Extended Data Fig. 3: Histological analysis of electrophysiological recording locations.

Left, atlas locations and histology photomicrographs for each rat (IM-657, IM-1002, IM-1003, IM-1037 and IM-1078) from which opto-tagged dopamine cells were obtained. Red, TH-staining; green: ChR2–eYFP; blue: DAPI. Scale bars, 1 mm. IM-1037 and IM-1078 brains were sliced horizontally, so fibre tracks appear as a circle. Font colours for rat ID numbers correspond to colours of tick marks in coronal atlas sections, indicating estimated recording locations for opto-tagged dopamine cells. For IM-1078, virus was injected into NAc core, and retrogradely infected dopamine neurons were recorded in VTA. Right, retrograde tracing of CTb from NAc core (top) to VTA-l (bottom). Top panel shows approximate extent of NAc labelling in each of the three rats (each rat indicated by a different colour). Bottom left panels show close-ups of TH labelling (blue), CTb (green) and merged image. Bottom right panels show reconstructed locations of TH⁺ and double-labelled TH⁺CTb⁺ midbrain neurons, on horizontal atlas sections. Estimated optrode locations are shown by red circles (or orange circle, in the case of the retrograde tagging rat IM-1078). Labelled neurons were counted within the red rectangles that span the AP and ML extent of estimated recording locations. Percentages shown are the fraction of TH⁺ neurons that are also CTb⁺. Brain atlas outlines in this figure were reproduced with permission from Paxinos and Watson, 2005⁵¹.