Activation of alpha(2)-adrenergic receptors into the lateral parabrachial nucleus enhances NaCl intake in rats

Water and NaCl intake is strongly inhibited by the activation of alpha(2)-adrenergic receptors with clonidine or moxonidine (alpha(2)-adrenergic/imidazoline agonists) injected peripherally or into the forebrain and by serotonin and cholecystokinin in the lateral parabrachial nucleus (LPBN). Considering that alpha(2)-adrenergic receptors exist in the LPBN and the similar origin of serotonergic and adrenergic afferent pathways to the LPBN, in this study we investigated the effects of bilateral injections of moxonidine alone or combined with RX 821002 (alpha(2)- adrenergic antagonist) into the LPBN on 1.8% NaCl and water intake induced by the treatment with s.c. furosemide (10 mg/kg)+captopril (5 mg/kg). Additionally, we investigated if moxonidine into the LPBN would modify furosemide+captopril-induced c-fos expression in the forebrain. Male Holtzman rats with cannulas implanted bilaterally in the LPBN were used. Contrary to forebrain injections, bilateral LPBN injections of moxonidine (0.1, 0.5 and 1 nmol/0.2 mul) strongly increased furosemide+captopril-induced 1.8% NaCl intake (16.6 +/- 2.7, 44.5 +/- 3.2 and 44.5 +/- 4.3 ml/2 h, respectively, vs. vehicle: 6.9 +/- 1.5 ml/2 h). Only the high dose of moxonidine increased water intake (23.3 +/- 3.8 ml/2 h, vs. vehicle: 12.1 +/- 2.6 ml/2 h). Prior injections of RX 821002 (10 and 20 nmol/0.2 mu1) abolished the effect of moxonidine (0.5 nmol) on 1.8% NaCl intake. Moxonidine into the LPBN did not modify furosemide+captopril-induced c-fos expression in forebrain areas related to the control of fluid-electrolyte balance. The results show that the activation of LPBN a2-adrenergic receptors enhances furosemide+captopril-induced 1.8% NaCl and water intake. This enhancement was not related to prior alteration in the activity of forebrain areas as suggested by c-fos expression. Previous and present results indicate opposite roles for alpha(2-)adrenergic receptors in the control of sodium and water intake according to their distribution in the rat brain. (C) 2004 IBRO. Published by Elsevier Ltd. All rights reserved.

5-HT2 and 5-HT3 receptors in the lateral parabrachial nucleus mediate opposite effects on sodium intake

The present study investigated the role of several 5-HT receptor subtypes in the lateral parabrachial nucleus (LPBN) in the control of sodium appetite (i.e. NaCl consumption). Male Holtzman rats had cannulas implanted bilaterally into the LPBN for the injection of 5-HT receptor agonists and antagonists in conjunction with either acute fluid depletion or 24-h sodium depletion. Following these treatments, access to 0.3 M NaCl was provided and the intakes of saline and water were measured for the next 2 h. Bilateral injections of the 5-HT2A receptor antagonist, ketanserin or the 5-HT2C receptor antagonist, mianserin into the LPBN increased 0.3 M NaCl intake without affecting water intake induced by acute fluid-depletion. Bilateral injections of the 5-HT2B receptor agonist, BW723C86 hydrochloride, had no effect on 0.3 M NaCl or water intake under these conditions. Treatment of the LPBN with the 5-HT2B/2C receptor agonist, 2-(2-methyl-4-clorophenoxy) propanoic acid (mCPP) caused dose-related reductions in 0.3 M NaCl intake after 24 h sodium depletion. The effects of mCPP were prevented by pretreating the LPBN with the 5-HT2B/2C receptor antagonist, SDZSER082. Activation of 5-HT3 receptors by the receptor agonist, 1-phenylbiguanicle (PBG) caused dose-related increases in 0.3 M NaCl intake. Pretreatment of the LPBN with the 5-HT3 receptor antagonist, 1-methyl-N-[8-methyl-8-azabicyclo (3.2.1)-oct-3-yl]-1H-indazole-3-carboxamide (LY-278,584) abolished the effects of PBG, but LY-278,584 had no effects on sodium or water intake when injected by itself. PBG injected into the LPBN did not alter intake of palatable 0.06 M sucrose in fluid replete rats. The results suggest that activation of the 5-HT2A and 5-HT2C receptor subtypes inhibits sodium ingestion. In contrast, activation of the 5-HT3 receptor subtype increases sodium ingestion. Therefore, multiple serotonergic receptor subtypes in the LPBN are implicated in the control of sodium intake, sometimes by mediating opposite effects of 5-HT. The results provide new information concerning the control of sodium intake by LPBN mechanisms. (C) 2007 IBRO. Published by Elsevier Ltd. All rights reserved.

Serotonergic mechanisms of the lateral parabrachial nucleus on DOCA-induced sodium intake

It has been shown that the serotonergic mechanisms of the lateral parabrachial nucleus (LPBN) inhibit NaCl intake in different models of angiotensin II (ANG II)-dependent NaCl intake in rats. However, there is no information about the involvement of LPBN serotonergic mechanisms on NaCl intake in a model of NaCl intake not dependent on ANG II like deoxycorticosterone (DOCA)-induced NaCl intake. Therefore, in this study we investigated the effects of bilateral injections of serotonergic agonist and antagonist into the LPBN on DOCA-induced 1.8% NaCl intake in rats. Male Holtzman rats were treated with s.c. DOCA (10 mg/rat each every 3 days). After a period of training, in which the rats had access to 1.8% NaCI during 2 h for several days, the rats were implanted with stainless steel cannulas bilaterally into the LPBN. Bilateral injections of the serotonergic receptor antagonist methysergide (4 mug/0.2 mul each site) in the LPBN increased 1.8% NaCI intake (32.2+/-3.9 versus vehicle: 15.0+/-1.6 ml/2 h, n = 10) and water intake (11.5+/-3.5 versus vehicle: 3.2+/-1.0 ml/2 h). Injections of the serotonergic 5HT(2A/2C) receptor agonist DOI (5 mug/0,2 mul each site) in the LPBN reduced 1.8% NaCl intake (6.8+/-1.7 versus saline: 12.4+/-1.9 ml/2 h, n = 10) and water intake (2.2+/-0.8 versus saline: 4.4+/-1.0 ml/2 h). Besides the previously demonstrated importance for the control of ANG II-dependent water and NaCl intake, the data show that the serotonergic inhibitory mechanisms of the LPBN are also involved in the control of DOCA-induced NaCl intake. (C) 2000 Elsevier B.V. B.V. All rights reserved.

Serotonergic mechanism of the lateral parabrachial nucleus and relaxin-induced sodium intake

It has been shown that central or peripheral injections of the peptide relaxin induces water intake, not sodium intake in rats. Important inhibitory mechanisms involving serotonin and other neurotransmitters in the control of water and NaCl intake have been demonstrated in the lateral parabrachial nucleus (LPBN). In the present Study, we investigated the effects of bilateral injections of methysergide (serotonergic receptor antagonist) into the LPBN on intracerebroventricular (i.c.v.) relaxin-induced water and NaCl intake in rats. Additionally, the effect of the blockade of central angiotensin AT(1) receptors with i.c.v. losartan on relaxin-induced water and NaCl intake in rats treated with methysergide into the LPBN was also investigated. Male Holtzman rats with cannulas implanted into the lateral ventricle (LV) and bilaterally in the LPBN were used. Intracerebroventricular injections of relaxin (500 ng/l mul) induced water intake (5.1+/-0.7 ml/120 min), but not significant 1.8% NaCl intake (0.5+/-0.4 ml/120 min). Bilateral injections of methysergide (4 mug/0.2 mul) into the LPBN strongly stimulated relaxin-induced 1.8% NaCl intake (34.5+/-10.9 ml/120 min) and slightly increased water intake (10.5+/-4.9 ml/120 min). The pretreatment with i.c.v. losartan (100 mug/l mul) abolished the effects of i.c.v. relaxin combined with LPBN methysergide on 1.8% NaCI intake (0.5+/-0.4 ml/120 min). Losartan (100 mug/l mul) also abolished relaxin-induced water intake in rats injected with methysergide into the LPBN (1.6+/-0.8 ml/120 min) or not (0.5+/-0.3 ml/120 min). Losartan (50 mug/l mul) partially reduced the effects of relaxin. The results show that central relaxin interacting with central angiotensinergic mechanisms induces NaCl intake after the blockade of LPBN serotonergic mechanisms. (C) 2004 Elsevier B.V. All rights reserved.

Lesions of the commissural nucleus of the solitary tract reduce arterial pressure in spontaneously hypertensive rats

It has been suggested that increased sympathetic activity and arterial chemoreceptors are important for the high blood pressure in spontaneously hypertensive rats (SHR). Electrolytic lesions of the commissural nucleus of the solitary tract (commNTS) abolish (1) the cardiovascular responses to chemoreflex activation with potassium cyanide (KCN) in normotensive rats and (2) the hypertension that follows acute aortic baroreceptor denervation in rats. Therefore, in this study we investigated the effects of electrolytic lesions of the commNTS on basal mean arterial pressure (MAP), baroreflex, and chemoreflex in SHR and in normotensive control Wistar-Kyoto (WKY) and Wistar rats. CommNTS lesions elicited a dramatic fall in MAP to normal levels during the period of Study (from the first to fourth day following lesions) in SHR and almost no changes in WKY and Wistar rats. The pressor responses to chemoreflex activation with KCN tested in the days 1 and 4 after commNTS lesions were abolished in SHR and in normotensive strains. The reflex tachycardia induced by sodium nitroprusside was also attenuated in days 1 and 4 after commNTS lesions in SHR, WKY, and Wistar rats. The data suggest that the integrity of commNTS is important for the maintenance or high blood pressure in SHR and for the reflex responses dependent on sympathetic activation either in SHR or in normotensive strains.

Alpha(2)-adrenergic activation in the lateral parabrachial nucleus induces NaCi intake under conditions of systemic hyperosmolarity

The inhibition of sodium intake by increased plasma osmolarity may depend on inhibitory mechanisms present in the lateral parabrachial nucleus. Activation of alpha(2)-adrenergic receptors in the lateral parabrachial nucleus is suggested to deactivate inhibitory mechanisms present in this area increasing fluid depletion-induced 0.3 M NaCl intake. Considering the possibility that lateral parabrachial nucleus inhibitory mechanisms are activated and restrain sodium intake in animals with increased plasma osmolarity, in the present study we investigated the effects on water and 0.3 M NaCl intake produced by the activation of alpha(2)-adrenergic receptors in the lateral parabrachial nucleus in rats with increased plasma osmolarity. Male Holtzman rats with stainless steel cannulas implanted bilaterally into the lateral parabrachial nucleus were used. One hour after intragastric 2 M NaCl load (2 ml), bilateral injections of moxonidine (alpha(2)-adrenergic/imidazoline receptor agonist, 0.5 nmol/0.2 mu l, n=10) into the lateral parabrachial nucleus induced a strong ingestion of 0.3 M NaCl intake (19.1 +/- 5.5 ml/2 h vs. vehicle: 1.8 +/- 0.6 ml/2 h), without changing water intake (15.8 +/- 3.0 ml/2 h vs. vehicle: 9.3 +/- 2.0 ml/2 h). However, moxonidine into the lateral parabrachial nucleus in satiated rats not treated with 2 M NaCl produced no change on 0.3 M NaCl intake. The pre-treatment with RX 821002 (alpha(2)-adrenergic receptor antagonist, 20 nmol/0.2 mu l) into the lateral parabrachial nucleus almost abolished the effects of moxonidine on 0.3 M NaCl intake (4.7 +/- 3.4 ml/2 h). The present results suggest that alpha(2)-adrenergic receptor activation in the lateral parabrachial nucleus blocks inhibitory mechanisms, thereby allowing ingestion of hypertonic NaCl under conditions of extracellular hyperosmolarity. We suggest that during cell dehydration, circuits subserving sodium appetite are activated, but at the same time strongly inhibited through the lateral parabrachial nucleus. (c) 2006 IBRO. Published by Elsevier Ltd. All rights reserved.

Participation of alpha-1 and alpha-2 adrenoceptors of the lateral hypothalamic area in water intake, and renal sodium, potassium and urinary Volume excretion induced by central administration of angiotensin II

The circumventricular structures and the lateral hypothalamus (LH) have been shown to be important for the central action of angiotensin II (ANGII) on water and electrolyte regulation. Several anatomical findings have demonstrated neural connection between circumventricular structures and the LH, the present experiments were conducted to investigate the role of the alpha-adrenergic antagonists and agonistic injected into the LH on the water intake, sodium and potassium excretion elicited by injections of ANGII into the lateral ventricle (LV), the water intake was measured every 30 min over a period of 120 min. The sodium, potassium and urinary volume were measured over a period of 120 min in water-loaded rats. The injection of ANGII into the LV increased the water intake, which was reduced by previous injection of clonidine (an alpha-2-adrenergic agonist) into the LH. The injection of yohimbine (an alpha-2-adrenergic antagonist) and prazosin (an alpha-l-adrenergic antagonist) into the LH, which was done before injecting ANGII into the LV, also reduced the water intake induced by ANGII. The injection of ANGII into the LV reduced the sodium, potassium and urinary volume. Previous treatment with clonidine attenuated the action of ANGII in reducing the sodium, potassium and urinary volume, whereas previous treatment with yohimbine attenuated the effects of ANGII but with less intensity than that caused by clonidine. Previous treatment with prazosin increased the inhibitory effects of ANGII in those parameters. The injection of yohimbine and prazosin, which was done before the injection of clonidine, attenuated the effect of clonidine on the ANGII mechanism. The results of this study led us to postulate that when alpha-2-adrenergic receptors are blocked, the clonidine may act on the imidazoline receptors to produce its effects on the ANGII mechanism. We may also conclude that the LH is involved with circumventricular structures, which present excitatory and inhibitory mechanisms. Such mechanisms are responsible for regulating the renal excretion of sodium, potassium and water, (C) 2000 Elsevier B.V.

L-Type calcium channels mediate water intake induced by angiotensin injection into median preoptic nucleus

Calcium ions are widely accepted as critically important in responses of neurons to a stimulus. We have show previously the central involvement of angiotensin II (ANGII) in water intake. This study determined whether voltage-dependent calcium channels are involved in ANGII-induced behavioral drinking implicating nitrergic mechanism. The antidipsogenic actions of L-type calcium channel antagonists nifedipine, on ANGII-induced drinking behavior were studied when it is injected into the median preoptic nucleus (MnPO). The influence of nitric oxide (NO) on nifedipine antidipsogenic action was also studied by utilizing the N-W-nitro-L-arginine methyl ester (L-NAME) a constitutive nitric oxide synthase inhibitor constitutive (cNOSI) and 7-nitroindazol (7-NIT) a specific neuronal nitric oxide synthase inhibitor (nNOSI) and L-arginine a NO donor. Rats 200-250 g, with cannulae implanted into MnPO, pre-treated into MnPO with either nifedipine, followed by ANGII, drank significantly less water than controls during the first 15 min after injection. However, L-NAME potentiated the dipsogenic effect of ANGII that is blocked by prior injection of nifedipine and L-arginine. 7-NIT injected prior to ANGII into MnPO also potentiated the dipsogenic effect of ANGII but with a less intensity than L-NAME that it is also blocked by prior injection of nifedipine. The results described in this paper provide evidence that calcium channels play important roles in the ANGII-induced behavioral water intake. The structures containing NO in the brain such as MnPO include both endothelial cells and neurons might be responsible for the influence of nifedipine on dipsogenic effect of ANGII. These data shows the correlation between L-type calcium channel and a free radical gas NO produced endogenously from amino acids L-arginine by endothelial and neuronal NO synthase in the control of ANGII-dipsogenic effect. This suggests that an L-type calcium channel participates in both short- and longer-term neuronal actions of ANGII by nitrergic way. (c) 2006 Elsevier B.V. All rights reserved.

Nitric oxide of the supraoptic nucleus influences the salivary secretion, sodium renal excretion, urinary volume and arterial blood pressure induced by pilocarpine

Male Holtzman rats weighting 200-250 g were anesthetized with zoletil 50 mg/Kg (tiletamine chloridrate 125.0 mg and zolazepan chloridrate 125.0 mg) into quadriceps muscle and stainless steel cannulas were implanted into their supraoptic nucleus (SON). We investigated the effects of the injection into the supraoptic nucleus (SON) of FK 409, a nitric oxide donor, and N(W-)nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor (NOS), on the salivary secretion, arterial blood pressure, sodium excretion and urinary volume induced by pilocarpine, which was injected into SON. The drugs were injected in 0.5 mul volume over 30-60 s. Controls was injected with a similar volume of 0.15 M NaCl. FK 409 and L-NAME were injected at doses of 20 mug/0.5 mul and 40 mug/0.5 mul. respectively. The amount of saliva secretion was studied over a five-minute period after injection of pilocarpine into SON. Injection of pilocarpine (10, 20, 40, 80, 160 mug/mul) into SON produced a dose-dependent increase in salivary secretion. L-NAME was injected into SON prior to the injection of pilocarpine into SON, producing an increase in salivary secretion due to the effect of pilocarpine. FK 409 injected into SON attenuating the increase in salivary secretion induced by pilocarpine. Mean arterial pressure (MAP) increase after injections of pilocarpine into the SON. L-NAME injected into the SON prior to injection of pilocarpine into SON increased the MAP. FK 409 injected into the SON prior to pilocarpine attenuated the effect of pilocarpine on MAP. Pilocarpine (0.5 mumol/0.5 mul) injected into the SON induced an increase in sodium and urinary excretion. L-NAME injected prior to pilocarpine into the SON increased the urinary sodium excretion and urinary volume induced by pilocarpine. FK 409 injected prior to pilocarpine into the SON decreased the sodium excretion and urinary volume induced by pilocarpine. All these roles of pilocarpine depend on the release of nitric oxide into the SON. In summary the present results show: a) SON is involved in pilocarpine-induced salivation; b) that mechanism involves increase in MAP, sodium excretion and urinary volume. (C) 2003 Elsevier B.V. All rights reserved.

Lateral hypothalamus lesions influences water and salt intake, and sodium and urine excretion, and arterial blood pressure induced by L-NAME and FK 409 injections into median preoptic nucleus in conscious rats

Male Holtzman rats weighting 200-250 g were anesthetized with zoletil 50 mg/Kg (tiletamine chloridrate 125,0 mg and zolazepan chloridrate 125,0 mg) into quadriceps muscle and submitted an electrolytic lesion of the lateral hypothalamus (LH) and a stainless steel cannula was implanted into their median preoptic nucleus (MnPO). We investigated the effects of the injection into the (MnPO) of FK 409 (20 mug/0.5 mul), a nitric oxide (NO) donor, and N-W-nitro-L-arginine methyl ester (L-NAME) 40 mug/0.5 mul, a nitric oxide synthase inhibitor (NOSI), on the water and sodium appetite and the natriuretic, diuretic and cardiovascular effects induced by injection of L-NAME and FK 409 injected into MnPO in rats with LH lesions. Controls were injected with a similar volume of 0.15 M NaCl. L-NAME injected into MnPO produced an increase in water and sodium intake and in sodium and urine excretion and increase de mean arterial pressure (MAP). FK 409 injected into MnPO did not produce any change in the hydro electrolytic and cardiovascular parameters in LH-sham and lesioned rats. FK 409 injected before L-NAME attenuated its effects. These data show that electrolytic lesion of the LH reduces fluid and sodium intake as well as sodium and urine excretion, and the pressor effect induced by L-NAME. LH involvement with NO of the MnPO excitatory and inhibitory mechanisms related to water and sodium intake, sodium excretion and cardiovascular control is suggested. (C) 2004 Elsevier B.V. All rights reserved.

Activation of serotonergic 5-HT1A receptors in the lateral parabrachial nucleus increases NaCl intake

Previous studies using non-specific serotonergic agonists and antagonists have shown the importance of serotonergic inhibitory mechanisms in the lateral parabrachial nucleus (LPBN) for controlling sodium and water intake. In the present study, we investigated whether the serotonergic 5-HTIA receptor subtype in the LPBN participates in this control. Male Holtzman rats had cannulas implanted bilaterally into the LPBN. Bilateral injections of the 5-HTIA receptor agonist, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT, 0.1, 1.25, and 2.5 mu g/ 0.2 mu l), into the LPBN enhanced 0.3 M NaCl and water intake of rats injected subcutaneously with the diuretic furosemide (10 mg/kg bw) and a low dose of the angiotensin-converting enzyme inhibitor, captopril (5 mg/kg bw). The increase in NaCl intake produced by 8-OH-DPAT injections was reduced in dose-related manner by pre-treating the LPBN with the selective 5-HTIA serotonergic antagonist, WAY-100635 (WAY, I and 2 mu g/0.2 mu l). In contrast, WAY did not affect water intake produced by 8-OH-DPAT. WAY-100635 injected alone into the LPBN had no effect on NaCl ingestion. Injections of 8-OH-DAPT (0.1 mu g/0.2 mu l) into the LPBN also increased 0.3 M NaCl intake induced by 24-h sodium depletion (furosemide, 20 mg/kg bw plus 24 h of sodium-free diet). Serotonin (5-HT, 20 mu g/0.2 mu l) injected alone or combined with 8-OH-DPAT into the LPBN reduced 24-h sodium depletion-induced 0.3 M NaCl intake. Therefore, the activation of serotonergic 5-HTIA receptors in the LPBN increases stimulated hypertonic NaCl and water intake, while 5-HT injections into the LPBN reduce NaCl intake and prevent the effects of serotonergic 5-HTIA receptor activation. (c) 2005 Elsevier B.V. All rights reserved.

Ablation of NK1 receptor bearing neurons in the nucleus of the solitary tract blunts cardiovascular reflexes in awake rats

The nucleus of the solitary tract (NTS) receives primary afferents involved in cardiovascular regulation. We investigated the role of NK1-receptor bearing neurons in the NTS on cardiovascular reflexes in awake rats fitted with chronic venous and arterial cannulae. These neurons were lesioned selectively with saporin conjugated with substance P (SP-SAP, 2 mu M, bilateral injections of 20 nL in the subpostremal NTS, or 200 nL in both the subpostremal and the commissural NTS). Before, and 7 and 14 days after injection of SP-SAP, we measured changes in blood pressure and heart rate induced by i.v. injection of phenylephrine and nitroprusside (baroreceptor reflex), cyanide (arterial chemoreceptor reflex), and phenylbiguanide (Bezold-Jarisch reflex). The smaller injections with SP-SAP completely abolished NK1 receptor staining in the subpostremal NTS. The larger injections abolished NK1 receptor immunoreactivity in an area that extended from the commissural NTS to the rostral end of the subpostremal NTS. The lesions seemed to affect only a limited number of neurons, since neutral red stained sections did not show any obvious reduction in cell number. The smaller lesions reduced the gain of baroreflex bradycardia and the hypotension induced by phenylbiguanide. The larger lesions completely abolished the response to phenylbiguanide, blocked the baroreflex bradycardia induced by phenylephrine, severely blunted the baroreflex tachycardia, and blocked the bradycardia and reduced the hypertension induced by cyanide. Thus, these responses depend critically on NK1-receptor bearing neurons in the NTS. (c) 2006 Elsevier B.V. All rights reserved.