走査型電子顕微鏡によるラット内喉頭筋神経下装置の形態学的研究

Abstract

We investigated the subneural apparatus (SNA) of the cricothyroid (CT), thyroarytenoid (TA) and posterior cricoarytenoid (PCA) muscles in an adult rat using scanning electron microscopy. The excised muscle was fixed in 3% glutaraldehyde and postfixed in 1% osmium tetraoxide. The specimen was subsequently treated with 8N - HC1 for 30 minutes at 60°C to remove the intramuscular connective tissue components. A histochemical study of the fibers, a myosin ATPase stain, in the three muscles was also performed. All of the primary synaptic clefts observed in the TA and PCA muscles were of the depression type, while those in the CT muscle consist of both depression and labyrinthine type. Furthermore, we classified the depression type SNA into two types, one with a predominance of the slit type (Ds type) and the other a mixture of the slit and pit types (Dmix type), based on differences in the appearance of the secondary synaptic cleft. In contrast, the labyrinthine type SNA consisted of a single component, a predominantly slit-type (L type). Of these three SNA types, two were found in the TA and PCA muscles, while the CT muscle showed the three types of SNA. Two types of muscle fiber, type 1 and 2B fibers, were differentiated in the three different kinds of muscles. In the TA and PCA muscles, the fact that proportion of each of the SNA types was equal to that of each of the muscle fiber types indicated that the SNA of the type 1 muscle fiber corresponded to the Dmix type, and that of the type 2B fiber corresponded to the Ds type. In the CT muscle, assuming that both the Ds and L types served as the SNA of the type 2B muscle fiber, the proportion of the Ds and L types to the total number of the SNA was nearly equal to the proportion of type 2B muscle fibers. In conclusion, we inferred that each type of muscle fiber had a specific type of SNA in the case of the intrinsic laryngeal muscles of the adult rat.