Whole-brain images were acquired of every section at 10X magnification with an Aperio Versa Slide Scanner (Leica Biosystems). Individual sections on each slide were isolated then registered to the Allen Brain Atlas using NeuroInfo software with Brainmaker module (MBF Bioscience) and all RV+ neurons outside of the hippocampus (with the exception of contralateral CA3)were mapped and counted. In ventral hippocampal sections, cells co-expressing mCherry and EGFP (starter cells) were imaged with a CSU-W1 spinning disk widefield confocal microscope (Nikon Imaging Center, UCSF) at 40X magnification, then registered to the Allen Brain Atlas using NeuroInfo (MBF Bioscience) and counted.
For each brain, the number of input neurons in a specific brain region was normalized to the total number of input neurons (RV+) counted across the brain outside of the hippocampus. All data collection and counts were made blinded to the experimental group. The mean and standard error of the mean are listed inSupplementary Data Table 3 for each brain region. For analysis one- way ANOVAs were run and those regions with P<0.05 were run with multiple t-tests with Holm-Sidak correction for multiple comparisons. All statistical results for significant effects are in Supplementary Data Table 4 . Data was analyzed using Prism 8 (GraphPad).
For each brain, the number of input neurons in a specific brain region was normalized to the total number of input neurons (RV+) counted across the brain outside of the hippocampus. All data collection and counts were made blinded to the experimental group. The mean and standard error of the mean are listed in