The target phenomenon in rat muscle following tenotomy and neurotomy. A comparative light microscopic and histochemical study.

Target fibers were checked at regular intervals in two groups of rat gastrocnemius muscle namely after tenotomy and neurotomy. The highest amount of target fibres was observed during the first week following tenotomy and around the seventh week, when the muscle became again functional by spontaneous union of the tendon. The target phenomenon was restricted to the type II fibres. It appeared also in the early stage of re-innervation, 5 weeks following neurotomy and remained present subsequently in a transitional zone between denervated and re-innervated muscle fibres and was restricted to the type I muscle fibres. The target phenomenon was not the only histochemical alteration observed following tenotomy and neurotomy. This experimental study allowed to determinate more precisely the causal factors of the target phenomenon.