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B Halász

Publications and source records attributed to B Halász.

At least 55 records · Page 3Linked to original sources
PubMed1989

Regulation of the gonadotropin-releasing hormone (GnRH) neuronal system: morphological aspects.

This paper gives a brief survey of the structural organization of the GnRH neuronal system and of the chemically identified axons impinging directly on GnRH neurons. There are great species differences in the localization of the GnRH nerve cells. In the human and monkey brain, they are concentrated in the medial basal hypothalamus. GnRH neurons project not only to the median eminence, but terminate also on other nerve cells including GnRH elements. Under physiological circumstances the GnRH neurons are influenced by nervous structures in- and outside the medial basal hypothalamus and by ovarian and other hormones. Recent, primarily immunocytochemical studies indicate that catecholaminergic, serotoninergic, GABA-ergic, opioid peptidergic, immunoreactive substance-P and corticotropin releasing factor-immunoreactive axons synapse on GnRH neurons. These findings provide morphological basis for the view that neurons operating with these compounds can act directly on GnRH release. Direct connections of the GnRH neurons demonstrated so far does not exclude the possibility that these neurotransmitters or neuromodulators influence GnRH release also at other levels of the CNS.

Animals↗
PubMed1989

Transitory increase in plasma FSH and LH levels induces early vaginal opening and corpus luteum formation in ovarian transplants of rats ovariectomized at 20 days of age.

The effect of a transitory increase in plasma FSH and LH levels on puberty has been investigated. Hormonal changes were induced by bilateral ovariectomy (OVX) at 20 days of age followed by implantation of two ovaries (donor animals 20-day-old) beneath the kidney capsule 1, 2 or 3 days later. In an other group of animals the two interventions were made in reversed order. Rats in which OVX was made first showed early vaginal opening. If ovarian implantation preceded OVX, these two interventions did not affect the time of vaginal opening. More than 1/3 of the ovarian implanted animals exhibiting early opening of the vagina contained corpora lutea three days after vaginal opening. FSH and LH levels of OVX + ovary implanted rats were from the third day on following implantations markedly different from the OVX controls and were in the range of intact or sham-operated rats. The present findings indicate that a transitory increase in plasma gonadotropin levels around twenty days of age may lead to precocious puberty.

Age Factors↗
PubMed1988

Further studies on circadian hormone rhythms after local pharmacological destruction of the serotoninergic innervation of the rat suprachiasmatic region before the onset of the corticosterone rhythm.

In previous studies we observed that local pharmacological destruction of the serotoninergic innervation of the hypothalamic suprachiasmatic nucleus before the onset of the circadian plasma corticosterone rhythm interferes with the appearance of the corticosterone rhythm up to the age of two months. In the present investigations we studied other hormone rhythms in such rats and tested animals for corticosterone rhythm when they were older than two months. We found normal circadian fluctuations in plasma testosterone and prolactin levels, variations in growth hormone concentrations, but no changes in plasma corticosterone levels of 63-day-old rats receiving 5,7-dihydroxytryptamine, a neurotoxin selectively destroying the serotoninergic structures, into the suprachiasmatic nucleus at the age of 16 days. Rats did show circadian variations in plasma corticosterone concentrations when tested 3 months after treatment with the neurotoxin. In these latter animals, a significant amount of serotonin-immunoreactive fibers and terminals were evident in the suprachiasmatic nucleus. Only a very few of such elements were seen in rats with a shorter postoperative survival. Our data support the view that serotoninergic innervation of the suprachiasmatic nucleus is essential for the onset of the circadian fluctuations of plasma corticosterone concentrations.

5,7-Dihydroxytryptamine↗
PubMed1988

Demonstration of serotoninergic axon terminals on somatostatin-immunoreactive neurons of the anterior periventricular nucleus of the rat hypothalamus.

Using a combination of electron microscopic autoradiography and immunocytochemistry, the connections between serotoninergic axons and somatostatin neurons of the anterior periventricular nucleus of the rat hypothalamus were examined. The serotoninergic elements were identified after selective uptake of tritiated serotonin and the somatostatin neurons with immunocytochemistry. Synaptic connections between labeled serotoninergic nerve endings and somatostatin-immunoreactive neurons were observed. This finding provides morphological evidence for a direct influence of serotoninergic elements on somatostatin neurons of the anterior periventricular nucleus projecting to the median eminence of the hypothalamus.

Animals↗
PubMed1988

Hypothalamus and puberty.

The effect of a transitory increase in plasma FSH and LH levels during the prepubertal period on puberty has been investigated. Twenty-day-old rats had been bilaterally ovariectomized and 24 hr later they received two ovaries of infantile rats beneath the kidney capsule. These rats exhibited precocious puberty. Animals into which two additional ovaries had been transplanted first and the next day their own ovaries removed showed puberty at the same time as controls. Additional investigations provided evidence that the ovariectomized and ovary implanted rats plasma FSH and LH levels were in the control range four days after implantation. The findings support the assumption that the hypothalamic lesion-induced precocious puberty is due rather to a transitory enhanced release of gonadotropin releasing hormone by the lesion than to the destruction of sex-steroid sensitive structures inhibiting the release of gonadotropic hormones in prepubertal rats.

Animals↗
PubMed1988

Neural control of ovulation.

Pituitary gonadotrophin function is controlled to a great extent by the central nervous system and by the feedback action (positive and negative) of sex steroids. Neural structures involved in this mechanism may be divided into two levels. The first level is represented by the nervous structures releasing gonadotrophin-releasing hormone (GnRH) in a pulsatile manner into the portal circulation. The gene encoding the precursor protein for GnRH has been described recently. The precursor protein appears to be composed of 92 amino acids, in which the GnRH decapeptide is preceded by a signal peptide and followed by a peptide termed GAP for GnRH-associated peptide. The GnRH-synthesizing neurones and the nervous structures synchronizing the GnRH discharge (pulse generator) in the monkey, and probably also in the human, reside in the medial basal hypothalamus, which appears to have a highly integrated structure. The GnRH pulse generator is influenced by nervous structures outside the medial basal hypothalamus (second level of control) as well as by ovarian and other hormones. These influences probably impinge directly or indirectly on the hypothalamic oscillator. Concerning the chemical nature of the substances mediating the action, a large number of neurotransmitters and neuropeptides have been reported to influence GnRH secretion.

Animals↗
PubMed1988

Pituitary gonadotropin-releasing hormone binding sites in persistent estrous rats.

Pituitary gonadotropin-releasing hormone (GnRH) binding sites were studied in persistent estrous rats. For comparison females at different stages of the estrous cycle, ovariectomized animals, and intact males were examined. Persistent estrus was induced by a hypothalamic knife cut, administering testosterone to neonatal rats, or by constant illumination. Rats showing spontaneously such alteration were also used in the experiment. Besides pituitary GnRH-binding sites, the GnRH content of the median eminence and plasma luteinizing hormone, follicle-stimulating hormone, estradiol, and progesterone concentrations were determined. Pituitary GnRH receptors changed during the estrous cycle with the highest concentrations observed on proestrus. In rats in persistent estrus, pituitary GnRH-binding sites varied between proestrous and estrous values of cyclic females. Ovariectomy resulted in a significant increase in receptors. Depending on how the persistent estrous syndrome was induced, very different amounts of GnRH were found in the median eminence of the various groups. Our data indicate that the GnRH-binding sites on pituitary cells of persistent estrous rats are in essence not changed.

Animals↗
PubMed1988

Ontogenesis of the three parts of the fetal rat adenohypophysis. A detailed immunohistochemical analysis.

The sequential changes in the histological pattern of anterior pituitary cytodifferentiation of the rat are described. The first labeled cells were ACTH positive and were detected in the pars tuberalis on postconceptual day 13. On day 14 ACTH cells also appeared in the ventral periphery of the pars distalis. On fetal day 15 the pars tuberalis anlage was characterized by numerous well-stained ACTH cells and by some weakly labeled FSH-beta, LH-beta, TSH-beta, GH and PRL cells while the pars distalis showed only ACTH positivity. On day 16 of gestation the ACTH cells were equally distributed throughout the whole pars distalis, while LH-beta, FSH-beta, TSH-beta, PRL and GH immunoreactive cells were localized either in the ventral region of the pars distalis only or were evenly distributed throughout the pars distalis. The present immunocytochemical data suggest that in the pars distalis the hypophyseal cell differentiation follows a clear rostrocaudal, ventrodorsal direction and that the time sequence of the functional differentiation of the adenohypophysis is pars tuberalis, pars distalis and pars intermedia.

Adrenocorticotropic Hormone↗
PubMed1986

Circadian corticosterone rhythm did not develop in rats seven weeks after destruction with 5,7-dihydroxytryptamine of the serotoninergic nerve terminals in the suprachiasmatic nucleus at the age of 16 days.

In order to study the role of the serotoninergic innervation of the hypothalamic suprachiasmatic nucleus (SCN) in the development of the circadian rhythm of corticosterone 5,7-dihydroxytryptamine (5,7-DHT) selectively destroying the serotoninergic structures was injected into the cell group of 16-day-old male rats prior to the appearance of the corticosterone rhythm. Rats treated with 5,7-DHT did not show circadian fluctuations in plasma corticosterone concentrations 3, 5 and 7 weeks after the injection of the neurotoxin. Their hypothalamo-pituitary-adrenal system responded to ether stress. Immunocytochemistry revealed that only a very few serotonin immunoreactive elements were visible in the SCN of the 5,7-DHT-treated rats. The results indicate that serotoninergic innervation of the SCN is essential for the development of the corticosterone rhythm.

5,7-Dihydroxytryptamine↗
PubMed1986

Synaptic connections between serotoninergic axon terminals and tyrosine hydroxylase-immunoreactive neurons in the arcuate nucleus of the rat hypothalamus. A combination of electron microscopic autoradiography and immunocytochemistry.

A combination of electron microscopic autoradiography and immunocytochemistry was used to examine the connections between serotoninergic axons and dopaminergic neurons of the arcuate nucleus of the rat hypothalamus. The serotoninergic elements were identified after selective uptake of tritiated serotonin and the dopaminergic neurons with tyrosine hydroxylase cytochemistry. Synaptic junctions between labeled serotoninergic nerve endings and tyrosine hydroxylase-immunoreactive neurons were observed, providing a structural basis for a direct influence of serotoninergic elements on tuberoinfundibular dopaminergic neurons.

Animals↗
PubMed1986

Quantitative analysis of dendritic protrusions in the medial preoptic area during postnatal development.

Dendritic architecture and distribution of dendritic protrusions were studied on Golgi-impregnated neurons in the medial preoptic area (MPOA) of infant rats (7 and 20 days old), of animals at puberty (34 days old) and of postpubertal rats (90 days old) using computerized image analysis. The protrusions showed a peak distribution on the proximal portion of the dendritic tree in infant rats. At puberty and in postpubertal animals protrusions disappeared almost completely along the most proximal portion of the dendritic tree. The data suggest that differentiation of certain MPOA neurons is still in progress at puberty.

Age Factors↗
PubMed1986

Ependymal lining of infundibular recess in perinatal rats: relationships with portal capillaries and permeability.

Structure and permeability of the ependymal lining the infundibular recess were studied in perinatal rats with silver impregnation, electron microscopy, radioautography, and tracer techniques. According to our data basal processes of ependymal cells reach the primary portal plexus linking the 3rd ventricle and the hypophysial portal system all through the perinatal period. After birth, some of the processes penetrate into the perivascular space of the primary portal plexus and abut there on the endothelium of capillaries. Ependymal cells of fetuses and neonates are joined by specialized junctions (tight junctions, gap junctions and zonulae adhaerentes). Intraventricularly injected ionic lanthanum crosses the ependymal lining of fetuses both trans- and extra-cellularly everywhere in the infundibular recess. By postnatal day 9 only the rostral portion of the recess remains readily permeable. Caudally, extracellular leakage becomes highly restricted, apparently due to the appearance of circumferential tight junctions. Finally, [3H]dopamine seems to penetrate through the ependymal lining in the same way as ionic lanthanum entering the portal capillaries. These findings suggest that the adenohypophysiotropic neurohormones can penetrate from the cerebrospinal fluid into the portal circulation from the very beginning of the establishment of the hypothalamo-hypophysial functional relationships during ontogenesis.

Animals↗
PubMed1986

Episodic prolactin and growth hormone secretion not related to the actual suckling activity in lactating rats.

In order to characterize the secretion pattern of prolactin and GH in freely behaving lactating rats, frequent serial blood samples were collected through indwelling atrial cannulae and their prolactin and GH concentrations determined by radioimmunoassay. At the time of blood sampling, physical contact with the pups was recorded. Plasma prolactin and GH levels showed episodic changes which were independent of each other and there was no apparent correlation between hormone levels and contact between mother and pups. The data suggest that there are episodic fluctuations in plasma prolactin and GH concentrations in lactating rats. These changes do not appear to be closely correlated with the proximity of the mother to her pups.

Animals↗
PubMed1986

Further data on the origin of gonadotropin releasing hormone in the median eminence of the rat hypothalamus.

Gonadotropin releasing hormone (GnRH) content of the two halves of the median eminence of the rat hypothalamus was determined by radioimmunoassay three weeks after three different unilateral knife cuts around the preoptic area. A unilateral cut in front or above the area caused a more than 25% decrease in the GnRH content of the two halves of the median eminence. A cut lateral to the preoptic region had only a slight effect similar to that observed after sham operations. The data suggest that probably more than 50% of the rat median eminence GnRH derives from outside the preoptic-suprachiasmatic region. The GnRH fibres projecting to the median eminence but arising from outside the preoptic region, probably mainly from GnRH perikarya in the limbs of the diagonal band of Broca and septum, enter this area partly from rostral and partly from above, but not from lateral direction. partly from rostral and partly from above, but not from lateral direction. Several of these fibres probably cross before terminating in the median eminence.

Animals↗
PubMed1986

Unilateral vagotomy inhibits compensatory kidney growth after unilateral nephrectomy in rats.

The effect of unilateral vagotomy on compensatory renal growth that follows unilateral nephrectomy was studied. Unilateral vagotomy inhibited the usual compensatory growth of the remaining kidney. Unilateral vagotomy did not effect kidney weight in animals with two kidneys. Data indicate that the vagus nerve is involved in the development of compensatory kidney hypertrophy.

Animals↗
PubMed1985

Demonstration of serotoninergic axons terminating on luteinizing hormone-releasing hormone neurons in the preoptic area of the rat using a combination of immunocytochemistry and high resolution autoradiography.

The synaptic relationship between serotoninergic terminals and luteinizing hormone-releasing hormone-containing neurons was investigated in the medial preoptic area using a combined technique. Axon terminals selectively taking up 5-[3H]hydroxytryptamine were labelled autoradiographically and luteinizing hormone-releasing hormone-containing neuronal elements were identified by means of immunocytochemistry. Synaptic contacts were observed between tritiated 5-hydroxytryptamine-labelled boutons and luteinizing hormone-releasing hormone-immunoreactive dendrites. About 5% of the boutons which formed synapses with luteinizing hormone-releasing hormone-immunoreactive dendrites were found to be labelled by the tritiated indolamine. Luteinizing hormone-releasing hormone-immunoreactive axon terminals occurred as presynaptic elements in contact with unidentified dendritic spines, shafts or perikarya. These observations provide morphological basis for the idea that 5-hydroxytryptamine-containing neurons can act directly on luteinizing hormone-releasing hormone release. Further, they support the assumption that luteinizing hormone-releasing hormone is not only a neurohormone but may also function as a neurotransmitter or neuromodulator.

Animals↗
PubMed1984

Serotoninergic endings on VIP-neurons in the suprachiasmatic nucleus and on ACTH-neurons in the arcuate nucleus of the rat hypothalamus. A combination of high resolution autoradiography and electron microscopic immunocytochemistry.

A combination of immunocytochemistry with transmitter specific autoradiography at the electron microscopic level was used to identify vasoactive intestinal polypeptide (VIP)- or ACTH-containing neurons and serotoninergic nerve terminals in the suprachiasmatic (SCN) and arcuate nuclei (AN). We observed nerve terminals showing selective uptake of [3H]serotonin forming synaptic contact with perikarya or dendrites where the postsynaptic structures exhibited VIP-like immunoreactivity in the SCN and ACTH-like immunoreactivity in the AN. The findings provide ultrastructural evidence that serotoninergic nerve fibers terminate on VIP-neurons in the SCN and on ACTH-neurons in the AN.

Adrenocorticotropic Hormone↗