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Biomedical subjects

B Halász

Publications and source records attributed to B Halász.

At least 73 records · Page 4Linked to original sources
PubMed1984

(D-Met2,Pro5) enkephalinamide causes a decrease in plasma prolactin levels of lactating rats continuously suckled and an increase in those deprived of their litter.

The effect of an enkephalin analogue, (D-Met2,Pro5)enkephalinamide (EKNH2) on prolactin (PRL) secretion of lactating rats continuously suckled or separated from their pups was investigated. In rats together with their pups 0.5 mg/kg EKNH2 caused a dramatic decrease, 0.25 mg/kg a mild and short-lasting reduction in plasma PRL levels. In contrast, in lactating rats separated for 4 h from their pups 0.5 mg/kg of the drug induced a slight and 1.0 mg/kg a considerable increase in plasma PRL levels. The data indicate that in lactating rats depending on the circumstances the enkephalin analogue causes opposite effects on PRL secretion.

Animals↗
PubMed1984

Changes in hypophyseal luteinizing hormone (LH) content during fetal and early postnatal life, and capacity of fetal and early postnatal pituitaries to synthesize and release LH in vitro.

The developmental pattern of hypophyseal luteinizing hormone (LH) during fetal and early postnatal life, and the capacity of fetal and early postnatal pituitaries to synthesize, release and store LH in the absence of any hypothalamic influence were investigated. Pituitary radioimmunoassayable LH was detectable by fetal day 12; its level remained low up to fetal day 17 and thereafter continued to increase up to postnatal day 2 with sharp rises occurring between day 17 and 18 of gestation and after birth. Cultured fetal and early postnatal pituitary primordia were able to synthesize, to release and store the hormone, however, the pattern of these cellular functions varied according to the animal age when explantation was performed. Data derived from cultured pituitaries showed a gradual rise in the daily hormone content of the medium between fetal day 13 to 17. From fetal day 19 onwards, however, the daily discharge of LH decreased. These findings suggest that the fetal and early postnatal pituitary has the capacity to synthesize and release LH, furthermore after a period of independent differentiation hypothalamic signals appear to be required for pituitary hormone release.

Animals↗
PubMed1983

Is the knife-cut in the hypothalamus a permanent barrier to regrowth of nerve fibers? -an affirmative answer.

The regenerative capacity of nerve fibers was studied in adult female rats. Horseradish peroxidase was injected into the anterior hypothalamus lateral to the suprachiasmatic nucleus 4 days, 6 weeks and 4 months, respectively, following an archiform retrochiasmatic knife-cut. The trajectory of the stained fibers was examined on horizontal sections of the hypothalamus. No nerve fibers could be seen sprouting across the scar-tissue of the knife-cut regardless of the survival time. In one rat (6-week survival time) a bundle of fine nerve fibers turned in a medial direction at the caudal end of the knife-cut, suggesting that sprouting fibers were destined to reinnervate parts of the deafferented medial-basal hypothalamus.

Animals↗
PubMed1983

Time course of the litter removal-induced depletion in plasma prolactin levels of lactating rats. An immediate full blockade of the hormone release after separation.

The decreases in plasma prolactin (PRL) levels in lactating rats that follow the separation of mother and pups have been studied. Blood samples were taken via an indwelling cannula from conscious primiparous animals between days 5 and 11 of lactation. Significant depressions of plasma prolactin levels have been detected within 3 min of separation. These decreases in hormone levels were most pronounced after 3 min, and continued up to the end of the 1st hour, but did not change during the 2nd hour. Disappearance of PRL from the blood during the first 3 min was identical to that occurring after hypophysectomy. Pretreatment of mothers, 90 min prior to separation, with alpha-methyl-p-tyrosine (250 mg/kg i.p.), pimozide (2 mg/kg i.p.), or haloperidol (2 mg/kg i.p.), completely blocked the decreases in PRL levels. L-Dopa (20 mg/rat i.p.) counteracted the inhibitory effect of alpha-methyl-p-tyrosine. These data suggest that separation of lactating rats from their litter resulted in a marked and complete blockade of PRL release from the pituitary. They also suggest that a dopaminergic mechanism plays an important role in this inhibition of PRL release.

Animals↗
PubMed1982

On the origin of luteinizing hormone releasing hormone and somatostatin in the median eminence of the rat hypothalamus.

Luteinizing hormone releasing hormone (LHRH) and somatostatin content of the two halves of the median eminence of the rat hypothalamus were determined by radioimmunoassay three weeks after following deafferentations: (1) unilateral knife cut in front of, laterally and above the preoptic area (preoptic deafferentation); (2) unilateral arched cut at the midlevel of the suprachiasmatic region (suprachiasmatic deafferentation); (3) unilateral arched cut behind the optic chiasm (retrochiasmatic deafferentation); (4) cutting around the medial basal hypothalamus on one side starting with the cut at the posterior level of the optic chiasm (complete deafferentation). Preoptic deafferentation caused a more than 50% decrease in the LHRH content of the ipsilateral half of the median eminence. The reduction in LHRH was even greater (about 70%) in rats with suprachiasmatic deafferentation and only about 15% of the neurohormone was found in the ipsilateral half of the median eminence after unilateral retrochiasmatic or complete deafferentation. The median eminence somatostatin showed practically no change after unilateral preoptic deafferentation, while it was reduced by about 50, 60 and 80% in the ipsilateral half median eminence after a unilateral suprachiasmatic, retrochiasmatic and complete deafferentation, respectively. The results are consistent with the assumption that the majority of the LHRH perikarya projecting to the median eminence are located partly in the preoptic-anterior hypothalamic area and partly in brain regions in front of or above this area. Most of the somatostatin perikarya with terminals in the median eminence are in the preoptic-anterior hypothalamic region.

Afferent Pathways↗
PubMed1982

Unilateral posterior deafferentation of hypothalamus and mitotic activity of thyroid follicular cells under normal conditions and after hemithyroidectomy.

The effect of unilateral posterior deafferentation of the hypothalamus on the mitotic activity of thyroid follicular cells was studied in hemithyroidectomized and sham-operated rats. Left side posterior deafferentation of the hypothalamus reduced significantly the basal mitotic activity of both thyroid lobes and prevented the hemithyroidectomy-induced increase in mitotic activity of the remaining thyroid lobe. Right side posterior deafferentation of the hypothalamus or sham operation did not interfere with the normal or stimulated activity of the follicular cells. These data suggest left side dominance in the mitosis control of the thyroid cells but the mechanism resulting in these findings remains unclear.

Afferent Pathways↗
PubMed1982

Effect of naloxone on the suckling induced prolactin release in rats.

2.0 mg/kg b.w. of naloxone--a specific opiate antagonist--injected i.p. 10 min before a brief (lasting for 10 min) suckling and 10 min before a second suckling 30 min after the first suckling significantly inhibited the rise in plasma prolactin levels induced by the suckling stimuli. 0.2 mg/kg of naloxone caused only a slight inhibition on the pituitary prolactin response, the inhibitory effect being more evident on the response to the second suckling stimulus. The data are consistent with the view that endogenous opioids might be involved in the control of prolactin secretion of lactating rats.

Animals↗
PubMed1981

(D-Met2,Pro5)-enkephalinamide-induced blockade of ovulation and its reversal by naloxone in the rat.

The effects of (D-Met2,Pro5)-enkephalinamide--a superactive enkephalin analogue--on the preovulatory discharge of gonadotrophic hormones and on ovulation were investigated. Injection of the opioid (16 nmol) into a lateral cerebral ventricle of regularly cycling female rats immediately before the critical period on the day of proestrus resulted in a blockade of ovulation and in a concomitant depression of the preovulatory plasma luteinizing hormone and follicle-stimulating hormone levels. A smaller dose of the opioid (2 nmol) did not inhibit ovulation. The inhibition of the preovulatory gonadotrophic hormone discharge and the blockade of ovulation by the opioid were reversed by naloxone administration. Our data are consistent with the view that the endogenous opioid peptides may be involved in the physiological regulation of the central neural events which lead to ovulation in the rat.

Animals↗
PubMed1980

Reversed effect of chlorpromazine on hypothalamic serotonin levels of rats with complete deafferentation of the medial basal hypothalamus.

The effect of chlorpromazine (CPZ) treatment, the complete deafferentation of the medial basal hypothalamus (MBH) and their combination on 5-HT, DA and NE levels of the MBH, hypothalamic structures outside the MBH (RH), mesencephalon and amygdala were studied. Monoamines were determined by fluorimetry. CPZ reduced 5-HT in the hypothalamus (MBH, RH), DA in the amygdala and NE concentration in the RH. Complete deafferentation of the MBH decreased 5-HT in the MBH, DA in the amygdala and NE in the hypothalamus. CPZ + deafferentation of the MBH increased 5-HT concentrations in the hypothalamus (MBH and RH) and mesencephalon, and depressed DA levels in the amygdala and NE in the hypothalamus. The data suggest that the interruption of the neural connections of the MBH results in an inverse response of the hypothalamic serotoninergic elements to CPZ.

Afferent Pathways↗
PubMed1979

Short-term effect of the lesion of the organum vasculosum of the lamina terminalis on hypothalamic LH-RH and serum LH, FSH and prolactin in adult female rats.

The short-term effect of the mechanical lesion of the organum vasculosum of the lamina terminalis (OVLT) was investigated in 4-day cycling female rats. The lesions were performed on the 2nd day of diestrus, and the animals were killed by decapitation 30 h after the lesion. Serum LH, FSH and prolactin and hypothalamic LH-RH content of 3 different parts of the hypothalamus were determined with radioimmunoassay. OVLT lesion caused a significant increase in the LH-RH content of the mid-basal hypothalamus and in serum prolactin levels and a decrease in LH and FSH serum levels. The results support the view that the OVLT may play a role in the control of pituitary gonadotrophic hormone secretion.

Animals↗
PubMed1978

Fine structure of the palisade zone of the rat median eminence as revealed by freeze-fracturing.

Nerve terminals in the palisade zone of the rat median eminence were investigated with freeze-fracture electron microscopy. Fracture face P of the specific terminals showed two populations of intramembranous particles (IMP): a large and a small variety. The large IMP-s often formed small irregular clusters. In nerve terminals the total number of both populations of IMP-s was considerably less than that found on P membrane faces of ependymal feet. On fracture face E of the nerve terminals, the number of IMP-s was about a quarter of that seen on fracture face P. On both fracture faces of most terminals a few small round impressions (or elevations respectively) were found which may be interpreted as broken necks of either exo- or endocytotic vesicles. Neither gap nor tight junctions occurred at lateral membranes of the specific axon terminals. Similarly, no membrane specializations were observed with freeze-fracturing on membrane areas adjacent to the basement membrane. The findings are discussed in relation to a possible exocytosis mechanism of the hypothalamic releasing and inhibiting hormones.

Animals↗
PubMed1976

Cell differentiation of the fetal rat anterior pituitary in vitro.

Adenohypophysial primordia of rat embryos at 13 to 15 days gestation were cultured in Parker 199 synthetic medium for 2 to 11 days. At the end of the culture period their fine structure and the presence of immunoreactive trophic hormones using the peroxidase-labeled antibody technique were investigated. The degree of differentiation in the glands depends largely on the age of the embryos furnishing the explants. Cultured pituitaries explanted on the 13th day of gestation contain only ACTH-positive cells and about 15% of the cells are granular. The granules are 50-100 nm in diameter in some cells, while in other cells they range from 50 to 200 nm. In cultivated adenohypophysial primordia of embryos on the 15th day of intrauterine life ACTH, prolactin, LH and TSH cells are evident, but only the same two kinds of granular cells can be observed with the electron microscope. The extent of cytodifferentiation in the glands explanted on the 14th day of gestation is intermediate between the two other groups. The data suggest that the fetal rat pituitary has the capacity of self-differentiation but to a lesser extent than that of the in situ hypophysis.

Adrenocorticotropic Hormone↗
PubMed1976

Hemigonadectomy-induced unilateral changes in the protein-synthesizing activity of the rat hypothalamic arcuate nucleus.

The effect of unilateral ovariectomy on the protein-synthesizing activity of the hypothalamic arcuate and dorsomedial nucleus on both sides was studied in vivo as well as in vitro. Four weeks after the removal of 1 ovary, there was a significant increase in labelled amino acid incorporated into the arcuate neurons contralateral to the removed ovary as compared to those incorporated into the nerve cells of the nucleus on the ipsilateral side. In the dorsomedial nucleus, there was no difference between the 2 sides. On the basis of the present findings, the existence of a neural pathway between the ovary and the hypothalamic arcuate nucleus is assumed.

Animals↗