Do rats like boozing?
That's an odd question to ask. But it's an important one because much laboratory research on the effects of drinking is carried out with rats. Extrapolation of scientific findings from one species to another — always a risky business — is thus particularly intriguing in this instance. Oddly enough, however, the question of whether rats crave alcohol the way some humans do has not been clearly answered until very recently.
The answer to the question (wait for it . . . ) has just emerged from the research laboratories in Helsinki of Finland's State Alcohol Monopoly (Alko). The scientist who has provided it is Dr J. D.
Sinclair. Describing the background to his work in this week's issue of Nature (vol 249, p 590), Dr Sinclair points out that despite the continual use of animals as research tools, there has been little evidence whether or not they develop what he calls "the most important factor in al coholism, a strong motivation to obtain alcohol for drinking."
Dr Sinclair tackled the problem as follows. He took sixty male albino rats and allowed them fiftyfive days' unlimited access to food tap water, and a ten per cent solution of ethyl alcohol. Six, which appeared to have a marked preference for alcohol, were then selected for further tests in a "Skinner box" — a standard cage, used in psychological testing, in which an animal can gain measured quantities of, say, food by pressing a lever. In this case food and water were freely available, and there were two levers. One yielded a small amount of the alcohol solution when pressed, the Other released the same amount of water.
The question was: would the rats learn which was which and show any preference? Dr Sinclair arbitrarily decided that a rat could be considered motivated towards the alcohol if it pressed that lever more than 100 times a day, and at the same time selected alcohol at least twice as often as water.
The results were quite unambiguous. All six rats quickly reached the arbitrary standard. Four did so during the first night in the box, one on the second night, and one on the third night. (It was known previously that rats tend to drink alcohol during night-time rather than day.) Once a rat had learned to work for alcohol, it continued to perform at or above the standard level every day afterwards. Moreover, all but one of the animals rapidly adjusted their behaviour when the positions of the water and alcohol levers were switched.
Next, Dr Sinclair tried to discover how strongly the rats were motivated, by the ingenious trick of progressively adding weights to the back of the alcohol lever, making it more difficult to operate. Earlier experiments had proved that (other things being equal) rats select a lever that is lighter to press.
Again, the evidence was clear. Both of the animals tested continued to prefer the alcohol lever, until over 140 grammes in weights had been added to it. Some rats, it seems, will learn to work relatively hard to obtain alcohol in preference to water. Unlike many previous reports, Dr Sinclair's findings cannot be interpreted in terms of motivation by hunger or thirst, as both food and water were continuously available in the cages.
Added, therefore, to existing knowledge that animals can show tolerance and withdrawal symptoms to alcohol, we now know that some rats, like some humans, can develop a marked motivation towards alcohol. Though too soon to be sure, this new discovery may have great relevance to the increasing social problem of alcoholism. All the more odd, then, that such fascinating experiments have not been carried out before.
Dr Bernard Dixon is editor of New Scientist and writes fortnightly in The Spectator