Electroretinographic assessment of rod- and cone-mediated bipolar cell pathways using flicker stimuli in mice.

Naoyuki Tanimoto,Martin Biel,Mathias W. Seeliger,Mineo Kondo,Vithiyanjali Sothilingam,Peter Humphries

doi:10.1038/srep10731

Abstract

Mouse full-field electroretinograms (ERGs) are dominated by responses of photoreceptors and depolarizing (ON-) bipolar cells, but not much of hyperpolarizing (OFF-) bipolar cells under conventional recording conditions. Here we investigate a novel ERG protocol in mice for functional assessment of the major ON- and OFF-bipolar cell pathways using flicker stimuli for a high luminance with varying frequency up to 30 Hz. Wild-type (WT) and functionally specific transgenic mice (Cnga3-/-, no cone photoreceptor function; rho-/-, no rod photoreceptor function; mGluR6-/-, no ON-bipolar cell function) were examined. The Cnga3-/- flicker ERG was similar to the WT flicker ERG at very low stimulus frequencies, whereas ERGs were comparable between WT and rho-/- mice at 5 Hz and above. Between 5 and 15 Hz, ERGs in mGluR6-/- mice differed in configuration and amplitude from those in WT and rho-/- mice; in contrast, response amplitudes above 15 Hz were comparable among WT, rho-/- and mGluR6-/- mice. In summary, we found three frequency ranges with these conditions that are dominated by activity in the rod pathways (below 5 Hz), cone ON-pathway (between 5 and 15 Hz), and cone OFF-pathway (above 15 Hz) that enables a quick overview of the functionality of the major bipolar cell pathways.

Highlights

Mouse full-field electroretinograms (ERGs) are dominated by responses of photoreceptors and depolarizing (ON-) bipolar cells, but not much of hyperpolarizing (OFF-) bipolar cells under conventional recording conditions
The response size is measured and analyzed without any mathematical treatment, allowing a quick diagnosis directly after or even during the recording. Another important aspect is the value of the recording protocol in terms of functional diagnostics; the question at the beginning of this study was whether this flicker protocol could provide any additional information about retinal function that is not assessable by single-flash ERGs only; for instance, OFF-cone bipolar cell (CBC)-associated responses because mouse full-field ERGs are dominated by responses of photoreceptors, rod bipolar cells (RBCs), and ON-CBCs, but not much of OFF-CBCs under conventional recording conditions
Up to the luminance of -2.0 log cd s/m2, responses are comparable between wild-type (WT) and Cnga3-/- mice, whereas there is no discernible response in rho-/- mice, indicating that only rod photoreceptors are activated at those luminances, i.e. scotopic range (Fig. 1, above the horizontal dashed line)

Summary

Introduction

Mouse full-field electroretinograms (ERGs) are dominated by responses of photoreceptors and depolarizing (ON-) bipolar cells, but not much of hyperpolarizing (OFF-) bipolar cells under conventional recording conditions. The response size is measured and analyzed without any mathematical treatment, allowing a quick diagnosis directly after or even during the recording Another important aspect is the value of the recording protocol in terms of functional diagnostics; the question at the beginning of this study was whether this flicker protocol could provide any additional information about retinal function that is not assessable by single-flash ERGs only; for instance, OFF-cone bipolar cell (CBC)-associated responses because mouse full-field ERGs are dominated by responses of photoreceptors, rod bipolar cells (RBCs), and ON-CBCs, but not much of OFF-CBCs under conventional recording conditions. Based on our ERG findings in these knockout mouse models, we could identify three frequency ranges according to the different pathway-contributions, including a cone OFF-pathway dominated frequency range that cannot be assessed in single-flash ERG experiments, and proving the value of the flicker ERG protocol for detailed functional diagnosis in mice

Methods

Results

Conclusion