Figure 9. Firing pattern properties are different between Ih(+) dopaminergic and non-dopaminergic neurons.
A, stably spontaneously active Ih(−) neurons (n = 10) have a higher firing rate than either group of Ih(+) neurons (TH(+) n = 25; TH(−) n = 18; Ih(+) TH(+) versus Ih(−) and Ih(+) TH(−) versus Ih(−), P < 0.0005). B, in these neurons, the mean standard deviation of interspike intervals (ISIs) from a train of 601 consecutive action potentials is not different among cell types, although most Ih(−) neurons exhibit very small deviations (ANOVA: P = 0.13). C, the skew of the same sample of ISIs is significantly higher in Ih(−) neurons than in Ih(+) neurons (Ih(+) TH(+) versus Ih(−), P < 0.001; and Ih(+) TH(−) versus Ih(−), P < 0.005). D, there is an inverse relationship between firing rate and ISI standard deviation shared by the three cell types (note the exponential scales of axis and ordinate). E, there is a relationship between ISI skew and firing rate in spontaneously active VTA neurons.