In an experiment in which long-distance runners were tested for pain tolerance, ran a mile, and then were tested again for pain tolerance.All of the runners were found to be able to withstand pain about 70 percent longer than before.They were then given naloxone and ran another mile.The naloxone
A)increased the runner's pain tolerance by another 20 percent.
B)had no effect on the runner's pain tolerance.
C)caused the runners to lose their earlier protection from pain.
D)caused the runners to suffer from excruciating muscle pain.

Question

Quizplus · Accepted Answer

Naloxone is an opioid antagonist, meaning it blocks the effects of opioids in the brain. In this experiment, the runners had previously experienced an increase in pain tolerance, presumably due to the release of endorphins during exercise. However, when given naloxone, this protection from pain was blocked, causing the runners to lose their earlier protection from pain.

In an Experiment in Which Long-Distance Runners Were Tested for Pain