Electron microscopic study of retinas of macular mice.

BACKGROUND

Menkes' disease may be due to a lack or deficiency of copper in various organs. The macular mouse is known as a model for Menkes' disease. We examined melanin granules in the retinal pigment epithelium and the activity of cytochrome oxidase, a copper-containing enzyme, in the retinas of macular mice by electron microscopy.

METHODS

In the retinas of hemizygote macular mice we demonstrated cytochemically (oxidative polymerization of diaminobenzidine to an osmophilic reaction product) the activity of cytochrome oxidase. The distribution of melanin granules in the retinal pigment epithelium related to the activity of another copper-containing enzyme, tyrosinase was also studied. Stereological methods were applied to obtain quantitative data.

RESULTS

In the retinal photoreceptor inner segments of the macular mouse, the mitochondria were more numerous than in normal litermates and they appeared swollen. There were fewer melanin granules in the retinal pigment epithelium of macular mice than in that of normal littermates. The cytochrome oxidase activity was significantly lower in the macular mice than in the controls.

CONCLUSION

Macular mice have lower activity of cytochrome oxidase and fewer melanin granules than do normal mice. Both changes may be related to copper deficiency. These results correspond to the retinal changes seen in patients with Menkes' disease.