Divergent maternal behavioral patterns in two genetic animal models of depression

Maternal behavior was examined in Flinders Sensitive-Line (FSL) and Wistar-Kyoto (WKY) rats, two different genetic animal models of depression. Behavioral patterns were assessed by undisturbed observations in the nest [Post-Partum Days (PPD) 4 and 9] and post-disturbance observations ("retrieval tests") on PPD 10. Litters were randomly allocated to a mild chronic-stress condition (limiting available bedding between PPD 2 and 9) or a standard rearing condition. The findings indicated that FSL dams did not differ from control dams in the undisturbed observations. However, in the post-disturbance observations FSL dams exhibited less pup-directed behaviors, a shorter latency to first pup carrying/retrieval and more self-directed behaviors than controls (the latter effect only in dams' interaction with whole litter). In contrast, WKY dams performed more pup-directed activities (e.g., nursing and licking) and less self-directed activities in both the undisturbed and post-disturbance observations (in both dams' interaction with single-pup and with the whole-litter) compared to controls. Accordingly, WKY dams exhibited a shorter latency for first pup-licking bout (in both post-disturbance observations). The early life mild chronic-stress used in the study ('limited-bedding') had a minor effect on the dams' behavior. Overall, the study investigated for the first time the maternal behavior of WKY dams and suggests that these dams show an almost opposite behavioral pattern to that of FSL dams. The results are discussed with regard to earlier findings in the FSL strain and behavioral patterns documented in depressed human mothers.