Ethanol as a discriminative stimulus: effects of cyanamide, acetaldehyde and chlormethiazole.

Two groups of gerbils were trained to discriminate between either 2 g/kg of ethanol (ETOH) and saline or 2 g/kg of ETOH and 1 g/kg of ETOH. Acetaldehyde and a combination of cyanamide, an aldehyde dehydrogenase inhibitor, plus ETOH were tested to determine if augmented levels of acetaldehyde would enhance ETOH-like responses. The CNS depressant drug chlormethiazole (CMZ) was also tested, separately and in combination with ETOH. The effects of ETOH and acetaldehyde were also tested in an open-field (O--F). Some effect of acetaldehyde (ED50 = 160 mg/kg) was observed in the group trained to discriminate between saline and 2 g/kg of ETOH (ED50 = 800 mg/kg) but not in the group trained to discriminate between 1 and 2 g/kg ETOH. Cyanamide (50 mg/kg) given before 1 g/kg of ETOH did not markedly change the amount of ETOH (2 g/kg) appropriate responses as compared to the saline control. The percentage of ETOH (2 g/kg) appropriate choices increased after testing combinations of CMZ and ETOH as compared to testing either drug separately. ETOH stimulated ambulation (horizontal locomotor activity), whereas acetaldehyde resulted in a dose related decrease of all the behaviour patterns recorded in the O--F test. The major conclusions from these studies are that the behavioural pharmacology of acetaldehyde differs from that of ETOH, that acetaldehyde plays only a limited role in the discriminative stimulus effects of ethanol in gerbils, and that the stimulus effects of ETOH and CMZ are additive.