Activities of acetylcholinesterase, choline acetyltransferase, and catecholamine production in the spinal cord of the axolotl Ambystoma mexicanum during forelimb regeneration

Abstract

Amputation of an axolotl limb causes severance of the brachial nerves, followed by their regeneration into a blastema. It is known that these nerves provide a neurotophic factor to blastemal cells. To approach the problem of the response of spinal cord nerve centers to forelimb amputation, we have studied biosynthetic activities in the nerve centers involved in axonal injury during limb regeneration. We report that the acetylcholinesterase (AChE) activity in the spinal cord is elevated 2 days (+ 69%) and 7 days (+ 28%) after limb amputation compared with levels in unamputated control animals, but is not significantly elevated at 3 h or 15 days. The percentages of slow (3.6 S and 6.0 S) and fast (18 S) sedimenting forms of AChE progressively decrease 2 and 7 days after amputation, while those of intermediate sedimenting forms (10.5 S and 14.0 S) increase. Fifteen days after amputation, lower molecular weight forms return to the control level, but the heavy molecular weight form of AChE is absent as at 7 days; consequently intermediate molecular weight forms are in a greater proportion than the other two forms. Choline acetyltransferase activity was measured only 2 days after amputation (when AChE was at its highest level). It increases by about 34% with regard to the controls. Adrenaline is higher than controls 2 days after amputation, while noradrenaline is not significantly modified. The metabolic changes observed in the spinal cord during limb regeneration probably are the result of a general reaction to the stress of amputation (transection of brachial nerves) and regeneration of nerve fibers, since similar metabolic activities were observed after a simple denervation of the two unamputated forelimbs.Key words: acetylcholinesterase, choline acetyltransferase, catecholamines, regeneration, axolotl.