Transneuronal regulation of neuronal specific gene expression in the mouse olfactory bulb

Peripheral afferent denervation (deafferentation) of the rodent main olfactory bulb produces a marked decrease in tyrosine hydroxylase (TH) activity and immunoreactivity in a population of juxtaglomerular dopaminergic neurons. Preservation of activity and immunostaining for aromatic L-amino acid decarboxylase implies that these cells do not die, but change phenotype. We now report that the steady-state level of TH mRNA markedly decreases in the adult mouse olfactory bulb in response to deafferentation. This reduction is permanent following intranasal irrigation with 0.17 M zinc sulphate (ZnSO4) but reversible following deafferentation produced by intranasal irrigation with 0.7% Triton X-100. The initial declines in TH activity, protein and mRNA of dopaminergic juxtaglomerular neurons observed after Triton X-100 treatment are all reversible as the steady-state level of TH mRNA gradually returns to control levels. Steady-state levels of mRNA for olfactory marker protein (OMP), a protein found in high concentrations in olfactory receptor neurons and their processes which innervate the olfactory bulb, were also monitored following deafferentation. Following treatment with either ZnSO4 or Triton X-100, the pattern of changes in steady-state levels of OMP mRNA was similar to that observed for TH. The steady-state level of PEP19 mRNA, a peptide previously localized to granule cells in the olfactory bulb, was not altered by deafferentation. These data indicate selective and parallel regulation of TH and OMP message and protein levels following deafferentation.