Acta histochem. 89, 107 -111 (1990) Gustav Fischer Verlag Jena

Department of Ophthalmology, Nagasaki University School of Medicine, Nagasaki, Japan

Histochemical localization of zinc and copper in rat ocular tissues By YOSHIAKI HIRAYAMA With 7 Figures (Received February 28, 1990)

Summary Zinc and copper were histochemically localized in rat ocular tissues. Zinc was demonstrated by the dithizone method, and copper by the rubeanic acid and rhodanine methods. The retinal photoreceptor's outer segment showed the presence of zinc, but no zinc reaction was seen in other parts of the retina or other ocular tissues, even in rats fed excess zinc. It seems that photoreceptor cells contain the highest concentration of zinc. Copper was seen in the corneal epithelium and endothelium, iris, ciliary body, lens epithelium, retinal outer nuclear layer, photoreceptor inner and outer segments, retinal pigment epithelium, choroid, sclera, and optic nerve. These trace elements seems to play roles as components of some metalloenzymes and may have other functions till now unknown.

1. Introduction Zinc and copper are trace elements essential for metabolism in animals and humans. Important zinc metalloenzymes are carbonic anhydrase, alkaline phosphatase, superoxide dismutase, and alcohol dehydrogenase; copper metalloenzymes are cytochrome oxidase, superoxide dismutase, uricase, and DOPAmine ~-hydroxylase. Zinc has been shown chemically to be present in high concentrations in the ciliary body, retina, and choroid (BOWNESS et a1. 1952, GALIN et a1. 1962), and copper in the iris, ciliary body, retina, choroid, and cornea (BOWNESS et a1. 1952, ECKHERT 1983, GALIN et a1. 1962, TAUBER and KRAUSE 1943). There have been few histochemical studies of the localization of zinc and copper in ocular tissues. Histochemically, we demonstrated the localization of zinc and copper in rat ocular tissues.

2. Materials and methods For zinc detection: Wistar rats were divided into 3 groups.

Group I included 4 to 15 week old normal rats. Group II was fed a usual diet and water containing 30 mg/l zinc (as zinc acetate) for 3 or 4 weeks (zinc excess group). Group III was fed a zinc deficient diet (CZar Japan, Tokyo) for 6 weeks (zinc deficient group). The eyes were enucleated under intraperitoneal sodium pentobarbital anesthesia and fixed in cold absolute alcohol. Paraffin blocks were made and cut into 5 /-lm slices, which were deparaffinized and then covered with a dithizone complex-forming solution (MAGER et al. 1953) for 10 min. Free excess dye was washed away by flooding with chloroform, and after a quick rinse with distilled water, the slices were mounted in glycerol gelatin. For copper detection: The eyes of 4 week old normally fed Wistar rats were enucleated and fixed in 10% formalin. Paraffin blocks were made and cut into 5 /-lm slices, which were deparaffinized. Some slices were incubated in rubeanic acid solution (dithiooxamide) for 12 to 24 h at 37°C, dehydrated, cleared, and mounted in permount (OKAMOTO and UTAMURA 1938, UZMAN 1956, LiNDQUIST 1969). Other slices were incubated in

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Histochemical localization of zinc and copper in rat ocular tissues.

Zinc and copper were histochemically localized in rat ocular tissues. Zinc was demonstrated by the dithizone method, and copper by the rubeanic acid a...
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