Figure 1.

In vivo classification of direct and indirect pathway murine MSNs and confirmation of S2 projections to MSNs. A, Confirmation of substantial S2 projections to the DLS via BDA (red) injection in S2, showing axonal boutons present in the striatum (showed with white arrows). Str, striatum; WM, white matter; LV, lateral ventricle. B, Schematic representation of the stimulation electrode placement in S2, optopatch pipette in dorsal striatum, and LFP electrode in the contralateral S2. In total 38 MSNs (21 D1 MSNs and 17 D2 MSNs) have been recorded. C, Representatives of LFP traces in S2 and of whole-cell optopatch–clamp traces in the striatum. D, Classification of D2 (ChR2+, top) and D1 (ChR2−, bottom) MSNs based on the presence or absence of membrane depolarization in response to pulsed blue light (vertical shading). E, Postmortem validation of D1 (ChR2−) or D2 (ChR2+) MSN identity through immunostaining against biocytin with streptavidin-Cy3 (red) and DAPI (blue) to unveil the recorded neuron and the neuronal nuclei, respectively. Notice how D2 ChR2+ cells display fluorescence for YFP (green), showing its positiveness for ChR2.