Position- and quantity-dependent responses in zebrafish turning behavior

Neural reflexes are stereotypical automatic responses often modulated by both intrinsic and environmental factors. We report herein that zebrafish larval C-shaped turning is modulated by the stimulated position of Rohon-Beard (RB) neurons. Targeted stimulation of more anterior RB neurons produces larger trunk flexion, which anticipates adult escape behavior by coordinated turning toward the appropriate direction. We also demonstrated that turning laterality varies with the numbers of stimulated neurons. Multi-cell stimulation of RB neurons elicits contralateral turning, as seen in the touch response to physical contact, while minimum input from single-cell stimulation induces ipsilateral turning, a phenomenon not previously reported. This ipsilateral response, but not the contralateral one, is impaired by transecting the ascending neural tract known as the dorsolateral fascicule (DLF), indicating that two, distinct neural circuits trigger these two responses. Our results suggest that RB neurons transmit the position and quantity of sensory information, which are then processed separately to modulate behavioral strength and to select turning laterality.