Clinical research indicates that environmental context plays a very important role in altering individual responsiveness to addictive drugs. For example, traumatic life experiences have been shown to be associated with the development of a drug addiction, or a relapse back to a former drug addiction. This type of environmental influence on drug self-administration has also been seen in laboratory animals, such as rats. Previous studies have found that non-resident rats (rats transferred to a separate chamber different from the one they were living in) self-administered higher levels of cocaine and amphetamines than resident rats that were presented with the drugs in their chamber of residence. Conversely, the same study found that the opposite was found for heroin, where resident rats self-administered higher levels of the drug than non-resident rats. Based on these results, it is suggested that environmental context and the drug type play important roles in self-administration in the rat model.
These differing responses between resident and non-resident rats and their self-administration rates of different types of drugs may, according to researchers, reflect an influence of contextual stimuli on the evaluation of the drug reward. More specifically, researchers speculate that the environmental setting provides an ecological background against which drugs are rated as more adaptive or less adaptive. What this means in plain English is that the sedative/depressive effects of heroin (or other depressants) are more suitable for a safe at-home environment, whereas activating/stimulating effects of cocaine (or other stimulants) are more suitable in unfamiliar, exciting environments.
For the current study presented today, the authors built upon this previous knowledge of self-administration of various drugs in different environmental contexts in the rat model, and expanded it to include alcohol. Simply put, this study aimed to evaluate the oral self-administration of alcohol in resident and non-resident rats. The authors predicted that alcohol self-administration in rats should be similar to heroin administration in rats, as both as depressants that display very similar symptoms in the consumer. Specifically, the authors predicted that self-administration of alcohol would be higher in resident rats than non-resident rats.
167 male Sprague-Dawley rats between the weights of 220 and 240 grams were used for this study. They were housed and tested in a single temperature and humidity controlled room, with continual access to food and water, except during the experimental sessions, and were kept under a 14 hour dark and 10 hour light cycle. Rats were housed individually, and randomly assigned as resident or non-resident.
Goal: To measure the intake of different solutions of alcohol in resident and non-resident rats.
There were 12 groups of rats tested for 14 consecutive sessions. Sessions lasted 3 hours each and took place during the dark cycle between 12pm and 3pm. At the start of each session, food was removed, and then replaced immediately after the session ended. Alcohol solutions were prepared fresh and at room temperature. Bottles of solution were weighed before and after each session.
Baseline Sessions: One week after arriving at the facility, non-resident rats underwent 3 sessions to measure baseline water intake in their home cages (to compare when in non-resident cages)
First Baseline Session: Non-resident rats were given the alcohol test solution in their home cages to measure their baseline intake (to compare when in non-resident cages). Three groups of rats received three ethanol solutions using 95% ethanol diluted with tap water: 2.5%v/v, 5%v/v, and 10%v/v. Three other groups of rats were given a commercial white wine (Castellino, 11% alcohol by volume) diluted with tap water to produce the same levels of alcohol as the ethanol solutions: 2.5%v/v, 5%v/v, and 10%v/v.
One Bottle Test Sessions: Immediately before the experiment, non-resident rats were transferred into the testing chamber. One bottle containing the same alcohol solution as the baseline session was provided to each rat. At the end of each session, non-resident rats were returned to their home cages.
Two Bottle Test Sessions: These sessions were nearly identical to the one bottle sessions, however during these sessions, two bottles of water were provided to each rat (choice), with one containing the alcohol test solution, and the other containing water.
Procedures for Resident Rats: The procedures for resident rats were nearly identical to those for the non-resident rats, except that resident rats were tested in their home cage and were not transferred into any other cages throughout the experiment. There was the same number of groups of resident rats as there were non-resident rats.
Goal: After analyzing Experiment 1, the researchers found that there were significant differences between the resident rat groups and the non-resident rat groups. Therefore, the goal of Experiment 2 was to determine if these groups also differed in their intake of water.
Procedures for Experiment 2 were almost identical to the procedures for Experiment 1, except that the alcohol test solution was replaced by water.
Goal: The goal of Experiment 3 was to determine if there were any differences between resident and non-resident rats in the intake of a saccharine-quinine solution.
This was the goal of Experiment 3 since research has shown that there is a relationship between the preference for ethanol and a preference for bitter-sweet solutions in the rat model. Some studies suggest that saccharine-quinine solutions more approximately reflect the bitter-sweet taste of alcohol solutions.
The procedures of Experiment 3 were nearly identical to the procedures in Experiments 1 and 2, except during this experiment, the alcohol (or water) solution was replaced by a saccharin-quinine solution.
For All Experiments
Each bottle that contained test solutions or water was checked repeatedly for any dripping. For 7 days in a row, each bottle was weighed before being placed in a cage, and again after the 3 hour experimental session. The average differences between the weights of the bottles were subtracted from the raw data. Intake data was corrected by body weight, which was measured twice per week. Intake of pure ethanol in Experiment 1 was calculated after correcting for concentration and relative density.
- There were no significant differences in body weights at the beginning of the experiment between resident and non-resident rats.
- All groups increased body weight throughout the duration of the experiment.
- Weight gain was significantly greater in the resident group than the non-resident group.
o This was expected, as alcohol intake was higher in the resident group than the non-resident group.
§ Weight gain x environment interactions were not quite significant (approaching significance). This means weight gain was similar between resident and non-resident rats.
§ There were no other significant interactions.
- During the 1 bottle test, alcohol intake was a function of environmental context, with no significant differences in the baseline intake between groups.
- Alcohol intake was significantly greater in the resident group than in the non-resident group.
- Alcohol intake was a function of concentration, though there was no environment x concentration interaction.
- Differences between resident and non-resident groups appeared to be greatest at the 5% concentration (up to 2 times greater).
- There was a significant effect of session, though no significant interactions with session and environment, session and concentration, or session and test solution.
o As sessions wore on, resident rats greatly increased their alcohol intake, whereas non-resident rats greatly reduced their alcohol intake.
- There were no differences between ethanol solution intake and wine solution intake.
- For the 2 bottle tests, preference for alcohol over water was a function of both the environment and the concentration.
o Intake of alcohol solutions relative to intake of water was greater in the resident rat groups than the non-resident rat groups.
§ This was due to a preference for alcohol over water in the resident rat group.
- The effect of environment was greatest at 5% alcohol concentrations.
o Alcohol was preferred to water at concentrations of 2.5% and 5%.
o Water was preferred to alcohol at the 10% concentration.
- There were no significant differences between resident and non-resident rats in the intake of water at baseline or the entirety of the experiment, nor were there any significant interactions between any of the other variables.
- There was no effect of environment on saccharin-quinine intake between resident and non-resident rats.
o Resident and non-resident rats differed when non-resident rats were transferred into another cage during the first session of the one bottle test.
o There was a significant effect of session, but not a significant effect of environment, and nor were there any significant interactions between the two.
- During the 2 bottle test sessions, there was a significant effect of choice, but not of environment, and there was only one significant interaction between them (the three-way choice x environment x session interaction).
Based on the results of this study, the authors concluded that alcohol self-administration in the rat is influence by the environmental setting in which that alcohol is consumed. Specifically, they found that alcohol intake was greater for those rats living in the experimental chambers than those rats temporarily moved into an experimental chamber while living in a completely separate chamber while not undergoing testing.
As far as the type of alcohol is concerned, it didn’t seem to matter if the rats were consuming ethanol alone or wine. In regards to the saccharin-quinine results, it appears as though this choice was influenced in a different manner than the alcohol solutions. Resident rats increased their intake of the test solution during Experiments 1 and 3, while non-resident rates decreased their intake of the test solution during the experiments. During later sessions of the experiment, this effect of changing intake preferences rapidly declined when it came to testing the saccharin-quinine solutions, but not the alcohol intake. The authors suggest this means that when exposed to new tastes, the rats are a little cautious, but then this cautiousness wears off over time.
As the authors predicted, resident rats consumed greater amounts of alcohol than non-resident rats, which they attribute to the depressant characteristics of the drug and the results of previous studies with heroin. While a stimulating drug, such as cocaine, would be more likely experienced as more suitable in a strange, exciting environment, a depressant such as heroin (or in this case, alcohol), would be more suitable for safe, comfortable environments such as the home.
Overall, the authors of this study claim that based on these results, this paper shows at the preclinical level that setting or environment plays a very important role for the self-administration of alcohol. These results seem to complement the one survey study of humans that concluded that there was a clear preference for heavy drinkers to consume larger amounts of alcohol in the comfort of their own home. These results could have many implications in the health and psychological fields.
I’d love to hear what you all think! Please feel free to comment below!
Source: Testa, A., Nencini, P., and Badiani, A. 2011. The role of setting in the self-administration of alcohol in the rat. Psychopharmacology 215: 749-760.
I am not a health professional, nor do I pretend to be. Please consult your doctor before altering your alcohol consumption habits. Do not consume alcohol if you are under the age of 21. Do not drink and drive. Enjoy responsibly!