Immunofluorescence staining on 35-mm glass-bottomed dishs was described previously [11 (link)]. The primary antibodies were used at dilutions recommended by the manufacturers. The antibodies (anti human in all cases) used were mouse anti-Tuj1 (Covance, 1:800), rabbit anti-TH (Pel-Freez, 1:1 000), rat anti-DAT (Chemicon, 1:5 000), rabbit anti-DDC (Chemicon, 1:500), rat anti-Serotonin (Chemicon, 1:200), goat anti-ChAT (Chemicon, 1:100), mouse anti-HN (Millipore, 1:200). The immunostaining was developed with appropriate fluorescent-tagged secondary antibodies (Invitrogen, Carlsbad, CA, USA). In all cases, cellular nuclei were stained with DAPI in VectorShield mounting medium (Vector Laboratories, Burlingame, CA, USA). Images were collected with a Ziess or Leica SP5 confocal laser-scanning microscope.