PMC

Rats were preheated in darkness in a humidified atmosphere at 97 °C for 2 hours. Core body temperature was 100.5 ° F at the beginning of exposure to 1100 lux green light for 2 hours. After exposure, animals were returned to darkness at room temperature. Retinas were excised from rats at various times thereafter and DNA extracted as described ().

Enzymatic and oxidative mechanisms of docosahexaenoate metabolism and degradation. The esterified form of DHA (docosahexaenoate) is converted to free DHA by phospholipase activity. A lipoxygenase then forms picomolar levels of neuroprotectin D-1 (NPD1), primarily in RPE cells. Molecular oxygen reacts with docosahexaenoate to form a 7 carbon reactive aldehyde intermediate (HOHA) that is capable of forming carboxyethylpyrrole (CEP) protein adducts. The first 7 carbons in docosahexaenoate (shown in red) give rise to HOHA; R= glycerophospholpid esterified with DHA.

Morphometric analysis of ONL thickness (Figure 1A) and ROS length (Figure 1B) in retinas from rats treated with light at 1am, 9am or 5pm. Figure 1C is a composite of data from panels A and B comparing relative changes in retina ONL thickness and ROS length for rats treated with light at 1am. Figure 1D is a composite of data from rats exposed to light at 9am. All data are the means of 3 separate determinations for cyclic light reared rats exposed to approximately 1200lux green light for 8 hours. (Adapted from Vaughan et al., Photochem Photobiol. 75: 547–53, 2002)

Confocal microscope image of a labeled vertical section of 13-lined ground squirrel outer retina collected during midwinter torpor. Red, PNA labels the extracellular matrix surrounding cone outer segments (OS). Green, anti-cytochrome oxidase-1 label indicates mitochondrial function. Blue, Anti-rhodopsin labels ROS. Amongst lightly-labeled cone inner segment (IS) ellipsoids, a rod IS ellipsoid retains the robust anti-COX 1 label (arrow) found uniformly in all ellipsoids of retinas collected during summer arousal (data not shown). Magnification bar equal to 20 micrometers. (Adapted from Gruber et al., Assn Res Vis Ophthalmol., 2006).

Extensive rhodopsin bleaching releases nanomolar amounts of all- trans retinal (t-Ral) which is then transported across the ROS disk membrane by an ATP-binding cassette (ABCR). Most of the t-Ral is converted to all-trans retinol (t-Rol) by RDH. T-Rol is then transported to the RPE where it is either converted back into 11-cis retinal (11-Ral), or stored as retinyl esters (t-RE). The RPE enzymes involved include: lecthin retinol acyl transferase (LRAT), RPE-65, isomerohydrolase (IMH) and 11-cis retinol dehydrogenase (11-RDH). Picomolar levels of t-Ral are converted to trans-retinoic acid by retinaldehyde dehydrogenase (RALDH), which may then be isomerized to 9-cis retinoic acid. RAR/RXR heterodimers are formed after binding retinoic acid and then migrate to the photoreceptor cell nucleus. (Adapted from Saari, Invest Ophthalmol Vis Sci 41; 337–48, 2000).

Real time, RT-PCR analysis of mRNA levels in rat retinas at different times of the day and night. Rats were dark adapted for 16 hours before sacrifice at 1 am, 9 am, or 5 pm (panel A). Retinas were excised and RNA extracted with a Direct mRNA Kit (Qiagen# 72022) from 9 individual retinas from 9 different animals. Some rats were treated with intense light (1200 lux, 490–580 nm) starting at 1 am (panel B), or starting at different times of the day (panel C). The antioxidant DMTU (500mg/Kg), or saline, was given IP 1 hour before light exposure. Average mRNA values are shown for rats exposed to light from 1 am to 9 am (1–9), 9 am to 5 pm (9-5), or 5 pm to 1 am (5-1). Data from animals pretreated with DMTU are represented by closed triangles. (Adapted from Barsalou et al., Assn Res Vis Ophthalmol., 2004).

Retinal morphology and rhodopsin recovery in rats exposed to light. Dark adapted rats were treated with DMTU (1X IP; 500mg/kg) 30 minutes before the start of light, or at various times thereafter. Light exposures (490–580 nm; ~1200lux) began at 1 am and lasted for 8 hours. The animals were then allowed to recover for 2 weeks in darkness before retinal histology or rhodopsin measurements were made. Retinal histology from the superior hemisphere of rats treated 30 minutes before light (A), 60 minutes after the onset of light (B), or given the saline vehicle (C). Arrow heads denote cone nuclei in the ONL (A) or remnant ONL layer after light damage (B, C). Morphometric measurements of ONL thickness, along the vertical meridian, for rats treated as above (D). Average whole eye rhodopsin levels measured in rats (n=4–5) treated with DMTU at various times before or after light exposure (E). The unexposed controls (open square) and light exposed controls (open triangle) were given an equal volume of saline 30 minutes before exposure. (Adapted from Vaughan et al., Photochem Photobiol. 75: 547–53, 2002 and Organisciak et al., Invest Ophthalmol Vis Sci. 41: 3694–3701, 2000).