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K Halasy

Publications and source records attributed to K Halasy.

At least 37 records · Page 2Linked to original sources
PubMed1995

Properties of unitary IPSPs evoked by anatomically identified basket cells in the rat hippocampus.

Hippocampal pyramidal cells receive GABA-mediated synaptic input from several distinct interneurons. In order to define the effect of perisomatic synapses, intracellular recordings were made with biocytin-containing microelectrodes from synaptically connected inhibitory and pyramidal cell pairs in subfields CA1 and CA3 of the rat hippocampus. Subsequent physiological analysis were restricted to the category of cells, here referred to as basket cells (n = 14), which had an efferent synaptic target profile (n = 282 synaptic contacts) of predominantly somatic (48.2%) and proximal dendritic synapses (45.0%). Electron microscopic analysis revealed that in two instances identified postsynaptic pyramidal cells received a total of 10 and 12 labelled basket cell synapses respectively. At an average membrane potential of -57.8 +/- 4.6 mV, unitary inhibitory postsynaptic potentials (IPSPs; n = 24) had a mean amplitude of 450 +/- 238 microV, a 10-90% rise time of 4.6 +/- 3.2 ms and, measured at half-amplitude, a mean duration of 31.6 +/- 18.2 ms. In most instances (n = 19) the IPSP decay could be fitted with a single exponential with a mean time constant of 32.4 +/- 18.0 ms. Unitary basket cell-evoked IPSPs (n = 5) was extrapolated to be at -74.9 +/- 6.0 mV. Averages of unitary IPSPs had a mean calculated conductance of 0.95 +/- 0.29 nS, ranging from 0.52 to 1.16 nS. Unitary basket cell IPSPs (n = 3) increased in amplitude by 26.6 +/- 19.9% following bath application of the GABAB receptor antagonist CGP 55845A [correction of CGP 35845A] (1-4 microM), whereas subsequent addition of the GABAA receptor antagonist bicuculline (10-13 microM) reduced the IPSP amplitude to 13.5 +/- 3.1% of the control response. Rapid presynaptic trains of basket cell action potentials resulted in the summation of up to four postsynaptic responses (n = 5). However, any increase in the rate of tonic firing (2- to 10-fold) led to a > 50% reduction of the postsynaptic response amplitude. At depolarized membrane potentials, averaged IPSPs could be followed by a distinct depolarizing overshoot or postinhibitory facilitation (n = 4). At firing threshold, pyramidal cells fired postinhibitory rebound-like action potentials, the latter in close temporal overlap with the depolarizing overshoot. In conclusion, hippocampal basket cells have been identified as one source of fast, GABAA receptor-evoked perisomatic inhibition. Unitary events are mediated by multiple synaptic release sites, thus providing an effective mechanism to avoid total transmission failures.

Action Potentials↗
PubMed1994

[Injection sclerotherapy in acute peptic ulcer hemorrhage from the upper gastrointestinal system].

In the last 7 years the author has used urgent endoscopy together with injection sclerotherapy with 1% Aethoxysklerol at 172 times on 153 acute bleeding peptic ulcers patients. He has successfully ceased the bleeding at 92.9% of the active bleeding patients. Only 11 patients had to be operated on in acute bleeding. Repetitive bleeding occurred at 9.15%, most of them could be overcome by resclerosing. The mortality among the patients treated by injection sclerotherapy was 4.92%, among the operated and partly repetitive bleeding patients 27.2%. The total mortality rate of the 153 patients was 6.5%. In his essay the author discusses the indications and contraindications of the injection sclerotherapy, the marking of correct time limit between the injection sclerotherapy and consideration of operation, the questions of acute bleeding peptic ulcer patients admission to hospital and hospitalizing.

Acute Disease↗
PubMed1994

Diverse sources of hippocampal unitary inhibitory postsynaptic potentials and the number of synaptic release sites.

Dual intracellular recordings from microscopically identified neurons in the hippocampus reveal that the synaptic terminals of three morphologically distinct types of interneuron act through GABAA receptors. Each type of interneuron forms up to 12 synaptic contacts with a postsynaptic principal neuron, but each interneuron innervates a different domain of the surface of the postsynaptic neuron. Different kinetics of the postsynaptic effects, together with the strategic placement of synapses, indicate that these GABAergic interneurons serve distinct functions in the cortical network.

Animals↗
PubMed1993

Subdivisions in the multiple GABAergic innervation of granule cells in the dentate gyrus of the rat hippocampus.

The sources of GABAergic innervation to granule cells were studied to establish how the basic cortical circuit is implemented in the dentate gyrus. Five types of neuron having extensive local axons were recorded electrophysiologically in vitro and filled intracellularly with biocytin (Han et al., 1993). They were processed for electron microscopy in order to reveal their synaptic organization and postsynaptic targets, and to test whether their terminals contained GABA. (1) The hilar cell, with axon terminals in the commissural and association pathway termination field (HICAP cell), formed Gray's type 2 (symmetrical) synapses with large proximal dendritic shafts (n = 18), two-thirds of which could be shown to emit spines, and with small dendritic branches (n = 6). Other boutons of the HICAP neuron were found to make either Gray's type 1 (asymmetrical) synapses (n = 4) or type 2 synapses (n = 6) with dendritic spines. Using a highly sensitive silver-intensified immunogold method for the postembedding visualization of GABA immunoreactivity, both the terminals and the dendrites of the HICAP cell were found to be immunopositive, whereas its postsynaptic targets were GABA-immunonegative. The dendritic shafts of the HICAP cell received synapses from both GABA-negative and GABA-positive boutons; the dendritic spines which densely covered the main apical dendrite in the medial one-third of the molecular layer received synapses from GABA-negative boutons. (2) The hilar cell, with axon terminals distributed in conjunction with the perforant path termination field (HIPP cell), established type 2 synapses with distal dendritic shafts (n = 17), most of which could be shown to emit spines, small-calibre dendritic profiles (n = 2) and dendritic spines (n = 6), all showing characteristics of granule cell dendrites. The sparsely spiny dendrites of the HIPP cell were covered with many synaptic boutons on both their shafts and their spines. (3) The cell with soma in the molecular layer had an axon associated with the perforant path termination field (MOPP cell). This GABA-immunoreactive cell made type 2 synapses exclusively on dendritic shafts (n = 20), 60% of which could be shown to emit spines. The smooth dendrites of the MOPP cell were also restricted to the outer two-thirds of the molecular layer, where they received both GABA-negative and GABA-positive synaptic inputs.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Calretinin is present in non-pyramidal cells of the rat hippocampus--III. Their inputs from the median raphe and medial septal nuclei.

The subcortical innervation of a recently described subpopulation of non-pyramidal neurons, containing the calcium binding protein, calretinin, was investigated in the rat hippocampus using the anterograde tracer Phaseolus vulgaris-leucoagglutinin and double immunocytochemistry for calretinin and serotonin at the light and electron microscopic levels. Our results show that the GABAergic component of the septohippocampal pathway and the serotonergic raphe afferents establish multiple synaptic contacts with the calretinin-immunoreactive interneurons. The majority of the targets of both pathways were spine-free calretinin neurons known to innervate the dendritic region of the principal cells, but the GABAergic septal pathway was found to terminate also on the spiny neurons of stratum lucidum of the CA3 region and in the dentate hilus. The present results demonstrate that the serotonergic raphe-hippocampal and the GABAergic septohippocampal pathways are able to modulate dendritic inhibition of principal cells via calretinin-containing GABAergic interneurons.

Animals↗
PubMed1993

Distribution of GABAergic synapses and their targets in the dentate gyrus of rat: a quantitative immunoelectron microscopic analysis.

The dentate gyrus has been shown to receive a laminated and target selective GABAergic input (Han et al., 1993; Halasy and Somogyi, 1993), but the numerical parameters of this innervation are not known. In order to establish the relative weight of GABAergic inputs to the dendritic versus somatic regions of granule cells the numerical density and proportion of GABA-immunopositive and immunonegative synaptic boutons and their postsynaptic targets were determined in the molecular and granule cell layers of the dentate gyrus using the postembedding immunogold method. The granule cell layer contained 9% of all synapses with the remaining 91% being in the molecular layer. Altogether 17% of all synaptic boutons were GABA-immunoreactive, and they formed either type 1 or type 2 synaptic junctions. About 88% of synaptic boutons in the granule cell layer and 7-8% in the molecular layer were GABA-positive. However, the numerical density (number of synapses per unit volume) of GABA-immunoreactive type 2 synapses was calculated to be only slightly less in the molecular layer than in the granule cell layer (100 x 10(6)/mm3 tissue in the granule cell layer and about 86 x 10(6)/mm3 in the molecular layer). In addition, GABA-positive type 1 synapses were found in lower number at the border region of the two layers. The mean volume of the molecular layer of the dentate gyrus in the Wistar rat was calculated to be nearly 4 times larger than the volume of the granule cell layer (West and Andersen, 1980). This means that 25-26% of all GABAergic type 2 synapses are located in the granule cell layer, and 74-75% in the molecular layer. The mean postsynaptic targets of the GABA-immunoreactive boutons in the granule cell layer were granule cell somata (46-60%), followed by dendritic shafts (26-29%), spines (up to 14%), and axon initial segments (7-9%). In the molecular layer the dominant postsynaptic targets of GABAergic synapses were dendritic shafts (63-72%), followed by dendritic spines (26-37%). About 2-3% of the targets of all GABA-immunoreactive synapses were GABA-immunoreactive dendritic shafts or somata. Up to 98% of all GABA-immunonegative synaptic boutons were found in the molecular layer, most of them terminating on dendritic spines. These results show that the dendritic region of the granule cells provides sites for GABAergic inhibition which in quantitative terms highly outnumber the somatic region in the dentate gyrus.

Animals↗
PubMed1990

Distribution of GABA-like immunoreactivity in myenteric plexus of carp, frog and chicken.

The distribution of GABA-like immunoreactivity was studied by means of indirect immunocytochemical methods in some lower vertebrate species (carp, frog, chicken). An immunoreactive network was revealed in the myenteric plexus of the alimentary canal of carp. GABA-positive nerve cells were attached closely to the fibres in the stomach. In other gut regions immunostained neurons were less frequent. Immunoreactive fibres often formed baskets on the surfaces of immunonegative neurons along the whole length of the alimentary canal. The number of immunopositive nerve fibres and pericellular baskets seemed to be lower in the mid- and hingut than in the foregut region. A similar distribution of GABA-immunoreactivity was revealed in the frog myenteric plexus. The ganglionated foregut region possessed a relatively dense GABAergic innervation. This part of the gut contained immunostained nerve cells and fibres, while the mid- and hindgut possessed only a scanty fibre system. Chicken exhibited an extensive immunoreactive plexus for GABA, although the GABA-stained perikarya were restricted mainly to the duodenum. Further regions of the small intestine were poor in immunoreactive cell bodies, which suggests a segmental origin and arrangement of GABAergic innervation within the plexus. In all three species studied, GABA-positive fibres run into the circular muscle layer. The varicosity suggests their influence on the movement of the smooth muscles through modifying the transmitter release of neighbouring terminals.

Animals↗
PubMed1990

Histochemical characterization of myenteric plexus in domestic fowl small intestine.

The myenteric plexus of the domestic fowl (Gallus domesticus) small intestine was studied by means of silver staining, glyoxylic acid-induced fluorescence, the modified Koelle-Friedenwald method for the detection of acetylcholinesterase, NADH-diaphorase techniques and the unlabelled antibody method involving the use of an antiserum raised against GABA conjugated by glutaraldehyde to bovine serum albumin. The majority of the perikarya were in the ganglia, with an average density of 3370 +/- 942 nerve cells/cm2. Cholinesterase-positive and a few GABA-immunoreactive nerve cell bodies were seen in the myenteric ganglia, while fluorescent ganglion cells were not observed. In addition to AChE and GABA-positive nerve fibres, a rich fluorescent network of varicose and nonvaricose nerve fibres was detected, pointing to the presence of an extrinsic aminergic system in the domestic fowl myenteric plexus. Electron microscopic observations on nerve cells, axon profiles and varicosites with various vesicle populations were in good agreement with the histochemical findings.

Acetylcholinesterase↗
PubMed1989

Acetylcholinesterase in the alimentary canal of fish: light and electron microscopic detection, quantitative distribution in different segments of the gut.

The acetylcholinesterase activity was measured and histochemically localized in the alimentary tract of 2 fish species, carp (Cyprinus carpio) and tench (Tinca tinca). A comparison was made of the activities in the different gut segments. Light and electron microscopic histochemistry revealed acetylcholinesterase-positive cell bodies along the entire length of the alimentary canal in both species, between the muscular layers. Acetylcholinesterase-positive, cholinergic motor endplates were frequent in the esophagus of both carp and tench, and they were also present in the striated muscular layers of the tench stomach and midgut. The enzyme activity detected by the method of Ellman et al. (1961) was highest (16.3 U/mg protein) in the tench foregut and midgut, while it was at the same lower level (9.5 U/mg protein) in each segment of the carp gut and in the tench hindgut. The morphological findings and the higher acetylcholinesterase activity in the tench foregut and midgut suggest that the enteric striated musculature is endowed with denser cholinergic innervation than the enteric smooth musculature.

Acetylcholinesterase↗
PubMed1989

Consecutive diaphorase-acetylcholinesterase histochemistry in the myenteric plexus of frog stomach.

An investigation was made on the frog stomach myenteric plexus with 2 different histochemical techniques. Neuronal perikarya were stained with nicotinamide-adenine-dinucleotide-diaphorase (NADHd), while the acetyl-cholinesterase (AChE) staining showed rather the axoarchitectonic arrangement of the frog myenteric plexus. In double-labelled "whole mounts", NADHd-positive cell bodies and AChE-positive nerve processes were revealed. Some of the nerve cells and neuronal processes did not exhibit AChE activity at all. Since glyoxylic acid-induced fluorescence (GIF) was not detected in the myenteric plexus, the presence of catecholamines can be excluded. As a consequence of these observations, we suggest the presence of a non-cholinergic, non-adrenergic intrinsic neuronal system in the frog stomach myenteric plexus, containing purines or peptides as transmitters.

Acetylcholinesterase↗
PubMed1988

Enteric neuromuscular junctions: comparison of ultrastructural features in different phylogenetic groups.

The enteric neuromuscular junctions of snail (Helix pomatia), locust (Locusta migratoria migratorioides), cockroach (Periplaneta americana), carp (Cyprinus carpio) and tench (Tinca tinca) were studied by means of different light and electron microscopic methods. The nitroblue tetrazolium staining revealed that the myenteric plexuses of the above species are composed of nerve cells, a network of varicose nerves and nerve bundles. Instead of highly organized ganglia, single neurons or small groups of 2-4 cells are characteristic of the invertebrates and fish studied. Catecholaminergic fluorescence induced by glyoxylic acid was detected in the muscular layer of the entire alimentary tract in snail and the hindgut of tench. Fluorescent nerves and perikarya were frequent in the snail gut, while only nerves and no perikarya were found in tench. A close contact between enteric muscles and nerves is the most common form of enteric neuromuscular junction in both the smooth (i.e. the molluscan and fish gut) and the striated (i.e. the insect gut) musculature. The striated musculature (i.e. the insect gut, the oesophagus of carp, and the oesophagus, stomach and the midgut of tench) also receives a synaptic input. Cytochemical evidence is provided of the cholinergic character of fish motor endplates. The ultrastructural appearance and vesicle population of certain nerve terminals suggest a universal role of aminergic and peptidergic control in gut motility.

Animals↗
PubMed1988

Visualization of non-synaptic release sites in the myenteric plexus of the snail Helix pomatia.

Following conventional glutaraldehyde-osmium tetroxide fixation, a rich myenteric plexus was detected in the gastrointestinal tract of the snail Helix pomatia. Although hundreds of nerve processes were observed in the extensive myoneural neuropil, true synaptic specializations were not recognized in them. In the absence of synaptic specializations, tannic acid-Ringer incubation was applied to visualize the non-synaptic release sites in the enteric nerve plexus. After incubation for 1 h, a great number of exocytosis profiles were recorded at nerve-muscle contacts, at axoglial connections and in the myoneural neuropil. The frequency of occurrence of exocytosis profiles was the same for adrenergic and peptidergic fibres. In some gut wall areas, a dense staining of both basal lamina and collagen fibres was observed. Invagination of dense basal lamina into the omega-shaped profiles of the axolemma led to "false exocytosis" profiles. A detailed morphological analysis is needed to distinguish false exocytosis profiles from the true transmitter-releasing loci.

Animals↗
PubMed1987

On the nerve plexus of the chicken gizzard.

The Auerbach's plexus of the gizzard was stained in toto in adult chicken and in young and newly-hatched chicks. The plexus lies immediately beneath the serosa and extends over 55% of the surface of the organ, covering its cranial and caudal poles and the two curvatures. The areas into which the plexus does not extend (i.e., most of the ventral and the dorsal surface) are those where the muscle is covered by the laminar tendon of the gizzard. The ganglia are large, often with hundred of neurons, and have short and broad connecting strands. They are surrounded by a capsule of connective tissue. The ganglion neurons are discoidal and in the adult they measure up to 50 microns in diameter, each being surrounded by a set of glial cells. A few small neurons persist in the adult; in the newly-hatched chick these are predominant, but some large neurons up to 25 microns in diameter are already present. The ultra-structural features of the ganglia of the Auerbach's plexus include the abundance of axo-somatic synapses, as well as numerous axo-dendritic synapses, the presence of intra-ganglionic bundles of collagen fibrils and blood vessels, the abundance of glial cells. In addition to the plexus beneath the serosa, the gizzard has many small intramuscular ganglia located throughout the musculature (which is exclusively circular). These ganglia do not have a connective tissue capsule and are made of small and tightly packed neurons.

Animals↗
PubMed1987

Fine structure of the neuromuscular junctions in the alimentary tract of phylogenetically different animal species.

Authors studied the fine structural characteristics of the neuromuscular junctions in the alimentary tract of phylogenetically different animal species. Nearly in each studied species the so-called close contacts were observable, where the sarcolemma and axolemma establish a junction; the gap of this contact is 10-100 nm wide, and the neurotransmitters can affect the muscles through non-synaptic release (exocytosis). The junctional gap is widest in the gut wall of earthworm: 100-200 nm. Only close contacts are to be found in the alimentary canal of snail, and here, the junctional gap is as narrow as 10-15 nm. Beside close contacts synaptic neuromuscular junctions also occur in the locust gut. Their fine structural organization refer to that of chemical synapses. As in the tench intestine both striated and smooth muscular elements can be found, motor endplates as well as close contacts take part in their innervation. Only close contacts are in the smooth muscular layer of domestic fowl. Authors emphasize the role of close contacts in the regulation of gut peristalsis and only secondary importance is attached to other different junctions.

Animals↗
PubMed1986

Quantification of immunogold labelling reveals enrichment of glutamate in mossy and parallel fibre terminals in cat cerebellum.

The glutamate immunoreactivity of different cell populations was compared quantitatively in the cerebellar cortex of cat, using an antiserum raised against glutamate coupled to bovine serum albumin by glutaraldehyde. Neuronal and glial processes were identified on serial electron microscopic sections which were processed by a postembedding immunogold procedure. The surface density of colloidal gold particles was used for statistical comparison of the relative levels of glutamate in cell populations, or in different parts of the same population. The terminals of mossy and parallel fibres had significantly higher levels of glutamate immunoreactivity than Golgi cell terminals, granule cell dendritic digits, Purkinje cell dendrites or dendritic spines. Golgi cell terminals were identified by their position and GABA immunoreactivity as revealed by immunogold in serial sections. The dendritic digits of the putative glutamatergic granule cells had significantly higher glutamate immunoreactivity than did Purkinje cell dendrites and dendritic spines. Glial cell processes in the molecular layer had lower level of glutamate immunoreactivity than any of the neuronal processes. The results demonstrate that the highest levels of glutamate immunoreactivity occur in mossy and parallel fibre presynaptic terminals that are known to have an excitatory effect. This supports previous suggestions that glutamate may be a transmitter at these synapses. The measurement of the levels of putative amino acid transmitters in identified neuronal populations, or in different parts of the same population, could have wide applications in studies on the chemical neuroanatomy of the nervous system.

Animals↗
PubMed1986

Fine structure of the neuromuscular junction in the small intestine of a teleostean fish: tench (Tinca tinca L.).

Innervation of the midgut musculature has been studied in the tench (Tinca tinca) by light and electron microscopic methods. Smooth and striated muscle layers of the tunica muscularis of the gut are innervated by the same nerve bundles. Thick nerve bundles are found in the connective tissue between the two muscle layers projecting branches into both the smooth and striated muscle layers. The nerve fibres are varicose, the varicosities contain various vesicle populations. Some of these comprise small clear vesicles (measuring 40 nm in diameter), and a few dense-core vesicles (120 nm in diameter), while in others the amount of dense-core vesicles is higher; furthermore there are varicosities containing granules of peptidergic character measuring 200 nm in diameter. Nerve fibres often form neuropil in which synapses have not been observed. Axon terminals establish parallel membrane contacts with the muscle cells without synaptic specialization in the smooth muscle layer. Innervation of the striated muscle layer seems to be poor. Motor end-plates could not be found on the muscle fibres of the midgut, while these are common in the oesophagus, where the occurrence of striated muscle fibres is dominant.

Animals↗