Investigating motion detection of aging zebrafish with optomotor response

Abstract

Various aspects of visual functioning including motion perception have been shown to be significantly altered throughout aging. Contrary to the traditional view focusing on structural changes in the eye and retina, accumulating evidence suggests that subtle alterations in neural circuitry and functioning are respon-sible for the age-related changes in visual sensitivity and perception. However, the mechanisms underlying age-related changes in motion perception are still poorly understood. This thesis was aimed to investigate the detection of first-and second-order motion direction during aging by using zebrafish optomotor re-sponses (OMR). Furthermore, exposure-based visual learning was investigated by repeated presentation of first-order motion. The studies included both wild-type and achesb55/+ zebrafish with decreased levels of acetylcholinesterase which has been previously shown to delay age-related cognitive decline. In this way, it was also aimed to explore the possible functional links between cholinergic functioning and age-related changes in visual motion processing. The results indicated that adult zebrafish mainly exhibit negative OMR (i.e., position shift in the opposite direction of visual motion) to drifting first-order gratings which is significantly dependent on spatial frequency and contrast level of the motion. Rather than an overall effect of aging, the results revealed a three-way interaction between the contrast level of first-order motion, genotype, and age. Therefore, the findings pointed out a complex relationship between the physical characteristics of first-order motion stimulation and the cholinergic system during neural aging. Contrary to the first-order motion, the second-order motion did not induce strong optomotor responses in adult zebrafish. Although young and old zebrafish exhibited OMR with different polarities (negative and positive OMR, respectively), future work revealing robust responses will be informative to better understand and characterize age-related changes. Lastly, passive exposure of repeated first-order motion induced significant improvements in negative OMR of young and old zebrafish, suggesting that adult zebrafish can be used as a model organism to study passive forms of visual perceptual learning. Overall, these behavioral results pave the way for a detailed investigation of the functional links between the physical motion characteristics and the cholinergic system in the zebrafish aging model which will ultimately have important implications for developing interventions to improve human visual performance during aging.