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M Palkovits

Publications and source records attributed to M Palkovits.

At least 253 records · Page 14Linked to original sources
PubMed1984

Analysis of the ACTH/beta-End/alpha-MSH-immunoreactive afferent input to the hypothalamic paraventricular nucleus of rat.

Immunoreactive fibers and varicosities in the hypothalamic paraventricular nucleus (PVN) were examined by light- and electronmicroscopy, following treatment of brain slices with specific antibodies to adrenocorticotropin (ACTH), beta-endorphin (beta-End) and alpha-melanotropin (alpha-MSH) peptides. In an attempt to provide a more precise, quantitative definition of the densities of immunoreactive elements, sections were analyzed by computer based image-analysis techniques. Fibers and varicosities immunostained with the 3 different antibodies displayed an identical distribution pattern throughout the nucleus suggesting that they are parts of the same, arcuate pro-opiomelanocortin (POMC) neuron system. Although immunoreactive varicosities were found all over the PVN, it was possible to identify a characteristic, density distribution pattern. At the ultrastructural level, immunoreactive presynaptic nerve terminals were observed forming symmetrical synaptic contacts with unlabeled dendrites. The majority of immunoreactive elements were found in the dorsal parvo- and caudal magnocellular subdivisions which give rise to long projections to the lower brainstem. Moderate density of POMC neural elements was observed in the anterior and medial (ventral portion) parvocellular subdivisions which project to the external zone of the median eminence. Only a few, widely scattered immunostained varicosities are found in the medial and lateral magnocellular subdivisions which project to the neurohypophysis. A combined lesion and immunocytochemical approach has shown that the bulk of the afferent neuronal input from arcuate POMC cells enters the PVN from a ventral direction.

Adrenocorticotropic Hormone↗
PubMed1984

Beta-adrenergic mechanism of insulin-induced adrenocorticotropin release from the anterior pituitary.

Intraperitoneal administration of insulin to control rats and to rats with pituitary stalk transections or with lesions of the median eminence resulted in increased plasma adrenocorticotropin (ACTH) levels. The insulin-induced stimulation of ACTH release was blocked in both the control and lesioned animals by prior treatment with either the beta-adrenergic antagonist propranolol or the glucocorticoid analog dexamethasone. The direct application of insulin to primary cultures of the anterior pituitary did not evoke ACTH release or affect the maximal ability of corticotropin-releasing factor or epinephrine to stimulate ACTH secretion. The results suggest that insulin stimulates ACTH release by a mechanism in which catecholamines of peripheral origin act directly on the anterior pituitary.

Adrenocorticotropic Hormone↗
PubMed1984

Distribution and projections of cholecystokinin-immunoreactive neurons in the hypothalamic paraventricular nucleus of rat.

Analysis of coronal sections from colchicine-treated rat brains reveals that CCK-immunoreactivity (CCK-ir) is present in two distinguishable neuronal systems in the paraventricular nucleus (PVN). More than 60% of these cells were found to be typical parvicellular neurons; the remainder were magnocellular neurons. The magnocellular CCK-ir neurons were concentrated in the medial magnocellular subdivision, while more caudally they formed a ring around a zone of unstained magnocellular neurons. Immunostained parvicellular neurons predominate in medial and periventricular parvicellular subdivisions. The efferent projections of CCK-ir neurons were investigated by looking for retrograde accumulation of CCK-ir in cell bodies after selective knife cuts. A parasagittal cut of the lateral retrochiasmatic area as well as transection of the rostral median eminence resulted in an accumulation of CCK-ir material in a large number of both parvi- and magnocellular neurons. After pituitary stalk lesions, however, increased staining was only seen in magnocellular neurons. It is inferred that the magnocellular (presumed oxytocin-CCK) cells send their axons to the pituitary, whereas axons of CCK-ir parvicellular neurons appear to terminate in the median eminence. After transection of the medial forebrain bundle (MFB), immunostaining increased in a small number of scattered transected fibers proximal to the knife cut and in a few perikarya in the PVN, indicating that very few CCK cells may send descending fibers to the lower brainstem.

Animals↗
PubMed1984

Distribution of immunoreactive dynorphin A1-8 in discrete nuclei of the rat brain: comparison with dynorphin A.

The distribution of immunoreactive (ir)-dynorphin A1-8 (Dyn A1-8) in 78 microdissected rat brain areas as well as in the neurointermediate lobe of pituitary gland was determined using a highly specific radioimmunoassay. The highest concentrations of Dyn A1-8 in brain were found in substantia nigra (673.8 fmol/mg protein) and lateral preoptic area (565.1 fmol/mg protein). High concentrations of ir-Dyn A1-8 (greater than 240 fmol/mg protein) were found in 5 nuclei: ventral premamillary nucleus, anterior hypothalamic nucleus, dorsomedial nucleus, arcuate nucleus, and medullary reticular nuclei. Moderate concentrations of the peptide (between 120 and 240 fmol/mg protein) were found in 55 brain nuclei such as septal and amygdaloid nuclei, most diencephalic structures, mesencephalic nuclei, pons and medulla oblongata nuclei and others. Low concentrations of ir-Dyn A1-8 (less than 120 fmol/mg protein) were found in 16 regions, e.g. frontal cortex, hippocampus, caudate-putamen cortical amygdaloid nucleus, several thalamic nuclei, mamillary body superior and inferior colliculi, cerebellar nuclei and others. The posterior thalamic nucleus has the lowest ir-Dyn A1-8 concentration (62.0 fmol/mg protein). The neurointermediate lobe of the pituitary gland is extremely rich in ir-Dyn A1-8 (4063.0 fmol/mg protein).

Animals↗
PubMed1984

Brainstem projection to the hypothalamic ventromedial nucleus in the rat: a CCK-containing long ascending pathway.

In order to identify the source and topography of cholecystokinin-containing fibers innervating the hypothalamic ventromedial nucleus (VMN), radioimmunoassay, immunocytochemistry, retrograde tracing of horseradish peroxidase and anterograde degeneration techniques were used. Cholecystokinin (CCK) disappeared almost totally from the VMN following a caudal diencephalic knife cut, which transected the medial fibers of the internal capsule, and the dorsolateral portion of the medial forebrain bundle at the level of the mammillary body. A number of cells in the ipsilateral dorsal parabrachial nucleus, furthermore, showed intense CCK-like immunoreactivity. The ascending CCK-containing fibers in the lateral part of the medial forebrain bundle reach the VMN from the lateral side. Neither the fibers of the stria terminalis, nor of the medial corticohypothalamic tract seem to carry any significant amount of CCK to the VMN.

Afferent Pathways↗
PubMed1984

Distribution of immunoreactive dynorphin B in discrete areas of the rat brain and spinal cord.

The distribution of immunoreactive (ir)-dynorphin B in 101 microdissected rat brain and spinal cord regions was determined using a specific radioimmunoassay. The highest concentration of dynorphin B in brain was found in the substantia nigra (1106.2 fmol/mg protein). Very high concentrations of ir-dynorphin B (greater than 400 fmol/mg protein) were also found in the lateral preoptic area, parabrachial nuclei and globus pallidus. Relatively high concentrations of ir-dynorphin B (250-400 fmol/mg protein) were found in 19 nuclei, including the periaqueductal gray matter, anterior hypothalamic nucleus, median eminence, nucleus accumbens and hippocampus. Moderate levels of the peptide (between 100 and 250 fmol/mg protein) were found in 42 brain nuclei such as the perifornical nucleus, nucleus of the diagonal band, medial forebrain bundle, and dorsal premamillary nucleus. Low concentrations of ir-dynorphin B (less than 100 fmol/mg protein) were found in 28 brain areas, e.g. cerebral cortical structures (parietal, cingulate, frontal), claustrum, olfactory bulb, lateral and periventricular thalamic nuclei. The cerebellar cortex has the lowest dynorphin B concentration (53.7 fmol/mg protein). Spinal cord segments exhibit low or moderate (cervical segment) levels of the peptide. The neurointermediate lobe of the pituitary gland is extremely rich in ir-dynorphin B (11,047.1 fmol/mg protein).

Animals↗
PubMed1984

Cholecystokinin in the hypothalamo-hypophyseal system.

Immunohistochemical studies on cholecystokinin-like (CCK-ir) substances in colchicine-pretreated rats demonstrated that in addition to CCK-ir cells in the magnocellular portion of the paraventricular nucleus. CCK-ir cells are also present among the parvocellular neurons. Radioimmunoassay of CCK after paraventricular lesions indicate that most, if not all, of the CCK in the posterior pituitary and in the median eminence originates from the paraventricular nucleus. It appears that CCK-fibers, like other neuropeptidergic fibers from the paraventricular nucleus (vasopressin, oxytocin, TRH, CRF) enter the medial basal hypothalamus through a common gate--the lateral retrochiasmatic area--in traveling to the median eminence.

Animals↗
PubMed1984

Mapping of LH-RH-containing projections to the mediobasal hypothalamus by differential deafferentation experiments.

Luteinizing hormone-releasing hormone (LH-RH) was immunoassayed in several hypothalamic structures of male rats after complete, anterior, posterior or lateral deafferentation of that structure performed with a rotating knife, as well as after discrete frontal or sagittal transections placed with a glass knife in various parts of the mediobasal hypothalamus (MBH). Survival time in all cases was two weeks. Taken together, the results indicate that most fibers containing LH-RH and originating in the preoptic area of the hypo-thalamus (APO) take a lateral course upon leaving that structure and travel along the medial forebrain bundle (MFB). Along that tract, they proceed caudally over some distance and enter the median eminence from the side; fibers innervating the posterior median eminence bend back towards the midline at a more posterior level than those terminating in the zona externa. A limited amount of fibers also reaches the median eminence from a midsagittal location. In addition, a few medial arcuate-median eminence connections may account for the small proportion of MBH LH-RH spared by complete, anterolateral or lateral transections. Projections to the organum vasculosum laminae terminalis, whether proceeding from the APO in an independent manner or as collaterals of fibers terminating in the median eminence, are unaffected by any of the transections tested. A partly common organization pattern of fibers supplying the median eminence in several neuropeptides (for instance somatostatin, CRF, cholecystokinin or dynorphin) is suggested.

Afferent Pathways↗
PubMed1984

On the origin of the serotonergic input to the intermediate lobe of the rat pituitary.

Serotonin-containing nerve fibers have been visualized immunocytochemically in the intermediate lobe of the rat pituitary. A 50% depletion of the serotonin level in the intermediate lobe was obtained in our previous experiment in rats with pituitary stalk transection, which may represent the total neuronally derived serotonin there. In the present studies we have attempted to determine the source of these fibers by examining the effect of hypothalamic and midbrain lesions or fiber transections on serotonin levels and serotonin-containing neuronal elements. Complete hypothalamic deafferentation resulted in a significant reduction of immunostained fibers in the intermediate lobe. A 27% fall in the serotonin content (measured by HPLC and electrochemical detection) and a significant disappearance of immunostained fibers were observed after transecting the ascending fibers from the raphe nuclei towards the hypothalamus. The transection combined with the lesioning of the hypothalamic dorsomedial nuclei resulted in a 50% decrease of serotonin level in the intermediate lobe. The present data therefore suggest that serotonin fibers in the intermediate lobe may originate from cells both in the midbrain raphe and hypothalamic dorsomedial nuclei.

Animals↗
PubMed1984

On the origin of dynorphin A and alpha-neo-endorphin in the substantia nigra.

The substantia nigra contains among the highest dynorphin A (Dyn A) and alpha-neo-endorphin (alpha-Neo) concentrations in the central nervous system. No dynorphin positive cell bodies are found there, only a dense network of nerve fibers and terminals. The present study provides evidence that the Dyn A and alpha-Neo in the substantia nigra are in neural processes arising from cells located in the head of the caudate nucleus. This neuronal system has been characterized by assaying Dyn A and alpha-Neo in the substantia nigra after a number of surgical transections of neuronal pathways in the rat forebrain and midbrain. Fibers containing dynorphins and neo-endorphins seem to pass through the internal capsule, ansa lenticularis, and medial forebrain bundle on their way from the striatum to the substantia nigra.

Animals↗
PubMed1984

Neuropeptides in the hypothalamo-hypophyseal system: lateral retrochiasmatic area as a common gate for neuronal fibers towards the median eminence.

The source and topography of neuropeptide-containing axons in the median eminence are summarized. Several of these neuropeptide-containing neurons (thyrotropin-releasing hormone, corticotropin-releasing hormone, vasopressin, oxytocin, cholecystokinin) are localized in the paraventricular nucleus. The periventricular and medial preoptic nuclei constitute the main sources of somatostatin and luteinizing hormone releasing hormone axons in the median eminence, respectively. Dynorphins and alpha-neo-endorphin-synthetizing neurons in the supraoptic nucleus also project to the median eminence. Wherever they originate, the projections may follow a common organization pattern and use a common gate--the lateral retrochiasmatic area--to enter the median eminence.

Animals↗
PubMed1984

Growth hormone releasing factors in the brain and the gut: chemistry, actions, and localization.

Within the physiological range of other known releasing factors, human pancreatic tumor growth hormone releasing factor (hpGRF) is specific for GH release. Data concerning hpGRF action on cAMP and GH are consistent with the concept of cAMP acting as a second messenger for this releasing factor. hpGRF-stimulated GH release is Ca++ dependent. Exogenous hpGRF40 does not alter the interdigestive gastric motility or secretion of gastrin and motilin in dogs, while large doses of hpGRF stimulate somatostatin release into the hepatic portal blood of the rat. Significant GRF activity as determined by a rat pituitary perifusion system is confined within the median eminence and the arcuate nucleus, though detectable but insignificant GRF activity is present in other area of the hypothalamus and cortex in the rat. GRF activity is present in the ovine brain as well as in the gut. Both tissues contain large (between 4000-5000 daltons) and small (but possibly larger than 1000 daltons) m.w. GRF materials. GRF appears to be structurally different between species and more than one GRF may be present within the same species. One of the ovine brain peptides with GH-releasing activity was partially characterized as His-Ser-Asp-Gly-Ile-Phe-Thr-Asp-Ser-Tyr- Lys-Arg-Try-Asn-Lys-Glu-Met- Ala-Lys--which is similar to rat GRF and porcine VIP having His at the N-terminus. Another peptide with GRF activity which eluted earlier on reverse phase HPLC and later on cation exchange chromatography has also been obtained in a pure form.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-3-isobutylxanthine↗
PubMed1984

Ultrastructure and synaptic connections of vasoactive intestinal polypeptide-like immunoreactive non-pyramidal neurons and axon terminals in the rat hippocampus.

In the hippocampus, antibody raised against vasoactive intestinal polypeptide (VIP) labeled perikarya and processes of non-pyramidal neurons whereas these structures remained unlabeled in pyramidal cells and granule cells. In the present study, VIP-immunostaining was used to investigate the fine structure and synaptic connections of identified non-pyramidal neurons and of immunoreactive axon terminals in the CA1 region of the rat hippocampus by means of electron microscopic immunocytochemistry. From a number of cells studied, two VIP-like immunoreactive non-pyramidal neurons in the regio superior were selected for an electron microscopic analysis of serial thin sections. These cells were different with regard to the location of their cell bodies and the orientation of their dendrites. One cell was located in the stratum lacunosum-moleculare with dendritic processes oriented parallel to the hippocampal fissure. The second neuron was found in the inner one-third of the stratum radiatum. The dendrites of this cell ran nearly parallel to the ascending apical dendrites of the pyramidal cells. Both cells had a round or ovoid perikaryon and an infolded nucleus. The aspinous dendrites of both neurons were densely covered with synaptic boutons. These terminals were small, filled with spherical vesicles, and established asymmetric synaptic contacts. No variations in the fine structure of the presynaptic boutons were found along the course of the labeled dendrites through the various hippocampal layers, although different afferents are known to terminate in these layers. Vasoactive intestinal polypeptide-like immunopositive axon terminals course through all layers of the hippocampus. In the stratum pyramidale they established symmetric synaptic contacts with the perikarya of pyramidal cells. In the stratum radiatum they made symmetric contacts with the shafts of apical dendrites of pyramidal cells but never contacted dendritic spines. The symmetric contacts with pyramidal cell perikarya suggest an involvement of the VIP-like immunoreactive axon terminals in pyramidal cell inhibition.

Animals↗
PubMed1984

Differential processing of prodynorphin and proenkephalin in specific regions of the rat brain.

Prodynorphin-derived peptides [dynorphin A (Dyn A)-(1-17), Dyn A-(1-8), Dyn B, alpha-neo-endorphin, and beta-neo-endorphin] and proenkephalin-derived peptides [[Leu]enkephalin [( Leu]Enk) and [Met]enkephalin-Arg6-Gly7-Leu8 [( Met]Enk-Arg-Gly-Leu]) in selected brain areas of the rat were measured by specific radioimmunoassays. We report here that different regions of rat brain contain strikingly different proportions of the prodynorphin and proenkephalin-derived peptides. There is a molar excess of alpha-neo-endorphin-derived peptides over Dyn B and Dyn A-derived peptides in many brain areas. [Leu]Enk concentrations exceed those of [Met]Enk-Arg-Gly-Leu in certain brain areas such as the substantia nigra, dentate gyrus, globus pallidus, and median eminence (areas rich in dynorphin-related peptides). These results indicated that (i) there is differential processing of prodynorphin in different brain regions and (ii) [Leu]Enk may be derived from Dyn A or Dyn B (or both). In certain brain regions [Leu]Enk may derive from two separate precursors (prodynorphin and proenkephalin) in two distinct neuronal systems.

Amygdala↗
PubMed1984

Preoptic LH-RH and somatostatin in the rat median eminence. An experimental light and electron microscopic immunocytochemical study.

Glass microknife lesions and immunocytochemistry were used to evaluate luteinizing hormone-releasing hormone (LH-RH)- and somatostatin (SS)-immunoreactive pathways from the preoptic region to the rat median eminence. Cuts were so placed that axons of more caudally located neurons in the periventricular hypothalamic areas were spared. Light and EM observations of LH-RH-immunostained preparations indicated that following the midline periventricular cuts the density of LH-RH labelled axons and axon terminals in the ME appeared similar to that of nonlesioned animals. Following bilateral lateral hypothalamic cuts placed between the preoptic area and the ME, LH-RH immunostaining in the ME was markedly reduced. This provides evidence that the preponderance of LH-RH axons originating from the preoptic area reach the ME by a lateral hypothalamic route. In contrast to the LH-RH findings, midline lesions made using the same coordinates caused a noticeable reduction in SS immunostaining in the accurate nucleus and ME. There was either no change or only minimal change after the lateral cut. Somatostatin axons arising from the preoptic periventricular nucleus take a periventricular route and contribute to median eminence innervation, but much less extensively than the more caudally located somatostatin neurons in the hypothalamic periventricular nucleus [19].

Animals↗
PubMed1984

Changes in the vasopressin content of discrete brain regions in response to stimuli for vasopressin secretion.

In order to better understand the function of vasopressin-containing axons which project to areas outside the hypothalamus, we measured vasopressin content in hypothalamic and extrahypothalamic brain regions following various periods of oral hypertonic saline or 1 week after pituitary stalk section. The supraoptic and paraventricular nuclei and nearly all of the brain regions examined which are known to receive vasopressin-containing axons from these nuclei showed parallel changes in vasopressin levels in response to both stimuli. In response to hypertonic saline there was an initial rise followed by a fall in vasopressin content. The suprachiasmatic and lateral septal nuclei, as well as the nucleus of the solitary tract, were unaffected by either stimulus. These results indicate that there are at least two functionally different vasopressin systems within the central nervous system, one of which is responsive to osmotic stimulation.

Amygdala↗