Development of glomerular structure in rabbit olfactory bulb: three-dimensional reconstruction under the confocal laser scanning microscopy.

Confocal laser scanning imaging was used to reconstruct the three-dimensional distribution of the aggregates of olfactory receptor axons terminating within individual glomeruli in the rabbit main olfactory bulb. Two monoclonal antibodies, R2D5 and R4B12, were used to mark selectively the olfactory receptor axons. Thick coronal sections (100-200 microns in thickness) through the bulb were labeled with either of the antibodies, and then serial optical sectioning was performed to reconstruct three-dimensional optic images of the labeled axons in the glomeruli. The results revealed an intricate internal structure of the glomeruli with a mesh-like arrangement of bundles of terminal olfactory axons. Developmental study showed that primitive glomeruli lacking the internal structure of the adult form first appear in the 22-day embryo and that the characteristic internal structure of the glomeruli develops mainly during postnatal days. The confocal laser scanning image method together with specific molecular markers provides a simple tool for the three-dimensional analysis of the glomerular structure.