Conditions under which chlordiazepoxide influences gustatory contrast.

Rats shifted from 32% sucrose to 4% sucrose consumed less 4% than animals without prior experience with 32% sucrose. The influence of chlordiazepoxide (CDP) on this successive negative contrast obtained in sucrose ingestion was investigated in four experiments. The results indicated that (1) rats injected with CDP during both preshift experience with 32% sucrose and post-shift experience with 4% sucrose showed an essentially unchanged contrast effect compared with saline-injected rats, (2) CDP injection for the first time on post-shift day 2 eliminated contrast but post-shift day 1 injections had little effect, (3) animals injected with CDP throughout preshift and switched to saline coincident with the sucrose shift showed a contrast effect at least as great as control animals, and (4) injections of CDP tended to elevate lick rate regardless of other conditions. These results indicate a disinhibitory effect of CDP and possible neophobia operating on the first post-shift day.

Incentive contrast undiminished by extended testing, imipramine, or chlordiazepoxide.

In three experiments rats were given alternating 1-minute access periods to two tubes containing sucrose solutions. When the tubes contained disparate concentrations (32% versus 4%), lick-rate was higher for the 32% solution than it was when both tubes contained 32% (a positive contrast effect) and less for 4% than when both tubes contained 4% (a negative contrast effect). Similar, but generally less pronounced, contrast effects were obtained in latency to initiate drinking. These contrast effects showed no sign of diminution with repeated exposure (32 days of repeated shifts in Experiments 1 and 3); they were not greatly influenced by injections of imipramine (Experiment 2) or chlordiazepoxide (Experiment 3), nor by deprivation conditions (Experiment 3), nor by deprivation conditions (Experiment 3). The results supported an explanation of simultaneous contrast in terms of sensory-perceptual processes rather than in terms of generalization decrement or emotional responses.