Genetic and environmental models of stress-induced depression in rats

The present communication briefly reviews four rat models, two environmental and two genetic, which have engendered depressive-like behavior following exposure to stressors. Learned helplessness is a model in which a depressive-like behavioral state is induced by exposure of the rat to a series of inescapable aversive stimuli, normally foot shock. Chronic mild stress induces an anhedonic state (reduced responding for reward) by exposing the animals to a series of mild, unpredictable stressors. On the other hand, the genetic models were created by selectively breeding animals for either increased cholinergic (Flinders Sensitive Line (FSL) rats) or serotonergic (High DPAT Sensitive (HDS) rats) responses. The HDS and FSL rats are more immobile in the forced swim test than their selectively bred counterparts. Each of these models bears some resemblance to some of the key symptoms of depressed individuals and therefore has limited face validity. The depressive-like behavioral and/or anhedonic states have also been counteracted by a variety of antidepressants, indicating that the models have predictive validity. Thus, depressive-like behaviors can be produced in rats either by environmental manipulations involving stress or predisposing genetic/pharmacological factors. © 1998 John Wiley & Sons, Ltd.