Effect of extrinsic neuronal connections on development of acetylcholinesterase and choline acetyltransferase activity in the ventral half of the chick spinal cord

Abstract

Microsurgical operations were performed on the neural tube of chick embryos of 50–53 hr incubation. The ventral half of the brachial spinal cord subsequently developed in the absence of extrinsic fiber connections. The levels of acetylcholinesterase and choline acetyltransferase activity were measured in the ventral half of the brachial enlargement in both experimental and control embryos from 11–21 days of development. Acetylcholinesterase activity was identical in both experimental and control embryos. The expeirmental values for choline acetyltransferase were less than those of the control: This difference was maximal at 19 days and statistically significant from 15 through 19 days of development. The ontogenetic pattern for each enzyme was similar to that observed for the entire brachial spinal cord. The data suggest that the reduced level of choline acetyltransferase activity in the experimental embryos is a direct result of the operative deficit, i.e., a reduction in the number of cholinergic boutons terminaux in the ventral spinal cord, although possible trophic effects on the motor neuroblast per se cannot be ruled out.