Localization of the MOR in myenteric neurons. Ileal segments were untreated (A), incubated with 1 μM endomorphin-1 for 15 min (B), or 15 min with 10 μM naloxone (C), or incubated with 1 μM endomorphin-2 for 15 min (D) or 1 μM DAMGO for 15 min (E). The MOR was detected using an antibody to MOR384–398. Images are single optical sections. In unstimulated tissues, the MOR was present at the plasma membrane (arrowheads) and in a few superficial endosomes of the soma, dendrites and axons. After incubation with agonists, the MOR was present in many superficial and perinuclear endosomes, and there was no detectable surface immunoreactivity. Naloxone caused retention of the MOR at the plasma membrane (arrowheads). Scale bar = 10 μm.