PubMed Health⌕ Search

Biomedical subjects

A Baranyi

Publications and source records attributed to A Baranyi.

32 records · Page 2Linked to original sources
PubMed1987

Mechanism of aminopyridine-induced ictal seizure activity in the cat neocortex.

Intracellular recordings were obtained from neurons in the motor cortex of anesthetized cats in order to examine membrane and synaptic processes involved in aminopyridine (AP)-induced ictal seizure activity. Depolarizing and hyperpolarizing membrane potential sequences which behaved as large, synchronized excitatory and inhibitory postsynaptic potentials, were found to accompany the ictal seizure potentials. After several repetitions of the seizure attack, partial responses, bursts and depolarizing plateaus with spike inactivation occurred. In layers IV and V we found non-pyramidal tract neurons showing endogenous bursting ability activated by AP. These neurons seemed to be the initiators of the rhythmic synchronous activity of the epileptic neuron population. Our results suggest that AP-induced epileptogenesis represents an adequate model of ictal events in the neocortex.

Action Potentials↗
PubMed1987

Phorbol esters that activate protein kinase C induce long-term changes of membrane excitability and postsynaptic currents in neocortical neurons.

Intracellularly injected tumor promoter phorbol esters (PhEs) that activate protein kinase C (PKC) increased the excitability and altered the postsynaptic responses of neurons of the motor cortex of awake cats. PhEs increased the amplitude and duration of EPSPs and decreased the amplitude and durations of IPSPs. No consistent changes in resting membrane parameters that would account for these modifications were found. Corresponding changes in peak excitatory and inhibitory postsynaptic currents (EPSCs, IPSCs) were measured directly with the single electrode voltage clamp technique. The changes lasted for 50 min or longer. Quantitative analysis of EPSCs in response to ventrolateral thalamic stimulation and IPSCs in response to pyramidal tract stimulation made in a subgroup of fast PT cells suggested that PhE acted within the injected neuron rather than presynaptically to alter the synaptic currents. PhE also reduced a voltage-dependent, 3-aminopyridine sensitive fast outward current (IA) and an apamin and EGTA sensitive slow outward current (IK(Ca]. Control injections of a phorbol ester that did not activate PKC failed to induce changes in synaptic responses or resting membrane properties. These observations provide the first evidence that activation of PKC, in vivo, can induce long-lasting changes in synaptic responses of neocortical neurons by direct modification of postsynaptic ion channel conductivities.

Action Potentials↗
PubMed1987

Application of the glycine labelling method to the cerebellum, hippocampus and spinal cord.

3H-glycine was applied to the cat cerebellar cortex under resting conditions and during inferior olive stimulation which activated the climbing fiber system on a restricted area. Electric recording was made. The autoradiograms showed, that under resting condition labelled glycine was incorporated mainly in granule, Golgi and basket cells and only a few Purkinje and stellate cells were active. Also cerebellar glomeruli remained without labelling. On climbing fiber stimulation Purkinje cells became activated singly and grouped, also Golgi and stellate cells increased in number. Granule cells were totally inhibited. 3H-glycine, when applied to the rat hippocampus, the dentate gyrus, CA1 and CA4 fields showed labelling at low frequency stimulation. When 400 Hz high frequency stimulation periods were interposed, long-term potentiation ensued. The overall labelling of each hippocampal region was intensified significantly, indicating that glycine incorporation may be a sign not only of excitation but also of long-term potentiation. 3H-glycine was applied to frog spinal cord during rest and dorsal root stimulation. Interneurons and motor neurons excited by the afferent fibers showed intensive glycine uptake. It is concluded that the glycine labelling method is suitable for detecting neural excitation in the structures dealt with in this paper.

Animals↗
PubMed1984

Ethanol-induced modulation of the membrane potential and synaptic activity of trigeminal motoneurons during sleep and wakefulness.

In the present study we investigated the direct actions of ethanol on the membrane properties and excitatory and inhibitory postsynaptic potentials of trigeminal motoneurons in chronic cats. During states of sleep and wakefulness, extracellular and intracellular recordings were carried out together with juxtacellular (somatic and dendritic) and intracellular pressure injections of 0.05-2.5 M ethanol solutions in femtoliter quantities. Juxtacellularly applied ethanol induced: a sequence of excitatory-inhibitory alterations in firing activity which were accompanied by depolarizing-hyperpolarizing shifts in the resting membrane potential; a decrease in the amplitude of action potentials; and a depression in excitatory and inhibitory postsynaptic potentials. Intracellular ethanol injections resulted in depolarization of the membrane potential and a decrease in the amplitude of action potentials as well as a reduction in the amplitude of excitatory and inhibitory postsynaptic potentials. Both juxtacellularly and intracellularly applied ethanol affected the membrane potential and synaptic activity in a fashion that was not dependent upon the animal's behavioral state of sleep or wakefulness.

Action Potentials↗
PubMed1983

Effects of juxta- and intracellular microinjection of ethanol on trigeminal motoneurons in the chronic cat.

The direct cellular effects of ethanol on trigeminal motoneurons were studied in chronic cats during sleep and wakefulness. Intracellular and extracellular recordings were obtained while simultaneously injecting ethanol microdroplets onto the surface (juxtacellularly) or within the soma (intracellularly) of these motoneurons. Juxtacellular ethanol injection resulted in a suppression of neuronal excitability as well as a reduction in the amplitude of action potentials and monosynaptically-induced excitatory postsynaptic potentials. Intracellular ethanol injection led to a slight increase in excitability (i.e. membrane depolarization); concurrently, however, there was a reduction in the amplitude of spike and synaptic potentials. We conclude that the predominant response of trigeminal motoneurons to the direct application of ethanol entails a dose-dependent reduction in membrane excitability in addition to a depression of excitatory synaptic transmission. This pattern of ethanol action was observed throughout the states of quiet sleep and active sleep as well as when the animal was awake.

Animals↗
PubMed1983

Function-dependent glycine incorporation into neurons of the cat motor cortex.

Filter papers soaked with 3H-2-glycine solution were applied to the motor cortex of chloralosed and nembutalized cats for one hour. Then underlying cortical samples were excised, fixed in Bouin solution and processed for light-microscopic autoradiography. Sections stained with haematoxylin-eosin were made to determine total cell counts. The cortical samples were sectioned in series so that 10 micron sections at every 50 micron were preserved. From resting and stimulated cortices 10 sections were used for counting pyramidal cells and interneurons in different layers. The electric background activity and the potentials evoked by thalamic VL and antidromic PT stimulation were recorded and averaged. In chloralose anaesthesia, only 7%, while under nembutal 22% of the cells incorporated glycine, on the average. VL stimulation, which induced the appearance of typical evoked potentials, enhanced the glycine incorporation of pyramidal cells in layers II-III and Vb and some activation in the interneurons of layer II was also seen. Antidromic PT stimulation did not change the autoradiographic pattern in chloralosed preparations, while in nembutalized cats it depressed the labelling of pyramidal cells in layers II, III and Va drastically with some enhancement in interneurons of layer II. The changes of autoradiographic patterns are in harmony with theories about cortical effects of VL and antidromic PT stimulation.

Anesthesia↗
PubMed1981

Long-term facilitation of excitatory synaptic transmission in single motor cortical neurones of the cat produced by repetitive pairing of synaptic potentials and action potentials following intracellular stimulation.

The effects of postsynaptic firing activity on excitatory postsynaptic potentials (EPSPs) were studied in the motor cortex of anaesthetized cats. Postsynaptic firing was induced by 1-5 nA cathodal current pulses via the recording intracellular microelectrode, while EPSPs were elicited by thalamic, callosal, pyramidal tract and somatosensory stimuli. In 102 cells, EPSP-spike stimulus pairs were applied with 0.2-1/sec frequency and 10-100 msec interstimulus intervals. In 42 neurones, reversible facilitation of paired EPSPs appeared lasting from 4 to 47 min. The synaptic facilitation in most cases was accompanied by membrane depolarization and an increase in input resistance. The effectiveness of current induced action potentials upon test EPSPs provided evidence for the postsynaptic localization of plastic changes occurring in conditioning experiments.

Action Potentials↗
PubMed1981

Selective facilitation of synapses in the neocortex by heterosynaptic activation.

Heterosynaptic facilitation (HF) of different excitatory postsynaptic potentials (EPSPs) can be recorded in the motor cortex os anesthetized cats following repetitively applied EPSP-spike stimulus pairs. HF turned out to be synapse-specific in many cases, because not all of the stimulated inputs in the same neuron could produce it. Furthermore, membrane depolarization, increase in membrane resistance and firing activity, can appear with or without HF of a test EPSP.

Animals↗
PubMed1981

Synaptic facilitation requires paired activation of convergent pathways in the neocortex.

In associative learning, the activated neurones undergo a variety of concomitant functional alterations--increases or decreases of firing activity and modifications of membrane potential or resistance and of synaptic responsiveness. Synaptic transmission which can be strengthened only when there is paired activity in two pathways is of particular interest in relation to mechanisms for associative learning. For the neocortex, there are few observations of the plastic changes, induced by conditioning procedures, in the effectiveness of individual synapses. We now report that various regimes with joint stimulations of convergent excitatory pathways on to intracellularly recorded neurones in the motor cortex of the cat result in synaptic facilitation lasting for up to 30 min.

Action Potentials↗
PubMed1981

Intracellular studies on cortical synaptic plasticity. Conditioning effect of antidromic activation on test-EPSPs.

1. An intracellular study on pyramidal tract (PT) neurons in the cat's motor cortex was carried out to examine whether their antidromic activation would be able to induce plastic changes in the efficacy of the synapses situated on their membrane. 2. The experimental paradigm was based on the principles of classical conditioning. It included habituation, pseudoconditioning, conditioning and extinction procedures. The antidromic spike was regarded as an unconditioned stimulus while excitatory postsynaptic potentials (EPSPs) evoked by thalamic (n. ventralis lateralis), callosal and somatosensory afferents served as conditioned stimuli. Stimulus pairs were given, consisting of EPSPs and antidromic spikes with various time intervals, and the stimulus sequences were at a 0.2--1.0/s frequency. 3. Reversible, short-term (3--28 min) enhancement of synaptic excitability was observed in 27% of the PT cells after conditioning with 60--150 stimulus pairs. 4. EPSP-spike and spike-EPSP sequences were equally effective, but plastic changes were induced only by stimulus pairs with less than 100 ms interstimulus intervals. 5. Facilitated EPSP states were frequently accompanied by changes in membrane potential, membrane resistance and firing activity. 6. In repeated conditioning series, the temporal parameters of conditioning changes, the number of stimuli necessary for full development of facilitation, and some membrane parameters showed marked alterations. 7. Conditioned plastic changes in synaptic efficacy showed analogies with associative learning: (a) they were specific to the pairing procedure, because randomized presentation of EPSPs and antidromic spikes never produced synaptic facilitation; (b) unpaired spike trains used as unconditioned stimuli (of 10--200/s frequency and 1--20 s duration) caused only a minor degree of facilitation as compared with EPSP-spike pairings; (c) changes in synaptic efficacy were subject to extinction. 8. The present findings indicate that the plastic changes in synaptic transmission may be localized to the postsynaptic membrane of the conditioned PT cells.

Action Potentials↗
PubMed1979

Convulsive effects of 3-aminopyridine on cortical neurones.

The authors examined the effects of 3-aminopyridine (3-AP) on pyramidal tract neurones in the motor cortex of anesthetised cats. 3-AP proved to be a strong convulsive agent. Local application of 3-AP in concentrations of 15-20 mM resulted in typical paroxysmal alterations of neuronal activity: (a) enhancement of background firing, (b) augmentation of EPSPs, (c) depression of IPSPs and (d) single and serial paroxysmal depolarization shifts (PDSs). Serial PDSs were reflected by large synchronous waves in the surface ECoG.

Administration, Topical↗
PubMed1978

Conditioned changes of synaptic transmission in the motor cortex of the cat.

Intracellular recordings were made from 117 neurons in the motor cortex of anesthetized cats. The pyramidal tract (PT) and VL nucleus of thalamus were stimulated in order to activate the neurons from two directions. 1. PT cells were conditioned by antidromic trains (10--50 cps for 4--15 s) and by paired PT and VL stimuli with different intervals and sequences. The VL-EPSPs were examined before and after conditioning, to find differences in efficacy in giving rise to spikes. The conditioning procedures resulted in a remarkable facilitation of VL-EPSPs, manifesting itself as a significant rise of efficacy in generating spikes, a shortening of peak latency and in some cases, an enhancement of background firing. 2. In non-PT neurons the same conditioning procedures elicited heterosynaptic facilitation and a rise in firing activity. 3. Intracellularly injected square wave pulses also resulted in facilitation of VL-EPSPs. 4. Pairings of PT and VL stimuli were more effective than trains in evoking conditioned changes. 5. Plastic modifications were observed in the 13.7% of the neurons subjected to conditioning procedures. 6. The authors assume that synchronous activity of the pre- and postsynaptic neurons is a highly important condition for plastic changes in the efficacy of synaptic transmission.

Animals↗