Colocalized neurotransmitters in the hindbrain cooperate in adaptation to chronic hypernatremia

Chronic hypernatremia activates the central osmoregulatory mechanisms and inhibits the function of the hypothalamic-pituitary-adrenal (HPA) axis. Noradrenaline (NE) release into the periventricular anteroventral third ventricle region (AV3V), the supraoptic (SON) and hypothalamic paraventricular nuclei (PVN) from efferents of the caudal ventrolateral (cVLM) and dorsomedial (cDMM) medulla has been shown to be essential for the hypernatremia-evoked responses and for the HPA response to acute restraint. Notably, the medullary NE cell groups highly coexpress prolactin-releasing peptide (PrRP) and nesfatin-1/NUCB2 (nesfatin), therefore, we assumed they contributed to the reactions to chronic hypernatremia. To investigate this, we compared two models: homozygous Brattleboro rats with hereditary diabetes insipidus (DI) and Wistar rats subjected to chronic high salt solution (HS) intake. HS rats had higher plasma osmolality than DI rats. PrRP and nesfatin mRNA levels were higher in both models, in both medullary regions compared to controls. Elevated basal tyrosine hydroxylase (TH) expression and impaired restraint-induced TH, PrRP and nesfatin expression elevations in the cVLM were, however, detected only in HS, but not in DI rats. Simultaneously, only HS rats exhibited classical signs of chronic stress and severely blunted hormonal reactions to acute restraint. Data suggest that HPA axis responsiveness to restraint depends on the type of hypernatremia, and on NE capacity in the cVLM. Additionally, NE and PrRP signalization primarily of medullary origin is increased in the SON, PVN and AV3V in HS rats. This suggests a cooperative action in the adaptation responses and designates the AV3V as a new site for PrRP's action in hypernatremia

A hypothalamus és az autonóm idegrendszer szabályozó mechanizmusaiban részt vevő agypályák topográfiája és neurokémiai karakterizálásuk = Topography and neurochemical characterization of hypothalamic and central autonomic pathways

1. Feltérképezték a hypothalamus orexin-termelő neuronjainak agytörzsi projekcióit, pályáit, valamint elsőként mutatták ki kapcsolatait az agytörzs valamennyi noradrenalint és adrenalint termelő sejtcsoportjának neuronjaival. A vizsgálat eredménye alapvető fontosságú neuromorfológiai adat a táplálékfelvétel, valamint az agyi catecholamine rendszer kapcsolatának tisztázására a szervezet energia-háztartásának szempontjából. 2. Különböző neuroanatómiai és immunhisztokémiai vizsgálatokkal először írták le a korábban ismeretlen mediális paralemniscális magot patkány, majom és az emberi alsó agytörzsben. Igazolták egy speciális peptiderg (TIP39-PTH2 receptor) rendszer jelenlétét e mag területén. Tisztázták a magcsoport afferens és efferens neuronális kapcsolatait és adatot szolgáltattak ezen mag neuronjainak az akusztikus stresszben vitt szerepéről. 3. Igazolták egy limbikus agykéregből leszálló, a gyomor működésében szerepet vivő pálya multiszinaptikus jelenlétét és topográfiáját: infralimbic anterior cingulate cortex - centralis amygdala - paraszimpatikus dorsalis vagus mag - n. vagus pálya. 4. Elsőként írták le a ""jóllakottság"" érzés (satiety) agypályáját a gyomor - n. vagus - nucleus tractus solitariii - hypothalamus nucleus dorsomedialis. Igazolták az ezen pályán belüli szignál transzdukcióban a glucagon-like peptide-1 és a prolactin-releasing hormon neuropeptidek meghatározó szerepét. | In order to attain major objectives of the project, a number of various neuromorphological techniques have been successfully applied to identify, localize and characterize neuronal pathway that interconnect the hypothalamus and lower brainstem nuclei. The major new findings and observations are the follows: 1) Pathways and lower brainstem projections of hypothalamic orexin-expressing neurons have been verified a mapped topographically. Termination and synaptic contacts of orexin-containing fibers have been demonstrated on adrenaline- and noradrenaline-expressing neurons in each lower brainstem catecholamine cell group indicating the existence of a descending hypothalamic pathway that influence the body energy metabolism by controlling the peripheral catecholamine outflow. 2) The afferent and efferent neuronal connections of the pontine medial paralemniscal nucleus have been first described in the rat, monkey and human brains providing evidence for the hypothalamic connections of this cell group that may participate in acoustic stress response. 3) The description of a multisynaptic pathway between the limbic system and the lower brainstem autonomic centers via hypothalamus and the amygdala has been completed in the present study demonstrating the functional importance of limbic cortical areas on the functional activity of the stomach. 4) The complete neuronal pathway of the “satiety signal” from the stomach to the hypothalamic regulatory center has been first verified by demonstrating of the ascending glucagon-like peptide-1 projections from the nucleus of the solitary tract to dorsomedial hypothalamic neurons. This may represent one of the most important link in the mechanism that control the central regulation of food intake

Perivascular Expression and Potent Vasoconstrictor Effect of Dynorphin A in Cerebral Arteries

BACKGROUND: Numerous literary data indicate that dynorphin A (DYN-A) has a significant impact on cerebral circulation, especially under pathophysiological conditions, but its potential direct influence on the tone of cerebral vessels is obscure. The aim of the present study was threefold: 1) to clarify if DYN-A is present in cerebral vessels, 2) to determine if it exerts any direct effect on cerebrovascular tone, and if so, 3) to analyze the role of κ-opiate receptors in mediating the effect. METHODOLOGY/PRINCIPAL FINDINGS: Immunohistochemical analysis revealed the expression of DYN-A in perivascular nerves of rat pial arteries as well as in both rat and human intraparenchymal vessels of the cerebral cortex. In isolated rat basilar and middle cerebral arteries (BAs and MCAs) DYN-A (1-13) and DYN-A (1-17) but not DYN-A (1-8) or dynorphin B (DYN-B) induced strong vasoconstriction in micromolar concentrations. The maximal effects, compared to a reference contraction induced by 124 mM K(+), were 115±6% and 104±10% in BAs and 113±3% and 125±9% in MCAs for 10 µM of DYN-A (1-13) and DYN-A (1-17), respectively. The vasoconstrictor effects of DYN-A (1-13) could be inhibited but not abolished by both the κ-opiate receptor antagonist nor-Binaltorphimine dihydrochloride (NORBI) and blockade of G(i/o)-protein mediated signaling by pertussis toxin. Finally, des-Tyr(1) DYN-A (2-13), which reportedly fails to activate κ-opiate receptors, induced vasoconstriction of 45±11% in BAs and 50±5% in MCAs at 10 µM, which effects were resistant to NORBI. CONCLUSION/SIGNIFICANCE: DYN-A is present in rat and human cerebral perivascular nerves and induces sustained contraction of rat cerebral arteries. This vasoconstrictor effect is only partly mediated by κ-opiate receptors and heterotrimeric G(i/o)-proteins. To our knowledge our present findings are the first to indicate that DYN-A has a direct cerebral vasoconstrictor effect and that a dynorphin-induced vascular action may be, at least in part, independent of κ-opiate receptors

Nesfatin-1/NUCB2 may participate in the activation of the hypothalamic-pituitary-adrenal axis in rats

Nesfatin-1 is an anorexigenic peptide originating from nucleobinding-2 (NUCB2) protein. Nesfatin-1/NUCB2-immunoreactive neurons are present in the hypothalamic paraventricular nucleus, the center of the stress-axis, and in the medullary A1 and A2 catecholamine cell groups. The A1 and A2 cell groups mediate viscerosensory stress information toward the hypothalamic paraventricular nucleus. They contain noradrenaline, but subsets of these neurons also express prolactin-releasing peptide acting synergistically with noradrenaline in the activation of the hypothalamic paraventricular nucleus during stress. We investigated the possible role of nesfatin-1/NUCB2 in the stress response. Intracerebro-ventricular administration of nesfatin-1 elevated both plasma adrenocorticotropin and corticosterone levels, while in vitro stimulation of the hypophysis was ineffective. Single, long-duration restraint stress activated (Fos positivity) many of the nesfatin-1/NUCB2-immunoreactive neurons in the parvocellular part of the hypothalamic paraventricular nucleus, evoked nesfatin-1/NUCB2 mRNA expression in the parvocellular part of the paraventricular nucleus and in the A1, but not in the A2 cell group. Nesfatin-1/NUCB2 was shown to co-localize in a high percentage of prolactin-releasing peptide producing neurons, in both medullary catecholamine cell groups further supporting its involvement in the stress response. Finally, bilateral adrenalectomy evoked an increasing nesfatin-1/NUCB2 mRNA expression, indicating that it is under the negative feedback of adrenal steroids. These data provide the first evidence for possible participation of nesfatin-1/NUCB2 in the stress-axis regulation, both at the level of the brainstem and in the hypothalamus

Dynorphin A (DYN-A) (2–13) induces contraction of rat cerebral arteries independently of κ-opiate receptors.

<p>Effects of DYN-A (2–13) on the tone of rat basilar (A) and middle cerebral (B) arteries before and after treatment with the κ-opiate receptor antagonist <i>nor</i>-Binaltorphimine dihydrochloride (NORBI, 50 µM). DYN-A (2–13), which is reportedly inactive at opiate receptors, evoked weaker [in comparison to DYN-A (1–13) shown in previous figures] but significant contractions in both vessels, and these effects were resistant to NORBI. Values are expressed as mean±SEM percentage of the reference contraction induced by 124 mmol/L K⁺ Krebs solution, n = 6–9.</p

Dynorphin A (DYN-A) induced cerebral vasoconstriction is partly mediated by κ-opiate receptors.

<p>Effect of the κ-opiate receptor antagonist <i>nor</i>-Binaltorphimine dihydrochloride (NORBI, 50 µM) on the responsiveness of rat basilar (A) and middle cerebral (B) arteries to DYN-A (1–13). NORBI was able to reduce the vasoconstrictor effect of DYN-A in both vessels, whereas its vehicle (saline) was without any effect (C and D). Values are expressed as mean±SEM percentage of the reference contraction induced by 124 mmol/L K⁺ Krebs solution, n = 8–10. Asterisks indicate significant (**<i>P</i><0.01, ***<i>P</i><0.001) differences between values before and after NORBI treatment.</p

Dynorphin A (DYN-A) is present in perivascular nerves of rat and human intraparenchymal arteries.

<p>Oblique sections of rat (A and B) as well as longitudinal sections of rat (C and D) and human (E and F) cerebral arteries are shown. Merged images of DYN-A (1–13) immunoreactivity (green fluorescence) and transmitted-light (grayscale) indicate the perivascular localization of DYN-A. Broken line shows the surface of the brain on panels A and B, asterisks indicate red blood cell clots in the lumen of the artery on panel F. Bar = 50 µm on each panel.</p

Dynorphin A (DYN-A) (1–13) and (1–17) induce strong contraction of rat cerebral arteries.

<p>Effects of cumulative concentrations of DYN-A (1–8), (1–13), (1–17) and Dynorphin B (DYN-B) on the resting tension of rat basilar (A) and middle cerebral (B) arteries. DYN-A (1–13) and DYN-A (1–17) induce strong, dose-dependent vasoconstriction in both vessels, whereas DYN-A (1–8) and DYN-B have no significant effect. Values are expressed as mean±SEM percentage of the reference contraction induced by 124 mmol/L K⁺ Krebs solution, n = 6–37. *<i>P</i><0.05, **<i>P</i><0.01, ***<i>P</i><0.001 vs. DYN-A (1–8); ^##<i>P</i><0.01, ^###<i>P</i><0.001 vs. DYN-B.</p

Dynorphin A (DYN-A) is present in perivascular nerves of the rat basilar artery.

<p>Localization of DYN-A in perivascular nerve fibers of rat basilar artery by immunofluorescent confocal microscopy. Anti-synaptophysin staining (red fluorescence) indicates the synaptic vesicles of perivascular nerves on the surface of the basilar artery (A). DYN-A (1–13) (green fluorescence) is abundantly found in the adventitia (B) and co-localized with synaptophysin (C). Bar = 100 µm.</p