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H Korn

Publications and source records attributed to H Korn.

At least 91 records · Page 5Linked to original sources
PubMed1990

Characteristics of miniature inhibitory postsynaptic currents in CA1 pyramidal neurones of rat hippocampus.

1. Recordings were made in vitro from chloride-loaded CA1 rat hippocampal pyramidal neurones in the presence of tetrodotoxin (TTX) to examine miniature inhibitory postsynaptic currents (IPSCs). 2. Most spontaneous synaptic events recorded before TTX was applied, and all events that were resolved in the presence of TTX, were blocked by the GABAA receptor antagonist bicuculline. 3. At 25 degrees C, averaged miniature IPSCs had time to peak of about 3 ms and in most cases decayed with a single time constant close to 25 ms. 4. With a driving force for chloride ions between 70 and 80 mV, the mean miniature IPSC amplitude was 19.6-27.9 pA, yielding a conductance of 258-326 pS. The mean amplitude of unitary IPSCs recorded before TTX was applied was in the range of 31-73 pA. 5. When intervals between miniature IPSCs were compared with an exponential distribution, there was an excess of events at intervals shorter than 5 ms. Some individual events appeared to represent the nearly simultaneous release of two inhibitory quanta. 6. Miniature IPSC amplitude distributions were better fitted with the sum of two Gaussians than with one Gaussian. The variance in amplitude of a single quantal event exceeded that of the baseline noise. 7. Comparison of the conductance changes corresponding to the first Gaussian distribution with single GABA channel data suggests that one inhibitory quantum opens twelve to twenty chloride channels and that GABA molecules bind once to a postsynaptic receptor.

Animals↗
PubMed1990

Transmission at a central inhibitory synapse. IV. Quantal structure of synaptic noise.

1. Continuous segments of synaptic noise were recorded, in 12 experiments, from the voltage-clamped goldfish Mauthner (M-)-cell soma during depolarizations beyond the Cl- equilibrium potential so that spontaneous inhibitory postsynaptic currents (IPSCs) were outward going, i.e., opposite in polarity to excitatory transients. Inhibitory components constituting the noise were detected with a program based on their expected waveforms, and their amplitude distributions were analyzed according to a quantal model to determine whether these responses, presumably because of asynchronous impulses in a population of presynaptic cells, were integral multiples of the same minimal unit. 2. Synaptic noise in the M-cell is predominantly inhibitory, as it is abolished by the glycine antagonist strychnine. IPSC amplitudes varied by 20-fold or more and about one-third were grouped in bursts, with one or several components often occurring during the falling phase of a preceding one. To measure individual amplitudes, a base-line correction procedure was designed to extrapolate the decay of the leading IPSC, on the assumption that it was exponential with a time constant, tau, equal to that obtained by fitting averaged waveforms of distinct IPSCs recorded in quiet periods. Currents were expressed in nanoamperes and, for comparison between experiments, as percentages of the full-sized IPSC evoked by activation of the collateral network. 3. The probability distribution functions (PDFs) of inhibitory events generated with such an analysis had from 5 to 12 clear and equally spaced peaks, larger transients not being included because of their sparsity. These PDFs were fit with a sum of Gaussians, on the assumption that all peaks were integral multiples of the smallest unit and had the same standard deviation, sigma. The fits were statistically satisfactory, according to a chi 2 test, and mean quantal size was 0.63 +/- 0.17% (SD; range, 0.42-1.0%) of the collateral IPSC. 4. In eight experiments, tetrodotoxin (TTX) was subsequently applied topically to block presynaptic impulses and isolate "miniature" responses because of single exocytotic events. It had no apparent nonspecific effects, as indicated by the constancy of M-cell input conductance (8.01 +/- 3.11 microS vs. 7.90 +/- 2.89 microS). Amplitude distributions of residual IPSCs were unimodal and Gaussian, with their mean size (0.60 +/- 0.19%) and average rise time (0.548 +/- 0.128 ms) the same as those of the first peaks of control histograms. The latter parameter was also comparable with that of unitary IPSCs studied previously. These results thus confirmed that spontaneous and evoked events are due to transmitter release from the same afferent population.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Size and shape of glycine receptor clusters in a central neuron exhibit a somato-dendritic gradient.

The overall surface disposition of receptors for the neurotransmitter glycine was examined in situ on the teleost Mauthner cell. For this purpose, a monoclonal antibody specific for the glycine receptor was used in immunofluorescence experiments in association with the technique of confocal microscopy. Previous work had shown that on the Mauthner cell and other neurons, receptors for this transmitter are concentrated in discrete microdomains apposed to single presynaptic terminals. We now report that the size and the shape of these clusters depend on their cellular location, that is, their area increases regularly from the soma to the tip of the dendrites. Conversely, the number of clusters per unit area declines so that the final proportion of immunoreactive membrane remains constant at any portion of the cell. These results raise the question of the functional consequences of such an organized subcellular distribution of receptors.

Animals↗
PubMed1989

Effect of serotonergic afferents on quantal release at central inhibitory synapses.

Although most examples of modulation of synaptic transmission have been obtained from excitatory rather than from inhibitory connections, serotonin (5HT) is now shown to cause a presynaptic facilitation of release of the inhibitory neurotransmitter glycine. Brief local injections of this amine, or application of a 5HT uptake blocker, produce a long-lasting enhancement of both spontaneous and evoked inhibitory currents in the teleost Mauthner cell. Quantal analysis showed that the probability of release is increased. Focal recording indicated that 5HT acts directly on the inhibitory terminals, possibly reducing potassium conductances. Double staining with specific antibodies demonstrated a morphological substrate for this effect. Nerve endings that contain 5HT contact inhibitory terminals directly apposed to postsynaptic glycine receptors.

Afferent Pathways↗
PubMed1989

Consequences of stochastic release of neurotransmitters for network computation in the central nervous system.

Neuronal membrane potentials vary continuously due largely to background synaptic noise produced by ongoing discharges in their presynaptic afferents and shaped by probabilistic factors of transmitter release. We investigated how the random activity of an identified population of interneurons with known release properties influences the performance of central cells. In stochastic models such as thermodynamic ones, the probabilistic input-output function of a formal neuron is sigmoid, having its maximal slope inversely related to a variable called "temperature." Our results indicate that, for a biological neuron, the probability that given excitatory input signals reach threshold is also sigmoid, allowing definition of a temperature that is proportional to the mean number of quanta comprising noise and can be modified by activity in the presynaptic network, a notion which could be included in neural models. By introducing uncertainty to the input-output relation of central neurons, synaptic noise could be a critical determinant of neuronal computational systems, allowing assemblies of cells to undergo continuous transitions between states.

Animals↗
PubMed1988

Does beta-alanine activate more than one chloride channel associated receptor?

In order to define which receptor-channel complexes are activated by beta-alanine, we performed cross-desensitization experiments between this amino acid and the classical inhibitory neurotransmitters, glycine and gamma-aminobutyric acid (GABA), all of which increase chloride conductances. Using the whole-cell patch-clamp technique and cultured chick spinal neurons, we found that beta-alanine completely desensitizes the glycine response, and only partially reduces GABA evoked currents. No interaction occurred between GABA and glycine at the level of their respective receptors. Conversely, both GABA and glycine reduced the beta-alanine response. These results indicate that beta-alanine activates the glycine receptor, and also suggest that it could be a partial agonist of GABAA receptor(s).

Alanine↗
PubMed1988

Dual effects of serotonin on a voltage-gated conductance in lymphocytes.

The effects of serotonin (5-HT), a well-known immunomodulator and neurotransmitter, on the ionic permeability of a pre-B lymphocyte cell line was investigated with the whole-cell patch-clamp technique. We found that physiological doses of this biogenic amine regulate a voltage-gated potassium channel by activating different subsets of receptors. More specifically, 5-HT induces in the recorded cells (i) increase in the maximum potassium conductance, which is due to activation of 5-HT1-like receptors, and (ii) acceleration of the inactivation process that is under the control of 5-HT3 receptors and, accordingly, is mimicked by the 5-HT3 agonist, 2-methyl-5-HT; involvement of those two distinct categories of receptors was demonstrated by using specific antagonists that block predominantly one or the other of these two actions. These two results show that hormones can affect lymphocyte physiology through modulation of their ionic conductances in a way that might help explain some of the diverse effects of 5-HT on neuronal cells.

Abelson murine leukemia virus↗
PubMed1988

Synergism at central synapses due to lateral diffusion of transmitter.

Recordings of inhibitory postsynaptic currents in the goldfish (Carassius auratus) Mauthner cell demonstrate nonlinear interactions when adjacent synapses are coactivated. Responses evoked by single presynaptic neurons were paired with those due to activation of a limited pool of similar inhibitory cells. In about 50% of the experiments the compound currents were substantially larger than the sum of their individual components. Potentiation was maximal when the two responses occurred nearly simultaneously, and its decay paralleled that of the conditioning current; it started with a delay of about 300 microsec, and calculations indicate that in this time transmitter molecules would diffuse laterally 0.5-1.1 micron, which equals the separation of adjacent synapses. Iontophoretically applied glycine produced a comparable enhancement of the eighth nerve evoked inhibitory current. When quantal inhibitory responses were simulated, taking into consideration glycine diffusion, transmitter-receptor interactions, and channel activation, with the latter requiring two binding steps, the results demonstrated that the facilitation when neighboring inputs are active is due to lateral diffusion of the transmitter, glycine, to fringe areas where single bound receptors are available for further interactions and channel opening.

Animals↗
PubMed1988

Unitary conductance changes at teleost Mauthner cell glycinergic synapses: a voltage-clamp and pharmacologic analysis.

1. The magnitude and kinetics of inhibitory postsynaptic currents (IPSCs) evoked in the goldfish Mauthner (M-) cell by intracellular stimulation of identified presynaptic interneurons (unitary responses) and by activation of the recurrent collateral network were determined with single-and double electrode voltage-clamp techniques. 2. The peak magnitude of the inhibitory conductance changes were 5610 +/- 4800 nS (mean +/- SD; n = 13) for the collateral response, and 144 +/- 44 nS (n = 7) for the unitary IPSCs. These synaptic conductances, which are due to the opening of Cl- channels, were independent of the degree of Cl- -loading of the M-cell. 3. The peak amplitude of the collateral inhibitory postsynaptic potential (IPSP) was a constant fraction (0.52 +/- 0.06) of the driving force, which was determined from current-voltage plots for both types of IPSCs and ranged from 10 to 37 mV. These findings confirm indirect measurements from previous current-clamp studies and validate the normalization procedure used to previously calculate synaptic conductances from IPSP amplitudes, a method that therefore may be applicable to other central neurons. 4. At the resting membrane potential, the rise time of the unitary IPSCs was 0.34 +/- 0.07 ms (n = 18), whereas their decay was exponential, with a time constant of 5.7 +/- 1.1 ms (n = 16). 5. Iontophoretic and intramuscular applications of the glycine antagonist strychnine reduced or blocked M-cell inhibitory responses, without altering the excitability of the presynaptic neurons, or the driving force. 6. Amplitude fluctuations of unitary IPSPs recorded during partial blockade by strychnine were analyzed according to a binomial model of quantal transmitter release. In one experimental series, comparison of the binomial parameters before and after applying the antagonist indicated that only quantal size, q, was reduced, whereas n, the number of available release units, and p, the probability of release, were unaffected by strychnine. In a second series, the individual presynaptic cells were injected with horseradish peroxidase (HRP), and it was found that the correlation between n and the number of stained presynaptic boutons and, therefore, of active zones, was maintained in the presence of the drug. No evidence was found for silent synapses in these conditions. 7. The quantal conductance, gq, was estimated from the binomially derived quantal size, in millivolts, and the voltage-clamp measurements of the IPSP driving force and M-cell input conductance. gq averaged 21.5 nS in control conditions and 12.3 nS in the presence of strychnine.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Distribution of glycine receptors on the membrane of a central neuron: an immunoelectron microscopy study.

The distribution of glycine receptors on the plasmalemma of the teleost Mauthner cell was examined with light and electron microscopy using monoclonal antibodies raised against the glycine receptors of the rat. These immunoglobulins recognize a peptide of 93 kDa associated with the intracellular side of the receptor complex. With indirect immunofluorescence, labeling appeared as small clusters over the whole surface of the neuron. This distribution indicates that, unlike other neurons, the Mauthner cell can express glycine receptors at the dendritic and at the somatic level as well. Vestibular or reticular neurons lying in the proximity of the Mauthner cell were also stained. At the ultrastructural level, the immunoenzymatic reaction product, localized in front of the presynaptic active zones, slightly overextends the limits of the synaptic complex. This observation may account for vesicular exocytosis at the border of the presynaptic grid. More generally, inside and outside the axon-cap, stained postsynaptic membranes were apposed to terminals identified as unmyelinated club endings and some small vesicle boutons, respectively. Each of them could establish classical flat synapses or spinelike contacts, the latter being described here for the first time. Patches of membrane remained unstained, however, particularly along the lateral and ventral dendrites of the cell; they corresponded to the contact sites of excitatory afferents. In order to enhance the penetration of immunoreactive substances, a particular fixation procedure was used; its effect on the shape of the synaptic vesicles is described. Our results support the notion that glycine is responsible for both somatic and remote dendritic Cl- -dependent inhibition of the Mauthner cell. The first one is produced by the so-called PHP exhibiting neurons, which correspond to cells of recurrent collateral network and vestibulovestibular pathway. In contrast, cells giving rise to the more distal inhibitory synapses on both dendrites are not yet characterized.

Animals↗
PubMed1987

Cyclic AMP-modulated potassium channels in murine B cells and their precursors.

A voltage-dependent potassium current (the delayed rectifier) has been found in murine B cells and their precursors with the whole-cell patch-clamp technique. The type of channel involved in the generation of this current appears to be present throughout all stages of pre-B-cell differentiation, since it is detected in pre-B cell lines infected with Abelson murine leukemia virus; these cell lines represent various phases of B-cell development. Thus, the presence of this channel is not obviously correlated with B-cell differentiation. Although blocked by Co2+, the channel, or channels, does not appear to be activated by Ca2+ entry. It is, however, inactivated by high intracellular Ca2+ concentrations. In addition, elevation of intracellular adenosine 3', 5'-monophosphate induces at all potentials a rapid decrease in the peak potassium conductance and increased rates of activation and inactivation. Therefore, potassium channels can be physiologically modulated by second messengers in lymphocytes.

Animals↗
PubMed1987

Spontaneous quantal currents in a central neuron match predictions from binomial analysis of evoked responses.

Inhibitory postsynaptic currents occurring spontaneously in the teleost Mauthner cell were analyzed with the single-electrode voltage-clamp technique. They were collected during depolarizing steps and were outward-going; this procedure allowed them to be isolated from possible excitatory currents flowing in the opposite direction. Their amplitude histograms were found to exhibit regularly spaced multiple peaks, each of which had a Gaussian distribution of the same width. These compound inhibitory postsynaptic currents represent responses evoked by background firing of presynaptic neurons, and when tetrodotoxin was applied topically, only the first peak in the frequency histogram, which can be attributed to single exocytotic events, remained. The mean conductance of this quantal unit equalled 46.0 nS, which corresponds to the opening of 1000-2000 Cl- channels activated by glycine--the transmitter at these synapses. Its waveform and those of the larger units were essentially the same. Furthermore, in each set of data provided by a given Mauthner cell, the size of a quantum was quite constant, with its variance and those of further peaks being equivalent to that of background noise. These properties, which characterize the quantal events on the basis of spontaneous synaptic activity, were strikingly similar to those of the basic units derived by the simple binomial to those of the basic units derived by the simple binomial analysis of unitary postsynaptic potentials, thus validating the use of this statistical model to quantify the quantal nature of release at central connections. The quite straightforward method used here to extract single miniature currents from complex signals should be applicable to the other systems of the central nervous system, where the pertinence of this probabilistic model of release has yet to be demonstrated.

Animals↗
PubMed1987

gamma-Aminobutyric acid-containing terminals can be apposed to glycine receptors at central synapses.

The distributions of terminals containing gamma-aminobutyric acid (GABA) and of endings apposed to glycine receptors were investigated cytochemically in the ventral horn of the rat spinal cord. For this purpose, a polyclonal antibody raised to recognize glutamic acid decarboxylase (GAD), a synthetic enzyme for GABA, and three monoclonal antibodies (mAb's) directed against the glycine receptor were used. Double immunofluorescence showed that, surprisingly, GAD-positive terminals are closely associated in this system with glycine receptors at all the investigated cells, most of which were spinal motoneurons. Furthermore, double labeling was performed with immunoenzymatic recognition of GAD and indirect marking of mAb's with colloidal gold. With this combined approach, it was found, at the electron microscopic level, that all GAD-positive terminals are in direct apposition with glycine receptors while, on the other hand, not all glycine receptors are in front of GABA-containing boutons. This result is not due to a cross-reactivity of mAb's with GABA receptors as shown by using as a control synapses known to use GABA as a neurotransmitter in the cerebellar cortex. Indeed, no glycine receptor immunoreactivity was detected on Purkinje cells facing basket axon terminals. However, Purkinje neurons can express glycine receptor immunoreactivity at other synaptic contacts. Assuming that the presence of postsynaptic receptors for glycine indicates that this amino acid is used for neurotransmission at a given synapse, our results strongly support the notion that GABA and glycine, two classical inhibitory transmitters, coexist at some central connections. However, such is not always the case; in the cerebellum, Golgi terminals impinging on the dendrites of granule cells are either GAD-positive or face glycine receptors, in a well-segregated manner.

Animals↗
PubMed1987

Voltage-clamp analysis of a crayfish rectifying synapse.

1. The rectifying crayfish giant motor synapse has been studied in the second abdominal ganglion, using the double-voltage-clamp technique which allowed direct measurements of junctional current at various fixed transjunctional potentials. 2. The transjunctional potential (Vj), defined as the difference between the voltages recorded in the lateral giant axon and the giant motor fibre, was varied from -70 to +50 mV, the minimum and maximum junctional chord conductances (gmin and gmax, respectively) were found to be 1.2 +/- 1.3 microS (n = 10) and 22.9 +/- 6.3 microS (n = 10), respectively. 3. For a given Vj, changes in the lateral giant axon or giant motor fibre membrane potential over a range of +/- 30 mV around their resting levels did not influence the junctional permeability (gj), indicating that the inside-outside potential of the junctional channel does not control gj. 4. Therefore, the steady-state junctional chord conductances were dependent only upon Vj. 5. The voltage dependence of the chord conductance was well fitted by a modified Boltzmann relation given by the equation (Formula: see text) with the constants: A = 0.15 +/- 0.03 mV-1 (n = 10) and V0 = 28 +/- 4 mV (n = 10); the latter two parameters were also found to be independent of both transmembrane potentials. 6. The junctional currents were already constant 1 ms after step changes in the junctional voltage; this was three orders of magnitude faster than the other known examples of voltage-controlled gap junctions between embryonic cells. 7. Our results may be interpreted by a highly voltage-dependent probability of opening of the junctional channels. They also suggest that the gap-junction channels forming the giant motor synapse respond very rapidly to potential and that the hemi-channels which constitute them may not be symmetric.

Action Potentials↗
PubMed1987

Voltage-dependence of glycine-activated Cl- channels: a potentiometer for inhibition?

Single- and double-electrode voltage-clamp techniques have been employed in situ to analyze Mauthner cell inhibitory synaptic responses produced both by activation of the recurrent collateral network and by direct intracellular stimulation of single presynaptic interneurons. The results demonstrate that the synaptically evoked glycinergic postsynaptic currents exhibit a striking voltage sensitivity. Specifically, the time constant of the decay of the synaptic conductance is increased by depolarization and decreased by hyperpolarization. This parameter is exponentially related to membrane potential, changing e-fold for a 45 mV potential shift, regardless of the degree of intracellular chloride loading or the magnitude of the underlying synaptic conductance. In addition, the amplitude of this inhibitory conductance change is decreased by membrane hyperpolarizations of 15 mV or more. Computer modeling demonstrates that the voltage dependence of the kinetics of the synaptic response may serve to enhance the magnitude and duration of inhibitory responses appreciably in the face of increased excitation.

Animals↗