library_construction_protocol: 1% PFA perfusion then brain microdissection in cold physiological buffer, then RNA extracted (input) or ribosomal pulldown via Ribotag protocol (Sanz et al PNAS 2009): HA-tagged ribosome pulled down with Cst Rb anti-HA antibody, isolated via Pierce IgG beads. All RNA extracted with Qiagen RNeasy Micro kit. standard Illumina protocol (PolyA beads)