Fig. 2. Action potential activation during current clamp step protocol. Representative action potentials elicited in 1- and 4-week-old animals are shown in A . Note the much greater change in membrane potential deflection from a fixed current in the 1-week-old animals when compared with the 4-week-old animals at baseline. This is consistent with the greater resistance in the younger animals. B demonstrates oscillations and multiple spikes in a cell from a 1-week-old animal. This was not seen in cells from the older animals.