DISTRIBUTION AND FEATURES OF MELANOCYTES DURING INNER-EAR DEVELOPMENTIN PIGMENTED AND ALBINO-RATS

In this developmental study, the distribution and features of melanocy tes in the inner ear of pigmented and albino rats was investigated wit h the use of an antibody, which specifically reacts with a melanocyte differentiation antigen present in the membranes of (pre)melanosomes. Melanocyte precursors could be traced from 13 days post conception onw ards and the course was followed to their targets in the inner ear. Me lanocytes which settle in the modiolus appeared to reach their target along another pathway than strial and vestibular melanocytes. No diffe rence was observed in the melanocyte distribution between pigmented an d albino rats. The integration of melanocytes into the stria vasculari s was associated with an increased rate of melanosome production in bo th strains, but in the albinos far fewer melanosomes were produced. Af ter the stria had reached maturity, melanosome production was arrested and melanosomes were subject to lysosomal digestion. In the stria of the pigmented rats, cells with aggregations of disintegrating melanoso mes appeared and persisted into adulthood. In the adult, the majority of the intermediate cells contained only a few scattered melanosomes, while melanosomes could only rarely be detected in the albinos. These observations indicate that there is a close relationship between melan osome production and the process of interdigitation of melanocytes wit h the marginal cells. It seems unlikely that melanosomes or melanin ma ke any important contribution to the function of the adult stria vascu laris. Outside the stria, the features of melanocytes in both strains were similar to skin melanocytes.