Ultrastructural and cytochemical study of the pinealocyte nucleolus in rats.

The pinealocyte nucleolus has practically not been studied, although many studies have been carried out on this particular cell. In order to study the pinealocyte nucleolus, we have used conventional electron microscopy techniques, as well as cytochemical methods: silver nitrate, phosphotungstic acid (PTA) and ethylenediaminetetraacetic acid (EDTA). The pinealocyte nucleolus shows a reticular structure formed by a dense fibrillar component and closely packed granules (granular component), as well as electron lucent spaces which contain nucleoplasm. There are also places of light fibrillar material (fibrillar centers). Using the Ag-staining we have observed spherical aggregates of argyrophylic granules densely packed (fibrillar centers) and other granules loosely packed in its periphery (dense fibrillar component). PTA stains preferentially the fibrillar centers. We have identified as heterochromatin a dense granular aggregate that appears associated to the nucleolus. We present the pinealocyte nucleolus as an excellent model for the study of the functional meaning of nucleolar components.