In the present experiments we investigated a possible involvement of imidazoline receptors of the paraventricular nucleus (PVN) of the hypothalamus on the presser effects of the angiotensin LI (ANG II) injected into the subfornical organ (SFO), in male Holtzman rats (250-300 g) with a cannula implanted into the third ventricle (3rdV), PVN and SFO. At first we tested the participation of alpha(2) and imidazoline agonist and antagonist compounds on the presser effect of ANG II injected into the 3rdV. Based on the results we may conclude that clonidine associated with rilmenidine was able to block the hypertensive response to ANG IT. The ANG II (20 pmol) injected into SFO induced a robust increase in blood pressure (37 +/- 2 mmHg). Isotonic saline (0.15 M) NaCl did not produce any change in blood pressure (5 +/- 2 mmHg). The injection of rilmenidine (30 mu g/kg/l mu L), an imidazoline agonist agent injected into PVN before ANG II injection into SFO, blocked the presser effect of ANG II (5 +/- 2 mmHg). Also, the injection of idazoxan (60 mu g/kg/mu L) before rilmenidine blocked the inhibitory effect of rilmenidine on blood pressure (39 +/- 4 mmHg). The injection of clonidine (20 nmol/mu L) prior to ANG II into the 3rdV produced a decreased in arterial blood pressure (37 +/- 2 mmHg) to (15 +/- 4 mmHg). The injection of yohimbine (80 nmol/mu L) prior to clonidine blocked the effect of clonidine on the effect of ANG II (27 +/- 2 mmHg). The injection of rilmenidine prior to ANG TI also induced a decrease in arterial blood pressure (10 +/- 3 mmHg). The injection of idazoxan prior to rilmenidine also blocked the inhibitory effect of rilmenidine (24 +/- 3 mmHg). In summary...
We have studied the effects of L-NG-nitro arginine methyl esther (L-NAME), L-arginine (LAR), inhibitor and a donating nitric oxide agent on the alterations of salivary flow, water intake, arterial blood pressure (MAP) and heart rate (HR) induced by the injection pilocarpine into the subfornical organ (SFO). Rats (Holtzman 250-300 g) were anesthetized with 2, 2, 2-tribromoethanol (20 mg/100 kg b. wt.) and a stainless steel carmula were implanted into their SFO. The volume of injection was 0.2 mu l. The amount of saliva secretion was studied over a 5-min period. Pilocarpine (40 mu g), L-NAME (40 mu g) and LAR (30 mu g) were used in all experiments for the injection into the SFO. Pilocarpine (10, 20, 40, 80 and 160 mu g) injected into SFO elicited a concentration-dependent increase in salivary secretion. L-NAME injected prior to pilocarpine into the SFO increased salivary secretion and water intake due to the effect of pilocarpine. LAR injected prior to pilocarpine into the SFO attenuated the salivary secretion and water intake. Pilocarpine, injected into the SFO increased the MAP and decreased heart rate (HR). L-NAME injected prior to pilocarpine into the SFO potentiated the pressor effect of pilocarpine with a decrease in HR. LAR injected into the SFO prior to pilocarpine attenuated the increase in MAP with no changes in HR. The present study suggests that the SFO nitrergic cells interfere in the cholinergic pathways implicated in the control of salivary secretion...
The present experiments were conducted to investigate the role of the alpha (1A)-, alpha (1B), beta (1),- and beta (2)-adrenoceptors of the lateral hypothalamus (LH) on the water and salt intake responses elicited by subfornical organ (SFO) injection of angiotensin II (ANG II) in rats. 5-methylurapidil (an alpha (1A)-adrenergic antagonist), cyclazosin (an alpha (1B)-adrenergic antagonist) and ICI-118,551 (a beta (2)-adrenergic antagonist) injected into the LH produced a dose-dependent reduction, whereas efaroxan (an alpha (2)-antagonist) increased the water intake induced by administration of ANG II into the SFO. These data show that injection of 5-methylurapidil into the LH prior to ANG II into the SFO increased the water and sodium intake induced by the injection of ANG II. The present data also show that atenolol (a beta (1)-adrenergic antagonist), ICI-118,551, cyclazosin, or efaroxan injected into the LH reduced in a dose-dependent manner the water and sodium intake to angiotensinergic activation of SFO. Thus, the alpha (1)- and beta -adrenoceptors of the LH are possibly involved with central mechanisms dependent on ANG II and SFO that control water and sodium intake. (C) 2000 Elsevier B.V. B.V. All rights reserved.
In the present study we investigate the effect of electrolytic lesion of the medial septal area (MSA) on the pressor and dipsogenic response to cholinergic activation and angiotensin II (ANGII) injection into the subfornical organ (SFO) in rats. In addition the effect of MSA lesion on the natriuresis, kaliuresis and diuresis after cholinergic activation of the SFO was also investigated. Sham- and MSA-lesioned rats with a stainless steel cannula implanted into the SFO was used. The injection of ANGII (12 ng) into the SFO in sham rats produced pressor (24 +/- 2 mmHg) and dipsogenic (9.6 +/- 1.1 ml/h) responses. MSA lesion, both acute (2-6 days) and chronic (15-19 days), reduced the pressor (14 +/- 2 mmHg) and dipsogenic (2.7 +/- 1 ml/h) responses to ANGII into SFO. The injection of the cholinergic agonist carbachol (2 nmol) into the SFO in sham rats produced pressor (48 +/- 4 mmHg), dipsogenic (10 +/- 1.2 ml/h), natriuretic (457 +/- 58 muEq/2 h) and kaliuretic (249 +/- 16 muEq/2 h) responses. Acute, but not chronic MSA lesion reduced the pressor (27 +/- 3 mmHg), natriuretic (198 +/- 55 muEq/2 h) and kaliuretic (128 +/- 16 muEq/2 h) responses to carbachol into SFO. No change in the dipsogenic response to carbachol into the SFO was observed in MSA-lesioned rats. Antidiuresis after carbachol was observed only in MSA-lesioned rats. The present results show that the MSA plays a role on the pressor...
1. Water intake induced by injection of 0.2 M-NaCl into the lateral preoptic area was increased by the injection of angiotensin II into the subfornical organ of rats. The injection of hypertonic saline solution into the subfornical organ increased water intake. However, the increase was lower than when the solution was injected into the lateral preoptic area. The injection of 4 μg angiotensin II into the lateral preoptic area further augmented this effect. 2. Injection of angiotensin II into the subfornical organ caused a rise in blood pressure which preceded the thirst-inducing effect. The injection of 0.2 M NaCl into the subfornical organ caused no changes in blood pressure, whereas the injection of angiotensin II into the lateral preoptic area caused some increase. 3. Dehydration of the lateral preoptic area by means of 0.2 M NaCl in combination with intravenous infusion of angiotensin II caused a summation of effects in terms of the water intake, without changing cardiovascular alterations induced by the infusion of angiotensin II. A summation of effects in the water intake, but not in blood pressure, was also observed when 0.5 M NaCl was infused intravenously in combination with the injection of angiotensin II into the subfornical organ and into the lateral preoptic area. 4. The results indicate that there are interactions between the subfornical organ and lateral preoptic area in the regulation of cardiovascular and thirst mechanisms.
Cholinergic and adrenergic agonists and antagonists were injected directly into the subfornical organ (SFO), via implanted cannulae, and the volume of water ingested was recorded over a period of 1 hour after injection. Application of 2 nmol carbachol caused intense water intake in 100% of the animals (8.78±0.61 ml), with a very short intake latency. When the 2 nmol carbachol dose was preceded by increased doses of atropine, a progressive reduction in water intake was observed, with complete blockage of the thirst-inducing response to carbachol at the 20 nmol dose level with atropine. Followed by several doses of hexamethonium, the water intake caused by application of 2 nmol carbachol was reduced, although the response was not totally blocked. Injection of 80 nmol of nicotine had a significant thirst-inducing inducing effect in 50% of the animals studied (1.06±0.18 ml) and increase in water intake was further reduced by application of increased doses of hexamethonium. Raising the dose levels of noradrenaline into th SFO caused an increase in water intake although to a lesser degree than was observed after carbachol injection. When the 40 nmol dose of noradrenaline was preceded by increased doses of propranolol (5 to 40 nmol), there was a gradual reduction in water intake...
The subfornical organ (SFO) and the lateral hypothalamus (LH) have been shown to be important for the central action of angiotensin II (ANG II) on water and salt regulation. Several anatomical findings have demonstrated neural connections between the SFO and the LH. The present experiments were conducted to investigate the role of the α-adrenergic antagonists and agonists injected into the LH on the water and salt intake elicited by injections of ANG II into the SFO. Prazosin (an α1-adrenergic antagonist) injected into the LH increased the salt ingestion, whereas yohimbine (an α2-adrenergic antagonist) and propranolol (a β-adrenergic antagonist) antagonized the salt ingestion induced by administration of ANG II into the SFO. Previous administration of clonidine (an α2-adrenergic agonist) or noradrenaline into the LH increased, whereas pretreatment with phenylephrine decreased the sodium intake induced by injection of ANG II into the SFO. Previous treatment with prazosin and propranolol reduced the water intake induced by ANG II. Phenylephrine increased the dipsogenic responses produced by ANG II, whereas previous treatment with clonidine injected into the LH reduced the water intake induced by ANG II administration into the SFO. The LH involvement with SFO on the excitatory and inhibitory mechanisms related to water and sodium intake is suggested.
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Pós-graduação em Ciências Fisiológicas - FOAR; Estudos recentes mostraram a existência de importantes mecanismos de controle da ingestão de sódio e água no núcleo parabraquial lateral (NPBL), uma estrutura pontina localizada dorsolateralmente ao pedúnculo cerebelar superior. Lesões eletrolíticas ou neurotóxicas do NPBL aumentam a ingestão de água induzida por administração central ou periférica de angiotensina II (ANG II). O bloqueio dos receptores serotoninérgicos, colecistocinérgicos ou glutamatérgicos com injeções bilaterais no NPBL de metisergida, proglumide ou DNQX, respectivamente, aumentam a ingestão de solução hipertônica de NaCl induzida por tratamento com o diurético furosemida combinado com doses baixas do inibidor da enzima conversora de angiotensina captopril injetados subcutaneamente. Metisergida injetada no NPBL ainda aumenta a ingestão de NaCl induzida por ANG II administrada no ventrículo lateral (VL) ou no órgão subfornical (OSF) e por privação hídrica por 24 h, depleção de sódio ou DOCA. Além disso, a ativação de receptores adrenérgicos a2 com injeções de moxonidina ou noradrenalina no NPBL aumenta a ingestão de NaCl induzida por furosemida + captopril. Sendo assim...
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 11/50770-1; Bilateral injections of the GABA(A) agonist muscimol into the lateral parabrachial nucleus (LPBN) induce 0.3 M NaCl and water intake in satiated and normovolemic rats, a response reduced by intracerebroventricular (icv) administration of losartan or atropine (angiotensinergic type 1 (AT(1)) and cholinergic muscarinic receptor antagonists, respectively). In the present study, we investigated the effects of the injections of losartan or atropine into the subfornical organ (SFO) on 0.3 M NaCl and water intake induced by injections of muscimol into the LPBN. In addition, using intracellular calcium measurement, we also tested the sensitivity of SFO-cultured cells to angiotensin II (ANG II) and carbachol (cholinergic agonist). In male Holtzman rats with cannulas implanted bilaterally into the LPBN and into the SFO, injections of losartan (1 mu g/ 0.1 mu l) or atropine (2 nmol/0.1 mu l) into the SFO almost abolished 0.3 M NaCl and water intake induced by muscimol (0.5 nmol/0.2 mu l) injected into the LPBN. In about 30% of the cultured cells of the SFO...
Angiotensin II has been implicated in the regulation of adrenocorticotropin and vasopressin secretion. Angiotensin II may influence the secretion of these hormones either directly at the pituitary gland or by increasing corticotropin-releasing hormone or vasopressin release from cells that are located in the paraventricular hypothalamic nucleus. Pituitary hormone release may also be influenced by circulating angiotensin II through receptors outside the blood-brain barrier in the subfornical organ. We have used alterations in angiotensin II receptors in hypophysectomized, adrenalectomized, and vasopressin-deficient Brattleboro rats as indicators of the activity of angiotensin II in the regulation of adrenocorticotropin and vasopressin secretion. Angiotensin receptor number in the paraventricular nucleus and the subfornical organ, but not in the anterior pituitary gland, was significantly decreased by adrenalectomy, and this effect was reversed by corticoids. Vasopressin deficiency decreased angiotensin receptors in the subfornical organ and increased them in the anterior pituitary gland but did not affect angiotensin II binding in either magnocellular or parvocellular subnucleus of the paraventricular nucleus. Our results suggest that angiotensin II may have a corticoid-dependent role in the regulation of corticotropin-releasing hormone secretion...
1. Intracellular recordings from neurones in the subfornical organ in vitro showed that there were two classes of neurones. One class lay within 55 micron of the ventricular surface and was synaptically excited but not inhibited by stimulation of the body or columns of the fornix. These neurones could not be excited antidromically. The other class lay more deeply and was antidromically and synaptically excited and inhibited by stimulation of the body and columns of the fornix. 2. The neurones of the subfornical organ appeared to have the characteristics of neurosecretory neurones. Their action potentials were prolonged and their antidromic spike was easily broken down into components by repetitive stimulation. 3. The organization of the subfornical organ inferred from extracellular recording was confirmed by the results of intracellular recording.
1. Extracellular action potentials (units) were recorded from rat subfornical organ explants in vitro in response to addition of angiotensin II (AII) or carbamyl-choline (carbachol) or serotonin (5-HT) to the superfusion solution. The frequency recorded was dose dependent over a wide range (AII, 0.05--5 nM; carbachol, 2.7--2700 nM; 5-HT, 1--100 nM). Appropriate antagonists, sarc1-ala2 angiotensin (saralasin) for AII, atropine sulphate for carbachol and methysergide maleate for 5-HT, blocked these excitations. The effects were reversible except for that of atropine. 2. Two populations of AII-excited units were found. A superficial population lying between 15 and 45 microns from the ependymal surface was blocked only by saralasin and another population lying more than 55 microns below the ependymal surface could be blocked by atropine as well as saralasin. Carbachol-evoked units generally lay below 45 microns, and 5-HT-evoked units were scattered evenly over the subfornical organ. It is suggested that superficial AII-excited neurones have a cholinergic excitatory synapse with the deeper carbachol-excited neurones. 3. No evidence was found for the hypothesis that neurones of the subfornical organ are excited by morphine or by changes in extracellular osmotic pressure. 4. All types of drug-excited unit...
Although angiotensin II inhibits transient outward K+ currents (IAs) in subfornical organ neurones, there is no evidence concerning which Kv channels are involved. We investigated IA-generating Kv channels in dissociated rat subfornical organ neurones, using molecular, electrophysiological and pharmacological techniques, and studied the effects of angiotensin II. Conventional RT-PCR showed the presence of mRNAs for channels of the Kv3.4, Kv1.4 and Kv4 families, which are capable of generating IAs. Tetraethylammonium at 1 mm, which blocks Kv3 channel-derived currents, and blood-depressing substance-I, a Kv3.4-specific blocker, at 2 μm suppressed the IA-like component of whole-cell outward currents in some neurones. 4-Aminopyridine at 5 mm inhibited IAs in the presence of tetraethylammonium at 1 mm. Cd2+ at 300 μm shifted the activation and inactivation curves of the 4-aminopyridine-sensitive and tetraethylammonium-resistant IAs positively. The tetraethylammonium-resistant IAs showed fast and slow components during the process of recovery from inactivation, but the slow component was not seen in all neurones. The time constant of the fast recovery component was less than 200 ms, while that of the slow recovery component was around 1 s. Using single-cell RT-PCR...
Hypertension caused by chronic infusion of angiotensin II (AngII) in experimental animals is dependent, in part, on increased activity of the sympathetic nervous system. This chronic sympathoexcitatory response is amplified by a high salt diet suggesting an interaction of circulating AngII and dietary salt on sympathetic regulatory pathways in the brain. The present study tested the hypothesis that the subfornical organ (SFO), a forebrain circumventricular organ known to be activated by circulating AngII, is crucial to the pathogenesis of hypertension induced by chronic AngII administration in rats on a high salt diet (AngII-salt model). Rats were randomly selected to undergo either subfornical organ lesion (SFOx) or sham surgery (SHAM) and then placed on a high salt (2% NaCl) diet. One week later rats were instrumented for radiotelemetric measurement of mean arterial pressure (MAP) and heart rate (HR) and placed in metabolic cages to measure sodium and water balance. Baseline MAP was slightly (but not statistically) lower in SFOx compared to SHAM rats during the 5 day control period. During the subsequent 10 days of AngII administration, MAPwas statistically lower in SFOx rats. However, when MAP responses to AngII were analyzed by comparing the change from the 5 day baseline period...
The objective of this study was to analyze
the proteins in the cerebrospinal fluid of spontaneously
hypertensive rats and to study their possible role in the
relationship between hydrocephalus, arterial
hypertension and variations in the subfornical organ.
Brains and cerebrospinal fluid from control Wistar-
Kyoto rats and spontaneously hypertensive rats
sacrificed with chloral hydrate were used. Cerebrospinal
fluid and extract of subfornical organ were processed by
protein electrophoresis. Antisera against protein bands of
141, 117 and 48 kDa and Concanavalin A were used for
immunohistochemical and western blot study of the
subfornical organ, adjacent circumventricular structures
and cerebrospinal fluid. Ventricular dilation in the
spontaneously hypertensive rats and the presence of
quite a lot of protein bands in the cerebrospinal fluid of
the hypertensive rats, which were either not observed or
scarcely present in the cerebrospinal fluid of the Wistar-
Kyoto rats, were confirmed. The subfornical organ, third
ventricle ependyma and choroideus plexus showed
immunoreactive material for antibodies against 141kDa,
117 and 48 kDa proteins band (anti-B1, anti-B2 and anti-
B3). The larger amount of the immunoreactive material
was found in the subfornical organ of the spontaneously
hypertensive rat. Our results and the alterations observed
by other authors in the subfornical organ in
hydrocephalic and hypertensive rats support the
possibility that this circumventricular organ...
Leptin is an adipokine that acts centrally to regulate feeding behaviour, energy expenditure and autonomic function via activation of its receptor (ObRb) in nuclei in the central nervous system (CNS). This thesis investigates the involvement of two sensory circumventricular organs (CVOs), the subfornical organ (SFO) and area postrema (AP), in mediating the central effects of leptin using a variety of experimental approaches.
We first show that acute electrical stimulation of the SFO elicits feeding in satiated rats, supporting a role for this specialized CNS structure in the control of food intake. We then demonstrate, using RT-PCR, the presence of ObRb mRNA in SFO and, using whole cell current clamp electrophysiology, reveal that leptin influences the excitability of individual SFO neurons, causing both excitatory and inhibitory responses. Furthermore, we find that leptin activates the same SFO neurons activated by amylin.
Given the association between obesity and hypertension and the well-established role of the SFO in cardiovascular regulation, we show that leptin microinjection into the SFO decreases blood pressure in young rats, effects that are abolished in leptin-resistant, diet induced obese rats, suggesting that leptin-insensitivity in the SFO of obese...
Adiponectin (ADP) is an adipokine, which acts as an insulin sensitizing hormone. Recent studies have shown that adiponectin receptors (AdipoR1, AdipoR2) are present in the CNS; however, there is some debate as to whether or not ADP crosses the blood brain barrier (BBB). Circumventricular organs (CVO) are CNS sites outside the BBB, and thus represent sites at which circulating adiponectin may act to influence the CNS without having to cross the BBB. The subfornical organ (SFO) is a CVO that is responsive to a number of different circulating satiety signals including amylin, CCK, and ghrelin. We report here that the SFO also shows a high density of mRNA for both adiponectin receptors. These observations support the concept that the SFO may be a key player in sensing circulating ADP. To test the hypothesis that ADP influences the excitability of SFO neurons, we used current-clamp electrophysiology on dissociated SFO neurons to observe changes in membrane potential. ADP (10 nM) application effected the excitability of SFO neurons, where the cells either depolarized (8.9±0.9 mV, 21 of 97 cells) or hyperpolarized (-8.0±0.5 mV, 34 of 97 cells). Using single-cell RT-PCR we found that the majority of the responsive neurons expressed AdipoR1 or R2 and the non-responsive neurons expressed neither.
In view of the recognized role of ADP in the regulation of energy balance...
In the present study we investigated the effect of electrolytic lesion of the medial septal area (MSA) on the pressor and dipsogenic response to cholinergic activation and angiotensin II (ANGII) injection into the subfornical organ (SFO) in rats. In addition the effect of MSA lesion on the natriuresis, kaliuresis and diuresis after cholinergic activation of the SFO was also investigated. Sham- and MSA-lesioned rats with a stainless steel cannula implanted into the SFO was used. The injection of ANGII (12 ng) into the SFO in sham rats produced pressor (24 ± 2 mmHg) and dipsogenic (9.6 ± 1.1 ml/h) responses. MSA lesion, both acute (2-6 days) and chronic (15-19 days), reduced the pressor (14 ± 2 mmHg) and dipsogenic (2.7 ± 1 ml/h) responses to ANGII into SFO. The injection of the cholinergic agonist carbachol (2 nmol) into the SFO in sham rats produced pressor (48 ± 4 mmHg), dipsogenic (10 ± 1.2 ml/h), natriuretic (457 ± 58 μEq/2 h) and kaliuretic (249 ± 16 μEq/2 h) responses. Acute, but not chronic MSA lesion reduced the pressor (27 ± 3 mmHg), natriuretic (198 ± 55 μEq/2 h) and kaliuretic (128 ± 16 μEq/2 h) responses to carbachol into SFO. No change in the dipsogenic response to carbachol into the SFO was observed in MSA-lesioned rats. Antidiuresis after carbachol was observed only in MSA-lesioned rats. The present results show that the MSA plays a role on the pressor...