Chronic Opioid Therapy and Opioid Tolerance: A New Hypothesis

Figure 3

In vivo distribution of opioid receptors in human brain with decrease in receptors in area of S1 (arrow). Photo Researchers Picture Number: SF2688. Credit: Philippe Psaila/Photo Researchers, Inc. License: Rights Managed. Description: Opioid receptors. Colored sagittal Positron Emission Tomography. (PET) scan showing the normal distribution of opioid receptors in the human brain. By injecting a patient with an opioid tagged with carbon-11 (radioactive tracer), a color-coded scan is produced, showing the concentration of opioid receptors from red (highest) through yellow and green to blue (lowest).