Scopolamine affects response-to-change test involving 20-min retention interval after locomotor exploration in rats

The tendency to select the T-maze arm that has been changed in brightness between two successive trials (response-to-change) was investigated. Our previous findings indicated that scopolamine injections (1.0 mg/kg) impaired responding to change of brightness in a choice trial (trial II) following a 1-min retention interval, when in the first acquisition trial rats could only inspect the white-black T-maze arms through transparent partitions (the passive test). The drug was ineffective when rats were allowed locomotor exploration of the maze (the active test). The aim of the present experiment was to investigate the effect of the same dose of scopolamine on the active test involving a longer 20-min retention interval between the acquisition trial and the choice trial. The effect of cue salience also was examined by using grey-black arms. Rats injected with scopolamine (Scopo) 20 min before the acquisition trial performed in the white-black maze on the chance level, whereas saline-injected rats (Sal) showed significant preference for the changed arm. Decreasing the cue salience impaired response-to-change in Sal rats (50% of changed arm choices) but had no further effect on performance of Scopo rats, presumably because of a floor effect. The postacquisition injection had a somewhat stronger effect than the injections preceding acquisition, which most probably reflects the state dependency phenomenon. The deficient performance due to scopolamine treatment that appeared in the present study at a longer retention interval could be interpreted in terms of increased forgetting.