Studying the central actions of angiotensin using the expression of immediate-early genes: expectations and limitations (original) (raw)
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Calcium channels mediate angiotensin II-induced drinking behaviour and c-fos expression in the brain
Brain Research, 1997
It is widely accepted that calcium ions are critically important in both short-andror long-lasting responses of neurons to a stimulus. We have shown previously that NMDA receptors play a role in dipsogenic responses and c-fos expression induced by intracerebroventric-Ž. Ž. ular icv infusion of angiotensin II Ang II. Since NMDA receptors are known to be linked to receptor-operated calcium channels, this Ž. study determined whether voltage dependent calcium channels are also involved in Ang II-induced behavioural drinking and endocrine responses as well as c-fos expression. The antidipsogenic actions of three L-type calcium channel antagonists, nifedipine, diltiazem and verapamil on Ang II-induced drinking behaviour were studied. These bind to the dihydropyridine, phenylalkylamine and benzothiazepine Ž. sites respectively. Rats Lister-hooded pre-treated icv with either 25 or 100 mg nifedipine, followed by 25 pmol Ang II, drank significantly less water than controls during the first 15 min after infusion. However, rats pre-treated with icv 100 mg diltiazem or verapamil showed no change in Ang II-induced drinking behaviour. The antidipsogenic actions of N-and P-type calcium channel antagonists v-conotoxin GVIA and v-conotoxin MVIIC were also evaluated. Rats pre-treated with 5 pmol or 20 pmol v-conotoxin GVIA did show a slight but not significant suppression of water intake, particularly after the higher dose. Rats pre-treated with v-conotoxin MVIIC drank almost the same amount of water as those pre-treated with saline. Nifedipine was found to suppress both Ang Ž. II-induced corticosterone release and c-fos expression in the following areas: organum vasculosum of the lamina terminalis OVLT , Ž. Ž. Ž. median preoptic nucleus MNPO , hypothalamic paraventricular nucleus PVN and supraoptic nucleus SON. The results described in this paper provide evidence that calcium channels play important roles in the Ang II-induced behavioural and endocrine responses, and in the expression of the immediate-early gene c-fos. This suggests that an L-type calcium channel may participate both short-and longer-term neuronal actions of Ang II. q 1997 Elsevier Science B.V.
Roles of brain angiotensins II and III in thirst and sodium appetite
Brain Research, 2005
The current study examined the effects of intracerebroventricular (icv) infused aminopeptidase-resistant analogs of angiotensin II (AngII) and angiotensin III (AngIII) on thirst and sodium appetite. The analogs, [D-Asp 1 D-Arg 2 ]AngII and [D-Arg 1 ]AngIII, were further protected from degradation by pretreatment with the aminopeptidase A inhibitor, EC33, or the aminopeptidase N inhibitor, PC18. Prior to icv infusions, rats were sodium depleted with furosemide, followed by the angiotensin-converting enzyme inhibitor captopril, to block endogenous angiotensin formation. Both angiotensin analogs, at either of the two doses, were capable of eliciting fluid intakes of water and 0.3 M NaCl. Water and saline intakes were increased to a similar extent by 125 and 1250 pmol of [D-Asp 1 D-Arg 2 ]AngII. [D-Arg 1 ]AngIII produced a dose-dependent increase in water intake, whereas saline intake was equivalently increased by the 125 and 1250 pmol infusions. Pretreatment with EC33 or PC18 decreased water and saline intakes in response to [D-Asp 1 D-Arg 2 ]AngII, while pretreatment with PC18 altered the time course of the [D-Arg 1 ]AngIII-induced water and saline intakes. The ability of both inhibitors to decrease, but not completely block, AngII analog-induced intakes, coupled with the altered time course of the responses induced by the AngIII analog in the presence of PC18, supports the hypothesis that both AngII and AngIII are active ligands in brain angiotensin-mediated thirst and sodium appetite. However, these results do not resolve the primary question of whether conversion of AngII to AngIII is a prerequisite to dipsogenic and salt appetite responses in the brain. D
Pharmacology Biochemistry and Behavior, 1980
Angiotensin 11 (All) was microiontophoretically applied on neurones located in the septum and the medial preoptic area (MPOA). All the septal neurones sensitive to All (15/37) responded by an inhibition to the peptide application. Of 44 units tested in the MPOA 21 cells (48%) were sensitive to All and responded either by an increase (11/21) or decrease (10/21) in their firing. The specificity of these responses were ascertained by simultaneous application of the antagonist SarMle"-Angiotensin II. These data suggest that Angiotensin II acts directly on neurones of the septum and medial preoptic area, structures implicated in the control of drinking behaviour.
Local production of angiotensin II in the subfornical organ causes elevated drinking
Journal of Clinical Investigation, 2007
We generated double-transgenic mice expressing human renin (hREN) from a neuron-specific promoter and human AGT (hAGT) from its own promoter (SRA mice) to emulate this expression. SRA mice exhibited an increase in water and salt intake and urinary volume, which were significantly reduced after chronic intracerebroventricular delivery of losartan. Ang II-like immunoreactivity was markedly increased in the subfornical organ (SFO). To further evaluate the physiological importance of de novo Ang II production specifically in the SFO, we utilized a transgenic mouse model expressing a floxed version of hAGT (hAGT flox ), so that deletions could be induced with Cre recombinase. We targeted SFO-specific ablation of hAGT flox by microinjection of an adenovirus encoding Cre recombinase (AdCre). SRA flox mice exhibited a marked increase in drinking at baseline and a significant decrease in water intake after administration of AdCre/adenovirus encoding enhanced GFP (AdCre/AdEGFP), but not after administration of AdEGFP alone. This decrease only occurred when Cre recombinase correctly targeted the SFO and correlated with a loss of hAGT and angiotensin peptide immunostaining in the SFO. These data provide strong genetic evidence implicating de novo synthesis of Ang II in the SFO as an integral player in fluid homeostasis.
Neuroscience, 1995
The effect of intracereboventricular injections of angiotensin II (0.1 nm), angiotensin-(1-7) (1 or 100 nm) and carbachol (500 ng) on c-fos expression was examined in the forebrain of Lister hooded rats. Intense staining of the c-Fos protein was found in the median preoptic nucleus, organum vasculosum of the lamina terminalis, subfornical organ, paraventricular nucleus, and supraoptic nucleus after angiotensin lI and carbachol Angiotensin II caused significantly more c-fos expression in the ventral median preoptic nucleus and organum vasculosum of the lamina terminalis than carbachol, whereas in the paraventricular and supraoptic nuclei this was reversed, with carbachol having a greater effect on c-fos expression in these areas. Angiotensin-(1-7), however, only induced c-Fos protein in the organum vasculosum of the lamina terminalis and median preoptic nucleus with the number and the intensity of staining of the nuclei significantly less in both areas than after angiotensin II or carbachol. Separate groups of Lister rats were given i.c.v, injections of the same substances at the same doses, but excluding the lower dose of angiotensin-(1-7), and the intakes of water and 1.8% NaC1 over 60rain were measured. Angiotensin II stimulated intakes of both water and NaC1. The effect on water intake was almost immediate (< 1 min), whereas NaCI intake did not usually start until at least 5 min after injection. Over 60rain, water (12.4 + 1.0ml) and NaCI (4.2+0.9ml) intakes were significantly greater than water (1.1 + 0.2 ml) and NaC1 (0.6 + 0.5 m) intakes of the controls. Carbachol caused less drinking than angiotensin II, the water intake over 60 min being significantly less (4.8 + 0.7 ml) and the latency of response greater (> 5 min). Carbachol, unlike angiotensin II, had little effect on NaC1 intake (0.7 + 0.4 ml). Angiotensin-(1-7) had no effect on water (1. l + 0.3 ml) or NaC1 (0.3 + 0.3 ml) intakes. The plasma levels of vasopressin were measured after i.c.v, injection of the same three substances in the same doses, again excluding the lower dose of angiotensin-(1-7), in further groups of rats. Angiotensin II and carbachol caused an approximate five-fold increase in plasma vasopressin levels compared to cerebrospinal fluid-injected rats, but angiotensin-(1-7) had no effect on vasopressin release. Therefore, three compounds with widely differing effects on thirst, sodium appetite and vasopressin release induce distinctive patterns of c-fos protein expression in the forebrain. By combining experimental approaches in this way it is possible to determine areas of the brain which are involved in certain bebavioural and endocrine responses.
Glial Cells Are Involved in ANG-II-Induced Vasopressin Release and Sodium Intake in Awake Rats
Frontiers in Physiology, 2018
It is known that circulating angiotensin II (ANG-II) acts on the circumventricular organs (CVOs), which partially lack a normal blood-brain barrier, to stimulate pressor responses, vasopressin (AVP), and oxytocin (OT) secretion, as well as sodium and water intake. Although ANG-II type 1 receptors (AT1 R) are expressed in neurons and astrocytes, the involvement of CVOs glial cells in the neuroendocrine, cardiovascular and behavioral responses induced by central ANG II remains to be further elucidated. To address this question, we performed a set of experiments combining in vitro studies in primary hypothalamic astrocyte cells (HACc) and in vivo intracerebroventricular (icv) microinjections into the lateral ventricle of awake rats. Our results showed that ANG-II decreased glutamate uptake in HACc. In addition, in vivo studies showed that fluorocitrate (FCt), a reversible glial inhibitor, increased OT secretion and mean arterial pressure (MAP) and decreased breathing at rest. Furthermore, previous FCt decreased AVP secretion and sodium intake induced by central ANG-II. Together, our findings support that CVOs glial cells are important in mediating neuroendocrine and cardiorespiratory functions, as well as central ANG-II-induced AVP release and salt-intake behavior in awake rats. In the light of our in vitro studies, we propose that these mechanisms are, at least in part, by ANG-II-induced astrocyte mediate reduction in glutamate extracellular clearance.
The brain angiotensin system Insights from mapping its components
Trends in Endocrinology & Metabolism, 1990
Mapping of components of the angiotensin (Ang) system in the brain suggests that it serves multiple central roles, including regulation of fluid and electrolyte balance, central autonomic control, and pituitary hormone release. Circulating Ang II (see Table 1 on page 195 for abbreviations) conserves NaCl and water, and maintains blood pressure by means of actions on the cardiovascular, endocrine, renal, and peripheral autonomic nervous systems. Ang II may also act in the brain to augment these peripheral actions, as it stimulates drinking and salt appetite, causes central neurogenic elevation of blood pressure, and modulates the release of hormones from both the anterior and posterior pituitary lobes. Blood-borne Ang II does not penetrate the brain except at specialized regions, the CVOs, which have a deficient BBB. Most of these regions are neural targets for circulating Ang II. Ang II may also be synthesized in the CNS and act on receptors at sites within the BBB (Phillips 1987). This article focuses on mapping components of the brain Ang system.
eneuro
The median preoptic nucleus (MnPO) is a putative integrative region that contributes to body fluid balance. Activation of the MnPO can influence thirst, but it is not clear how these responses are linked to body fluid homeostasis. We used designer receptors exclusively activated by designer drugs (DREADDs) to determine the Significance Statement The median preoptic nucleus (MnPO) is an important regulatory center that influences thirst, cardiovascular and neuroendocrine function. Activation of different MnPO neuronal populations can inhibit or stimulate water intake. However, the role of the MnPO and its pathway-specific projections during angiotensin II (ANG II) and hyperosmotic challenges still have not yet been fully elucidated. These studies directly address this by using designer receptors exclusively activated by designer drugs (DREADDs) to acutely and selectively inhibit pathway-specific MnPO neurons, and uses techniques that measure changes at the protein, neuronal, and overall physiologic and behavioral level. More importantly, we have been able to demonstrate that physiologic challenges related to extracellular (ANG II) or cellular (hypertonic saline) dehydration activate MnPO neurons that may project to different parts of the hypothalamus. New Research March/April 2019, 6(2) e0473-18.2019 1-19 role of the MnPO in drinking behavior and vasopressin release in response to peripheral angiotensin II (ANG II) or 3% hypertonic saline (3% HTN) in adult male Sprague Dawley rats (250-300 g). Rats were anesthetized with isoflurane and stereotaxically injected with an inhibitory DREADD (rAAV5-CaMKIIa-hM4D(G i)-mCherry) or control (rAAV5-CaMKIIa-mCherry) virus in the MnPO. After two weeks' recovery, a subset of rats was used for extracellular recordings to verify functional effects of ANG II or hyperosmotic challenges in MnPO slice preparations. Remaining rats were used in drinking behavior studies. Each rat was administered either 10 mg/kg of exogenous clozapine-N-oxide (CNO) to inhibit DREADD-expressing cells or vehicle intraperitoneal followed by a test treatment with either 2-mg/kg ANG II or 3% HTN (1 ml/100-g bw, s.c.), twice per week for two separate treatment weeks. CNO-induced inhibition during either test treatment significantly attenuated drinking responses compared to vehicle treatments and controls. Brain tissue processed for cFos immunohistochemistry showed decreased expression with CNO-induced inhibition during either test treatment in the MnPO and downstream nuclei compared to controls. CNO-mediated inhibition significantly attenuated treatment-induced increases in plasma vasopressin compared to controls. The results indicate inhibition of CaMKIIa-expressing MnPO neurons significantly reduces drinking and vasopressin release in response to ANG II or hyperosmotic challenge.
Brain Research, 1976
The possibility that water intake elicited by the administration of angiotensin-II to the preoptic region (POA), subfornical organ and anterior third ventricle is mediated by separate neural systems was investigated in 58 male Wistar rats using electrolytic lesion techniques. (2) Lesions of the midlateral hypothalamus and paramedial rostral midbrain produced a significant reduction in water intake to angiotensin-II microinjected into the POA but did not affect drinking following administration of angiotensin-II to the subfornical organ or anterior third ventricle. (3) Ablation of the midlateral hypothalamus, paramedial rostral midbrain, habenular nucleus or interpeduncular nucleus had no significant effect on water intake elicited in response to microinjection of carbachol or hypertonic saline into the preoptic region, subfornical organ or anterior third ventricle. (4) In a second series of 12 animals lesions of the subfornical organ attenuated water intake in response to a peripheral injection of renin or isoproteronol without disrupting drinking to peripheral administration of hypertonic saline or polyethylene glycol or to 24 h water deprivation. (5) It is concluded that separate neural systems mediate water intake elicited by administration of angiotensin-II to the preoptic area, subfornical organ and anterior third ventricle. The possible physiological significance of independent and parallel peripheral and cerebral renin-angiotensin systems for the control of drinking behavior mediated by angiotensin-II is discussed. (6) The present results are in agreement with previous work which indicates that water intake induced by central administration of angiotensin-II, carbachol and hypertonic saline is subserved by different neural substrates.