Some biochemical and behavioural aspects of the paradoxical sleep window.

It has recently been proposed that there is a vulnerable period of time following successful learning when paradoxical sleep (PS) is necessary for learning. This vulnerable time period has been called the PS window. In Experiment 1, the protein synthesis inhibitor anisomycin (ANI) was administered following shuttle avoidance training in the Sprauge-Dawley rat to coincide with the onset of an established PS window. Control groups received either saline or ANI either 3 hours before or 3 hours after the beginning of the PS window. Three hours after the injection, each group was retested. Then animals were immediately sacrificed, and whole brain biochemical analyses were done on levels of acetylcholine (ACh) and activity of acetylcholinesterase (AChE). Only the rats given ANI timed to coincide with the beginning of the PS window showed learning deficits. All ANI-treated groups had less ACh and AChE activity. In Experiment 2, the ACh antagonist scopolamine (SCOP) was injected at the same times as in Experiment 1, and each of these groups had a corresponding saline control group as before. Retesting was done 1 day later; once again, the only group to show learning deficits was the group receiving SCOP timed to coincide with the PS window. Results suggested that the transmitter ACh plays an important role in learning/memory processes at the PS window.