Ontogeny of special endoplasmic reticulum complexes in neurons of the lateral geniculate body in rats]

1. The ultrastructure of special membranous convolutions (MC) of the endoplasmic reticulum (complex convolutions, KARLSSON 1966), was studied in neurons of the lateral geniculate body in postnatal and adult rats. 2. The MC situated in the perikaryon are often attached to the nuclear membrane. Their average diameter is about 2 mum. Some MC of elongated form are extended over 6 mum. 3. Smaller MC of similar structure occur within basal dendrites, mainly in the environment of large axo-dendritic desmosomoid junctions. 4. The MC consist of smooth double membranes in a laminar or irregular arrangement, and are in connexion with the rough endoplasmic reticulum. 5. After incubation with ethanolic phosphotungstic acid the intermembranous material of the MC is stained in the same high intensity as this is the case with synaptic junctions. 6. The MC are developed by the rough endoplasmic reticulum during the 5 th and 6 th postnatal weeks. 7. The ultrastructure of the MC of both, normal and dark raised rats shows no significant differences.