Phenobarbital-inducible aldehyde dehydrogenase in the rat. to RALDH 1+ sites in the OE and LP, and RALDH 2+ sites, primarily surrounding nerve fiber bundles in the LP. Vitamin A deficiency altered RALDH 1, but not RALDH 2 protein expression. The isozymes and binding proteins exhibited random variability in levels and areas of expression both within and between animals. These findings support the hypothesis that RA is usually synthesized in the postnatal OE (catalyzed by RALDH 1) and underlying LP (differentially catalyzed by RALDH 1 and RALDH 2) at sites that could influence the development, maturation, targeting, and/or turnover of olfactory receptor neurons throughout the olfactory organ. via a two-step enzymatic pathway that oxidizes retinols, such as vitamin A ((Table 1A) and as exhibited in experiments using transfected Xenopus oocytes and cultured cell reporter systems (Haselbeck et al., 1999; Suzuki et al., 2000). RALDH 4 also catalyzes synthesis of retinoic acid showing greater activity with retinaldehyde than with retinaldehyde as substrate (Lin et al., 2003). All four RALDHs exhibit different spatial and temporal LF3 patterns of expression throughout the LF3 life of vertebrates. Of the four known RALDHs, RALDH 2 is usually expressed during early periods of mouse embryogenesis, and inactivation of this gene leads to death of embryos due to a lack of retinoic acid, which is required for morphogenesis, growth and differentiation of trunk, hindbrain and heart (Niederreither et al., 1999). Expression of RALDHs 1, 3, and 4, in addition to expression of RALDH 2, is usually observed at later stages of embryonic development and in postnatal animals throughout life in nonoverlapping areas of the same tissues and/or in discrete locations within the developing fetus or adult (Haselbeck et al., 1999; Grun et al., 2000; Li et al., 2000; Zhai et al., 2001; Wagner et al., 2002; Niederreither et al., 2002a; Hind et al., 2002a; Lin et al., 2003; Duester et al., 2003). Table 1A Comparison of kinetic constants for RALDHs using retinaldehyde as substrate. underlying the sensory epithelium is composed of a loose connective tissue framework that encompasses the (bundles of unsheathed individual axons that are ensheathed by the overlapping processes of one or more olfactory ensheathing cells), Bowman’s glands, blood vessels, fibroblasts, lymphocytes and other immune cells. This network of supporting cells and extracellular matrix is also referred to as stroma. Olfactory ensheathing cells are nucleated glial cells with two structurally and functionally distinct surfaces. The outer surface of the processes surrounding the axons faces a collagen-containing extracellular space and is completely covered by a basal lamina. The inner surface of the encircling olfactory ensheathing cell processes send out a ramification of processes that subdivide the nerve bundle into Cd8a interconnected compartments of axons. One to six olfactory nerve fibroblast processes form an outer boundary layer separated from the olfactory ensheathing cells by the collagen-containing space (Field et al., 2003). Previous studies from our laboratory and others have provided evidence that this cytosolic retinoic acid binding proteins (CRABP I and CRABP II) and the nuclear retinoic acid binding protein (RAR-) are present in the postnatal rodent olfactory epithelium (Gustafson et al., 1999; Asson-Batres et al., 2003a; Yee and Rawson, 2005). CRBP I, a protein that avidly binds vitamin A retinol and retinaldehyde, LF3 the precursors of retinoic acid, has been localized to the stroma underlying postnatal mouse olfactory epithelium (Gustafson et al., 1999), and the distribution of RALDH mRNA in the olfactory organ of three to six week aged mice has been exhibited by hybridization (Norlin et al., 2001; Niederreither et al., 2002a; Kawauchi et al., 2004). To date, this is the first formal report describing immunolocalization of RALDHs in postnatal olfactory epithelium. Some of these results were reported in abstract form at Annual Meetings of the Association for Chemoreception Sciences (Asson-Batres, 2002 Chem Senses 27:662; Asson-Batres and Smith, 2003 Chem Senses 28:560; Asson-Batres and Smith, 2005 Chem Senses 30:A89). Available data support.