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Current Injection (current + injection)
Selected AbstractsXenopus 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] Differential maturation of motoneurons innervating ankle flexor and extensor muscles in the neonatal ratEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2000L Vinay Abstract The first postnatal week is a critical period for the development of posture in the rat. The use of ankle extensor muscles in postural reactions increases during this period. Changes in excitability of motoneurons are probably an important factor underlying this maturation. The aim of this study was to identify whether variations in the maturation exist between motor pools innervating antagonistic muscles. Intracellular recordings in the in vitro brain stem,spinal cord preparation of neonatal rats (from postnatal day 0,5) were used to examine the developmental changes in excitability of motoneurons innervating the ankle flexors (F-MNs) and the antigravity ankle extensors (E-MNs). No significant difference in resting potential, action potential threshold, input resistance or rheobase was observed at birth. The age-related increase in rheobase was more pronounced for F-MNs than for E-MNs. The development of discharge properties of E-MNs lagged behind that of F-MNs. More F-MNs than E-MNs were able to fire repetitively in response to current injection at birth. F-MNs discharged at a higher frequency than E-MNs at all ages. Differences in the duration of action potential afterhyperpolarization accounted, at least partly, for the differences in discharge frequency between E-MNs and F-MNs at birth, and for the age-related increase in firing rate. These results suggest that E-MNs are more immature at birth than F-MNs and that there is a differential development of motoneurons innervating antagonistic muscles. This may be a critical factor in the development of posture and locomotion. [source] The Influence of Film Morphology in High-Mobility Small-Molecule:Polymer Blend Organic TransistorsADVANCED FUNCTIONAL MATERIALS, Issue 14 2010Jeremy Smith Abstract Organic field-effect transistors (OFETs) based upon blends of small molecular semiconductors and polymers show promise for high performance organic electronics applications. Here the charge transport characteristics of high mobility p-channel organic transistors based on 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene:poly(triarylamine) blend films are investigated. By simple alteration of the film processing conditions two distinct film microstructures can be obtained: one characterized by small spherulitic grains (SG) and one by large grains (LG). Charge transport measurements reveal thermally activated hole transport in both SG and LG film microstructures with two distinct temperature regimes. For temperatures >115,K, gate voltage dependent activation energies (EA) in the range of 25,60 meV are derived. At temperatures <115,K, the activation energies are smaller and typically in the range 5,30 meV. For both film microstructures hole transport appears to be dominated by trapping at the grain boundaries. Estimates of the trap densities suggests that LG films with fewer grain boundaries are characterized by a reduced number of traps that are less energetically disordered but deeper in energy than for small SG films. The effects of source and drain electrode treatment with self-assembled monolayers (SAMs) on current injection is also investigated. Fluorinated thiol SAMs were found to alter the work function of gold electrodes by up to ,1,eV leading to a lower contact resistance. However, charge transport analysis suggests that electrode work function is not the only parameter to consider for efficient charge injection. [source] Intraspinally mediated state-dependent enhancement of motoneurone excitability during fictive scratch in the adult decerebrate catTHE JOURNAL OF PHYSIOLOGY, Issue 15 2010Kevin E. Power This is the first study to report on the increase in motoneurone excitability during fictive scratch in adult decerebrate cats. Intracellular recordings from antidromically identified motoneurones revealed a decrease in the voltage threshold for spike initiation (Vth), a suppression of motoneurone afterhyperpolarization and activation of voltage-dependent excitation at the onset of scratch. These state-dependent changes recovered within 10,20 s after scratch and could be evoked after acute transection of the spinal cord at C1. Thus, there is a powerful intraspinal system that can quickly and reversibly re-configure neuronal excitability during spinal network activation. Fictive scratch was evoked in spinal intact and transected decerebrate preparations by stroking the pinnae following topical curare application to the dorsal cervical spinal cord and neuromuscular block. Hyperpolarization of Vth occurred (mean ,5.8 mV) in about 80% of ipsilateral flexor, extensor or bifunctional motoneurones during fictive scratch. The decrease in Vth began before any scratch-evoked motoneurone activity as well as during the initial phase in which extensors are tonically hyperpolarized. The Vth of contralateral extensors depolarized by a mean of +3.7 mV during the tonic contralateral extensor activity accompanying ipsilateral scratch. There was a consistent and substantial reduction of afterhyperpolarization amplitude without large increases in motoneurone conductance in both spinal intact and transected preparations. Depolarizing current injection increased, and hyperpolarization decreased the amplitude of rhythmic scratch drive potentials in acute spinal preparations indicating that the spinal scratch-generating network can activate voltage-dependent conductances in motoneurones. The enhanced excitability in spinal preparations associated with fictive scratch indicates the existence of previously unrecognized, intraspinal mechanisms increasing motoneurone excitability. [source] Intrinsic properties and mechanisms of spontaneous firing in mouse cerebellar unipolar brush cellsTHE JOURNAL OF PHYSIOLOGY, Issue 2 2007Marco J. Russo Neuronal firing patterns are determined by the cell's intrinsic electrical and morphological properties and are regulated by synaptic interactions. While the properties of cerebellar neurons have generally been studied in much detail, little is known about the unipolar brush cells (UBCs), a type of glutamatergic interneuron that is enriched in the granular layer of the mammalian vestibulocerebellum and participates in the representation of head orientation in space. Here we show that UBCs can be distinguished from adjacent granule cells on the basis of differences in membrane capacitance, input resistance and response to hyperpolarizing current injection. We also show that UBCs are intrinsically firing neurons. Using action potential clamp experiments and whole-cell recordings we demonstrate that two currents contribute to this property: a persistent TTX-sensitive sodium current and a ruthenium red-sensitive, TRP-like cationic current, both of which are active during interspike intervals and have reversal potentials positive to threshold. Interestingly, although UBCs are also endowed with a large Ih current, this current is not involved in their intrinsic firing, perhaps because it activates at voltages that are more hyperpolarized than those associated with autonomous activity. [source] Efficient generation of mature cerebellar Purkinje cells from mouse embryonic stem cellsJOURNAL OF NEUROSCIENCE RESEARCH, Issue 2 2010Osamu Tao Abstract Mouse embryonic stem cells (ESCs) can generate cerebellar neurons, including Purkinje cells (PCs) and their precursor cells, in a floating culture system called serum-free culture of embryoid body-like aggregates (SFEB) treated with BMP4, Fgf8b, and Wnt3a. Here we successfully established a coculture system that induced the maturation of PCs in ESC-derived Purkinje cell (EDPC) precursors in SFEB, using as a feeder layer a cerebellum dissociation culture prepared from mice at postnatal day (P) 6,8. PC maturation was incomplete or abnormal when the adherent culture did not include feeder cells or when the feeder layer was from neonatal cerebellum. In contrast, EDPCs exhibited the morphology of mature PCs and synaptogenesis with other cerebellar neurons when grown for 4 weeks in coculture system with the postnatal cerebellar feeder. Furthermore, the electrophysiological properties of these EDPCs were compatible with those of native mature PCs in vitro, such as Na+ or Ca2+ spikes elicited by current injections and excitatory or inhibitory postsynaptic currents, which were assessed by whole-cell patch-clamp recordings. Thus, EDPC precursors in SFEB can mature into PCs whose properties are comparable with those of native PCs in vitro. © 2009 Wiley-Liss, Inc. [source] Long life operations over 5000 hours of BeZnSeTe/MgZnCdSe visible light emitting diodes on InP substratesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2006Ichirou Nomura Abstract Aging characteristics of BeZnSeTe yellow light emitting diodes (LEDs) fabricated on InP substrates by molecular beam epitaxy were investigated under direct current injections at room temperature. It was shown that the decay speed of the light output during the aging was slower than that of conventional ZnCdSe/MgZnSSe LEDs. A long lifetime more than 5000 h and a half lifetime of 5180 h were obtained at a current density of 130 A/cm2. The half lifetimes of the BeZnSeTe LEDs were about three orders of magnitude greater than that of the ZnCdSe/MgZnSSe LEDs. These results proved high reliability of the BeZnSeTe LED. Investigating the aging characteristics of the applied voltage, the injection current, and the emission spectra showed that the output decay was caused by degradation of the active layer of the LEDs. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Integration of K+ and Cl, currents regulate steady-state and dynamic membrane potentials in cultured rat microgliaTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005Evan W. Newell The role of ion channels and membrane potential (Vm) in non-excitable cells has recently come under increased scrutiny. Microglia, the brain's resident immune cells, express voltage-gated Kv1.3 channels, a Kir2.1-like inward rectifier, a swelling-activated Cl, current and several other channels. We previously showed that Kv1.3 and Cl, currents are needed for microglial cell proliferation and that Kv1.3 is important for the respiratory burst. Although their mechanisms of action are unknown, one general role for these channels is to maintain a negative Vm. An impediment to measuring Vm in non-excitable cells is that many have a very high electrical resistance, which makes them extremely susceptible to leak-induced depolarization. Using non-invasive Vm -sensitive dyes, we show for the first time that the membrane resistance of microglial cells is several gigaohms; much higher than the seal resistance during patch-clamp recordings. Surprisingly, we observed that small current injections can evoke large Vm oscillations in some microglial cells, and that injection of sinusoidal currents of varying frequency exposes a strong intrinsic electrical resonance in the 5- to 20-Hz frequency range in all microglial cells tested. Using a dynamic current clamp that we developed to actively compensate for the damage done by the patch-clamp electrode, we found that the Vm oscillations and resonance were more prevalent and larger. Both types of electrical behaviour required Kv1.3 channels, as they were eliminated by the Kv1.3 blocker, agitoxin-2. To further determine how the ion currents integrate in these cells, voltage-clamp recordings from microglial cells displaying these behaviours were used to analyse the biophysical properties of the Kv1.3, Kir and Cl, currents. A mathematical model that incorporated only these three currents reproduced the observed Vm oscillations and electrical resonance. Thus, the electrical behaviour of this ,non-excitable' cell type is much more complex than previously suspected, and might reflect a more common oversight in high resistance cells. [source] | ||||||||||