Behavior of the cholinergic system in the rat brachial plexus after contralateral neurotomy

Changes in the activity of specific proteins of the cholinergic system were measured in the rat spinal cord (C5 through T1 levels), secondary trunks of the brachial plexus, and extensores carpi muscles of one antimere, at various periods after contralateral transection of the brachial plexus. Choline acetyltransferase (ChAc) specific activity significantly decreased to approximately 50% of the control in all three regions tested within 7 to 16 days; by the 35th day, it had returned to the control values. The behavior of acetylcholinesterase (AChE) specific activity was similar to that for ChAc in nerves and muscles, whereas in the spinal cord it did not display any significant variation. The total (per muscle) activity of the cholinergic receptor (ACh-R) increased to more than 200% of the control muscles, even though its specific activity did not change during the experiment. We suggest that some alteration in the transfer of information between normal and contralateral (axotomized) motoneurons occurs after transection of a peripheral nerve. Several factors could be involved, particularly the interruption of crossed reflex arcs. The neurochemical changes observed may be triggered by a marked decrease in ChAc synthesis in the motoneuron cell body. Whatever the mechanism involved, it appears that some events occurring in the damaged neurons also occur, either wholly or in part, in the contralateral, unimpaired neurons. It also appears that the changes in cholinergic protein activities that develop in muscles after contralateral neurotomy partially mimic those observed after muscular denervation.