Morphological properties of experimentally produced target fibres in tenotomized rat gastrocnemius muscle.

The gastrocnemius muscles of 3 groups of 10 rats, sacrified 5, 7, and 12 days respectively, following tenotomy, were submitted to different types of fixation, fixative and embedding. The occurrence of target fibres is shown not to be an artefact due to the histological procedures. Further examination demonstrates that the target phenomenon occurs in the shortest fibres on the medial side of both heads of the gastrocnemius muscle and that it consists mainly of a disarrangement of the contractile elements of the muscle fibres. This study argues that this phenomenon represents some kind of myotonic state of a pathological muscle.