Acquisition and extinction of schedule-induced polydipsic consumption of alcohol and water

Intermittent presentations of ethanol sipper tube induce ethanol drinking in rats

AIMS

Intermittent presentations of the ethanol sipper have been reported to induce more ethanol drinking in rats than when the ethanol sipper was continuously available during the session. This intermittent sipper effect was observed in a social drinking situation, in which subjects experienced intermittent opportunities to interact briefly with a conspecific rat. The objective of this study was to evaluate the effects of the intermittent sipper procedure in situations providing for intermittent presentations of food, and, in addition, in situations that do not provide for intermittent presentations of another rewarding event.

METHODS

Four groups of male Long-Evans hooded rats, arranged in a 2 x 2 factorial design with two levels of Sipper Procedure (Intermittent vs Continuous) and two levels of Food procedure (Food vs No Food), were trained in drinking chambers. During each daily session, Intermittent Sipper groups received access to the ethanol sipper during each of 25 trials of 10 s each, while Continuous Sipper groups had access to the ethanol sipper during the entire session (approximately 30 min). During each session, Food groups received 25 presentations of food pellets while No Food groups received no food pellets. Ethanol concentrations in the sipper [3, 4, 6, 8, and 10% (vol./vol.)] increased across sessions.

RESULTS

More rapid escalation of ethanol intake was observed in the Intermittent Sipper groups than in the Continuous Sipper groups, and this effect was observed in both the Food and No Food conditions (P's < 0.05), which did not differ from one another.

CONCLUSIONS

Intermittent Sipper procedures provide less access to the ethanol sipper, yet induced more ethanol drinking than Continuous Sipper procedures. The intermittent sipper effect is not dependent on presentations of food. Implications for schedule-induced polydipsia and Pavlovian autoshaping are discussed.

Consequences of Surprising Reward Omissions

A surprising reward omission (SRO) occurs when an appetitive reinforcer is not presented (or it is reduced in magnitude or quality) even though there are signals for its impending presentation. Evidence supporting the hypothesis that SROs produce an aversive emotional reaction with physiological and behavioral consequences is reviewed. SROs are followed by pituitary–adrenal activation; changes in immune function; odor emissions in rodents; distress vocalizations in rodents and primates; and increases in locomotion, aggressive behavior, drinking, and eating. SROs can support the acquisition of new escape responses and invigorate previously acquired responses. The review identifies common aspects of these phenomena and areas in which more research is needed.

What schedule-induced polydipsia can tell us about alcoholism

An animal model of chronic and excessive voluntary (unforced) alcohol ingestion is presented in which, by drinking, animals produce repeated, substantial elevations in blood ethanol concentration and develop physical dependence. The overindulgence is elective in that ethanol is chosen in preference to certain other fluid-ingestive alternatives. Beside the usual demonstrations of acutely compromised motor performance, tolerance development, cross-tolerance, etc., the model demonstrates that the consequences of even short, but continued, daily drinking episodes results in the disruption of reinforced behavior that occurs later in the day when blood ethanol is absent (impaired general functioning). The conditions which induce the ethanol overindulgence can generate a variety of behavioral excesses which places alcoholism in a context of environmentally determined malfunctions that are subject to therapeutic change by altering situational parameters. Efficacious experiments utilizing therapeutic and preventive strategies are described that may serve as suggestions for corresponding human alcoholism intervention strategies.

Schedule-induced polydipsia: attenuating effects of decreased size of food granulations

The effect of food texture on the development of schedule-induced polydipsia was examined in six groups of rats (n = 8), each receiving one of six grades of food granulation. A seventh group received pellets. By the end of 15 sessions of FT 60-sec food delivery, rats receiving pellets and the coarser granulations had developed polydipsia. The volume of water drunk at asymptote by the remaining groups declined with decreased coarseness of the food. Ethological analyses of the behavioral repertoire of the rats during the fifteenth session showed that the polydipsic groups sustained their drinking throughout the session, rather than turning from ingestive to exploratory behaviors near the end of the session, as was the case with animals receiving finer granulations. The enhanced drinking induced by the coarser food texture was reciprocally related to the amount of time the animal spent with its head in the feeder hole during the period of maximum drinking. The results support the conclusion that the schedule-induced polydipsia traditionally demonstrated with pellets as the reinforcer is critically dependent on the fact that pellets are coarse in texture.

Is adjunctive behavior a third class of behavior?

Research during the past 20 years has revealed that intermittent food presentation to a variety of organisms results in an inordinately excessive consumption of water as well as other behaviors including attack, pica, escape, and alcohol consumption. Such behavior has not been thought to be either respondent or operant behavior, but instead has been regarded as a new behavioral category termed "adjunctive behavior." This paper reexamines the rejection of adjunctive behavior as either operant or respondent behavior and concludes that the rejection was premature. This paper also reexamines the argument that there is a unique class of adjunctive behavior and concludes that there is not. It is recommended that given the growing difficulties in maintaining an operant-respondent dichotomy, rather than admitting adjunctive behavior into either of these categories, research efforts should de-emphasize preconceived and outdated notions about categories of behavior and how such behaviors should behave and instead focus on mapping functional relationships between behavior and various procedures for presenting non-contingent stimuli.

Schedule-induced drinking: rate of food delivery and Herrnstein's equation

Schedule-induced drinking was measured in four rats exposed to fixed-time schedules of food ranging from 30 to 480 seconds. Herrnstein's (1970, 1974) equation relating rate of a single response as a hyperbolic function of reinforcement rate provided a good fit to three measures of drinking: lick rate, ingestion rate, and relative time spent drinking. The functions relating the three measures of drinking to reinforcement rate were of similar form. Herrnstein's equation also provided a good description of some already published data on schedule-induced drinking. The fit both to the present data and to the already published data was improved somewhat by computing the measures by subtracting from the time base a latency constant representing the minimal time required to consume the food pellet and travel to the water source. The data from this study provide two correspondences between operant behavior and schedule-induced behavior: (a) conformity to Herrnstein's equation and (b) equivalence of rate and relative time measures.

Food, water and ethanol consumption by rats under a fixed-interval schedule of food presentation

Rats could lever press 24 hours a day for 97 mg food pellets under a fixed-interval (FI) 90 second schedule. During the first 4 days, an ethanol solution was the only available fluid, after which both water and ethanol solutions were available. At ethanol concentrations (w/v) of 5%, 7.5% and l0%, total caloric intake and total fluid intake remained constant, while ethanol consumption was inversely proportional to the concentration of the solution. When the FI 90s schedule was changed to FI 45 s, or to FI 180 s, there were only small changes in total caloric intake, total fluid intake and in percentages of total fluid consumption and total caloric intake as ethanol. The data suggest that the intake of ethanol under this fixed-interval schedule depends more on the ethanol concentration than on the calories obtained from ethanol drinking.

Suppression of ethanol-reinforced lever pressing by delaying food availability

When food was initially available to rats under a fixed-interval 26-second schedule and each liquid-reinforced lever press delayed food availability 8 seconds, suppression of liquid-reinforced lever pressing and liquid consumption occurred when the liquid presented was 4, 8, 16, 32, and 0% ethanol. Suppression did not occur in yoked-control animals, which received food coincidentally with experimental animals but were not directly exposed to the delay dependency. After exposure to the food schedule, each ethanol solution served as a reinforcer in the absence of food presentation. Delaying food availability for increasingly long periods (8 to 2048 seconds) suppressed ethanol-reinforced lever pressing and consumption relative to baseline levels, with the maximum decrease being below the level maintained in the absence of food. However, degree of suppression did not increase monotonically with delay length. Liquid-reinforced performance of yoked-control animals indicated that suppression did not result from changes in the sequencing of food presentation alone.

Attenuation of ethanol intake by contingent punishment of food-maintained responding

Two food-deprived rats responded under a concurrent fixed-ratio 12 (food) fixed-ratio 1 (8% ethanol) reinforcement schedule in which a tone occurred during every second or every fourth interpellet interval. When ethanol-maintained lever presses during the presence of the tone shifted the food schedule to one in which electric shock punishment occurred, ethanol-maintained responding consistently decreased. The decrease in the frequency of ethanol-maintained responding varied directly with shock voltage from 25 to 100 V, and occurred during intervals with the tone present and absent. These results indicate that ethanol intake may be attenuated by contingent changes in a concurrent food schedule.

Effects of feeding regimen on ethanol intake by guinea pigs

During daily two-hr sessions, guinea pigs licked a drinking tube filled with either 0 (tap water), 2,4 or 8% (v/v) ethanol solution under three feeding regimens. Consumption of each solution was highest when sufficient food to maintain subjects at 90% of free-feeding weight was provided during sessions, lower when the same food ration was provided after sessions, and lowest when ad lib access to food was provided within and between sessions. However, this decrease in consumption across feeding regimens was inversely related to ethanol concentration. Under all feeding regimens, volume of solution consumed decreased with increasing ethanol concentration while milligrams ethanol consumed increased with ethanol concentration. These results are similar in some respects to previous findings with rats and monkeys, suggesting that further studies of oral ethanol self-administration by guinea pigs may be merited.

Establishment of etonitazene as a reinforcer for rats by use of schedule-induced drinking

Drinking of etonitazene HCl by 6 rats was studied during daily 4-hr sessions. Five related experiments were conducted sequentially. In the first experiment schedule-induced polydipsia was established. Subsequently, etonitazene concentrations (1.25, 2.5 and 5.0 microgram/ml) were substituted for water, and intake of large quantities of the drug occurred. In the second experiment the concurrent food reinforcement schedule was discontinued and lever presses maintained by etonitazene (5 microgram/ml) persisted. In the third experiment the number of lever presses, required per dipper presentation of etonitazene (5 microgram/ml) was increased, and rate of lever pressing increased directly with the response requirement whereas number of dipper presentations remained constant. In the fourth experiment water was substituted for the 5 microgram/ml etonitazene solution. Water responding declined to low rates, but when etonitazene was reintroduced, responding increased to previous levels. Thus, etonitazene (5 microgram/ml) was functioning as a positive reinforcer. In the final experiment, progressive increases in the etonitazene concentration (5, 10, 20 and 40 microgram/ml) resulted in both systematic decreases in response rate and increases in quantity (microgram) consumed.

Characteristics of ethanol drinking patterns under schedule-induced polydipsia

Rats were induced to consume concentrations of ethanol between 5% and 10% (w/v) using the schedule-induced polydipsia technique. Although the substitution of ethanol solutions for water disrupted the usual post-pellet pattern of drinking, large amounts of ethanol were consumed and sound-induced convulsions were observed during ethanol withdrawal. In subsequent experiments, other rats chose 5% and sometimes 10% ethanol solutions over water where both water and ethanol were freely available during the first session of exposure to ethanol. Convulsions and wild running behavior could be observed in some of these rats after only 8 days of drinking, even though ethanol was freely available at all times. Use of the schedule-induced polydipsia technique served to bring the rats into early contact with the ethanol, but rats that received the same number of food pellets in a dish rather than by the schedule drank almost as much ethanol as did the rats receiving ethanol by the schedule. Rats with free access to food pellets drank very little ethanol.

Effects of conflict upon schedule-induced consumption of water and alcohol

Schedule-induced polydipsic consumption of water and ethanol was conditioned in two groups of 6 Charles River rats which were then exposed to approach-avoidance (food-shock) conflict. Water intake was attenuated by conflict but ethanol consumption remained essentially unaltered. Alcohol's pharmacodynamic effect was implicated as responsible for differences in fluid consumption by the two groups.