus that evokes the McGurk effect in susceptible individuals (lips /ka/ voice /pa/), or (iv) the converse combination that does not cause the McGurk effect (lips /pa/ voice/ ka/). This paradigm was predicted to show increased release from adaptation (i.e. stronger brain activation) when the fourth movie and the related percept was increasingly different from the three previous movies. A stimulus change in either the auditory or the visual stimulus from /pa/ to /ka/ (iii, iv) produced within-modality and cross-modal responses in primary auditory and visual areas. A greater release from adaptation was observed for incongruent non-McGurk (iv) compared to incongruent McGurk (iii) trials. A network including the primary auditory and visual cortices, nonprimary auditory cortex, and several multisensory areas (superior temporal sulcus, intraparietal sulcus, insula, and pre-central cortex) showed a correlation between perceiving the McGurk effect and the fMRI signal, suggesting that these areas support the audiovisual illusion. Hum Brain Mapp, 2010. © 2009 Wiley-Liss, Inc. [source] Cultural differences in conceptual models of ride comfort for high-speed trainsHUMAN FACTORS AND ERGONOMICS IN MANUFACTURING & SERVICE INDUSTRIES, Issue 2 2009Joo Hwan Lee This study focuses on an analysis of the difference in cultural experiences for similar services through analyzing the difference in conceptual models of ride comfort for passengers of KTX (Korea Train eXpress) and TGV (Train a Grand Vitesse). These trains operate with identical platforms; KTX was introduced by K-TGV (Korea-TGV) based on TGV (French high-speed train). For the conceptual models of ride comfort, this study surveyed 200 KTX passengers on the Seoul--Busan line (duration: 2 hours 30 minutes) and surveyed 150 France TGV passengers on the Paris--Marseilles line (duration: 2 hours 40 minutes). The conceptual models of ride comfort were analyzed using structural equation modeling (SEM). In the results of the study, though there were differences in cultural environment (e.g., physical environment, body size, etc.) and cultural mentality (e.g., preference, unconscious rule, etc.), the models of ride comfort for both countries shared similar critical factors. However, there were significant differences in loading values of ride comfort for these critical factors. In particular, there were differences of 1.5 to 2 times between the two models regarding the subfactors seat factor and human fatigue factor. In conclusion, this study elicits that experience factor is the most influential on ride comfort, and cultural factors are applied as essential variables in ride comfort improvement. © 2009 Wiley Periodicals, Inc. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||