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J Dudel

Publications and source records attributed to J Dudel.

At least 91 records · Page 5Linked to original sources
PubMed1986

Neurotransmitter release and its facilitation in crayfish. VIII. Modulation of release by hyperpolarizing pulses.

Quantal postsynaptic currents were recorded by a macro-patch-clamp electrode from synaptic spots on the opener muscle of the walking leg of large crayfish at 0 degrees to 4 degrees C. Through the same electrode, current pulses were applied which de- or hyperpolarized the nerve terminal. The depolarizing test pulse of fixed amplitude and duration elicited EPSCs with an average quantum content m1. If the test pulse was preceded or followed immediately by a modulatory hyperpolarizing pulse, the quantum content m1p of the EPSC was reduced by factors m1/m1p up to 10. This modulation of release increased with amplitude and duration of hyperpolarization, reaching a saturation level for durations greater than 3 ms. If an interval was interposed between modulatory hyperpolarization and test pulse, the reduction of release decayed with increasing interval with a time constant of about 2 ms. The release m2 due to a second test pulse following the first one with 10 ms interval was facilitated, m2/m1 greater than 1. If release by the first test pulse was modulated by associated hyperpolarizing pre- or post-pulses, facilitation of the second test EPSC was not reduced in comparison to facilitation without modulation. The time course of phasic release (distribution of delays of quanta after test pulse) was not appreciably affected by hyperpolarizing pre-pulses, but such post-pulses shortened the delay of the maximum of release. The effects of modulatory pre- and post-pulses could be described by an extension of the model given in H. Parnas et al. (1986). Release 'sites', S, are assumed to have two inactive states, T1 and T.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

High-resolution measurements of single-channel currents activated by glutamate in crayfish muscle.

Patch-clamp pipettes filled with 50-5000 microM glutamate were placed on crayfish muscle fibers treated with collagenase, formed G omega seals and elicited single-channel currents with a main amplitude of about -8 pA at -70 mV membrane potential, representing a conductance of about 100 pS (19 degrees C). Evaluation of the channel openings longer than 1 ms yielded three sublevels of this conductance. The channels opened in bursts, the durations of which were distributed in two exponential components with time constants of about 0.1 and 0.3 ms at low glutamate concentrations, which rose to about 0.4 and 1.8 ms, respectively, at high glutamate concentrations. The distributions of closed times could be described by three time constants which also varied with glutamate concentration. Comparison of the burst durations with the decay time constants of natural synaptic currents indicates effective glutamate concentrations in the millimolar range during transmission.

Animals↗
PubMed1984

Depolarization dependence of the kinetics of phasic transmitter release at the crayfish neuromuscular junction.

Quantal synaptic currents were recorded at nerve terminals on the crayfish opener muscle by means of a macro-patch-clamp electrode. Release could be elicited by graded depolarization pulses through the recording electrode. At low temperature, distributions of delays of single quantal currents from the onset of depolarization were determined for depolarizations varying from threshold to saturation range. This time course of release was little affected by the amplitude of depolarization: There was a tendency for release to start earlier and to rise faster for larger depolarizations, while the termination of release showed no significant variations. The time course of release after an action potential in the motor axon was similar to that of release after a depolarization pulse. It is concluded that the time course of quantal release is rather independent of amplitude of depolarization and of the amount of calcium (Ca) inflow, which seems to rule out the control of the release after a depolarization by the time course of [Ca]i.

Animals↗
PubMed1984

Excitability and depolarization-release characteristics of excitatory nerve terminals in a tail muscle of spiny lobster.

In the deep abdominal L1-extensor muscle of the spiny lobster (Panulirus penicillatus) quantal excitatory postsynaptic currents (EPSCs) were recorded through macro-patch-clamp electrodes. Release of transmitter quanta from terminals was also elicited by depolarizing current pulses given through the recording electrode. The majority of terminals were excitable: on increasing the depolarization pulses, release was triggered at a threshold in an all-or-nothing manner. If excitation was blocked by tetrodotoxin (TTX), release was graded with depolarization reaching the amplitude of the all-or-nothing response at pulse amplitudes several times higher than the former threshold level. Some inexcitable terminals were also found: in these, release was graded for increasing depolarization pulses, and TTX did not alter the depolarization-release relation. Among the other types of terminals studied with the same technique, the proportion of excitable terminals in this lobster tail muscle is higher than in the crayfish opener and lower than in the frog's cutaneous pectoris muscle. The contribution of the increase in intraterminal Ca concentration to the control of release was estimated using facilitation of a test EPSC as an indicator of Ca inflow during a preceding depolarization pulse. This facilitation was found to have a maximum at a certain pulse amplitude, PF, and to decline for larger depolarizations. Release, however, rose considerably for depolarizations larger than those effected at PF. It is concluded that, like in crayfish and frog motor terminals, release is controlled directly by depolarization in addition to the control by Ca-inflow.

Action Potentials↗
PubMed1984

Control of quantal transmitter release at frog's motor nerve terminals. I. Dependence on amplitude and duration of depolarization.

Motor terminals on the cutaneous pectoris muscle of the frog were depolarized by current pulses through the recording macro-patch-clamp electrode and the resulting quantal release was measured (excitation blocked with TTX). Above a threshold release increased very steeply with depolarization until saturation was approached. The dependence of release on duration of depolarization was even steeper: doubling pulse duration often produced more than 100-fold release ('early facilitation'). Distributions of delays of quantal release after the depolarization pulse were determined for wide ranges of depolarizations and pulse durations. The shape of these distributions was little affected by large changes in average release; increasing the temperature from 0 degrees C to 10 degrees C about halved the time scale of the distributions. Lengthening the depolarization from 0.5 to 6 ms produced a 'latency shift': the distributions of delays were shifted by almost the increase in pulse duration. At 5-6 ms pulse duration a few releases occurred during the final millisecond of the pulse. It is suggested that the time course of the phasic release is not controlled by the time course of changes in intracellular calcium concentration, but by an activator which is produced about proportional to supra-threshold pulse amplitude and duration, and that this activator effects release with a cooperativity of 6-7. An additional depolarization produced repressor is responsible for the minimum delay.

Animals↗
PubMed1984

Control of quantal transmitter release at frog's motor nerve terminals. II. Modulation by de- or hyperpolarizing pulses.

Quanta of transmitter were released from motor nerve terminals of the frog by a depolarizing 'releasing pulse'. 'Modulating pulses' were subthreshold for release; pre-pulses were added directly before and post-pulses directly after the releasing pulse. Modulating depolarization pulses enhanced release up to 20-fold, and such hyperpolarizations suppressed release up to 10-fold. Pre- and post-pulses were about equally effective. In a wide range these modulations did not affect the facilitation of a test-EPSC by the preceding releasing pulse; modulation thus is not mediated by changes in Ca-inflow. It is suggested that phasic release is largely controlled by an 'activator' which is generated by depolarization, and that modulating pulses increase this activator when depolarizing, and decrease this activator below its resting level if hyperpolarizing. If an interval was interposed between pre- and releasing pulse, the modulating effect decreased very steeply with increasing interval for the first 2 ms, and much slower for longer intervals. Distributions of delays of quantal releases showed a time course of decay very similar to the decay of modulation with increasing interval. Both decays may reflect the exponential decay of activator. Depolarizing post-pulses increased the minimal synaptic delay and the delay of maximal release, and hyperpolarizing ones had the opposite effects. They are interpreted to modulate the generation and decay of a 'repressor', which is produced by depolarization and is responsible for the minimal synaptic delay and the delayed maxima of release. A speculative scheme of interactions of [Ca]i, activator and repressor is discussed.

Animals↗
PubMed1984

Strengthening of synaptic contacts of an excitatory axon on elimination of a second excitatory axon innervating the same target.

In the deep abdominal extensor muscles of spiny lobsters (Panulirus-pennicillatus), the common excitor axon of segment II was eliminated by intracellular injection of pronase. At 1 to 23 days after the operation, the quantal content of excitatory postsynaptic currents (EPSCs), elicited by stimulation of the specific excitor of the L1 muscle, was determined in a specific area of the L1 muscle, both in the operated and in the contralateral control side. The EPSCs in the operated muscles had about a 5 times higher quantal content compared to those in the controls, the change developing within 1 to 2 days after operation. In camera lucida drawings of preparations stained with methylene blue, increased branching of the remaining excitatory axon was obvious at more than 4 days after the operation. To investigate the possibility of contribution of central mechanisms (Rotshenker, S. (1979) J. Physiol. (Lond.) 292: 535-547). to this effect, the bundle of five axons to the deep abdominal extensors of segment II was cut immediately after injection of pronase into the common excitor axon. This caused a reduction of the quantal content of EPSCs and shrinking of the field of innervation in the operated L1 muscle as compared to the control. Therefore, axonal continuity or central connections seem to be necessary for the development of an increased innervation by the specific excitor to L1 after eliminating the common excitor axon. Possible postsynaptic effects of the elimination of the common excitor axon were controlled by recording synaptic single channel currents elicited by the excitatory transmitter glutamate, using the patch clamp method. These single current events did not show appreciable changes in operated L1 muscles. Therefore, the presynaptic strengthening effect on the nerve terminals of the specific L1 excitor is predominant after elimination of the common excitor axon.

Animals↗
PubMed1983

Single synaptic channels recorded at glutamate sensitive patches on a crayfish muscle.

When a patch clamp pipette filled with 50 mumol/l glutamate was placed on a muscle fiber of the deep abdominal extensor of crayfish, in some locations current pulses were recorded which were identified as synaptic, glutamate-operated ionic channel openings. At a given site all current pulses had approximately the same amplitude. At resting potential and 19 degrees C, their mean amplitudes were 7-8 pA, corresponding to channel conductances of 70-80 pS. The distribution of open times of the channels could be described by the sum of two exponentials with time constants tau 1 of 0.3-0.5 ms for the longer, and tau 2 of 0.03-0.06 ms for the shorter component. Bursts of channel openings interrupted by gaps occurred in about 10% of the events only. The longer time constant tau 1 conforms to the channel open times estimated by noise analysis [11].

Animals↗
PubMed1983

Transmitter release triggered by a local depolarization in motor nerve terminals of the frog: role of calcium entry and of depolarization.

Quantal synaptic currents (EPSCs) were elicited at neuromuscular junctions of frogs, applying current pulses through the recording current-clamp electrode. Facilitation of a test-EPSC by a preceding EPSC of variable amplitude was determined. This facilitation after a prepulse and release during the prepulse were found to have different dependences on depolarizing current amplitude. In addition, if intraterminal calcium [( Ca]i) was raised by a train of EPSCs, small depolarizations with little additional Ca entry elicited release which depended strongly on pulse amplitude. It is concluded that, in addition to [Ca]i, depolarization of the terminal directly controls quantal release. This depolarization dependence of release is shown to be the probable cause for termination of release after a large Ca entry.

Animals↗
PubMed1983

Graded or all-or-nothing release of transmitter quanta by local depolarizations of nerve terminals on crayfish muscle?

In opener muscles of the first walking leg of 3 species of crayfish, quantal synaptic currents were recorded focally at synaptic spots by means of a macro-patch-clamp electrode. Proximal stimulation of the motor axons elicited excitatory postsynaptic currents (nEPSCs). In addition, current pulses through the recording electrode depolarizing the nerve terminal elicited similar synaptic release (pEPSCs). Artefact waveforms generated in the recording electrode after a pulse were compensated by a special circuit, allowing the pEPSC to be recorded from 0.3 to 1.5 ms after the pulse. In all terminals identified by recording nEPSCs, pEPSCs were also elicited, with a threshold pulse amplitude between -0.1 and -2 microA at 2 ms pulse duration. Most of the investigated terminals showed graded pEPSCs to rising amplitudes and durations of depolarizing pulses, and no effect of tetrodotoxin (TTX) on the pEPSCs. In these inexcitable terminals pEPSCs and nEPSCs showed mutual facilitation, with no signs of refractoriness for intervals as short at 3 ms. Some excitable terminals were found also: in these the amplitude of the pEPSC rose very steeply in an approximately all-or-nothing response on passing a threshold, while application of TTX reduced this response to one similar to that of inexcitable terminals. However, stimulation of such excitable terminals did not lead to antidromic conduction of action potentials into the main axon. In both inexcitable and excitable terminals, approximately the product of suprathreshold pulse amplitude and pulse duration determined the rate of release. The dependence of this response on pulse amplitude showed characteristic differences in proximal and distal synapses. The maximal double-logarithmic slope of this relation (sD) was 3.3 on the average in proximal synapses, while for distal synapses the average sD was 6.3. Further, in proximal synapses the nEPSC reached on average 86% of the maximum pEPSC, while the nEPSC in distal synapses amounted to only 5% of the maximum pEPSC. Therefore, the point of block of conduction in the terminal branch seems to lie father from the terminal in distal than in proximal synapses.

Animals↗
PubMed1983

Glutamate activated postsynaptic channels in crayfish muscle investigated by noise analysis.

Excitatory synaptic channels in crayfish muscle were investigated under various experimental conditions. Small muscle fibres of length l less than or equal to 0.6 mm were voltage clamped, spatial control of the voltage being sufficient up to at least 500 Hz. Excitatory synaptic current was induced by superfusion of glutamate. The power density spectra of this current could be fitted by single component Lorentz curves. The analysis revealed a mean open time tau noise = 0.93 ms and a conductance gamma = 32.3 pS of the glutamate operated ion channels (membrane potential E = -60 mV, temperature T = 8 degrees C). Both the conductance gamma and the channel closing rate alpha = tau -1 noise increased significantly with temperature (Q10 approximately 2). The temperature dependence of gamma and alpha could be described by Arrhenius equations with the temperature independent activation energies E gamma = 42.3 kJ/mol and E alpha = 50.2 kJ/mol. alpha also dependent on the membrane potential, increasing about e-fold when the membrane was hyperpolarized by 120 mV. The potential dependence varied considerably from fibre to fibre. The mean channel open time tau noise agreed with the time constant of decay tau (sEPSC) of spontaneous excitatory postsynaptic currents (sEPSCs).

Animals↗
PubMed1983

Effects of concanavalin A on glutamate operated postsynaptic channels in crayfish muscle.

Small crayfish muscle fibres were voltage clamped, and synaptic current noise induced by bath application of glutamate was measured. Desensitization of the glutamate receptors was blocked by preincubating the fibres with 0.3-1.0 mumol/l concanavalin A (Con A) for at least 30 min. The power density spectra of the glutamate current noise could be fitted by single component Lorentz curves. The lectin Con A did not influence significantly the conductance gamma of the glutamate channels but increased their mean open time, tau noise. The respective mean values found at T = 8 degrees C and E = -60 mV were gamma = 23.5 +/- 7.0 pS and tau noise = 1.5 +/- 0.2 ms. Both the conductance gamma and the closing rate alpha = tau -1 noise increased with temperature (Q10 approximately 1.9). This temperature dependence was characterized by the activation energies E gamma = 35.2 +/- 7.1 kJ/mol and E alpha = 46.9 +/- 2.1 kJ/mol. The potential dependence of tau noise was almost completely abolished by Con A.

Animals↗
PubMed1983

Neurotransmitter release and its facilitation in crayfish muscle. VI. Release determined by both, intracellular calcium concentration and depolarization of the nerve terminal.

In excitatory neuromuscular junctions of crayfish quantal synaptic currents were recorded focally by means of a macro-patch-clamp electrode. Through the same electrode the nerve terminal was depolarized by current pulses which elicited quantal postsynaptic currents (pEPSCs). The terminals were electrically inexcitable and the quantum content (m) of pEPSCs increased gradually to a saturation level with rising pulse amplitude. A test-pEPSC was elicited by constant current pulses, and its facilitation (Fc) by a preceding pEPSC of varying amplitude was studied. Amplitude and duration of Fc are measures of the amount of Ca entry during the prepulse. These values had a maximum consistently at a much lower prepulse amplitude than necessary to reach maximum release during the prepulse. The potential dependence of Fc is as expected for a potential dependent Ca-entry into the terminal. The fact that release during the prepulse rose for large depolarizations while Fc and thus Ca-entry decreased, indicates a direct promotion of release by depolarization. In another type of experiment the Ca concentration in the terminal ([Ca]i) was increased greatly by series of depolarizations. During a following test-pEPSC thus [Ca]i was at an approximately constant high level. However, variations of the amplitude of the test depolarization pulse caused changes of the test-pEPSC by several orders of magnitude, which must be attributed to a direct control of quantal release by depolarization. The mechanism of this direct effect of membrane potential is discussed, extending our model of synaptic release which only contained control by [Ca]i. The decisive role of control of release by membrane potential for the termination of release after Ca entry is emphasized.

Action Potentials↗
PubMed1982

Transmitter release by graded local depolarization of presynaptic nerve terminals at the crayfish neuromuscular junction.

Synaptic currents were recorded at single nerve terminals on the crayfish opener muscle by means of a patch-clamp electrode. Current pulses depolarizing the terminal were applied through the electrode which caused release of transmitter quanta. Such 'pulse-elicited excitatory postsynaptic currents' (pEPSCs) were not affected by the presence of tetrodotoxin, and no antidromic action potentials were detected in the motor nerve fiber after terminal depolarizations eliciting maximal pEPSCs. The amplitude of pEPSCs was graded in a wide range depending on amplitude and duration of the pulse, with different quantitative relationships for 'fast' and 'slow' synapses. It appears that these nerve terminals are inexcitable and are depolarized by the electronic spread of the motor nerve action potential.

Animals↗
PubMed1982

Neurotransmitter release and its facilitation in crayfish muscle. V. Basis for synapse differentiation of the fast and slow type in one axon.

Excitatory postsynaptic currents (EPSCs) were recorded extracellularly from synaptic spots on crayfish opener muscle fibers. Synapses on the proximal fiber bundle were characterized as fast, with a relatively high quantal-release rate m of 0.2-5 and a low twin-pulse facilitation Fs of 1.1-3, at 13.5 mM [Ca]o and low (0.5/s) repetition rate. Under the same conditions, distal "slow" synapses had a release rate m of 0.02-0.4 and a facilitation Fs of 2-4. When the [Ca]o was varied between 1.7 and 27 mM, release and facilitation were much less affected in proximal, fast synapses than in distal, slow ones. The average maximal slope of the log release to log [Ca]o relation was 1.5 in proximal, and 3.1 in distal synapses, while the average maximal facilitation Fs was 2.5 in proximal and 4.7 in distal synapses, respectively. Assuming saturation kinetics for entry of Ca into the terminal and release of transmitter, possible variations of parameters generating the fast-slow differentiation were explored. Excluding a number of possibilities, it was found that in addition to a higher maximal release level, fast synapses seem to have a higher resting [Ca]i and/or a lower cooperativity of the release mechanism, as compared to slow synapses.

Animals↗
PubMed1982

Neurotransmitter release and its facilitation in crayfish. I. Saturation kinetics of release, and of entry and removal of calcium.

Release and facilitated release of transmitter at neuromuscular junctions of the crayfish Astacus were measured as a function of [Ca]0 at single junctions using a patch clamp technique. Tests were made of a quantitative model that relates release of transmitter to [Ca]i. The model assumes three processes, entry of Ca during the action potential, release of transmitter as a function of [Ca]i, and removal of Ca after the action potential. Each process is described alternatively by linear kinetics or saturation kinetics, and predictions for different combinations of the equations are given. The main findings were in agreement with those predicted by the "saturation" model. The amplitude of synaptic current varies non-linearly with [Ca]0, log-log plot yielding a slope of about 1.6. The degree of facilitation at long intervals is an increasing function of [Ca]0. In addition, the duration of facilitation is prolonged as [Ca]0 is increased, to saturate at [Ca]0 of 9 mM.

Animals↗
PubMed1982

Neurotransmitter release and its facilitation in crayfish. II. Duration of facilitation and removal processes of calcium from the terminal.

Excitatory postsynaptic currents (EPSCs) were recorded extracellularly from synaptic spots on crayfish opener muscles. Facilitation was measured in twin pulses with different intervals. When the extracellular calcium concentration, [Ca]0, was raised from 1.7 to 13.5 mM, the duration of facilitation was increased more steeply than can be explained by the higher entry of Ca. The discrepancy can be accounted for by assuming two saturable Ca removal processes, one being inhibited at high [Ca]0. If [Na]0 was reduced to 50 or 25%, facilitation at low [Ca]0 (e.g. 3.4 mM) was greatly prolonged, while at high [Ca]0 (13.5 mM) no effect was observed. It is concluded that one of the Ca removal processes, R1, depends on [Na]0 and is inhibited by [Ca]0; probably it is a Cai in equilibrium with Na0 exchange. R1 is predominant at low [Ca]0 and is largely responsible for the short duration of facilitation there. Other removal processes, R2, are not affected appreciably by [Ca]0 and [Na]0, and they predominate at high [Ca]0. Approximate values for the kinetic constants of R1 and R2 and the inhibition of R1 were estimated.

Animals↗