AGE-RELATED ASTROCYTIC AND MICROGLIAL ALTERATIONS IN THE HUMAN OLFACTORY BULB

The olfactory bulb (OB) serves as a critical interface between the central nervous system and the peripheral environment, supporting immune surveillance and lymphatic communication. Astrocytes and microglia are involved in maintaining this immune and lymphatic balance. This study aimed to evaluate age-associated alterations in these cell types in OB. Postmortem OB tissues from four young individuals (aged 22–34 years) and four aged individuals (aged 60–73 years), obtained from the Istanbul Council of Forensic Medicine, were analysed. Samples were immunohistochemically stained with anti-GFAP (astrocyte marker) and anti-IBA1 (microglia marker). Layer-specific immunoreactivity was evaluated. Macroscopically, aged OBs appeared less uniform, while no overt abnormalities were observed in the rest of the brain. Further, GFAP expression was predominantly perivascular in all cases; increased astrocytic process complexity was observed in the ventral glomerular layer of young individuals, whereas in aged cases, increased vascular and non-vascular astrocytes extended into the inner layers. Also, microglial evaluation revealed predominantly ramified (resting) morphology in both age groups. In young OBs, IBA1 expression was most pronounced in the glomerular layer, whereas in aged cases, IBA1 expression was increased in inner layers as well. In conclusion, increased astrocytic and microglial activity within the glomerular layer, exposed to the external environment, likely represents a physiological response. However, the shift of glial activity toward inner layers reflects age-associated changes rather than overt pathology. The OB may serve as an early vulnerable site for protein-accumulating neurodegenerative diseases, with age-associated glial remodeling representing a physiological process that may increase susceptibility to pathology.