How serotonin and dopamine are connected to each other?

Serotonin and dopamine interact within brain circuits: dopamine is more associated with seeking, motivation, and action, while serotonin is more associated with contentment and satisfaction with what is present. These are tendencies, not an either-or switch, and both systems can be active at once. 1

• Seeking and contentment: Dopamine more often supports motivation, craving, reward, and pursuit; serotonin is more associated with feeling happy and content with what you have, and generally drives action less strongly. 2
• They influence each other: Serotonin and dopamine neurons communicate, and serotonin release in the nucleus accumbens can modulate dopamine release. Their effects depend on the circuits and receptors involved, not just the overall amount of either chemical. 3
• MDMA illustrates the interaction: MDMA raises both chemicals. In the account discussed, serotonin acting at the 1B receptor in the nucleus accumbens is linked to prosocial effects, while dopamine helps reinforce reward and motivation. 4 5