Abstract
Purpose :
Evidence from both pharmacological and retinal gene expression studies suggest a link between retinal glucagon and the regulation of eye growth and refractive errors. The purpose of this study is to investigate the effect of selective ablation of retinal glucagonergic (GLUC) amacrine cells on the visually-guided eye growth.
Methods :
To eliminate these cells, 10 ul of quisqualic acid (QA), biotinylated anti-glucagon conjugated to a toxin (ITX) or saline (SS) was injected intravitreally to 7 day-old chicks. In vivo retinal imaging combined with 3-D segmentation was used to track changes in the retina (NFL, IPL, INL) and choroid up to 10 days post-injections. Wholemounts and vertical sections of retina immunolabeled with anti-glucagon and TUNEL were imaged under fluorescent and confocal microscopy to assess the effect on the GLUC cells ex vivo. Ganzfeld, pattern and multifocal electroretinography (ERG) [W1] were used to assess function, 1 and 2 weeks after injections. A separate group of birds wore +10 D lenses over their injected eyes for 5 days. Changes in the choroid (CT), axial length (AL) and vitreous chamber (VC), and refractive errors (RE) were tracked with high-resolution ultrasonography and retinoscopy resp.
Results :
While ITX minimally affected the thickness of the retina or its sublayers (in vivo imaging), it selectively eliminated the GLUC cells as evidenced by their disappearance in the INL/IPL. TUNEL staining revealed cell death the INL/IPL border as well as in the INL and IPL. Functionally, ITX only reduced the photopic negative response of the flash ERG, while QA affected all components of the flash ERG and attenuated the P50 amplitude of the pattern ERG. ITX did not impair the CT response to +10 D lenses although AL, VC and RE were relatively reduced by day 5. In contrast, QA attenuated the CT response to the same lenses and reversed the direction of induced changes in AL, VC and RE.
Conclusions :
The selective elimination of GLUC cells with ITX did not prevent eyes responding in the correct direction to imposed myopia, contrasting with results with QA, which reverses the response direction. The results from the ITX-lens experiment suggests that GLUC amacrine cells are not necessary for decoding the sign of imposed defocus but may be involved in the fine-tuning of compensatory responses.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.