Fine structure of neurons of the hypertrophied human inferior olive

Ultrastructural study of hypertrophied inferior olives from three cases of palatal myoclonus revealed tha nerve cells not infrequently contained numerous round, homogeneously electron-dense granules (mean diameter, 360 nm) located within expanded cisternal profiles of rough endoplasmic reticulum (RER). Control tissue did not contain similar structures. These granules may consist of proteinaceous secretion of the RER which, for reason unknown, accumulates during transsynaptic degeneration of the inferior olive. Additional noteworthy electron microscopic features of neurons of the hypertrophied olive were as follows: 1. neurofilamentous hyperplasia, greater in dendrites than in perikarya; 2. vacuoles in intermediate and large (up to 15 mum) size, derived from RER; and 3. prominent intracytoplasmic protrusions by boutons containing dense core vesicles (mean diameter, 98 nm). Glomeruloids were identified ultrastructurally and consisted of numerous boutons interspersed among neurofilament-rich dendrites and occasional, filament-packed astrocytic profiles. Frequently, these boutons also contained dense-core vesicles. It seems possible that the boutons mentioned may arise from collateral axonal sprouts.