[Motor innervation of muscle fibers in thyrotoxic myopathy]

In patients and test animals similar changes in innervation have been revealed. Degeneration of some preterminal axons has been shown. The most manifested feature's increased ramification of distal axons. No signs of real reinnervation have been found. New collateral branches of preterminal, terminal and ++ultra-terminal axons usually have their ends at the same muscle fiber in the form of additional nervous terminals. Decreased average diameter of motor end-plates, revealed in the test animals, depends not on their degeneration, but on formation of new small motor end plates as a result of immature axonal ramification of distal axons. Acetylcholinesterase activity in the end-plates is decreased. A suggestion is made that excess of thyroid hormones in the skeletal muscle disturbs both the system of cyclic nucleotides and mechanisms of muscular contraction, connected with it and axoplasmic transport, respectively. The changes of the terminal intramuscular innervation revealed, structures of the motor end-plates with a decrease of acetylcholinesterase activity are supposed to result from disturbances of neurotrophic regulation of the muscle fibers because of the disturbances of the axoplasmic current as the excess of thyroid hormones.