SIMPLIFIED GANGLIOSIDE COMPOSITION OF PHOTORECEPTORS COMPARED TO OTHER RETINAL NEURONS

Purpose. The quantitative and qualitative ganglioside composition of r etinal photoreceptor cells is unknown. The aim of this study was to an alyze the lipid, especially ganglioside, makeup of photoreceptors comp ared to other retinal cells. Methods. Retinas from adult normal rats w ere mechanically separated into outer (photoreceptors) and inner (othe r retinal neurons and glia) halves by planar vibratome sectioning. Tot al lipids were extracted, and each fraction (neutral, phospholipids, a nd glycosphingolipids) was eluted sequentially by column chromatograph y and quantitated through high-performance thin layer chromatogram ana lysis. Similar analyses were performed on entire retinas from adult no rmal rats, adult dystrophic rats lacking photoreceptors (RCS-rdy-p+ st rain), and isolated photoreceptor outer segments. Results. Whereas pho spholipids were distributed equally between the two halves, inner reti na contained significantly more cholesterol (68% total) and gangliosid es (74% total) than outer retina on a unit protein basis. The distribu tion on a percent molar basis of specific gangliosides also was signif icantly different between the two halves: Outer retina was dominated b y GD3 (45% total ganglioside) and contained only trace amounts (<4%) o f complex species (GT1b and GQ1b); inner retina was more typical of ma ture brain tissue, exhibiting substantial amounts (similar to 25%) of more complex species. These data were supported by lipid compositional analyses of mutant photoreceptor-less retina. However, isolated outer segments resembled whole retina in containing higher levels of comple x gangliosides. Conclusions. These data indicate that, compared to oth er central nervous system-derived neurons, photoreceptor cell body mem branes exhibit a highly unusual simplified ganglioside composition. Su ch an unusual neuronal lipid composition may reflect structural adapta tions to their specialized function.