Mutations in the gene ANT1 may confer a risk for bipolar disorder through a complex interplay between serotonin and mitochondrial signaling in the brain. These two pathways have been separately implicated in bipolar disorder, but the link between levels of the neurotransmitter serotonin and mitochondrial dysfunction had not been established. Researchers now report that mitochondrial dysfunction affects the activity of serotonergic neurons in mice with mutations of ANT1.