Representative photomicrographs of oviductal epithelial cells processed by immunoelectron microscopy with gold labeled-antibodies of 10 nm for ESR1 (a-c) or ESR2 (d-f). Ampullary and isthmic sections of cyclic (a-c) and pregnant (d-f) rats are shown in the upper and lower panels, respectively. Arrows denotes ESR1-or ESR2 reacting gold particles in the epithelial cells. Arowheads emphasize the association of estradiol receptor immunoreactivity with cilia (cl, see insert in d). Asterisks indicate unspecific background laleling. Bar: 0.5 μm. PM = plasma membrane, C = cytoplasm, N = nucleus, L = lumen, SV = secretory vesicle.