During 30 minutes of dark-adaptation, the body temperature was lowered in five steps from 38°C to 33°C, 28°C, 23°C, and 18°C. At each selected body temperature, ERGs were recorded. The body temperature was kept within ±1°C during the ERG recordings. The number of animals tested at each of the five temperatures was five, five, six, eight, and eight, respectively.
Responses were recorded beginning with a 6.0 log NDF, and the stimulus intensity was increased by 0.5-log steps to the full-intensity stimulus with a 1-minute interval between one stimulus intensity and the next. The bandwidth of the preamplifier was set at 1 and 100 Hz, and the amplitudes of a- and b-waves were measured. From the stimulus intensity-response curves, we determined the maximal amplitude (V max).