Whole body sodium depletion modifies AT1 mRNA expression and serotonin content in the dorsal raphe nucleus

Angiotensin II (Ang II) acts on Ang II type 1 (AT1) receptors located in the organum vasculosum and subfornical organ (SFO) of the lamina terminalis as a main facilitatory mechanism of sodium appetite. The brain serotonin (5‐HT) system with soma located in the dorsal raphe nucleus (DRN) provides a main inhibitory mechanism. In the present study, we first investigated the existence of Ang II AT1 receptors in serotonergic DRN neurones. Then, we examined whether whole body sodium depletion affects the gene expression of the AT1a receptor subtype and the presumed functional significance of AT1 receptors. Using confocal microscopy, we found that tryptophan hydroxylase‐2 and serotonin neurones express AT1 receptors in the DRN. Immunofluorescence quantification showed a significant reduction in 5‐HT content but no change in AT1 receptor expression or AT1/5‐HT colocalisation in the DRN after sodium depletion. Whole body sodium depletion also significantly increased Agtr1a mRNA expression in the SFO and DRN. Oral treatment with the AT1 receptor antagonist losartan reversed the changes in Agtr1a expression in the SFO but not the DRN. Losartan injection into either the DRN or the mesencephalic aqueduct had no influence on sodium depletion‐induced 0.3 mol L^‐1 NaCl intake. The results indicate the expression of Agtr1a mRNA in the DRN and SFO as a marker of sodium depletion. They also suggest that serotonergic DRN neurones are targets for Ang II. However, the function of their AT1 receptors remains elusive.     

Lateral parabrachial afferent areas and serotonin mechanisms activated by volume expansion

Recent evidence has shown that the serotonergic mechanism of the lateral parabrachial nucleus (LPBN) participates in the regulation of renal and hormonal responses to isotonic blood volume expansion (BVE). We investigated the BVE-induced Fos activation along forebrain and hindbrain nuclei and particularly within the serotonergic clusters of the raphé system that directly project to the LPBN. We also examined whether there are changes in the concentration of serotonin (5HT) within the raphé nucleus in response to the same stimulus. With this purpose, we analyzed the cells doubly labeled for Fos and Fluorogold (FG) following BVE (NaCl 0.15 M, 2 ml/100 g b.w., 1 min) 7 days after FG injection into the LPBN. Compared with the control group, blood volume-expanded rats showed a significant greater number of Fos-FG double-labeled cells along the nucleus of the solitary tract, locus coeruleus, hypothalamic paraventricular nucleus, central extended amygdala complex, and dorsal raphé nucleus (DRN) cells. Our study also showed an increase in the number of serotonergic DRN neurons activated in response to isotonic BVE. We also observed decreased levels of 5HT and its metabolite 5-hydroxyindoleacetic acid (measured by high-pressure liquid chromatography) within the raphé nucleus 15 min after BVE. Given our previous evidence on the role of the serotonergic system in the LPBN after BVE, the present morphofunctional findings suggest the existence of a key pathway (DRN-LPBN) that may control BVE response through the modulation of 5HT release.     

Expression of Fos in rat brain in relation to sodium appetite: furosemide and cerebroventricular renin

Two experiments were performed to investigate the relationship between the expression of sodium appetite and the appearance of Fos-like immunoreactivity (Fos-IR) in the brain of rats. In the first experiment, rats were depleted of sodium by treatment with furosemide 24 h prior to sacrifice and without access to either food or sodium solution. Some rats had access to distilled water, and others had no fluids available during the 24 h. All of the furosemide-treated rats showed Fos-IR in both the subfornical organ (SFO) and around the organum vasculosum laminae terminalis (OVLT). Rats with access to distilled water during the depletion period showed no Fos-IR in the supraoptic (SON) or paraventricular hypothalamic nuclei (PVN) and, in parallel behavioral studies, comparably-treated rats consumed only 0.3 M NaCl solution at the end of the 24 h. In rats that had no fluids during the deprivation period, only about one half showed Fos-IR in SON and PVN and, in parallel behavioral studies, comparably treated rats consumed both water and 0.3 M NaCI solution at the end of 24 h. In a second experiment, cerebroventricular administration of renin stimulated short latency intake of 0.3 M NaCI and water. The relative intakes of water and NaCl were comparable at a low dose of renin, but intake of water exceeded that of NaCl after higher doses. Renin induced Fos-IR in SFO, MnPO, peri-OVLT region, SON and PVN. Both Fos-IR and fluid intake were antagonized by administration of losartan, an angiotensin 11 type 1 receptor antagonist. Thus, only the circumventricular organs of the lamina terminalis showed Fos-IR during each natriorexigenic regimen in these studies. These data support the view that Ang 11 of both central and peripheral origin activates the SFO and/or peri-OVLT region and contributes to sodium appetite.     

Activation of lateral parabrachial afferent pathways and endocrine responses during sodium appetite regulation

Modulation of salt appetite involves interactions between the circumventricular organs (CVOs) receptive areas and inhibitory hindbrain serotonergic circuits. Recent studies provide support to the idea that the serotonin action in the lateral parabrachial nucleus (LPBN) plays an important inhibitory role in the modulation of sodium appetite. The aim of the present work was to identify the specific groups of neurons projecting to the LPBN that are activated in the course of sodium appetite regulation, and to analyze the associated endocrine response, specifically oxytocin (OT) and atrial natriuretic peptide (ANP) plasma release, since both hormones have been implicated in the regulatory response to fluid reestablishment. For this purpose we combined the detection of a retrograde transported dye, Fluorogold (FG) injected into the LPBN with the analysis of the Fos immunocytochemistry brain pattern after sodium intake induced by sodium depletion. We analyzed the Fos-FG immunoreactivity after sodium ingestion induced by peritoneal dialysis (PD). We also determined OT and ANP plasma concentration by radioimmunoassay (RIE) before and after sodium intake stimulated by PD. The present study identifies specific groups of neurons along the paraventricular nucleus, central extended amygdala, insular cortex, dorsal raphe nucleus, nucleus of the solitary tract and the CVOs that are activated during the modulation of sodium appetite and have direct connections with the LPBN. It also shows that OT and ANP are released during the course of sodium satiety and fluid reestablishment. The result of this brain network activity may enable appropriate responses that re-establish the body fluid balance after induced sodium consumption.     

Sodium depletion induces Fos immunoreactivity in circumventricular organs of the lamina terminalis

Acute sodium depletion by peritoneal dialysis (PD) induces c-fos expression in the subfornical organ (SFO) and organum vasculosum laminae terminalis (OVLT), in conscious rats. Fos immunoreactive (Fos-ir) neurons detected by immunohistochemistry first appeared in these nuclei 60 min after PD, increased gradually in the next 4 h and remained high for 27 h following PD. Fos-ir cells were distributed throughout the body of SFO, being the core of the posterior sections preferentially activated, whereas Fos-ir neurons occurred around the periphery of OVLT (annular disposition). When rats were allowed to drink sodium salt (1.8% NaCl) 24 h after PD, there was a marked reversion of the c-fos expression in the OVLT and a comparatively smaller effect in the SFO. Intracerebroventricular infusion of hypertonic CSF (170 mM NaCl) from 30 min before and during 4 h after PD, significantly inhibited the c-fos expression in both nuclei.These results demonstrate that an acute body sodium deficit induces c-fos activity in SFO and OVLT neurons, indicating the special role of these structures in sodium balance regulation. They also show that the sodium-depletion-induced production of Fos in neurons of the lamina terminalis can be modulated by central or systemic reposition of sodium.     

Moxonidine and central alpha2 adrenergic receptors in sodium intake

Central injections of the alpha(2) adrenergic/imidazoline receptor agonist moxonidine inhibit water and NaCl intake in rats. In the present study, we investigated the possible involvement of central alpha(2) adrenergic receptors on the inhibitory effect of moxonidine in 0.3 M NaCl intake induced by 24 h sodium depletion. Male Holtzman rats with stainless-steel cannulas implanted into the lateral ventricle (LV) were used. Sodium depletion was produced by the treatment with the diuretic furosemide (20 mg/kg of body weight) injected subcutaneously +24 h of sodium-deficient diet. Intracerebroventricular (icv) injections of moxonidine (20 nmol/1 microl) reduced sodium depletion-induced 0.3 M NaCl intake (6.6+/-1.9 ml/120 min vs. vehicle: 12.7+/-1.7 ml/120 min). Pre-treatment with the alpha(2) adrenoreceptor antagonists RX 821002 (80 nmol/1 microl), SK&F 86466 (640 nmol/1 microl) and yohimbine (320 nmol/3 microl) injected icv abolished the inhibitory effect of icv moxonidine on sodium depletion-induced 0.3 M NaCl intake (13.3+/-1.4, 15.7+/-1.7 and 11.8+/-2.2 ml/120 min, respectively). The results show that the activation of alpha(2) adrenoreceptors is essential for the inhibitory effect of central moxonidine on sodium depletion-induced NaCl intake.     

Distribution of Fos-immunoreactivity in rat brain following a dipsogenic dose of captopril and effects of angiotensin receptor blockade

Immunohistochemical techniques were used to detect Fos in the brain following subcutaneous administration of the angiotensin converting enzyme inhibitors captopril or enalapril at 0.5 mg/kg to conscious rats. Increased Fos-like immunoreactivity was observed in many neurons in the lamina terminalis, and in regions of the hypothalamus. Captopril at this dose also caused water drinking in other rats. Pre-treatment with the angiotensin AT₁ receptor antagonist ZD7155 (10 mg/kg) given subcutaneously prevented the captopril-induced increase in Fos in the lamina terminalis. This dose of ZD7155 also prevented captopril-induced drinking in other rats. With a higher dose (50 mg/kg) of captopril or enalapril, there was no increase in Fos in the lamina terminalis. This dose of captopril was not dipsogenic. The results are consistent with the proposal that the lower dose (0.5 mg/kg) of captopril or enalapril increases circulating angiotensin I levels which are then converted to angiotensin II in the organum vasculosum of the lamina terminalis and subfornical organ. Stimulation of neurons at these sites may subserve water drinking and sodium appetite.     

Effect of Intravenous Captopril on c-fos Expression Induced by Sodium Depletion in Neurons of the Lamina Terminalis

Peripheral administration of the angiotensin converting enzyme (ACE) inhibitor, captopril, and the central infusion of sarile, an angiotensin II (Ang II) receptor antagonist, were used to evaluate the role of renal and brain generated Ang II in sodium depletion-induced production of Fos in cells of the subfornical organ (SFO) and organum vasculosum lamina terminalis (OVLT). Pretreatment with intravenous captopril (100 mg/kg) significantly inhibited the c-fos expression induced by sodium depletion in the SFO and OVLT. In contrast, continuous intracerebroventricular infusion of sarile (22.5 μg/4.5 h, 5 μl/h) did not affect the expected pattern of c-fos expression observed in both nuclei, 4 h after peritoneal dialysis. These results show that systemic interference with the angiotensin system of renal origen by captopril inhibited the production of Fos induced by sodium depletion in cells of the SFO and OVLT. These findings are consistent with the hypothesis that a rise in peripheral Ang II levels, triggered by sodium deficiency, could be an important mediator of the physiological and behavioral responses that lead to the restoration of sodium balance. In addition, this study suggests that increased circulating Ang II levels in response to body sodium deficit can directly stimulate neural pathways in the SFO and OVLT.     

The lamina terminalis and its role in fluid and electrolyte homeostasis

The lamina terminalis, which forms most of the anterior wall of the third ventricle, consists of the median preoptic nucleus and two circumventricular organs (CVOs), the subfornical organ and organum vasculosum of the lamina terminalis. These latter two regions lack a blood-brain barrier and, unlike other regions of the brain, are influenced by the hormonal and ionic composition of the blood. The CVOs of the lamina terminalis are rich in receptors for a number of circulating peptides and the subfornical organ and the OVLT are clearly established as the prime cerebral targets for circulating angiotensin II, atrial natriuretic peptide (AVP) and relaxin to influence central nervous system pathways regulating body fluid homeostasis. Together with the median preoptic nucleus, these two CVOs also detect changes and relay neural signals relating to the tonicity of body fluids and play important roles in osmoregulatory fluid intake and excretion. The neural circuitry of the lamina terminalis involves both afferent and efferent connections to several other regions of the brain, and neurons within the individual components of lamina terminalis are reciprocally connected with each other. This neural circuitry subserves the influence that the lamina terminalis exerts on vasopressin secretion, thirst, the appetite for salt, renal sodium excretion and renin secretion by the kidney.     

Comparing salt appetites: Induction with intracranial hormones or dietary sodium restriction

To raise a natural sodium appetite in the laboratory requires approximately 10 days on a very low sodium diet. Most other regimens induce sodium appetite more rapidly, but also result in behavioral or physiological changes not observed in the deprivation-induced state. We compared the characteristics of need-free sodium appetite induced either by systemic aldosterone combined with an intracerebroventricular (ICV) injection of angiotensin II or by a single ICV injection of renin with an appetite induced by 10 days of sodium deprivation. We measured the latency to drink water and 3% NaCl, as well as the amount of these fluids consumed at 30 min, 3 h, and 24 h. Angiotensin induced the shortest latency for both water and salt drinking, but the overall salt intake was lower. In 24 h, renin and sodium deprivation both induced about 14 ml of NaCl consumption, but the time course of the fluid intake differed for the two regimens.     

Forebrain lesions that disrupt water homeostasis do not eliminate the sodium appetite of sodium deficiency in sheep

Brain structures located within the anterior wall of the third brain ventricle (subfornical organ, median preoptic nucleus and organum vasculosum of the lamina terminalis) are known to be involved in thirst as well as other aspects of body fluid and electrolyte balance. The present studies evaluated the role of these structures in the Na appetite of mildly or moderately Na-depleted sheep (sheep with a parotid fistula deprived of Na solution for 22 or 46 h). In addition, the role of these structures was tested in mildly Na-depleted sheep in which the Na appetite was enhanced by decreasing cerebrospinal fluid and brain extracellular fluid Na concentration (i.e., i.c.v. infusion of hypertonic saccharide solution) or was decreased by systemic infusion of hypertonic saline. The results indicated that sheep with lesions which reduced or eliminated daily water intake or water intake in response to hypertonicity of body fluids had, in all situations tested, appropriate changes in Na appetite (i.e., similar to their prelesion changes). Thus, the present experiments demonstrated that the brain areas involved in thirst as well as other aspects of body fluid and electrolyte balance are anatomically different from those involved in regulating Na appetite.     

Topographic organization of serotonergic dorsal raphe neurons projecting to the superior colliculus in the Mongolian gerbil (Meriones unguiculatus).

Recent evidence suggests that the dorsal raphe nucleus (DRN) of the brainstem is a collection of neuronal clusters having different neurochemical characteristics and efferent projection patterns. To gain further insight into the neuroanatomic organization of the DRN, neuronal populations projecting to the superior colliculus (SC) were mapped in a highly visual rodent, the Mongolian gerbil (Meriones unguiculatus). Retrograde tracers Fluoro-Gold (FG) or cholera toxin subunit-B (CTB) were injected into the superficial layers of the SC, and serotonin (5-hydroxytryptamine, 5-HT) -positive cells were identified by using immunocytochemistry in the FG-injected animals. Based on its projections to the SC, the DRN was divided into five rostrocaudal levels. In the rostral and middle levels of the DRN, virtually all FG-filled cells occurred in the lateral DRN, and 36-55% of 5-HT-immunoreactive (5-HT-ir) cells were also double-labeled with FG. Caudally, FG-filled cells occurred in the lateral, ventromedial, and interfascicular DRN; and 44, 12, and 31% of 5-HT-ir cells, respectively, were also FG-filled. The dorsomedial DRN contained only a small proportion of FG-filled cells at its most caudal level and was completely devoid of FG-filled cells more rostrally. The CTB-injected animals showed a similar distribution of retrogradely labeled cells in the DRN. Topographically, the dorsal tegmental nucleus and the laterodorsal tegmental nucleus appeared to be closely associated with 5-HT-ir cells in the caudal DRN. These results suggest that the lateral DRN and the ventromedial/interfascicular DRN may be anatomically, morphologically, and neurochemically unique subdivisions of the gerbil DRN.     

Expression and colocalization of NADPH-diaphorase and Fos in the subnuclei of the parabrachial nucleus in rats following visceral noxious stimulation

To investigate whether neural nitric oxide synthase (nNOS) in the parabrachial nucleus (PB) is involved in processing visceral noxious stimulation, we mapped the distribution of histochemical staining for nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d), a marker for nNOS, and immunohistochemical staining for Fos, a neuronal activity marker, in the subnuclei of the PB following 2% formalin injection into the stomach of rats. NADPH-d and noxious-stimuli induced Fos staining were also examined in tissue containing PB cells labeled by the retrograde transport of fluogold (FG) injected into the central nucleus of the amygdala (CeA). We found that the number of Fos immunoreactive (Fos-IR) neurons was significantly increased in the dorsal lateral (dl), external lateral (el) and K?lliker-Fuse (KF) subnuclei of the PB. We observed that intensely labeled (type 1) NADPH-d positive neurons were mainly located in the rostral part of the PB; they extended long processes adjacent Fos-IR neurons, but no Fos/type 1 NADPH-d double-labeled neurons were seen. In contrast, lightly labeled (type 2) NADPH-d positive neurons were principally localized in the dl of the PB, in which a few Fos/type 2 NADPH-d double-labeled neurons were detected. Additionally, a large number of FG/Fos double-labeled neurons were observed to be surrounded closely by the intensive NADPH-d staining in the el of the PB. These results suggest that neurons in the el of the PB that project to the CeA are activated by visceral noxious stimulation and could be indirectly influenced by nitric oxide in the PB.     

Tachykinin receptor subtypes involved in the central effects of tachykinins on water and salt intake

The present study was aimed at investigating which tachykinin receptor subtypes mediate the inhibitory effects of tachykinins a) on salt intake induced by sodium depletion, b) on water intake induced by subcutaneous hypertonic NaCl administration and c) on water intake induced by central angiotensin II injection. The study was carried out by evaluating the potency of action, following intracerebroventricular injection, of several peptides, including both naturally occurring tachykinins and synthetic peptides selective for a given receptor subtype. The results obtained show different rank orders of potency of the agonists in the different behavioral tests, thus suggesting that different receptor subtypes are involved in the effects of tachykinins on water and salt intake. NK-3 receptors appear to be involved in the inhibitory effect of tachykinins on depletion-induced salt appetite. NK-2 receptors apparently mediate the inhibitory effect of tachykinins on drinking induced by hyperosmotic NaCl administration, while NK-1 receptors are probably involved in the inhibition of angiotensin II-induced drinking.     

The consequences of uncontrollable stress are sensitive to duration of prior wheel running

The behavioral consequences of uncontrollable stress, or learned helplessness (LH) behaviors, are thought to involve hyperactivity of serotonergic (5-HT) neurons in the dorsal raphe nucleus (DRN). Other brain regions implicated in LH and capable of affecting 5-HT systems, such as the bed nucleus of the stria terminalis (BNST), amygdala, and habenula, could contribute to DRN 5-HT hyperactivity during uncontrollable stress. Six weeks of wheel running prevents LH and attenuates uncontrollable stress-induced c-Fos expression in DRN 5-HT neurons, although the duration of wheel running necessary for these effects is unknown. In the current study, 6 but not 3, weeks of wheel running blocked the shuttle box escape deficit and exaggerated fear produced by uncontrollable tail shock in sedentary rats. Corresponding to the duration-dependent effects of wheel running on LH behaviors, 6 weeks of wheel running was required to attenuate uncontrollable stress-induced 5-HT neural activity, indexed by c-Fos protein expression, in the DRN and c-Fos expression in the lateral ventral region of the BNST. Wheel running, regardless of duration, did not affect c-Fos expression anywhere in the amygdala or habenula. These data indicate that the behavioral effects of uncontrollable stress are sensitive to the duration of prior physical activity and are consistent with the hypothesis that attenuation of DRN 5-HT activity contributes to the prevention of LH by wheel running. The potential role of the BNST in the prevention of LH by wheel running is discussed.     

Role of the 5-HT1A somatodendritic autoreceptor in the dorsal raphe nucleus on salt satiety signaling in rats

We investigated the possible role of 5-HT_1A somatodendritic autoreceptors in the dorsal raphe nucleus (DRN) on salt intake response during basal conditions and following natriorexigenic challenge aroused by sodium depletion in rats. Acute systemic administration (76–1520 nmol/kg s.c.) of 8-OH-DPAT, a selective 5-HT_1A somatodendritic autoreceptor agonist, induced a clear and dose-dependent preference for salt intake through free choice between water and 0.3 M NaCl simultaneously offered under basal conditions. Acute intra-DRN microinjection (7.5 nmol/rat) of 8-OH-DPAT significantly mimicked the acute systemic protocol in sodium-replete rats. Interestingly, microinjection of 8-OH-DPAT into the DRN raised an additional long-lasting increase of 0.3 M NaCl intake in sodium-depleted rats despite a high volume ingested 30 min after central injection. Conversely, chronic systemic treatment (1520 nmol/kg s.c.) with 8-OH-DPAT for 2 and 3 weeks or repeated intra-DRN microinjection (7.5 nmol/rat) evoked a significant long-term decrease in 0.3 M NaCl intake in sodium-depleted rats given only water and a sodium-deficient diet over the course of 24 h after furosemide injection. These results show a clear-cut involvement of the DRN 5-HT_1A somatodendritic autoreceptors in sodium satiety signaling under basal conditions and during the consummatory phase of salt intake in sodium-depleted rats.     

Induction and expression of salt appetite: effects on Fos expression in nucleus accumbens

Sodium depletion is a strong natural motivator that creates a pronounced sodium appetite and has been shown to activate neural regions associated with fluid and sodium balance. However, it is not known whether sodium appetite affects the mesolimbic circuitry associated with reward motivation. The present studies examined expression of the immediate early gene Fos in the nucleus accumbens (NAc) as a marker of neuronal activation following the induction and expression of furosemide-induced sodium appetite. During sodium appetite expression, sham-drinking and normal drinking were used to dissociate effects of NaCl taste stimulation from the repletion that follows absorption of sodium. These studies revealed that the combination of NaCl taste stimulation and persistent sodium depletion experienced by sham-drinking animals dramatically activates the NAc, while neither induction nor expression of sodium appetite alone is sufficient to increase Fos expression in this region. Results are discussed in terms of current theories of reward motivation.     

GABAergic mechanisms of the lateral parabrachial nucleus on sodium appetite

GABAergic activation in the lateral parabrachial nucleus (LPBN) induces sodium and water intake in satiated and normovolemic rats. In the present study we investigated the effects of GABAA receptor activation in the LPBN on 0.3M NaCl, water, 2% sucrose and food intake in rats submitted to sodium depletion (treatment with the diuretic furosemide subcutaneously+sodium deficient food for 24h), 24h food deprivation or 24 h water deprivation. Male Holtzman rats with bilateral stainless steel cannulas implanted into the LPBN were used. In sodium depleted rats, muscimol (GABAA receptor agonist, 0.5 nmol/0.2 microl), bilaterally injected into the LPBN, produced an inconsistent increase of water intake and two opposite effects on 0.3M NaCl intake: an early inhibition (4.3+/-2.7 versus saline: 14.4+/-1.0 ml/15 min) and a late facilitation (37.6+/-2.7 versus saline: 21.1+/-0.9 ml/180 min). The pretreatment of the LPBN with bicuculline (GABAA receptor antagonist, 1.6 nmol) abolished these effects of muscimol. Muscimol into the LPBN also reduced food deprivation-induced food intake in the first 30 min of test (1.7+/-0.6g versus saline: 4.1+/-0.6g), without changing water deprivation-induced water intake or 2% sucrose intake in sodium depleted rats. Therefore, although GABAA receptors in the LPBN are not tonically involved in the control of sodium depletion-induced sodium intake, GABAA receptor activation in the LPBN produces an early inhibition and a late facilitation of sodium depletion-induced sodium intake. GABAA activation in the LPBN also inhibits food intake, while it consistently increases only sodium intake and not water, food or sucrose intake.     

Inhibitory effect of kassinin on salt intake induced by different natriorexigenic treatments in the rat

Pulse intracerebroventricular (i.c.v.) injection of kassinin, 100–500 ng/rat, potently inhibits salt intake induced by sodium depletion. The effect appears to bc selective since the same doses of kassinin do not inhibit milk intake or solid food intake. When given by continuous i.c.v. infusion kassinin elicits a clear anti-natriorexic effect at doses of 1–10 ng/min/rat. Kassinin not only suppresses sodium depletion-induced salt appetite, but it also inhibits sodium intake induced by pulse i.c.v. injection of renin or by subcutaneous (s.c.) deoxycorticosterone. Finally it also suppresses the elevated need-free intake of 1.5% NaCl in multidepleted female rats, which is not mediated by the renin-angiotensin-aldosterone system. These findings show that kassinin exerts a general suppressive effect on salt intake, irrespective of the natriorexigenic treatment. The present study suggests that the kassinin-like peptides that are endogenous to the rat brain may be involved in the behavioral regulation of extracellular body fluids in the rat by inhibiting sodium intake.