Fig. 9
Properties of bursting activity in control mDA and grafted mDA neurons: (A) Spikes in burst (SIB) percentage. Statistical analyses were performed using the Mann-Whitney test (p = 0.469) and the Fisher test for value distribution (F(DFn, Dfd) = 4.584 [3, 14]; p = 0.235). Each plot represents a single neuron. (B) Mean spike number in bursts. Each plot represents the average spike number in bursts from 150–180 s of spontaneous activity in a single neuron. Statistical analysis was performed using the Mann-Whitney test (p = 0.961). (C) Relative occurrence of bursts depending on spike number within burst. Bursts were categorised into 6 groups based on spike number (2,3,4,5,6 and ≥ 7 spikes), with their distribution determined relative to the total number of bursts. Each plot represents the average distribution from the considered neurons in each population. Statistical comparison was performed using a 2-way ANOVA (F [5, 107] = 4.078; p = 0.998). Only bursts with more than 7 spikes showed differing proportions between the dopaminergic populations (multiple unpaired t-tests; df = 6.598, q < 0.00001). (D) Mean intraburst frequency. Statistical analysis was performed using the Mann Whitney test (p = 0.262). (E) First ISI (Isi1) to start a burst. Each plot represents the Isi1 in burst averages, calculated from all bursts in a single neuron. Statistical analysis was performed using a Mann Whitney test (p = 0.152). (F) Consecutive ISIs in bursts (Isi1, Isi2, Isi3) from bursts within 4 spikes. Isi increment within the burst course was shown in control mDA (paired one-way ANOVA test: F(Dfd, Dfd) = F(1.679, 23.50) = 41.03; p < 0.0001) and in grafted mDA (non-parametric paired Friedman test, p = 0.004) neurons. In control mDA neurons, paired t-test showed significant increases in consecutive Isis over time (Isi1 < Isi2: t-test(t, df)=(5.551,14), n = 15, p < 0.0001; Isi2 < Isi3: t-test(t, df)=(3.705,14), n = 15, p < 0.002) but not in grafted mDA neurons (wilcoxon matched-pairs signed rank test). Each plot represents the average Isi between 2 spikes in a burst from a single neuron. Scatterplots and analyses were performed on 15 control mDA and 4 grafted mDA bursty neurons. All data are means ± SD. Abbreviations: ISI, interspike interval; SIB, spike in burst