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Selected AbstractsGenetic manipulation, whole-cell recordings and functional imaging of the sensorimotor cortex of behaving miceACTA PHYSIOLOGICA, Issue 1 2009C. C. H. Petersen Abstract Sensory processing, sensorimotor integration and motor control are amongst the most basic functions of the brain and yet our understanding of how the underlying neuronal networks operate and contribute to behaviour is very limited. The relative simplicity of the mouse whisker sensorimotor system is helpful for detailed quantitative analyses of motor control and perception during active sensory processing. Recent technical advances now allow the measurement of membrane potential in awake-behaving mice, using whole-cell recordings and voltage-sensitive dye imaging. With these recording techniques, it is possible to directly correlate neuronal activity with behaviour. However, in order to obtain causal evidence for the specific contributions of different neuronal networks to behaviour, it is critical to manipulate the system in a highly controlled manner. Advances in molecular neurobiology, gene delivery and mouse genetics provide techniques capable of layer, column and cell-type specific control of gene expression in the mouse neocortex. Over the next years, we anticipate considerable advances in our understanding of brain function through measuring and manipulating neuronal activity with unprecedented precision to probe the molecular and synaptic mechanisms underlying simple forms of active sensory perception and associative learning. [source] Electrical and Chemical Long-term Depression Do Not Attenuate Low-Mg2+,induced Epileptiform Activity in the Entorhinal CortexEPILEPSIA, Issue 4 2005Jörg Solger Summary:,Purpose: Low-frequency electrical and magnetic stimulation of cortical brain regions has been shown to reduce cortical excitability and to decrease the susceptibility to seizures in humans and in vivo models of epilepsy. The induction of long-term depression (LTD) or depotentiation of a seizure-related long-term potentiation has been proposed to be part of the underlying mechanism. With the low-Mg2+ -model of epilepsy, this study investigated the effect of electrical LTD, chemical LTD, and depotentiation on the susceptibility of the entorhinal cortex to epileptiform activity. Methods: The experiments were performed on isolated entorhinal cortex slices obtained from adult Wistar rats and mice. With extracellular recording techniques, we studied whether LTD induced by (a) three episodes of low-frequency paired-pulse stimulation (3 × 900 paired pulses at 1 Hz), and by (b) bath-applied N -methyl- d -aspartate (NMDA, 20 ,M) changes time-to-onset, duration, and frequency of seizure-like events (SLEs) induced by omitting MgSO4 from the artificial cerebrospinal fluid. Next we investigated the consequences of depotentiation on SLEs themselves by applying low-frequency stimulation after onset of low-Mg2+,induced epileptiform activity. Results: LTD, induced either by low-frequency stimulation or by bath-applied NMDA, had no effect on time-to-onset, duration, and frequency of SLEs compared with unconditioned slices. Low-frequency stimulation after onset of SLEs did not suppress but induced SLEs that lasted for the time of stimulation and were associated with a simultaneous increase of the extracellular K+ concentration. Conclusions: Our study demonstrates that neither conditioning LTD nor brief low-frequency stimulation decreases the susceptibility of the entorhinal cortex to low-Mg2+,induced epileptiform activity. The present study does not support the hypothesis that low-frequency brain stimulation exerts its anticonvulsant effect via the induction of LTD or depotentiation. [source] Voltage-Dependent Block of N -Methyl- d -Aspartate Receptors by the Novel Anticonvulsant Dibenzylamine, a Bioactive Constituent of l -(+)-,-HydroxybutyrateEPILEPSIA, Issue 10 2003Sean D. Donevan Summary:,Purpose: Previously we demonstrated that l -(+)-,-hydroxybutyrate (L-BHB), acetoacetate (ACA), acetone, and dibenzylamine (DBA) were anticonvulsant in an audiogenic seizure,susceptible model, and that DBA was a bioactive contaminant identified in commercial lots of L-BHB. In the present study, we asked whether these effects could be mediated by ionotropic glutamate or ,-aminobutyric acidA (GABAA) receptors. Methods: We studied the effects of both stereoisomers of BHB (as well as the racemate), ACA, and DBA on N -methyl- d -aspartate (NMDA), ,-amino-3-hydroxy-5methyl-4-isoxazole-proprionic acid (AMPA), and GABAA receptors in cultured rodent neocortical neurons by using whole-cell voltage-clamp recording techniques. Results: Only L-BHB and DBA exerted a concentration- and voltage-dependent block of NMDA-evoked currents, whereas none of the tested substrates affected AMPA- or GABA-activated currents. The kinetics of whole-cell block by L-BHB and DBA were similar, providing additional evidence that DBA is responsible for the anticonvulsant activity of L-BHB. Conclusions: BHB and ACA do not exert direct actions on GABAA or ionotropic glutamate receptors in cultured neocortical neurons. In addition, we provide additional evidence that DBA is responsible for the anticonvulsant activity of L-BHB, and that this action may be mediated in part by voltage-dependent blockade of NMDA receptors. [source] Fenfluramine Blocks Low-Mg2+ -Induced Epileptiform Activity in Rat Entorhinal CortexEPILEPSIA, Issue 8 2000K. Gentsch Summary: Purpose: The entorhinal cortex (EC) represents the main input structure to the hippocampus and seems to be critically involved in temporal lobe epilepsy. Considering that the EC receives a strong serotonergic projection from the raphe nuclei and expresses a high density of serotonin (5-HT) receptors, the effect of the 5-HT,releasing drug fenfluramine (FFA) on epileptiform activity generated in the EC was investigated in an in vitro model of epilepsy. Methods: The experiments were performed on 43 horizontal slices containing the EC, the subiculum, and the hippocampal formation obtained from 230,250 g adult Wistar rats. Using extracellular recording techniques, we investigated the effect of bath-applied FFA (200 ,mol/L to 1 mmol/L) on epileptiform activity induced by omitting MgSO4 from the artificial cerebrospinal fluid. Results: We demonstrate that FFA reversibly blocks epileptiform activity in the EC. Surprisingly, in the presence of the 5-HT uptake blocker paroxetine, the FFA-induced effect was diminished. Coapplication of the 5-HTIA receptor antagonist WAY 100635 prevented the FFA-induced anticonvulsive effect, suggesting that (a) the FFA-induced suppression of epileptiform activity is mediated by the release of 5-HT from synaptic terminals within the EC rather than by an unspecific effect of FFA and (b) released 5-HT most likely blocks the activity by activation of 5-HTIA receptors. Conclusion: FFA, which is primarily used because of its anorectic activity, might get an additional therapeutic value in the treatment of temporal lobe epilepsy with parahippocampal involvement. [source] Electrophysiological sensory demyelination in typical chronic inflammatory demyelinating polyneuropathyEUROPEAN JOURNAL OF NEUROLOGY, Issue 7 2010Y. A. Rajabally Background:, The presence of electrophysiological demyelination of sensory nerves is not routinely assessed in the evaluation of suspected chronic inflammatory demyelinating polyneuropathy (CIDP). Whether this can be useful is unknown. Methods:, We compared, using surface recording techniques, in 19 patients with typical CIDP and 26 controls with distal large fibre sensory axonal neuropathy, the forearm median sensory conductions, sensory nerve action potential (SNAP) amplitudes and durations and sensory nerve conduction velocities (SNCVs) of median, radial and sural nerves. Results:, Median nerve sensory conduction block (SCB) across the forearm was greater in CIDP patients than in controls (P = 0.005). SNAP durations were longer in CIDP patients for median (P = 0.001) and sural nerves (P = 0.004). Receiver operating characteristic (ROC) curves provided sensitive (>40%) and specific (>95%) cut-offs for median nerve SCB as well as median and sural SNAP durations. SNCVs were significantly slower for median and sural nerves in CIDP patients, but ROC curves did not demonstrate cut-offs with useful sensitivities/specificities. Median SCB or prolonged median SNAP duration or prolonged sural SNAP duration offered a sensitivity of 73.7% for CIDP and specificity of 96.2%. Used as additional parameters, they improved diagnostic sensitivity of the American Academy of Neurology (AAN) criteria for CIDP of 1991, from 42.1% to 78.9% in this population, with preserved specificity of 100%. Discussion:, Sensory electrophysiological demyelination is present and may be diagnostically useful in typical CIDP. SCB detection and SNAP duration prolongation appear to represent more useful markers of demyelination than SNCV reduction. [source] Excitatory actions of substance P in the rat lateral posterior nucleusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2010Kush Paul Abstract The lateral posterior nucleus (LP) receives inputs from both neocortex and superior colliculus (SC), and is involved with integration and processing of higher-level visual information. Relay neurons in LP contain tachykinin receptors and are innervated by substance P (SP)-containing SC neurons and by layer V neurons of the visual cortex. In this study, we investigated the actions of SP on LP relay neurons using whole-cell recording techniques. SP produced a graded depolarizing response in LP neurons along the rostro-caudal extent of the lateral subdivision of LP nuclei (LPl), with a significantly larger response in rostral LPl neurons compared with caudal LPl neurons. In rostral LPl, SP (5,2000 nm) depolarized nearly all relay neurons tested (> 98%) in a concentration-dependent manner. Voltage-clamp experiments revealed that SP produced an inward current associated with a decreased conductance. The inward current was mediated primarily by neurokinin receptor (NK)1 tachykinin receptors, although significantly smaller inward currents were produced by specific NK2 and NK3 receptor agonists. The selective NK1 receptor antagonist RP67580 attenuated the SP-mediated response by 71.5% and was significantly larger than the attenuation of the SP response obtained by NK2 and NK3 receptor antagonists, GR159897 and SB222200, respectively. The SP-mediated response showed voltage characteristics consistent with a K+ conductance, and was attenuated by Cs+, a K+ channel blocker. Our data suggest that SP may modulate visual information that is being processed and integrated in the LPl with inputs from collicular sources. [source] Muscarine activates the sodium,calcium exchanger via M3 receptors in basal forebrain neuronsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2006Changqing Xu Abstract Neurons of the medial septum/diagonal band of Broca (MSDB) project to the hippocampus. Muscarinic cholinergic mechanisms within the MSDB are potent modulators of hippocampal functions; intraseptal scopolamine disrupts and intraseptal carbachol facilitates hippocampus-dependent learning and memory tasks, and the associated hippocampal theta rhythm. In earlier work, we demonstrated that, within the MSDB, the septohippocampal GABAergic but not cholinergic neurons are the primary target of muscarinic manipulations and that muscarinic activation of septohippocampal GABAergic neurons is mediated directly via M3 receptors. In the present study, we examined the ionic mechanism(s) underlying the excitatory actions of muscarine in these neurons. Using whole-cell patch-clamp recording techniques in rat brain slices, we demonstrated that M3 receptor-mediated muscarinic activation of MSDB neurons is dependent on external Na+ and is also reduced by bath-applied Ni2+ and KB-R7943 as well as by replacing external Na+ with Li+, suggesting a primary involvement of the Na+,Ca2+ exchanger. We conclude that the M3 receptor-mediated muscarinic activation of MSDB septohippocampal GABA-type neurons, that is important for cognitive functioning, is mediated via activation of the Na+,Ca2+ exchanger. [source] NMDA receptors are essential for the acquisition, but not expression, of conditional fear and associative spike firing in the lateral amygdalaEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2004Ki A. Goosens Abstract We examined the contribution of N -methyl- D -aspartate (NMDA) receptors (NMDARs) to the acquisition and expression of amygdaloid plasticity and Pavlovian fear conditioning using single-unit recording techniques in behaving rats. We demonstrate that NMDARs are essential for the acquisition of both behavioral and neuronal correlates of conditional fear, but play a comparatively limited role in their expression. Administration of the competitive NMDAR antagonist ±-3-(2-carboxypiperazin-4-yl) propyl-1-phosphonic acid (CPP) prior to auditory fear conditioning completely abolished the acquisition of conditional freezing and conditional single-unit activity in the lateral amygdala (LA). In contrast, CPP given prior to extinction testing did not affect the expression of conditional single-unit activity in LA, despite producing deficits in conditional freezing. Administration of CPP also blocked the induction of long-term potentiation in the amygdala. Together, these data suggest that NMDARs are essential for the acquisition of conditioning-related plasticity in the amygdala, and that NMDARs are more critical for regulating synaptic plasticity and learning than routine synaptic transmission in the circuitry supporting fear conditioning. [source] Synaptic and non-synaptic mechanisms of amygdala recruitment into temporolimbic epileptiform activitiesEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2003Julia Klueva Abstract Lateral amygdala (LA) activity during synchronized-epileptiform discharges in temporolimbic circuits was investigated in rat horizontal slices containing the amygdala, hippocampus (Hip), perirhinal (Prh) and lateral entorhinal (LEnt) cortex, through multiple-site extra- and intracellular recording techniques and measurement of the extracellular K+ concentration. Application of 4-aminopyridine (50 µm) induced epileptiform discharges in all regions under study. Slow interictal-like burst discharges persisted in the Prh/LEnt/LA after disconnection of the Hip, seemed to originate in the Prh as shown from time delay analyses, and often preceded the onset of ictal-like activity. Disconnection of the amygdala resulted in de-synchronization of epileptiform discharges in the LA from those in the Prh/LEnt. Interictal-like activity was intracellularly reflected in LA projection neurons as ,-aminobutyric acid (GABA)A/B receptor-mediated synaptic responses, and depolarizing electrogenic events (spikelets) residing on the initial phase of the GABA response. Spikelets were considered antidromically conducted ectopic action potentials generated at axon terminals, as they were graded in amplitude, were not abolished through hyperpolarizing membrane responses (which effectively blocked evoked orthodromic action potentials), lacked a clear prepotential or synaptic potential, were not affected through blockers of gap junctions, and were blocked through remote application of tetrodotoxin at putative target areas of LA projection neurons. Remote application of a GABAB receptor antagonist facilitated spikelet generation. A transient elevation in the extracellular K+ level averaging 3 mm above baseline occurred in conjunction with interictal-like activity in all areas under study. We conclude that interictal-like discharges in the LA/LEnt/Prh spread in a predictable manner through the synaptic network with the Prh playing a leading role. The rise in extracellular K+ may provide a depolarizing mechanism for recruitment of interneurons and generation of ectopic action potentials at axon terminals of LA projection neurons. Antidromically conducted ectopic action potentials may provide a spreading mechanism of seizure activity mediated by diffuse axonal projections of LA neurons. [source] NMDA receptor-mediated metaplasticity during the induction of long-term depression by low-frequency stimulationEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2002Bruce Mockett Abstract Metaplasticity refers to the activity-dependent modification of the ability of synapses to undergo subsequent synaptic plasticity. Here, we have addressed the question of whether metaplasticity contributes to the induction of long-term depression (LTD) by low-frequency stimulation (LFS). The experiments were conducted using standard extracellular recording techniques in stratum radiatum of area CA1 in hippocampal slices made from adult Sprague,Dawley rats. The degree of LTD induction was found to be a nonlinear function of the number of pulses during a 1-Hz LFS. Little LTD was observed following 600 or 900 pulses, but a significant LTD occurred following 1200 pulses of LFS, whether delivered in one episode, or in two bouts of 600 pulses given 10 min apart. A similar pattern was observed for 3 Hz LFS. The data support the suggestion that pulses occurring early in the LFS train prime synapses for LTD induction, as triggered by later occurring stimuli. The priming effect lasted at least 120 min, when tested by giving two bouts of 1 Hz LFS (600 pulses each) at different intervals. Neither heterosynaptic nor homosynaptic stimulation by itself was sufficient to prime LTD. However, a combination of the stimuli, induced by increased stimulus strength during the LFS, appeared necessary for inducing the effect. An N -methyl- d -aspartate (NMDA) receptor antagonist markedly reduced total LTD induction, regardless of whether it was administered during the first or second LFS in a protocol employing two bouts of 600 pulse LFS, 30 min apart. These findings strongly support the hypothesis that NMDA receptor-dependent metaplasticity processes contribute to the induction of LTD during standard LFS protocols. [source] The action of high K+ and aglycaemia on the electrical properties and synaptic transmission in rat intracardiac ganglion neurones in vitroEXPERIMENTAL PHYSIOLOGY, Issue 2 2009Jhansi Dyavanapalli We have investigated the action of two elements of acute ischaemia, high potassium and aglycaemia, on the electrophysiological properties and ganglionic transmission of adult rat intracardiac ganglion (ICG) neurones. We used a whole-mount ganglion preparation of the right atrial ganglion plexus and sharp microelectrode recording techniques. Increasing extracellular K+ from its normal value of 4.7 mm to 10 mm decreased membrane potential and action potential after-hyperpolarization amplitude but otherwise had no effect on postganglionic membrane properties. It did, however, reduce the ability of synaptically evoked action potentials to follow high-frequency (100 Hz) repetitive stimulation. A further increase in K+ changed both the passive and the active membrane properties of the postganglionic neurone: time constant, membrane resistance and action potential overshoot were all decreased in high K+ (20 mm). The ICG neurones display a predominantly phasic discharge in response to prolonged depolarizing current pulses. High K+ had no impact on this behaviour but reduced the time-dependent rectification response to hyperpolarizing currents. At 20 mm, K+ practically blocked ganglionic transmission in most neurones at all frequencies tested. Aglycaemia, nominally glucose-free physiological saline solution (PSS), increased the time constant and membrane resistance of ICG neurones but otherwise had no action on their passive or active properties or ganglionic transmission. However, the combination of aglycaemia and 20 mm K+ displayed an improvement in passive properties and ganglionic transmission when compared with 20 mm K+ PSS. These data indicate that the presynaptic terminal is the primary target of high extracellular potassium and that aglycaemia may have protective actions against this challenge. [source] Block of IKs Does Not Induce Early Afterdepolarization Activity but Promotes ,-Adrenergic Agonist-Induced Delayed Afterdepolarization ActivityJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 4 2000ALEXANDER BURASHNTKOV Ph.D. Block of IK Does Not Induce EADs.Introduction: An early afterdepolarization (EAD)-induced triggered heat is thought to precipitate torsade de pointes (TdP) in the long QT syndrome (LQTS). Previous studies demonstrated the development of EAD activity and dispersion of repolarization under LQT2 (reduced IKr) and LQT3 (augmented late INa). but not LQTl (reduced IKs), conditions. The present study examines these electrophysiologic characteristics during IKs block. Methods and Results: Canine epicardial (Epi), M, and endocardial (Endo) tissues and Purkinje fibers isolated from the canine left ventricle were studied using standard microelectrode recording techniques. The IKs blocker chromanol 293B (293B, 30 ,M), produced a homogeneous rate-independent prolongation of action potential duration (APD) in Epi, M, and Endo, but little to no APD prolongation in Purkinje. Chromanol 293B I to 30 ,M failed to induce EADs or delayed afterdepolarizations (DADs) in any of the four tissue types. Isoproterenol (ISO, 0.1 to 1.0 ,M) in the presence of 293B 30 ,M significantly prolonged the APD of the M cell (basic cycle length , sec), abbreviated that of Purkinje, and caused little change in that of Epi and Endo. The combination of 293B 30 ,M and ISO 0.2 ,M did not induce EADs in any of the four tissue types, but produced DAD activity in 4 of 8 Epi, 7 of 10 M cells, and 3 of 8 Endo. Conclusion: Our results indicate that IKs block alone or in combination with ,-adrenergic stimulation does not induce EADs in any of the four canine ventricular tissue types, but that the combination of the two induces DADs as well as accentuated dispersion of repolarization. [source] 1-Methyl-4-phenylpridinium (MPP+)-induced functional run-down of GABAA receptor-mediated currents in acutely dissociated dopaminergic neuronsJOURNAL OF NEUROCHEMISTRY, Issue 1 2002Jie Wu Abstract We have evaluated GABAA receptor function during treatment of 1-methyl-4-phenylpridinium (MPP+) using patch-clamp perforated whole-cell recording techniques in acutely dissociated dopaminergic (DAergic) neurons from rat substantia nigra compacta (SNc). ,-Aminobutyric acid (GABA), glutamate or glycine induced inward currents (IGABA, IGlu, IGly) at a holding potential (VH) of ,45 mV. The IGABA was reversibly blocked by the GABAA receptor antagonist, bicuculline, suggesting that IGABA is mediated through the activation of GABAA receptors. During extracellular perfusion of MPP+ (1,10 ,m), IGABA, but neither IGlu nor IGly, declined (termed run-down) with repetitive agonist applications, indicating that the MPP+ -induced IGABA run-down occurred earlier than IGly or IGlu under our experimental conditions. The MPP+ -induced IGABA run-down can be prevented by a DA transporter inhibitor, mazindol, and can be mimicked by a metabolic inhibitor, rotenone. Using conventional whole-cell recording with different concentrations of ATP in the pipette solution, IGABA run-down can be induced by decreasing intracellular ATP concentrations, or prevented by supplying intracellular ATP, indicating that IGABA run-down is dependent on intracellular ATP concentrations. A GABAA receptor positive modulator, pentobarbital (PB), potentiated the declined IGABA and eliminated IGABA run-down. Corresponding to these patch-clamp data, tyrosine hydroxylase (TH) immunohistochemical staining showed that TH-positive cell loss was protected by PB during MPP+ perfusion. It is concluded that extracellular perfusion of MPP+ induces a functional run-down of GABAA receptors, which may cause an imbalance of excitation and inhibition of DAergic neurons. [source] Ethanol Acutely Inhibits Ionotropic Glutamate Receptor-Mediated Responses and Long-Term Potentiation in the Developing CA1 HippocampusALCOHOLISM, Issue 4 2010Michael P. Puglia Background:, Developmental ethanol (EtOH) exposure damages the hippocampus, causing long-lasting alterations in learning and memory. Alterations in glutamatergic synaptic transmission and plasticity may play a role in the mechanism of action of EtOH. This signaling is fundamental for synaptogenesis, which occurs during the third trimester of human pregnancy (first 12 days of life in rats). Methods:, Acute coronal brain slices were prepared from 7- to 9-day-old rats. Extracellular and patch-clamp electrophysiological recording techniques were used to characterize the acute effects of EtOH on ,-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptor (AMPAR)- and N -methyl- d -aspartate receptor (NMDAR)-mediated responses and long-term potentiation (LTP) in the CA1 hippocampal region. Results:, Ethanol (40 and 80 mM) inhibited AMPAR- and NMDAR-mediated field excitatory postsynaptic potentials (fEPSPs). EtOH (80 mM) also reduced AMPAR-mediated fEPSPs in the presence of an inhibitor of Ca2+ permeable AMPARs. The effect of 80 mM EtOH on NMDAR-mediated fEPSPs was significantly greater in the presence of Mg2+. EtOH (80 mM) neither affected the paired-pulse ratio of AMPAR-mediated fEPSPs nor the presynaptic volley. The paired-pulse ratio of AMPAR-mediated excitatory postsynaptic currents was not affected either, and the amplitude of these currents was inhibited to a lesser extent than that of fEPSPs. EtOH (80 mM) inhibited LTP of AMPAR-mediated fEPSPs. Conclusions:, Acute EtOH exposure during the third-trimester equivalent of human pregnancy inhibits hippocampal glutamatergic transmission and LTP induction, which could alter synapse refinement and ultimately contribute to the pathophysiology of fetal alcohol spectrum disorder. [source] Assessment of middle ear disease in the dog: a comparison of diagnostic imaging modalitiesJOURNAL OF SMALL ANIMAL PRACTICE, Issue 4 2007R. Doust Objectives: To compare radiography and ultrasound for the assessment of the tympanic bulla against computed tomography results. Methods: Thirty-one dogs had dorsoventral, left and right lateral oblique and rostrocaudal open mouth radiographs compared with ultrasound images and computed tomography scans of the tympanic bullae. Results: Radiography was superior to ultrasonography for the evaluation of the middle ear. However, computed tomography assessment was best predicted by a combination of radiographic and ultrasonographic findings. Clinical Significance: A combination of radiography and ultrasound can provide a more accurate assessment of the bulla than either of them alone. Ultrasound may have a role in the evaluation of middle ear disease in the dog. Results are operator dependent and not reproducible with current recording techniques. [source] Validation of 2 Techniques for Electrocardiographic Recording in Dogs and CatsJOURNAL OF VETERINARY INTERNAL MEDICINE, Issue 4 2006Luca Ferasin Background: Standard electrocardiographic (ECG) recording in the dog and cat is commonly performed in right lateral recumbency, by connecting the ECG leads to the skin of the patient via metallic alligator clips. The jaws of the alligator clips are usually filed or flattened to reduce their uncomfortable pressure on the patient's skin. However, filed and flattened alligator clips can occasionally lose their grip to the skin, causing lead detachment during standard ECG recording. Hypothesis: The aim of the study was to validate two novel ECG recording techniques ("gel" and "pads"). Animals: Six-lead standard ECG recording was obtained from 42 dogs and 40 cats using the standard technique, as well as the two novel methods. Methods: Measurements were taken of the amplitude and duration of P waves and QRS complexes, duration of PQ and QT intervals, and mean electrical axis (MEA). In each recording, five representative complexes were measured, and the results were averaged for each parameter. Results: A good quality ECG recording was obtained with all the three different techniques, although a degree of wandering trace was observed in one third of cats with the "pads" technique. Bland-Altman analysis showed good agreement between the ECG values recorded with the two novel techniques and those recorded with the standard traditional technique. Furthermore, the observed differences were not clinically relevant, except for the R wave amplitude recorded with the "pads" method in cats (-0.35 to 0.37 mV). Conclusions and Clinical Importance: In conclusion, this study supports the reliability and clinical validity of the "gel" and "pads" techniques for ECG recording both in the dog and the cat, with some limitations for the "pads" technique in cats. [source] Anthelmintic paraherquamides are cholinergic antagonists in gastrointestinal nematodes and mammalsJOURNAL OF VETERINARY PHARMACOLOGY & THERAPEUTICS, Issue 4 2002Erich W. Zinser Oxindole alkaloids in the paraherquamide/marcfortine family exhibit broad-spectrum anthelmintic activity that includes drug-resistant strains of nematodes. Paraherquamide (PHQ), 2-deoxoparaherquamide (2DPHQ), and close structural analogs of these compounds rapidly induce flaccid paralysis in parasitic nematodes in vitro, without affecting adenosine triphosphate (ATP) levels. The mechanism of action of this anthelmintic class was investigated using muscle tension and microelectrode recording techniques in isolated body wall segments of Ascaris suum. None of the compounds altered A. suum muscle tension or membrane potential. However, PHQ blocked (when applied before) or reversed (when applied after) depolarizing contractions induced by acetylcholine (ACh) and the nicotinic agonists levamisole and morantel. These effects were mimicked by the nicotinic ganglionic blocker mecamylamine, suggesting that the anthelmintic activity of PHQ and marcfortines is due to blockade of cholinergic neuromuscular transmission. The effects of these compounds were also examined on subtypes of human nicotinic ACh receptors expressed in mammalian cells with a Ca2+ flux assay. 2DPHQ blocked nicotinic stimulation of cells expressing ,3 ganglionic (IC50 , 9 µm) and muscle-type (IC50 , 3 µm) nicotinic cholinergic receptors, but was inactive at 100 µm vs. the ,7 CNS subtype. PHQ anthelmintics are nicotinic cholinergic antagonists in both nematodes and mammals, and this mechanism appears to underlie both their efficacy and toxicity. [source] Plasticity and ambiguity of the electrophysiological phenotypes of enteric neuronsNEUROGASTROENTEROLOGY & MOTILITY, Issue 9 2009K. Nurgali Abstract, Advances in knowledge of enteric neurons electrophysiological characteristics have led to the realisation that the properties of the neurons are dependent on the state of the intestine, the region, the method of recording and the species. Thus, under different experimental conditions, electrophysiological studies cannot provide a reliable signature that identifies the functional type of neuron. In the normal guinea-pig small intestine, taken as a model tissue, neurons can be separated into two electrophysiological groups, S and AH neurons. Combined morphological and physiological studies place several classes of motor and interneurons in the S group, and intrinsic primary afferent neurons in the AH group. There is some evidence for subgroups of S neurons, in which electrophysiological differences are correlated with functional subtypes, but these subgroups have been incompletely investigated. Morphologically characterized Dogiel type II (DII) neurons are recognisable in many species, from mouse to human, but their electrophysiological characteristics are only partly conserved across species or cannot be satisfactorily defined due to technical difficulties. There is a strong need for a comprehensive analysis of channels and currents of S/Dogiel type I neuron subtypes, similar to the comprehensive analysis of AH/DII neurons in the guinea-pig, and similar studies need to be conducted in human and other species. The purpose of this review is to highlight that criteria used for electrophysiological definition of enteric neurons might not be sufficient to distinguish between functional classes of neurons, due to intrinsic properties of neuronal subpopulations, plasticity in pathological conditions and differences in recording techniques. [source] The role of synaptotagmin I C2A calcium-binding domain in synaptic vesicle clustering during synapse formationTHE JOURNAL OF PHYSIOLOGY, Issue 1 2007Peter Gardzinski Synaptic vesicles aggregate at the presynaptic terminal during synapse formation via mechanisms that are poorly understood. Here we have investigated the role of the putative calcium sensor synaptotagmin I in vesicle aggregation during the formation of soma,soma synapses between identified partner cells using a simple in vitro synapse model in the mollusc Lymnaea stagnalis. Immunocytochemistry, optical imaging and electrophysiological recording techniques were used to monitor synapse formation and vesicle localization. Within 6 h, contact between appropriate synaptic partner cells up-regulated global synaptotagmin I expression, and induced a localized aggregation of synaptotagmin I at the contact site. Cell contacts between non-synaptic partner cells did not affect synaptotagmin I expression. Application of an human immunodeficiency virus type-1 transactivator (HIV-1 TAT)-tagged peptide corresponding to loop 3 of the synaptotagmin I C2A domain prevented synaptic vesicle aggregation and synapse formation. By contrast, a TAT-tagged peptide containing the calcium-binding motif of the C2B domain did not affect synaptic vesicle aggregation or synapse formation. Calcium imaging with Fura-2 demonstrated that TAT,C2 peptides did not alter either basal or evoked intracellular calcium levels. These results demonstrate that contact with an appropriate target cell is necessary to initiate synaptic vesicle aggregation during nascent synapse formation and that the initial aggregation of synaptic vesicles is dependent on loop 3 of the C2A domain of synaptotagmin I. [source] Physiological properties of rod photoreceptor electrical coupling in the tiger salamander retinaTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005Jian Zhang Using dual whole-cell voltage and current clamp recording techniques, we investigated the gap junctional conductance and the coupling coefficient between neighbouring rods in live salamander retinal slices. The application of sinusoidal stimuli over a wide range of temporal frequencies allowed us to characterize the band-pass filtering properties of the rod network. We found that the electrical coupling of all neighbouring rods exhibited reciprocal and symmetrical conductivities. On average, the junctional conductance between paired rods was 500 pS and the coupling coefficient (the ratio of voltage responses of the follower cell to those of the driver cell), or K -value, was 0.07. Our experimental results also demonstrated that the rod network behaved like a band-pass filter with a peak frequency of about 2,5 Hz. However, the gap junctions between adjacent rods exhibited linearity and voltage independency within the physiological range of rods. These gap junctions did not contribute to the filtering mechanisms of the rod network. Combined with the computational modelling, our data suggest that the filtering of higher frequency rod signals by the network is largely mediated by the passive resistive and capacitive (RC) properties of rod plasma membranes. Furthermore, we found several attributes of rod electrical coupling resembling the physiological properties of gene-encoded Cx35/36 gap junctions examined in other in vitro studies. This indicates that the previously found Cx35/36 expression in the salamander rod network may be functionally involved in rod,rod electrical coupling. [source] Phorbol esters and adenosine affect the readily releasable neurotransmitter pool by different mechanisms at amphibian motor nerve endingsTHE JOURNAL OF PHYSIOLOGY, Issue 2 2003T. J. Searl Phorbol esters and adenosine have been proposed to interact at common sites downstream of calcium entry at amphibian motor nerve endings. We thus studied the actions and interactions of phorbol esters and adenosine using electrophysiological recording techniques in conjunction with both binomial statistical analysis and high-frequency stimulation at the amphibian neuromuscular junction. To begin this study, we confirmed previous observations that synchronous evoked acetylcholine (ACh) release (reflected as endplate potentials, EPPs) is well described by a simple binomial distribution. We then used binomial analysis to study the effects of the phorbol ester phorbol dibutyrate (PDBu, 100 nm) and adenosine (50 µm) on the binomial parameters n (the number of calcium charged ACh quanta available for release) and p (the average probability of release), where the mean level of evoked ACh release (m) =np. We found that PDBu increased m by increasing the parameter n whilst adenosine reduced m by reducing n; neither agent affected the parameter p. PDBu had no effect on either the potency or efficacy of the inhibition produced by adenosine. Subtle differences between these two agents were revealed by the patterns of EPPs evoked by high-frequency trains of stimuli. Phorbol esters increased ACh release during the early phase of stimulation but not during the subsequent plateau phase. The inhibitory effect of adenosine was maximal at the beginning of the train and was still present with reduced efficacy during the plateau phase. When taken together with previous findings, these present results suggest that phorbol esters increase the immediately available store of synaptic vesicles by increasing the number of primed vesicles whilst adenosine acts at a later stage of the secretory process to decrease the number of calcium-charged primed vesicles. [source] Voltage-activated proton currents in human lymphocytesTHE JOURNAL OF PHYSIOLOGY, Issue 1 2002Tom Schilling Voltage-activated proton currents are reported for the first time in human peripheral blood T and B lymphocytes and in the human leukaemic T cell line Jurkat E6-1. The properties of H+ currents studied using tight-seal voltage-clamp recording techniques were similar in all cells. Changing the pH gradient by one unit caused a 47 mV shift in the reversal potential, demonstrating high selectivity of the channels for protons. H+ current activation upon membrane depolarisation had a sigmoidal time course that could be fitted by a single exponential function after a brief delay. Increasing pHo shifted the activation threshold to more negative potentials, and increased both the H+ current amplitude and the rate of activation. In lymphocytes studied at pHi 6.0, the activation threshold was more negative and the H+ current density was three times larger than at pHi 7.0. Increasing the intracellular Ca2+ concentration to 1 ,m did not change H+ current amplitude or kinetics detectably. Extracellularly applied Zn2+ and Cd2+ inhibited proton currents, slowing activation and shifting the voltage-activation curve to more positive potentials. The H+ current amplitude was 100 times larger in CD19+ B lymphocytes and in Jurkat E6-1 cells than in CD3+ T lymphocytes. Following stimulation with the phorbol ester PMA, the H+ current density in peripheral blood T lymphocytes and Jurkat T cells increased. In contrast, the H+ current density of phorbol ester (PMA)-stimulated B lymphocytes was reduced and activation became slower. The pattern of expression of H+ channels in lymphocytes appears well suited to their proposed role of charge compensation during the respiratory burst. [source] Origin and propagation of spontaneous excitation in smooth muscle of the guinea-pig urinary bladderTHE JOURNAL OF PHYSIOLOGY, Issue 2 2001Hikaru Hashitani 1The origin and propagation of waves of spontaneous excitation in bundles of smooth muscle of the guinea-pig bladder were examined using intracellular recording techniques and visualization of the changes in the intracellular calcium concentration ([Ca2+]i). 2Bladder smooth muscle cells exhibited spontaneous transient increases in [Ca2+]i which originated along a boundary of each smooth muscle bundle and then spread to the other boundary with a conduction velocity of 2.0 mm s,1. 3Spontaneous increases in [Ca2+]i were always preceded by action potentials. Nifedipine (10 ,M) abolished increases in both [Ca2+]i and action potentials. Caffeine (10 mM), ryanodine (50 ,M) and cyclopiazonic acid (10 ,M) reduced the amplitude of the associated increases in [Ca2+]i without preventing the generation of action potentials. 4Spontaneous action potentials had conduction velocities of 40 mm s,1 in the axial direction and 1.3 mm s,1 in the transverse direction. The electrical length constants of the bundles of muscle were 425 ,m in the axial direction and 12.5 ,m in the transverse direction. 5Neurobiotin, injected into an impaled smooth muscle cell, spread more readily to neighbouring cells located in the axial direction than those located in the transverse direction. The spread of neurobiotin was inhibited by 18,-glycyrrhetinic acid (18,-GA, 40 ,M), a gap junction blocker. 6Immunohistochemistry for Connexin 43 showed abundant punctate staining on the smooth muscle cell membranes. 7These results suggested that spontaneous action potentials and associated calcium waves occur almost simultaneously along the boundary of bladder smooth muscle bundles and then propagate to the other boundary probably through gap junctions. [source] Voltage-dependent inhibition of the muscarinic cationic current in guinea-pig ileal cells by SK&F 96365BRITISH JOURNAL OF PHARMACOLOGY, Issue 4 2000A V Zholos The effects of SK&F 96365 on cationic current evoked either by activating muscarinic receptors with carbachol or by intracellularly applied GTP,S (in the absence of carbachol) were studied using patch-clamp recording techniques in single guinea-pig ileal smooth muscle cells. SK&F 96365 reversibly inhibited the muscarinic receptor cationic current in a concentration-, time- and voltage-dependent manner producing concomitant alteration of the steady-state I-V relationship shape which could be explained by assuming that increasing membrane positivity increased the affinity of the blocker. The inhibition was similar for both carbachol- and GTP,S-evoked currents suggesting that the cationic channel rather than the muscarinic receptor was the primary site of the SK&F 96365 action. Increased membrane positivity induced additional rapid inhibition of the cationic current by SK&F 96365 which was more slowly relieved during membrane repolarization. Both the inhibition and disinhibition time course could be well fitted by a single exponential function with the time constants decreasing with increasing positivity for the inhibition (e -fold per about 12 mV) and approximately linearly decreasing with increasing negativity for the disinhibition. At a constant SK&F 96365 concentration, the degree of cationic current inhibition was a sigmoidal function of the membrane potential with a potential of half-maximal increase positive to about +30 mV and a slope factor of about ,13 mV. Increasing the duration of voltage steps at ,80 or at 80 mV, increased the percentage inhibition; the degree of inhibition was almost identical at both potentials providing evidence that the same cationic channel was responsible for the cationic current both at negative and at positive potentials. It is concluded that the distinctive and unique mode of SK&F 96365 action on the muscarinic receptor cationic channel is a valuable tool in future molecular biology studies of this channel. British Journal of Pharmacology (2000) 129, 695,702; doi:10.1038/sj.bjp.0703115 [source] ARE GAP JUNCTIONS TRULY INVOLVED IN INHIBITORY NEUROMUSCULAR INTERACTION IN MOUSE PROXIMAL COLON?CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 8 2006Andrei Sibaev SUMMARY 1Gap junctions exist between circular muscle cells of the colon and between interstitial cells of Cajal (ICC) in the myenteric plexus of the gastrointestinal tract. They also probably couple intramuscular ICC with smooth muscle cells. Recent functional evidence for this was found in dye-coupling and myoelectrical experiments. 2In the present study, we tested the hypothesis of gap junctions putatively being involved in neuromuscular interaction in mouse colon by using different classes of gap junction blockers. 3Electrical field stimulation of the myenteric plexus elicited tetrodotoxin-sensitive and hexamethonium-independent fast and slow inhibitory junction potentials (fIJP and sIJP, respectively) in circular smooth muscle cells, as evaluated by intracellular recording techniques in impaled smooth muscle cells. Heptanol produced a time-dependent hyperpolarization of the membrane potential (MP) and abolished fIJP and sIJP. Octanol had no effect on the MP and abolished fIJP and sIJP. Carbenoxolone produced a time-dependent depolarization of the MP without any effect on fIJP or sIJP. The connexin 43 mimetic gap junction blocker GAP-27 had no effect on MP, fIJP or sIJP. 4Based on the presently available gap junction blockers we found no evidence that gap junctions are involved in neuromuscular transmission in mouse colon, as suggested by morphological studies. [source] | |||||||||||||||||||||||||