CYP1A1 immunolocalization in the olfactory organ of rainbow trout and its possible induction by beta-naphthoflavone: analysis in adults and embryos around hatching

Cytochrome P4501A1 (CYP1A1) isoform, which is known as being of major toxic ological significance, has been well-studied in the mammalian olfactory muc osa. Only few studies have dealt with this biotransformation system in the fish olfactory organ which is particularly vulnerable to waterborne xenobio tics since sensory neurons are in direct contact with the aquatic environme nt. The present immunocytochemical study describes the cellular and subcell ular distributions of CYP1A1 in the olfactory organ of rainbow trout in bot h adults and embryos around hatching. The enzyme inducibility in response t o a 4-day exposure to waterborne beta-naphthoflavone (0.1 mg l(-1)), a mode l inducer of CYP1A1, was also examined. In untreated adult fish, CYP1A1 was almost exclusively expressed in the nonsensory epithelium which covers the edges and the tip of the lamellae. Both goblet and ciliated nonsensory cel ls appeared immunoreactive. In beta-naphthoflavone-treated fish, in additio n to a strong labeling in the nonsensory epithelium, ciliated nonsensory ce lls in the olfactory epithelium appeared well-labeled. Four days before hat ching, only a few cells were weakly stained in the placodal epithelium of s ome embryos. By 7 days post-hatching, the enzyme expression was increased i n the olfactory pit and it was restricted to ciliated nonsensory cells. No evident CYP1A1 induction was detected in either embryos or alevins. Results suggest the presence of a two-line CYP1A1 biotransformation system in the adult fish olfactory organ: a basal level of enzyme expression insured by t he nonsensory epithelium and an additional line in which the sensory epithe lium is activated in response to CYP1A1 inducers. This system might take pl ace during development in parallel with the onset of the nonsensory epithel ium.