Aversive factors in alcohol drinking in humans and animals.

In human subjects there is a wide range of response to the taste of alcohol in varying concentrations. What some people find totally aversive may be accepted with relish by others. Both individual and racial responses to ingested or injected alcohol can be aversive, since markedly dysphoric experiences can occur. Human studies also suggest that the euphorigenic properties of alcohol are very variable between subjects and that this correlates with characteristics of biogenic amines present in the body. Except for relatively low concentrations, the laboratory rat, used commonly in alcohol drinking experiments, avoids the selection of alcohol. Paralleling human studies are animal investigations that manipulate the levels of chemical substances in the brain and demonstrate effects of this upon alcohol self-selection. When certain tetrahydroisoquinolines or beta-carboline substances are infused into the brain of the rat or monkey, the aversive nature of orally ingested alcohol, particularly in very high concentrations, is overcome. In contrast, however, when a high dose of a tetrahydropapaveroline is infused, the animal's volitional intake of alcohol is inhibited and even weak concentrations of alcohol are rejected. The possible mechanisms for this phenomenon and the recent investigations of agents acting on CNS opiate receptors in reinstating alcohol aversion are considered.