Electroretinography.
ERGs were recorded from dark-adapted mice as described [72]. Briefly, mice were dark-adapted overnight and anaesthetized by subcutaneous injection of ketamine (66.7 mg/kg body weight) and xylazine (11.7 mg/kg body weight). The pupils were dilated and single-flash ERG recordings were obtained under dark-adapted (scotopic) and light-adapted (photopic) conditions. Light adaptation was accomplished with a background illumination of 30 candela (cd) per square meter starting 10 min before recording. Single white-flash stimulation ranged from 10−4 to 25 cd·s/m2, divided into ten steps of 0.5 and 1 log cd·s/m2. Ten responses were averaged with an inter-stimulus interval of either 5 s (for 10−4, 10−3, 10−2, 3 × 10−2, 10−1, and 3 × 10−1 cd·s/m2) or 17 s (for 1, 3, 10, and 25 cd·s/m2). Band-pass filter cut-off frequencies were 0.1 and 3,000 Hz.