The target phenomenon in tenotomized rat gastrocnemius muscle. A comparative electrophysiological and morphological study.

In ten female rats electrophysiological recordings and subsequent histological and histochemical examinations were performed at different time intervals and in different parts of the gastrocnemius muscle, following tenotomy and following combined tenotomy and neurotomy. Repetitive motor action potentials were more easily evoked during the period and at the sites of occurrence, of target fibres in tenotomized gastrocnemius muscle with an intact nerve supply. Both phenomena, the electrophysiological as well as the morphological one, were strongly inhibited by the simultaneous neurotomy. This study suggested that the target phenomenon is a morphological expression of an increased irritability of the muscle, following tenotomy.