Figure 1

Anatomical validation of fiber position relative to target side and optogenetic intracranial self-stimulation (A) Schematic overview of fiber implant position for optogenetic stimulation of the VTA, and the ipsilateral AI recording side. Dashed boxes indicate representative regions of interest shown in B) identified by yellow and red asterisks. (B) Top, YFP expression in the temporal cortex covering the region of AI after virus transduction of the VTA indicates fiber terminals from the VTA targeting mainly upper layers and collaterals in deeper layers (white arrows). YFP expression was detectable in multiple regions of the neocortex (not shown). Bottom, co-fluorescence of YFP (AAV-CamKIIα-C1V1 (E162T)-p2A-eYFP) and TH-immunostaining (Alexa Fluor 546). Area of co-fluorescence is indicative of overlapping neuronal populations expressing the virus and TH mainly found in the VTA, and not the substantia nigra²⁴. Scale bars indicate 250 and 200 µm, respectively. (C) Schematic representation of optogenetic intracranial self-stimulation: While nose-poking the lever, animals induce a light flash towards the VTA resulting in extensive self-stimulating behavior²⁵. (D) Gerbil skull with prominent landmarks (bregma, lambda and occipital crest) for anatomical reference modified from Radtke-Schuller et al. 2016. For experiments, bregma has been used for reference of medio-lateral (ML) and anterior-posterior (AP) position of the VTA. (E) Estimated actual AP/ML coordinates with mean coordinates (AP:−3.57 mm; ML: 584.14 µm) relative to bregma of the C1V1group (n = 7) as estimated with the gerbil brain atlas⁸⁴. (F) Fiber distance (mean ± SEM) towards area of co-fluorescence (146.8 ± 38.9 µm; n = 7). Compare with bottom picture of B). (G) Averaged lever pressing rates (lever presses/min) of the C1V1 (n = 12) and YFP (n = 8) groups over 10 days. A representative video of a C1V1 animal is accessible as Movie (See Video S1).