Optic Nerve of Zebrafish (Danio rerio): An Animal Model for Human Aging
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The optic nerve is the cranial nerve that sends messages from the eyes to the brain and is part of the central nervous system (CNS). Astrocytes help maintain neuronal health within the CNS. In humans, senescence of astrocytes is thought to be a factor in aging-related diseases. Glial fibrillary acidic protein (GFAP, or in fish Gfap) is a protein uniquely expressed by astrocytes. Higher than normal expression of GFAP is an indicator of reactive astrocytosis, which in turn occurs as a consequence of injury or insult to the central nervous system. With an eye toward determining whether zebrafish are a suitable model for studying aging-related changes to the central nervous system, I hypothesized that increased expression of Gfap in the optic nerve of zebrafish correlates with aging of zebrafish. I also investigated p16-ARC, a protein that has been associated with aging-related diseases. Additionally, a study that observed optic nerve of human cadavers revealed that the diameter of the optic nerve was greater in aged persons than in younger persons. Therefore, I measured the optic nerve of the zebrafish to see if it increased in diameter as the fish aged. I used immunohistochemistry to examining Gfap and p16-ARC expression in fish aged 3 – 12 months, and I found labeling intensity increased as the fish aged. The diameter of the optic nerve increased as well. Taken together, these results suggest further investigations of zebrafish optic nerve are warranted to lend support to using it as a model system to understand aging in humans.