library_construction_protocol: SON samples were collected using a 1-mm micropunch (Fine Scientific Tools) from 100 um brain coronal sections in a cryostat. RNA from individual SONs was extracted with RNeasy Mini Kit (74106, Qiagen) according to manufacturer's instructions and eluted in a final volume of 30 ul. Poly(A) enriched mRNA libraries were prepared and tested for quality by High Sensitivity D100 ScreenTape on Agilent 2100 Bioanalyzer. All libraries were uniquely indexed with specific adaptors ligated and normalised across to 2mM concentration. This allows libraries to be pooled and run together on the flow cell.