Coating procedure with polyethyleneimine
Polyethyleneimine (PEI; Mw: 750,000 and Mn: 60,000; # P3143, Sigma Aldrich) was used to coat culture flasks to spontaneously isolate microglial cells, as previously described (Sepulveda-Diaz et al., 2016). PEI was diluted at 1 mg/ml in a pH 8.3 borate buffer solution prepared with borax decahydrate (#B3545) [30-32]. After at least a 2 h incubation at 37°C, PEI was discarded, and culture flasks washed 4 times with Dulbecco’s phosphate-buffered saline (PBS) until further use.