Three-dimensional organization of tubular and filamentous nuclear inclusions and associated structures in sympathetic neurons as revealed by serial sections and tilting experiments

Abstract

Fifty nuclear inclusions (N.I.) in neurons of cat superior cervical, celiac, and stellate ganglia were examined by serial sections and tilting experiments. The two basic elements, i.e., microfilaments and microtubules, are assembled in five main types of N.I., two of which are described for the first time in the three ganglia. Furthermcre, use of both techniques allows to identify four so-called associated structures: dense bodies, a granulofibrillar envelope, granulofibrillar bodies, and an accessory microtubular bundle. The three-dimensional organization and dimensions of each type of N.I. and their associated structures are established. Particularly the two types of crystalloids lie in a right prism with a lozenge-shaped base whose two axes display a constant length. These ultrastructural data, analyzed in light of previously experimental observations, are compatible with a working hypothesis according to which the simplest N.I. could evolve toward more complex ones (crystalloids) and are discussed with respect to biochemical studies on nuclear contractile proteins.