Cell-specific differential expression of Na+-channel β1-subunit mRNA in the olfactory system during postnatal development and after denervation

Abstract

Activity-dependent mechanisms have been implicated in olfactory system development but, although such activity requires ion channels, few reports have described their expression in the olfactory system. We investigated the developmental and denervation-induced regulation of the Na+-channel β1 subunit (Naβ1) in rat olfactory bulb (OB) and piriform cortex (PC). In situ hybridization shows that Naβ1 mRNA expression is upregulated developmentally, but with different time courses in mitral, tufted, and pyramidal cells. In mitral cells, label was detected at postnatal day 4 (P4) and gradually increased to P14. Tufted cells were devoid of Naβ1 mRNA before P14, when most cells expressed adult levels. In pyramidal cells of PC, Naβ1 expression was not detectable clearly until P14, with maximal expression at P28. To examine the regulation of Naβ1 mRNA, we surgically deafferented the OB at P30 and compared the effects on Naβ1 with those for Na+-channel α- subunit (Naα) mRNAs. Within 5 d of surgery, the Naβ1 and NaαII signals within tufted cells disappeared almost completely. Naβ1 and NaαII expression was decreased in mitral cells to low-to-moderate levels. In pyramidal cells, Naβ1 mRNA expression was decreased moderately without significant changes in NaαII mRNA. Deafferentation had no detectable effects on NaαI or III mRNAs in either OB or PC. These data indicate that Naβ1 mRNA is expressed differentially in subpopulations of cells in the olfactory system during development and after deafferentation and suggest that the expression of Naλ is regulated independently of Naα mRNAs via cell-specific and pathway-specific mechanisms.