Figure 8

Rohon-Beard and Rohon-Beard-like cells fire action potentials with different properties. (A, B) Action potentials were evoked from dorsal spinal neurons in 24 hours post-fertilization (hpf) embryos (see Methods). (A) Rohon-Beard (RB) action potentials waveform have a distinctive overshoot and afterhyperpolarization (AHP). (B) RB-like cells of E3 morphants fire action potentials without a prominent AHP. (C) Aligning the peaks of RB and RB-like action potentials highlights kinetic differences. (D, E) Several properties of action potentials (rate of rise, rise time, rate of decay, decay time, duration) were evaluated at rheobase. (D) RBs fire action potentials with faster rates of rise and decay than those elicited from dorsal lateral ascending interneurons (DoLAs) and dorsal commissural interneurons (Dorsal Comms) (*P < 0.001 versus RB). Compared to RBs, RB-like cells fire action potentials with slower rates of rise (^#P < 0.01 versus RB) and decay (^†P < 0.05). Compared to DoLAs and Dorsal Comms, RB-like cells fire action potentials with faster rates of rise (^P < 0.01 versus DoLAs and Dorsal Comms) and decay (^•P < 0.01 versus DoLA; °P < 0.05 versus Dorsal Comm). (E) Compared to RBs, DoLAs fire action potentials with increased rise time, prolonged decay time and longer duration (*P < 0.001 versus RBs). Dorsal Comms fire action potentials with longer decay time (^#P < 0.01) and duration (^†P < 0.05) than do RBs. DoLAs and Dorsal Comms fire impulses that have significantly different durations (^#P < 0.01 versus DoLA). RB-like cells fire impulses with decreased rise times and briefer decay time than do DoLAs (^P < 0.001 versus DoLAs). (F) RB-like cells fire impulses with small AHP amplitudes in contrast to those of RBs (*P < 0.001) or DoLAs (^†P < 0.05). (G) The input resistances of RB-like and RB cells are not significantly different but significantly lower than those of DoLAs and Dorsal Comms (*P < 0.001).