Proximity of food, sex, and access to running wheels: Effects on food intake in rats.

To test the hypothesis that the addition and withdrawal of a running wheel affects food intake because of a manipulation of the proximity of the rat to the food dish, a 2nd source of food was made available to the rat when in the running wheel. Ss were 24 male and 24 female ARS/Sprague-Dawley albino rats. Results fail to support the hypothesis. Additional findings were that both sexes showed the reduction in food intake when given access to running wheels, but only the males showed an increase in food intake when deprived of access to running wheels. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Chlordiazepoxide attenuates activity-induced anorexia and weight loss in rats.

Studied the effects of chlordiazepoxide (CDP) on body weight and food intake in male rats. In Exp 1, the effect of repeated injections of 2.5, 5.0, or 10.0 mg/kg of CDP on food intake and body weight was studied in rats on an activity anorexia (AA) regimen. For several days before CDP testing began, rats lived in activity wheels and had one 60-min meal/day. During CDP testing, this regimen continued except that each rat was injected with an appropriate dose of CDP or saline 30 min before each meal. CDP enhanced food intake; 5.0 mg/kg seemed most effective. However, the CDP-induced increase in eating did not noticeably stem weight loss. In Exp 2, after several days of AA training, CDP (5.0 mg/kg) was tested under less severe conditions; food remained restricted, but access to the wheels was discontinued. Rats given CDP ate more and gained more weight than controls. These findings suggest that benzodiazepines such as CDP may help in treating anorexia nervosa and other anorectic conditions in humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Tolerance to amphetamine: Contingent suppression of stereotypy mediates recovery of feeding.

In this article, the effect of chronic injections of amphetamine on feeding and behavioral activation was analyzed. Rats were given milk either through an intraoral cannula or in a standard drinking tube, and the level of their behavioral activation was monitored before, during, and after access to the milk. Cannula- and bottle-fed rats given saline showed similar patterns of intake and activity. Bottle-fed rats given amphetamine (2 mg/kg) showed substantially greater suppression of intake than did cannula-fed rats, but recovered more rapidly, confirming earlier findings (Salisbury & Wolgin, 1985). Such recovery was accompanied by a suppression of stereotyped head scanning movements during access to milk, but not before and after milk access. In contrast, cannula-fed rats given amphetamine showed stereotyped head scans throughout the session for the duration of the experiment. These results suggest that tolerance to the suppression of intake by amphetamine involves learning to suppress stereotyped head movements. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rats with area postrema lesions have lengthy eating and drinking bouts when fed ad libitum: implications for feedback inhibition of ingestive behavior

Ad libitum ingestive behavior of rats with area postrema lesions (APX) was monitored electronically every 6 s for 23 hr. Whereas control rats ate on average 32.2 g of food each day in 16.3 distinct bouts, rats with APX ate comparable amounts of food (28.6 g) in much fewer daily bouts (5.8) that were very large. Controls drank 38.4 ml of water daily in 17.8 bouts, whereas rats with APX consumed more than twice as much water (101.5 ml) in a similar number of bouts (18.5). Controls drank 5.3 ml of 0.5 M NaCl daily in 7.0 bouts, whereas rats with APX consumed 9 times as much saline (45.5 ml) in more bouts (18.2) that were relatively large. These and other results suggest that the area postrema plays an important role in detecting inhibitory signals generated by food or fluid intake and that feeding and drinking bouts may increase in size after APX, because the feedback inhibition provided by those signals is diminished.     

Variation in genome organization of the plant pathogenic fungus Colletotrichum lindemuthianum

The effects of 5-HT3 receptor antagonists on ethanol intake were examined in the selectively bred alcohol-preferring P line of rats under continuous and limited access to 10% (v/v) ethanol with food and water ad lib. Single daily injections of either MDL 72222 (MDL) or ICS 205-930 (ICS) (0.01-3.0 mg/kg, SC) given 60 min before a 4-h scheduled access period for 4 consecutive days failed at all doses to alter the intake of a 10% (v/v) ethanol solution by P rats. However, multiple daily injections of either MDL (1-3 mg/kg, SC) or ICS (3.0 and 5.0 mg/kg, SC), given three times daily at 4-h intervals, significantly reduced ethanol intake under 24-h free-choice conditions on the first treatment day. Additionally, a single administration of 1.0 mg/kg MDL reduced 24-h free-choice ethanol intake by approximately 50% of control values and had no effect on 24-h saccharin intake. The effects of MDL were further examined in a 2-h schedule access paradigm in which rats received the access period at the same time every day (Fixed) or randomly during the dark cycle (Variable). Although 1.0 mg/kg MDL had little effect on ethanol drinking in the Fixed group, ethanol intake was reduced by 55% of control levels in the Variable group. Overall, the data indicate that drinking conditions influence the effectiveness of 5-HT3 antagonists to reduce ethanol consumption. Furthermore, the results suggest that conditions, associated with limited access ethanol drinking, markedly reduce the actions of 5-HT3 antagonists on ethanol intake.     

The role of drinking in the suppression of food intake by recent activity.

The standard activity-based anorexia procedure provides rats with access to a running wheel while restricting their access to dry food. This can produce reduced food intake and progressive weight loss. Using this procedure, in the present study (Experiment 1) the authors found changes in drinking patterns both in the period of high activity preceding food access and during the feeding period. Varying the procedure by providing wet mash (Experiment 2) or by prior adaptation to a drinking schedule (Experiment 3) prevented the self-starvation effect. These results indicate the importance of drinking when analyzing the effect of recent activity on food intake. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Running and addiction: Precipitated withdrawal in a rat model of activity-based anorexia.

Exercise improves cardiovascular health, strengthens muscles and bones, stimulates neuroplasticity, and promotes feelings of well-being. However, when taken to extremes, exercise can develop into an addictive-like behavior. To assess the addictive potential of exercise, withdrawal symptoms following injections of 1.0 mg/kg naloxone were compared in active and inactive male and female rats. Active and inactive rats were given food for 1 hr or 24 hr/day. Additionally, a group of inactive rats was pair-fed the amount of food consumed on the previous day by food-restricted active rats. Rats fed for 1 hr/day decreased food intake and lost weight. Additionally, food-restricted active rats increased wheel running. There was a direct relationship between the intensity of running and the severity of withdrawal symptoms. Active food-restricted rats displayed the most withdrawal symptoms, followed by active rats given 24-hr access to food. Only minimal withdrawal symptoms were observed in inactive rats. These findings support the hypothesis that exercise-induced increases in endogenous opioid peptides act in a manner similar to chronic administration of opiate drugs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differences in food, water, and food-deprivation water intake in 16 strains of rats.

Measured daily food and water intake during 24-hr food deprivation in 181 adult male rats of 15 inbred strains and 1 outbred stock of Rattus norvegicus. Strain differences in absolute and relative food intake were moderate but significant, whereas strain differences in absolute and relative water intake under both conditions were dramatic. During food deprivation, some strains showed little depression of daily water intake, while other strains consumed less than 20% of their usual ad lib intake. Both genetic and environmental explanations for the divergent patterns of water intake during food deprivation are presented. In light of such strain differences, generalizations about the drinking behavior or water intake regulation of the rat must be made with caution. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of ethanol drinking and naltrexone on subsequent drinking in rats

The effects of several days of oral ethanol drinking paired with naltrexone (NTX) on subsequent ethanol drinking were investigated in rats. We hypothesized that repeated pairings of NTX combined with forced oral ethanol intake would extinguish ethanol drinking so that when NTX injections were terminated, voluntary oral ethanol drinking would be suppressed. Thirty-two male. Long-Evans rats were provided with alternate days of either 8% ethanol solution or water as the sole source of fluid. Intraperitoneal injections of 0, 2.5, or 5.0 mg of NTX hydrochloride were administered on the ethanol days. Following the termination of injections, rats were returned to unrestricted access to water and ethanol and 24-h measurements of fluid intake were recorded. NTX decreased ethanol intake 4 h, but not 24 h, after NTX injections. Despite the consumption of significant amounts of ethanol during NTX treatment, there was no change in voluntary oral ethanol intake patterns after NTX injections were terminated (reinstatement of voluntary ethanol drinking). Thus, NTX's reduction in ethanol intake was limited in duration and did not result in long-term extinction of ethanol drinking behavior.     

Histamine H3 receptors contribute to drinking elicited by eating in rats

A role for endogenous histamine and its H3 receptor subtype for mediating drinking elicited by eating was examined in adult male Sprague-Dawley rats. The i.p. injection of the H3 agonist R-alpha-methylhistamine (Ramh, 2.5 mg/kg) shortened the latency to initiate drinking and increased 1-h water intake in nondeprived rats freely eating pellets and drinking water. The ICV injection (through a surgically implanted chronic cannula) of 10 micrograms Ramh increased water intake; this Ramh-induced drinking was abolished by previous ICV injection of the H3 antagonist thioperamide (Th, 60 micrograms). For rats drinking and eating after 24-h food deprivation, s.c. Th inhibited drinking behavior: for example, 10 mg/kg Th s.c. delayed the latency to initiate drinking and inhibited 1-h water intake without inhibition of food intake. In contrast, 60 micrograms Th ICV failed to inhibit food-related drinking in rats eating after food deprivation. For nondeprived rats eating a small cracker, 10 mg/kg Th s.c. delayed the latency to initiate drinking and abolished water intake without effect of eating, and 60 micrograms Th ICV had similar effects upon drinking elicited by ingestion of cracker. The IG infusion (through a surgically implanted gastric catheter) of 2 ml 600 or 900 mOsm/kg NaCl, a treatment that is subthreshold for increase in systemic plasma osmolality at the initiation of drinking, elicited drinking that was abolished by 10 mg/kg Th s.c. and attenuated by 60 micrograms Th ICV. The IG infusion of 2 ml 1800 mOsm/kg NaCl, a treatment that is above threshold for increase in systemic plasma osmolality, elicited drinking that was attenuated by 10 mg/kg s.c. or 60 micrograms Th ICV. These results demonstrate that peripheral and central H3 receptors for histamine have a role in drinking elicited by eating and the postprandial gastrointestinal osmotic consequences of eating. These findings extend the evidence demonstrating a histaminergic contribution to food-related drinking in rats.     

Novel food and novel running wheels: Conditions for inhibition of sucrose intake in rats.

In 3 experiments with ARS/Sprague-Dawley albino rats it was found that both males (n = 16) and females (n = 40), when first given free access to running wheels, showed a marked reduction in sucrose intake relative to stock diet intake when the sucrose was novel. Further tests showed that both the novelty of the sucrose and the novelty of the running wheel were necessary for the inhibition of sucrose intake. The selective inhibition of sucrose intake is considered to be an example of neophobia in the domestic rat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

System-specific differences in behavior regulation: Overrunning and underdrinking in molar nondepriving schedules.

In two experiments we tested the molar regulation prediction that animals adjust schedule performance to reduce deviations from baseline response totals. Both experiments constrained the baseline drink-burst length under molar nondepriving schedules but allowed rats to continue running without drinking. In Experiment 1, rats were required to run in order to drink. In Experiment 2, water was delivered independently of running by fixed-time (FT) schedules. Under the run-to-drink contingency, rats exceeded their baseline amounts of running (overrunning) but failed to maintain their baseline water intake (underdrinking). The total amount of running that did not lead to drinking approximated a baseline running. Under the FT schedules, rats again underdrank, but total running approximated baseline. These results do not support previous studies that have shown molar equlibrium effects under nondepriving reciprocal schedules. We conclude that (a) contingent running may not substitute for independent running; (b) intermittent access to water reduces the total instigation for drinking; (c) molar regulation differs under reciprocal and nonreciprocal schedules; and (d) more dynamic, system-specific regulatory models need to be developed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of hysterectomy on sexual receptivity, food intake, running wheel activity, and hypothalamic estrogen and progestin receptors in rats.

Ovariectomized-hysterectomized (OH) CD rats given sequential treatments with 2 μg of estradiol benzoate (EB) and .5 mg of progesterone (P) showed significantly higher lordosis quotients than ovariectomized (OV) Ss in 2 tests, 1 and 2 wks after surgery. To test whether the effects of hysterectomy persist, 3 groups of OV and OH Ss received weekly injections of EB, EB?+?P, or sesame oil for 4 wks, were given 2 μg of EB followed 24 hrs later by .5 mg of P, and tested for receptivity. Only the OH Ss that had received hormones for 4 wks showed a significantly higher lordosis score than OV Ss. The effects of hysterectomy on food intake, weight gain, and running wheel activity were also tested. After 1 wk of 2 μg/day EB, OH Ss lost significantly more weight and consumed less food than OV Ss, but by 2 wks the effects of hysterectomy were no longer evident. Treatment with .5 μg/day EB resulted in a significant loss in weight and food intake in OH Ss throughout the experiment. OH Ss implanted with Silastic capsules containing EB were significantly more active in running wheels than OV Ss over the 1st 9 days, but by Day 23 the activity of both groups was similar. 24 hrs following a single injection of EB, hypothalamic-preoptic area cell nuclear estrogen receptors and cytoplasmic progestin receptors were significantly higher in OH than in OV Ss. Possible mechanisms by which hysterectomy might act to enhance hormone-dependent behaviors are discussed. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Tolerance pattern of the anorexigenic action of amphetamines, fenfluramine, phenmetrazine and diethylpropion in rats

The tolerance pattern to anorectic drugs was studied in starved rats by measuring two consecutive 2 h food intakes. 2 There was a reduction in the first 2 h food intake with development of complete tolerance after fenfluramine and phenmetrazine, and of partial tolerance after amphetamine, (+)-amphetamine and diethylpropion. 3 During the second 2 h intake, the anorectic effect was transient after fenfluramine and diethylpropion; while there was an absolute increase in the intake after amphetamine and (+)-amphetamine. 4 A pair-feeding experiment revealed that the increase in the second 2 h food intake was not a direct effect of the drug but a consequence of the deficit in food intake during the preceding 2 hours. 5 There was an overall correlation between the food and water intake. 6 A significant loss in body weight was observed after amphetamine, fenfluramine and phenmetrazine but not after (+)-amphetamine or diethylpropion. 7 The results indicate that so-called tolerance to the anorexigenic effect of drugs is apparent rather than real and that the duration of food access is a determining factor. The body weight changes may be brought about by the metabolic effects of these drugs rather than their effect on food and water intake.     

Water intake induced by spaced deliveries of salted and sweetened liquid food

The water intake of food-deprived rats was evaluated under conditions where liquid food was presented occasionally. In the first experiment, when soybean milk alone was presented every 30 sec, little water was consumed. However, when sodium chloride was added to the soybean milk, water intake increased directly with salt concentration from 0.9 to 14.4%. At salt concentrations of 7.2 and 14.4%, the drinking induced by soybean milk resembled in several respects the adjunctive drinking educed by spaced presentations of dry food. In a second experiment, adulterating soybean milk with sugar in concentrations of 7 to 56% did not affect water intake significantly when the food was delivered every 30 seconds. These findings extend the range of conditions known to generate schedule-induced drinking, and point out a previously unknown constraint on the phenomenon.     

Four-week ethanol intake decreases food intake and body weight but does not affect plasma leptin, corticosterone, and insulin levels in pubertal rats

Long-term intake of ethanol decreases food intake and inhibits growth in experimental rats. The aim of this study was to determine the effect of 4-week oral ethanol ingestion on plasma leptin and adrenal function. Male 45-day-old Wistar rats were divided into three groups: absolute control (AC), ethanol (E) administered 10% (wt/vol) ethanol instead of tap water, and pair-fed (PF) given an amount of food corresponding to the food intake of E animals. E rats consumed less pelleted diet (74% cumulative total intake); however, this caloric deficit was compensated by ethanol ingestion. Net water intake in E animals was 76% of that in the control groups. The body growth of both E and PF rats was stunted compared with AC animals, but E rats were heavier than PF rats. The plasma leptin level was similar in E and AC and decreased in PF animals. There were no differences in plasma osmolality or glycemia among the three groups. Plasma insulin was decreased in PF compared with both AC and E rats. Plasma corticosterone was not affected by ethanol, but was increased in the food-restricted (PF) group. Although there were no differences in basal adrenal corticosterone production in vitro, there was a slightly higher response to corticotropin (ACTH) in E rats. We conclude that drinking 10% ethanol decreased the dietary intake and body growth. These changes were not mediated by plasma leptin changes. Although alcohol ingestion and its energy content theoretically normalized the total energy intake and prevented the decrease of plasma leptin, the growth of young rats was inhibited. Drinking 10% ethanol instead of tap water for 4 weeks did not stimulate basal adrenal activity.     

Chronic morphine treatment exaggerates the suppressive effects of sucrose and cocaine, but not lithium chloride, on saccharin intake in Sprague-Dawley rats.

Three experiments examined the effect of chronic morphine treatment on cocaine-, sucrose-, and lithium chloride (LiCl)-induced suppression of saccharin intake in Sprague-Dawley rats. All rats were either water- or food-deprived and then implanted subcutaneously with 1 morphine (75 mg) or vehicle pellet for 5 days. They were then given brief access to 0.15% saccharin and soon thereafter injected with either cocaine (10 mg/kg sc) LiCl (0.009 M, 1.33 ml/100 g body weight ip), or saline, or in Exp 2, given a 2nd access period to either a preferred 1.0 M sucrose solution ot the same 0.15% saccharin solution. There was 1 taste–drug or taste–taste paring per day for a number of days. The results showed that a history of chronic morphine treatment exaggerated the suppressive effects of a rewarding sucrose solution and cocaine but not those of the aversive agent, LiCl. These data provide further support for the reward compairison hypothesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sodium appetite in lactating rats.

Lactating rats that were given free access to sodium-deficient food, water, and 0.51 M NaCl solution showed no evidence of sodium appetite. The estimated daily loss of 1–2 mEq Na in milk was replaced by basal daily intake of 2–5 ml of saline. Sodium loss in urine was minimal, but milk sodium concentration was unchanged, and pups grew normally. Saline intake was enhanced when lactating rats that had been maintained on standard laboratory chow were injected with 30% polyethylene glycol solution to reduce plasma volume but no more so than when virgin female rats or male rats were similarly colloid-treated. Lactating rats markedly increased their intake of NaCl solution after simply depriving them of dietary sodium for 4 days, whereas male and virgin female rats did not. These findings indicate that pronounced sodium appetite does not invariably accompany lactation in rats, although it can occur whenever such animals become hypovolemic or sodium deficient. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dehydroepiandrosterone-sulfate (DHEAS) reduces adipocyte hyperplasia associated with feeding rats a high-fat diet

OBJECTIVE: To determine if chronic administration of a low level of dehydroepiandrosterone-sulfate (DHEAS) (10 micrograms/ml drinking water) attenuates adiposity in male Osborne-Mendel rats fed low-fat (11% of kcals) vs high fat (46% of kcals) diets. DESIGN: Rats were randomly assigned to one of four treatment groups for 6 wk in this 2 x 2 factorial study. The main effects tested were diet (low vs high fat) and DHEAS (- or +). SUBJECTS: Male Osborne-Mendel rats (initial body wt approximately 265 g). MEASUREMENTS: Adipocyte mass, size and number from two major fat depots (retroperitoneal, epididymal); mass of one subcutaneous adipose depot (inguinal); serum levels of triglycerides, insulin, glucose and DHEAS; brown adipose tissue (BAT) mass; body weight gain, food and water consumption, and residual carcass composition. RESULTS: DHEAS treatment had no effect on weight gain, food consumption or water intake. DHEAS-treated rats fed the high-fat diet had smaller fat pads containing fewer adipocytes and less carcass lipid than the non DHEAS-treated rats fed the high-fat diet. In contrast, DHEAS-treated rats fed the low-fat diet had similar levels of adipose tissue mass and cellularity compared to control animals fed the low-fat diet. CONCLUSION: Administration of a low dose of DHEAS (10 micrograms/ml or 0.8 mg/kg body wt/d) in the drinking water of young male Osborne-Mendel rats fed a high-fat diet for 6 wk reduced carcass lipid, fat depot mass and retroperitoneal and epididymal adipocyte number compared to their high-fat-fed cohorts. In this study, the antiobesity effects of DHEAS were specific to the level of dietary fat used.     

Effects of "anorexia" in appetitive and consummatory behavior.

To assess the effects of anorexigenic agents on appetitive and consummatory behavior, rats were given sweetened milk either in a bottle or by infusion through an intraoral cannula. In the first experiment, amphetamine (AMP; 0, 0.25, 0.5, and 1 mg/kg) had no effect on the intake of cannula-fed rats but suppressed the intake of bottle-fed rats at the highest two doses. Although increased activity was observed at the highest dose, bottle-fed rats drank less than cannula-fed rats at each dose of the drug. Fenfluramine (FEN; 0, 2.5, 5, and 10 mg/kg) produced a dose-dependent decrease in intake with both methods of feeding, but the effect was greater in bottle-fed rats. Although FEN had marked sedative effects at the highest two doses, bottle-fed rats drank less than cannula-fed rats at each dose of the drug. In a second experiment, cannula- and bottle-fed rats were given milk adulterated with various concentrations of quinine hydrochloride (QHCl; 0, 0.0025, 0.005, and 0.02%). QHCl had no effect on the intake of cannula-fed rats but decreased the intake of bottle-fed rats at the highest two concentrations. In a final experiment, the effect of AMP (1 mg/kg) was assessed in a conditioned aversion paradigm. Rats were given four conditioning trials in which access to a 0.1% sodium saccharin solution was followed by an injection of AMP. Again, bottle-fed rats showed greater suppression of intake than cannula-fed rats. Taken together, these results demonstrate that anorexigenic drugs affect appetitive behavior more than consummatory behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)