Transient aversion and long-lasting amnesia following cycloheximide injection in the rat

Rats were first trained to press a bar for water reinforcement. The day after reaching criterion, the animals received a subcutaneous injection of cycloheximide (CXM-2.5 mg/kg) or saline, 15 minutes before a single punishment (P) session where bar pressing was followed by a strong inescapable footshock (CXM-P and saline-P groups). No punishment was given to control groups (CXM-NP and saline-NP groups). Retention for this learning experience was tested 24 hr, one week or two weeks later. Performances of the control groups were similar at the three retention intervals although some CXM-induced aversion appeared at 24 hr. The saline-P groups always demonstrated good retention of prior aversive experience. By contrast, a long-lasting CXM-induced amnesia was apparent among the CXM-P groups. This deficit is not easily explained by nonspecific effects of the drug such as altered motor activity or motivational changes. Moreover, CXM-induced amnesia seems to be the result of impaired memory formation rather than impaired memory retrieval.