Alterations in contractile properties of extensor digitorum longus muscle from C57BL/6J mice following denervation at 1 day of age.

Changes in contractile properties of developing fast-twitch skeletal muscle of the C57/BL6J mouse were studied following neonatal denervation. A sciatic neurectomy was performed at 1 day of age and then denervated and control muscles were examined at 7, 14, and 21 days postdenervation. In addition, normal muscles were studied at 1 day of age. The denervated muscles exhibited prolongation of time-to-peak twitch tension and half-relaxation time, a slowing of the maximum velocity of shortening, and a marked increase in resistance to fatigue compared with controls. Isometric tetanus tension was reduced compared to the control muscle both in absolute terms and when expressed relative to body weight at all ages studied. The absolute isometric twitch tension was reduced at 7 and 14 days, but was reduced only at 21 days when expressed as a fraction of the muscle weight. Post-tetanic twitch potentiation failed to appear in the denervated muscle. It would appear that neonatal denervation results in an uncoupling of the developmental pattern of skeletal muscle.