Awareness of Fluid Losses Does Not Impact Thirst during Exercise in the Heat: A Double-Blind, Cross-Over Study.

BACKGROUND: Thirst has been used as an indicator of dehydration; however, as a perception, we hypothesized that it could be affected by received information related to fluid losses. The purpose of this study was to identify whether awareness of water loss can impact thirst perception during exercise in the heat. METHODS: Eleven males participated in two sessions in random order, receiving true or false information about their fluid losses every 30 min. Thirst perception (TP), actual dehydration, stomach fullness, and heat perception were measured every 30 min during intermittent exercise until dehydrated by ~4% body mass (BM). Post exercise, they ingested water ad libitum for 30 min. RESULTS: Pre-exercise BM, TP, and hydration status were not different between sessions (p > 0.05). As dehydration progressed during exercise, TP increased significantly (p = 0.001), but it was the same for both sessions (p = 0.447). Post-exercise water ingestion was almost identical (p = 0.949) in the two sessions. CONCLUSION: In this study, thirst was a good indicator of fluid needs during exercise in the heat when no fluid was ingested, regardless of receiving true or false water loss information.

The awareness of water intake and its correlation with BMI among students attending national and international secondary schools in Riyadh, Saudi Arabia.

Dehydration is linked to worse cognitive functions and preference for beverages that are linked to obesity and other health conditions. Saudi Arabia's hot climate can exacerbate these effects and it is important to ensure that children in the region understand the benefits of adequate water intake. To evaluate secondary school student perceptions and practices regarding water intake, investigate how water intake is related to BMI and school performance, and compare international schools to national schools. This cross-sectional study surveyed understanding and practices relating to water intake of national and international secondary school students using a questionnaire based on a random selection of schools and students. One-hundred and sixty-two students from international schools (I) and 157 from national schools (N) responded. Most were aged 16 and 17 years old (I:61.1%, N:76.5%, p = .005). The average BMI of all students was 24.9 ± 6.013 (I:23.6 ± 4.658, N:26.1 ± 6.931, p < 0.001). Students understood beverages do not replace water intake (I:80.2%, N:75.8%, p = .337) and preferred water when thirsty (I:77.8%, N:75.2%, p = .549). However, water consumption was low with more than 50% of students drinking less than 1500 ml a day (I:54.3%, N:70.7%, p = .002). A positive correlation between BMI and water intake was observed only among international school students. Students have inadequate water intake despite understanding the importance of hydration. There are some differences between international school students and national school students that can be attributed to the availability and sources of water, though other factors cannot be excluded.

Does Hydration Status Influence Executive Function? A Systematic Review.

BACKGROUND: Cognitive function, including executive function (EF)-related capacities (eg, working memory, inhibitory and attentional control), has been linked to adherence to healthy lifestyle behaviors. Dehydration is associated with impaired cognitive function, whereas improvements in hydration status may improve inhibitory and attentional performance. No systematic reviews have examined the effects of both dehydration and euhydration on EF. OBJECTIVE: The objectives of this systematic review are to examine studies that have investigated the spectrum of hydration status and EF in adults, and to identify future research needs. DESIGN: The review was conducted according to the 2015 Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) guidelines. The database search was initially conducted on May 12, 2019 and then updated on April 26, 2020. Databases searched included PubMed, Medline, Psyc Info, SCOPUS, Proquest, and ISI Web of Science. Data extraction included the following: method used to assess de/hydration status, study design, participant characteristics, EF tasks and domain, and results. Article quality ratings were performed on included studies using the Academy of Nutrition and Dietetics Quality Rating Checklist. PARTICIPANTS/SETTING: Studies done with healthy or diseased adults, aged older than 18 years, in any setting, were included. Studies of individuals with disease states that impact fluid balance or require fluid restrictions as treatments were excluded. MAIN OUTCOME MEASURE: All EF-related outcomes were included, such as working memory, inhibitory control, task switching, and attention. RESULTS: Four thousand eight hundred thirty-three articles were screened using title/abstracts. Seventy-one full-text articles were assessed for eligibility; 33 were included (26 included investigations of dehydration; 27 included investigations of rehydration/euhydration) with 3,636 participants across all studies. Little consistency was found across outcomes. Roughly half of the available studies suggested unclear or neutral EF effects, and half suggested effects on EF domains, particularly working memory, inhibitory control, and attention. Studies including a euhydration condition were slightly more likely to demonstrate improvements to EF capacities. CONCLUSIONS: Overall, there is a strong need for consistent methodological approaches and a greater number of long-term (ie, >3 days) studies of dehydration and euhydration and EF.

Cellular dehydration acutely degrades mood mainly in women: a counterbalanced, crossover trial.

It is unclear if mild-to-moderate dehydration independently affects mood without confounders like heat exposure or exercise. This study examined the acute effect of cellular dehydration on mood. Forty-nine adults (55 % female, age 39 (sd 8) years) were assigned to counterbalanced, crossover trials. Intracellular dehydration was induced with 2-h (0·1 ml/kg per min) 3 % hypertonic saline (HYPER) infusion or 0·9 % isotonic saline (ISO) as a control. Plasma osmolality increased in HYPER (pre 285 (sd 3), post 305 (sd 4) mmol/kg; P < 0·05) but remained unchanged in ISO (pre 285 (sd 3), post 288 (sd 3) mmol/kg; P > 0·05). Mood was assessed with the short version of the Profile of Mood States Questionnaire (POMS). The POMS sub-scale (confusion-bewilderment, depression-dejection, fatigue-inertia) increased in HYPER compared with ISO (P < 0·05). Total mood disturbance score (TMD) assessed by POMS increased from 10·3 (sd 0·9) to 16·6 (sd 1·7) in HYPER (P < 0·01), but not in ISO (P > 0·05). When TMD was stratified by sex, the increase in the HYPER trial was significant in females (P < 0·01) but not in males (P > 0·05). Following infusion, thirst and copeptin (surrogate for vasopressin) were also higher in females than in males (21·3 (sd 2·0), 14·1 (sd 1·4) pmol/l; P < 0·01) during HYPER. In conclusion, cellular dehydration acutely degraded specific aspects of mood mainly in women. The mechanisms underlying sex differences may be related to elevated thirst and vasopressin.

Inputs to Thirst and Drinking during Water Restriction and Rehydration.

Current models of afferent inputs to the brain, which influence body water volume and concentration via thirst and drinking behavior, have not adequately described the interactions of subconscious homeostatic regulatory responses with conscious perceptions. The purpose of this investigation was to observe the interactions of hydration change indices (i.e., plasma osmolality, body mass loss) with perceptual ratings (i.e., thirst, mouth dryness, stomach emptiness) in 18 free-living, healthy adult men (age, 23 ± 3 y; body mass, 80.09 ± 9.69 kg) who participated in a 24-h water restriction period (Days 1-2), a monitored 30-min oral rehydration session (REHY, Day 2), and a 24-h ad libitum rehydration period (Days 2-3) while conducting usual daily activities. Laboratory and field measurements spanned three mornings and included subjective perceptions (visual analog scale ratings, VAS), water intake, dietary intake, and hydration biomarkers associated with dehydration and rehydration. Results indicated that total water intake was 0.31 L/24 h on Day 1 versus 2.60 L/24 h on Day 2 (of which 1.46 L/30 min was consumed during REHY). The increase of plasma osmolality on Day 1 (297 ± 4 to 299 ± 5 mOsm/kg) concurrent with a body mass loss of 1.67 kg (2.12%) paralleled increasing VAS ratings of thirst, desire for water, and mouth dryness but not stomach emptiness. Interestingly, plasma osmolality dissociated from all perceptual ratings on Day 3, suggesting that morning thirst was predominantly non-osmotic (i.e., perceptual). These findings clarified the complex, dynamic interactions of subconscious regulatory responses with conscious perceptions during dehydration, rehydration, and reestablished euhydration.

Pre- and during-labour predictors of low birth satisfaction among Iranian women: a prospective analytical study.

BACKGROUND: Maternal childbirth dissatisfaction has short- and long-term negative effects on the mothers' health and life, as well as on relation with her child and family. Due to lack of studies in Iran and other counties, we aimed to determine pre- and during- labour predictors of low birth satisfaction. METHODS: Seven hundred women with low risk singleton pregnancy participated in this prospective analytical study. The participants were hospitalized for vaginal delivery with fetus in cephalic presentation and gestational age of 370-416 at two teaching centers in Tabriz (Iran). Woman characteristics, anxiety state (using Spielberger inventory) and dehydration were assessed at cervical dilatation of 4-6 cm. Iranian (Persian) birth satisfaction scale-revised was applied 12-24 h after birth. Multiple linear regression was used to determine the predictors. RESULTS: Excluding 26 women who were outliers, 674 women were analyzed. The mean birth satisfaction score was 23.8 (SD 6.5) from an attainable score of 0-40. The during-labour predictors of low birth satisfaction score were severe and moderate anxiety, labour dystocia, insufficient support by staff, vaginal birth with episiotomy and tear, emergency cesarean section, labour induction and labour augmentation with oxytocin, and woman dehydration. The pre-labour predictors included being primiparous, sexual and emotional violence during pregnancy, gestational age of 400-416, preference for cesarean section, no attendance at pregnancy classes, and insufficient household income. The proportion of the variance explained by the during-labour variables was 75%, by pre-labour variables was 14% and by overall was 76%. CONCLUSIONS: The controllable during-labour predictors explains most of the variance of the satisfaction score. It seems that responding to women's physical and psychological needs during labour and applying less interventions could improve women's childbirth satisfaction.

Cognitive performance in relation to hydration status and water intake among older adults, NHANES 2011-2014.

PURPOSE: Risks of dehydration and cognitive decline increase with advancing age, yet the relation between dehydration, water intake, and cognitive performance among older adults remains understudied. METHODS: Using data from the 2011-2014 cycles of the Nutrition and Health Examination Survey (NHANES), we tested if calculated serum osmolarity (Sosm) and adequate intake (AI) of water among women (n = 1271) and men (n = 1235) ≥ 60 years old were associated with scores of immediate and delayed recall, verbal fluency, and attention/processing speed. Sosm was categorized as < 285 (hyperhydrated), 285-289, 290-294, 295-300, or > 300 (dehydrated) mmol/L. AI of water was defined as ≥ 2 L/day for women and ≥ 2.5 L/day for men. RESULTS: Women with Sosm between 285 and 289 mmol/L scored 3.2-5.1 points higher on the Digit Symbol Substitution test (DSST) of attention/processing speed than women in other Sosm categories (P values < 0.05). There was evidence of a curvilinear relationship between DSST scores and Sosm among women and men (P values for quadratic terms < 0.02). Meeting an alternative AI on water intake of ≥ 1 mL/kcal and ≥ 1500 mL, but not the sex-specific AI, was associated with scoring one point higher on a verbal fluency test (P = 0.02) and two points higher on the DSST (P = 0.03) among women. Significant negative associations between dehydration or inadequate water intake and test scores were not observed among men. CONCLUSION: Hydration status and water intake were moderately associated with attention/processing speed among females. Future work should consider the effects of both dehydration and overhydration on cognitive function and investigate potential sex differences in cognitive responses to hydration status.

Effects of Dehydration and Rehydration on Cognitive Performance and Mood among Male College Students in Cangzhou, China: A Self-Controlled Trial.

Water accounts for 75% of brain mass. Associations may exist between hydration and cognitive performance. The objective of this study was to investigate the effects of dehydration and rehydration on cognitive performance and mood. In this self-control trial, 12 men were recruited from a medical college in Cangzhou, China. After 12 h of overnight fasting, the participants took baseline tests at 8:00 AM on day 2. First morning urine and blood osmolality were analyzed to determine hydration state. Height, weight, and blood pressure were measured following standardized procedures. A visual analog scale for the subjective sensation of thirst was applied, and a profile of mood states questionnaire was applied. Tests were conducted for cognitive performance, including a test of digit span forward and backward, digit-symbol substitutions, dose-work, and stroop effects. Participants were required not to drink water for 36 h but were given three meals on day 3. On day 4, the same indexes were tested as a baseline test. At 8:30 AM, participants drank 1500 mL of purified water over 15 min. After a 1 h interval, the same measurements were performed. Compared with baseline test results, during the dehydration test, participants had lower scores of vigor (11.9 vs. 8.8, %, p = 0.007) and esteem-related affect (8.2 vs. 5.7, %, p = 0.006), lower total scores of digit span (14.3 vs. 13.3, %, p = 0.004), and higher error rates for dose-work (0.01 vs. 0.16, %, p = 0.005). Compared with the dehydration test scores, rehydration test scores showed that fatigue (4.3 vs. 2.1, %, p = 0.005) and total mood disturbance (TMD) (99.0 vs. 90.2, %, p = 0.008) improved, and scores of forward, backward, and total digit span increased (7.7 vs. 8.6, p = 0.014; 5.7 vs. 1.2, p = 0.019; 13.3 vs. 15.4, p = 0.001). Increases were also noted in correct number of digit symbol substitutions, reading speed, and mental work ability (70.8 vs. 75.4, p < 0.001; 339.3 vs. 486.4, n/min, p < 0.001; 356.1 vs. 450.2, p < 0.001), and reaction time decreased (30.2 vs. 28.7, s, p = 0.002). As a conclusion, dehydration had negative effects on vigor, esteem-related affect, short-term memory, and attention. Rehydration after water supplementation alleviated fatigue and improved TMD, short-term memory, attention, and reaction.

Gonadal hormones in female rats protect against dehydration-induced memory impairments in the novel object recognition paradigm.

Dehydration impairs cognitive performance in humans and rodents, although studies in animal models are limited. Estrogens have both protective effects on fluid regulation and improve performance in certain cognitive tasks. We, therefore, tested whether sex and gonadal hormones influence object recognition memory during dehydration. Because past studies used fluid deprivation to induce dehydration, which is a mixture of intracellular and extracellular fluid loss, we tested the effects of osmotic (loss of intracellular fluid) and hypovolemic (loss of extracellular fluid) dehydration on object recognition memory. After training trials consisting of exposure to two identical objects, rats were either treated with hypertonic saline to induce osmotic dehydration, furosemide to induce hypovolemic dehydration, or received a control injection and then object recognition memory was tested by presenting the original and a novel object. After osmotic dehydration, regardless of group or treatment, all rats spent significantly more time investigating the novel object. After hypovolemic dehydration, regardless of treatment, both the males and estrous females spent significantly more time investigating the novel object. While the control-treated diestrous females also spent significantly more time investigating the novel object, the furosemide-treated diestrous females spent a similar amount of time investigating the novel and original object. Follow up studies determined that loss of ovarian hormones after ovariectomy, but not loss of testicular hormones after castration, resulted in impaired memory performance in the object recognition test after hypovolemic dehydration. This series of experiments provides evidence for a protective role of ovarian hormones on dehydration-induced memory impairments.

Knowledge and Belief Toward Heat Safety and Hydration Strategies Among Runners: A Preliminary Evaluation.

CONTEXT: Little is known about how educating runners may correct common misconceptions surrounding heat safety and hydration strategies. OBJECTIVE: To investigate (1) beliefs and knowledge about heat safety and hydration strategies among recreational runners and (2) the effectiveness of an educational video in optimizing performance in the heat. DESIGN: Cross-sectional study. SETTING: Survey. PATIENTS OR OTHER PARTICIPANTS: A total of 2091 (25.1%) of 8319 runners registered for the 2017 Falmouth Road Race completed at least 1 of the 3 administered surveys. INTERVENTION(S): A 5.3-minute video and an 11-question survey regarding heat safety and hydration strategies were developed, validated, and implemented. The survey was e-mailed to registrants 9 weeks before the race (PRERACE), after they viewed the video (POSTEDU), and the afternoon of the race (POSTRACE). MAIN OUTCOME MEASURE(S): The total score for responses to 2 multiple choice questions and nine 5-point (response range = strongly agree to strongly disagree) Likert-scale questions. RESULTS: The PRERACE results showed that more than 90% of respondents recognized the importance of staying hydrated beginning the day before the planned activity, correctly identified that dark color urine is not a sign of euhydration, and believed that dehydration may increase the risk for heat syncope. Conversely, fewer than 50% of respondents knew the number of days required to achieve heat acclimatization, the role of sweat-rate calculation in optimizing one's hydration strategy, or the risk of water intoxication from drinking too much water. An improvement in survey score from PRERACE to POSTEDU was observed (mean difference = 2.00; 95% confidence interval = 1.68, 2.33; P < .001) among runners who watched the video, and 73% of the improvement in their scores was retained from POSTEDU to POSTRACE (mean difference = -0.54; 95% confidence interval = -0.86, -0.21; P < .001). CONCLUSIONS: The video successfully shifted runners' beliefs and knowledge to enable them to better optimize their performance in the heat.

The effect of active hypohydration on cognitive function: A systematic review and meta-analysis.

Hypohydration is generally considered to have a negative effect on cognitive function, despite several studies reporting comparable findings between hydration states. Recommendations to avoid moderate dehydration (≥ 2% loss in body mass) are commonly made to athletes, on the provision that this deficit may impair optimal cognitive performance. To determine whether cognitive function is impaired by hypohydration, and investigate the existence of the proposed critical water deficit of ≥2% loss in body mass purported to diminish cognitive performance, we conducted a systematic search of the literature and examined appropriate studies by meta-analysis. Overall, cognitive performance was not found to be impaired by hypohydration (g = -0.177; 95% CI = -0.532-0.179; P = .331). Nor were the underlying cognitive domains (complex attention, executive function, learning and memory) impaired (all P > .236), independent of the incurred fluid loss (less than or >2% loss in body mass), although results were not always homogenous (I2 ranging between 0% and 93%). Collectively, these results suggest that hypohydration may not compromise cognitive function, nor any of the investigated subdomains to a greater extent than if euhydration had been maintained. Furthermore, recommendations to avoid moderate hypohydration on the basis of maintaining optimal cognitive function are not substantiated by this meta-analysis.

The effects of hydration on cognitive performance during a simulated wildfire suppression shift in temperate and hot conditions.

The effects on dehydration and cognitive performance from heat and/or physical activity are well established in the laboratory, although have not yet been studied for personnel working in occupations such as wildland firefighting regularly exposed to these types of conditions. This study aimed to investigate the effects of temperature and dehydration on seventy-three volunteer firefighters (35.7 ±â€¯13.7 years, mean ±â€¯standard deviation) during a simulation of wildfire suppression under either control or hot (18-20; or 33-35 °C) temperature conditions. Results showed cognitive performance on the psychomotor vigilance task declined when participants were dehydrated in the heat and Stroop task performance was impaired when dehydrated late in the afternoon. Firefighters may be at risk of deteriorations in simple cognitive functions in the heat whilst dehydrated, although may also experience impairments in complex cognitive functions if dehydrated late in the day, irrespective of the environmental temperature.

Exercise-heat stress with and without water replacement alters brain structures and impairs visuomotor performance.

Effects of exercise-heat stress with and without water replacement on brain structure and visuomotor performance were examined. Thirteen healthy adults (23.6 ± 4.2 years) completed counterbalanced 150 min trials of exercise-heat stress (45°C, 15% RH) with water replacement (EHS) or without (~3% body mass loss; EHS-DEH) compared to seated rest (CON). Anatomical scans and fMRI Blood-Oxygen-Level-Dependent responses during a visuomotor pacing task were evaluated. Accuracy decreased (P < 0.05) despite water replacement during EHS (-8.2 ± 6.8% vs. CON) but further degraded with EHS-DEH (-8.3 ± 6.4% vs. EHS and -16.5 ± 10.2% vs. CON). Relative to CON, EHS elicited opposing volumetric changes (P < 0.05) in brain ventricles (-5.3 ± 1.7%) and periventricular structures (cerebellum: 1.5 ± 0.8%) compared to EHS-DEH (ventricles: 6.8 ± 3.4, cerebellum: -0.7 ± 0.7; thalamus: -2.7 ± 1.3%). Changes in plasma osmolality (EHS: -3.0 ± 2.1; EHS-DEH: 9.3 ± 2.1 mOsm/kg) were related (P < 0.05) to thalamus (r = -0.45) and cerebellum volume (r = -0.61) which, in turn, were related (P < 0.05) to lateral (r = -0.41) and fourth ventricle volume (r = -0.67) changes, respectively; but, there were no associations (P > 0.50) between structural changes and visuomotor accuracy. EHS-DEH increased neural activation (P < 0.05) within motor and visual areas versus EHS and CON. Brain structural changes are related to bidirectional plasma osmolality perturbations resulting from exercise-heat stress (with and without water replacement), but do not explain visuomotor impairments. Negative impacts of exercise-heat stress on visuomotor tasks are further exacerbated by dehydration.

Effect of Dehydration on Passing Decision Making in Soccer Athletes.

It seems that dehydration may impair decision-making performance in athletes. PURPOSE: This study aimed to investigate the influence of dehydration on passing decision-making performance in soccer players. METHOD: Participants were 40 male soccer players (Mage = 22.3 ± 2.3 years) who agreed to participate in the study and were randomly assigned to the following conditions: control (CON), dehydration (DEH), and euhydration (EUH). The players played in 2 games of 90 min in duration (2 45-min halves) followed by 2 15-min halves (overtime) with and without proper hydration. The Game Performance Assessment Instrument (GPAI) was considered for the analysis of passing decision making. RESULTS: The GPAI analysis indicated effective reduction in the decision-making index in the DEH condition compared with the EUH and CON conditions, F(2, 38) = 31.4, p < .05, ES = 0.8. CONCLUSIONS: In conclusion, dehydration may be considered a mediating factor in the passing decision-making performance of male soccer athletes.

Water intake reverses dehydration associated impaired executive function in healthy young women.

INTRODUCTION: Healthy women do not always consume Recommended Daily Levels of fluid intake ad libitum. We hypothesized that 1) women lose≥1.0% BW during daily activities, 2) that mild body water loss impairs memory and executive function, 3) water intake to recommended daily levels will improve cognitive function. METHODS: We tested 12 women (26±5yr, 22.5±2.6kg/m2 BMI). Session 1 was a control (CON) session, during which subjects monitored their food and fluid intake (diary) and activity (Fitbit®). The next two sessions were applied in balanced order: dehydration (DEH) session, where subjects minimized drinking, and a euhydration (EUH) session, where subjects drank Recommended Daily Levels of fluid for their age and sex, or 2500ml/24h. We compared emotion, sensory perception and cognition with computer based visual analog tests and computer based cognitive tasks (Cogstate) at 5PM, i.e. baseline (BL) on the evening prior to the session, and at 7AM, 12PM, and 5PM during the session. RESULTS: Urine specific gravity (USG) was similar at BL across conditions (CON 1.013±0.002, DEH 1.015±0.002, EUH 1.014±0.002) and increased with dehydration (CON 1.011±0.003, DEH 1.021±0.002, EUH 1.010±0.002, P<0.05) by 5PM of the session. Uncontrolled fluid intake and physical activity were similar across sessions. The water challenges did not impact Detection, Identification, One-Card Learning, but EUH improved visual and working memory (Groton Maze Learning Test) errors: CON 40.1±11.1, DEH 40.5±10.1, EUH 33.9±10.9, P<0.05. Executive function [Set Shifting (SETS)] also improved under EUH, errors: BL 22.5±12.7 vs. 5PM 17.8±6.2, P<0.05. CONCLUSIONS: Mild dehydration caused deficits in visual and working memory and executive function in healthy young women. These deficits were reversed by drinking water to the European Food Safety Authority and Institute of Medicine requirements of 2.5l/day for adult women.

Oxytocin-receptor-expressing neurons in the parabrachial nucleus regulate fluid intake.

Brain regions that regulate fluid satiation are not well characterized, yet are essential for understanding fluid homeostasis. We found that oxytocin-receptor-expressing neurons in the parabrachial nucleus of mice (OxtrPBN neurons) are key regulators of fluid satiation. Chemogenetic activation of OxtrPBN neurons robustly suppressed noncaloric fluid intake, but did not decrease food intake after fasting or salt intake following salt depletion; inactivation increased saline intake after dehydration and hypertonic saline injection. Under physiological conditions, OxtrPBN neurons were activated by fluid satiation and hypertonic saline injection. OxtrPBN neurons were directly innervated by oxytocin neurons in the paraventricular hypothalamus (OxtPVH neurons), which mildly attenuated fluid intake. Activation of neurons in the nucleus of the solitary tract substantially suppressed fluid intake and activated OxtrPBN neurons. Our results suggest that OxtrPBN neurons act as a key node in the fluid satiation neurocircuitry, which acts to decrease water and/or saline intake to prevent or attenuate hypervolemia and hypernatremia.

Thirst-associated preoptic neurons encode an aversive motivational drive.

Water deprivation produces a drive to seek and consume water. How neural activity creates this motivation remains poorly understood. We used activity-dependent genetic labeling to characterize neurons activated by water deprivation in the hypothalamic median preoptic nucleus (MnPO). Single-cell transcriptional profiling revealed that dehydration-activated MnPO neurons consist of a single excitatory cell type. After optogenetic activation of these neurons, mice drank water and performed an operant lever-pressing task for water reward with rates that scaled with stimulation frequency. This stimulation was aversive, and instrumentally pausing stimulation could reinforce lever-pressing. Activity of these neurons gradually decreased over the course of an operant session. Thus, the activity of dehydration-activated MnPO neurons establishes a scalable, persistent, and aversive internal state that dynamically controls thirst-motivated behavior.

Artificial Hydration at the End of Life.

Initiation or continuation of artificial hydration (AH) at the end of life requires unique considerations. A combination of ethical precedents and medical literature may provide clinical guidance on how to use AH at the end of life. The purpose of this review is to describe the ethical framework for and review current literature relating to the indications, benefits, and risks of AH at the end of life. Provider, patient, and family perspectives will also be discussed.

Shortened preoperative fasting for prevention of complications associated with laparoscopic cholecystectomy: a meta-analysis.

Objective Routine fasting (12 h) is always applied before laparoscopic cholecystectomy, but prolonged preoperative fasting causes thirst, hunger, and irritability as well as dehydration, low blood glucose, insulin resistance and other adverse reactions. We assessed the safety and efficacy of a shortened preoperative fasting period in patients undergoing laparoscopic cholecystectomy. Methods We searched PubMed, Embase and Cochrane Central Register of Controlled Trials up to 20 November 2015 and selected controlled trials with a shortened fasting time before laparoscopic cholecystectomy. We assessed the results by performing a meta-analysis using a variety of outcome measures and investigated the heterogeneity by subgroup analysis. Results Eleven trials were included. Forest plots showed that a shortened fasting time reduced the operative risk and patient discomfort. A shortened fasting time also reduced postoperative nausea and vomiting as well as operative vomiting. With respect to glucose metabolism, a shortened fasting time significantly reduced abnormalities in the ratio of insulin sensitivity. The C-reactive protein concentration was also reduced by a shortened fasting time. Conclusions A shortened preoperative fasting time increases patients' postoperative comfort, improves insulin resistance, and reduces stress responses. This evidence supports the clinical application of a shortened fasting time before laparoscopic cholecystectomy.

The use of moderated mediated analysis to study the influence of hypo-hydration on working memory.

INTRODUCTION: To date, dehydration has been typically reported to infl uence psychological parameters when there has been at least a 2% loss of body mass, although there has been little examination of those going about their everyday lives, those who have lost less than 1% of body mass. In such situations factors such as the initial hydration status and individual differences in the response to a reduced fl uid intake are likely to be infl uential. Yet to study the complexity added by such additional variables novel methods of statistical analysis are required. OBJECTIVES: The present study describes the use of moderated mediation, an approach that asks various questions: fi rstly, is drinking infl uential?; secondly, does a mediator (e.g.,thirst) sit between an independent and dependent variable?; and thirdly, does an effect only occur under certain conditions such as initial osmolality? METHOD: In the study, 118 subjects were exposed to 30 °C for four hours during which they half drank 300 ml water. The serial sevens test of working memory was performed before and at the end of the procedure. RESULTS: A 0.6% loss of body mass reduced the effi ciency of working memory. Those who consumed water had better working memory; working memory was worse in participants who lost more body mass or became thirstier, but only in those with higher levels of baseline osmolality. CONCLUSIONS: Small variations in hydration status infl uenced cognitive functioning although there were individual differences in the response. The parameters that influence an adverse response to hypo-hydration need to be established to allow giving appropriate advice.