Abstract

Tanycytes, specialized ependymal cells lining the third ventricle of the hypothalamus, serve as crucial intermediaries between the cerebrospinal fluid and the neuroendocrine centers of the brain, playing a vital role in metabolic and neurogenic regulation. The structural organization of the nucleus, particularly the nucleolus and heterochromatin, reflects the cell's transcriptional activity and functional state. This study aimed to characterize the ultrastructural organization of the nucleolus and constitutive heterochromatin aggregates in different subtypes of rat brain tanycytes across postnatal development and aging. Using transmission electron microscopy and specific cytochemical staining, we analyzed the nuclear morphology of $\alpha$- and $\beta$-tanycytes. Our findings reveal that constitutive heterochromatin in tanycytes forms distinct, single rounded aggregates, predominantly localized along the nuclear periphery. Furthermore, the nucleolar structure, characterized by the ratio and distribution of its components (fibrillar centers, dense fibrillar component, and granular component), exhibits age- and subtype-dependent variations, suggesting differential ribosomal biogenesis and transcriptional activity. These structural characteristics provide a morphological basis for understanding the unique functional plasticity of tanycytes and their role in maintaining hypothalamic homeostasis and neurogenesis throughout the lifespan.