Serotonin neurotransmission has pervasive effects on behavior. While it is not responsible for any single behavior, serotonin helps shift between myriad of different behavioral repertoires and mood is perhaps related to our subjective experience of this shifting. It’s unknown how serotonin neurons perform this function. A current theory in the field is that there are small subsets of serotonin neurons that are highly specialized to facilitate specific behaviors. However, the extent of specialization and the identity of functionally relevant units remain poorly resolved. Here we review current understanding of the organization of brain serotonin neurons and discuss how these networks could function at the systems level. While ascending serotonin neurons exhibit substantial diversity, they are organization into two major families. Feedback inhibitory networks regulate these networks and are likely particularly important for the etiology of psychopathology and designing treatment strategies. Experiments using rodents modeling the behavioral response to both chronic developmental and acute stress suggest some hypotheses for how serotonin neurotransmission could be involved in depression and how antidepressants could work to modify their action.
Audience take away:
- The serotonin system may be composed of many highly specialized subunits, although the extent of specialization remains controversial.
- Feedback inhibitory circuits may exist between functionally distinct groups of serotonin neurons.
- Disorders such as depression could be related to imbalances within the serotonin system rather then simply a serotonin deficit.