Serotonin neurons in the dorsal raphe nucleus encode reward signals
The dorsal raphe nucleus (DRN) is involved in organizing reward related behaviours; however, it remains unclear how genetically defined neurons in the DRN of a freely behaving animal respond to various natural rewards. Here we addressed this question using fibre photometry and single unit recording from serotonin (5 HT) neurons and GABA neurons in the DRN of behaving mice. Rewards including sucrose, food, sex and social interaction rapidly activate 5 HT neurons, but aversive stimuli including quinine and footshock do not. Both expected and unexpected rewards activate 5 HT neurons. After mice learn to wait for sucrose delivery, most 5 HT neurons fire tonically during waiting and then phasically on reward acquisition. Finally, GABA neurons are activated by aversive stimuli but inhibited when mice seek rewards. Thus, DRN 5 HT neurons positively encode a wide range of reward signals during anticipatory and consummatory phases of reward responses. Moreover, GABA neurons play a complementary role in reward processing.
Nature communications