Rostro-caudal patterning of receptor-expressing olfactory neurones in the rat nasal cavity.

The rostro-caudal extent of odorant receptor expression zones in the rat olfactory epithelium was analysed by means of in situ hybridization. Three broad non-overlapping zones were identified that extended along almost the entire anterior-posterior axis; each zone was composed of several separate bands running anterior to posterior throughout the olfactory epithelium. Super-imposed onto these broad zones was the expression area of a particular receptor subtype (OR37); it was restricted to a small region of the epithelial sheet with a high density of reactive neurones in the centre and declining numbers towards the periphery of the region. A quantitative evaluation of the reactive cells revealed that, despite their different distribution patterns, all receptor subtypes were expressed in an equal number of neurones.