Histochemical Fiber Composition of Some Facial Muscles in the Cat in Relation to their Contraction Properties

A histochemical analysis has been performed of the activity of myofibrillar ATPase, succinic dehydrogenase. NADH 2 tetrazolium reductase and phosphorylase and of the content of glycogen and fat in the orbicularis oculi, orbicularis oris and the depressor conchae muscles in the cat. All three muscles contain fibers with a low activity (type I) and such with a high activity (type II) of myofibrillar ATPase. The type II fibers predominate. In general, the type II fibers of the orbicularis oris have a higher activity of oxidative enzymes than those of the other two muscles. Differences in contraction times in relation to fiber composition are discussed. Stimulation of the orbicularis oculi at 5 Hz causes a contractile fatigue of 22–48 % in a 10 min period, which is related to a depletion of glycogen in muscle fibers with a low activity of succinic dehydrogenase. The orbicularis oris fatigues very little (2–21 %) during such a period and no significant glycogen depletion is seen. This is explained by a higher activity of oxidative enzymes in this muscle.