Figure 1.
Intrinsic excitability is reduced in VPA neurons during the early postnatal period but not the late postnatal period. Control (CTL) data are in black and VPA data are in gray. A, Examples of responses to current steps at four postnatal ages. Each step was 1 s long. Vertical scale bar: 25 mV for membrane potentials, 250 pA for current steps. B, Average measurements of resting potential (Vm), input resistance (MΩ), membrane time constant (τ), rheobase current (Rheo), threshold potential (VT), and spike height (Height). Vertical error bars are SEM. Horizontal error bars indicate the age ranges into which data were grouped. The numbers of control and VPA animals in each age range were, respectively: 4 and 3 (P4–P5), 10 and 10 (P8–P10), 16 and 14 (P15–P19), 5 and 6 (P22–P26), 8 and 8 (P35–P38). On average, four neurons were recorded per animal. Age group was a significant main effect for every parameter (p < 0.001, ANOVA), but VPA exposure was not significant for any parameter. C, Firing rate-current (f–I) curves for three age groups, constructed by measuring the total number of spikes elicited by current steps (1 s long) of different amplitudes. Numbers of animals were as in B. VPA exposure was a significant effect for the youngest age group (p < 0.05, repeated-measures ANOVA), but not for the oldest.