Microglial activation has been associated with the pathogenesis of neurodegenerative disease. To characterize microglial responses in the zitter mutant rat, which shows progressive spongy degeneration, the development of microglial cells was investigated using ionized calcium-binding adaptor molecule (Iba1) antibody as a specific marker of microglial cells. Neurochemical analysis showed transiently increased Iba1 protein levels in the brains of developing Sprague-Dawley (SD) rats. However, high Iba1 protein readings continued in aged zitter rats. Immunohistochemical analysis revealed time-course differences in the transformation of microglia between SD and zitter rats and prolonged activation of microglial cells in the zitter rat. In the zitter rat, activated microglial cells characterized by swollen cell bodies and shorter, thicker processes were distributed throughout the brain from 2-weeks- to 2-months-old. After 2-months-old, numbers of activated microglial cells gradually decreased. However, these cells were not observed in SD rats. Iba1-immunoreactive cell-clusters organized by at least five activated microglial cells were also prominent in the zitter brain. These differences reflect the neuropathology of this mutant rat triggered by deletion of the attractin gene. The present data may thus suggest that microglial cells directly or indirectly contribute to progressive spongy degeneration in zitter mutant rats.
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