An ultrastructural study of the craniocaudal continuation of the glycogen body.

An ultrastructural analysis of the chicken glycogen body and its craniocaudal continuation areas shows a continuum of astroglial cell types. Characteristic glycogen body astroglia are confined to the classically defined body located in the chicken lumbosacral spinal cord. These are large cells which have an eccentric dark nucleus surrounded by a rim of dense cytoplasm which contains the usual complement of organelles. The remainder of the cell volume is occupied by alpha and beta glycogen particles interspersed with a flocculo-granular material continuous with the main cytoplasmic mass. Astroglial cells of continuation areas usually have a light cytoplasm and a centrally placed nucleus. They contain beta glycogen particles of varying sizes, but like the glycogen body cells, may have beta particles as large as 48 nm. Such particles, which resemble four leaf clovers in shape, are suggestive of an ordered substructure. Gliofilaments are not always conspicuous in astroglial perikarya, but large numbers of them are present in the processes. Although the continuation areas are mostly confined to gray matter regions, the contained astroglial processes exhibit circular, triangular, or cylindrical shapes and form an unpatterned mosaic. Astrocytic processes forming the glia limitans on the anterior and posterior margins of the cord often contain conspicuous amounts of glycogen. The ultrastructural identification of such large amounts of glycogen within the chicken nervous system suggests that it plays a major role in avian neural metabolism.