42.9 Thursday, Jan. 5 Activity of Mauthner cells and their serial homologues during alternative startles in larval zebrafish LIU, Y.-C.*; HALE, M. E.; Univ. Chicago; Univ. Chicago email@example.com
Fishes perform a range of escape responses to threatening stimuli. Many species perform C-starts, characterized by a C-shaped body bend during stage 1, the initial turn away from the point of attack. Some species, such as northern pike and muskellunge, can also perform S-starts, where the stage 1 body bend takes on an S shape. We have previously shown that larval zebrafish also perform both C- and S-starts, the latter more likely triggered by a stimulus from the caudal end. Studies have shown that a set of hindbrain neurons, a pair of Mauthner (M-) cells and their serial homologues MiD2cm and MiD3cm, play roles in generating C-starts; however, the neural circuitry responsible for the S-start is as yet unknown. Ablation experiments point to the M-cell and its homologues as likely candidate neurons for driving the S-start, thus we aimed to investigate the Mauthner array’s involvement in this alternative startle behavior. We used electrical tail stimulation to elicit startles and recorded from peripheral motor axons to identify and classify startle types. We performed whole-cell patch recordings from M-cells ipsi- or contralateral to the stimulus during startles and found bilateral firing during S-starts, while only the ipsilateral M-cell fired during C-starts as had been shown in previous studies. We also recorded from the Mauthner homologues and performed spinal cord transection experiments to explore their contributions to startle neural control more broadly. The S-start may provide a valuable comparative startle model to the C-start for understanding the organization of simple neural circuits. The interaction and overlap of C- and S-start neural control systems provides opportunities to understand coordination and control of the startle behavioral repertoire more broadly.