Fig. 5. Large angle C-start responses to dark-flash stimuli are Mauthner independent. (A) Laser ablation of Mauthner cells. Cell bodies (asterisks) and axons (arrows) visible in control lesions (top) are absent in immunohistochemical staining 48 h after ablation (bottom), while fibers coursing around the Mauthner cells, including the axon cap (arrowheads) are unaffected. Scale bar, 20 µm. (B) High performance startle responses elicited by acoustic/vibratory stimuli in control larvae (`control', N=8) are completely abolished after bilateral Mauthner cell lesion (`ablation', N=6 larvae). Slower, long latency responses to the same stimulus are not affected by Mauthner cell lesions (data not shown). (C) Mauthner cell ablation does not impair dark-flash responsiveness in the same set of larvae, showing that O-bend responses to dark-flash stimuli are not initiated by the Mauthner cell startle circuitry (two-tailed t-test, P=0.89). Larvae were tested individually with a series of 10 dark flash stimuli from 65 µW cm^–2 to darkness, at 1 min intervals. (D) O-bend kinematics during the dark-flash test in control larvae (`C') and ablated larvae (`A') are almost identical, arguing that the Mauthner cell is not involved in larval dark-flash responses. No statistical differences are present between any pair of kinematic values (two-tailed t-test, P>0.1 for all measures). Values are means ± s.d. of O-bend responses.