Extended Data Fig. 1: Injection site in dorsal hippocampus CA1.

a-b. Schematic depicting horizontal sections through the mouse brain at ventral distance of -1600 µm (a) and -2800 µm (b) from bregma. AAV 2.5 EF1α-double floxed-ChR2-eYFP injected into dorsal CA1 (a; inset). Abbreviations used: Sub – subiculum, dentate gyrus (DG), lateral ventricle (LV), PrS – presubiculum, PaS – parasubiculum, MEC – medial entorhinal cortex, PRh – perirhinal cortex, and TeA – temporal association cortex. c. Confocal image of a brain slice of a mouse injected with AAV 2.5 EF1α-double floxed-ChR2-eYFP into dorsal CA1 and immunostained for GFP to demarcate the injection site (left). The viral infection is contained within CA1 and subiculum (marked by white arrowhead). Expanded views of the areas within the white dotted boxes on the right show infected CA1 pyramidal neurons (top), and no infection in the adjacent area CA2 (bottom). Duration of viral incubation is depicted on bottom right corner (d16). d. Confocal image of horizontal brain slice from the same mouse as in c immunostained for GFP. Green hippocampal axons were observed in entorhinal cortex (EC) layers 5 and 2/3. White dotted lines demarcate the different cortical layers and brain regions. Note the absence of infected neurons in EC. e. Same as c but the duration of viral incubation was 21 days. f. Same as d but the duration of viral incubation was 21 days. g. Same as c but the duration of viral incubation was 21 days. h. Same as d but the duration of viral incubation was 21 days. i. Same as c but the duration of viral incubation was 25 days. The slice was stained for GFP and DAPI (nuclear marker). j. Same as d but the duration of viral incubation was 25 days. k. Same as c but the duration of viral incubation was 25 days. l. Same as d but the duration of viral incubation was 25 days. m. Same as c but the duration of viral incubation was 25 days. n. Same as d but the duration of viral incubation was 25 days. A single infected neuron was observed in EC_L2/3 pointed by the white arrowhead with a magnified view in the inset. This is an example of an animal that was excluded from the dataset due retrograde viral infection in cortical layers. All scale bars are 100 µm. For incubation days of 16, 21, and 25 days, we repeated the experiment 1, 10, and 3 times.