Fig. 2. (A) In situ hybridization expression patterns of CYP1A mRNA in juvenile lake trout midbrain of control fish and fish exposed to ß-naphthoflavone (BNF) for 4 days. CYP1A mRNA-positive cells are denoted by blue stain. Control fish were injected with corn oil vehicle daily for 4 days before sacrifice. Scale bars, 100 µm. (B) Higher magnification of BNF-exposed fish midbrain showing blue-stained glial cells (black arrows) and endothelia (gray arrow). Scale bar, 10 µm. Horizontal sections were counterstained with nuclear Fast Red.