Meeting Abstract

P2.89  Jan. 5  The Role of Excitatory Spinal Interneurons in the Mechanics of Startle Movement in Zebrafish. BIERMAN, HS*; FAN, J; HALE, ME; Univ. of Chicago; Univ. of Chicago; Univ. of Chicago hilaryb@uchicago.edu

During Mauthner cell (M-cell) elicited startle responses, circumferential descending (CiD) interneurons of zebrafish, and their homologs in other species, are believed to relay excitatory signals from M-cells to secondary motoneurons and augment M-cell excitation of primary motoneurons. We examined the roles of CiD cells in the startle response of the larval zebrafish in two ways, (1) by utilizing simultaneous calcium and kinematic imaging to assess cell activity in a behavioral context and (2) by ablating a series of CiD neurons and determining the effect on movement. Calcium imaging indicated that CiDs are generally, but not exclusively, active unilaterally during the initial bend (stage 1) and that they also are active during the second bend (stage 2), which is contralateral to the first. We found that CiD ablation did not change the duration of the startle movements, but decreased the stage 1 turn angle and increased the stage 2 turn angle when cells were killed on the side of the stage 1 bend. These results support the hypothesis that, by increasing motoneuron activity, CiDs function to increase excitation of axial muscle and thus increase the stage 1 turn angle. We suggest that the stage 2 turn angle increases after CiD ablation because there is less resistance to bending than normal due to the decreased stage 1 side contraction. Further, we suggest that the lack of change in duration of startle movements supports the idea that the timing of the stage 2 startle movement is determined in large part by reticulospinal input and not adjusted with sensory feedback during the response. Supported by NS043977 to MEH.