κ-Opioid receptor (KOR) trafficking under oxygen–glucose deprivation (OGD) was observed with immunoelectron microscopy. (A) Healthy cells in normoxia had a large spindle-shaped nucleus; (B) nucleus shrinkage and cytoplasmic vacuolization were observed in the OGD group; (C) KOR-conjugated gold particles located around the cell membrane (green arrows = cell membrane; blue arrows = gold particles); (D) KOR-conjugated gold particles distributed in the periphery of the nucleus area. (E) There was no difference in the total gold particles between the normoxia and OGD groups; however, more cytoplasmic particles were founded in the OGD group (n = 10 per group). (F) Distribution of gold particles within the cytoplasm after 1 h of normoxia (control) or OGD conditions (n = 10 per group). Data are shown as mean ± SD. *P < 0.001. CM = cell membrane particles number; CP = cytoplasmic particles number; Total = the total number of particles in one cell.