ゲンタマイシンの前庭器・神経節におよぼす影響

Abstract

Morphological changes in the vestibular sensory epithelial cells and the vestibular ganglia following gentamicin (GM) intoxication were demonstrated three dimensionally by scanning electron microscopy.A single dose of 4mg (0.1ml) of GM was injected into the middle ears of guinea pigs through the tympanic membrane. The vestibular organs and ganglia were observed from one day to 6 months after the treatment. Four days after the injection, fusion, ballooning and disappearance of sensory cilia were observed in the vestibular sensory epithelium. These changes were more marked in type I than in type II hair cells. Earlier morphological signs of degeneration were observed in the mitochondria of the supranuclear portion of type I hair cells.Eater dilatation of the cisterns in the Golgi apparatus as well as of the endoplasmic reticulum were noted. Nerve chalices also revealed disintegration in the earlier phase of degeneration. The changes of the sensory cell progressed and extended from the central toward the peripheral area of the crista and the macula.These findings suggest that GM may induce some metabolic changes in the vestibular sensory cells which result in fusion or loss of sensory hairs and later complete disappearance of sensory cells.Changes in the vestibular ganglia were first observed seven days after the treatment. The degenerative process started with destruction of the mitochondrial cristae of the Schwann cells and the ganglion cells. These changes were followed by dissociation of the myelin sheath around the ganglion cells. The cytoplasmic organelles in the ganglion cells gradually deteriorated. At a later stage, the myelin sheath around the ganglion cell disappeared and the number of cells was reduced.The changes in the ganglia are direct effects of GM.