Nucleolus-like bodies in the posterior subnucleus of the rat paraventricular nucleus during postnatal development. An ultrastructural, cytochemical and morphometric study.

Dense intracytoplasmic bodies which lack surrounding membranes and referred to as nucleolus-like bodies (NLBs), have been observed in the big sized neurons of the rat posterior subnucleus in the hypothalamic paraventricular nucleus (PVNP) during neonatal stages. The NLBs suddenly appear from 8th to 16th postnatal days, coinciding with an increase of the nuclear activity in these neurons. NLBs present a granular aspect, showing a close morphological association with ribosomes and rough endoplasmic reticulum. The specific silver-staining procedure used in the study of the nucleolar organizing regions shows no silver grains deposited in the NLBs. The hypothetical nuclear origin of NLBs and the relationship of its frequency within the neuronal cytoplasm, when an increased protein synthesis process takes place, are discussed.