Swim test immobility in a genetic rat model of depression is modified by maternal environment: a cross-foster study

The Flinders sensitive line (FSL) genetic animal model of depression exhibits marked immobility during forced swimming, an accepted index of depressive like behavior in rodent depression models. The present experiment tested the hypothesis that swim test behavior in the FSL rats is influenced in part by early experience, specifically maternal environment. Male FSL and control Flinders resistant line (FRL) pups were cross fostered onto dams of the same or complementary strain. Nest quality and dam behavior during pup retrieval were measured on PN5 and PN8, and swim test behavior assessed in the adult males on PN60. FSL rats reared by foster FRL dams were significantly less immobile than FSL rats raised by FSL dams, but still significantly more immobile that the two FRL groups, which did not differ from each other. FSL dams took significantly longer to retrieve their pups and dropped them more often than the FRL control dams. Moreover, strain differences in maternal retrieval behavior significantly predicted later swim test immobility in the FSL animals. These findings suggest that swim test immobility in the FSL rats is modified by maternal environment. In contrast, the FRL control rats were relatively insensitive to the influence of maternal environment. The FSL model offers promise for understanding the interactions of genetic vulnerabilities and environmental influences in the etiology of clinical depression.