library_construction_protocol: Neurons were washed twice briefly with ice-cold PBS supplemented with 5 μM harringtonine. 400 μl cold cell lysis buffer (20 mM HEPES, pH 7.4, 100 mM KCl, 5 mM, MgCl2, 500U/ml RNasin-Plus (Promega), 1x protease inhibitor cocktail (200X, Millipore), 5 μM harringtonine) was added directly to the cells, which were then scraped off of the dishes and transferred to 2 ml microcentrifuge tube containing Lysing Matrix-D (MP Biomedicals). Cells were lysed by vortexing 6 times (20 seconds each) with 40 s intervals on ice. After centrifugation for 10 min at 13,000 g at 4 °C. The supernatant was transferred into a new microcentrifuge tube and supplemented with 10 mM creatine phosphate, 0.1 mM spermidine, 40 μg/mL creatine phosphokinase, 0.8 mM ATP, and 25 μM puromycin, before incubation at 35 °C for 15 min. After incubation, RNA concentrations of the cell lysates were measured using Qubit RNA High Sensitivity Assay Kit (Thermo Fisher, Q32855). 10U RNase I (Thermo Fisher, EN0601) was added into cell lysate for every 100 μg RNA, and digestion was carried out at 4°C overnight with gentle rotation. The next day, RNase I digestion was stopped by adding Superase-In RNase inhibitor (Thermo Fisher, AM2696) at 1 U/μl. Digested cell lysate was loaded on top of 0.8 ml sucrose cushion (1 M sucrose, 20 mM HEPES, pH 7.4, 100 mM KCl, 5 mM, MgCl2, 5 μM harringtonine, 25 μM of puromycin) in a 1.5 ml ultracentrifuge tube (Beckman Coulter, 343778) and centrifuged for 1.5 h at 75,000 rpm at 4°C using a TLA-120.2 rotor (Beckman Coulter). After carefully removing the supernatant, the ribosome pellet was solubilized in TRIzol (ThermoFisher) for RNA extraction. The extracted RNA was separated in a 15% Urea-TBE gel, and RNA fragments of 25 - 35 nt in length were excised for subsequent library construction. Extracted RNA fragments were first treated with T4 Polynucleotide Kinase (T4 PNK, NEB, M0201L) without adding ATP to remove the 3' end phosphates. A 5ʹ pre-adenylated and 3' blocked adaptor (/5rApp/NNNNNNNNNNCACGGCGATCTTGCCGCC/3ddC/) was ligated to the 3' ends of RNA fragments by using T4 RNA Ligase 2, truncated KQ (NEB, M0373L). The 5' ends of RNA fragments were phosphorylated by T4 PNK and ligated to 5' adaptor (CGATCTCCAATTCCCACTCCTTTCAAGACCTrC) using T4 RNA Ligase 1 (NEB, M0437M). Ribosomal RNA (rRNA) was depleted using RiboPOOL probes against human/mouse/rat rRNAs (siTOOLs BIOTECH). Reverse transcription (RT) was conducted using SuperScript IV Reverse Transcriptase (Thermo Fisher, 18090050) with RT primer GGGCGGCAAGATCGCCGTG. Libraries were amplified by PCR using Q5 Hot Start High-Fidelity DNA Polymerase (NEB, M0493L) with P5 primer (AATGATACGGCGACCACCGAGATCT ACACTCTTTCCCTACACGACGCTCTTCCGATCTNNAGGGCGGCAAGATCGCCGTG) and P7 primers (DMSO sample: CAAGCAGAAGACGGCATACGAGATCGGTTCAAGTGACTGGAGTTCAGACGTGTGCTCTTCCGATCTCCAATTCCCACTCCTTTCAAGACCT; Bicuculline sample: CAAGCAGAAGACGGCATACGAGATGCTGGATTGTGACTGGAGTTCAGACGTGTGCTCTTCCGATCTCCAATTCCCACTCCTTTCAAGACCT).