Preoptic-hypothalamic periventricular lesions after food-associated drinking and circadian rhythms

For assessment of the effect of anteroventral third ventricle (AV3V) periventricular lesions on food-associated drinking, the free-feeding patterns of eating and drinking were continuously monitored before and after rats had undergone either AV3V lesions or control surgical procedures. Feeding and drinking were monitored with pellet-detecting eatometers and lick-detecting drinkometers. "Recovered" animals with AV3V lesions did not exhibit normal diurnal patterns of ingestion but consumed only half of their daily food and water during the dark portion of the day-night cycle. The strong temporal association between eating and drinking as well as a normal intrameal pattern of ingestion, i.e., minimal drinking within meals, was evident in animals with AV3V lesions. However, the significant positive correlation between meal size and meal-associated water intake characteristic of normal animals was absent in animals with AV3V lesions. These results suggest that the mechanism responsible for precise adjustment of water intake and meal size is disrupted by AV3V periventricular ablation. These findings indicate that AV3V periventricular tissue is critical for normal body-fluid homeostasis.

Plasma angiotensin II: dipsogenic levels and angiotensin-generating capacity of renin

Activation of the renin-angiotensin system (RAS) or administration of angiotensin II (AII) will induce water intake. In the rat, the species in which the physiological mechanisms of thirst have been most thoroughly studied, the levels of circulating AII produced by systemic administration of dipsogenic doses of the octapeptide have not been established. Furthermore, the capacity of the endogenous RAS to generate AII sufficient to contribute to the production of a thirst state has not been well studied. In the present series of investigations, plasma levels of AII were determined following infusions of the peptide over a range of doses frequently employed in studies on thirst. In addition, a series of manipulations ranging from mild water deprivation or ingestion of a dry meal to ether stress of rats with malignant renal hypertension was applied to examine the capacity of the RAS to generate angiotensin. The results indicate that the endogenous RAS can readily produce the major effector peptide of the system so that circulating levels are well in excess of the dipsogenic threshold for AII.

Role of central catecholamines in the control of blood pressure and drinking behavior

The role of central nervous system (CNS) catecholamines in the development of hypertension and the control of drinking behavior was assessed in rats by depleting these amines with 6-hydroxydopamine (6-OHDA). Intraventricular administration of 6-OHDA completely prevented the development of one-kidney renal hypertension and abolished the associated increase in water consumption. 6-OHDA-treated rats showed deficits in drinking behavior when challenged with subcutaneous injections of angiotensin II (AII) and hypertonic sodium chloride. The acute pressor responses produced by intraventricular injections of AII and carbachol were virtually abolished by central catecholamine depletion. However, drinking produced by central cholinergic stimulation remained intact while AII drinking was significantly reduced. These data demonstrate that the integrity of CNS catecholamines is required for the development of one-kidney renal hypertension and the increased drinking which accompanies it. In addition, destruction of central catecholamine-containing neurons allows for a specific dissociation of the pressor and drinking responses produced by central cholinergic but not AII stimulation.

Anteroventral third ventricle lesions reduce antidiuretic responses to angiotensin II

Ablation of anteroventral third ventricle (AV3V) periventricular tissue renders animals temporarily adipsic with no compensatory change in urine volume or concentration. The present experiment was designed to determine whether lesions of the AV3V region attenuate vasopressin (AVP) release in response to intraventricular (ivt) injections of angiotensin II (AII), hypertonic NaCl, and phenylephrine during the adipsic period. Blood pressure, urine conductance, and urine flow rate were monitored in awake, unrestrained animals during a continuous intravenous hydrating infusion. Changes in blood pressure and urine parameters were recorded following ivt injections of 100 ng AII, 500 ng AII, 1 microliter 3% NaCl, and 50 microgram phenylephrine. In addition, a radioimmunoassay (RIA) measured AVP following 500 ng AII ivt in lesioned and nonlesioned animals. Antidiuretic and pressor responses to ivt AII were attenuated after AV3V lesions. In addition, RIA analysis showed a significantly smaller concentration of AVP in lesioned animals following AII injections. These data suggest that the AV3V region is important for AVP release in response to central AII and osmotic stimuli.

Sodium consumption following lesions surrounding the anteroventral third ventricle

Consumption of sodium solution was measured in rats with lesions of the anteroventral third ventricle (AV3V) and maintained on sodium deficient chow. Rats with AV3V lesions consumed less sodium than control animals, and increased their sodium consumption following a subcutaneous injection of Formalin. These data indicate that the AV3V ablation alters the nature of the regulatory control of sodium but does not render animals insensitive to plasma sodium levels.

Osmosensitivity of rat third ventricle and interactions with angiotensin

Injections of hyperosmotic solutions (1- to 5-microliter injections of NaCl or sucrose solutions ranging in osmolarity from 0.34 to 0.90 osmol/l) into the anteroventral third ventricle (AV3V) of rats resulted in short latency drinking antidiuretic, and pressor responses. AV3V injections or infusions of combined angiotensin-hyperosmotic NaCl solution did not result in drinking greater than the sum of drinking to angiotensin and hyperosmotic NaCl separately administered. Differences in water versus saline drinking fluid preferences provided a behavioral dissociation of angiotensin and hyperosmotic sensitive neural mechanisms. Comparison of AV3V and lateral preoptic injection sites provided an additional separation since angiotensin was equally effective at both sites whereas osmotic stimulation was more effective at the AV3V site. AV3V lesions have previously been reported to abolish drinking, antidiuretic, and pressor responses to angiotensin and hyperosmotic stimulation. The data reported here provide additional evidence that angiotensin and hyperosmotic stimuli may both act on tissue surrounding AV3V but suggest that the neural substrates for these stimuli are not identical.

Petide antagonists of the renin-angiotensin system in the characterisation of receptors for angiotensin-induced drinking

The two naturally occurring analogues of angiotensin II (AII), Asp1-Val5-AII and Asp1-Ile5-AII, were equally effective as intracranial dipsogens in the water-replete rat. Renin, synthetic tetradecapeptide renin substrate (SRS) and angiotensin I (AI) also produced copious drinking when injected into the brain, but the naturally occurring renin substrate of rat caused little drinking and was much less effective than SRS. Prior intracranial injection of pepstatin, a competitive antagonist of the renin-angiotensinogen reaction, reduced drinking in response to renin and SRS but not to AI and AII. Renin-, SRS- and AI-induced drinking were inhibited by the converting enzyme inhibitor SQ 20881 injected through the same intracranial cannula in antagonist to agonist ratio of 1000:1, whereas the AII response was enhanced, although not significantly so, and the carbachol response was unaffected. Finally, position 8 aliphatic substituted analogues of AII were competitive antagonists of AII-induced drinking, and also inhibited drinking induced by renin, SRS and AI injected through the same intracranial cannula, but they did not inhibit carbachol-induced drinking. In conclusion, the angiotensin-sensitive receptor for thirst does not accept SRS or AI. It responds best to AII.

Angiotensin-induced thirst: effects of third ventricle obstruction and periventricular ablation

The role of periventricular tissue surrounding the anteroventral third ventricle (AV3V) in mediating drinking behavior induced by angiotensin II was investigated rats. Electrolytic lesions which bilaterally destroyed preoptic-hypothalamic periventricular tissue surrounding AV3V abolished drinking responses normally elicited by intracerebral injections of angiotensin. In another experiment, ventricular obstruction in AV3V had no effect on drinking of a palatable sweet milk solution while the drinking responses induced by peripheral versus central administration of angiotensin were dissociated. Drinking normally induced by lateral preoptic injections of angiotensin was no longer observed when AV3V obstruction prevented drug distribution via cerebrospinal fluid circulation to AV3V periventricular tissue; the drinking response induced by subcutaneous injection of angiotensin was enhanced, however, after placement of the ventricular obstruction. These results, coupled with the earlier observation that AV3V lesions also abolish drinking induced by subcutaneous angiotensin injectin, suggest that, after central or peripheral administration, angiotensin acts on AV3V periventricular tissue to arouse drinking. In contrast to centrally injected angiotensin, peripherally administered angiotensin does not contact receptors by entry and spread in cerebrospinal fluid. After peripheral injection angiotensin may contact sensitive AV3V tissue directly from blood, perhaps via the organum vasculosum of the lamina terminalis, a highly vascularized circumventricular organ within the AV3V which lacks a blood-brain barrier.

Inhibition of apomorphine-induced behaviors by derivatives of 2-amino-1, 2, 3, 4-tetrahydronaphthalene

In order to elucidate the pharmacological properties of a series of 1-phenyl-2-aminopropane and 2-amino-1, 2, 3, 4-tetrahydronaphthalene derivatives, their ability to inhibit a number of apomorphine-induced behaviors was investigated. Several members of the series under study were potent inhibitors of apomorphine-induced pecking behavior in pigeons, emesis in dogs, and gnawing in rats. In addition, these compounds were able to inhibit responding in self-stimulating rats and to a lesser degree counteracted the depression of the linguomandibular reflex induced by 5, 6-dihydroxy-2-dimethylamino-1, 2, 3, 4-tetrahydronaphthalene (M-7) in the cat. The most effective member of the experimental compounds was N-methyl-5, 8-dimethoxy-2-amino-1, 2, 3, 4-tetrahydronaphthalene; however, neither this material nor any of the related structures were able to inhibit apomorphine-induced rotational behavior in substantia nigra lesioned rats. The possibility that the more effective members of the experimental series are able to inhibit certain apomorphine-induced behaviors by stimulation of central alpha adrenergic receptors is discussed.

Periventricular preoptic-hypothalamus is vital for thirst and normal water economy

A midline stereotaxic lesion in rats destroying the periventricular tissue (lamina terminalis and preoptic-anterior hypothalamic periventricular stratum) surrounding the anteroventral third ventricle (AV3V) produces adipsia without other marked behavioral changes. Although food consumption is reduced in animals rendered adipsic by the lesion, feeding continued and intake is comparable to that of water-deprived-sham-lesioned animals. About half the rats recover drinking after a period of adipsia, but the others never resume water intake and become moribund. An analysis of urinary output indicates that adipsic animals fail to reduce urine volume and continue to elaborate an inappropriately dilute urine. The periventricular lesion-induced adipsia without compensating antidiuresis produces a significant rise in plasma protein, sodium, osmolality, and urea nitrogen which if untreated often results in acute encephalopathy leading to death. These data suggest that preoptic-anterior hypothalamic periventricular tissue houses vital neural elements which function in the modulation of water ingestive and conservation mechanisms directed at the maintenance of body fluid homeostasis.

Interruption of the maintenance phase of established hypertension by ablation of the anteroventral third ventricle (AV3V) in rats

Ablation of tissue surrounding anteroventral third ventricle (AV3V) was studied in three models of hypertensive rats. Lesions were placed in the AV3V at one and six weeks following the initiation of one kidney Grollman renal hypertension. At one week the rise in blood pressure was arrested and water intake was reduced; at six weeks arterial pressure returned to prehypertensive levels in animals surviving the post-lesion hydrational crisis. In two kidney (one clip) Goldblatt animals lesioned two weeks post-clip, arterial pressure was significantly reduced but did not become fully normotensive. Finally, the AV3V was also lesioned in spontaneously hypertensive rats (SHR-Okamoto strain) with established hypertension. The lesion did not reduce arterial pressure in adult SHR although characteristic initial adipsia and weight loss occurred. Ablation of the AV3V thus altered the course of maintenance of renal hypertension; however, the arterial pressure of SHR was not affected.

Increased blood pressure responses to central angiotensin II in spontaneously hypertensive rats

The blood pressure responses following infusions of angiotensin II (ANG II) into the brain ventricles (i.v.t.) have been tested in spontaneously hypertensive (SH) rats and in normotensive Wistar Kyoto (WK) rats. The mean arterial blood pressure increases were significantly higher in SH rats than in WK rats. Propranolol treatment reduced blood pressure increases to i.v.t. ANG II in WK, but not in SH rats. The higher sensitivity to i.v.t. ANG II in SH rats supports a role of central ANG II in the maintenance of high blood pressure in SH rats.

Prevention of the development of renal hypertension by anteroventral third ventricular tissue lesions

Several reports have suggested that a central action of the renin-angiotensin system plays a role in the development of renal hypertension. Based on the identification of the anteroventral thrid ventricle (AV3V) as a site of central angiotensin dipsogenic and pressor mechanisms, the present study examined the effect of electrolytic lesions in the AV3V region on the development of renal hypertension in rats. Lesioning alone produced a temporary but profound adipsia and, in one-half of the rats, a substantial transient elevation in arterial pressure. After lesioned rats had recovered normal drinking and blood pressure, unilateral nephrectomy with figure-of-eight wrapping of the remaining kidney failed to produce the hypertension and increased drinking observed after renal wrapping in shamlesioned rats. The possibility that the failure of lesioned rats to increase water intake after wrapping prevents hypertension development was ruled out by experiments demonstrating that normal rats exhibited identical rises in arterial pressure after wrapping regardless of whether or not they were allowed to increase water intake. The fact that unanesthetized lesioned rats exhibit attenuated drinking and pressor responses to systemically administered angiotensin suggests this mechanism as a possible explanation for the failure of AVV-lesioned rats to increase drinking and blood pressure after renal wrapping.

Angiotensin-induced dipsogenesis in domestic fowl (Gallus gallus)

Both systemic (100 mug, 200 mug, and 400 mug im) and intracranial (75 ng, 150 ng, and 300 ng) injections of Val5-angiotensin II-amide produce copious and dose-related drinking in White Leghorn chickens in normal water balance. Angiotensin-induced drinking has been reported in several mammalian species and in Barbary doves and white-crowned sparrows. The findings reported here extend the species generality of angiotensin-induced thirst and are evaluated in light of current biochemical and pharmacological analyses of the renin-angiotensin system in chickens.

Cephalic angiotensin receptors mediating drinking to systemic angiotensin II

In rats implanted with cannulae to allow delivery of solutions to the cerebral ventricular system, pretreatment with 5 mug or 0.5 mug of saralasin acetate (Sar1 Ala8 Angiotensin II), an angiotensin II competitive analog, significantly attenuated drinking to subcutaneous (SC) injections of 500 mug of angiotensin II. However, pretreatment with either SC (5 mug or 20 mug) or with intravenous (5 mug) saralasin had no effect on drinking to SC angiotensin II (500 mug). Intracranial (IC) injections of 5 mug of saralasin had no effect on drinking in response to SC injections of 0.8 cc of a 10 percent NaCl solution and did not attenuate ingestion of a milk solution in a dessert test. On the basis of the specificity and the greater efficacy shown by IC saralasin in attenuating drinking to systemically applied angiotensin II, it was concluded that circulating angiotensin II reaches brain periventricular receptors which mediate drinking.

The cerebral ventricles as the avenue for the dipsogenic action of intracranial angiotensin

Using low doses of angiotensin II (1-128 ng), a mapping study was carried out to redefine the region within the brain from which the dipsogenic response can be elicited. The most sensitive sites were either close to the anterior cerebral ventricles or were at the tips of cannulae that traversed a ventricular space en route to the tissue site. Conversely, insensitive sites were remote from the ventricles and were not reached by cannulae with a ventricular trajectory. Therefore, a thorough assessment of the role of the ventricular system in the angiotensin thirst phenomenon was demanded. Further studies revealed that direct intraventricular injections were as effective as those made into any tissue site tested. Also, regardless of the similarity in the sites of their termination, cannulae which passed through a ventricular space en route to that site yielded highly sensitive preparations whereas those which did not were insensitive to the hormone. Autoradiographic and radioassay studies showed that tritiated angiotensin II injected into anterior diencephalic tissue through cannulae which traversed the ventricles was rapidly distributed throughout the ventricular system. Thus, efflux of the injected material up the cannula shaft and its entry into the ventricular system is essential for a dipsogenic response to low doses of the hormone. These results support the hypothesis of a periventricular receptor site for angiotensin. It is suggested that systemically generated angiotensin and angiotensin endogenous to the brain may use the ventricular route as a means of access to the sensitive periventricular site.