Discriminative stimulus effects of ethanol with a conditioned taste aversion procedure: lack of acetaldehyde substitution.

Acetaldehyde has been suggested to mediate a number of the pharmacological and behavioural effects of ethanol. Recently, several studies investigated the role of acetaldehyde in the subjective effects of ethanol, but obtained conflicting results. With the discriminative taste aversion (DTA) procedure, high acetaldehyde doses were shown to substitute for the discriminative stimulus effects of ethanol. In contrast, the operant drug discrimination protocol failed to show any substitution effect of acetaldehyde. Several methodological differences between the two procedures could explain these discrepancies, and particularly the absence of an individual discrimination criterion in the DTA procedure. In the present study, the DTA procedure was adapted to introduce such a criterion. In addition, the effects of acetaldehyde were compared with those of other drugs, for which the substitution effects for ethanol are well known. Rats were trained to discriminate 1.0 g/kg ethanol from saline in a DTA protocol. When the rats met the criterion of ethanol discrimination, various doses of several drugs were tested for their ethanol stimulus substitution effects: ethanol, acetaldehyde, dizocilpine, diazepam and nicotine. The results showed a clear dose-dependent discrimination of ethanol stimulus effects. In addition, dizocilpine fully substituted for ethanol, while diazepam only partially substituted. In contrast, both acetaldehyde and nicotine failed to substitute for ethanol. These results show that acetaldehyde is not significantly involved in the subjective and discriminative stimulus effects of ethanol. Acetaldehyde up to toxic doses did not substitute for the ethanol discriminative stimulus in the DTA protocol, when non-specific effects were carefully controlled.