STUDY OF STRUCTURES OF OPTIC NERVE IN HYPERLIPIDEMIC MODEL RAT BY ELECTRON MICROSCOPE

Abstract

Abstract: : Purpose: To evaluate the influence of hypercholesterolemia to optic nerve, we investigated the structure of optic nerve in hypercholesterolemia model rat by ectron microscope. Methods: As hypercholesterolemia model rats RICO (Rats with inherited hypercholesterolemia) rats (18 months old, n = 5) were used, and as controls Wistar Kyoto rats (18 months old, n = 5) were used. They were given standard foods and aqueduct water. Room was illuminated for 12 hours a day. In the room temperature was set 21± 2°C and humidity was set 55± 5%. The eyes were enucleated and cut into small pieces. Then they are fixed in 4% glutaraldehyde for 1 hour, washed in 0.05 M cacodylate buffer overnight, placed in Caulfield osmium fixative for 1 hour, dehydrated in a series of ethanols and embedded in Luveak 812. Ultrathin sections were cut and double stained with uranyl acetate and lead citrate, and examined under transmission electron microscope. The differences of optic nerve structure between RICO rat and Wistar Kyoto rat were investigated. Results:In the optic nerve of RICO rat, decrease of medullated nerve fiber diameter and the disorder of the myelin sheath were observed. The number of medullated nerve fibers was 30.57±6.78/100 µm² (n=40) in the opic nerve of RICO rat and 27.38±6.39/100 µm² (n=30) in that of Wistar Kyoto rat (P < 0.05). We compared the number of medullated nerve fibers in different diameters in RICO rat and Wistar Kyoto rat. The number of medullated nerve fibers with the diameter of 0.75 µm or less were 5.65±3.80/100 µm² and 1.45±3.19/100 µm² respectively (P< 0.01). With the diameter from 0.75 to 2.00 µm, the number were 4.25±1.71/100 µm² and 2.10±1.57/100 µm² respectively (P< 0.01). With the diameter of 200 µm or more, 3.10±1.68/100 µm² and 3.30±1.59/100 µm² respectively. Conclusions: In RICO rat, the medullated nerve fibers of the optic nerve were thin, and the number of medullated nerve fibers with small diameter was significantly higher than in Wistar Kyoto rat. In addition, the disorder of the myelin sheath and destruction of neuroglia were observed. It was suggested that hypercholesterolemia led to the destruction of optic nerve structure.

Keywords: neuro–ophthalmology: optic nerve • microscopy: electron microscopy • lipids