Human olfactory receptor neurons contain OMP mRNA in their dendritic and axonal processes

The cellular expression of olfactory marker protein (OMP) mRNA and protein was investigated in the olfactory mucosa of humans ranging in age from 26 weeks of gestation to 85 years using in situ hybridization and immunocytochemistry. OMP mRNA and protein were most abundant in the somas of olfactory receptor neurons (ORNs). The hybridization signal over the ORN somal layer was greater in older subjects than in younger ones, reflecting either a higher neuronal density or more OMP mRNA per cell. In contrast, it was significantly lower in subjects with Alzheimer's disease when compared with an age-matched control. Characteristics of older subjects were patchiness in the distribution of OMP-expressing ORNs and the occurrence of subepithelial invaginations containing OMP-positive neurons. In addition, a significant hybridization signal was detected in the apical olfactory epithelium containing the dendrites, dendritic knobs, and cilia of ORNS, and over olfactory nerve bundles in the lamina propria, indicating the occurrence of OMP mRNA in dendritic and axonal domains.