Supplementary Figure 4: Histological analyses of ChR2 expression
From: Tactile frequency discrimination is enhanced by circumventing neocortical adaptation
a, Macroscopic image of ChR2-YFP fluorescence (green) of a bilaterally injected rat brain with equal expression in BC of both hemispheres. b, Coronal brain section, stained with DAPI (blue) showing the middle of the injection site. c, Examples of ChR2 expression in all three animals that were used for behavioral assessment with light stimulation. The spatial profile of ChR2 expression was highly comparable across animals and injection sites. d, Theoretical estimates for changes in light irradiance with distance from the fiber tip. e, Overview of ChR2 expression site in the right BC. The illustration shows the glass fiber (blue square) on the brain surface and a rough estimation of the cortical area that is affected by blue light stimulation (blue cone). f, Magnified view on local projections of ChR2+ neurons in cortex. White arrow denotes a localized accumulation of ChR2-YFP, indicating occurrence of a local axonal swelling. These local changes in morphology were observed repeatedly in all animals and might be due to long-term expression of ChR257. No other signs of cellular damage from ChR2 expression were observed. g, ChR2-YFP labeled projections from cortex to the ventral posteromedial nucleus (VPM) in thalamus. Nuclei of thalamic cells (identified by DAPI staining in blue) showed no overlap with ChR2-YFP fluorescence and were surrounded by non-fluorescent areas (dotted white circles) that are presumably cell bodies. This indicates that thalamic neurons were not retrogradely labeled with ChR2-YFP. Similar results were also seen in cortical area S2 (not shown).
