The influence of aging and low zinc nutrition on the choroid in the pig: I. The melanocyte

Abstract

The effects of low zinc nutrition and aging on central choroidal melanocytes were examined in the pig. Three populations of pigs (young, pregnant and aged), were maintained on either control (C) or low zinc (LZ) diets. Twenty-five weanling boars were sacrificed at 2, 4, 8, 10, and 12-month intervals, and nine pregnant sows and eight aged sows were sacrificed after a 6-month interval. Melanocytes of the central choroid were morphologically and morphometrically examined. The melanocyte was found to be conservative in its form, which was mostly elliptical longitudinal profile, throughout the different age populations that were fed the C diet. Morphometric observations revealed that this cell type increased in size in the oldest animals, having been 40% greater than that in the younger two populations. However, the overall percentage area occupied by melanocytes remained the same throughout all age groups. In the animals that were fed the LZ diets, a large subpopulation of choroidal melanocytes was oval to round in shape in the pregnant and aged groups. Many members of this subpopulation possessed less opaque pigment than the elliptically shaped cell. Measurements of the size and percentage area occupied in these oldest groups increased significantly. In addition to the change of size, shape and melanin opaqueness, unusually large melanosomes were consistently observed in the pregnant and aged LZ groups. Low zinc nutrition had a remarkable age-related impact on the usually quiescent melanocyte.

Zinc Deficiency Leads to Lipofuscin Accumulation in the Retinal Pigment Epithelium of Pigmented Rats

“…We assume that melanosomes without adequate uptake of zinc change their structural and probably functional properties, which was shown before in pig eyes [31]–[32]. Here we found that this mechanism also applies for rat eyes.…”

“…The large melanosomes that appeared can be the result of reduced normal cellular function and/or fusion of altered melanosomes. It has been reported that a zinc deficient diet results in an “ageing-like” process, with melanosomal morphological changes [31]–[32], severe degeneration of the photoreceptor outer segments and osmiophilic inclusion bodies in the RPE [33]–[34]. Such alterations are typically found in pigmentary disorders [35]–[36].…”

Zinc and the Eye

“…Samuelson et al have reported ultrastructural changes in the RPE and choroidal melanocytes of adult pigs when they were maintained on diets deficient in zinc. These included displacement of cone nuclei towards the RPE, swollen outer segments of photoreceptors and altered choroidal melanosomes [31,38,39,82,83]. Cataracts and exophthalmos have been reported in trout and salmon associated with zinc deficiency [64 -67].…”

The retina of the collared peccary (Pecari tajacu): structure and function

“…). In the domestic pig, in which many fundi are subalbinotic, changes in choroidal melanocytes and melanosomes have been associated with aging and dietary concentration of trace elements …”