Arginine vasopressin modulates expression of neuronal NOS in rat renal medulla.
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Arginine vasopressin (AVP) plays a central role in water balance. In principal cells of the collecting duct system, AVP controls the expression of several genes, including aquaporin-2. Because nitric oxide (NO) participates in the regulation of water reabsorption by the collecting duct system, we analyzed the effect of AVP on the expression of NO synthase (NOS) isoforms in the kidney. Rats were either water restricted or water loaded to modify the circulating AVP levels, and expressions of NOS isoforms were assessed by Western blot analysis. In water-restricted rats, endothelial NOS (eNOS) expression increased in the outer medulla, and neuronal NOS (nNOS) expression rose in both the outer medulla and the papilla. Conversely, water loading induced a decrease in expression of nNOS in the outer medulla and papilla but did not alter eNOS expression. Oral administration of the specific V(2)-receptor antagonist SR-121463B decreased nNOS expression in the outer medulla and papilla but did not alter eNOS expression levels. Finally, the very low nNOS expression levels observed in AVP-deficient Brattleboro rats was restored by AVP infusion for 1 wk. Thus AVP specifically increases nNOS expression levels in the renal outer medulla and papilla. Because nNOS is specifically expressed in principal cells of the collecting duct system, the stimulation of nNOS expression by AVP may participate in the control of water reabsorption. (+info)
Limbic thalamic lesions, appetitively motivated discrimination learning, and training-induced neuronal activity in rabbits.
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A substantial literature implicates the anterior and mediodorsal (limbic) thalamic nuclei and the reciprocally interconnected areas of cingulate cortex in learning, memory, and attentional processes. Previous studies have shown that limbic thalamic lesions severely impair discriminative avoidance learning and that they block development of training-induced neuronal activity in the cingulate cortex. The present study investigated the possibility that the limbic thalamus and cingulate cortex are involved in reward-based discriminative approach learning, wherein head-extension responses yielding oral contact with a drinking spout that was inserted into the conditioning chamber after a positive conditional stimulus (CS+) were reinforced with a water reward but responses to the spout after a negative conditional stimulus (CS-) were not reinforced. In this task, the rabbits learned primarily to omit their prepotent responses to the spout on CS- trials. Acquisition was severely impaired in rabbits given limbic thalamic lesions before training. As during avoidance learning, posterior cingulate cortical neurons of control rabbits developed learning-related neuronal responses to task-relevant stimuli, but this activity was severely attenuated in rabbits with lesions. These results support a general involvement of the cingulothalamic circuitry in instrumental approach and avoidance learning. The fact that learning consisted of response omission indicated that the cingulothalamic role is not limited to acquisition or production of active behavioral responses, such as locomotion. It is proposed that cingulothalamic neurons mediate associative attention, wherein enhanced neuronal responses to stimuli associated with reinforcement facilitate the selection and production of task-relevant responses. (+info)
Environmental factors and reproduction in the female hopping mouse, Notomys alexis.
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Australian hopping mice (Notomy alexis) were subjected to short or long photoperiods, different social environments and/or water deprivation. The age at which vaginal opening and first oestrus occurred was delayed by short photoperiods and by the absence of male proximity. Water deprivation prevented normal maturation. The normal 7 to 8 day oestrous cycle was prolonged by short photoperiods or water deprivation. Animals deprived of water had lighter body, ovarian and uterine weights, and follicular growth seemed to be impaired. No differences in organ weights were found between animals in the two photoperiods. The significance of the findings is discussed. (+info)
Urinary concentrating defect in hypothyroid rats: role of sodium, potassium, 2-chloride co-transporter, and aquaporins.
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Hypothyroidism is associated with impaired urinary concentrating ability in humans and animals. The purpose of this study was to examine protein expression of renal sodium chloride and urea transporters and aquaporins in hypothyroid rats (HT) with diminished urinary concentration as compared with euthyroid controls (CTL) and hypothyroid rats replaced with L-thyroxine (HT+T). Hypothyroidism was induced by aminotriazole administration. Body weight, water intake, urine output, solute and urea excretion, serum and urine osmolality, serum creatinine, 24-h creatinine clearance, and fractional excretion of sodium were comparable among the three groups. However, with 36 h of water deprivation, HT rats demonstrated significantly greater urine flow rates and decreased urine and medullary osmolality as compared with CTL and HT+T rats at comparable plasma vasopressin concentrations. Western blot analyses revealed decreased renal protein abundance of transporters, including Na-K-2Cl, Na-K-ATPase, and NHE3, in HT rats as compared with CTL and HT+T rats. Protein abundance of renal AQP1 and urea transporters UTA(1) and UTA(2) did not differ significantly among study groups. There was however a significant decrease in protein abundance of AQP2, AQP3, and AQP4 in HT rats as compared with CTL and HT+T rats. These findings demonstrate a decrease in the medullary osmotic gradient secondary to impaired countercurrent multiplication and downregulation of aquaporins 2, 3, and 4 as contributors to the urinary concentrating defect in the hypothyroid rat. (+info)
Enhanced food and water intake in renin transgenic rats.
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In short term experiments angiotensin II (Ang II) is a potent stimulant of thirst, however it is not known whether prolonged activation of the renin-angiotensin system is associated with chronic alteration of water or food intake. Renin transgenic rats TGRmRen(2)27 (TGR) exhibit significant elevation of AngII in the brain regions involved in regulation of body fluid balance. The purpose of the present study was to find out whether TGR rats manifest also different water (WI) and food (FI) intake and renal excretory functions in comparison to their parent Sprague Dawley (SD) strain. To this end 24 h WI and FI as well as urine excretion (Vu) and urinary outputs of solutes (Cosm), sodium (UNaV) and potassium (UKV) were compared under baseline conditions in 16 TGR and 15 SD rats having free access to water and food. In 15 TGR and 17 SD rats effect of 24 h dehydration on water intake was investigated. Under baseline conditions TGR rats consumed significantly greater amount of food and water than SD rats. Vu, UNaV and UKV were not significantly different in both strains. Cumulative water intakes in SD and TGR rats subjected to 24 h dehydration did not differ. The results reveal that under baseline conditions TGR rats manifest greater food and water intakes than SD rats whereas stimulation of thirst by water deprivation is similar in both strains. The results suggest that the ingestive behavior may be chronically altered by upregulation of the renin-angiotensin system. (+info)
Gurmarin suppression of licking responses to sweetener-quinine mixtures in C57BL mice.
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Gurmarin (Gur) is a peptide that selectively suppresses responses of the chorda tympani nerve to sweet substances in rats and mice. In the present study, we examined the effect of Gur on behavioral responses to sweet substances in C57BL mice. To accomplish this, we developed a new short-term lick test and measured numbers of licks for 10 s for sweet substances mixed with quinine hydrochloride (QHCl) in water-deprived mice. Numbers of licks for sucrose mixed with 1 or 3 mM QHCl increased with increasing concentration of sucrose from 0.01 to 1.0 M. Oral infusion with 30 micro g/ml Gur produced significant decreases in responses to concentration series for sucrose mixed with 3 mM QHCl, whereas no such effect by Gur was observed in responses to QHCl alone or QHCl-mixed HCl, NaCl or monosodium glutamate. The Gur suppression of QHCl-mixed sucrose responses, which otherwise lasted for 2-3 h, rapidly returned to approximately 80% of control levels after oral infusion with beta-cyclodextrin. These results are comparable to neural data previously found in chorda tympani responses, and thereby provide further evidence for Gur as a sweet response inhibitor in C57BL mice. In the other aspect, our newly developed short-term test can also provide a tool for measurements of taste-guided behavioral responses to sweeteners. (+info)
TTF-1, a homeodomain-containing transcription factor, participates in the control of body fluid homeostasis by regulating angiotensinogen gene transcription in the rat subfornical organ.
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In recent years, it has become increasingly evident that angiotensins synthesized in the brain contribute to regulating body fluid homeostasis. Although angiotensinogen, the unique angiotensin precursor, is produced in the brain, the factors that regulate its gene expression remain unknown. We recently found that TTF-1, a homeodomain-containing transcription factor essential for the development of the fetal diencephalon, is postnatally expressed in discrete areas of the hypothalamus. We now report that the subfornical organ, an important site of angiotensinogen synthesis, is an extra-hypothalamic site of TTF-1 expression. Double in situ hybridization histochemistry demonstrated the presence of TTF-1 mRNA in angiotensinogen-producing cells of the rat subfornical organ. RNase protection assays showed that TTF-1 and angiotensinogen mRNA levels are simultaneously increased in the subfornical organ by water deprivation. The angiotensinogen promoter contains seven presumptive TTF-1 binding motifs, four of which are recognized by the TTF-1 homeodomain. In the C6 glioma cell line, TTF-1 transactivates the angiotensinogen promoter in a dose-dependent manner. This transactivation is abolished by deletion of the TTF-1 binding motif at -125. Intracranial administration of an antisense TTF-1 oligodeoxynucleotide decreased angiotensinogen mRNA in the subfornical organ and dramatically reduced the animal's water intake while increasing urine excretion. Moreover, plasma arginine vasopressin content was decreased by the same treatment. These results demonstrate a novel role for TTF-1 in the regulation of body fluid homeostasis, exerted via the transactivational control of angiotensinogen synthesis in the subfornical organ. (+info)
Quantitative analysis of acid-base balance in Bos indicus steers subjected to transportation of long duration.
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There is a lack of information pertaining to the effects of transport stress on the acid-base physiology of ruminants. The effect of transportation and/or feed and water deprivation on acid-base balance was studied using 19 2-yr-old Bos indicus steers. The steers were allocated to one of three groups: 1) control, offered ad libitum access to feed and water (n = 8); 2) water and feed deprived, offered no feed or water for 60 h (n = 6); and 3) transported, offered no feed or water for 12 h, and then transported for 48 h (n = 5). Blood gases, electrolytes, lactate, total protein, albumin, anion gap, strong ion difference, and total weak acids were determined at the conclusion of transportation. Arterial blood pH did not differ among the experimental groups. Partial pressure of carbon dioxide (pCO2) was lower for the water and feed deprived (P = 0.023) group than for the control group. Plasma total protein, albumin and total weak acid concentrations were higher for the transported (P = 0.001, P = 0.03, P = 0.01) and water- and feed-deprived (P = 0.000, P = 0.003, P = 0.001) groups, respectively, compared with the control group. Transported animals had a lower plasma concentration of potassium (P = 0.026) compared with the control animals. This study demonstrates that although blood pH remains within normal values in transported and fasted steers, the primary challenge to a transported or feed- and water-deprived animal is a mild metabolic acidosis induced by elevated plasma proteins, which may be the result of a loss of body water. The loss of electrolytes had little effect on the acid-base balance of the animals. (+info)