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Action Potential Frequency (action + potential_frequency)
Selected AbstractsEnhanced synaptic excitation,inhibition ratio in hippocampal interneurons of rats with temporal lobe epilepsyEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2007F. Stief Abstract A common feature of all epileptic syndromes is the repetitive occurrence of pathological patterns of synchronous neuronal activity, usually combined with increased neuronal discharge rates. Inhibitory interneurons of the hippocampal formation control both neuronal synchronization as well as the global level of activity and are therefore of crucial importance for epilepsy. Recent evidence suggests that changes in synaptic inhibition during temporal lobe epilepsy are rather specific, resulting from selective death or alteration of interneurons in specific hippocampal layers. Hence, epilepsy-induced changes have to be analysed separately for different types of interneurons. Here, we focused on GABAergic neurons located at the border between stratum radiatum and stratum lacunosum-moleculare of hippocampal area CA1 (SRL interneurons), which are included in feedforward inhibitory circuits. In chronically epileptic rats at 6,8 months after pilocarpine-induced status epilepticus, frequencies of spontaneous and miniature inhibitory postsynaptic currents were reduced, yielding an almost three-fold increase in excitation,inhibition ratio. Consistently, action potential frequency of SRL interneurons was about two-fold enhanced. Morphological alterations of the interneurons indicate that these functional changes were accompanied by remodelling of the local network, probably resulting in a loss of functional inhibitory synapses without conceivable cell death. Our data indicate a strong increase in activity of interneurons in dendritic layers of the chronically epileptic CA1 region. This alteration may enhance feedforward inhibition and rhythmogenesis and , together with specific changes in other interneurons , contribute to seizure susceptibility and pathological synchronization. [source] Developmental expression of Na+ currents in mouse Purkinje neuronsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2006Mark Fry Abstract As Purkinje neurons mature during postnatal development, they change from electrically quiescent to active and exhibit high frequency spontaneous action potentials. This change in electrical activity is determined by both alteration in ion channel expression and the acquisition of synaptic input. To gain a better understanding of the development the intrinsic electrical properties of these neurons, acutely isolated Purkinje neurons from mice aged postnatal day 4 (P4) to P18 were examined. This included recording action potential frequency, threshold, height and slope, and input resistance and capacitance. Changes in a number of these properties were observed, suggesting significant changes in voltage-gated Na+ currents. Because voltage-gated Na+ currents, including the transient, resurgent and persistent currents, are known to play important roles in generating spontaneous action potentials, the developmental changes in these currents were examined. A large increase in the density of transient current, resurgent current and persistent current was observed at times corresponding with changes in action potential properties. Interestingly, the developmental up-regulation of the persistent current and resurgent current occurred at rate which was faster than the up-regulation of the transient current. Moreover, the relative amplitudes of the persistent and resurgent currents increased in parallel, suggesting that they share a common basis. The data indicate that developmental up-regulation of Na+ currents plays a key role in the acquisition of Purkinje neuron excitability. [source] Hyperpolarization-activated cyclic nucleotide-modulated ,HCN' channels confer regular and faster rhythmicity to beating mouse embryonic stem cellsTHE JOURNAL OF PHYSIOLOGY, Issue 3 2008Yang Qu The hyperpolarization-activated cation current (If), and the hyperpolarization-activated cyclic nucleotide-modulated ,HCN' subunits that underlie it, are important components of spontaneous activity in the embryonic mouse heart, but whether they contribute to this activity in mouse embryonic stem cell-derived cardiomyocytes has not been investigated. We address this issue in spontaneously beating cells derived from mouse embryonic stem cells (mESCs) over the course of development in culture. If and action potentials were recorded from single beating cells at early, intermediate and late development stages using perforated whole-cell voltage- and current-clamp techniques. Our data show that the proportion of cells expressing If, and the density of If in these cells, increased during development and correlated with action potential frequency and the rate of diastolic depolarization. The If blocker ZD7288 (0.3 ,m) reduced If and the beating rate of embryoid bodies. Taken together, the activation kinetics of If and results from Western blots are consistent with the presence of the HCN2 and HCN3 isoforms. At all stages of development, isoproterenol (isoprenaline) and acetylcholine shifted the voltage dependence of If to more positive and negative voltages, respectively, and they also increased and decreased the beating rate of embryonic cell bodies, respectively. Together, the data suggest that current through HCN2 and HCN3 channels confers regular and faster rhythmicity to mESCs, which mirrors the developing embryonic mouse heart, and contributes to modulation of rhythmicity by autonomic stimulation. [source] Response properties of isolated mouse olfactory receptor cellsTHE JOURNAL OF PHYSIOLOGY, Issue 1 2001Johannes Reisert 1Response properties of isolated mouse olfactory receptor cells were investigated using the suction pipette technique. Cells were exposed to the odour cineole or to solutions of modified ionic content by rapidly changing the solution superfusing the cilia. All experiments were performed at 37°C. 2Mouse olfactory receptor cells displayed a steep dependence of action potential frequency on stimulus concentration, a 3-fold increase in stimulus concentration often saturating the firing frequency at 200-300 Hz. The receptor current increased more gradually with increasing cineole concentration and did not saturate within the 100-fold range of cineole concentrations applied. 3When stimulated for 30 s with a low odour concentration, cells responded with sporadic spike firing. Higher concentrations led to the generation of a large receptor current at the onset of stimulation which returned to baseline levels within a few seconds, accompanied during its rising phase by a short burst of action potentials. Thereafter an oscillating response pattern was observed during the remainder of the stimulus, consisting of repetitive increases in receptor current of around 1 s duration accompanied by short bursts of action potentials. 4Olfactory adaptation was studied by comparing the responses to two closely spaced odour stimuli. The response to the second odour stimulus recovered to 80% of its original magnitude when the cell was superfused with Ringer solution during the 5 s interval between odour exposures. In contrast, exposure to a choline-substituted low Na+ solution between odour stimuli had two effects. First, the receptor current response to the first odour stimulus did not terminate as quickly as in the presence of Na+, suggesting the presence of a Na+ -Ca2+ exchanger. Second, the response to the second stimulus only recovered to 55% of its original magnitude, demonstrating the involvement of Na+ -Ca2+ exchange in the recovery of sensitivity in mouse olfactory receptor cells following stimulation. [source] | ||||||||||