Coiled bodies in supraoptic nuclei of the rat hypothalamus during the postnatal period.

In electron microscopic studies of the supraoptic nuclei of the rat hypothalamus, structures identified as "coiled bodies" were found in magnocellular neurons. Although they could be seen elsewhere in mature neurosecretory cells, coiled bodies were commonly encountered in developing neurons during the postnatal period in both sexes. They appeared as distinctive nuclear inclusions consisting of round-to-oval networks of short electron-dense strands embedded in a less dense, fibrillar matrix, and lacking a limiting membrane. In fine structure and stain-affinity, they bore a resemblance to the fibrillar component of the nucleolus. Coiled bodies were located either in close association with the nucleolus or free within the nucleoplasm, showing no specific relationships with the perinucleolar chromatin or with the nuclear envelope. Their origin and functional meaning is discussed in the light of recent ultrastructural and biochemical data on cellular differentiation and nucleolar behavior.