Cholinesterase in Developing Amblystoma

Abstract

The physiological significance of cholinesterase (ChE) in neuro-muscular activity and its importance in the development of behavior has recently been reviewed by Nachmansohn. 1 He has shown that ChE first appears in appreciable quantities with the beginning of motility in the chick embryo. The concentration of the enzyme at nerve endings is considered high enough to hydrolyze and thereby inactivate, within the refractory period of the contracting muscles, the acetylcholine (ACh) concerned with the neuromuscular transmission. Since the development of behavior pattern in Amblystoma has been so completely elaborated by Coghill, 2 this form seems ideal material on which to study the relationship between enzyme development and behavior. Studies revealing a sharp rise in the esterase content of whole Amblystoma larvae at the time when rapid movements first occur, have already appeared. 3 , 4

The results reported in the present paper represent an extension of this work and an attempt to localize the enzyme throughout ontogeny, i. e., to determine what element or elements in the embryonic neuromuscular apparatus are most active in its production. Direct estimations of enzyme activity were made by means of a modification of Click's microtitration procedure. 5

Small amounts of the esterase are present in the premotile embryo where it is already more highly concentrated in nerve and muscle than in other tissues. With the onset of non-tetanic S-flexure responses in the embryo, the concentration of ChE increases to a level more than twice that for the earlier stages. Fig. 1 shows the developmental curves of the esterase in nervous tissue and innervated muscle throughout ontogeny and in nerveless muscle during the prefeeding stages. Both the nerve and innervated muscle esterase curves reach a peak during the early feeding stages and decline through metamorphosis.