Reversal of a drug versus drug discrimination task with different exteroceptive conditions.

The effects of a change of an exteroceptive context (light and dark) on a drug vs. drug discrimination reversal task was investigated. Rats were trained to discriminate between either 1750mg/kg ethanol and 17.5mg/kg pentobarbital (high dose) or 1000mg/kg ethanol and 10.0mg/kg pentobarbital (low dose), using an electrified T-maze procedure. Once the initial acquisition had been acquired (phase I), the response requirements were reversed (phase II). For the experimental groups, this was accompanied by a change in exteroceptive conditions (light became dark and vice versa). For the control groups, the reversal phase was without any change in exteroceptive context. Finally, the animals were tested with saline and the training doses of the drugs, for both exteroceptive conditions. It was found that both original and reversal acquisition occurred faster in the high dose group. This is consistent with previous findings. There were no effects of a changed exteroceptive context on the speed of reversal learning, or on discriminative performance during final testing, in either dose group. A possible explanation is suggested for these findings.