Fig. 5. Functional connections are established in the OB of adult O/E3^GFP/GFP mutants. (A) The ORN projection to dorsal OB and olfactory glomeruli formation in this region were visualized by GFP fluorescence and OMP immunofluorescence. The patterns of GFP and OMP in the coronal sections clearly show the absence of olfactory glomeruli in the dorsal aspect of O/E3^GFP/GFP mutant OB. (B) Tyrosine hydroxylase (Th) expression in the periglomerular neurons is dependent on innervation and activity from the olfactory epithelium. Immunofluorescence demonstrates that Th expression overlaps the GFP-positive glomeruli and suggests that ORNs transduce signals and form functional connections within the OB of O/E3^GFP/GFP animals. (C) Characterization of OB neurons in O/E3^GFP/GFP mice. The soma of mitral, tufted and periglomerular cells are visualized with a fluorescent Nissl stain in heterozygous and homozygous O/E3^GFP/GFP mice. Although there is considerable disorganization of the glomerular layer, many neurons are present. The intensity of dendritic marker Map2 staining is considerably diminished in O/E3^GFP/GFP animals, consistent with the thinning of the external plexiform layer on the dorsal surface. The intrinsic GFP labeling of ORN axons and their convergence into glomeruli is shown in green.