Regulation of the neuronal norepinephrine transporter by endothelin-1 and -3 in the rat anterior and posterior hypothalamus

We previously reported that endothelin-1 and endothelin-3 modulate norepinephrine neuronal release and tyrosine hydroxylase activity and expression in the hypothalamus. In the present study we sought to establish the role of endothelin-1 and -3 in the regulation of norepinephrine uptake in the anterior and posterior hypothalamus. Results showed that in the anterior hypothalamus endothelin-3 increased neuronal norepinephrine uptake whereas endothelin-1 decreased it. Conversely, in the posterior hypothalamic region both endothelins diminished the neuronal uptake of the amine. Endothelins response was concentration dependent and maintained at all studied times. Endothelins also modified the kinetic and internalization of the NE neuronal transporter. In the anterior hypothalamic region endothelin-3 increased the V_max and the B_max whereas endothelin-1 decreased them. However, in the posterior hypothalamic region both endothelins diminished the V_max as well as B_max. Neither endothelin-1 nor endothelin-3 modified neuronal norepinephrine transporter K_d in the studied hypothalamic regions. These findings support that in the posterior hypothalamic region both endothelins diminished neuronal norepinephrine transporter activity by reducing the amine transporter expression on the plasmatic membrane. Conversely, in the anterior hypothalamic region endothelin-3 enhanced neuronal norepinephrine transporter activity by increasing the expression of the transporter on the presynaptic membrane, whereas endothelin-1 induced the opposite effect. Present results permit us to conclude that both endothelins play an important role in the regulation of norepinephrine neurotransmission at the presynaptic nerve endings in the hypothalamus.     

Regulation of the neuronal norepinephrine transporter by endothelin-1 and -3 in the rat anterior and posterior hypothalamus

We previously reported that endothelin-1 and endothelin-3 modulate norepinephrine neuronal release and tyrosine hydroxylase activity and expression in the hypothalamus. In the present study we sought to establish the role of endothelin-1 and -3 in the regulation of norepinephrine uptake in the anterior and posterior hypothalamus. Results showed that in the anterior hypothalamus endothelin-3 increased neuronal norepinephrine uptake whereas endothelin-1 decreased it. Conversely, in the posterior hypothalamic region both endothelins diminished the neuronal uptake of the amine. Endothelins response was concentration dependent and maintained at all studied times. Endothelins also modified the kinetic and internalization of the NE neuronal transporter. In the anterior hypothalamic region endothelin-3 increased the V_max and the B_max whereas endothelin-1 decreased them. However, in the posterior hypothalamic region both endothelins diminished the V_max as well as B_max. Neither endothelin-1 nor endothelin-3 modified neuronal norepinephrine transporter K_d in the studied hypothalamic regions. These findings support that in the posterior hypothalamic region both endothelins diminished neuronal norepinephrine transporter activity by reducing the amine transporter expression on the plasmatic membrane. Conversely, in the anterior hypothalamic region endothelin-3 enhanced neuronal norepinephrine transporter activity by increasing the expression of the transporter on the presynaptic membrane, whereas endothelin-1 induced the opposite effect. Present results permit us to conclude that both endothelins play an important role in the regulation of norepinephrine neurotransmission at the presynaptic nerve endings in the hypothalamus.     

Short-term regulation of tyrosine hydroxylase activity and expression by endothelin-1 and endothelin-3 in the rat posterior hypothalamus

Brain catecholamines are involved in several biological functions regulated by the hypothalamus. We have previously reported that endothelin-1 and -3 (ET-1 and ET-3) modulate norepinephrine release in the anterior and posterior hypothalamus. As tyrosine hydroxylase (TH) is the rate-limiting enzyme in catecholamine biosynthesis, the aim of the present work was to investigate the effects of ET-1 and ET-3 on TH activity, total enzyme level and the phosphorylated forms of TH in the rat posterior hypothalamus. Results showed that ET-1 and ET-3 diminished TH activity but the response was abolished by both selective ET(A) and ET(B) antagonists (BQ-610 and BQ-788, respectively). In addition ET(A) and ET(B) selective agonists (sarafotoxin S6b and IRL-1620, respectively) failed to affect TH activity. In order to investigate the intracellular signaling coupled to endothelins (ETs) response, nitric oxide (NO), phosphoinositide, cAMP/PKA and CaMK-II pathways were studied. Results showed that N(omega)-nitro-l-arginine methyl ester and 7-nitroindazole (NO synthase and neuronal NO synthase inhibitors, respectively), 1H-[1,2,4]-oxadiazolo[4,3-alpha]quinozalin-1-one and KT-5823 (soluble guanylyl cyclase, and PKG inhibitors, respectively) inhibited ETs effect on TH activity. Further, sodium nitroprusside and 8-bromoguanosine-3',5'-cyclic monophosphate (NO donor and cGMP analog, respectively) mimicked ETs response. ETs-induced reduction of TH activity was not affected by a PKA inhibitor but it was abolished by PLC, PKC and CaMK-II inhibitors as well as by an IP(3) receptor antagonist. On the other hand, both ETs did not modify TH total level but reduced the phosphorylation of serine residues of the enzyme at positions 19, 31 and 40. Present results suggest that ET-1 and ET-3 diminished TH activity through an atypical ET or ET(C) receptor coupled to the NO/cGMP/PKG, phosphoinositide and CaMK-II pathways. Furthermore, TH diminished activity may result from the reduction of the phosphorylated sites of the enzyme without changes in its total level. Taken jointly present and previous results support that ET-1 and ET-3 may play a relevant role in the modulation of catecholaminergic neurotransmission in the posterior hypothalamus of the rat.     

Long-term modulation of tyrosine hydroxylase activity and expression by endothelin-1 and -3 in the rat anterior and posterior hypothalamus

Brain catecholamines are involved in the regulation of biological functions, including cardiovascular activity. The hypothalamus presents areas with high density of catecholaminergic neurons and the endothelin system. Two hypothalamic regions intimately related with the cardiovascular control are distinguished: the anterior (AHR) and posterior (PHR) hypothalamus, considered to be sympathoinhibitory and sympathoexcitatory regions, respectively. We previously reported that endothelins (ETs) are involved in the short-term tyrosine hydroxylase (TH) regulation in both the AHR and PHR. TH is crucial for catecholaminergic transmission and is tightly regulated by well-characterized mechanisms. In the present study, we sought to establish the effects and underlying mechanisms of ET-1 and ET-3 on TH long-term modulation. Results showed that in the AHR, ETs decreased TH activity through ET(B) receptor activation coupled to the nitric oxide, phosphoinositide, and CaMK-II pathways. They also reduced total TH level and TH phosphorylated forms (Ser 19 and 40). Conversely, in the PHR, ETs increased TH activity through a G protein-coupled receptor, likely an atypical ET receptor or the ET(C) receptor, which stimulated the phosphoinositide and adenylyl cyclase pathways, as well as CaMK-II. ETs also increased total TH level and the Ser 19, 31, and 40 phosphorylated sites of the enzyme. These findings support that ETs are involved in the long-term regulation of TH activity, leading to reduced sympathoinhibition in the AHR and increased sympathoexcitation in the PHR. Present and previous studies may partially explain the cardiovascular effects produced by ETs when applied to the brain.     

Endothelin-1 and -3 diminish neuronal NE release through an NO mechanism in rat anterior hypothalamus

The existence of endothelin binding sites on the catecholaminergic neurons of the hypothalamus suggests that endothelins (ETs) participate in the regulation of noradrenergic transmission modulating various hypothalamic-controlled processes such as blood pressure, cardiovascular activity, etc. The effects of ET-1 and ET-3 on the neuronal release of norepinephrine (NE) as well as the receptors and intracellular pathway involved were studied in the rat anterior hypothalamus. ET-1 (10 nM) and ET-3 (10 nM) diminished neuronal NE release and the effect blocked by the selective ET type B receptor antagonist BQ-788 (100 nM). N(omega)-nitro-L-arginine methyl ester (10 microM), methylene blue (10 microM), and KT5823 (2 microM), inhibitors of nitric oxide synthase activity, guanylate cyclase, and protein kinase G, respectively, prevented the inhibitory effects of both ETs on neuronal NE release. In addition, both ETs increased nitric oxide synthase activity. Furthermore, 100 microM picrotoxin, a GABA(A)-receptor antagonist, inhibited ET-1 and ET-3 response. Our results show that ET-1 as well as ET-3 has an inhibitory neuromodulatory effect on NE release in the anterior hypothalamus mediated by the ET type B receptor and the involvement of a nitric oxide-dependent pathway and GABA(A) receptors. ET-1 and ET-3 may thus diminish available NE in the synaptic gap leading to decreased noradrenergic activity.     

Effect of endothelin-1 on release of arginine-vasopressin from perifused rat hypothalamus

Endothelin-1 (ET-1) is an endothelium-derived vasoconstrictor peptide with potent pressor activity. We studied the effect of ET-1 on release of arginine-vasopressin (AVP) from perifused rat hypothalamus. ET-1 (10(-10) to 10(-8) M) significantly stimulated AVP release. The ET-1-induced AVP release was completely blocked in the presence of nicardipine. Our results suggest a possible involvement of ET in the regulation of AVP release.     

Inhibitory effect of norepinephrine on immunoreactive corticotropin-releasing factor release from the rat hypothalamus in vitro

Effects of catecholamines on immunoreactive corticotropin-releasing factor (I-CRF) release from the rat hypothalamus were examined using a rat hypothalamic perifusion system and a rat CRF RIA in vitro. Norepinephrine had a potent inhibitory effect on I-CRF release in a dose-dependent manner at 0.1 nM-1 microM concentrations, but dopamine did not. This inhibitory effect of norepinephrine was completely blocked by propranolol, but only partially blocked by phentolamine. Isoproterenol also had a potent inhibitory effect at 0.01-100 nM concentrations, and a high dose of phenylephrine (10 nM) inhibited I-CRF release. Clonidine did not influence I-CRF release. These results suggest that norepinephrine inhibits I-CRF release mainly through the beta-adrenergic receptor and partially through the alpha 1-receptor.     

Effects of atrial natriuretic factor on norepinephrine release in the rat hypothalamus.

The effects of atrial natriuretic factor on the mechanisms involved in norepinephrine release were studied 'in vitro' in slices of Wistar rat hypothalamus. Atrial natriuretic factor (10, 50 and 100 nM) decreased spontaneous [3H]norepinephrine secretion in a concentration dependent way. In addition, the peptide (10 nM) also reduced acetylcholine induced output of norepinephrine. The atrial factor (10 nM) was unable to alter the amine secretion when the incubation medium was deprived of calcium or when a calcium channel blocker such as diltiazem (100 microM) was added. In conclusion, atrial natriuretic factor reduced both spontaneous and acetylcholine evoked [3H]norepinephrine release in the rat hypothalamus. These findings suggest that the atrial natriuretic factor may alter catecholamine secretion by modifying the calcium available for the exocytotic process of catecholamine output.     

Regulation of hypoxia-induced release of corticotropin-releasing factor in the rat hypothalamus by norepinephrine

Corticotropin-releasing factor (CRF) peptide release was activated by hypoxia in the rat hypothalamus. The mechanisms, however, of the hypoxia-induced CRF release remains unclear. In this study, we demonstrated that the norepinephrine (NE) and its receptors in the paraventricular nucleus (PVN) mediated the CRF release in a simulated altitude hypoxia. When rats were exposed to 5 or 7 km altitude of hypoxia for a short or long term: (1) NE levels in the PVN and the CeA, using the HPLC analysis, were intensity and time course dependently increased, but the increase in the PVN were potential than in the CeA. Restraint-induced NE increase was much higher in both the PVN and the CeA, compared with hypoxia-induced response. (2) Hypoxia and restraint significantly enhanced CRF release in the ME and the PVN but not in the CeA, through RIA assay, which result in stimulating corticosterone secretion. (3) Hypoxia-induced CRF release was reversed by an injection of prazosin (i.c.v.), an alpha-1 adrenoceptor antagonist, while administration of yohimbine (i.c.v.), an alpha-2 receptor antagonist, facilitated further CRF release. These data suggested that hypoxia induced NE activation centrally, via alpha-1 and -2 receptors, leading to improving hypothalamic CRF release, which in turn stimulated pituitary and adrenal cortex. Restraint presented much potential action on NE activation than hypoxia.     

Effect of environmental stress on release of norepinephrine in posterior nucleus of the hypothalamus in awake rats: role of sinoaortic nerves

Norepinephrine(NE) release in posterior nucleus(PH) of the hypothalamus was examined before and during acute shaker (oscillation) stress in sinoaortic denervated(SAD) and sham-operated(SO) rats. NE in PH extracellular fluid of freely moving rats was collected by microdialysis and measured by sensitive radioenzymatic assay. Three days after SAD or SO operation, mean arterial pressure(MAP) and heart rate(HR) were significantly higher in SAD rats than SO rats. Baseline levels of NE in PH dialysate were also significantly elevated in SAD rats. Although five minutes of shaker stress elicited pressor and tachycardic responses coupled with increased NE release in PH of both groups, the increases in MAP and dialysate NE were larger in SAD than SO rats. These findings indicate that noradrenergic neurons in the PH respond to stress-induced stimuli and receive tonic input from baroreflex pathways.     

Inhibitory effects of endothelin-1 and endothelin-3 on prolactin release: possible involvement of endogenous endothelin isopeptides in the rat anterior pituitary.

Spontaneous prolactin release from the isolated rat anterior pituitary was inhibited by endothelin-1 in a dose-dependent manner (10(-8)-10(-6) M). Endothelin-3 also inhibited spontaneous prolactin release with an almost identical dose-response relationship as endothelin-1. These inhibitory effects were unaffected by application of a dopamine D2-receptor antagonist, YM-09151-2 (10(-7) M). Rat anterior and posterior pituitary glands were abundant in both endothelin-1 and endothelin-3, as compared with other regions of the brain. The present results suggest that endogenous endothelin-1 and endothelin-3 in the anterior and posterior pituitary are involved in the inhibitory regulation of prolactin secretion as autocrine or paracrine factors.     

烫伤对大鼠下丘脑室旁核内皮素—1合成和分泌的影响

目的研究烫伤后下丘脑室旁核(PVH)内皮素-1(ET-1)的合成和分泌改变,探讨PVHET-1在烫伤中的病理生理学意义。方法用原位杂交和免疫组织化学方法观察了烫伤后PVHET-1合成和分泌的变化,并用通用图象颗粒分析法检测单位面积内ET-1mRNA阳性杂交信号的强度和ET-1样免疫反应物(ET-1-ir)免疫反应强度。结果烫伤后15minPVH神经元胞浆内ET-1mRNA阳性杂交信号与对照组相比未见明显差异,烫伤后60min和180minPVH神经元胞浆内ET-1mRNA阳性杂交信号较对照组(100％±25％)明显增多,强度明显增高,分别为138％±26％(P<0．05)和167％±18％(P<0.01);而烫伤后15minPVH神经元胞浆内ET-1阳性反应物明显减少,免疫反应物强度为6．3％±1．5％,显著低于对照组(P<0．01),烫伤后60min和180min逐渐回升,分别为23．1％±2．9％和44．1％±3．8％,但仍显著低于对照组(P＜0．01)。结论烫伤后PVHET-1合成和分泌增加。     

Stimulatory effect of somatostatin on norepinephrine release from rat brain cortex slices

The effect of somatostatin (SRIF) on norepinephrine (NE) release from the brain tissue was determined on the superfused rat cerebral cortex slices preloaded with ³HNE. SRIF (0.38 μM–1.53 μM) was found to stimulate dose-dependently tritium (³H) overflow evoked electrically by 30%—116% although SRIF did not affect on the spontaneous ³H overflow. SRIF at the concentrations which exhibited the stimulatory effect inhibited scarecely the uptake of ³HNE by cortex slices, while the reference drug, cocaine (50 μM, 10 μM) markedly depressed the uptake. The stimulatory effect of SRIF was not reduced by phentolamine (3.14 μM), α-adrenoceptor blocker, which increased the evoked ³H overflow from the slices itself. These results suggest that SRIF does not produce its stimulatory effect by inhibiting the NE reuptake mechanisms or by interacting with the presynaptic α-adrenoceptors. Elevating of Ca²⁺ concentrations from 0.75 mM to 2.25 mM in the superfusion fluid reduced the stimulatory effect of SRIF. It is possible that SRIF stimulates NE release by facilitating the availability of Ca²⁺ for the release mechanisms.     

烫伤对大鼠下丘脑视上核内皮素-1基因转录和蛋白含量的影响

用原位杂交和免疫组织化学方法观察了烫伤后下丘脑视上核（ＳＯＮ）内皮素－１（ＥＴ－１）基因转录和蛋白含量的变化,并用通用图像颗粒分析法估计ＥＴ－１ ｍＲＮＡ阳性杂交信号的强度和ＥＴ－１样免疫反应物（ＥＴ－１－ｉｒ）的免疫反应强度。与对照组相比,烫伤后１５ｍｉｎ,ＳＯＮ神经元胞浆内ＥＴ－１ ｍＲＮＡ阳性杂交信号未见明显变化;而在烫伤后６０和１８０ｍｉｎ,ＥＴ－１ ｍＲＮＡ阳性杂交信号强度分别较比照组增     

Modulatory effect of HCO3- on rat mast cell exocytosis: cross-talks between bicarbonate and calcium.

HCO-3 modulation of histamine release and its relationship with the Ca2+ signal were studied in serosal rat mast cells. Histamine release was induced by Ca2+ mobilizing stimuli, namely compound 48/80, thapsigargin, Ca2+ chelators, ionophore A23187, and PMA and ionophore A23187 in a HCO-3-buffered medium or a HCO-3-free medium. The presence of HCO-3 reduced histamine release by 48/80, Ca2+ chelators, A23187, and PMA/A23187, but increased histamine release induced by thapsigargin. Histamine release by PMA was significantly higher in a HCO-3-free medium than in a HCO-3-free medium, as it was the PMA potentiation of histamine release by A23187. [Ca2+]i changes induced by these drugs were measured in fura-2-loaded mast cells. In thapsigargin and EGTA or BAPTA preincubated mast cells [Ca2+]i increase was higher in a HCO-3-buffered medium than in a HCO-3-free medium in the presence of Ca2+. On the contrary, in compound 48/80 and PMA/A23187 activated mast cells the [Ca2+]i increase is the same both in the presence and in the absence of HCO-3. The effect of HCO-3 on histamine release in serosal rat mast cells depends on the stimulus, but it is not related to the presence of Cl-. In thapsigargin-stimulated mast cells the effect of HCO-3 on histamine release may be related to the Ca2+ signal, but in compound 48/80, EGTA, and PMA/A23187-activated mast cells there is no relationship between intracellular Ca2+ and the inhibitory effect of HCO-3 on histamine release. Additionally, the PKC pathway is implicated in the inhibitory effect of HCO-3 on histamine release, the higher the chelation of calcium rendering the higher the enhancement of the response after adding calcium in the absence of HCO-3.     

Stimulatory effect of acetylcholine on immunoreactive corticotropin-releasing factor release from the rat hypothalamus in vitro

Effects of acetylcholine (Ach) and gamma-aminobutyric acid (GABA) on immunoreactive corticotropin-releasing factor (CRF) release from the rat hypothalamus were examined using a rat hypothalamic perifusion system and a rat CRF RIA in vitro. Ach stimulated CRF release in a dose-dependent manner (1 pM-1 nM). One nM Ach-induced CRF release was inhibited by atropine in a dose-dependent manner (1-100 nM), but was inhibited by only a high concentration (100 nM) of hexamethonium. In addition, such Ach-induced CRF release was inhibited by norepinephrine. GABA did not influence basal CRF release. These results suggest that Ach stimulates CRF release mainly through muscarinic receptors at least under our conditions.     

Immunohistochemistry of endogenous L-DOPA in the rat posterior hypothalamus

The aim of this work was to study L-DOPA-containing neuronal structures of the rat posterior and dorsal hypothalamus by means of immunohistochemistry using antiserum against glutaraldehyde conjugated L-DOPA. Aspects and distribution of L-DOPA immunoreaction among cells of the supramammillary nucleus and the A11, A13c and A13 cell groups are described and compared to dopamine immunoreactivity, mainly through a double colored labelling procedure employing a color modification of the DAB reaction by metallic ions. Differences between L-DOPA and dopamine stainings within cell groups as the presence of cells with predominant or exclusive L-DOPA coloration are tentatively explained under the light of previous findings using immunohistochemistry of catecholamines synthesizing enzymes and catecholamines histofluorescence.     

Immunohistochemistry of endogenous l-DOPA in the rat posterior hypothalamus

Summary The aim of this work was to study l-DOPA-containing neuronal structures of the rat posterior and dorsal hypothalamus by means of immunohistochemistry using antiserum against glutaraldehyde conjugated l-DOPA. Aspects and distribution of l-DOPA immunoreaction among cells of the supramammillary nucleus and the A11, A13c and A13 cell groups are described and compared to dopamine immunoreactivity, mainly through a double colored labelling procedure employing a color modification of the DAB reaction by metallic ions. Differences between l-DOPA and dopamine stainings within cell groups as the presence of cells with predominant or exclusive l-DOPA coloration are tentatively explained under the light of previous findings using immunohistochemistry of catecholamines synthesizing enzymes and catecholamines histofluorescence.     

In vitro effect of neuropeptide Y on melatonin and norepinephrine release in rat pineal gland

1. To study neuropeptide Y (NPY) effect on melatonin production, rat pineal explants were incubated for 6 hr with 10-1,000 nM NPY in the presence or absence of 10 microM norepinephrine (NE). Melatonin content in the pineal gland and media was measured by radioimmunoassay (RIA). 2. NPY (10-1,000 nM) increased melatonin production and, at 10 or 100 nM concentrations (but not 1,000 nM), enhanced NE stimulation of melatonin production. 3. NPY (1,000 nM) impaired 3H-labeled transmitter release induced by a K+ depolarizing stimulus in rat pineals incubated with 3H-NE. 4. These results suggest that NPY affects both pre- and postsynaptic pineal mechanisms.