The presence and distribution of OGF and OGFr in human papillary thyroid cancer cells. (A) Photomicrographs of log-phase KTC-1 cells visualized with differential interference (DIC) or stained with antibodies to [Met5]-enkephalin (OGF) or OGFr. Immunoreactivity was associated with the cytoplasm and a speckling of stain was noted in cell nuclei; no staining was detected with secondary antibodies only (inset). Scale bar = 10 μm. (B) KTC-1 cells were treated for 72 h with 10-6 M OGF or NTX, or sterile water (Co). Values represent mean ± SE for cells counted from 2 wells/treatment group from three experiments. Significantly different from controls at p < 0.05 (*) or p < 0.001 (***).