Pigment-dependent differences in the stria vascularis of albino and pigmented guinea pigs and rats

Abstract

Functional models of the stria vascularis (SV) have ascribed roles for the marginal and basal cells, but not for the intermediate cells, which remain poorly understood. Intermediate cells have been identified as melanocytes, which produce melanin in most pigmented animals including humans. The relationship of melanin to intermediate cell function may be addressed through comparisons with the albino inner ear. Albinos have a normal distribution of melanocytes that are unable to synthesize melanin pigment. In the present study, the SV was compared between albino and pigmented littermates in both the guinea pig and the rat. Photomicrographic montages of the SV were analyzed from each of 7 cochlear regions in the guinea pig and 5 regions in the rat. Stereological procedures were used to determine the volume density (V v) for each of the three main cell types in the stria, the surface density (S v) of the marginal cells, and to derive estimates of absolute cell volume and surface area. In the guinea pig, comparisons between pigment groups showed that marginal cell V v was larger across cochlear turns in the albinos, while intermediate cell V v was smaller. Intermediate cell cytoplasmic and total cell volumes were smaller in the albino guinea pigs; however, marginal cell S v and absolute area were larger. In the rat, intermediate cell V v was also smaller across cochlear turns in the albinos. Similarly, intermediate cell cytoplasmic and total cell volumes were smaller in the albinos, while marginal cell total surface area per radial cross-section of the SV was larger. These results demonstrate that amelanotic melanocytes occupy significantly less volume than do pigmented melanocytes, and suggest that melanin may influence the structure and function of the SV.