Depression is believed to be mediated by 5-HT and norepinephrine through the raphe nucleus and locus coeruleus projections to the cerebral cortex and forebrain limbic systems, whereas pain is believed to be mediated in part through descending 5-HT and norepinephrine pain pathways that provide inhibitory input to the dorsal horn neurons in the spinal cord. Global deficiences in 5-HT or norepinephrine neurotransmission would be predicted to affect both mood and pain thresholds, possibly accounting for the hgh comorbidity of painful symptoms in patients with depression.Accordingly, enhancement of both neurotransmitter or 5-HT alone would be expected both to improve symptoms of depression and to normalize pain thresholds.