Meeting Abstract
The S-start startle behavior is produced in response to caudal stimuli in zebrafish and other taxa. By examining the mechanistic basis of the S-start behavior, we aim to gain insight into how the organization of the spinal sensory network influences behavioral choice. First, we performed behavioral kinematic studies in larval zebrafish to describe the initial “S” shaped double bend of the startle and to determine its relationship to stimulus position. We found that the bend pattern is conserved despite variation in the rostrocaudal location of the tail stimulation, indicating that there is a morphological demarcation between the anterior and posterior bends. Second, we investigated the neural basis of the double bend movement pattern. There is no evidence of regional organization of motor neurons or premotor interneurons that could explain this pattern of bending. We identified Rohon Beard (RB) cells, a type of somatosensory cell, as a key sensory input that produces local caudal bending. Paired recordings have shown that caudal RBs indirectly inhibit contralateral caudal motor neurons and predispose the axis to generating an S bend. This finding led us to investigate sensory input as a potential mechanism for regionalized motor activity. Because we only observe RB-elicited inhibition in the caudal region, it suggests that there is regionalization in RB subtype distribution or connectivity. Using in vivo light sheet imaging of GFP-labeled somatosensory neurons, we explore rostrocaudal differences in RB arborization and dendritic projections in zebrafish larvae to better understand how these subtypes may be distributed. This work sheds light on the roles of tail sensation and local spinal circuits in behavioral decision-making and regionalization of the body axis.
