Expression and signalling of protease-activated receptors in distinct layers of rat olfactory bulb and olfactory sensory neurons.

By using biochemical, immunological and immunohistochemical techniques, we have investigated the expression and functional activity of protease-activated receptor (PARs) 1 and 2 in the rat olfactory system. Western blot analysis of microdissected main olfactory bulb indicated the presence of both PAR1 and PAR2 in olfactory nerve-glomerular cell layer (ON-GL), external plexiform layer (EPL) and granule cell layer (GRL). In functional assays, PAR1 and PAR2 selective peptides stimulated [35S]GTPyS binding and phosphoinositide hydrolysis and inhibited cyclic AMP formation in ON-GL but not in EPL and GRL, whereas they induced RhoA activation in both ON-GL and EPL+GRL. Olfactory bulb deafferentation by lesions of the olfactory mucosa elicited a significant decrease of PAR1 and PAR2 immunoreactivity in ON-GL and a reduced stimulation of [35S]GTPyS binding by PAR selective peptides. In primary cultures of olfactory neurons both PAR1 and PAR2 were detected by immunofluorescence and their activation by thrombin and trypsin, respectively, caused distinct morphological changes, including neurite retraction. These data indicate that in ON-GL a population of PAR1 and PAR2 is localized on terminals of olfactory sensory neurons and it may regulate axonal growth and synaptogenesis.