Opiates have been known to suppress pain for a long time. In the early 1970s, scientists had only hypothesized that the brain has a specific protein receptor for opiates but had never tested the idea. With the discovery of opiate receptors, researchers used a simple yet effective experiment to search for such proteins. The key tool is naloxone, an opiate antagonist, which binds to the opiate receptor without activating it. Naloxone can treat narcotic overdose in an emergency.
Read the description of the experiment below, and fill in blanks when needed.