Is acetylcholine involved in memory consolidation of over-reinforced learning?

Systemic administration of anticholinergic drugs produces amnesia. To determine whether this effect can be prevented by increasing the magnitude of the learning experience, independent groups of rats were trained in passive avoidance, using a 3.0-mA footshock, and then injected with scopolamine (2, 4, 6, 8 or 12 mg/kg). When retention of the task was evaluated, a dose-dependent amnesic effect was found. When footshock intensity was increased to 6.0 and 9.0 mA, injections of 8 and 12 mg/kg of scopolamine did not produce memory impairments. These findings indicate that acetylcholine plays an important role in consolidation of passive avoidance, but it does not seem to be involved in memory processes when the magnitude of the negative reinforcer is increased.