THE DEVELOPMENT OF SEROTONERGIC PROJECTIONS TO THE OLFACTORY-BULB OF MONODELPHIS-DOMESTICA (THE GRAY, SHORT-TAILED OPOSSUM)

The offspring of Monodelphis domestica (grey, short-tailed opossum) ar e born in a very immature state after a short (14-day) gestation perio d. As a result, they provide a useful mammalian model for examining qu ite early stages of brain maturation. The present study demonstrates t hat the onset and development of serotonergic (5-HT) projections to th e Monodelphis olfactory bulb can be traced entirely after birth. 5-HT was visualized in tissue sections from postnatal day 5 (P5), P10, P20, P30, and adult opossums using avidin-biotin peroxidase immunocytochem istry. 5-HT afferent fibers are rare in the bulb until P10. Maturation occurs slowly, but by P30, 5-HT fibers assume the adult form characte rized by preferential glomerular innervation. Due to the postnatal dev elopment, slow maturation, and specificity of innervation patterns, th e Monodelphis bulb provides a model with which to study the regulation of serotonergic development.