Unilateral naris closure in young ued for 30 or 60 days. Laminar volume measurements rodents leads to striking alterations in the developrevealed a significant reduction in the size of the exment of the ipsilateral olfactory system. One of the most pronounced effects is a 25% reduction in the perimental bulb following 60, but not 30, days of early size of the experimental olfactory bulb, a change that olfactory deprivation. Mitral cell number estimates stems in part from decreased cell survival. Since naris indicated a significant reduction after both 30 and 60 occlusion in rodents alters the system more during days of naris closure. The immaturity of Monodelphis development than in adulthood, we investigated the offspring may render the population of mitral cells consequences of olfactory deprivation in a species that susceptible to the effects of olfactory deprivation. is born in a very immature state, Monodelphis domes-These findings suggest that afferent activity plays a tica. In this pouchless marsupial, offspring are born role in the survival of all bulb neurons, irrespective after a short 14-day gestation. In the present study, of cell class. α§ 1997 John Wiley & Sons, Inc. J Neurobiol 33: the thymidine analogue bromodeoxyuridine was used 429-438, 1997. to examine early postnatal neurogenesis in the olfac-Keywords: olfactory bulb development; Monodelphis tory bulb. Unlike rats and mice, neurogenesis of the domestica; bromodeoxyuridine; unilateral naris clomain output neurons (the mitral cells) continues into sure; sensory deprivation postnatal life. Unilateral naris closure was begun on