The emergence of compartmental organization in olfactory bulb glomeruli during postnatal development

The olfactory bulb glomerulus is a discrete and heterogeneous neuropil wher e olfactory receptor cell axons synapse with dendrites of mitral, tufted, a nd periglomerular neurons. To understand better the maturation of glomeruli and the spatiotemporal interactions that occur during postnatal developmen t, we employed confocal microscopy and markers for immature and mature olfa ctory receptor cell axons in parallel with a marker for synaptic structure in maturing glomeruli. Sprague-Dawley rats at postnatal days 1, 6, 12, and 18 were processed for single- and double-label immunocytochemistry for olfa ctory marker protein (OMP), growth-associated protein (GAP-43), and synapto physin. Mature or adult-like subcompartmental organization within the glome rulus emerged by postnatal day 12. Earlier in development immature axons en tered the core of the glomerulus and moved to the periphery as they matured . However, beginning around 12 days postnatal, immature axons distributed i n the periphery and moved toward the core as they matured. This change in t he trajectories of axons into glomeruli suggests that different rules may b e followed in establishing versus maintaining glomeruli. Double labeling wi th OMP and synaptophysin demonstrated strong colocalization compared with G AP-43 and synaptophysin, which showed much less colocalization, consistent with the notion that OMP is associated with more mature axone. (C) 2000 Wil ey-Liss, Inc.