Fig. 4.

The presence of the gradient at stage 45. A: maximum peak Na⁺ currents, as well as peak Na⁺ current density (B) increase significantly along the RC axis in both stage 45 (black circles) and stage 49 (white circles) tadpoles. Also notice that both rostral and caudal peak Na⁺ current and current density are significantly higher in the stage 45 tectum, indicated by the asterisks (*). In other words, the entire gradient is shifted to higher values at stage 45, but the slope of the gradient appears constant. C: maximum persistent K⁺ current and K⁺ current density (D) increase similarly along the RC axis at both stages. The increase observed in maximum K⁺ currents expressed by rostral neurons is significant, but the slight increase in K⁺ current density is not significant across either axis, because the increase in the K⁺ current is matched closely with the increasing cell capacitance.