Biomedical subjects

B Halász

Publications and source records attributed to B Halász.

At least 19 recordsLinked to original sources

PubMed1992

Dehydration attenuates plasma prolactin response to suckling through a dopaminergic mechanism.

The tuberoinfundibular dopaminergic neurons projecting to the median eminence are well accepted as a major physiological regulator of adenohypophyseal PRL secretion. However, recent evidence has shown that dopamine (DA) in the neurointermediate lobe also has an inhibitory effect on PRL secretion by anterior pituitary. Since the neurointermediate is innervated by the tuberohypophyseal dopaminergic (THDA) neurons, which is known to be selectively activated by dehydration of the animal, the aim of this study was to investigate the physiological role of the THDA system in PRL release during lactation. On the day of the experiments, the litters were separated from the mothers for 4 h before initiation of the suckling stimulus. The suckling-induced PRL surge was detected on three consecutive days. On the first day the normal response was tested; then immediately after taking the last blood samples, drinking solutions were changed to the high salt (2.5% saline) containing bottles or were taken away. Suckling-induced PRL response was significantly decreased after 24 h and almost completely blocked 48 h later in dehydrated mothers. This effect could be prevented by haloperidol (a DA receptor antagonist) pretreatment (0.1 mg/kg BW sc), and it was only transient because rehydration of the mothers reestablished basal as well as suckling-induced PRL response. In addition, the effect of an acute osmotic stimulus on the plasma PRL levels (injecting 0.5 ml 10% saline solution iv) was also tested. There was a marked and immediate decrease in PRL concentration within 15 min of injection. Domperidone, another DA receptor blocker (20 micrograms/rat iv) completely abolished the depletion of plasma PRL in response to 10% saline injection. These results support our assumption that the dopaminergic regulation of PRL secretion during lactation involves the THDA system. Furthermore, these data underline the importance of an interaction between regulation of PRL secretion and water and sodium homeostasis.

Animals↗

PubMed1991

Mesencephalic sites of action of an enkephalin analogue (D-Met2, Pro5)-enkephalinamide and naloxone on the anterior pituitary of male rats.

(D-Met2, Pro5)-Enkephalinamide and naloxone injected into the dorsal raphe nucleus affected luteinizing hormone (LH) and prolactin (PRL) release. Drugs given into the reticular tegmental nucleus and dorsal part of the periaqueductal gray matter induced a PRL response and their administration into the central superior midbrain raphe nucleus caused changes in growth hormone (GH) secretion. The inferior colliculus and the lateral part of the periaqueductal gray matter were ineffective sites.

Animals↗

PubMed1991

Attenuation of the suckling-induced prolactin release and the high afternoon oscillations of plasma prolactin secretion of lactating rats by antiserum to vasopressin.

To investigate the role of vasopressin in prolactin (PRL) release during lactation, vasopressin antiserum (VP-Ab) was administered to lactating rats, giving it intravenously 15 min before permitting their previously isolated pups to suckle or to continuously suckled rats. The suckling-induced rise in plasma PRL levels was significantly less in VP-Ab-treated mothers than in rats receiving a similar amount of normal rabbit serum (NRS). The inhibitory effect of VP-Ab could not be detected on the next day. Angiotensin II antiserum (AII-Ab) had no effect on plasma PRL response induced by suckling. VP-Ab given to continuously suckled rats reduced the high amplitude oscillation of PRL concentration observed in NRS-injected rats. A transient increase of water intake was detected on the day of VP-Ab treatment only, which provides direct evidence for at least partial neutralization of vasopressin in the circulation. These findings suggest that vasopressin released from the neural lobe of the pituitary gland is essential for the normal PRL secretory response induced by suckling and the episodic pattern of PRL release in continuously suckled mother rats. Furthermore, these results support the assumption that disturbance in the regulation of water and electrolyte balance at the level of the neuro-intermediate lobe of the pituitary gland may alter PRL secretion during lactation.

Angiotensin II↗

PubMed1990

Ultrastructural analysis of the innervation of TRH-immunoreactive neuronal elements located in the periventricular subdivision of the paraventricular nucleus of the rat hypothalamus.

A combination of electron microscopic immunocytochemistry and autoradiography was employed to examine the synaptic organization of thyrotropin-releasing hormone (TRH) neurons in the periventricular subdivision of the paraventricular nucleus of the rat hypothalamus. TRH neurons were identified by immunocytochemistry. Selective uptake of tritiated serotonin (5-HT) was used to identify serotoninergic elements. TRH-immunoreactive axon terminals were found to be in synaptic contact with TRH-immunoreactive dendrites and with unlabeled dendritic branchlets. There were direct appositions between radiolabeled 5-HT terminals and TRH-immunoreactive dendrites, but differential synaptic contacts between 5-HT axonal elements and TRH neurons were not seen. TRH-immunopositive cell bodies and dendrites received a very intense innervation by unlabeled axon terminals or axonal varicosities showing morphologically defined synaptic junctions. These were mostly of the asymmetrical variety and different types could be distinguished. The findings substantiate the view that TRH neurons of the periventricular subvision of the paraventricular nucleus may be influenced by TRH axons, serotoninergic fibers and a large number of unidentified nerve terminals.

Animals↗

PubMed1990

Fetal pituitary graft is capable of initiating hormone synthesis in median eminence removed adult rat.

Rathke's pouches of 12- and 13-day-old rat embryos were implanted beneath the kidney capsule of adult male rats subjected to the removal of median eminence or to sham-operation. Host animals were sacrificed 28 days after grafting and the implanted pituitaries were processed for immunohistological examination. ACTH, LH-beta, FSH-beta, TSH-beta, GH and PRL immunopositive cells could be observed in fetal grafts of all experimental groups. However, the number and staining intensity of different hormone containing cells largely varied and presumably depended on the hormonal state of host animals. The results indicate that undifferentiated fetal pituitary does not require hypothalamic hypophysiotrophic neurohormones for proliferation and cytodifferentiation and that its development might be modulated by circulating trophic hormones of host animals.

Adrenocorticotropic Hormone↗

PubMed1989

Lack of the suckling-induced prolactin release in homozygous Brattleboro rats: the vasopressin-neurophysin-glycopeptide precursor may play a role in prolactin release.

Suckling stimulus did not induce significant release of prolactin (PRL) in lactating homozygous Brattleboro rats, whereas it did it in heterozygous animals. Daily treatment of homozygous rats with vasopressin partly restored the PRL response to suckling. Findings suggest that vasopressin-neurophysin-glycopeptide precursor missing in homozygous Brattleboro rats may play a role in suckling-induced PRL release.

Animals↗

PubMed1989

Cultured fetal rat pituitaries kept in synthetic medium are able to initiate synthesis of trophic hormones.

An immunohistochemical study was performed to determine the capacity of early fetal pituitaries to differentiate into specific hormone-synthesizing tissue in the absence of any influence from the central nervous system. Rathke's pouches from rats were removed from their juxtadiencephalic position on day 11 and 12 of gestation and maintained for 2-7 days in a chemically defined culture medium (M 199) without antibiotics and serum supplementation. The immunocytochemical observations provided evidence for the differentiation of ACTH-, TSH-beta-, LH-beta-, FSH-beta-, GH- and PRL-synthesizing cells in the isolated organ cultured from 11 to 12-day-old pituitary primordia. The appearance of specific hormone-synthesizing cells in vitro displayed a delay of 1.5-2 days compared to the day of appearance in vivo, however, the sequential order of developmental events occurred as observed in vivo. The present results suggest that endocrine or neuroendocrine signals are not required for the expression of specific secretory functions of fetal pituitaries, at least at an age of 11-12 days.

Animals↗

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↗