Repeated long separations from pups produce depression-like behavior in rat mothers

Abstract

Long maternal (LMS) versus brief maternal (BMS) daily separations of rat pups from their mothers have contrasting effects on their adult stress responses and maternal behavior by, respectively, decreasing and increasing licking received from their mothers. We hypothesized that LMS decreases pup-licking in mothers by inducing learned helplessness, creating a depression-like state. We subjected postpartum rats to LMS (3 h), BMS (15 min) or no separation (NMS) on postpartum days 2-14. After weaning, mothers were given a forced swim test (FST). LMS mothers exhibited more immobility and fewer escape attempts than BMS or NMS mothers. These results suggest that LMS induces a depression-like state, which may account for the reductions in maternal behavior seen in LMS mothers. Immobility in the FST is recognized as an animal model of depression. Therefore, LMS may be a model of maternal depression.

Figure 1

Mothers' immobility in the FST. Day 1 results are divided into three 5-min blocks. Mothers who experienced long separations from their pups (LMS) exhibited greater immobility in the FST at weaning. Lines indicate significant main effect that percent time immobile was greater in LMS than the other two groups on both the first and second days of testing.

Figure 2

Mothers' escape attempts in the FST. Day 1 divided into 3 5-min blocks. Legend as in figure 1. Lines indicated by "a" highlight the main effect that all animals exhibited more escape attempts on Day 1 than Day 2. Lines indicated by "b" highlight that mothers who experienced long separations from their pups exhibited fewer escape attempts during day 2 of the FST.

Figure 3

Relationship between mothers' pup licking and immobility on the second day of the FST. Mothers' pup-licking on postpartum days 2–6 was negatively correlated with immobility in the FST (r=−.41, p=.01). Separation experience of each individual is distinguished by symbols, as indicated in the graph.