Dibutylphthalate polystyrene xylene (dpx)

Histological sections of the retina were prepared from virgin female flies of w¹¹¹⁸, w¹, mini-w⁺ in w¹¹¹⁸ background, or w⁺ stocks, aged 5, 15, or 30 days. Five flies of each genotype and age were anesthetized and decapitated with a sharp needle. Heads were placed on a microscope slide within a droplet of physiological saline solution. The proboscis was cut off and the occipital cuticle was removed, using fine forceps and a sharp needle, to improve fixative penetration. Heads were fixed overnight in an ice-cold solution of 2.5% glutaraldehyde and 4% paraformaldehyde prepared in 0.1 M phosphate buffered saline pH 7.3. After rinsing in saline solution heads were post-fixed for 1 h in 0.5% osmium tetroxide, rinsed in water, dehydrated in 10 min steps (50, 70, 80, 90, and 100% ethanol and twice in acetone for 20 min), embedded in resin (AGAR 100, AGAR Scientific), and polymerized at 60°C for 48 h. Histological sections of 1 μm thickness were cut with a glass knife on a RMX MT-X ultramicrotome, stained with 0.1% boracic toluidine blue and mounted on microscope slides with DPX (AGAR Scientific) for observation with an Olympus IX81 microscope. Sections were carefully taken at about the same depth/region of the eye to allow proper comparison. Images were acquired with a digital microscope camera Olympus DP71 and processed with Adobe Photoshop.