Memory interfering effects of chlordiazepoxide on consummatory successive negative contrast

• Pre-session chlordiazepoxide (CDP) reduces the effects of incentive downshift.
• However, post-session CDP enhances the effects of incentive downshift.
• This post-session CDP effect requires an incentive downshift experience.
• CDP interferes with memory encoding of the downshifted incentive.

Long–Evans rats downshifted from 32% to 4% sucrose solution exhibit lower consummatory behavior during downshift trials than rats exposed only to 4% sucrose. In Experiment 1, this effect, called consummatory successive negative contrast (cSNC), was attenuated by administration of the benzodiazepine anxiolytic chlordiazepoxide (CDP, 5 mg/kg, ip) before the second downshift trial (Trial 12), but was not affected when CDP was administered before the first downshift trial (Trial 11). In Experiment 2, CDP administered after Trial 11 actually enhanced the cSNC effect on Trial 12. This posttrial effect of CDP was reduced by delayed administration (Experiment 3). This CDP effect was not present in the absence of incentive downshift (Experiments 4–5), or when animals were tested with the preshift incentive (Experiment 6) or after complete recovery from cSNC (Experiment 7). The posttrial CDP effect was observed after an 8-day interval between Trials 11 and 12 (Experiment 8) and when administered after Trial 12, rather than Trial 11 (Experiment 9). Experiment 10 extended the effect to Wistar rats. Because CDP is a memory interfering drug, it was hypothesized that its posttrial administration interferes with the consolidation of the memory of the downshifted incentive, thus prolonging the mismatch between expected (32% sucrose) and obtained (4% sucrose) incentives that leads to the cSNC effect.