Figure 7

Caudal primary motor neuron and caudal primary motor neuron-like neurons fire action potentials with different properties. (A, B) Action potentials were evoked from caudal primary motor (CaPs), ventral lateral descending (VeLDs) and CaP-like neurons (see Methods). The insets align action potentials at their peaks to highlight kinetic differences. (A) During an action potential, the membrane potential repolarizes faster in CaPs than it does in VeLDs. (B) For CaP action potentials, the 5-base mismatched islet1(Sp) E3 morpholino (CtlMO) has no obvious effect on repolarization. In comparison, CaP-like action potentials of E3 morphants repolarize slowly. (C) Kolmer-Agduhr neurons (KAs) do not fire action potentials in response to brief depolarizing current injections. (D) After prolonged injection of hyperpolarizing current, KA”s fire regenerative responses. A single regenerative response recorded from another KA” is enlarged (right). (E) KA” action potentials have slower rates of rise than those elicited from CaPs (*P < 0.001 versus CaP) or VeLDs (^#P < 0.01 versus VeLD). However, the rate of rise of CaP-like action potentials is not significantly different from that of KA”s, VeLDs or CaPs. In contrast, the rate of decay of CaP action potentials is significantly faster than that of VeLD (^†P < 0.01 versus CaP), KA”s (*P < 0.001 versus CaP) or CaP-like action potentials (^P < 0.01 versus CaP). (F) Regenerative responses fired by KA”s have prolonged rise (^#P < 0.01 versus CaP or CaP E3MO) and decay (*P < 0.001 versus CaP) times. VeLDs fire action potentials of significantly longer duration than do CaPs (^†P < 0.05 versus CaP). Similarly, KA” regenerative responses have significantly longer durations than do those elicited from CaPs (*P < 0.001 versus CaP) or CaP-like cells (^†P < 0.05 versus CaP E3MO). (G) CaPs, VeLDs and CaP-like neurons have similar input resistance. Compared to CaP, KA”s have significantly greater input resistance (*P < 0.001 versus CaP) or CaP-like cells (^#P < 0.01 versus CaP E3MO).