Anxiety and depression: a common neurobiological substrate?

The relationship between anxiety and depression may be more than the simultaneous expression of two commonly observed but distinct emotional states. Clinical studies suggest that anxiety is not only accompanied by symptoms of depression but may be an expected precursor syndrome in the development of at least some forms of depression. Recent genetic and epidemiological data further indicate that at least some forms of anxiety and depression may represent different phenotypic manifestations of the same genetic predisposition resulting from varying environmental conditions. Animal studies further suggest a causal relationship between anxiety and the development of a behavioral syndrome called "learned helplessness," an animal model of depression produced by exposing the animal to inescapable stress. Many of the behavioral and physiological features of the syndrome resemble those observed in depressed patients. Recent findings show that the administration to rats of anxiogenic inverse agonists of the benzodiazepine-GABA receptor complex produces the same behavioral syndrome evoked by inescapable stress. Moreover, pretreating animals with benzodiazepine anxiolytics can completely prevent the development of learned helplessness after exposure to inescapable stress. Together, the data suggest a common neurobiological substrate for some forms of anxiety and depression.