- Visual discrimination and reversal learning were tested in adult C57Bl/6 mice that had been treated on postnatal days (PND) 4-10 with diisopropylfluorophosphate (DFP), an acetylcholinesterase inhibitor. DFP-treated mice attained the learning criterion in the Y maze significantly earlier than saline-treated mice. Female mice treated with DFP showed a more rapid decline in errors in the initial discrimination task, compared to female mice treated with saline. There was no effect of DFP treatment on learning the reverse discrimination. The data suggest that long-lasting effects of treatment with an acetylcholinesterase inhibitor can improve discrimination learning, similarly to the improvement reported by acute administration in adults.