NOVEL VISUAL CYCLE IN THE CHICKEN INNER RETINA

NICOLAS M. DIAZ; LUIS P. MORERA; VERRA DM; BETTS B; TSIN A; GUIDO ME

Fort Lauderdale, Florida

Congreso; Annual meeting Association for Research in Vision and Ophthalmology (ARVO); 2012

Association for Research in Vision and Ophthalmology (ARVO)

Purpose: We demonstrated the presence of intrinsically photosensitive retinal ganglion cells (ipRGCs) expressing the photopigment melanopsin in the wild type (WT) chicken retina as well as light responses mediated by the inner retina of GUCY1* (blind) birds (Contin et al., 2006, 2010; Valdez et al., 2009; Verra et al 2011). In this sense, bistable photopigments presumably responsible for photosensitivity observed may use a secondary cycle of chromophore regeneration that relies upon distinct isomerases through light-dependent or -independent processes taking place in the same or different types of cell (Wang et al 2010). Here, we investigated the presence of the putative photoisomerases RGR and a zebrafish RPE65c homolog, the activity of visual cycle enzymes and levels of retinal chromophores (11-cis RAL and all-trans RAL) in the inner retina of WT birds. Methods: Dark-adapted young WT chickens were exposed to a 30 min light pulse (2000 lux) or kept in the dark and sacrificed under dim red light. Eyes were dissected and lyophilized, and the inner retina or different cell layers (ganglion cell layer: GCL, inner nuclear layer: INL) obtained by the Scotch tape method. Samples were processed for RNA extraction, RT-PCR, immunochemical or enzyme activity assays. Retinoids extracted were subjected to HPLC. Results: Levels of 11-cis RAL were mainly elevated in the GCL and INL samples from light-adapted birds as compared with levels of all-trans RAL which were higher in the dark samples. Also, we observed the presence of RGR and RPE65c-like protein in different inner retinal cell layers: RGR in the GCL while RPE65c-like protein in the INL and IPL. Isomerase activity was found in the INL only while lecithin retinal acyl transferase (??) (LRAT) was observed in both INL and GCL. Conclusions: The results demonstrate that in the chicken, different inner retinal cell layers differentially express RGR and RPE65c-like protein and display enzyme activities for the isomerase and LRAT selectively. The differential light effects on retinoids observed and the differential distribution of photoisomerases present in the inner retina strongly suggest that mechanisms triggered by light differ from those described in the classical and cone-visual cycles. The results support the idea of a parallel visual cycle that may help ipRGCs or other photosensitive cells with the retinoid regeneration in the inner retina.