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Biomedical subjects

M Palkovits

Publications and source records attributed to M Palkovits.

At least 307 records · Page 17Linked to original sources
PubMed1981

Topography of median eminence somatostatinergic innervation.

Somatostatin (SRIF) in the central nervous system is mostly concentrated in the median eminence (ME). Immunocytochemical methods have revealed high densities of SRIF-positive perikarya between the preoptic area and the periventricular nucleus of the hypothalamus (NPE). The aim of the present study was to define more precisely the specific pathways of SRIF neurons from NPE to the ME. SRIF levels were measured by radioimmunoassay, following various hypothalamic transections. Frontal periventricular sections decreased SRIF-ME content by 70% (P less than 0.01), when located at the anterior end of the ME but no diminution was observed when the cuts were located anteriorly or posteriorly. Parasaggital transections decreased SRIF-ME levels by 50% (P less than 0.05) when located at the outer border of the ventromedial and premammillary nucleus, but the decrease was not significant when cuts were located anteriorly. Taken together, our data indicate that most SRIF-containing neurons, originating in the NPE, do not reach the ME directly along the border of the 3rd ventricle; instead they form a loop across the medial forebrain bundle before re-entering the mediobasal hypothalamus at the ME level.

Afferent Pathways↗
PubMed1981

Regional distribution of [3H]imipramine binding in rat brain.

[3H]imipramine binding was measured in 23 microdissected areas of the rat brain and compared to published values for the endogenous levels of serotonin, noradrenaline and dopamine in the same areas. The density of [3H]imipramine binding sites appears to be highly correlated with the distribution of endogenous serotonin especially where the serotonin is located mainly in nerve terminals. A weak but still significant correlation also exists with the distribution of endogenous noradrenaline whereas no such correlation could be detected for endogenous dopamine.

Animals↗
PubMed1981

Circadian variations in substance P, luliberin (LH-RH) and thyroliberin (TRH) contents in hypothalamic and extrahypothalamic brain nuclei of adult male rats.

Using both the 'punch' microdissection and radioimmunological techniques, circadian variations in substance P, luliberin (LH-RH) and thyroliberin (TRH) concentrations can be statistically validated in some discrete brain regions of the (Wistar CFY) male rat investigated in May. Animals were synchronized with light from 06.00 to 18.00 h and darkness. Water and food were available ad libitum. Very well marked circadian rhythms were in evidence in brain areas where the neuronal peptides investigated are mostly present in nerve terminals in high concentrations: medial basal hypothalamus for luliberin and thyroliberin and substantia nigra for substance P. On the contrary, no significant rhythms were detected in a number of areas where luliberin (preoptic area) or substance P (preoptic area, central gray matter, amygdala, globus pallidus) synthetizing perikarya are present. This suggests that at least luliberin and substance P are not secreted according to a circadian rhythmicity. The most striking finding was that crest time locations were situated at only two different times of the day: 14.00 h for thyroliberin and 20.00 h for substance P and luliberin. This suggests that circadian variations are not solely dependent on the activity of the endocrine system.

Amygdala↗
PubMed1981

Effects of paraventricular lesions on stimulated ACTH release and CRF in stalk-median eminence of the rat.

The effects of destroying the paraventricular nucleus (PVN) of the rat hypothalamus on pituitary-adrenal function were studied. Four days after PVN lesions were placed with a rotating knife, the basal plasma corticosterone level was normal, but the corticosterone response to electrical stimulation of the medial basal hypothalamus, surgical trauma, and ether-venesection stress was significantly inhibited. Four and 8 days after PVN lesioning and adrenalectomy, the basal plasma ACTH level was lower, and the rise of plasma ACTH level elicited by a 3-min ether inhalation was significantly smaller than in the adrenalectomized controls. Corticotropin-releasing factor (CRF) activity in the stalk-median eminence extracts from PVN-lesioned rats was significantly less than in the control extracts. The weight of the adrenals was decreased by both 2 and 4 wk after PVN destruction, and 2 wk after hemiadrenalectomy, the compensatory adrenal hypertrophy was inhibited. The plasma corticosterone response to ether-venesection stress was inhibited only temporarily because it returned to normal by the end of the 4th postoperative week. The results are consistent with the hypothesis that a substantial portion of CRF-containing fibers in the stalk-median eminence region either originate from or run though the PVN or its immediate vicinity.

Adrenal Glands↗
PubMed1981

Lack of correlation between hypothalamic serotonin and the ether-induced ACTH secretion in adrenalectomized rats.

The central serotonergic system was manipulated using a serotonin receptor antagonist (cyproheptadine), electrolytic lesioning of the raphe nuclei and neurochemical destruction of the serotonergic terminals in the hypothalamus. The effects of these interventions on ether-induced ACTH secretion were studied in adrenalectomized rats. Serotonin, norepinephrine and dopamine concentrations were measured in the medial basal hypothalamus (MBH) or in individual nuclei of the hypothalamus and of certain midbrain regions. Cyproheptadine pretreatment inhibited ether-induced ACTH hypersecretion in adrenalectomized animals. Neither the electrolytic lesions of the midbrain raphe nuclei, nor the neurotoxic destruction of the hypothalamic serotonergic terminals (by intraventricular administration of 5,6-dihydroxytryptamine) caused any alteration of stimulated ACTH secretion after ether inhalation and/or long-term corticoid deficiency. These results suggest a lack of correlation between the activity of the central serotonergic system and the ACTH releasing effect of ether-stress in adrenalectomized rats.

5,6-Dihydroxytryptamine↗
PubMed1981

Distribution of catecholamines and serotonin in 17 portions of rat ventromedial nucleus and effect of acute immobilization stress.

The distribution of catecholamines (i.e. adrenalin -- A, noradrenalin -- NA, dopamine -- DA) and serotonin (5-HT) in 17 portions of hypothalamic ventromedial nucleus (VMN) and the effect of acute immobilization stress on their levels were studied in rats using of a special dissection technique and a sensitive radioenzymatic microassay. In unstressed rats distinct differences of biogenic amine concentrations between individual portions within the hypothalamic ventromedial nucleus subdivisions were found. The concentration of all catecholamines investigated, i.e. NA, A and DA was lower in the lateral half of VMN, while in the distribution of 5-HT we did not find such apparent regional differences. After acute immobilization stress for 30 min significant changes in all measured neurotransmitters, in NA and A decreases and in DA and 5-HT increases, were detected in several subdivisions of the nucleus. On the basis of the present data we suppose that not all subdivisions of the VMN are equally engaged in neuroendocrine processes activated during acute stress.

Animals↗
PubMed1980

Altered cyclic AMP levels in specific cardiovascular brain centers of spontaneously hypertensive rats (SHR).

The possible participation of cAMP in central regulation of arterial blood pressure was investigated in spontaneously hypertensive rats (SHR). Cyclic AMP concentrations of 36 microdissected individual brain areas-including primary and higher cardiovascular centers-were measured in adult SHR and compared with those of normotensive control rats of the same strain and age. In the adult SHR, elevated cAMP concentrations were found in brain areas which are in close connection with the central regulation of blood pressure: nucleus tractus solitarii, A1- and A2- catecholaminergic cell groups in the medulla oblongata, locus coeruleus, central grey matter (subnucleus medialis), and certain cortical areas (especially cingulate cortex and hippocampus). On the other hand, hypothalamic cell groups which have been also suggested to control blood pressure, such as paraventricular, anterior, ventromedial, dorsomedial and posterior hypothalamic nuclei, show lower concentrations of cAMP in the SHR than in normotensive controls. Cyclic AMP levels in 19 other brain areas of SHR which seem to be not involved in mechanisms of central blood pressure regulation practically do not differ from the values of normotensive rats. The results suggest that cAMP-dependent processes are involved in the regulatory mechanisms of central blood pressure control. The brain areas which show alterations of cAMP-levels are also distinguished by close neuronal connections to the baroreceptor reflex arc. It is supposed that these areas represent modulatory higher centers capable to affect baroreceptor reflex function.

Animals↗
PubMed1980

Noradrenergic innervation of the rat hypothalamus:experimental biochemical and electron microscopic studies.

The concentrations of noradrenaline in individual hypothalamic nuclei and in the median eminence were measured 7-10 days following surgical transections of the lower brain stem or electrolytic lesions of the medullary noradrenaline-containing cell groups. Terminal degeneration in the hypothalamus was studied after the same surgical procedures. Direct, monosynaptic connections between the dorsomedial hypothalamic nucleus and all the noradrenaline-containing cell groups investigated were found. Degenerated synaptic boutons were demonstrated in the median eminence, arcuate, dorsomedial, ventromedial, periventricular and paraventricular nuclei following lesions of the solitary tract and of the lateral reticular nucleus. Biochemical measurements indicate that the pontine-medullary noradrenergic cell groups are the source of hypothalamic norepinephrine. Ascending noradrenergic fibers destined to terminate in the hypothalamus are provided by several cell groups, though the bulk of the NA-fibers seem to originate in the A1-group, in the ventrolateral part of the medullary reticular formation. Most of these fibers join the ventral NA bundle, fewer join the dorsal periventricular tract and several probably also join the dorsal NA bundle. A significant overlap was found in the hypothalamic arborization of the noradrenergic fibers, so that no strict topographical organization seems to be present either in their origin or their termination.

Adrenergic Fibers↗
PubMed1980

Intrahypothalamic terminals of stress conducting fibers.

Surgical stress did not elevate plasma corticosterone level in rats with bilateral surgical transection of the lateral retrochiasmatic area (RCAL). After RCAL transections light and electron microscopic terminal degeneration was observed in both the external and the internal layers of the median eminence as well as in the arcuate and ventromedial nuclei. Incisions lateral to the medial forebrain bundle did not prevent the stress-induced rise in plasma corticosterone level and were not followed by degeneration in the median eminence. Transection of the medial forebrain bundle rostral or caudal to the RCAL caused degeneration in both the median eminence and the arcuate nucleus.

Animals↗
PubMed1980

Ultrastructural investigation of ACTH immunoreactivity in arcuate and supraoptic nuclei of the rat.

Fine structural localization of an ACTH-like substance was obtained in neurons of the rat arcuate nucleus using immuno-electron microscopy, whereas it could not be confirmed that ACTH-containing cell bodies are present in the supraoptic nucleus. The immunoreactive cells of the arcuate nucleus appeared to be more numerous than the unreactive neurons. Immunostaining was carried out before embedding in resin. Empty vesicles of irregular shape were found in dendrites of immunoreactive arcuate neurons, but their significance and nature remain enigmatic. The reaction product was distributed uniformly throughout the cytoplasm of the ACTH-positive cells, except that the mitochondria, rough endoplasmic reticulum and Golgi vesicles and cisternae were devoid of PAP molecules. This distribution differed from the localization reported in ACTH-secreting cells of the rat anterior pituitary, where the reaction product was found in the rough endoplasmic reticulum and Golgi complex as well as in secretory granules.

Adrenocorticotropic Hormone↗