Multifocal Electroretinograms and Scanning Laser Ophthalmoscopy in the Mouse Retina

Abstract

Purpose: : Local differences and changes in the mouse retina were studied using multifocal electroretinography (mfERG) and correlated with images of the same retinae. Further, it was determined if the down-regulation of a photoreceptor presynaptic protein can be detected in the mfERG.

Methods: : mfERGs were recorded using contact lens electrodes in the left and right eyes of four C57BL/6 mice using stimulus presentations in 19 hexagons. The mfERG equipment was integrated with a scanning laser ophthalmoscope (SLO) to visualize the retina. The mice received a subretinal injection of rAAV2/5 expressing GFP under the mouse opsin promoter together with shRNA targeting and down-regulating the presynaptic cytomatrix protein Piccolo in the right eyes. The left eyes were untreated.

Results: : Local response variations could be recorded in the left (control) eyes. These variations could not be correlated with structural retinal landmarks visualized by the SLO. However, a Monte-Carlo analysis showed that the responses were not randomly distributed and that the responses to adjacent hexagons were correlated. Blocking the stimulus presentation in a randomly chosen hexagon resulted in an extinguished response to this particular hexagon while leaving the responses to the other hexagons unaltered. The injected eyes displayed considerable GFP fluorescence and thus viral transduction and Piccolo down-regulation. The responses in the transduced retinal areas were substantially smaller than those in the control areas.

Conclusions: : With the mfERG it is possible to record local physiological variations in the mouse retina although there are no obvious structural correlates. This is possibly related to the fact that densities of all cell types are largest close to the optic nerve with only little density decrease at larger distances from the optic nerve (Jeon et al., J. Neurosc., 1998: 8936). Down-regulation of the presynaptic photoreceptor protein Piccolo leads to substantial functional loss in the mouse retina, which can be resolved with mfERG.

Keywords: electroretinography: non-clinical • retina: distal (photoreceptors, horizontal cells, bipolar cells) • synapse