The effects of tenotomy and overload on the postnatal development of medial gastrocnemius motor units in the cat.
Five-to 7-day-old kittens were subjected to tenotomy of either the medial gastrocnemius muscle (MG) or its synergists within the Achilles tendon. The effects of these operations on the postnatal differentiation of MG motor units were investigated when the cats had reached the adult stage. The MG tenotomy produced a substantial weight loss, while tenotomy of synergists induced only a minor weight gain of the MG muscle. Tenotomy of the MG synergists induced a marked prolongation of motoneuronal AHP durations in the overloaded MG. This prolongation affected equally motoneurones of the S and F types. The twitches of the tenotomized motor unit group showed a relatively slower relaxation than those of the overloaded group. The muscle unit properties of the tenotomized MG muscles showed a less distinct differentiation than those of the overloaded muscles. The basic features of the various motor unit types were, however, normal in both groups, and there was no evidence of a major shift in the proportions of different motor unit types. It is concluded that the postnatal differentiation of all types of MG motor units is largely unaffected by the abnormal situations introduced in the present study.
D000125:Achilles Tendon / Q000502:physiology*; D000367:Age Factors; D000818:Animals; D001369:Axons / Q000502:physiology; D002415:Cats; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction; D024510:Muscle Development; D009929:Organ Size