Induction and maintenance of ethanol self-administration without food deprivation in the rat

Oral ethanol self-administration in free-feeding rhesus monkeys

The ability of a conditioning procedure to establish oral ethanol self-administration in free-feeding rhesus monkeys was assessed. The conditioning procedure required the monkey to drink an ethanol solution in order to have access to a sweet orange-flavored solution. Following an average of 14 sessions under these conditions, the orange solution was no longer delivered and ethanol solution alone was made available in the sessions. During both the conditioning and the ethanol self-administration portions of the experiment each monkey was required to drink an average of 0.5 g/kg ethanol per session in order to continue in the experiment. Of the nine monkeys exposed to these contingencies, five monkeys continued to self-administer ethanol after the presentation of the orange drink was discontinued. However, two of these five monkeys decreased their ethanol solution intake below 0.5 g/kg within 3 weeks after the conditioning sessions had terminated. The three monkeys that sustained high ethanol intake were male and had histories of drug self-administration, suggesting that gender and drug history may influence the initiation of ethanol self-administration. Once ethanol self-administration was established, concentrations of ethanol from 4 to 15% (v/v) were made available. The monkeys consumed intoxicating amounts of ethanol, as indicated by average intakes ranging from 0.5 to 0.9 g/kg and blood ethanol levels over 100 mg/dl. These results demonstrate that ethanol self-administration can be established and maintained through the initial reinforcement of ethanol consumption by the contingent presentation of another reinforcing stimulus. However, the results of this study also indicate that individual differences may be an important determinant of animals initiating ethanol self-administration.

Oral ethanol self-administration in rats: models of alcohol-seeking behavior

While various methods have been used to initiate ethanol drinking in animals, the development of models in which animals will perform some specific behavior in order to obtain the opportunity to drink ethanol has been fraught with difficulty. In the past several years, new procedures have been developed in which rats, neither food nor fluid deprived, will perform an operant task reinforced by the presentation of ethanol. This paper reviews some of these recent findings and presents new data concerning these models of oral ethanol self-administration as measured in an operant paradigm.

Ethanol as a reinforcer for rats: factors of facilitation and constraint

This review examines some particular approaches that have been used to investigate factors that facilitate or constrain the self-administration of ethanol by rats. A technique for increasing ethanol self-administration in rats, the prandial drinking method, was examined and the effect of body-weight reduction on drug intake was discussed. Emphasis was placed on how ethanol intake may be controlled by processes in addition to the direct pharmacological actions of the drug in the CNS. These processes may be physiological. Evidence was presented for a relationship between activity in the renin-angiotensin system and the self-administration of ethanol. These processes may also be environmental. Using the place-conditioning technique, demonstrations were presented of how the context or situation in which ethanol is experienced may determine whether preference or aversion for the drug develops. Such a diversity in the factors that can potentially control ethanol intake may complicate the identification of the causes of alcohol abuse, but this same diversity also holds out greater hope that manipulations may be found to reduce excessive drinking in humans.

Relation of ethanol self-administration to feeding and drinking in a nonrestricted access situation in rats initiated to self-administer ethanol using the sucrose-fading technique

Free-feeding male Long-Evans rats (N = 8) were initiated to self-administer 10% ethanol using a sucrose-fading procedure. Following initiation, they were placed into chambers which allowed for the continuous monitoring of feeding, water drinking and ethanol self-administration. All rats continued to daily self-administer ethanol in the continuous access situation. Ethanol drinking at certain times during the day appeared to be related to feeding bouts (prandial drinking). However, at other times, nonprandial ethanol self-administration occurred. These nonprandial ethanol drinking episodes, while not at levels of excessive ethanol intakes, were at levels well above water intake when water was substituted for ethanol. These findings suggest that ethanol intake in continuous access conditions is not solely a function of feeding behavior and that following initiation, ethanol-seeking behavior was maintained in a continuous access situation.

Ethanol preference following the sucrose-fading initiation procedure

Lever responding maintained with ethanol reinforcement at concentrations up to 20% (v/v) was initiated in non-food and -water deprived rats via a sucrose-fading procedure. Home cage two-bottle preference tests between water and 10% ethanol were conducted before (pre) and after (post) the ethanol initiation procedure to determine the effect of initial ethanol preference on ethanol initiation and of initiation on later ethanol preference. Initial preference testing found that the rats could be divided into two groups, animals with low ethanol preference scores (preference below 25%) and those with moderate ethanol preference scores (preference between 25% and 50%). All animals were successfully initiated with the sucrose-fading procedure to lever press with ethanol reinforcement. Following initiation, home cage preference was markedly increased for the initially low-preferring rats (from 12% to 43%), while moderate-preferring rats showed only slight increases (from 37% to 47%). The shift in ethanol preference was discussed in terms of the relation between ethanol preference and behavioral history.

Alcohol consumption in free-feeding rats: procedural, genetic and pharmacokinetic factors

Voluntary consumption of alcohol by rats (i.e. in the absence of food or water deprivation, sweetening of the alcohol solution, etc.) that results in the attainment of behaviorally significant or pharmacologically detectable blood alcohol levels (BALs) has been difficult to demonstrate. In this study, we showed that free-feeding Wistar rats given access to increasingly concentrated solutions of alcohol in separate "drinking" cages on a 1-h per day basis drank on average close to 1 g/kg, resulting in average BALs close to 50 mg%. This drinking was comparable to that obtained by rats trained according to a procedure used widely by others in which animals are maintained at reduced body weights. Weight restriction alone, however, did not enhance amount of alcohol consumption over that of free-feeding animals in the 1-h session. There was also a strain difference in that Wistar rats drank significantly more than did Sprague-Dawley rats. Post hoc absorption curves showed that the initial absorption of alcohol from both the stomach and the peritoneum was slower in Wistar than in Sprague-Dawley rats, suggesting rate of absorption may be inversely related to amount of alcohol consumed; metabolic rates and volumes of distribution appeared unrelated to consumption. This periodic availability paradigm might be useful to investigate the effect of biological variables on individual bouts of alcohol consumption.

Initiation of ethanol reinforcement using a sucrose-substitution procedure in food- and water-sated rats

Rats, maintained on free access to both food and water, were trained to press a lever to obtain a 20% sucrose solution. When presentation of the sucrose solution was maintaining responding, low ethanol concentrations were added to the solution. Over 25 sessions, the solution presented as reinforcement was gradually reduced in sucrose concentration until a 10% ethanol solution with no sucrose was presented. Following this initiation procedure, ethanol concentrations up to and including 40% ethanol were found to maintain responding. At the higher ethanol concentrations, the rats consumed doses of ethanol between 0.90 and 0.95 g/kg in the 30-min session. When a concurrent choice between ethanol and water was available in the operant chamber, the rats responded on the lever associated with 10% ethanol presentation. Home cage preference between ethanol and water was found to be altered following the operant ethanol experience with the rats acceptability for 10% ethanol increased prior to the start of the experiment. This initiation procedure provides another manner in which ethanol reinforcement can be instigated in animals that have not been either food- or fluid-deprived. It is hypothesized that mechanisms which may regulate the intravascular and intragastric self-administration of ethanol may also be operating when the oral route is employed.

The induction of oral ethanol self-administration by contingent ethanol delivery

The necessity of delivering a highly reinforcing stimulus (20% sucrose) contingent upon ethanol consumption in order to induce ethanol self-administration in free-feeding rats was investigated. Rats water deprived for 12-16 h were placed in an environment in which ethanol drinking resulted in the presentation of ethanol. This procedure was successful in inducing and maintaining ethanol self-administration over concentrations of 5-20% (v/v). Compared to a group of rats initially reinforced for drinking ethanol with sucrose presentation, contingent ethanol delivery resulted in greater ethanol self-administration behavior. When 20% ethanol was available the group trained with ethanol had average intake of 0.91 g/kg, whereas the group trained with sucrose had a mean intake of 0.69 g/kg in a 30-min session. The results suggest that ethanol's reinforcing properties are sufficient to establish ethanol self-administration within the context of the inducing environment.