Thor Eysteinsson, Asya Esin Aksoy, Andrea García-Llorca, Miriam A. Hickey and Monika Jürgenson
Introduction. The microphthalmia-associated transcription factor (Mitf) gene is expressed in the retinal pigment epithelium (RPE) in the eye. Mitf mutations affect eye size, pigmentation and retinal and RPE function. Photoreceptor and bipolar cell function has been assessed with the flash electroretinogram (ERG) in Mitf mutant mice. Their inner retinal (amacrine and ganglion cells) function was unknown, but we measured ERG responses with stimuli that primarily activate these neurons. Methods. C57BL6 (wild type WT) , MitfEnu22(398)/Enu22(398) and MitfMi-Wh/+ mice at 3 and 6 months were examined. Mice were dark-adapted for 24 hours, anaesthetized with IP injection of ketamine/xylazine, and pupils dilated. ERGs were recorded with a Celeris system under two stimulus conditions. Black/White horizontal stripes were reversed, evoking a pattern reversal ERG (PERG) with two components, P1 (ON ganglion cells), and N2 (OFF ganglion cells). The photopic negative response (PhNR) was evoked with light flashes (amacrine cells). Results. Mean PERG P1 at 3 months was 6 µV in WT mice and 5.5 µV in MitfEnu22(398)/Enu22(398) (p=0.36, n=7), and the N2 9 µV in WT and 8 µV in mutants (p=0.9, n=7); MitfMi-Wh/+ results were similar. All PERG amplitudes were lower at 6 months, but only the P1 in WT mice was significantly reduced (p=0.04). Mean PhNR in WT was 8.6 µV and 7.1 µV in MitfEnu22(398)/Enu22(398) (p=0.2, n=7), with no significant changes with age. Conclusions. Results indicate that light evoked activity from inner neurons in these Mitf mutants are normal with minor change for 6 months.
