OLIGODENDROCYTE MYELIN-IMMUNOREACTIVITY IN THE DEVELOPING OLFACTORY SYSTEM/

Immunocytochemistry was used to characterize oligodendrocyte maturatio n in the developing mammalian olfactory system. Postnatal day 10-16, 2 0, 30 and adult rats were examined, as well as postnatal day 20, 30, 4 0 and adult Monodelphis domestica (the grey, short-tailed opossum). In rats, oligodendrocyte/myelin-immunoreactivity first appears in the ac cessory olfactory bulb by day 11, with labeling rapidly increasing thr oughout the entire bulb over the next five days. An adult pattern of i mmunoreactivity, characterized by dense labeling in the granule cell l ayer, sparse immunoreactivity in the external plexiform layer, and sta ining along the periphery of glomeruli, is attained by day 30. Stainin g is apparent in both the lateral olfactory tract and anterior commiss ure by day 11, and becomes heavy by day 20. While patterns of oligoden drocyte/myelin-immunoreactivity in the adult Monodelphis and rat bulb are similar, staining first appears much later in the opossum (around day 30), and maturation occurs more slowly. For example, rostral-cauda l gradients in the development of staining in the anterior commissure were noted which were not seen in the rat. These differences emerge be cause Monodelphis' slower growth allows more resolution into developme ntal sequences. Finally, in rats, unilateral naris closure on the day after birth, which significantly alters normal patterns of bulb develo pment, has no effect on the pattern and level of immunoreactivity even after long (30 day) survival periods. In both normal and naris occlud ed rats, oligodendrocyte/myelin-immunoreactivity is found in caudal as pects of the rat bulb on day 11 and subsequently progresses throughout the entire bulb over the next five days. Patterns in the Monodelphis bulb mirror those observed in the rat, however, staining appears later and progresses more slowly, suggesting Monodelphis is a useful animal for examining early myelin formation.