The primary role of dopamine is to initiate positively rewarding actions such as eating food, having sex or the pleasure of exerting dominance over other people (Herve Pickel, Joh and Beaude); as such dopamine, increases vigor of an animal to find and use resources. Serotonin on the other hand directs the body to undertake inhibitory actions on an animal in order to provide safety, avoid threats and escape from fear (Herve et al).
The effects that serotonin has on dopamine can either be tonic or conditional; serotonin displays functional tonic inhibitory control over dopamine by rationing the MRN or DRN, increasing metabolism of the dopamine in the nucleus accumbens and by controlling the PFC levels (Herve, et al).
More generally, serotonin technically inhibits the release of dopamine thus slowing activity that requires dopamine to be successfully executed. However, some serotonin receptors such as 5-HT1A, 5-HT2A, 5-HT3, and 5-HT4 generally stimulate dopamine release by design (Herve, et al). Two of these receptors, 5-HT2A and 5-HT2C are striking in behavior because they display constitutive activity behavior while at the same time exerting opposite control over dopamine in the nucleus accumbens and striatum (Berg et al).
