Figure 6.

L-type Ca²⁺ channels contribute to supralinear dendritic Ca²⁺ signals. A, The firing rate of dopamine neurons was altered by injection of holding current in the presence of nifedipine. B, AP-evoked Ca²⁺ signals during 1.3 Hz firing were averaged and fit as in Figure 3B. C, Predicted Ca²⁺ signals (black) were generated for the firing rates displayed in A. Blue lines represent the average values of the predicted Ca²⁺ signals. D, Dendritic Ca²⁺ signals (black) recorded at the firing rates displayed in A. Red lines indicate the average Ca²⁺ signal over the course of the scan. E, Summary plot of measured (red) and predicted (blue) Ca²⁺ signals plotted against the rate of tonic firing in the presence of nifedipine, and measured Ca²⁺ signals in control conditions (black). Light symbols are individual points; dark symbols are binned averages and SEM for all dendrites. Lines are lines of best fit to each dataset. The slopes of the lines of best fit were as follows: control measured data = 3.7% G/G_s per Hz; nifedipine-treated measured data = 2.2% G/G_s per Hz; nifedipine-treated predicted data = 1.3% G/G_s per Hz. Predicted data varies from the line of best fit due to variability in the size and kinetics of the AP-evoked Ca²⁺ transients between cells. F, Plot of the ratio of measured/predicted Ca²⁺ signals against firing rate. Pink lines represent data from individual nifedipine-treated dendrites. Red line represents binned averages and SEM for nifedipine data. Black line represents data for control neurons (replotted from Fig. 3F). G, Average ratio of measured/predicted Ca²⁺ signals for trials during which the frequency of tonic firing >3 Hz. Error bars are SEM. Individual points shown in white. Lines between control and nifedipine points represent paired data. H, Average ratio of measured/predicted Ca²⁺ signals before and after application CPA. Open symbols represent mean and SEM.