Abstract
Purpose :
Microglia are the resident macrophages of the central nervous system (CNS). In addition to removing dead cells and debris from the CNS, microglia play an important role in neural development and homeostasis. Microglia are known to prune synapses in various areas of the CNS, including the retina, and their synapse refinement roles have been shown to be important in the development and maintenance of healthy vision in the rod-dominant mouse retina. We used an optomotor response assay (OMR) on microglia-sufficient and microglia-deficient larval zebrafish to determine the role of microglia in the functional development of vision in the cone-dominant zebrafish retina.
Methods :
Retinas from irf8 mutant zebrafish were evaluated for microglial deficiency using 4C4 antibody staining, which recognizes lgals3bp. Optomotor response assays (OMRs) were performed on wildtype and irf8 mutant larval zebrafish daily from 6-10 days post-fertilization (dpf), before rod-mediated vision becomes functional, using MovingGrating v1.3. Three tests were used to assess visual acuity in the zebrafish larvae: normal grating size and contrast, low contrast grating, and large grating. Each test was performed three times, and group performance was averaged across these repeats. Four groups of 15 wildtype fish each and five groups of 15 mutant fish each were tested (135 fish total). Electroretinograms (ERGs) are currently in progress.
Results :
4C4 antibody staining confirmed deficiency of microglia in irf8 mutant zebrafish retinas (n=6). OMR success rate decreased on days 9 and 10 for both genotypes in each testing category, which could be due to the emergence of shoaling behavior. The wildtype and irf8 mutant zebrafish did not show a significant difference in OMR success rate in any condition from 6-10 dpf (p>0.05, n=60 wt, 75 mutant, Fisher’s Exact Test).
Conclusions :
Our experiments indicate that the lack of microglia does not significantly impact the circuits required for visually mediated behavior tested by OMR assay in larval zebrafish. Further, motor function is likely not impaired by the lack of microglia. ERG recordings will further our understanding of visual development and function in the absence of microglia. In the future, we will examine the role of microglia in restoring visual function after damage and regeneration in larval zebrafish.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.