Chlordiazepoxide and the moderation of the initial response to reward reduction

The effectiveness of chlordiazepoxide (CDP) in reducing negative contrast on the first day after a shift from 32% to 4% sucrose was investigated in four experiments using rats. Previous studies indicated that CDP was effective on the second, but not on the first postshift day. In Experiments 1 and 1a, neither initial experience (3 or 10 days) with the eventual postshift 4% solution (i.e. 4%, then 32%, then 4%), nor initial experience with alternating 4% and 32% sucrose, led to a reliable contrast-reducing effect of CDP on the first shift day. Evidence from Experiments 2 and 3 suggested that a range of doses of CDP (3, 5, 10, and 15 mg/kg) did not have reliable effects on the first postshift day, although the two lower doses did reduce contrast on the second postshift day (the higher doses were not administered on Day 2). The evidence suggests that the relative ineffectiveness of CDP in moderating the initial response to reward reduction is not related to a problem of recognizing the difference between the postshift solution and the memory of the preshift solution. Alternative interpretations in which CDP's lack of effect on the initial occurrence of contrast is related to an initial stage of unconditioned frustration and/or exploratory behaviour are considered.