The effect of antidepressants on aversive periaqueductal gray stimulation in rats.

The selective serotonin (5-HT) uptake inhibitors fluvoxamine and sertraline had anti-aversive effects when administered acutely. Imipramine and clomipramine, which combine noradrenaline (NA) and 5-HT uptake blocking properties, did not have significant effects, whereas the mixed dopamine (DA)/NA uptake blocker nomifensine decreased the thresholds for escape from aversive periaqueductal gray stimulation. These results suggest that indirect 5-HT receptor activation suppresses periaqueductal gray aversion. Conversely, indirect DA and perhaps NA receptor activation appears to enhance periaqueductal gray aversion in rats.