Expression, cellular distribution and induction of cytochrome p4501A (CYP1A) in gilthead seabream, Sparus aurata,...

The presence and induction of cytochrome p4501A (CYP1A) in the brain of a teleost fish, the seabream, Sparus aurata, was studied. Cerebral CYP1A expression of control fish or fish exposed to various concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was assessed at the enzyme activity level-measured as 7-ethoxyresorufin-O-deethylase; at the protein level-measured by means of Western blot and ELISA; and at the mRNA level-estimated by means of RT-PCR. Cellular localization of CYP1A in the brain tissue was studied using immunohistochemistry. In non-exposed control fish, expression of CYP1A could be demonstrated only in the olfactory bulbs. After TCDD exposure, the olfactory bulbs still showed the highest expression levels of CYP1A, however, other brain regions were now CYP1A-positive as well. Immunohistochemical examination of brain tissue sections from control fish demonstrated CYP1A immunoreactive fibers in the ventral telencephalon, in the glomerular layer of the olfactory bulbs, and in the endothelia of the cerebral vascular system. The same structures reacted positive in TCDD-exposed fish, but cell bodies and fibers from additional brain areas including telencephalon, diencephalon, mesencephalon and cerebellum showed CYP1A immunostaining. In the pituitary of TCDD-treated fish, putative GTH cells were positive for CYP1A, whereas in control fish no staining of the adenohypophysis was observed. The present findings provide evidence for basal expression of CYP1A in the telencephalon of Sparus aurata, and for the presence of inducible CYP1A in all other major brain regions, including the pituitary.