The effects of social isolation on the forced swim test in Fawn hooded and Wistar rats.

Although the forced swim test (FST) has long been used as a preclinical screen of antidepressant efficacy, locomotor stimulants are known to produce confounding effects using the traditional dependent measure in this test: immobility. It has recently been suggested that measurement of struggling behavior may be a better index of antidepressant activity. The present experiments examined behavior in the forced swim test in two potential animal models of depression: the Fawn hooded rat, and the isolation-reared rat. No evidence was found to support these assertions, indeed immobility was decreased in Fawn hooded compared to Wistar rats, however this appeared to be caused by increased struggling behavior in Fawn hooded socials and increased swimming in Fawn hooded isolates. Although these differential results are highly suggestive of different underlying causes of decreased immobility in Fawn hooded rats depending on rearing conditions, the data suggests that the underlying psychological functions assumed to be represented by behavior assessed in this paradigm may not be adequately discriminated.