Figure 3. Effect of lactational TCDD exposure on immunohistochemical staining for AhR (A–F) and CYP1A1 (G–L) in Pn22 rat upper first/second molars. (A,B,G,H) Control. Dam exposed to 50 µg/kg TCDD (C,D,I,J) and 1000 µg/kg TCDD (E,F,K,L). (A,B) AhR expression is still strong in ameloblasts and less intense in odontoblasts (see Figs. 2A, 2B). (C,D) AhR expression is clearly decreased in ameloblasts and odontoblasts. (E,F) AhR expression has virtually disappeared in both ameloblasts and odontoblasts. Some expression is still present in the papillary layer (arrowheads). (G,H) CYP1A1 expression in ameloblasts and odontoblasts is at the same level as at Pn9. (I,J) The expression has decreased considerably in all cell types. (K,L) No CYP1A1 expression is visible in any dental tissues. a, ameloblasts; d, dentin; e, enamel; o, odontoblasts. Bar: 100 µm in A-L.