[Ultrastructural bases for the synthesis of ribosomal RNA in the nuclei of the parotid gland. The role of intranuclear bodies].

Identification and numerations on electron microscopic samples of rat parotid glands revealed an unexpected high frequency of nuclear bodies in acini and in striated ducts. Three different morphological types of nuclear bodies were identified: type I corresponded to a circular outline of finely fibrillar or granular bodies. Type II exhibited an outer fibrillar cortex surrounding a central lucent core. Type III possessed a thick granular or fibrillar cortex surrounding dense granules. Type IV nuclear bodies appeared to be circumscribed by a thick lamellar cortex and contained dense and heavy stained granules. The biochemical content of the nuclear bodies mostly corresponds to proteins and it was possible to demonstrate slight quantities of RNA. Recent studies seem to confer to some of those nuclear bodies a possible role in RNA processing or transport. It is however peculiar to find nuclear bodies in striated ducts which are not involved in active protein synthesis as the acini.