Figure 8.
Electrical proprieties of DAn in SNpc of miR-218 KO mice. a-f, Functional characterization of native DA neurons in ex vivo midbrain slices of WT, miR-218 KO1, c-KO2, and c-dKO adult mice. Active and passive membrane properties of DA neurons are controlled by miR-218 expression level. Deletion of miR-218 in KO1, c-KO2, and c-dKO strongly increases DA neurons membrane input resistance (Rm). Data are mean ± SEM. KO-1, p < 0.05; c-KO2, p < 0.05; c-dKO, p < 0.001; unpaired Student t test. a, Spontaneous pacemaker firing in cell-attached recordings is significantly different only in c-KO2 WT DA neurons (b, box plot and example traces). KO-1, p = 0.052; c-KO2, p < 0.05, c-dKO, p = 0.105; unpaired Student t test. Evoked AP firing is severely modified in c-dKO DA neurons, which display hyperexcitability compared with WT, KO1, and c-KO2 DA neurons. Instantaneous frequency of the first two APs elicited by depolarizing currents (10-250 pA, 10 pA increment, 2 s) is dramatically increased in c-dKO versus WT DAn (d). 190 pA, p < 0.05; 240 pA, p < 0.01; 250 pA, p < 0.001; two-way repeated-measures ANOVA, followed by Bonferroni test. Data are mean ± SEM. Example traces of evoked firing refer to the highest stimulus intensity (250 pA) applied to WT, KO1, c-KO2, and c-dKO DA neurons (d, right). Rheobase is significantly lower in all groups (e). KO-1, p < 0.05; c-KO2, p = 0.01; c-dKO, p < 0.05; unpaired t test. The Ih current amplitude of WT, KO1, c-KO2, and c-dKO (f) was taken as the difference between the steady state (at the end of the 1 s pulse) and the current onset (at the start of the 1 s pulse) at −120 mV. Ih activation kinetics were calculated by fitting the current trace at −120 mV with a mixture of one or two standard exponential functions using Clampfit 9.