ErbB-4 and neuregulin expression in the adult mouse olfactory bulb after peripheral denervation

ErbB-4 is expressed by the periglomerular and the mitral/tufted cells of the adult mouse olfactory bulb (OB) and in the present work we tested whether this expression is regulated by the olfactory nerve input to the OB. Reversible zinc sulphate lesions of the olfactory mucosa were made in adult mice and the deafferented OB analysed by immunohistochemistry, Western blotting and semiquantitative RT-PCR. Following deafferentation, the expression of erbB-4, erbB-2 and neuregulin-1 (NRG-1) mRNAs in the OB was altered. At early stages (7-14 days) after lesion the levels of expression of olfactory marker protein (OMP), tyrosine hydroxylase (TH), erbB-4 and NRG-1 mRNAs were decreased, whilst expression of erbB-2 increased and that of NRG-2 was not significantly altered. We observed at least two distinct time courses for these expression changes. The lowest amounts of mRNA for erbB-4 and NRG-1 were observed at day 7 after lesion, whilst mRNAs for TH and OMP were lowest at day 14. At day 28 after the lesion, when olfactory receptor neuron axons had reinnervated the olfactory bulb, the expression levels of OMP, TH, erbB-2, erbB-4 and NRG-1 were identical to control values. These results indicate that the expression of erbB-4 mRNA and protein in periglomerular and mitral cells is controlled by peripheral olfactory innervation. The tight correlation in NRG-1 and erbB-4 expression levels also suggests a possible functional link that deserves further exploration.