Insight into the lack of rewarding effect with anti-depressant treatments
Responding appropriately to pleasant or unpleasant events, in scientific terms rewarding or aversive stimuli, is critical for our health. Neurons in a part of the brain called the dorsal raphe nucleus (DRN), that produce the neurotransmitter serotonin, play a key role in signalling reward. Yet drugs boosting serotonin levels do not restore rewarding feelings in patients with depression, suggesting additional pathways are also involved. In mice, other serotonin-producing neurons, in the median raphe nucleus (MRN), appear to have opposite effects to the DRN: rewarding stimuli inhibit MRN neurons, and stimulating them triggers negative responses. To measure mouse perception, scientists monitored their behaviour and facial expressions; as shown here, mice move their tongue and ears when enjoying a sugar solution, but stimulating MRN neurons dampens this response, suggesting their perception of reward has changed. Understanding this interplay between serotonin pathways will be crucial to developing better treatments for disorders like depression.
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