Ventral hippocampus was dissected from the brain, snap frozen in liquid nitrogen, and total nuclei were extracted using sucrose gradient centrifugation. Neuronal (NeuN+) nuclei were isolated by fluorescence-activated nuclei sorting with anti-NeuN antibody conjugated to AlexaFluor 488 on a FACSAria instrument. Detailed protocol for total nuclei isolation and purification of neuronal nuclei is provided in Kundakovic et al, 2017 (PMID:27113501). ATAC-seq libraries were prepared according to Buenrostro et al. 2013 (PMID:24097267) with some modifications. Illumina Nextera DNA Library Prep kit (FC-121-1030) and Nextera Index kit (FC 121-1011) were used to prepare the libraries.