Time-dependent effect of ethanol upon discrimination behavior.

The discriminative stimulus properties produced by ethanol were employed to demonstrate differences in discriminative performance over time in rats trained at different postinjection times. Thus, one group of rats was trained to discriminate between intraperitoneally administered 600 mg/kg ethanol and its distilled water vehicle at 6-min postadministration, whereas a second group of rats was trained to make this discrimination when trained at 30-min postinjection. Subsequent to reaching criterion performance, dose-response relations to doses of ethanol from 150-900 mg/kg were determined to be similar in both groups. This indicated that the discriminative stimulus effects at the two postadministration times were equally effective for training of behavioral responding to ethanol. The rats trained at 30 min postadministration maintained criterion level discrimination performance when tested at 6-, 15- and 60-min postinjection. In contrast, the rats trained at 6-min postadministration discriminated ethanol at a reduced level (40%) when tested at 30-min postinjection. These results suggest that the nature of the discriminable stimuli produced by a low dose of ethanol are different at 6-min and at 30-min postadministration. Evidence is cited to further suggest that the earlier stimuli are excitatory whereas the later stimuli are sedative.