Jw. Conlee et al., PIGMENT-DEPENDENT DIFFERENCES IN THE STRIA VASCULARIS OF ALBINO AND PIGMENTED GUINEA-PIGS AND RATS, Hearing research, 72(1-2), 1994, pp. 108-124
Functional models of the stria vascularis (SV) have ascribed roles for
the marginal and basal cells, but not for the intermediate cells, whi
ch remain poorly understood. Intermediate cells have been identified a
s melanocytes, which produce melanin in most pigmented animals includi
ng humans. The relationship of melanin to intermediate cell function m
ay be addressed through comparisons with the albino inner ear. Albinos
have a normal distribution of melanocytes that are unable to synthesi
ze melanin pigment. In the present study, the SV was compared between
albino and pigmented littermates in both the guinea pig and the rat. P
hotomicrographic montages of the SV were analyzed from each of 7 cochl
ear 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 an
d 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 cy
toplasmic and total cell volumes were smaller in the albino guinea pig
s; however, marginal cell S-v and absolute area were larger. In the ra
t, intermediate cell V-v was also smaller across cochlear turns in the
albinos. Similarly, intermediate cell cytoplasmic and total cell volu
mes were smaller in the albinos, while marginal cell total surface are
a per radial cross-section of the SV was larger. These results demonst
rate that amelanotic melanocytes occupy significantly less volume than
do pigmented melanocytes, and suggest that melanin may influence the
structure and function of the SV.