Effects of food deprivation on etonitazene consumption in rats

The Effect of Short-term Food Deprivation on the Reinforcing Value of Coffee in Bulimic and Control Women

The effect of short-term food deprivation on the reinforcing value of coffee was examined, utilising behavioural choice methodology. Four women with bulimia nervosa and six healthy controls underwent one food-deprivation day (19 hours) and one nondeprivation day. Subjects made significantly more attempts to earn coffee, earned more points toward coffee, and drank more grams of coffee when food deprived than when nondeprived. The effect was observed in both bulimic and control women. There was a significant diagnosis-by-deprivation interaction with reference to grams of coffee consumed, with bulimic women consuming over twice as much coffee when deprived than nondeprived. The results are discussed with reference to the role of food deprivation in the pathogenesis of substance abuse.

Underweight rats have enhanced dopamine release and blunted acetylcholine response in the nucleus accumbens while bingeing on sucrose

The present study tested whether rats release more accumbens dopamine (DA) during a sugar binge when they are underweight vs. normal weight. Since acetylcholine (ACh) in the nucleus accumbens (NAc) normally increases as a meal progresses and satiety ensues, we also tested whether ACh release is altered when an animal has lost weight. Rats were maintained on daily 8-h access to chow, with 10% sucrose solution available for the first 2 h. Microdialysis performed on day 21, at normal body weight, revealed an increase in extracellular DA to 122% of baseline in response to drinking sucrose. Extracellular ACh peaked at the end of the meal. Next, the rats were food and sucrose restricted so that by day 28 they were at 85% body weight. When retested, these animals released significantly more DA when drinking sucrose (179%), but ACh release failed to rise. A control group was tested in the same manner but given sugar only on days 1, 21 and 28. At normal body weight, control animals showed a non-significant rise in DA when drinking sucrose on day 21. On day 28, at 85% body weight, the controls showed a small increase (124%) in DA release; however, this was significantly lower than the 179% observed in the underweight rats with daily sugar access. These findings suggest that when an animal binges on sugar and then loses weight, the binge releases significantly more DA and less ACh than when animals are at a normal body weight.

A comparison of the effects of different operant training experiences and dietary restriction on the reinstatement of cocaine-seeking in rats

Studies on the reinstatement of drug-seeking after withdrawal from chronic drug self-administration have varied in terms of the procedures by which animals are initially trained to self-administer the drug. The current study directly compared whether prior operant training for food pellet reinforcement and/or maintained dietary restriction significantly altered the reinstatement of extinguished cocaine-seeking in the presence of cocaine-paired cues, a priming injection of cocaine (10 mg/kg; i.p.), and the pharmacological stressor, yohimbine (1.25 or 2.5 mg/kg, i.p.). Male Long Evans rats were divided into four groups as follows: a) trained to lever press for food pellets prior to cocaine self-administration and then maintained on a restricted diet, b) trained to lever press for food pellets prior to cocaine self-administration and then placed on an ad libitum diet, c) untrained and maintained on a restricted diet, or d) untrained and placed on ad libitum feeding. All rats readily self-administered cocaine (0.2 mg/50 mul/infusion) and were subsequently extinguished in the absence of cocaine or previously cocaine-paired cues (light+tone). Following extinction, rats experienced cue-, cocaine-, and yohimbine-induced reinstatement testing. No significant differences were seen between groups for lever responding during the maintenance phase and during extinction. Likewise, reinstatement of cocaine-seeking did not vary across groups for cue-, cocaine-, or yohimbine-induced reinstatement. Under these specific parameters, operant training prior to cocaine self-administration and/or dietary restriction do not significantly alter reinstatement of cocaine-seeking. The results arguably support the approach of not using prior lever training with a non-drug reinforcer and to limit the use of dietary restriction only to the acquisition phase of drug self-administration.

Food and cocaine self-administration by baboons: effects of alternatives

The effects of the availability of an alternative reinforcer on responding maintained by food pellets or drug solutions were examined in 8 adult male baboons (Papio hamadrayas anubis). During daily 23-hr experimental sessions, baboons had access to both food pellets and fluid under a two-choice procedure, in which the response requirement, under a fixed-ratio schedule, differed for the two commodities. There were no restrictions on access to water, which was continuously available from a spout at the rear of each cage. In Experiment 1, the fixed-ratio requirement, or cost, for fluid delivery remained constant while the fixed-ratio requirement for pellets was changed every 2 or 3 days when (a) no fluid, (b) a dilute dextrose vehicle, (c) 0.008 mg/kg per delivery cocaine, (d) 0.016 mg/kg per delivery cocaine, or (e) 0.032 mg/kg per delivery cocaine was available concurrently. In Experiment 1, progressively increasing the response requirement for pellets decreased pellet intake, but for 4 baboons pellet intake at maximum pellet cost was lower when cocaine, compared to the vehicle, was available. Increasing the response requirement for pellets had variable effects on vehicle intake. However, increasing the response requirement for pellets increased intake of at least one dose of cocaine to a greater extent than vehicle in all 8 baboons. Thus, cocaine could be considered a more effective economic substitute than vehicle for pellets. Experiment 2 systematically varied the order in which the response requirements for a pellet delivery were presented and added a control condition in which cocaine doses, yoked to the amount self-administered, were given three times during the session by the experimenter. Again, pellet intake at maximal pellet cost was lower when cocaine, compared to the vehicle, was available. In contrast, experimenter-given cocaine doses did not alter responding maintained by pellets. Thus, the effects of self-administered cocaine on responding maintained by food pellets differed from the effects of experimenter-given cocaine on responding maintained by food pellets.

Ethanol and food pellet self-administration by baboons

During daily 23-h sessions, baboons had concurrent access to food pellets and an oral ethanol/dextrose solution. The effect of increasing the fixed-ratio or "cost" for pellets on pellet and fluid intake was examined when baboons had access to 2%, 4%, or 8% (w/v) ethanol. Increasing the response requirement for a pellet decreased pellet intake. The rate of decrease in pellet intake with increasing pellet cost was unaffected by the availability of ethanol solutions, which were either self-administered or given in investigator-planned doses. Increasing the response cost for pellets significantly increased self-administration of 4% ethanol. The effect of increasing the cost for fluid on fluid and pellet intake was examined when baboons had access to vehicle, 4% or 8% (w/v) ethanol. Although the total daily number of fluid deliveries was significantly greater when 4% ethanol was available, compared to vehicle, increasing the cost for a fluid delivery to 32 responses and above decreased intake of all three fluids similarly. Increasing the cost of ethanol did not affect food intake.

Lever-press responding maintained by contingent intraperitoneal administration of etonitazene in Long Evans hooded rats

Lever pressing maintained by intraperitoneal (i.p.) injections of etonitazene was established in five Long Evans hooded rats. Each training session consisted of an 8-min fixed interval (FI) during which lever pressing was maintained by food pellets delivered at the end of the interval. Food delivery was accompanied by illumination of stimulus lights in the chamber. Every 20th response during the 8 min interval also produced a brief illumination of the stimulus lights (FI 8 min (FR 20:S)). Administration of etonitazene was then introduced. Immediately following food delivery, the rat received an i.p. drug injection and was returned to the operant chamber for 30 min. During this confinement, the stimulus lights remained illuminated. This procedure resembles conditioned place preference in that an environment is paired with the effects of an investigator-delivered drug. When food pellet delivery subsequently was discontinued, responding persisted when followed by drug, but not saline, administration. Alternating blocks of sessions with administration of etonitazene (6.0-9.0 microg/kg) or saline produced corresponding increases or decreases in responding. These results indicate that etonitazene can function as a reinforcer when administered to rats by the i.p. route, and thus extend the range of conditions under which drug reinforcement can be investigated.

Food and amphetamine self-administration by baboons: effects of alternatives

The effects of the availability of an alternative reinforcer on responding maintained by food pellets or fluid solutions were examined in 6 adult male baboons (Papio cynocephalus anubis). During daily 23-hr experimental sessions, baboons had concurrent access to both food pellets and fluid, with responding maintained under fixed-ratio schedules of reinforcement that varied between the two commodities. The fixed-ratio requirement, or cost, for pellets was increased when (a) no fluid, (b) a dilute dextrose vehicle, (c) 0.002 mg/kg d-amphetamine, or (d) 0.004 mg/kg d-amphetamine was available. When given nonrestricted concurrent access to food pellets and amphetamine at minimal cost (FR 2), baboons self-administered sufficient amphetamine to decrease pellet intake. Increasing the response requirement for pellets decreased pellet intake at a similar rate regardless of the available fluid and increased fluid intake in a variable manner among baboons such that there were no statistically significant increases in fluid intake. In contrast, when access to pellets was restricted to 70% of maximal intake under nonrestricted conditions, increasing pellet cost decreased pellet intake and increased fluid intake more rapidly when the high amphetamine dose was available. Thus, amphetamine was more effective as an economic substitute for pellets when access to pellets was restricted. The response cost for vehicle and both amphetamine concentrations was increased when baboons had nonrestricted and restricted access to pellets. Increasing the response requirement for fluid delivery decreased intake of all three fluids similarly under both pellet-access conditions. The results indicate that substitution between commodities with minimal commonalities can be studied under controlled laboratory conditions and is dependent upon reinforcement schedule and commodity restrictions.

Ethanol and cocaine intake by rats selectively bred for oral opioid acceptance

Lines which accept or reject the potent opioid etonitazene, and a randomly bred control line, were assessed for the specificity of selective breeding. Drug-naive subjects from generation 8 were offered a continuous choice between water and 10% ethanol for 20 days. There was no difference between the accepting and rejecting lines in preference for one fluid, or in amount of ethanol consumed. The same rats were then given a choice between water and increasing concentrations (0.08-0.64 mg/ml) of cocaine, 7 days at each concentration. There were no differences among the lines in preference for the drug, but the rejecting line drank more of the cocaine solution than the accepting line. Finally, these rats were subjected to the regimen used in choosing rats for selective breeding, 4 days of a water-etonitazene choice. In their preference for etonitazene the order of the lines was as expected: accepting > control > rejecting. In addition, the accepting line drank more of the etonitazene solution than the other two lines. These data suggest that selection has been rather specific and not for a generalized tendency to become intoxicated.

Intake of dietary sucrose or fat reduces amphetamine drinking in rats

The effects of intake of a palatable food source on oral amphetamine intake were assessed in adult male Long-Evans rats. In Experiment 1, six rats were given an amphetamine sulfate solution (0.1 mg/ml) and four rats were given water as their sole source of fluid. Rats were given a choice of chow and granulated sucrose for a week, alternated with weeks when only chow was fed. In Experiment 2, eight rats were given the amphetamine solution, and four rats water to drink. Rats were fed chow and hydrogenated vegetable fat for a week alternated with weeks when only chow was available. In both experiments, rats drank significantly less of the amphetamine solution when the palatable food choice was available than when given only chow to eat. Intake of palatable foods had a significantly smaller effect on water intake. In both experiments, rats drinking the amphetamine solution took in less fluid and less calories and gained less weight than rats drinking water. However, in Experiment 1, when sucrose was available, rats drinking amphetamine consumed a significantly greater proportion of their calories as sucrose than rats drinking water. Similarly, in Experiment 2, rats drinking the amphetamine solution chose a significantly greater percentage of their calories as fat than rats drinking water. These results demonstrate that intake of sucrose or fat leads to a significant reduction in amphetamine intake, and that the anorectic effects of amphetamine are not equivalent for different types of foods.

Food deprivation affects extinction and reinstatement of responding in rats

Food deprivation has been shown to increase the self-administration of a wide variety of drugs in a number of different species. However, the effects of food deprivation on other phases of drug taking have not been established. The purpose of the present study was to evaluate the effects of food deprivation on reinstatement of responding for cocaine. Rats trained to self-administer 0.2, 0.4, or 1.0 mg/kg cocaine intravenously (IV) under a fixed-ratio 1 schedule for the first 2 h during daily 7-h sessions were fed either before or after the experimental session. During hours 3-7, rats self-administered saline. Saline replaced cocaine in the infusion pumps at the beginning of hour 3 and a priming injection of either saline or cocaine (0.32, 1.0, or 3.2 mg/kg IV) was administered at the beginning of hour 4. The number of infusions that was self-administered was measured throughout the 7-h session. During hours 1 and 2 when cocaine was available, the number of infusions was inversely related to cocaine dose. During hour 3, rats typically self-administered several infusions of saline, which gradually decreased to near-zero levels by hours 4-7 (extinction responding). A priming injection of cocaine administered at the beginning of hour 4 reinstated responding in a dose-related manner. The magnitude of extinction responding during hour 3 and reinstatement of responding during hour 4 were similar regardless of cocaine maintenance dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise attenuates oral intake of amphetamine in rats

The effects of wheel running on oral intake of amphetamine were examined in six male Sprague-Dawley rats given a 0.075-mg/ml amphetamine sulfate solution as their sole source of liquid, six rats given a 0.15-mg/ml amphetamine solution, and four rats given water as their sole source of liquid. All animals were housed in Wahmann running wheels and adjoining cages, and had ad lib access to ground Purina Chow. For the first 7 days of the experiment, the doors to the running wheels were closed; the wheels were then opened for 6 days. This cycle was repeated a second time. Animals drinking the 0.15-mg/ml amphetamine solution consumed significantly less food and gained less weight than animals in the other two groups. Although there was no difference in food intake between rats drinking water and rats drinking the 0.075-mg/ml amphetamine solution, rats in the water group gained significantly more weight than rats in the 0.075-mg/ml amphetamine group. With respect to drug intake, rats consumed significantly less amphetamine when running in the wheels than when access to the wheels was prohibited. Access to running wheels did not alter water intake. These latter results suggest that drug intake can be reduced by the provision of an alternate behavior.

Cocaine's effects on food-reinforced pecking in pigeons depend on food-deprivation level

Four pigeons deprived to 80% of their laboratory free-feeding weights pecked keys under a multiple fixed-ratio 30 fixed-interval 5-min schedule of food presentation. Components alternated strictly with 15-s timeouts separating them; each was presented six times. When rates of pecking were stable, 2 pigeons' weights were reduced to 70%, and the other 2 pigeons' weights were increased to 82.5% to 85% of free-feeding levels. Cocaine (1.0, 3.0, 5.6, and 10.0 mg/kg and saline) was administered 5 min prior to sessions. When each dose had been tested twice, pigeons' weights were adjusted to the level that they had not yet experienced, and cocaine was tested again. Cocaine reduced response rates in a dose-dependent manner under the fixed-ratio schedule and under the fixed-interval schedule at high doses, and increased rates under the fixed-interval schedule at low low doses. Reductions in pecking rates occurred at lower doses under both schedules in 3 of 4 pigeons when they were less food deprived compared to when they were more food deprived. Low doses of cocaine increased low baseline rates of pecking in the initial portions of the fixed-interval schedules by a greater magnitude when pigeons were more food deprived. Thus, food-deprivation levels altered both the rate-decreasing and rate-increasing effects of cocaine. The implications of these results for the mechanisms by which food deprivation increases cocaine self-administration and for the dependence of cocaine's effects on the baseline strength of operant behavior are discussed.

Effects of food deprivation on cocaine base smoking in rhesus monkeys

Studies have shown that both food deprivation and response cost have important influences on the magnitude of self-administration of a wide variety of psychoactive drugs. In an attempt to extend these findings to the smoked route of drug self-administration, the effects of food allotment and fixed-ratio (FR) value were evaluated in four male rhesus monkeys trained to smoke cocaine base. In the first phase of the experiment, monkeys were trained to self-administer experiment, monkeys were trained to self-administer smoked cocaine base under a chained progressive-ratio (PR), fixed-ratio (FR) schedule during daily experimental sessions. Monkeys were required to make 20 lever-press responses and then five inhalations on a smoking spout to obtain the first smoke delivery. The lever ratio than increased to 60, 140, 300, 620, 1260, 2540, and 4940 for each successive smoke delivery. The initial lever ratio value was reset to 20 at the beginning of each daily session. The body weights of three monkeys were determined under free-feeding conditions. Monkeys were then restricted to 100 g food and, when body weights had stabilized, the daily food allotment was increased to 150 g, approximately 210 g, or greater than 400 g (satiation). As the daily food allotment and body weight increased, the mean number of smoke deliveries decreased in two of three monkeys. In the second phase of the experiment, three monkeys were maintained under either food-satiated or food-restricted conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of food deprivation on the reinforcing value of food and smoking in bulimic and control women

The reinforcing value of both food and cigarettes was examined in female smokers with and without bulimia nervosa. Subjects underwent two food-deprivation (18 h) and two nondeprivation conditions and worked for either food vs. money or cigarettes vs. money on concurrent progressive variable ratio schedules. Schedules for food/cigarettes increased progressively while schedules for money remained the same. Results indicated no differences in the amount of time subjects spent working for food or the number of points earned for food in either bulimics or controls when examining the entire eight-game trial. Results of the initial two-game trial indicated marked differences, with the reinforcing value of food increasing after deprivation in control but not bulimic women and the total amount of time spent working for cigarettes increased after deprivation in controls. These results highlight that the effects of experimental food deprivation are most salient immediately after the deprivation and at low unit prices, and that bulimic and control women respond differently to a food-deprivation paradigm.

The effect of food deprivation on alcohol consumption in bulimic and control women

The effect of food deprivation on alcohol self-administration was examined in five women with bulimia nervosa and five healthy controls in a semi-naturalistic experimental design. In this within-subjects study, each individual underwent two food-deprived and two non-deprived sessions. The deprivation condition consisted of no food or caloric beverages for 19 hours prior to the experimental procedure. On each of the 4 days, subjects watched a 2-hour segment of an epic movie and were permitted to drink ad libitum. No differences were observed in the number of grams of alcohol consumed under deprived and non-deprived conditions for either group. Breath alcohol levels were significantly higher under the non-deprived condition despite equivalent amounts of alcohol consumed and similar ratings of the subjective sense of tipsiness. Bulimic women consumed equivalent calories due to alcohol as control women but significantly fewer calories due to non-alcoholic beverages. These results do not support the hypothesis that food deprivation leads to increased self-administration of alcohol in women.

Etonitazene delivered orally serves as a reinforcer for Lewis but not Fischer 344 rats

Oral etonitazene self-administration was systematically investigated in two inbred strains of rats, Lewis (LEW) and Fischer 344 (F344). For LEW rats, etonitazene maintained higher rates of lever pressing and was consumed in larger volumes than the water vehicle when the reinforcement schedule was fixed ratio (FR) 8. In contrast, with F344 rats responding did not systematically exceed water values at any etonitazene concentration. LEW rats also drank substantially more etonitazene than F344 rats, and at FR 8 only LEW rats showed the typical inverted U-shaped function between etonitazene concentration and number of responses. For the LEW strain, response rate increased as FR size increased from FR 1 to FR 2 and FR 4, but decreased at FR 8. For the F344 strain, as FR size increased response rate showed small increases, but the response rates were far lower than those of the LEW strain. The results support the conclusion that etonitazene was an effective reinforcer for LEW but not F344 rats. These findings demonstrate genetic differences in opioid reinforcement of operant behavior and indicate that genotype can be an important determinant of whether etonitazene serves as a reinforcer.

Effects of fasting on responses to intravenous fentanyl in healthy volunteers

The effects of food deprivation on the subjective, psychomotor, and physiological responses to intravenous fentanyl (50 micrograms/70 kg) were studied in 6 healthy male volunteers. A randomized, placebo-controlled, crossover design was used in which subjects were injected with fentanyl or saline after either 2, 12, or 24 hours of fasting. Subjects completed several subjective effects questionnaires as well as psychomotor tasks prior to, and at regular intervals, following the intravenous injection for a 3-hour period. An observer-rated behavioral checklist was completed at regular intervals during the session and several physiological measures (including measurement of pupil size) were recorded. Fentanyl induced opiate-like mood changes, miosis (pupil constriction), and impairment of extraocular muscle control, and 4 of the 6 subjects reported liking the effects; however, fasting had no impact on any of fentanyl's effects. We conclude that food deprivation up to 24 hours does not alter the subjective, psychomotor, or physiological response to the opiate, fentanyl.

The relationship of eating disorders and substance abuse

Initial interest in the relationship between eating disorders, which occur primarily in women, and substance abuse, which is much more frequent in men than women, stemmed from the observations of Crisp (1968) who noted that chronic anorexics who developed bulimic behavior often abused alcohol. More recently, cross-sectional studies of women with eating disorders have documented prevalences of alcohol and other substance abuse in these women that are much higher than those reported in the general female population. Conversely, women with substance abuse disorders report eating-disordered behavior more often than the general population. This article first presents a definition of eating disorders and then addresses (1) the rate of coprevalence of eating disorders and substance abuse; (2) the mechanism of the coprevalence of these disorders; (3) the clinical similarities of these disorders; and (4) future directions.

Dietary modulation of the anorectic potency of amphetamine

The effects of intake of an amphetamine solution on food and fluid intakes, body weight (b.wt.) and feed efficiency (FE) were examined in rats fed either a high-carbohydrate (HC) (65% of total calories) or high-fat (HF) (65% of total calories) diet. During a 17-day predrug period, neither caloric intake, fluid intake, b.wt. nor feed efficiency (FE) differed as a function of diet. When given a 0.1 mg/ml amphetamine sulfate (AMPH) solution as their sole source of fluid, rats in both diet groups decreased fluid intake by an equivalent amount. While diet did not influence AMPH intake, it did alter the drug's effects on caloric intake, b.wt. and FE. In both diet groups, rats drinking AMPH decreased caloric intake, b.wt. gain and FE relative to rats which drank water. However, rats fed the HC diet decreased caloric intake less, but lost more weight than rats fed the HF diet. Further, rats fed the HC diet displayed a rapid tolerance to the anorectic effects of AMPH, with no tolerance to the drug's effect on b.wt. In contrast, rats fed the HF diet suppressed caloric intake throughout the drug period, but weighed more than rats fed the HC diet. Thus, when drinking the AMPH solution, FE of rats fed the HC diet was significantly lower than that of rats fed the HF diet. When the drug was removed, rats eating the HC diet failed to alter caloric intake and b.wt. In contrast, rats fed the HF diet increased caloric intake and gained weight. These data indicate that dietary factors must be considered when evaluating the anorectic actions of psychopharmacological agents.

Effects of food deprivation on subjective responses to d-amphetamine in humans

The effects of 24 hours of food deprivation on the subjective response to 10 mg oral d-amphetamine were studied in 12 healthy normal volunteers. A within-subjects design was used in which subjects ingested amphetamine and placebo capsules in both a fed and a fasting state. Each of the four experimental conditions-FED/DRUG, FED/PLACEBO, FAST/DRUG, FAST/PLACEBO--was enacted twice according to a randomized block design. Three subjective effects questionnaires, the Profile of Mood States, the Addiction Research Center Inventory, and the Visual Analogue Scale, were completed prior to and 1, 3 and 6 hr after the early morning capsule ingestion. Typical elevations in such subjective effects as elation and vigor were obtained after amphetamine ingestion in both feeding conditions, but fasting neither potentiated nor attenuated the drug response. Subjects at the end of the session, however, were more likely in the FAST/DRUG condition than in the FED/DRUG condition to label the capsule they had ingested at the beginning of the session as a stimulant.

Taste vs. CNS effects in voluntary oral opiate intake: studies with a novel device and technique

An apparatus is described which negates the influence of rats' position preferences by presenting alternative solutions at the same location. The licks for both solutions were monitored over consecutive short intervals by lick detectors with computer capture of data. Rats given a choice between water and dilute solutions of the high-potency opiates etonitazene (1.0-5.0 micrograms/ml) or fentanyl (10-50 microgram/ml) either licked equally for the two solutions, or gradually developed a preference or aversion regarding the opiate over the course of several days. In contrast, preferential licking for solutions with a definite taste, saccharin or quinine, was established in hours. These data indicate that the taste per se of these opiates is not aversive to rats, and that preferences for or aversions to the opiates have some other base, presumably one or more actions on the central nervous system.

Oral pentobarbital intake in rhesus monkeys: effects of drug concentration under conditions of food deprivation and satiation

Pentobarbital-reinforced behavior was studied in four rhesus monkeys. A pentobarbital solution and water were concurrently available during 3-hr sessions; water was freely available between sessions. Both pentobarbital concentration and feeding conditions (deprivation versus satiation) were varied. In two food-restricted monkeys subsequent food satiation eliminated pentobarbital-maintained responding. In two other food-restricted monkeys the effects of food satiation varied with the drug concentration. At the highest concentration, 4 mg/ml, food satiation did not alter responding, whereas at 2 mg/ml a moderate decrease occurred and at 1 mg/ml responding was greatly reduced. During the food satiation phase, when the concentration was 4 mg/ml, responding was well maintained under several fixed-ratio sizes. Large quantities of pentobarbital were consumed, and intoxication was observed. Water-maintained responding occurred at low rates and did not vary across feeding conditions or drug concentration. The results support an interpretation in terms of a behavioral mechanism of action. Specifically, the effects of food deprivation on drug self-administration are to increase the magnitude of the reinforcing effects of the drug.

Dietary modulation of oral amphetamine intake in rats

The interaction of sucrose availability and oral self-administration of amphetamine was examined in 23 male Sprague-Dawley rats. Fourteen rats were given a 0.075 mg/ml amphetamine sulfate solution as their sole source of fluid and 9 rats were given water. Feeding conditions were alternated between weeks with both granulated sucrose and chow available and weeks with only chow present. Rats drank significantly less of the amphetamine solution when consuming sucrose and chow than when eating chow alone. Sucrose intake had a slight effect on water intake. Rats drinking the amphetamine solution consumed significantly less food, gained significantly less weight, and were significantly less efficient at using calories for weight gain than rats drinking water. However, when given access to sucrose, rats drinking the amphetamine solution chose a significantly greater proportion of their daily caloric intake as sucrose (60%) than rats drinking water (42.5%). The present results demonstrate that 1) amphetamine intake alters nutrient choice and 2) that dietary variables can profoundly affect drug self-administration.

Effects of food deprivation on caffeine consumption in male and female rats

The effect of food deprivation on caffeine consumption was investigated in male and female rats utilizing two-bottle preference tests. During ad lib food and water access, proportional consumption of six increasingly concentrated caffeine solutions (0.01-0.125%) steadily declined as concentration increased with no sex differences. Across concentrations, females tended to ingest more mg/kg caffeine than males. Food deprivation increased both proportional and mg/kg caffeine consumption in both sexes. When returned to ad lib food, proportional, but not mg/kg, caffeine consumption returned to pre-deprivation levels. Consumption of a quinine solution (0.02%), comparable to the caffeine in two-bottle preference, declined somewhat during food deprivation. These results indicate that caffeine preference and mg/kg consumption are increased by food deprivation and that this effect does not result from increased preference for bitter tastes per se. Rather, the results suggest that increased caffeine intake during food deprivation is due to a specific interaction between reduced body weight and the drug. The results also suggest that the deprivation effect is somewhat weaker in females than males, perhaps due to sex differences in reactivity to caffeine.

Food deprivation reveals strain differences in opiate intake of Sprague-Dawley and Wistar rats

Two groups of naive, male, albino rats derived from different genetic strains (Sprague-Dawley and Wistar) were given a 5 micrograms/ml etonitazene solution as their only available liquid. Liquid intake and body weights were recorded every 24 hr. Etonitazene intake was compared to baseline water intake, and drug intake was then compared when the rats were food deprived (25 sessions) and food satiated (24 sessions). Both groups drank similar amounts of water and etonitazene during the initial food satiation phase, although drug intake was slightly below water intake. When they were food deprived, the Wistar group's mean etonitazene intake almost doubled, while the Sprague-Dawley group's drug intake decreased by nearly 50%. The etonitazene intake in the Sprague-Dawley group never exceeded that of the vehicle, water; thus, it appeared that the drug was not functioning as a reinforcer. Food deprivation increased etonitazene intake above water levels in the Wistar group, indicating that the drug was serving as a reinforcer. Both groups showed similar drug effects during food deprivation, such as erratic drinking patterns, self-mutilation and other forms of stereotypy. Thus, both strains were sensitive to etonitazene's effects; they appeared to differ only with respect to the reinforcing effects. These results suggest that genetically-based differences in the reinforcing effects of drugs may be revealed by food deprivation.

Genetic differences in the establishment of ethanol as a reinforcer

Ethanol, self-administered orally, has been shown to serve as an effective reinforcer in several species. Self-administration studies have also illustrated that ethanol-drinking behavior can be conceptualized as a specific type of operant behavior. The use of inbred and selectively bred animals in other areas of alcohol research has provided valuable information about the contribution of genetic factors to ethanol-related behaviors. Our research was designed to study genetic differences in oral self-administration in the ALKO AA (Alcohol Accepting) and ANA (Alcohol Non-Accepting) rat lines, selected for ethanol preference. Thus, we applied a behavior genetic analysis to aid in determining the contribution of genetic factors to behavior, specifically drug-seeking behavior. The results of our experiments indicate that genetic differences are important factors contributing to the establishment of a drug as a reinforcer. At least in the case of ethanol, the drug did not act as a reinforcer in non-preferring animals. Conversely, in preferring animals, ethanol was readily established as a reinforcer.

Self-administration of low-dose cocaine by rats at reduced and recovered body weight

Food deprivation significantly increases self-administration of cocaine in both rats and rhesus monkeys. The objective in the present investigation was to determine the effects of varying deprivational states on the level of IV low-dose (0.1 mg/kg/infusion) cocaine self-administration in rats. In the first experiment, 32 naive rats were assigned randomly to four equal-sized groups. Two groups self-administered cocaine, the other two saline over two consecutive 10-day phases. Across phase 1 all animals were free-feeding (FF), while in phase 2, one cocaine- and one saline-reinforced group were subjected to restricted feeding until they reached 80% free-feeding weight (FFW). Results showed that cocaine-reinforced responding was related inversely to body weight. In experiment 2 another 32 rats, reduced to 80% FFW, were assigned to four equal-sized groups. Two groups self-administered cocaine, the other two saline over two consecutive 10-day phases. Across phase 1 all animals were maintained at 80% FFW, while in phase 2, one cocaine- and one saline-reinforced group were abruptly food satiated. Findings showed that cocaine-reinforced responding decreased rapidly to low levels. Finally, the group of cocaine-reinforced rats maintained at 80% FFW across both phases of experiment 2 were also abruptly food satiated. Again, responding decreased rapidly to low levels.

Self-administration of orally-delivered methohexital in rhesus monkeys with phencyclidine or pentobarbital histories: effects of food deprivation and satiation

Orally-delivered methohexital was demonstrated to function as a reinforcer for rhesus monkeys with either phencyclidine or pentobarbital self-administration histories. The effects of food deprivation and food satiation were compared across a wide range of methohexital concentrations. Initially, three monkeys were trained to orally self-administer phencyclidine (0.25 mg/ml) and water, and three were trained to orally self-administer pentobarbital (0.5 mg/ml) and water under concurrent fixed-ratio (FR) schedules during daily 3-hr sessions. Liquid deliveries during the session (drug and water) and intersession (water) were contingent upon lip contact responses on solenoid-operated drinking spouts. The monkeys were first tested while food deprived by maintaining them at 85% of their free-feeding body weights. Methohexital concentrations were presented in the following order, and each concentration was held constant until at least five or six sessions of stable behavior were obtained: 2, 2.8, 4, 2 (retest), 1, 0.5, (plus 0.25 and 0.125 in monkey M-W) and 2 (retest) mg/ml. The monkeys were then food satiated by allowing them unlimited access to food, and the methohexital concentration series was repeated. During food deprivation, the concentration-response functions generally resembled an inverted U. Concurrent water-maintained responding was generally low, but it increased in some monkeys as methohexital concentrations increased in some monkeys. During food satiation, methohexital-maintained responding was not different from water-maintained responding in some monkeys, but in others it was substantially higher than water-maintained responding. Maximum drug intake ranged from 20.4 to 93.8 mg/kg during food deprivation and from 6.4 to 64.2 during food satiation among the six monkeys.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of food deprivation on water intake induced by intermittent delivery of salted liquid food

The water intake of rats maintained through food deprivation at 70, 80, 90, and 100% of free-feeding body weights was examined under conditions where a small amount of sweetened condensed milk containing 8% sodium chloride was presented at one-minute intervals. For each of two subjects, number of licks and milliliters of water consumed varied inversely with body weight. This finding agrees with earlier reports concerning the effects of food deprivation on adjunctive behaviors induced by intermittent delivery of dry food.

Animal studies of alcohol intake

Animal studies of alcohol intake can be divided into two groups based on the methodology. General findings of each group will be reviewed especially as they relate to current areas of research interest. Some implications of research findings for theories of alcoholism and drug addiction will be mentioned.

Rapid acquisition of oral phencyclidine self-administration in food-deprived and food-satiated rhesus monkeys: concurrent phencyclidine and water choice

Eight rhesus monkeys were trained to self-administer orally-delivered phencyclidine, with water concurrently available, under a fixed ratio (FR) schedule during daily 3-hr sessions. Liquid deliveries (0.55 ml) were contingent upon lip-contact responses on solenoid-operated drinking spouts. During the sessions, phencyclidine and water were available under FRs ranging from 1 to 16. Water was always available between sessions (FR 1), and food initially was available 24 hr/day. In Experiment 1 the monkeys initially were given access to water (FR 1) during the 3-hr sessions. Subsequently, phencyclidine (0.25 mg/ml) was substituted for water, and the monkeys were reduced to 85 percent of their free-feeding weights. The FR value was then increased from 1 to 8. Next, the monkeys received concurrent access to water from one spout and phencyclidine from the other (each under the FR 8 schedule), then the FR value was increased to 16 for both drug and water. Orally-delivered phencyclidine was rapidly demonstrated to function as a reinforcer (37.2 sessions) without using food to induce drinking. In Experiment 2 a similar procedure was used for another group of monkeys, except the monkeys remained food satiated throughout the acquisition phase. Phencyclidine was rapidly demonstrated to function as a reinforcer (25.9 sessions), although intakes were lower than in Experiment 1. After concurrent phencyclidine- and water-maintained performance stabilized at FR 16, the monkeys were food deprived, and phencyclidine intake increased to the levels reported in Experiment 1. Food deprivation greatly enhanced the reinforcing effect of phencyclidine and changed the temporal pattern of responding, but neither food deprivation nor food-induced drinking were necessary conditions to demonstrate the drug's reinforcing effects.

The effects of food deprivation and satiation on oral pentobarbital self-administration in rhesus monkeys

The effects of food deprivation and satiation on oral pentobarbital self-administration were studied in four rhesus monkeys. Pentobarbital (1.0 mg/ml) or water was available during alternate daily 3-hr session; between sessions, water was freely available. Lip contacts on a drinking spout activated a solenoid operated liquid delivery system. Liquid deliveries (0.56 ml) occurred after a fixed number of lip contact responses were emitted; that is, liquids were delivered according to fixed-ratio (FR) schedules. Under food deprivation conditions, pentobarbital-maintained behavior exceeded water-maintained behavior. Thus, pentobarbital functioned as a reinforcer. Abrupt unlimited access to food resulted in decreased pentobarbital intake. Pentobarbital-maintained behavior increased to previous levels when food intake was again restricted. In a second experiment, the effects of pentobarbital availability on water-maintained behavior were studied. Access to pentobarbital during alternate sessions produced elevated levels of water drinking during intervening sessions. Water drinking decreased to low levels when pentobarbital access was terminated and water was present for consecutive sessions. When pentobarbital was again available during alternate sessions, high levels of water drinking recurred. In the third experiment, water and pentobarbital (1.0 mg/ml) were concurrently available via separate drinking spouts. All three monkeys drank much more pentobarbital solution than water.

Determinants of increased drug self-administration due to food deprivation

Changes in oral etonitazene self-administration were compared in four groups of rats that were maintained at 100, 95, 85, or 75% of their pre-experimental free-feeding body weights. Etonitazene (5 micrograms/ml) or water was available for 16 h according to a fixed-ratio (FR) 1 schedule. Each liquid delivery (0.1 ml) was contingent upon a lever-press response. During food deprivation etonitazene intake gradually increased to over two-fold as body weights decreased over 25 sessions; etonitazene intake was inversely proportional to body weight. The 75% weight group showed stereotypy, self-mutilation and large variability in daily etonitazene intake. In another experiment a range of deprivation conditions was studied in a group of six rats with etonitazene (5 micrograms/ml) or water available on an FR 8 schedule during 1-h sessions. When the rats were gradually food satiated, etonitazene-maintained behavior declined but remained higher than water-maintained behavior; however, when they were abruptly food satiated, etonitazene-maintained behavior decreased to low levels.

Food deprivation increases oral and intravenous drug intake in rats

Rats given continuous access to etonitazene hydrochloride in their drinking water (5 micrograms per milliliter) more than doubled their drug intake while deprived of food. Another group of rats with implanted jugular catheters self-administered etonitazene (10 micrograms per kilogram) intravenously on a continuous reinforcement schedule, and the number of infusions increased significantly on days when they were deprived of food. These results suggest that feeding condition may be a powerful determinant of drug-reinforced behavior.

Ethanol drinking by rhesus monkeys with concurrent access to water

Three monkeys were provided concurrent access to water and ethanol in concentrations of either 8, 16 or 32% (w/v) during daily 3-hr sessions. The monkeys were those for whom ethanol had been established as a reinforcer in an earlier study in which only ethanol or water was available. Ethanol was preferred to water at all concentrations and volume of ethanol consumed was inversely related to ethanol concentration. Quantity of ethanol (g/kg of body wt.) consumed remained relatively constant, and blood ethanol determinations confirmed that the monkeys were drinking ethanol. Water drinking occurred at negligible levels except by one monkey at 16 and 32% who followed ethanol drinking bouts by water bouts (chasers) in a manner similar to that reported in other studies. Two monkeys were also provided concurrent access to 8% ethanol and water during 23-hr daily sessions. Under these conditions, ethanol was consumed every few hours to the near exclusion of water. The significance of this study lies largely in its procedure; that is, the development and application of a concurrent water-ethanol preparation in which ethanol serves as a reinforcer for rhesus monkeys. This preparation should be useful in the evaluation of a wide range of factors suspected to control alcoholic drinking.