Lines of mice were selectively bred to diverge in their spontaneous he
lplessness in the tail suspension test. By the second generation of se
lection, only mice of the helpless line were sensitive to the antidepr
essant imipramine. Genetic factors substantially contribute to the sus
ceptibility to helplessness in this mouse model. These selectively bre
d lines may represent potentially useful animal models to investigate
behavioural, neurochemical and neuroendocrine correlates of antidepres
sant action.