Fig. 1. Confocal microscopic images of μ-opioid receptor (MOR) internalization in lamina II of the spinal dorsal horn. Rats were perfused with a fixative 15 min after the intrathecal injection of 10 μg fentanyl (  A ), 100 ng [D-Ala²,MePhe⁴,Gly-ol⁵]enkephalin (DAMGO) (  B ), 20 μg morphine (  C ), or saline (  D ), to observe MOR internalization in the spinal dorsal horn neurons. Neuronal soma and MOR were stained with anti-NeuN antibody (  green ) and anti-MOR antibody (  red ), respectively. Confocal images (60×, zoom of 5) were two or three optical sections through the center of the neuron at intervals of 0.5 μm.  Scale bar = 10 μm.