Short-term desensitization of fast escape behavior associated with suppression of Mauthner cell activity in larval zebrafish

- Ca2+ imaging of Mauthner (M) cell is performed during C-start in larval zebrafish.
- A single firing of the M-cell is coupled with initiation of short-latency C-start.
- Desensitization of short-latency C-start is induced by repeated weak sound stimulus.
- Long-latency C-start is insensitive to the weak sound conditioning.
- A modified element may be located within the auditory afferent pathway to M-cell.

Escape is among the simplest animal behaviors employed to study the neural mechanisms underlying learning. Teleost fishes exhibit behavioral learning of fast escape initiated with a C-shaped body bend (C-start). C-starts are subdivided into short-latency (SLC) and long-latency (LLC) types in larval zebrafish. Whether these two can be separately modified, and the neural correlates of this modification, however, remains undetermined. We thus performed Ca2+ imaging of Mauthner (M-) cells, a pair of giant hindbrain neurons constituting a core element of SLC circuit, during behavioral learning in larval zebrafish. The Ca2+ response corresponding to a single spiking of the M-cells was coupled with SLCs but not LLCs. Conditioning with a repeated weak sound at subthreshold intensity to elicit C-starts selectively suppressed SLC occurrence for 10 min without affecting LLC responsiveness. The short-term desensitization of SLC was associated with the suppression of M-cell activity, suggesting that changes in single neuron responsiveness mediate behavioral learning. The conditioning did not affect the acoustically evoked mechanotransduction of inner ear hair cells, further suggesting plastic change in transmission efficacy within the auditory input circuit between the hair cells and the M-cell.