The area most widely associated with osmoreception has been the lateral preoptic nucleus. However, Hatton (1976) proposed that the nucleus circularis could be the actual osmoreceptor in the hypothalamus. The present study supported Hatton by using 30 rats which were randomly assigned to sham, lateral preoptic, and nucleus circularis lesion groups. After a 2-week post-operative period, half of each group was injected with isotonic saline while the other half was injected with hypertonic saline. Water consumption was measured at 10-minute intervals for one hour. Following a 4-day recovery period, the injection procedure was reversed. Analysis of difference scores, computed by subtracting the amount of water consumed after isotonic injection from the amount of water consumed after hypertonic injection, revealed a significant difference between the nucleus circularis group and the other two groups.

AIM: To contrast the effects of various modifications of body fluid volumes on thirst as reported by healthy volunteers. METHODS: Ten male volunteers aged between 19 and 37 years (mean 22 years) underwent four experiments each, which comprised infusion of 400-800 mL of acetated Ringer’s solution and intake of 600 mL of tap water. Half of the experiments were preceded by volume depletion (median 1.7 L) with furosemide. A visual analogue scale (0-100 mm) was used to assess perceived thirst during each experiment. RESULTS: Volume depletion (P < 0.001) and tap water (P < 0.03) both affected thirst by 13 mm per L of fluid, whereas spontaneous diuresis and infusion of Ringer’s acetate did not significantly change the thirst rating (multiple regressions). More detailed analyses showed that the volume depletion increased the median (25th-75th percentiles) thirst rating from 28 mm (21-43) to 59 mm (46-72, P < 0.001) while no change occurred in those who were only slightly thirsty (< 30 mm) before the volume depletion began. Ringer’s solution alleviated thirst in those who were very thirsty, but tended to increase thirst in the volunteers who were not thirsty before the infusion. Similarly, hydration with tap water decreased thirst (by 24 mm, P < 0.04) in those who were thirsty (> 60 mm) while the others reported no change. CONCLUSION: The change in thirst rating during volume depletion, administration of Ringer’s acetate, and ingestion of tap water were all dependent on the thirst rating obtained when the manipulation of the body fluid volume was initiated.

No description available.

The nucleus circularis has been linked to a role in regulating osmotic thirst but evidence has also shown that full bilateral destruction of the nucleus circularis was not necessary to achieve a deficit in drinking behavior after an osmotic challenge. The present study attempted to answer two primary research questions. The first question was whether osmoreceptive cells existed around the nucleus circularis in a homogeneous fashion or if these cells existed in a structured fashion stretching from the nucleus circularis forward. The second question was whether animals with lesions of the nucleus circularis and the surrounding areas were different in normal daily water intake than animals with no lesions. The first question was approached by lesioning the nucleus circularis, the area one millimeter anterior to the nucleus circularis, one millimeter posterior to the nucleus circularis, one half of a millimeter medial to the nucleus circularis and using a sham group which had the electrode passed through the brain to a spot one millimeter above the nucleus circularis but passing no current. All animals were then given an osmotic challenge which consisted of half of each group with an injection of hypertonic saline while the other half of each group was given isotonic saline. After a five-day recovery period, the injection procedure was reversed. Water consumption on each test day was measured at ten-minute intervals for one hour. Difference scores were then computed by subtracting the amount of water consumed after hypertonic saline injection from the amount of water consumed after isotonic saline injection. The difference scores were then used in an analysis of variance which revealed a significant difference between groups. A subsequent post hoc test showed that the nucleus circularis group was different from all other groups except for the anterior lesion group which showed a trend in the same direction as the nucleus circularis group. The second research question was approached in two ways. The first way was to simply record the amount of water consumed in each twenty-four hour period. An analysis of variance showed no significant difference between any of the groups. The second method for testing the second research question was to put the animals on a twenty-three hour water deprivation schedule and measure the amount of water consumed during the one hour when water was available. Once again, no significant differences were observed.

When most omnivores and herbivores become sodium depleted they engage in the motivated behavior of sodium appetite (AKA salt appetite), or the seeking out and ingestion of salty substances. Sodium appetite is associated with psychological processes that serve to enhance the incentive and rewarding value of salty substances in order to attract animals to salty substances and reinforce the ingestion of them. The experience of sodium depletion also produces long-lasting changes in behavior; one of the most apparent changes being a seemingly life-long increase in hypertonic salt intake which indicates sodium appetite is sensitized. Two neural circuits have been implicated in the sensitization of sodium appetite: 1) a forebrain neural circuit that regulates body fluid homeostasis, and 2) the mesolimbic dopamine system which mediates motivated behaviors. This dissertation has three aims that serve the overall purpose of providing a better understanding of the neurobiological mechanisms that mediate the sensitization of sodium appetite. The first aim is to develop a model of sodium depletion that is amenable to pharmacological manipulation in order to determine whether the -blockade of N-methyl-d-aspartate receptors, which are critical for neural plasticity, will prevent the sensitization of sodium appetite. The second aim is to determine whether sensitization is associated with relatively long-term molecular changes in forebrain areas that regulate body fluid homeostasis. The third aim is to identify how forebrain areas involved in body fluid homeostasis may connect to and influence activity in the mesolimbic dopamine system.

Understanding the physiological and behavioural reasons that result in voluntary water intake and the volume subsequently consumed in both the work place and during and following an exercise setting can provide further information on water balance and the necessity and requirements of water intake. The first study (Chapter 3) aimed to assess hydration status in the adult population at the start and end of a working day and the amount of water from beverages that was consumed. Urine osmolality and urine specific gravity (USG) suggested a large proportion of subjects arrived (osmolality: 54%; USG: 53%) and left (osmolality: 35%; USG: 33%) work in a hypohydrated state, with variation between subjects in the same and different places of work. Reported water intake varied between groups with males consuming more than females. To further examine hydration status it was proposed to assess the use of capillary blood sampling as an alternative to more restrictive venous blood sampling (Chapter 4), however, despite tracking changes in blood parameters in a similar capacity, the inconsistencies of results suggested capillary blood sampling could not be used reliably. The remaining chapters in the thesis examined voluntary water intake. In Chapter 5 this was during and following exercise in the cold. Less water was consumed compared to exercise in a warm environment and there was an indication of a blunted thirst response in the cold. Following high intensity intermittent exercise, more water was voluntarily consumed during a one hour recovery period compared to when continuous exercise of the same average power output was performed (Chapter 6). Following exercise there was increased serum osmolality, serum sodium concentration, plasma vasopressin concentration and blood lactate concentration compared to baseline values. The relative contribution that decreasing blood lactate concentrations and water intake during the recovery period had on serum osmolality could not be determined, so the study in Chapter 7 was carried out. The time period during which voluntary water intake was allowed was manipulated during a recovery period following a period of high intensity intermittent exercise. Allowing water intake for the full hour, the final 30 minutes or not at all, resulted in similar decreases in serum osmolality throughout the duration of the recovery period. A combination of finishing the period of exercise allowing plasma volume restoration, reduction in blood lactate concentration, reduction in serum sodium concentration, a restoration of blood lactate concentration and water intake appeared to contribute to decreased serum osmolality. Sensations of thirst were the main stimulants of voluntary water intake (Chapters 3, 5, 6 and 7), however, following exercise, sensations of thirst resulted in water consumption despite the majority of subjects not losing enough water (>2% body mass loss) to require additional rehydration. In this thesis, it can be concluded that voluntary water intake differs between individuals, between work environments, during and following exercise in different environments and following different exercise intensities. Water intake is generally initiated by sensations of thirst arising from physiological and behavioural mechanisms even in the absence of significant hypohydration and will reduce once satiated.

Adequate fluid consumption is central to human survival. Previous literature suggests that there some misconceptions regarding hydration and fluid balance in some populations. Available data also show that the role of thirst sensations in maintaining fluid balance in different settings is also equivocal. Therefore, this thesis aimed to examine the perception of hydration, thirst and fluid intake in freeliving populations, to examine the feasibility of thirst as a marker of hydration status and to investigate the effect of thirst related sensations on fluid balance in resting and exercising individuals under different ambient temperatures. The findings in this thesis (Chapter 3) show that individuals who work within the fitness industry demonstrated substantial knowledge about drinking practices, hydration status and health consequences of water consumption, but lack understanding on the type of beverages that adequately hydrate the body. Further, thirst perception and mood states did not affect (P>0.05) the fluid intake in free living individuals (Chapter 4) and resting individuals under cool and warm exposure (Chapter 6), but some other factors such as subjective feelings of mouth dryness and the extent of hydration status might influence the fluid intake behaviour in these populations. In addition, following ingestion of flavoured carbohydrate drinks, thirst sensations was rated lower over time (P<0.05) during exercise in the cool, but was higher over time in the warm temperature (Chapter 7). Moreover, subjective feelings related to dehydration such as mouth dryness, thirst perception, desire to drink (water pleasantness) and hunger rating could be used as index of hydration status to signify at least a 1% body mass loss due to food and fluid restriction in resting individuals (Chapter 5). In conclusion, the findings in this thesis provide some new insight with respect to hydration, thirst and fluid balance in different populations under different settings. Nevertheless, some inconclusive findings regarding the role of thirst related sensations in fluid balance require further investigations.

A manutenção da osmolalidade e do volume dos líquidos extra- (LEC) e intracelular (LIC) são fatores de extrema importância à conservação da vida. Na desidratação (por ingestão insuficiente ou perda excessiva de água), sistemas de controle autonômicos e endócrinos são acionados frente à ativação de barorreceptores (periféricos) e osmorreceptores (centrais e periféricos), visando estimular a sede e inibir o apetite ao sódio, além de reduzir a diurese, promover a natriurese e contrair a musculatura lisa dos vasos. Especificamente para o sistema de controle endócrino é evidente que tais respostas se dão pela secreção dos hormônios neuroipofisários vasopressina (AVP) e ocitocina (OT), e pelo aumento da concentração sanguínea de angiotensina II (ANGII). As secreções de AVP e OT são controladas por sistemas subjacentes, representados por neurotransmissores e também por moduladores gasosos, como óxido nítrico (NO) e monóxido de carbono (CO) (Calapai e cols., 1992; Ventura e cols., 2002 e 2008; Gomes e cols., 2004 e 2010; Reis e cols., 2010). Apesar da existência de modelos que investigassem a modulação do H2S sobre respostas hipocampais, modulação da frequência cardíaca e pressão arterial, e temperatura corporal (Abe e Kimura, 1996; Dawe e cols., 2008; Liu e cols., 2011; Ren e cols., 2011; Kwiatkoski e cols., 2012), nenhuma abordagem sobre a interação do H2S com a secreção de AVP e OT havia sido realizada. No presente estudo, portanto, objetivou-se avaliar, após a privação hídrica de 24 horas (estímulo potente à sede e secreção de AVP e OT), os efeitos do H2S sobre a resposta hipotalâmica. Para tanto, sulfeto de sódio (Na2S 65 mM, doador inorgânico), aminooxiacetato (AOA 50 ?M, inibidor da enzima cistationina ?-sintase) ou veículo (NaCl 0,9%) foram administrados intracerebroventricularmente (icv) em ratos adultos privados de água ou hidratados. Observou-se inicialmente que, em animais apenas submetidos à desidratação (vs. hidratados), houve um aumento da atividade das enzimas hipotalâmicas 8 geradoras de H2S; e, além disso, a administração aguda de Na2S a estes animais potencializou a secreção de AVP, OT e CORT (corticosterona), sem alterar a concentração plasmática de ANGII, ANP e prolactina (hormônios medidos após 5 min. da administração icv da droga ou veículo). O H2S exógeno foi também capaz de reduzir o conteúdo de NO hipotalâmico (medido indiretamente pelo metabólito nitrato/nitrito após 5 min.). O grande aumento na secreção plasmática de AVP e OT provavelmente foi o responsável pela maior concentração plasmática de CORT, uma vez que estes hormônios são secretagogos do hormônio adrenocorticotrófico (ACTH) adenoipofisário. Enquanto o aumento de OT pode ter sido o responsável pela redução da ingestão de água entre os animais privados. Inversamente, a administração de AOA (vs. veículo) aumentou a ingestão de água entre os animais desidratados. Desta forma, estes resultados sugerem que o gás H2S pode ser um importante agente modulador da resposta de sede e secreção neuroipofisária durante a privação hídrica; atuando ou diretamente sobre canais e receptores neuronais ou indiretamente através dos sistemas do NO e CO. / Osmolality and volume maintenance of extra- (ECF) and intracellular fluids (ICF) are factors of extreme importance to life preservation. During dehydration (from insufficient intake or excessive loss of water), autonomic and endocrine control systems are triggered mainly by (peripheral) baroreceptors and (central and peripheral) osmoreceptors to stimulate water intake and inhibit sodium appetite, in addition to restraining diuresis, promoting natriuresis and contracting smooth muscle of vessels. Specifically for endocrine control system, it is evident that such responses take place by neurohypophysis secretion of vasopressin (AVP) and oxytocin (OT), and by increase of plasma angiotensin II (ANGII) levels. Both AVP and OT secretion are controlled by underlying systems, which are represented by neurotransmitters and also by gaseous modulators like nitric oxide (NO) and carbon monoxide (CO) (Calapai et al., 1992; Ventura et al., 2002 and 2008; Gomes et al., 2004 and 2010; Reis et al., 2010). Despite the existence of models which investigated H2S modulation on hippocampus responses, heart frequency and blood pressure, and body temperature (Abe and Kimura, 1996; Dawe et al, 2008; Liu et al, 2011; Ren et al, 2011; Kwiatkoski et al, 2012), no approach of H2S interaction with AVP and OT secretion had been conducted. In this study, we thus aimed to evaluate the effects of H2S on hypothalamus response after a 24-hour water deprivation (a powerful stimulus for thirst and AVP/OT secretion). To that, 65 mM sodium sulfide (Na2S, inorganic donor), 50 ?M aminooxyacetate (AOA, cystathionine ?-synthase inhibitor) or vehicle (NaCl 0,9%) were administered intracerebroventricularly (icv) to water-deprived or euhydrated adult rats. It has been initially observed that hypothalamus H2S-generating enzymes activity of dehydrated-only animals was increased (vs. euhydrated); and, further, acute Na2S administration to dehydrated animals potentiated AVP, OT and CORT 10 (corticosterone) secretion without modifying ANGII, ANP and prolactin plasma levels (measured after 5 min. of drug or vehicle icv administration). Exogenous H2S could reduce hypothalamus NO content as well (indirectly measured by metabolite nitrate/nitrite after 5 min.). The great increase of AVP and OT secretion was probably responsible for higher levels of corticosterone, since these hormones are secretagogues of anterior pituitary adrenocorticotropic hormone (ACTH). While OT rise might have been the responsible for reduced water intake among deprived animals. On the other hand, AOA central injection (vs. vehicle) augmented water intake among water-deprived rats. These results therefore suggest that the gas H2S may be an important modulating agent of thirst and posterior pituitary secretion response during water deprivation; acting either directly on neuron channels and receptors or indirectly by NO and CO systems.

No description available.

High dietary sodium intake is hypothesized to increase food intake (FI), fluid intake and glycemic response. Two short-term randomized repeated-measures studies measured the effects of acute sodium intake on FI, water intake (WI), subjective appetite (SA), thirst, and blood glucose (BG) in young men. Sodium additions were 740 and 1480 mg to a solid food (beans) in Experiment 1; and 500, 1000, 1500 and 2000 mg to a beverage (tomato juice) in Experiment 2. FI and WI were measured at ad libitum pizza meals 120 and 30 min later, respectively. SA, thirst and BG were measured at intervals before and after pizza. Compared with controls, treatments with added-sodium had no effect on dependent measures. In conclusion, acute intake of sodium in a solid or liquid matrix does not increase subjective ratings of appetite or thirst, ad libitum food or water intakes, or blood glucose in healthy young adults.