Establishing an assay for visual desensitization in larval zebrafish for understanding synaptic plasticity

Synaptic plasticity, the ability of neurons to modify the strength of their connections, is essential for learning. Desensitization is a type of synaptic plasticity during which a behavioral response to a stimulus is reduced after repeated presentations of a weakened version of the stimulus which does not produce the behavioral response and thus is deemed a subthreshold stimulus. Here we explore whether the larval zebrafish escape response from visual threats, such as an expanding dark spot, can act as a potential model to study desensitization. We developed a novel experimental setup to investigate visual desensitization, exposing larvae to looming visual threats of varying contrast, and used high-speed cameras to verify rapid escape movements. First, we established stimuli which reliably acted as subthreshold and suprathreshold stimuli. Next, we quantified the response rate before and after desensitization and compared those data to control larvae who were not desensitized. We observed desensitized larvae reduced their response rate to threatening looming stimuli. By providing an opportunity to explore the plasticity mechanisms governing sensory-motor transformations and behavioral adaptation, this research contributes to our understanding of fundamental principles of learning and neural plasticity across vertebrates.