Figure 1. Amplitude of bioluminescence signals in spinal motor neurons correlates with the type of locomotor maneuver during active swimming.
(A) Bioluminescence signals emitted from spinal motor neurons in Tg(mnx1:gal4;UAS:GFP-aequorin-opt) zebrafish larvae at 4 dpf were recorded using a photomultiplier tube under infrared illumination during active behaviors elicited by an acoustic stimulus. (B) Live fluorescent image (upper panel) and immunohistochemistry for GFP (lower panel) in a 4 dpf Tg(mnx1:gal4;UAS:GFP-aequorin-opt) zebrafish larva showing selective expression in spinal motor neurons (arrowhead: dorsal primary, arrow: ventral secondary motor neurons), and strictly no expression in muscle fibers (n = 5). (C) Motor behaviors elicited by acoustic stimuli. Superimposed traces illustrate the amplitude of tail contractions over time, for each behavior. Traces are color-coded according to the delay from stimulus onset. Automated categorization classified maneuvers into escapes (n = 245/283) or swims (n = 21/283) (n = 10 larvae and 300 trials). (D) Example traces of typical bioluminescence signals and kinematic parameters observed for each category. (E) Mean bioluminescence amplitude was higher for escapes (28.4 ± 0.9 photons/10 ms; normalized amplitude per larva = 0.41 + /- 0.18) than swims (3.9 ± 1.4 photons/10 ms, p<0.001; normalized amplitude = 0.06 + /- 0.02, p<0.001). (F) Correlation between bioluminescence signal amplitude and maximum tail angle amplitude (R = 0.4, p<0.001).