PARANUCLEOLAR STRUCTURE, ACCESSORY BODY OF CAJAL, SEX CHROMATIN, AND RELATED STRUCTURES IN NUCLEI OF RAT TRIGEMINAL NEURONS - A CYTOCHEMICAL AND ULTRASTRUCTURAL STUDY

Comparative light and electron microscopic study of nuclei in rat trigeminal neurons identified two structures which are the ultrastructural equivalent of the paranucloelar structure and the accessory body of Cajal, two nucleoplasmic structures previously demonstrated in other neurons by light microscope silver staining methods. Ultrastructural evidence indicates that the dense component of the nucleolus is converted into the paranucleolar structure, which then detaches from the nucleolar surface to lie free in the nucleoplasm as the accessory body of Cajal. The cytochemistry, ultrastructure, and antimonate reactivity of the paranucleolar structure and accessory body were identical. Both structures lacked cytochemically demonstrable DNA, RNA, or basic protein. The neuronal nuclei also contained Feulgen‐positive sex chromatin bodies that adhered to the nucleolus, the nuclear membrane, or to both of these structures in specimens of female but not male rats. The ultrastructure and antimonate reactivity of these bodies closely resembled that of heterochromatin clumps but differed markedly from that of the paranucleolar structures and accessory bodies. Additional structures characterized ultrastructurally included patches, granular bodies, and flakes. These structures, like the paranucleolar structure and the accessory body of Cajal, are apparently unique to nuclei of neurons. Cytochemical methods showed that the patches contained basic protein but no nucleic acid. Copyright © 1969 Wiley‐Liss, Inc.