Changes in cholinesterase activity following partial denervation, collateral reinnervation, and hyperneurotization of muscle

Abstract

Denervated rat skeletal muscle loses about 50% of its cholinesterase (ChE) activity within 1 week and undergoes relatively little additional loss subsequently. Following reinnervation, several weeks are required for the normal level of ChE to be restored. The present study was performed to determine the effects of partial denervation, collateral reinnervation, and hyperneurotization on the ChE activity of muscle. The soleus and plantaris were partially denervated by transecting spinal nerves L4 or L5. The ChE activity of muscle homogenates was determined at 1 week (before collateral reinnervation) and at 8 weeks (after collateral reinnervation). In another group L4 was crushed and ChE determined 4 months post-operatively (at which time the muscles had become hyperinnervated by the collateral sprouts from L5 plus the regenerated axons from L4). Partial denervation produced a decrease in ChE that was proportional to the number of muscle fibers that had been denervated. Following collateral reinnervation the ChE was restored to normal levels. The ChE of the hyperneurotized muscle was not above normal. It is concluded that a decreased neuronal pool can, by virtue of collateral branching, maintain a normal level of ChE in the muscles it innervates. Furthermore, it appears that the upper and lower limits of ChE activity are established by factors intrinsic to the muscle, but that within these limits the enzymatic activity is proportional to the number of innervated muscle fibers.