Structurally, 5HT activity modulates DA activity both directly and indirectly. Concerning direct effects, there are 5HT receptors on some DA neurons: for those neurons, reception of 5HT reduces the rate of reception of DA (Daw, Kakade, & Dayan, 2002; Fink & Gothbert, 2007; Howell, Czoty, & Byrd, 1997). Concerning indirect effects, 5HT can bind to neurons in other locations that might otherwise be activated by DA firing, thus reducing that possible activation (Howell et al., 1997).
