library_construction_protocol: Brains were removed, flash frozen on dry ice, and VTA punmches dissected.  RNA was extracted using Norgen minicolumn ( Total RNA purification Kit)  and quality checked via Agilent   2100 bioanalyzer assay Universal Plus mRNA-Seq kit (Tecan Genomics, Redwood City, CA) has been used for library preparation following the manufacturer's instructions (library type: fr-secondstrand) . sequenced on single-end 75 bp mode on NextSeq 500 (Illumina, San Diego, CA)