Effects of exposure to an imprinting stimulus on the activity of enzymes involved in acetylcholine metabolism in chick brain.

One-day-old chicks were exposed for 60 min to either an imprinting stimulus or a dark-box. They were killed at 0, 1, 6 or 12 h after the end of this treatment, and the activities of acetylcholinesterase (AChE) and choline acetyltransferase (ChAc) assayed in the forebrain roof, forebrain base and midbrain. The activity of AChE increased by 11% in the roof of stimulus-exposed birds 1 h after exposure and in base (by 13%) and midbrain (by 8%) 6 h after exposure. At 12 h the only difference was a lowered AChE (14%) activity in midbrain of stimulus-exposed animals. By contrast only one difference was found in ChAc activity between the two types of birds: an elevation of 10% immediately after the end of treatment (0 h) in the midbrain of the stimulus-exposed birds.