Sodium consumption following lesions surrounding the anteroventral third ventricle

Renal responses produced by microinjection of the kappa opioid receptor agonist, U50-488H, into sites within the rat lamina terminalis

Activation of central kappa opioid receptors (KOR) has been demonstrated to produce marked free water diuresis with a concurrent increase in renal sympathetic nerve activity (RSNA). This study investigated the cardiovascular (CV) and renal effects evoked by central activation of KOR in two lamina terminalis sites, the median preoptic area (MPA) and anterolateral division of the bed nuclei of the stria terminalis (BST). Rats anesthetized with urethane alpha-chloralose were instrumented to record mean arterial pressure, heart rate, RSNA, and urine output (V). Rats were infused with isotonic saline (25 μL/min) and urine samples were collected during two 10-min control periods and six consecutive 10-min experimental periods following microinjection of vehicle, U50-448H (U50, KOR agonist) alone or norbinaltorphimine (nor-BNI, KOR antagonist) plus U50. Microinjection of U50 into the BST increased V (peak at 30 min, 84.8 ± 12.9 μL/min) as compared to its respective control, vehicle, or nor-BNI plus U50. This diuretic effect occurred without any significant changes in CV parameters, RSNA, or urinary sodium excretion. In contrast, U50 injection into the MPA significantly increased RSNA (peak at 20 mins: 129 ± 9.9) without increasing the other parameters. This study demonstrated novel sites through which activation of KOR selectively increases V and RSNA. The ability of U50 to increase V without affecting sodium excretion and RSNA raises the possibility that LT neurons could be an important substrate through which drugs targeting KOR could selectively facilitate water excretion in sodium-retaining diseases such as congestive heart failure.

The Sensory Psychobiology of Thirst and Salt Appetite

Thirst and the hunger for sodium containing fluids and food (i.e., sodium appetite) are the consequences of the generation of unique central nervous system states. Altered body fluid homeostasis produces sensory and perceptional changes that arise from signals generated in the body that serve as indices of body fluid balance and distribution. These signaling mechanisms activate networks of brain neurons that use specific neurochemicals to communicate between cells and process information. The brain integrates information derived from various bodily sources so that thirst and sodium appetite are in a true sense the synthetic products of the nervous system. In recent years much has been learned about the stimuli and receptor systems involved in signaling the brain to reflect the status of bodily fluids and about the central neural substrates that process such inputs to generate thirst and sodium appetite. Knowledge about the sensory nature of thirst and sodium appetite provides a basis for understanding the biological constraints under which thirst and sodium appetite operate. This information is important for appreciating the extent to which thirst and sodium appetite motivational states and behaviors can be relied on to maintain and repair disruptions of body fluid homeostasis.

Sodium deprivation and salt intake activate separate neuronal subpopulations in the nucleus of the solitary tract and the parabrachial complex

Salt intake is an established response to sodium deficiency, but the brain circuits that regulate this behavior remain poorly understood. We studied the activation of neurons in the nucleus of the solitary tract (NTS) and their efferent target nuclei in the pontine parabrachial complex (PB) in rats during sodium deprivation and after salt intake. After 8-day dietary sodium deprivation, immunoreactivity for c-Fos (a neuronal activity marker) increased markedly within the aldosterone-sensitive neurons of the NTS, which express the enzyme 11-beta-hydroxysteroid dehydrogenase type 2 (HSD2). In the PB, c-Fos labeling increased specifically within two sites that relay signals from the HSD2 neurons to the forebrain--the pre-locus coeruleus and the innermost region of the external lateral parabrachial nucleus. Then, 1-2 hours after sodium-deprived rats ingested salt (a hypertonic 3% solution of NaCl), c-Fos immunoreactivity within the HSD2 neurons was virtually eliminated, despite a large increase in c-Fos activation in the surrounding NTS (including the A2 noradrenergic neurons) and area postrema. Also after salt intake, c-Fos activation increased within pontine nuclei that relay gustatory (caudal medial PB) and viscerosensory (rostral lateral PB) information from the NTS to the forebrain. Thus, sodium deficiency and salt intake stimulate separate subpopulations of neurons in the NTS, which then transmit this information to the forebrain via largely separate relay nuclei in the PB complex. These findings offer new perspectives on the roles of sensory information from the brainstem in the regulation of sodium appetite.

Sodium depletion activates the aldosterone-sensitive neurons in the NTS independently of thirst

Thirst and sodium appetite are both critical for restoring blood volume. Because these two behavioral drives can arise under similar physiological conditions, some of the brain sensory sites that stimulate thirst may also drive sodium appetite. However, the physiological and temporal dynamics of these two appetites exhibit clear differences, suggesting that they involve separate brain circuits. Unlike thirst-associated sensory neurons in the hypothalamus, the 11-beta-hydroxysteroid dehydrogenase type 2 (HSD2) neurons in the rat nucleus tractus solitarius (NTS) are activated in close association with sodium appetite (16). Here, we tested whether the HSD2 neurons are also activated in response to either of the two physiological stimuli for thirst: hyperosmolarity and hypovolemia. Hyperosmolarity, produced by intraperitoneal injection of hypertonic saline, stimulated a large increase in water intake and a substantial increase in immunoreactivity for the neuronal activity marker c-Fos within the medial NTS, but not in the HSD2 neurons. Hypovolemia, produced by subcutaneous injection of hyperoncotic polyethylene glycol (PEG), stimulated an increase in water intake within 1-4 h without elevating c-Fos expression in the HSD2 neurons. The HSD2 neurons were, however, activated by prolonged hypovolemia, which also stimulated sodium appetite. Twelve hours after PEG was injected in rats that had been sodium deprived for 4 days, the HSD2 neurons showed a consistent increase in c-Fos immunoreactivity. In summary, the HSD2 neurons are activated specifically in association with sodium appetite and appear not to function in thirst.

Aldosterone target neurons in the nucleus tractus solitarius drive sodium appetite

Sodium appetite can be enhanced by the adrenal steroid aldosterone via an unknown brain mechanism. A novel group of neurons in the nucleus tractus solitarius expresses the enzyme 11-beta-hydroxysteroid dehydrogenase type 2, which makes them selectively responsive to aldosterone. Their activation parallels sodium appetite in different paradigms of salt loss even in the absence of aldosterone. These unique aldosterone target neurons may represent a previously unrecognized central convergence point at which hormonal and neural signals can be integrated to drive sodium appetite.

Lesions of periventricular tissue surrounding the anteroventral third ventricle (AV3V) attenuate salivation and thermal tolerance in response to a heat stress

The purpose of this study was to determine if ablation of the periventricular tissue that surrounds the anteroventral third ventricle (AV3V) would reduce an animal's ability to withstand a thermal challenge. The results show that AV3V-lesion rats are less capable of withstanding a 37 degrees C heat stress and that this is, at least in part, due to a reduced salivation response.

Forebrain-mediated adaptations to myocardial infarction in the rat

Recent studies suggest that the forebrain contributes to the circulatory derangements leading to heart failure after myocardial injury. We tested that hypothesis by examining the effect of myocardial infarction (MI) or sham MI (MI-s) on neurohumoral regulation in rats with prior anteroventral (AV) third ventricle lesion (AV3V-x) or sham lesion (AV3V-s). AV3V-s/MI rats had higher sodium intake, lower urine volume, and lower urinary sodium excretion than AV3V-s/MI-s rats. AV3V-x/MI rats had lower sodium intake and higher urine volume than AV3V-s/MI or AV3V-s/MI-s rats and urinary sodium excretion comparable to AV3V-s/MI-s rats. AV3V-x had no effect on baseline plasma renin activity (PRA). One week after MI, PRA had increased in AV3V-s but decreased in AV3V-x rats. AV3V-x reduced renal sympathetic nerve activity in MI and MI-s rats. AV3V-x improved baroreflex function in MI rats but diminished it in MI-s rats. Survival beyond 2 wk was lower in the AV3V-x/MI rats than in all other groups. These results confirm a critical role for the forebrain in the neurohumoral adjustments to MI.

The neuroendocrinology of thirst and salt appetite: visceral sensory signals and mechanisms of central integration

This review examines recent advances in the study of the behavioral responses to deficits of body water and body sodium that in humans are accompanied by the sensations of thirst and salt appetite. Thirst and salt appetite are satisfied by ingesting water and salty substances. These behavioral responses to losses of body fluids, together with reflex endocrine and neural responses, are critical for reestablishing homeostasis. Like their endocrine and neural counterparts, these behaviors are under the control of both excitatory and inhibitory influences arising from changes in osmolality, endocrine factors such as angiotensin and aldosterone, and neural signals from low and high pressure baroreceptors. The excitatory and inhibitory influences reaching the brain require the integrative capacity of a neural network which includes the structures of the lamina terminalis, the amygdala, the perifornical area, and the paraventricular nucleus in the forebrain, and the lateral parabrachial nucleus (LPBN), the nucleus tractus solitarius (NTS), and the area postrema in the hindbrain. These regions are discussed in terms of their roles in receiving afferent sensory input and in processing information related to hydromineral balance. Osmoreceptors controlling thirst are located in systemic viscera and in central structures that lack the blood-brain barrier. Angiotensin and aldosterone act on and through structures of the lamina terminalis and the amygdala to stimulate thirst and sodium appetite under conditions of hypovolemia. The NTS and LPBN receive neural signals from baroreceptors and are responsible for inhibiting the ingestion of fluids under conditions of increased volume and pressure and for stimulating thirst under conditions of hypovolemia and hypotension. The interplay of multiple facilitory influences within the brain may take the form of interactions between descending angiotensinergic systems originating in the forebrain and ascending adrenergic systems emanating from the hindbrain. Oxytocin and serotonin are additional candidate neurochemicals with postulated inhibitory central actions and with essential roles in the overall integration of sensory input within the neural network devoted to maintaining hydromineral balance.

The role of angiotensin II in ingestive behaviour: a brief review of angiotensin II, thirst and Na appetite

From the outset, the study of angiotensin II (Ang II) in body fluid homeostasis has been both complicated and intriguing. Since the publication of an early report of the dipsogenic action of this peptide, the pursuit of the role of Ang II in thirst and Na appetite has continued for the last 25 years. This pursuit captured the attention of all workers interested in the behavioural/physiological regulation of body fluid balance, with major contributions being made by James T. Fitzsimons and his colleagues. In spite of its powerful dipsogenic actions, delineation of its precise role in physiological thirst has been elusive and difficult to demonstrate. The influence of Ang II on Na intake took longer to show convincingly. However, in contrast to thirst, the role of Ang II in physiological Na appetite has been demonstrated clearly. The technological advances made during the recent years have greatly increased our ability to delineate the neurobiological context of Ang II-mediated responses. Thus, the future is promising in regard to illuminating the subtleties of the role of Ang II in body fluid balance.

Hypothalamic integration of body fluid regulation

The progression of animal life from the paleozoic ocean to rivers and diverse econiches on the planet's surface, as well as the subsequent reinvasion of the ocean, involved many different stresses on ionic pattern, osmotic pressure, and volume of the extracellular fluid bathing body cells. The relatively constant ionic pattern of vertebrates reflects a genetic "set" of many regulatory mechanisms--particularly renal regulation. Renal regulation of ionic pattern when loss of fluid from the body is disproportionate relative to the extracellular fluid composition (e.g., gastric juice with vomiting and pancreatic secretion with diarrhea) makes manifest that a mechanism to produce a biologically relatively inactive extracellular anion HCO3- exists, whereas no comparable mechanism to produce a biologically inactive cation has evolved. Life in the ocean, which has three times the sodium concentration of extracellular fluid, involves quite different osmoregulatory stress to that in freshwater. Terrestrial life involves risk of desiccation and, in large areas of the planet, salt deficiency. Mechanisms integrated in the hypothalamus (the evolutionary ancient midbrain) control water retention and facilitate excretion of sodium, and also control the secretion of renin by the kidney. Over and above the multifactorial processes of excretion, hypothalamic sensors reacting to sodium concentration, as well as circumventricular organs sensors reacting to osmotic pressure and angiotensin II, subserve genesis of sodium hunger and thirst. These behaviors spectacularly augment the adaptive capacities of animals. Instinct (genotypic memory) and learning (phenotypic memory) are melded to give specific behavior apt to the metabolic status of the animal. The sensations, compelling emotions, and intentions generated by these vegetative systems focus the issue of the phylogenetic emergence of consciousness and whether primal awareness initially came from the interoreceptors and vegetative systems rather than the distance receptors.

Strategies for investigation of CNS mechanisms of phenotypic variation in blood pressure and salt appetite in genetic hypertensive rats

Several characteristics of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY), make these homozygous strains particularly well suited for investigating the interactions of salt appetite, blood pressure control, and their neuroendocrine substrates. Appropriate genetic and developmental investigations of sources of variation in salt appetite, blood pressure, and their putative neuroendocrine substrates in these homozygous strains can provide valuable insights into fundamental mechanisms of disease, as well as factors controlling homeostatic behavioral and physiological processes. However, inappropriate use of these strains can produce misleading, although seductively plausible, conclusions regarding mechanisms. Selective inbreeding for hypertension has concentrated in SHR the "high pressure" allele for several genes that influence blood pressure, whereas breeding for normal blood pressure has left WKY with the "normal pressure" allele for all or most of these genes. In principle, inbred hypertensive strains could provide information about specific genetic alterations that mediate the hypertensive phenotype. The benefits of work with these strains are discussed, but several false assumptions and logical pitfalls are described that might cause misleading or erroneous interpretations of results from work with such strains. These problems illustrate the importance of the research strategy in elucidating the particular information that can be provided by these inbred animal models of hypertension. Two strategic approaches for studying hypertension and other genetically determined or influenced characteristics in inbred animal models such as SHR are discussed: cosegregation analysis for identifying or rejecting genetic linkage, and brain graft techniques for identifying brain specific genetic influences on cardiovascular or behavioral phenotypes. Examples of each approach are described.

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.

Forebrain circumventricular organs mediate captopril-enhanced ethanol intake in rats

Chronic peripheral treatments with low doses of the angiotensin-converting enzyme inhibitor, captopril, enhance daily intakes of dilute ethanol solutions in rats as they do the intakes of water and saline solutions. Placing captopril into the drinking water or infusing it SC increases daily intake of 6% (v/v) ethanol from 30-100% over 4-12 days of treatment. The present study examined the effects of electrolytic lesions either of the subfornical organ (SFO) or of the organum vasculosum laminae terminalis (OVLT), on captopril-enhanced ethanol intake. Captopril was infused in minipumps at 5 mg/day for 14 days. The intake of 6% (v/v) ethanol was abolished by SFO lesions and was temporarily reduced by OVLT lesions. The SFO, in particular, is essential for the expression of enhanced ethanol intake during low-dose peripheral captopril administration. Local angiotensin II synthesis and receptor activation at the SFO appear to be the mechanism of the enhanced ethanol drinking during captopril.

The effects of reversible lidocaine-induced lesion of the tissue surrounding the anterior ventral wall of the third ventricle on drinking in rats

The local anesthetic lidocaine (XILOCAINA), 2%, was injected into the tissue surrounding the anterior region of the third cerebral ventricle (AV3V) of the rat, through a permanently implanted cannula, to produce a temporary and reversible disruption of the nervous connections of this area with other cellular nuclei while leaving the vascular connections intact. Following 24 h water deprivation, lidocaine was injected, and after 20 min water intake decreased; subsequently, the lidocaine-injected rats behaved similarly to control rats injected with artificial cerebrospinal fluid. Osmotic drinking was not affected. Prolonged adipsia or hyperdipsia did not occur. In nondeprived rats, lidocaine prevented angiotensin II-induced drinking. Following 24 h sodium depletion by peritoneal dialysis, lidocaine decreased the specific sodium appetite by 50% in animals with different levels of body sodium depletion. The data indicate that the integrity of the neural tissue of the AV3V is essential for a correct body water-salt regulation. Temporary "ablation" with lidocaine, which blocked neural activity but maintained the blood supply, produced responses different from most of those reported after electrolytic lesions. Therefore, lidocaine may be used as a tool to assess the response of this neural tissue to body fluid regulation.

Deficits in NaCl ingestion after damage to the central nucleus of the amygdala in the rat

These studies examined the NaCl intake behaviors of rats with bilateral electrolytic lesions of the central nucleus of the amygdala (CeAX). Daily need-free intake of 3% NaCl was abolished by CeAX even in rats in which it had been enhanced preoperatively by a history of repeated sodium depletions but was slightly restored by three successive postoperative sodium depletions. CeAX rats drank water but not 3% NaCl to high doses of DOCA and to the activation of cerebral angiotensin II, and expressed small but reliable salt intake (need-induced salt intake or salt appetite) after postoperative sodium depletions. Other ingestive behaviors (water drinking, intake of food and 5% sucrose) were normal. When given decreasing concentrations of NaCl solution the CeAX rats rejected them until the concentration reached 0.2%. These findings suggest that lesions to the central nucleus of the amygdala produce a global impairment in salt intake behaviors that is possibly due to an alteration in the central processing of the salt taste signal.

The anteroventral wall of the third ventricle and the angiotensinergic component of need-induced sodium intake in the rat

Because the anteroventral wall of the third ventricle (AV3V) has been implicated in the control of sodium intake it was studied in rats with damage of the AV3V region in the sodium-replete and sodium-deplete states, and when they were treated with either pulse intracerebroventricular (pICV) injection of renin to activate brain angiotensin or daily subcutaneous injections of deoxycorticosterone (DOCA). The response of rats with AV3V damage to sodium depletion was retarded and the excess sodium intake that is induced by pICV renin was absent, but their daily need-free sodium intake and the sodium intake that is induced by DOCA were essentially normal. The results suggest that the AV3V is responsible for the angiotensinergic, but not the aldosteronergic, component of the ANG II/ALDO synergy that controls need-induced sodium appetite in the rat. The integrity of the AV3V is not necessary for daily need-free sodium intake or for its enhancement by sodium depletions, suggesting that ANG II is probably not important for these phenomena. But ANG II action within the AV3V might be important for the rapid burst of sodium intake that immediately follows a period of depletion.

Central administration of somatostatin suppresses the stimulated sodium intake of sheep

The effect of intracerebroventricular (i.c.v.) infusion (50 micrograms/h over 3 h) of somatostatin (SOM) on Na and water intake of sheep was determined. In Na-deplete sheep, infusion of SOM-(28) but not SOM-(14) decreased (P less than 0.05) Na intake, while both SOM-(28) and SOM-(14) increased water intake. I.c.v. infusion of SOM-(28) did not significantly affect Na or water intake of Na-replete sheep. I.c.v. infusion of SOM-(28) decreased (P less than 0.01) Na intake but did not alter the high water intakes of water-deprived sheep or sheep infused i.c.v. with angiotensin II. The results are compatible with an inhibitory action of somatostatin on stimulated brain mechanisms subserving Na appetite but not on stimulated brain mechanisms subserving thirst. Somatostatin may antagonize the inhibition of thirst in Na-deplete sheep. The results suggest that somatostatin may have a regulatory role in ingestive behavior concerned with body fluid and Na homeostasis. The difference between SOM-(14) and SOM-(28) in decreasing the Na intake of Na-deplete sheep may be due to a difference in potency or mechanism of action.

Cerebral sodium sensors in the sodium-deplete sheep

The sodium intake of sodium deplete sheep was studied during local, push-pull perfusion of different solutions within the third cerebral ventricle. Sheep were made sodium deplete by continuous loss of parotid saliva, and were allowed access to 0.6 M NaHCO3 solution for 2 h daily. Local perfusion within the third cerebral ventricle was performed before and during the access to sodium solution. Four perfusion sites were used: anterior dorsal and ventral, and posterior dorsal and ventral. Perfusion of 200 mM Na-csf caused a decrease in sodium intake at each perfusion site. Perfusion of ouabain, 10(-6) M, caused a reduction in sodium intake only during perfusions within the anterior portion of the third ventricle. The results may indicate that specific neuronal elements sensitive to changes in intracellular sodium concentration are located around the anterior portion of the third cerebral ventricle. These neurones, however, are not exclusive sites from where sodium intake of sodium deplete sheep can be influenced.

Elevated salt appetite and brain binding of angiotensin II in mineralocorticoid-treated rats

Angiotensin II (Ang II) and aldosterone levels increase with sodium deficiency, promoting sodium conservation and arousing a salt appetite in rats. The mechanism(s), by which these two hormones interact to produce salt appetite is not known. The experiments reported here tested the possibility that increased mineralocorticoids change the number and/or affinity of Ang receptors in the brain. Rats were given a series of deoxycorticosterone acetate (DOCA) injections (500 micrograms/day, s.c., for 4 days) which are known to produce a salt appetite when given in conjunction with an intracerebroventricular injection of Ang. The binding of 125I-Ang II to membranes prepared from the septal-anteroventral third ventricular region was then examined. DOCA treatment resulted in a significant increase in the number of Ang binding sites (Bmax) with no change in binding affinity (Kd). The binding of 125I-Ang II was then investigated in membranes prepared from 12 other brain regions as well as the pituitary and adrenal gland, showing that the increase in binding capacity occurred in only a few specific brain regions. A third experiment verified that the DOCA treatment used here was sufficient to arouse a salt appetite when combined with a single intracerebroventricular injection of Ang II. The mechanism that underlies the production of salt appetite by aldosterone and Ang II may at least partially consist of mineralocorticoid-induced increases in the number of Ang receptors in discrete brain regions.

The effects of a reversible colchicine-induced lesion of the anterior ventral region of the third cerebral ventricle in rats

Colchicine was injected into the region of the organum vasculosum lamina terminalis/anterior region of the third cerebral ventricle (OVLT/AV3V) to produce a temporary disruption of the nervous connections of this area and the rest of the anterior hypothalamus, but to maintain the vascular connections intact. Rats were kept in metabolism cages throughout the experiment and food and water intake plus urine and electrolyte excretion and body weight were measured each day. Food intake, body weight gain and urine and sodium excretion were reduced for several days after the injection of colchicine and the rats went into a marked positive sodium balance from the third day postinjection. Following 24 h water deprivation, 7 days after the colchicine injection, water intake was increased for 2 days. Urine and electrolyte excretion and food intake were also increased on the second day after the deprivation. Following a second deprivation, 10 days later, the colchicine-injected animals behaved as the control rats had done during both the deprivation periods. Injections of colchicine into the OVLT region of the AV3V, that would have blocked neural activity while maintaining a constant blood supply, produced some of the characteristics of a 'normal' lesion in this area; the rats decreased sodium excretion and increased their water intake in response to water deprivation. Therefore, colchicine may provide a useful means of investigating what role the constituent areas of the AV3V play in body fluid regulation.

The periventricular anteroventral third ventricle (AV3V): its relationship with the subfornical organ and neural systems involved in maintaining body fluid homeostasis

The periventricular tissue surrounding the anteroventral third ventricle (AV3V) is critically involved in the maintenance of normal body fluid balance and distribution. The present review examines the anatomical, neurochemical, and functional relationship of the AV3V with neural systems subserving body fluid homeostasis. In particular, the nature of AV3V afferents from the subfornical organ (SFO) and from brainstem noradrenergic cell groups is discussed. A model is presented proposing that specific structures within the AV3V, particularly along the ventral lamina terminalis, function to integrate information derived from blood-borne angiotensin II (via the SFO) with input arising from vascular pressure/volume receptors. The resultant of this integration is important for the generation of a normal component of thirst (i.e., drinking) associated with extracellular dehydration.

A reassessment of the brain mechanisms that control thirst

The classic " hypothalamocentric " theory of thirst has increasingly been challenged because the effects of hypothalamic lesions are not as behaviorally or anatomically specific as earlier research indicated. Instead, the attention of investigators in the field has increasingly been drawn to the lateral preoptic region and the tissues surrounding the anterior third ventricle. The present paper reviews these developments and proposes that still another diencephalic structure, the subthalamic region known as the zona incerta, may play a major role in the regulation of thirst and water intake.

Anteroventral third ventricle and renin-angiotensin system interaction in the two-kidney, one clip hypertensive rat

To test the peripheral mechanisms of prevention and reversal of two-kidney, one clip (2K1C) hypertension in the rat by lesion of the anteroventral third ventricle (AV3V) region, we studied blood pressure responses in rats to AV3V lesion produced before (n = 8) or after (n = 8) clipping the left renal artery. Two groups of sham-lesioned, clipped rats (n = 9 each) served as controls. At the end of the experiments, saralasin and captopril were given to evaluate the angiotensin-dependent component of blood pressure. To study the influence of the procedures on plasma renin activity (PRA), two parallel groups of rats (n = 26 and 24, respectively) were submitted to similar surgical protocols. We observed that increases in blood pressure were significantly smaller in the previously lesioned compared to previously sham-lesioned animals (delta BP = 21.5 +/- 3.7 vs. 32.9 +/- 2.5 mm Hg, p less than 0.01); also, AV3V lesion almost completely reversed hypertension (BP from 167.5 +/- 2.9 to 136.0 +/- 4.1 mm Hg, p less than 0.001), which was not observed in the sham-lesioned animals (BP from 172.0 +/- 2.8 to 168 +/- 2.7 mm Hg, NS). Saralasin produced a significantly smaller decrease in BP in the lesioned animals compared to those with sham lesions during both prevention and reversal experiments. Similar results were observed with captopril. Previous AV3V lesion did not significantly affect PRA with clipping of the renal artery, but AV3V destruction after hypertension had been established resulted in significantly lower PRA compared to sham-lesioned animals (4.58 +/- 0.72 vs 8.38 +/- 1.79, respectively, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of disconnecting the subfornical organ on behavioral and physiological responses to alterations of body sodium

Rats with knife cuts transecting the subfornical organ efferent projections were examined for behavioral and renal responses to experimental alterations in body sodium. Lack of subfornical organ efferent projections did not impair behavioral and renal compensatory responses either in the latency to respond or in magnitude of the response.

Role of the anteroventral third ventricle region and the renin angiotensin system in methylprednisolone hypertension

Methylprednisolone (M, 10 mg/kg/week subcutaneously) was administered to cause hypertension in rats, and the role of AV3V region was assessed before and after development of the hypertensive state. Participation of the renin angiotensin system (RAS) was evaluated by changes in mean arterial pressure (MAP) induced by administration of saralasin (S, 10 micron g/kg/min i.v.) or captopril (C, 20 mg/kg/p.o).aAnaAV3V lesion before M administration partially prevented and delayed the beginning appearance of M hypertension. Furthermore, a prior AV3V lesion abolished an angiotensin II (AII)-dependent pressor component normally identified by S and C administration in this type of hypertension. During the maintenance phase of the hypertension, an AV3V lesion caused a partial reduction in blood pressure. A spontaneous disappearance of a vasoconstrictor component mediated by AII was observed in the late phases of M hypertension. It is concluded that the AV3V region is essential to the full development and maintenance of M hypertension in the rat. Also in this model, integrity of the AV3V area is essential to the expression of the AII-mediated pressor component. Finally it is apparent tha M can cause hypertension even in the absence of the AV3V area or during chronic renin angiotensin blockade, indicating multiple pathogenetic mechanisms in this experimental model.

The control of sodium chloride intake: functional relationship between hypothalamic inhibitory areas and amygdaloid complex stimulating areas

Sodium chloride intake was studied in rats submitted to different neurosurgical procedures. Intake decreased in animals submitted to bilateral destruction of the basolateral amygdaloid complex, and increased after the same animals were submitted to destruction of the anterior lateral hypothalamus, a procedure which is known to cause increased intake in intact rats. In the reverse experiment, where the anterior lateral hypothalamus was destroyed before the basolateral amygdaloid complex, the effect of increased sodium chloride intake induced by destruction of the hypothalamus overcame the decreased expected upon destruction of the amygdaloid complex. These results permit us to conclude that the hypothalamic areas which inhibit sodium chloride intake predominate over the stimulating areas of the amygdaloid complex in the control of sodium chloride intake.