Genotype- and experience-dependent susceptibility to depressive-like responses in the forced-swimming test

Rationale: The forced-swimming test (FST) is utilized to reproduce passive coping responses to stress that may model a relevant aspect of human depression in rodent species. Animals showing high levels of passive responses to the FST are assumed to model pathologically depressed individuals. Objectives: We evaluated sensitivity of FST-induced behavioral responses to the interaction between genetic and environmental influences. Methods: Behavioral responses to FST were evaluated in naive mice of the C57BL/6 and DBA/2 strains, in mice of both strains pre-exposed to FST 14 days before test, and in FST-experienced animals subsequently exposed to 12 days of stress experience (food restriction). Results: C57BL/6 mice are characterized by high propensity to adopt passive coping responses in the FST. Moreover, stress enhances FST-induced immobility in mice of the C57BL/6 strain but reduces this response in DBA/2 mice. Finally, FST-induced immobility in C57BL/6 mice is reduced by chronic treatment with clinically effective antidepressants. Conclusions: These results support the view that behavioral and neural responses to FST exhibited by C57BL/6 mice can be usefully exploited by pre-clinical research on depression.