TREK-1; TREK-1 immunoreactivity was detected for multiple cell types in the adult mouse retina (Fig. 4). The highest levels of TREK-1 immunoreactivity were observed for cells located in the GCL (Fig. 4A,B), with 63.6% (75 of 118 cells counted) of Brn3a positive RGCs labelled for TREK-1 (Fig. 4D–F). Weaker labelling of TREK-1 was also detected for a number of cells located on the inner surface of the INL, likely amacrine cells (Fig. 4A), and a number of cells positioned towards the outer surface of the INL with morphologies resembling horizontal cells (Fig. 4C). TREK-1 immunoreactivity was also detected in the outer retina, with TREK-1 labelling observed for photoreceptor outer segments and also photoreceptor pedicles located in the outer plexiform layer (OPL) (Fig. 4A). Consistent with qPCR analysis (Supplementary Figure 1), expression of TREK-1 protein was not detected in the retina prior to P10 (Supplementary Figure 5).