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N Halász

Publications and source records attributed to N Halász.

At least 19 recordsLinked to original sources
PubMed1996

Modulation by thyroid hormones of the development of external plexiform layer in the rat olfactory bulb.

Width of the external plexiform layer in olfactory bulbs and mean area of mitral and granule cell dendritic and glial processes were measured of normal, hypo- and hyperthyroid rat pups at the age of 24 days. Hypothyroidism was induced by treating the rats with a reversible goitrogen 6-n-propyl-2-thiouracil dissolved in their drinking water, while the hyperthyroid group was given water containing thyroxine. The 6-n-propyl-2-thiouracil treatment was begun on gestational day 18 and on the day of birth. Thyroxine treatment started on the day of birth. Both treatments were continued till the day of sacrifice. A significant decrease in the width of the external plexiform layer of the olfactory bulb in the prenatally 6-n-propyl-2-thiouracil treated group and a significant increase in the width of the external plexiform layer of the hyperthyroid group was shown by the Student's paired t-test. The areas of neuronal and glial processes were measured at electron microscopic level by using an IBAS image analysing system. A significant decrease was found by the Kruskal-Wallis test and Dunn's range test in the mean area of (1) mitral cell dendrites in the prenatal 6-n-propyl-2-thiouracil treated group, (2) granule cell dendrites in both the postnatally 6-n-propyl-2-thiouracil treated and in the hyperthyroid groups and (3) glial processes in the thyroxine treated group comparing to controls.

Animals↗
PubMed1994

Maturation of the GFAP-immunopositive glial network is delayed in the olfactory bulbs of rats subjected to early, low-dose X-irradiation.

Young rats were subjected to low-level, repeated doses of x-irradiation from a Co60 source and examined for the presence and arrangement of their GFAP-immunopositive system at the light and electron microscopic levels. In 2-week-old control rats, labelled cells were already distributed homogeneously throughout the bulb, while in the experimental animals, a (newborn- and early postnatal-type) radial arrangement of immunoreactive fibres continued to persist even until the end of the fourth postnatal week. This delay in the maturation of the GFAP-immunopositive glial system may contribute to the hindered development of the bulbar neurones, neuronal connections, and field potentials, as found in earlier studies.

Animals↗
PubMed1994

Low-dose X-irradiation reduces neuronal and glial cell populations in the juxtaglomerular region of rat olfactory bulb.

Rats were subjected to fragmented, low-dose, whole body X-ray irradiation from last prenatal to third postnatal week of life. Consequences of the irradiation were examined at the cellular and synaptic level and evaluated by light- and electron microscopy. The fate of several cell types of the glomerular layer was assessed by semi-quantitative morphometry. All known neuronal and glial cell subtypes and varieties of synaptic connections of this layer were spared. X-irradiation, however, had a marked influence on the composition of the juxtaglomerular cell population even at the youngest examined, two week old rat pups and this impact still persisted, without recovery, at six weeks of age. Density (and so, absolute number) of the small periglomerular neurones and astrocytes was depressed to 52-55% and 32-48% of control, respectively, while the density of the superficial tufted cells and the rest of glial cells remained at the control level. These results suggest that the small periglomerular neurones may primarily be responsible for the shrinkage of this layer. This means, in the same time that, selective depression of the development of a superficial interneuron (in addition to the deeply situated granule cells) could be achieved.

Animals↗
PubMed1993

Early X-irradiation of rats. 5. Influence of irradiation on the development of extracellular field potentials evoked by antidromic stimulation.

Rat pups were treated by low, fragmented and repeated doses of X-rays, from late prenatal days until the end of the third postnatal week. Extracellular field potentials, evoked by antidromic stimulation of the lateral olfactory tract were recorded in different layers of the olfactory bulb at 1, 2, 3 and 6 weeks of age, from control (non-irradiated) and experimental rats. Development of the field potentials was analysed in both groups of animals. In controls, the amplitude of responses was gradually increasing along with age while the latency of peaks decreased; inhibitory waves were tuned even after the third postnatal week. When compared to controls at similar ages, irradiated rats had smaller peak amplitude of responses and the shortening of the response latency was delayed. In addition, a new, late-appearing excitatory wave component was observed in the granule cell layer by the sixth week. The effect of irradiation on field potentials of the olfactory bulb is discussed in light of the marked reduction of the inhibition in the local neuronal assembly, which is also indicated by the depressed development of its structural and neurochemical correlates.

Animals↗
PubMed1993

Fast regeneration of the olfactory nerve in goldfish: fine structure and behaviour.

Normal olfaction-guided behaviour in goldfish returns surprisingly fast after bilateral transection of the olfactory nerve (ON). In order to find correlation between morphological changes and behaviour we performed parallel studies on the behaviour of the fish and the ultrastructure of the olfactory bulb in axotomised fish. Signs of degeneration were most prominent between the 4th and 6th day post-operatively. First appearance of regenerated ON fibres and terminals was noted on the 10th post-operative day. ON terminals became frequent again two weeks after the operation. This supports earlier suppositions that morphological regeneration plays a crucial role in the fast and complete restoration of olfaction-guided behaviour.

Animals↗
PubMed1990

An unbiased estimation of the total number of synapses in the superior cervical ganglion of adult rats established by the disector method. Lack of change after long-lasting sodium bromide administration.

Previous physiological and morphological studies suggested that sodium bromide promotes synaptogenesis of implanted cholinergic nerves in the superior cervical ganglion of adult rats. To check whether sodium bromide also modifies synaptic numbers in the intact ganglion, quantitative electron microscopy was used to determine the total number of synaptic junctions in the superior cervical ganglion of adult rats. Untreated controls were compared with animals which drank water containing 280 mg ml-1 sodium bromide for 7 days. The disector method, an unbiased estimator of volume density of certain particles, has been adapted to this particular case. To accomplish the task, an on-line counting procedure was developed, which permitted the efficient adaptation of the disector method for the superior cervical ganglion, in which the synapses are known to be distributed sparsely. Three pairs of (control and treated) ganglia have been completely processed by three independent examiners. The estimated number of synapses in the ganglia ranged from 4 to 8 million while the volumes of the ganglia varied from 0.65 to 0.90 mm3. Evaluation of the results showed that variations in the total number of synapses were in each case proportional to differences in ganglionic volumes. This suggests that: (1) sodium bromide does not lead to changes in density of intrinsic synapses; and (2) the morphogenetic action of sodium bromide on principal ganglion cells previously described is essentially postsynaptic and requires additional presynaptic elements to increase the number of synapses.

Animals↗
PubMed1987

Plasticity of dendrodendritic microcircuits following mitral cell loss in the olfactory bulb of the murine mutant Purkinje cell degeneration.

Mitral cells of the olfactory bulb typically form reciprocal dendrodendritic synapses with anaxonic interneurons, granule cells, within a sublamina of the external plexiform layer. As a result of mitral cell loss in the murine mutant Purkinjie cell degeneration (PCD), subpopulations of these granule cells are denervated. The present report examines the capacity of these denervated interneurons to form new dendrodendritic microcircuits with a second population of olfactory bulb neurons, tufted cells. Quantitative ultrastructural assessments were made of the morphology and distribution of dendrodendritic circuits in the olfactory bulbs of normal heterozygous littermates and affected homozygous recessive PCD mice following mitral cell loss. There were no apparent morphological characteristics that distinguished the reciprocal synaptic connections formed by mitral cells from those formed by tufted cells. However, the segregation of mitral cell dendrodendritic circuits in the deep sublamina of the external plexiform layer (EPL) and tufted cell circuits in the superficial sublamina provided the basis for a comparative analysis of synaptic organization following mitral cell loss. Following mitral cell loss there was a significant reduction in the area occupied by characteristic mitral cell dendrites within the deep sublamina of the EPL. A slight but nonsignificant increase in the area occupied by granule cell spines was also observed. The number of synaptic appositions involving granule cells decreased slightly, the number involving tufted cells increased significantly in the mutant mice. This indicates that many granule cell spines survive denervation and establish new reciprocal dendrodendritic synapses at available sites on tufted cells. In both the control and mutant mice the ratios of symmetrical:asymmetrical dendrodendritic synapses closely approached 1. This demonstrates that not only do the denervated spines receive new afferent input from tufted cell dendrites, but they also establish the reciprocal efferent projection. These data are discussed in terms of the sublaminar organization of dendrodendritic microcircuits in the olfactory bulb and their capacity of plasticity and reorganization following pertubation.

Animals↗
PubMed1987

Early X-irradiation of rats--II. Effect on granule cells and their dendrodendritic synapses in the olfactory bulb.

Low, repeated doses of X-rays from a Co60 source were used to impair the development of the granule cells and their dendritic terminals in the olfactory bulb, and the resulting effect was studied under light and electron microscopes at 9 days of age. Irradiation of rats from embryonic day 18 (in utero) to postnatal day 5 resulted, among others, in maldevelopment of the (internal) granule cell and external plexiform layers. This was accompanied by a decrease in the number and the density of the granule cells, and the remaining granule cells contained less ribosomes, regardless of their position within the layer. This implies that both supposed subtypes of granule cells were effected. In the external plexiform layer, a reduced number of mature dendrodendritic synapses and signs of harmed granule gemmules were observed. The results suggest that intrauterinal plus postnatal irradiation with low, repeated doses of X-rays may be an effective tool impairing the development of prenatally forming neurons.

Animals↗
PubMed1987

Autoradiographic localization of high affinity uptake sites for 3H-D-aspartate in the rat olfactory bulb.

In order to reveal excitatory amino acid-ergic neuronal connections in the rat olfactory bulb, uptake sites for the tritiated D-aspartic acid were analyzed by high resolution autoradiography. Light microscopy revealed both cellular and terminal-like uptake. Based on electron microscopy, overwhelming majority of the cellular uptake was assigned to glial cells. A fairly high number of labelled terminals appeared in the surroundings of the mitral cell somata, within the deepest portion of the external plexiform layer, in the internal plexiform layer and in the outer half of the granule cell layer. Labelled terminals synapsed onto likely granule cell dendrites or spines, at asymmetric membrane thickenings. These results suggest that, although the output neurons may not utilize glutamic or aspartic acid as their transmitters, these amino acids may, however, contribute to the bulbar neurotransmission, as mediator substances of a subgroup of centrifugal fibers to the olfactory bulb.

Animals↗
PubMed1986

Early X-irradiation of rats. 1. Methodological description and morphological observations on the olfactory bulb.

X-ray irradiation of rats in utero and during early postnatal days was performed using low, fragmented doses from a 60Co radiation source. Different radiation schedules were applied in order to impair the development of certain neurons. The effect of radiation on the main olfactory bulb was characterized in several ways. Early X-ray irradiation resulted in retardation of dams and young pups and an underdevelopment of the bulb and its main histological layers, especially the granule cell and external plexiform layers, but a disturbed glomerular development was also apparent. The resulting damage was proportional to the magnitude of the irradiation. The present technique seems to be useful in eliciting damage in separate populations of pre- or postnatally forming neurons.

Age Factors↗
PubMed1985

Tyrosine hydroxylase and 28K-vitamin D-dependent calcium binding protein are localized in different subpopulations of periglomerular cells of the rat olfactory bulb.

Successive incubations of rat olfactory bulb cryostat sections with antibodies against the chick 28K-vitamin D-dependent calcium (Ca) binding protein and tyrosine hydroxylase were performed, and the distribution of the label was examined in the fluorescence microscope. Both antibodies labeled cells and processes in highest number in the glomerular layer. The two immunopositivities were not co-localized in the same neurons. This suggests that the presence of this Ca-binding protein is not a necessary prerequisite for dopaminergic neurotransmission in periglomerular neurons.

Animals↗
PubMed1983

Autoradiographic analysis of [3H]dopamine and [3H]dopa uptake in the turtle olfactory bulb.

Uptake and retention of exogenous tritiated dopamine and L-dopa was observed within turtle olfactory bulb slices. In the more superficial layers, periglomerular and superficial tufted cells, as well as their processes, and intraglomerular dendrites were recognized as labeled. Within the deeper part of the bulb, some labeled cells between the tanycytes, as well as nerve fibers and terminals within the granule cell layer, are reported. The results confirm the presence of specific intrinsic dopaminergic cells within the reptilian olfactory bulb.

Animals↗
PubMed1983

Evoked field potential analysis of dopaminergic mechanisms in the isolated turtle olfactory bulb.

Dopaminergic mechanisms were analyzed in an isolated preparation of the turtle olfactory bulb. Field potentials were evoked by antidromic or orthodromic stimulation, and the effects determined of pharmacological manipulations of the bathing medium. In the presence of dopamine or a dopamine agonist, apomorphine, there was a reduction of amplitude and delay of onset of the component of the field potentials due to granule cell responses; fluphenazine, a dopamine antagonist, had generally opposite effects. Using paired volleys, it was found that the suppression of the response to the second test volley was reduced in the presence of dopamine or apomorphine, but enhanced in the presence of fluphenazine. The most likely explanation of these results is that exogenous dopamine depresses the response of mitral cells, which in turn decreases the dendrodendritic synaptic excitation of granule cells and reduces their inhibitory feedback onto mitral cells. This suggests that the dopaminergic cells in the bulb may suppress mitral cells by modulating excitable mechanisms in the mitral dendritic membrane, or modulating long-lasting synaptic potentials.

Animals↗
PubMed1981

Selectivity of neuronal [3H]GABA accumulation in the visual cortex as revealed by Golgi staining of the labeled neurons.

[3H]GABA was injected into the visual cortex of rats in vivo. The labeled amino acid was demonstrated by autoradiography using semithin sections of Golgi material. Selective accumulation was seen in the perikarya of Golgi-stained, gold-toned, aspinous stellate neurons. Spine-laden pyramidal-like cells did not show labeling. This method gives direct information about the dendritic arborization of a neuron, and its putative transmitter, and allows the identification of its synaptic connections.

Animals↗
PubMed1981

Localization of glyceraldehyde-3-phosphate dehydrogenase in intact human erythrocytes. Evaluation of membrane adherence is autoradiographs at low grain density.

Human erythrocytes were treated with highly tritiated [3H]iodoacetate under conditions when half of the label became attached to glyceraldehyde-3-phosphate dehydrogenase. After fixation, the cells were subjected to electron microscopic autoradiography. For the evaluation of distribution of grains, which were relatively few, a computerized method was developed. Statistical analysis of data showed the significant adherence of grains to the cell membrane. The results support the view that glyceraldehyde-3-phosphate dehydrogenase is localized near the membrane in the intact erythrocyte.

Erythrocyte Membrane↗