Hunger, thirst and their interactive effects on the rat's drinking in a saccharin-water choice

In a 3 × 3 factorial in which hours of food and water deprivation were varied, Sprague-Dawley rats preferred water to 1.0% saccharin and drank large volumes of it providing hours of water deprivation (thirst), exceeded hours of food deprivation (hunger). All other, i.e. undeprived, equally hungry and thirsty rats, and those whose hunger exceeded thirst preferred 1.0% saccharin but drank small amounts relative to the amounts of water drunk by the thirsty rats. The combined results of this and previous studies employing both choice and single-tube conditions, suggested that thirsty rats drink saccharin primarily for water and to a lesser extent and only with experience, for the sensory stimulation which saccharin provides. Hungry rats drink it primarily for the sensory stimulation. Saccharin in a choice with water seems to provide a means for the determination of the momentarily dominant drive state in naive rats.     

Soup and satiety

Energy-yielding fluids generally have lower satiety value than solid foods. However, despite high water content, soups reportedly are satiating. The mechanisms contributing to this property have not been identified and were the focus of this study. A within-subject design, preload study was administered to 13 male and 18 female adults (23.7+/-0.9 years old) with a mean body mass index (BMI) of 23.0+/-0.7 kg/m2. At approximately weekly intervals, participants reported to the lab after an overnight fast and completed questionnaires on mood, appetite, psychological state, strength, and fine motor skills. After administration of motor tasks, participants consumed a 300-kcal preload in its entirety within 10 min. The test foods included isocaloric, solid, and liquefied versions of identical foods high in protein, fat, or carbohydrate. Single beverage and no-load responses were also tested. The same questionnaires and motor skills tests were completed at 15-min intervals for 1 h and at 30-min intervals for an additional 3 h after loading. Diet records were kept for the balance of the day. The soups led to reductions of hunger and increases of fullness that were comparable to the solid foods. The beverage had the weakest satiety effect. Daily energy intake tended to be lower on days of soup ingestion compared to the solid foods or no-load days and was highest with beverage consumption. Thus, these data support the high satiety value of soups. It is proposed that cognitive factors are likely responsible.     

Relationship between wheel running, feeding, drinking, and body weight in male rats

The amount of wheel running varies widely between rats. Wheel introduction and running also have profound effects on the animal's energy balance. We explored the effects of ad lib wheel access and running levels on feeding, drinking, and body weight in 30 young adult male rats with wheel access and in 30 rats without wheel access. The initial running period (Days 1-8) and a time of stable running [Days 29-32 (DEnd)] were analyzed using both between- and within-group approaches. Initially, wheel access suppressed feeding (by about 25% over the 8 days) but not drinking. There were no significant correlations between the amount of wheel running and the other behaviors. The degree of feeding suppression was also not correlated to the amount of running. When running had stabilized (animal ran from 841 to 13,124 wheel turns per day), food intake was increased by about 0.75 g per 1000 wheel turns. Running at this time correlated positively with feeding and drinking and negatively with body weight and weight gain. In animals without wheel access, feeding and drinking were positively correlated with weight and weight gain, but in animals with wheel access, these correlations were close to zero. Only early running predicted later levels of running but accounted for only 23% of the variance in running. Wheel access has profound but very different immediate and long-term effects on the rats' energy balance.     

Increased hunger and thirst during glucoprivation in humans

Five male volunteers received two intravenous infusions of 2-deoxy-D-glucose (2DG) and one of normal saline. Hunger and thirst ratings, solid-food and water intake, and plasma epinephrine and glucose levels were greater after both of the 2DG infusions than after the saline infusion. This study suggests that the increase in water intake caused by 2DG does not depend on elevated hunger, and demonstrates that increased caloric intake after 2DG infusions is not dependent on greater thirst. Behavioral and adrenomedullary responses to both 2DG infusions were qualitatively and quantitatively the same, suggesting that there are no residual effects of 2DG that diminish the ability of the subjects to respond to glucoprivation. Measurements of possible thirst stimuli revealed no clear mechanism for the dipsogenic effect of 2DG.     

Body fluid changes, thirst and drinking in man during free access to water

To investigate whether human thirst and drinking during ad lib access to water occur in response to body fluid deficits, we obtained blood samples and visual analog scale thirst ratings from five healthy, volunteer, young men at hourly intervals and when they were thirsty during a normal working day. Although there were significant increases in ratings of thirst, pleasantness of drinking water, mouth dryness and unpleasantness of the taste in the mouth when subjects were thirsty enough to drink compared with intervening intervals, there were no concomitant changes in body fluid variables (microhematocrit, plasma osmolality and plasma sodium, potassium, protein and angiotensin II concentrations). Subjects drank mainly in association with eating and were not overhydrated as indicated by constantly hypertonic urine and significant tubular reabsorption of free water over the experimental period. The results indicate that during free access to water humans become thirsty and drink before body fluid deficits develop, perhaps in response to subtle oropharyngeal cues, and so provide evidence for anticipatory thirst and drinking in man.     

Voluntary drinking and hydration in non-acclimatized girls exercising in the heat

The intent of this study was to assess the influence of drink flavor and composition on voluntary drinking and hydration status in girls exercising intermittently in the heat (35 ± 1°C, 45–50% relative humidity). Twelve physically active, nonacclimatized girls (9–12 years) performed three 3 h identical sessions, each consisting of four 20 min cycling bouts at 50% separated by 25 min of rest. One of the three beverages (chilled to 8–10°C) was assigned to each session: unflavored water (W), grape-flavored water (FW) and grape-flavored water plus 6% carbohydrate and 18 mmol l⁻¹ NaCl (CNa). Drinking was ad libitum. Body weight (BW), drink intake (DI), heart rate, rectal and skin temperatures, and perceptions of thirst and stomach fullness were monitored periodically. Total DI was 759, 940, 1,045 g in W, FW and CNa, respectively (P < 0.05 for CNa–W and FW–W). BW changes were −0.15, 0.16, and 0.45% in W, FW and CNa, respectively, but only the difference between CNa and W was significant (P < 0.05). Other physiological and perceptual variables were not different between trials. In conclusion, beverage flavoring regardless if its combination with carbohydrate and NaCl, mildly enhanced voluntary drinking in young non-acclimatized girls. In contrast to previous research in young boys, euhydration was maintained in the girls by an adequate intake of unflavored water.     

Ionic changes in cerebrospinal fluid and feeding, drinking and temperature of sheep

The effects of third ventricular injections of Ca⁺⁺, Mg⁺⁺, Na⁺ and K⁺ on feeding, drinking and intraperitoneal (IP) temperature were studied in sheep. The chloride salts were dissolved in synthetic CSF (control) and injected (0.5ml) at a rate of 0.2 ml/min into satiated sheep. Ca⁺⁺ and Mg⁺⁺ injections elicited dose dependent feeding responses but Ca⁺⁺ resulted in greater feeding. Doses as little as 1.5 μmoles/animal of either Ca⁺⁺ or Mg⁺⁺ elicited feeding with a latency of about 2 min and lasted for 15 min postinjection. With larger doses, the duration of the feeding response increased but the latency stayed the same. A 20 or 40 μmole dose of K⁺ elicited a decrease in feed intake. Na⁺ given at similar doses produced an increase in water consumption without affecting feeding. Injections of either Na⁺ or K⁺ 10 min prior to either Ca⁺⁺ or Mg⁺⁺ resulted in only normal feeding. K⁺ inhibited the feeding response to both Ca⁺⁺ and Mg⁺⁺ at dose levels lower than the doses of Na⁺ required (40 vs 550 μmoles). The inhibitory effect of Na⁺ on Ca⁺⁺ feeding was overcome by either increasing the dose of Ca⁺⁺ or decreasing the dose of Na⁺. Water intake was generally increased after injections of Ca⁺⁺, Mg⁺⁺ and Na⁺. Intraperitoneal temperatures increased after injections of Na⁺ and Mg⁺⁺ but remained unchanged after injections of Ca⁺⁺, K⁺ or synthetic CSF. We conclude that the CNS mechanisms for the control of feeding in sheep are sensitive to changes in the ionic environment of brain tissue, probably the hypothalamus. Ca⁺⁺ and Mg⁺⁺, known neurodepressants, probably exert their action by decreasing metabolism and neuroconductivity of inhibitory nerve fibers acting on the lateral hypothalamus. Preinjections with the neurostimulants Na⁺ or K⁺ would tend to neutralize such changes in neuroexcitability, so that the combination of ions would result in a net no effect, as far as feeding in concerned. Feeding and drinking behaviors were more sensitive than IP temperature to the ionic changes in the cerebrospinal fluid of sheep.     

Effects of two-hour light-dark cycles on feeding, drinking and motor activity of the rat

The effect of two-hour light-dark cycles on feeding, drinking and motor activity in the rat was compared with behavior under the usual $\text{12}\text{12}$ hour cycle. The two-hour cycles consisted of $\text{60}\text{60}$ min, $\text{80}\text{40}$ min and $\text{40}\text{80}$ min light-dark schedules which were maintained each for 7 days. Water intake, frequency of feeding, and motor activity were still significantly higher during dark than during light, although their occurrence during dark was reduced as compared to the $\text{12}\text{12}$ hour control schedule. A free-running circadian rhythm of consummatory behavior with a period length exceeding 24 hours was present throughout the experimental period. The amplitude of the circadian feeding rhythm gradually decreased over time, whereas the percentage of feeding during dark increased. During the circadian phase of minimal food intake, illumination changes affected feeding behavior more strongly than during the phase of maximal food intake. After restoration of the orginal $\text{12}\text{12}$ hour cycle, the amplitude of the nocturnal feeding rhythm increased gradually over several days, whereas the amplitude of the drinking rhythm showed a more rapid recovery. The experiments show that even short cycles of illumination may exert control over the rat's consummatory and motor activity. Short light-dark schedules provide a way for studying separately effects of illumination and of circadian rhythms.     

A microcomputer-based data acquisition system for continuous recording of feeding and drinking by rats

A monitoring system to continuously record the daily pattern of drinking and eating of rats is described. This system, based on a North Star microcomputer, can record the amount of food ingested with a temporal resolution of +/- 1.0 second and quantitative accuracy within +/- 5%. Drinking behavior is detected using a drinkometer which also has a temporal resolution of +/- 1.0 second. Data are analyzed by computer to determine absolute amounts of consumption and patterns of intake. The patterns of feeding and drinking recorded by this system are similar to those observed using other monitoring devices.     

Pattern of drinking and feeding produced by hypothalamic norepinephrine injection in the satiated rat.

Injection of norepinephrine into the perifornical region of the anterior hypothalamus elicited both drinking and feeding in satiated rats. Analysis of these behaviors revealed the following: (1) Both responses were dose-dependent, occurring at doses at least as low as 0.5 mug. (2) The drinking response (1-4 ml) had a latency of around 1.5 min and a duration of 2-3 min. It was followed within a minute or two by eating (2-4 g) that lasted approximately 20 min. It was also followed by a period of drinking suppression that lasted approximately 60 min. (3) Satiation from the ingestion process appeared to be a primary factor in terminating the elicited feeding response, whereas a time-related factor was important in terminating the elicited drinking. (4) These ingestive responses produced by noradrenergic stimulation of the anterior perifornical hypothalamus were found to bear striking similarities to the rat's natural feeding behavior and premeal component of his natural food-associated drinking behavior. (5) These noradrenergically elicited responses could not be observed with lateral hypothalamic stimulation, while only feeding was elicited by ventromedial hypothalamic stimulation. (6) The drinking induced by central noradrenergic stimulation, in contrast to that induced by peripheral beta-adrenergic stimulation, was unaffected by nephrectomy.     

Persistence of rat nocturnal feeding and drinking during diurnal presentation of palatable diet

Male laboratory rats were fed a highly palatable diet during the light phase of a 12:12 LD cycle. Nocturnality of feeding was reduced from approximately 77% of the total daily intake to 56%. Increase in diurnal feeding was attributable to the ingestion of a large meal at the beginning of the L phase. Reduction of nocturnal feeding was attributable to decreased ingestion in the first 3 hr of the D phase. Outside these times the daily feeding pattern was unmodified. These findings do not represent a reversal of the feeding rhythm as previously reported, but a modification which is not consistent with interpretation as a phase-shift. Throughout the testing period total daily food intake remained unchanged and body weight was defended despite the increase in calories ingested. Daily drinking patterns and total daily water intake were not significantly altered by the experimental manipulation.     

No difference in satiety or in subsequent energy intakes between a beverage and a solid food

Energy compensation following the consumption of caloric beverages is said to be imprecise and incomplete. This study compared the relative impact on satiety and energy intakes of the physical form of foods versus the timing of consumption. Thirty-two volunteers (16 men and 16 women), aged 18-35 years, consumed equal-energy preloads (1254 kJ, 300 kcal) of regular cola (710 ml, 24 oz) or fat-free raspberry cookies (87 g, 3 oz) on two occasions each. The preloads were presented either 2 h or 20 min before the test meal. Their principal ingredient was sugar. Participants rated motivational states prior to ingestion and at 30-min intervals. A tray lunch was presented at 12:30 p.m., and food consumption was measured. Regular cola and cookies suppressed hunger ratings equally and no temporal difference in satiety was observed. Cola, but not cookies, resulted in lower ratings of thirst. Energy intakes at lunch were lower when the preload was consumed closer to the test meal (20 min) but was not affected by physical form (liquid vs. solid). Cola, but not cookies, reduced water intakes at lunch. There was no satiety deficit following the ingestion of a beverage as compared with a solid food. The timing of consumption may be more important than the physical form of energy consumed.     

Acute effects of knowledge-based work on feeding behavior and energy intake

The aim of this study was to evaluate the impact of knowledge-based work (KBW) on feeding behavior and spontaneous energy intake with the use of a repeated measures/within-subjects design. We used a two-session protocol including an ad libitum buffet preceded by either rest in a sitting position for 45 min or a cognitive task (reading a document and writing a summary of 350 words using a computer) over the same time period. In this regard, 15 healthy Laval University female students (mean age = 24.1+/-2.2 years, mean BMI = 24.0+/-4.3 kg/m2) were recruited to participate in this study. Anthropometric variables, energy expenditure, heart rate, blood pressure, food intake (dietary record), and appetite sensation markers were measured at each testing session, and two questionnaires [Three-Factor Eating Questionnaire (TFEQ) and State-Trait Anxiety Inventory (STAI)] were administered. In addition, a buffet-type meal was used to measure spontaneous energy intake and macronutrient preferences. We found that the mean energy expenditure of the two conditions was about comparable (difference of 13 kJ between the two tasks) whereas the mean ad libitum energy intake after the KBW task exceeded that measured after rest by 959 kJ (p < 0.01). Although a higher absolute energy intake was observed for the three macronutrients after the KBW task (p < 0.05), no specific preference was detected, as reflected by the comparable percent of energy from each macronutrient in the two conditions. No significant difference in appetite sensation markers was observed between the two conditions, although the subjects ate more in the buffet-type meal after the KBW task. Furthermore, the subjects did not compensate by decreasing food intake for the rest of the day, suggesting a net caloric surplus. We also observed negative correlations between cognitive dietary restraint (TFEQ) and spontaneous energy intake in both conditions. In conclusion, our results demonstrate that mental work solicited by KBW has the potential to induce a higher spontaneous energy intake. This also raises the possibility that KBW adds a new component to sedentariness that might further accentuate the positive energy balance that is more likely to occur when one is inactive.     

Circadian rhythms and patterns of running-wheel activity,feeding and drinking behaviors of old male rats

Running-wheel activity of 7 young adult male rats (3 to 6.5 months of age) and 11 old male rats (22 to 34 months of age), feeding behavior of 10 each of young adult and old male rats and drinking behavior of 6 each of young adult and old male rats were recorded. Circadian rhythms were lost in 2, 6 and 1 old rats respectively in running activity, feeding and drinking behaviors. Loss of circadian rhythm of three behaviors seems not to occur concomitantly. Although the remaining old rats still showed as high a percentage of nocturnal activities in these three behaviors as young rats, the patterns of the behaviors revealed age-related changes. Old rats had decreased daily activity with small numbers and short duration of bursts of activity. Total frequencies of the head of rats interrupting the photobeam of a feeder during 24 hour period increased in old age with patterns of a small number of long meals with a rapid ingestion rate. Total numbers of licking the spout per day increased in old rats with patterns of a small number of short duration draft with a rapid licking rate. Old rats still maintained diurnal difference of drinking-to-feeding ratio. The similarity of the feeding and drinking patterns between old male rats and ventromedial hypothalamus lesioned rats was discussed.     

Intermittent drinking,oxytocin and human health

Looking at a waterhole, it is surprising that so many animals share the same space without visible signs of anxiety or aggression. Although waterholes are the preferred feeding locations of large carnivores, waterholes are shared by all type of herbivores of all sizes and shapes, including elephants. Recent research shows that the homeostatic disturbances leading to the “thirst feeling” not only activate specific substances regulating water and mineral household, but also the “trust and love” hormone oxytocin, while decreasing the production of the typical stress hormone cortisol. People using drugs, seem to be in search for oxytocin, as evidenced in studies with individuals on drugs such as ecstasy and gamma-hydroxybyturate. Hot environment, drought and increased sweating also activate specific oxytocin-producing parts of the hypothalamus, just as breastfeeding does in mother and infant. Water homeostasis is the only allostatic system activating trust neuro-anatomy and we suggest that this is due to the fact that all animals depend on water, whereas food type is species specific. Our hypothesis; regulating drinking behaviour through intermittent bulk drinking could increase oxytocin signalling, recover human trust and increase health by down-regulation of stress axis activity and inflammatory activity of the immune system. Intermittent bulk drinking should be defined as water (including tea and coffee) drinking up to a feeling of satiety and regulated by a mild feeling of thirst. This would mean that people would not drink less quantity but less frequently and that’s how all animals, but also human newborns behave. It is the latter group, which is probably the only group of humans with a normal fluid homeostasis.     

The effect of naloxone on feeding and spontaneous locomotion in the wolf

The effect of naloxone on food intake and activity levels was studied in the wolf (Canis lupus). Naloxone decreased food intake at both the 1 mg/kg and 5 mg/kg dose. There was no quantitative difference in the magnitude of the decrease in food intake produced by naloxone in winter or summer. Wolves ate significantly greater amounts of deer meat than dog chow after naloxone when expressed on a mass basis but there was no difference when the amounts of food ingested were expressed in calories. This suggests a role for endogenous opiates in the regulation of energy intake. The putative satiety factor, cholecystokinin-octapeptide, had no effect on food intake in wolves. Naloxone decreased spontaneous locomotion and increased time spent resting in wolves. The effects of naloxone on activity were significantly more marked in winter compared to summer.     

Failure of periodic presentation of palatable diet to entrain feeding,drinking and activity rhythms under constant conditions

Feeding, drinking and activity of two groups of male laboratory rats were studied across three experimental stages: LD 12:12; LL; and LD 12:12. In the first group (Control), ordinary diet was availabel ad lib for the entire experiment. In the second group (Experimental), palatable diet was available for the first 12 hr of each day and ordinary diet for the remainder of the day in stages 2 and 3. It was found that in stage 1 all behaviors were highly nocturnal. The nocturnality of feeding was achieved by the ingestion of more meals in the D phase as compared to the L phase. Dark ingested meals were not significantly larger than meals in the L phase. In stage 2, circadian rhythms in all three variables were damped and meals became evenly spaced across the day in both groups. In the Control group, meal sizes were also of the same magnitude across the day. However, periodic presentation of palatable diet resulted in larger meals and, therefore, the ingestion of 60% of total daily food intake during the 12 hr period when palatable food was available. Total daily food intake in LL did not change compared to stage 1 and did not differ between the groups. The size and number of significant meal size/post-meal interval correlations increased over the duration of the experiment but remained relatively small. In stage 2, water intake and activity were similarly evenly distributed over the 24 hr period in both groups and were not influenced by periodic presentation of palatable diet. No marked decreases in total daily water intake, but a substantial decrease in daily activity, were found. Under LL, daily body weight increments in both groups were maintained, but subtle changes were observed. In stage 3 when the LD cycle was reinstated, both groups ate a greater number of meals in the D phase despite the availability of palatable food in the L phase for the Experimental group. These animals ate fewer but larger meals of palatable diet than ordinary food resulting in 50% of their daily intake being ingested during the L phase. Activity and water intake returned to stage 1 levels and the distributions of these behaviors were similar to those found in stage 1 in both groups. It was concluded that palatable diet influenced meal size only and that the timing of meals depended on the illumination conditions only. Further, periodic presentation of palatable diet failed to entrain the damped rhythms of feeding, drinking and activity in LL. These results do not rule out the possibility that such an entraining effect of periodic presentation of palatable diet might be found in conditions of DD.     

Meal initiation controlled by learned cues: Effects of peripheral cholinergic blockade and cholecystokinin

Sated animals can be induced to initiate meals by exposing them to external stimuli which they have learned, via Pavlovian conditioning, to associate with food. This study examined physiological properties of this control of feeding. The initial hypothesis examined was that conditioned feeding depended on the elaboration of cholinergic cephalic phase responses (e.g., anticipatory insulin secretion). This idea was evaluated by comparing feeding responses to presentation of conditioned cues following an injection of either a peripheral cholinergic blocker, atropine methyl nitrate, or a control substance, physiological saline. Peripheral cholinergic blockade had no effect on the meal initiated by presentation of conditioned cues even though the dose of atropine methyl nitrate used was demonstrated to be sufficient to completely suppress cholinergic cephalic phase responses. These results indicate that cholinergic anticipatory digestive secretions do not contribute to feeding in this preparation. The effects of exogenously administered cholecystokinin on feeding controlled by learned cues were also studied. Cholecystokinin suppressed the size of the meal induced by presentation of conditioned stimuli but did not influence the latency, or initial rate of eating. The implications of these results to a conclusion that cholecystokinin is a satiety factor are discussed.     

The feeding response of obese mice (genotype,ob ob) and their wild-type littermates to cholecystokinin (pancreozymin)

Genetically obese mice that had been reared on a restricted diet and their wild-type littermates were deprived of food for 23 hours. Then, 10 minutes after an IP injection of either 0, 15, 30, 60 or 120 units/kg Cholecystokinin in saline vehicle, they were given behavioural tests. Consummatory feeding, drinking and exploratory activity were recorded for a period of 20 min. 15 Units/kg had no effect; higher doses caused a greater reduction in the feeding rates of obese than in wild-type mice. Frequencies of drinking and exploration remained unchanged. The results suggest that the characteristic hyperphagia of obese mice may be due, in part, to low levels of endogenous satiety hormones.