The effect of scopolamine on the Kamin effect: A test of the parasympathetic overreaction hypothesis

Abstract

The Kamin effect, the U-shaped curve of retention of a partially learned shuttle avoidance response, was replicated in animals trained and tested for retention after delays of 0, 1, 4, ov 24 h. Other animals treated with scopolamine hydrobromide, a cholinergic blocker, during the 1-h delay between learning and relearning showed no performance decrement. However, animals treated with methylscopoiamine, which does not cross the blood-brain barrier, during the 1-h delay did show the typical Kamin effect decrement in performance. The results were interpreted as supporting a central cholinergic basis for the Kamin effect.