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Biomedical subjects

M Palkovits

Publications and source records attributed to M Palkovits.

At least 379 records · Page 21Linked to original sources
PubMed1976

Brain-stem structures and catecholamines in the control of arterial blood pressure in the rat.

1. Noradrenaline, adrenaline and alpha-methylnoradrenaline administration into the nucleus tractus solitarii (NTS) of anaesthetized rats decreased blood pressure and heart rate in a dose-dependent fashion. 2. Bilateral injections were effective in lower doses than unilateral administration. alpha-Methylnoradrenaline given bilaterally produced hypotension in a dose of 0-08 nmol whereas after unilateral injection a dose of 0-32 nmol was needed to obtain the same degree of hypotension. 3. Electrical stimulation of the NTS caused hypotension and bradycardia. Conversely, bilateral electrolytic lesions or deafferentation of the NTS led to acute hypertension. Chronically such lesions caused neurogenic hypertension. 4. In spontaneously hypertensive rats increased concentrations of noradrenaline, adrenaline and dopamine were measured in the part of the NTS located just caudal to the obex (A2 region).

Animals↗
PubMed1976

Hypothalamic region and pathways responsible for adrenocortical response to surgical stress in rats.

Surgical stress produced no increase in the plasma corticosterone level in rats with complete deafferentation of the medial basal hypothalamus (MBH). 30 min after surgical stress, the adrenocortical response depended on the integrity of a well-circumscribed region of the hypothalamus: the lateral-basal region of the retroachiasmatic area (RCAL) that lies not more than 0.5 mm caudally from the optic chiasma and is about 0.2 mm high. One week after transsection of this region, surgical stress produced no elevation of plasma corticosterone; the effect of the operation was independent of whether various combinations of other regions and pathways to the MBH were left intact. In contrast, high plasma corticosterone levels were found after surgical stress with all kinds of hypothalamic deafferentation when the basal region of the RCAL was not transected. The possible origin of neuronal fibres running through the RCAL is discussed.

Animals↗
PubMed1976

Effect of stress on serotonin concentration and tryptophan hydroxylase activity of brain nuclei.

The effects of a single stressful stimulus on serotonin (5-HT) concentration and of repeated stressful stimuli on tryptophan hydroxylase (THy) activity were measured in individual hypothalamic nuclei and other rat brain regions using specific sensitive radioisotopic enzymatic microassays. Two h after formalin injection, 5-HT levels were increased in the dorsal raphe (RDN). Acute immobilization stress, however, reduced the concentrations of 5-HT in several of the hypothalamic nuclei: the medium eminence (ME), lateral amygdaloid nucleus, hippocampus, cingulate cortex (CCX) and RDN. Five consecutive daily immobilization periods failed to alter THy activity in any region examined. These results suggest a rapid release of 5-HT both from the cells and the axon terminals in the central nervous system, and failure, even with repeated stresses, to elicit induction of increased levels of the biosynthetic enzyme regulating the synthesis of the neurotransmitter.

Animals↗
PubMed1976

Releasing factors in the circumventricular organs in the rat brain.

With a recently developed microdissection technique, four circumventricular organs were removed from the rat brain, and their contents of LHRH and TRH were measured. The subfornical organ, the organon vasculosum lamia terminalis, the subcommissural organ, the area postrema all contained significant quantities of both releasing factors. The concentration of LHRH in the organon vasculosum (OVLT) was 14 ng/mg protein, 58% of that found in the median eminence. The concentration of LHRH in the remaining circumventricular organs ranged from 4.2 to 10.2 ng/mg protein. The concentration of TRH in these structures, however, was considerably lower, ranging from 0.7 to 1.8 ng/mg protein. The concentrations of LHRH and TRH in the tissue immediately adjacent to the organon vasculosum were nearly 50 times and 4 times less, respectively, than the concentration of these two releasing factors within the OVLT itself.

Animals↗
PubMed1976

The effect of surgical isolation of the hypothalamus on its luteinizing hormone-releasing hormone content.

The luteinizing hormone-releasing hormone (LHRH) content of the medical basal hypothalamus was determined by radioimmunoassay 10 days after the isolation of this region. Between 70 and 90% of the LHRH disappeared from the hypothalamus after the surgical procedure. Thus, it seems that most of the LHRH present in the medial basal hypothalamus arises from, or is controlled by, cells elsewhere in the brain.

Animals↗
PubMed1976

Distribution of releasing factors, biogenic amines, and related enzymes in the bovine median eminence.

The bovine median eminence was dissected into eight different subdivisions: rostral, anterior internal, anterior external, middle external medial, middle external lateral, middle internal medial, middle internal lateral, and caudal. Thyrotropin-releasing hormone (TRH) was found in the highest concentrations in the middle external medial and lateral subdivisions; luteinizing hormone-releasing hormone (LHRH) was concentrated in the middle external lateral and anterior internal subdivisions. Among the various neurotransmitters and enzymes assayed, only dopamine and choline acetyltransferase were present in highest concentrations in the same subdivisions of the bovine median eminence found to be rich in TRH and LHRH. The distributions of norepinephrine, dopamine-beta-hydroxylase, serotonin, tryptophan hydroxylase, phenylethanolamine-N-methyltransferase, glutamic acid decarboxylase, and histamine appeared to correlate poorly with the major distributions of TRH and LHRH. These findings suggest that at the level of the median eminence, central neuroendocrine regulation of TRH and LHRH release may involve an interaction only with dopamine and acetylcholine.

Animals↗
PubMed1976

Lack of effect of various endocrine manipulations on tryptophan hydroxylase activity of individual nuclei of the hypothalamus, limbic system, and midbrain of the rat.

The tryptophan hydroxylase activity of individual nuclei of the limbic system, hypothalamus, and midbrain was determined after various endocrine manipulations in an attempt to identify specific endocrine-responsive serotonergic structures in the rat brain. Following adrenalectomy, thyroidectomy, castration, or treatment with pharmacological doses of dexamethasone, testosterone, or thyroxine, no changes in tryptophan hydroxylase activity occurred in any of the areas of brain examined. Furthermore, in large sections of the hypothalamus and midbrain, total tryptophan hydroxylase activity was unaltered, and no changes in Km for substrate or co-factor were found after adrenalectomy. This study, therefore, has failed to detect any hormonally responsive tryptophan hydroxylase activity in the rat brain. These findings suggest that endocrine-induced alterations in serotonin turnover, if they occur, do so without measurable changes in the activity or kinetic properties of tryptophan hydroxylase.

Adrenal Glands↗
PubMed1976

Blood supply of the rat hypothalamus. IV. Retrochiasmatic area, median eminence, arcuate nucleus.

The vascular supply of the rat hypothalamo-hypophyseal complex was studied by aid of a double injection technique (two dyes different in colour injected successively). The vascular bed of the median eminence, the arcuate nucleus, and the retrochiasmatic area are intimately interconnected among themselves, but isolated from the vascular system of all other parts of the hypothalamus. The arterial supply of this ensemble of the medial basal hypothalamus is common from the hypophyseal arteries, via the primary plexus and the specific vascular loops of the median eminence. From here a separation of the vascular bed leads the blood flow towards the pituitary portal vessels on the one hand, and over a subependymal vascular network towards the arcuate nuclei on the other. The venous drainage of the arcuate nuclei and the retrochiasmatic area is secured by a special set of tuberal and retrochiasmatic veins. --The unity of the vascular bed of the median eminence, arcuate nucleus, retrochiasmatic area complex, with a blood flow largely in the direction indicated by this sequence, is of considerable importance for the interpretation of the results of experimental interference with this region.

Animals↗
PubMed1975

The effect of two diverse inhalation anesthetic agents on serotonin in discrete regions of the rat brain.

Sensitive radioisotopic enzymatic methods were used to determine 5-HT levels in 16 different regions of brain from rats anesthetized for 90-105 min with 1% halothane or 18% cyclopropane. These two anesthetics were chosen because of their differing effects on the electroencephalogram and on the cardiovascular and respiratory systems. 5-HT levels in the nucleus amygdaloideus centralis, substantia nigra, and nucleus centralis superior were increased after administration of either anesthetic, but only anesthesia with cyclopropane was associated with an increase in 5-HT level in the nucleus raphe dorsalis. The changes in levels of transmitter does not distinguish cause from effect of anesthesia, and further experiments are needed to delineate what role, if any, the specific areas play in muscle relaxation, analgesia, sleep or anesthesia.

Amygdala↗
PubMed1975

Quantitative studies on the supraoptic nucleus in the rat. I. Synaptic organization.

Four types of synapses: axo-axonic, axo-dendritic, axon-spine, and axo-somatic were distinguished in the supraoptic nucleus in the rat. The density of synaptic terminals (boutons) in this nucleus is 35.17-10(6)/mm3 hence there are over 5 million boutons on each side, and on the average 596 per neuron. Only about one third of the axon terminals in this nucleus originate outside the nucleus and its immediate neighbourhood. Two thirds appear to be of intranuclear or otherwise of local origin. This could be explained by assuming either numerous intranuclear axon collaterals or interneurons having richly arborizing axons, or possibly both.

Animals↗
PubMed1975

Quantitative studies on the supraoptic nucleus in the rat. II. Afferent fiber connections.

A quantitative electron microscopic study of synaptic terminal degeneration was performed in the supraoptic nucleus (NSO) after a variety of major transections or ablations, destroying or interrupting in different combinations the afferent pathways known from earlier and own light microscopic degeneration studies. Solutions of a set of equations, expressing the percentage degenerations in synaptic profiles after different combinations in which the several pathways are interrupted by the various interferences, enabled the authors to give the following percentage numbers for afferent synapses from different sources. 32.7% of supraoptic afferents originate from the brain stem probably representing the monoaminergic innervation of this nucleus. The medial basal hypothalamus (21.0%), amygdala (13.5%), septum (13.5%), hippocampus (8.5%) and olfactory tubercle and further rostral cortical region (17.0%) are the other main sites of origin of supraoptic nucleus afferents. There are no supraoptic afferents from the optic nerve, superior cervical ganglion or fimbria hippocampi.

Amygdala↗
PubMed1975

Lymphocytosis induced by polymethacrylic acid. Dose-effect and toxicity.

Intravenous polymethacrylic acid (PMAA) significantly increases the number of lymphocytes in the blood of the rat. The relationship between dose-effect and lymphocytosis is linear. The lethal dose in 30 days of PMAA is 120 mg/kg b.w. and the half-lethal dose 80 mg/kg b.w. The treatment with 40 mg/kg b.w. intravenous PMAA gives no toxic histological changes either in the lymph organs, the liver or the kidneys. Thus, PMAA appears to be, at present, a most suitable agent by which to provoke experimentally, migration of the reserve lymphocytes into the blood.

Acrylic Resins↗
PubMed1975

Effect of hypothalamic deafferentation on thyrotropin-releasing hormone levels in rat brain.

The medial basal hypothalamus was isolated from the remainder of the brain of the rat using a Halász knife. Ten to 14 days after the surgical procedure the concentration of thyrotropin-releasing hormone within the island of hypothalamic tissue was 76% lower than in tissue from sham-operated control rats. Thus, much of the thyrotropin-releasing hormone that is normally present in the medial basal hypothalamus may be synthesized by cells outside of this region. There were no reductions in hormone levels in regions outside of the hypothalamic island after the surgical procedure. Extrahypothalamic thyrotropin-releasing hormone does not appear to be produced by hypothalamic neurosecretory cells.

Animals↗