Effect of Serotonin Neuron Suppression

Researchers implanted a microdialysis probe into a part of the brain called the dorsal raphe nucleus (DRN), then tested rats’ performance on a waiting test before and after a serotonin-suppressing drug was delivered through the probe. In the test, five rats were trained to alternately visit a food site and a water site, where they had to poke their noses into a hole and wait for a reward in the form of either a food pellet or water. Sometimes the wait was only two seconds, while other times the reward wouldn’t arrive until seven to eleven seconds of waiting. While untreated rats were usually able to keep their noses in the hole for as long as it took to get the reward, once the suppressor was delivered, reducing the amount of serotonin in the DRN by more than half, the rats became much more likely to wander off if not rewarded after a few seconds.