The effect of urocortin on ingestive behaviours and brain Fos immunoreactivity in mice.

The influence of urocortin (UCN) on ingestive behaviours and brain neural activity, as measured immunohistochemically by the presence of Fos protein, was determined in mice. Rat UCN was administered by continuous intracerebroventricular (ICV) or subcutaneous (SC) infusion. ICV infusion of UCN (100 ng/h, 14 days) transiently reduced daily food and water intakes (days 1-4) but body weight was reduced from day 2 into the post-infusion period. Sodium intake was reduced from day 3 to the end of infusion. SC infusion of UCN caused similar but smaller reductions in food and water intakes and body weight, without change in sodium intake. In separate experiments, Fos immunoreactivity was increased in several brain nuclei known to be involved in the control of body fluid and energy homeostasis, e.g. central nucleus of the amygdala, median preoptic nucleus, bed nucleus of the stria terminalis and arcuate nucleus. Increased Fos expression was similar for ICV and SC infusions when measured on days 2-3 or 6-7 of infusion. In conclusion, increases of brain activity by UCN may be associated with stimulation of adrenocorticotrophic hormone release and sympathetic nervous activity, but increases may also indicate suppression of ingestive behaviours by stimulating central inhibitory mechanisms located in areas known to control body fluid and energy homeostasis.

Neural mechanisms subserving central angiotensinergic influences on plasma renin in sheep.

The mechanisms and brain regions subserving the suppression of plasma renin concentration caused by intracerebroventricular (ICV) infusion of angiotensin II were studied in sodium-depleted sheep. Infusion of angiotensin II (3 microg/h for 1 hour) into the lateral ventricle reduced plasma renin from 4.3+/-0.4 to 1.6+/-0.2 pmol angiotensin I/mL per hour at 1 hour after the commencement of infusion. This change persisted for at least another 90 minutes and was blocked by concomitant ICV infusion of the AT(1) antagonist losartan (1 mg/h). Arterial pressure did not change, but plasma vasopressin secretion was increased. ICV infusion of losartan (1 mg/h) significantly increased plasma renin in sodium-depleted sheep. The reduction of plasma renin concentration in response to either ICV angiotensin II or hypertonic NaCl (0.75 mol/L at 1 mL/h) and the increase in response to ICV losartan was prevented in sheep in which the lamina terminalis of the brain had been ablated. Lesions in the median eminence (MEL), which blocked the increased plasma vasopressin levels, did not prevent suppression of plasma renin in response to ICV angiotensin II. However, bilateral renal denervation largely blocked this inhibition of plasma renin concentration but not the increased plasma renin resulting from ICV infusion of losartan in sodium-depleted sheep. The results show that AT(1) receptors, probably located in the lamina terminalis, mediate a central inhibitory influence of angiotensin II on renin secretion. This inhibition of renin release is probably due to a reduction in activity of renal sympathetic nerves innervating the juxtaglomerular apparatus of the kidney.

Modulation of urocortin-induced hypophagia and weight loss by corticotropin-releasing factor receptor 1 deficiency in mice.

Intracerebroventricular injection of CRF or urocortin (Ucn) reduces appetite and body weight. CRFR1 and CRFR2, the receptors for CRF and Ucn, are expressed in neurons associated with appetite-control and metabolism, but their relative contributions in mediating CRF- or Ucn-induced hypophagia and weight loss are not known. We used homozygous mice lacking CRFR1 (CRFR1-/-) and wild-type littermates to determine the role of CRFR1 in mediating the changes in food intake and body weight following intracerebroventricular administration of Ucn. CRFR1-/- mice, which are glucocorticoid deficient, were given corticosterone in their drinking water to induce diurnal variations in circulating corticosterone. A 7-day intracerebroventricular infusion of Ucn transiently suppressed ad libitum food intake equally in CRFR1-/- and wild-type mice. Body weight reduction during Ucn infusion paralleled food intake in wild-type mice, but persisted throughout the infusion in CRFR1-/- mice. After food-deprivation, acute intracerebroventricular injection of Ucn suppressed food intake for 1.5 h in wild-type mice. By contrast, CRFR1-/- mice did not respond to Ucn 1.5 h after injection. At later time points, Ucn suppressed food intake equally in both genotypes. The distinct time courses of CRF-receptor-induced hypophagia suggest that separate pathways act cooperatively to adjust food intake during challenges to homeostasis.

Effect of adrenocorticotrophic hormone on sodium appetite in mice.

A main vector of the effects of stress is secretion of corticotrophin releasing factor (CRF), adrenocorticotrophin (ACTH), and adrenal steroids. Systemic administration of ACTH (2.8 microgram/day sc) for 7 days in BALB/c mice caused a very large increase of voluntary intake of 0.3 M NaCl equivalent to turnover of total body sodium content each day. Intracerebroventricular infusion of ACTH (20 ng/day) had no effect. Intracerebroventricular infusion of ovine CRF (10 ng/h for 7 days) caused an increase of sodium intake. The large sodium appetite-stimulating effect of systemic ACTH was not influenced by concurrent systemic infusion of captopril (2 mg/day). Induction of stress by immobilization of mice on a running wheel caused an increase in Na appetite associated with a 50% decrease of thymus weight, indicative of corticosteroid effects. The present data suggest that stress and the hormone cascade initiated by stress evoke a large sodium appetite in mice, which may be an important survival mechanism in environmental conditions causing stress.

Angiotensin II stimulates intake of ethanol in C57BL/6J mice.

The influence of intracerebroventricular (i.c.v.) infusion of angiotensin II on intake of water and ethanol solutions was determined in C57BL/6J mice. Compared to other mice, C57 mice do not show an aversion to ethanol solutions. With both water and ethanol solutions available, the C57 mice consumed 40-60% of their total daily fluid intake as ethanol solution when the concentration of ethanol solution offered was 4-14%. When given a choice between 0.3 M KCl and either 4 or 10% ethanol solution, the mice clearly preferred the ethanol solution. With water only available, i.c.v. infusion of angiotensin II increased intake from 3-5 mL/day (baseline) to 11-12 mL/ day (Day 4 of infusion). A similar increase in intake occurred in mice with access to a nonpreferred solution of 0.3 M KCl. In comparison, when only 4% ethanol solution was available, angiotensin II increased intake to 7-8 mL/day, and when only 10% ethanol solution was available, intake was transiently increased. The results demonstrated that thirst for water caused by i.c.v. infusion of angiotensin II in C57 mice is similar to that observed in BALB/C mice. Unlike BALB/C mice, however, i.c.v. infusion of angiotensin II stimulated intake of ethanol solution. The failure of angiotensin II to cause a large increase in 4% ethanol solution or a sustained increase in 10% ethanol solution intake does not seem to be caused by an aversion to the taste of ethanol solution, but most likely due to postingestional factors.

Sodium intake and reproduction in BALB/C mice.

The effect of sodium intake on the reproductive performance of BALB/C mice was assessed in four groups of 11 or 12 mice that received ad lib access to low or higher sodium food (LSF 4-5, HSF 120-143 mmol Na+/kg). The two groups that received HSF had (mean values) 100% matings, 83 and 91% litters, 5.9 pups/litter, pups weighing 2.05 and 2.22 g (3 days after birth) and 10.47 and 10.96 g at weaning (19 days). One of the HSF groups that also had 300 mM NaCl to drink did not show any benefit. Two groups received LSF, and one of them also received 30 mM NaCl. The group given LSF only had 83% matings, 20% litters, 1.5 pups/litter, and pups that were significantly smaller at birth and at weaning. However, the LSF group given 30 mM NaCl to drink performed almost as well as the two HSF groups. The results show that (a) the daily sodium requirement for optimal reproduction was > or = 400 (micromol/day, based on voluntary sodium intake late in gestation and lactation; (b) sodium deficiency was the cause of reproductive deficiency in mice on LSF; (c) severe sodium deficiency suppressed reproduction primarily at the gestation step; (d) this deficiency could be prevented by the voluntary sodium intake of mothers with access to salt solution; and (e) pups on the LSF showed an avid innate salt appetite when offered salt solution at 12 days of age.

The effect of adrenocorticotrophic hormone on water intake in mice.

The systemic administration of adrenocorticotrophic hormone (ACTH) stimulates the intake of sodium chloride and water in many species. In mice the daily intake of water may reach half of the total body water content. To establish whether this very high water intake was primary or secondary to the sodium chloride intake, Synacthen was infused s.c. at 2.8 micrograms/day by Alzet miniosmotic pump to mice that did not have access to sodium chloride solution. On low-sodium food, the daily water intake increased from 2.99 +/- 0.08 ml (mean +/- SEM) to 9.85 +/- 0.74 ml (p < 0.05, n = 6) by day 7 of infusion and remained significantly higher than the control value until the fourth postinfusion day. On high-sodium food, the daily water intake also increased 350% from a higher baseline, 4.55 +/- 0.14 ml, and returned to the control value by the second postinfusion day. The same ACTH treatment for 4 days increased plasma [Na] and appeared to expand plasma volume. The results show that a high water intake caused by ACTH administration in mice is not secondary to a concurrent increase in sodium chloride intake. The water intake may be induced by stimulation of the secretion of adrenal steroid hormones which increase plasma [Na].

The dipsogen angiotensin II does not stimulate ethanol intake in mice.

Mice that were habituated to drinking ethanol solution and mice that had drunk water only (naive mice) were given an ICV infusion of angiotensin II (Ang II) at 2.9 ng/h for 8 days to determine the effect of chronic ethanol intake on the ingestive response to this potent dipsogen. Ang II infusion in alcohol-naive mice increased daily water intake from 3.7 +/- 0.2 ml (mean +/- SE, n = 6) to 11.0 +/- 1.5 ml on day 4 (p < 0.001) and to 18.3 +/- 2.6 ml on day 8 (p < 0.001). In subsequent experiments, mice had access to 4% ethanol solution up to day 4 and then to water for 4 days during the Ang II infusion. Alcohol-naive mice did not increase daily fluid intake until the water was provided on day 5; intake increased to 17.5 +/- 2.3 ml on day 8 (p < 0.001, n = 7). Mice accustomed to drinking 4% ethanol (4.3 +/- 0.3 ml/day) also did not increase intake until the water was provided; intake reached 22.9 +/- 3.0 ml of water on day 8 (p < 0.001, n = 7). Mice accustomed to drinking 10% ethanol behaved similarly (n = 4). Thus, alcohol-naive or -habituated mice did not respond to this dipsogenic stimulus until water was available; the thirst for water was unimpaired. Preference-aversion tests showed that mice drank little or no 4% ethanol (or even 2% ethanol) when water was also available. Taste aversion, plus previous experience from ingestion of ethanol in habituated mice, may explain the rejection of ethanol to quench Ang II-induced thirst. Experimental results obtained using other aversive solutions, 3 mM quinine and 300 mM KCl, suggest that postingestional, metabolic effects of solutes may also contribute to such rejection.

Thirst induced by increasing brain sodium concentration is mediated by brain angiotensin.

Thirst, the longing or compelling desire to drink, arises physiologically by two main mechanisms-extracellular and cellular dehydration. The hormone angiotensin II has been implicated in the former but not in the latter brain mechanism. To test this apparent difference, experiments in 5 mammalian species examined the effect of intracerebroventricular infusion of losartan, an angiotensin II type I receptor antagonist, on the third induced by intracerebroventricular infusion of an artificial cerebrospinal fluid made hypertonic by the inclusion of 500 mM NaCl. The losartan infusion reduced the water intake due to increased brain sodium concentration in all 5 species, cattle, sheep, rabbits, rats and mice. Thus, the thirst evoked by cellular dehydration, as well as the thirst evoked by extracellular dehydration, may be mediated by angiotensin II.

Sodium and water intake of sheep, rabbits and cattle during ICV infusion of eledoisin.

The present study reports the effects of ICV administered eledoisin, the most potent anti/dipsogenic member of the tachykinin family, in three species. Sheep with chronic parotid fistula lost daily 200-400 mmol sodium in 3-4 l of saliva. During ICV infusion of eledoisin, 2 to 50 ng/min, a decrease in sodium intake was observed. If water was withheld for 22 hours, sheep normally drank 5.4 l water on presentation. During ICV infusion of eledoisin, 50 ng/min, water intake increased significantly. Wild rabbits lost 5 mmol sodium in 50 ml of urine after injection of furosemide. During ICV infusion of eledoisin, 30 ng/min, a decrease in sodium intake and an increase in water drinking was observed. Cows prepared with parotid fistula had access to sodium solution every other day to replace salivary sodium loss. During ICV infusion of eledoisin, 50 and 150 ng/min, a decrease in sodium intake occurred, and water intake was unaffected. These results confirm that central administration of eledoisin specifically influences ingestive behaviour in mammals and draws attention to some species differences in the observed effects.

Water and sodium intake of wild and New Zealand Rabbits following angiotensin.

Two rabbit strains, New Zealand (laboratory) rabbits and Australian wild rabbits, both members of the Oryctolagus cuniculus genus were studied. New Zealand rabbits under control conditions consumed 2-5 times more water and 8-30 times more 0.5 M NaCl/kg body weight than wild rabbits. Single injections of angiotensin II or III administered ICV did not induce water drinking in either strain. Acute ICV infusion of angiotensin II also did not influence water intake, but after several days of administration, induced increased sodium intake. Intravenous infusion of graded doses of angiotensin II induced diuresis only at the higher doses in both strains. In New Zealand rabbits, this was accompanied by a commensurate and concurrent increase in water intake. Intravenous infusion of angiotensin II also induced urinary sodium loss that was either accompanied or followed by increased sodium intake. The development of salt appetite in both strains was preceded by sodium loss.