library_construction_protocol: Poly(A)+ RNA was isolated from mouse hippocampal neuron total RNA (obtained with the RNeasy Mini Kit (Qiagen) and on-column DNase digestion) with the NEBNext Poly(A) mRNA Magnetic Isolation Module (New England Biolabs). cDNA libraries were prepared with NEBNext Ultra Directional RNA Library Prep Kit for Illumina (New England Biolabs). NEBNext Multiplex Oligos for Illumina (New England Biolabs) were used to provide adaptors and permit multiplexing.