A comparative study of an olfactory epithelial area lacking olfactory neurons and a nearby presence of TGF-alpha-like immunoreactive olfactory neurons.

Our previous study has shown that ddY mice have special patches of nasal epithelium in the posterior roof of the nasal cavity that exclusively consists of olfactory supporting cells and horizontal basal cells. Here, we extend this finding to Balb/c and DBA/2 mice, Wistar and Sprague-Dawley rats, hamsters, and guinea pigs. In the mice, rats, and hamsters studied, the patches lacked olfactory cells and their precursor, globose basal cells. In rats and hamsters, the supporting cells were arranged in a single layer, in mice as three or four layers. Horizontal basal cells were located in a single layer in these species. In the guinea pigs, the specialized roof structure was less clear and could be seen at the level of ultrastructure as an olfactory neuron-lacking area. Distinct populations of transforming growth factor (TGF)-alpha-like immunoreactive olfactory cells occupied an area close to the epithelial patches. In this region, the TGF-alpha-like immunoreactive neurons were negative for the usual olfactory markers, either OMP or protein gene product (PGP) 9.5 or beta-tubulin. These cells are suggested to project to the so-called 'necklace glomeruli' and use a different cGMP-driven, transduction pathway. Three-dimensional analysis of double-labeled (TGF-alpha, PGP9.5) serial sections revealed a unique relation among the epithelial patches, TGF-alpha-like immunoreactive neurons and olfactory epithelium.