Early life stress leads to sex differences in development of depressive-like outcomes in a mouse model

Abstract

Childhood trauma and neglect influence emotional development and increase the risk for and severity of mental illness. Women have a heightened susceptibility to the effects of early life stress (ELS) and are twice as likely as men to develop debilitating, stress-associated disorders later in life, such as major depressive disorder (MDD). Until now, mouse models of depression have been largely unsuccessful at replicating the diverse symptomatology of this disease and the sex bias in vulnerability. From P4 to P11, a limited bedding model that leads to fragmented maternal care, was used to induce ELS. Early adolescent and young adult mice were tested on an array of assays to test for depressive-like behavior. This included our newly developed automated home cage behavioral recognition system, where the home cage behavior of ELS and control mice could be monitored over a continuous 5-10 day span. ELS females, but not males, exhibited depressive-like behaviors on traditional assays. These effects emerged during adolescence and became more severe in adulthood. Using the novel home cage video monitoring method, we identified robust and continuous markers of depressive-like pathology in ELS females that phenocopy many of the behavioral characteristics of depression in humans. ELS effects on home cage behavior were rapidly rescued by ketamine, a fast-acting antidepressant. Together, these findings highlight that limited bedding ELS (1) produces an early emerging, female-specific depressive phenotype that responds to a fast-acting antidepressant and (2) this model has the potential to inform sex-selective risk for the development of stress-induced mental illness.

Fig. 1

ELS results in fragmented maternal care and altered somatic development in both male and female mice. a–c Timelines for groups of mice undergoing testing at early adolescence (a), young adulthood (b), or in adulthood (c). d A schematic illustration of control and ELS cages as well as activity traces of a control dam (yellow) and ELS dam (pink) over a 24-h period with her pups, traced in EthoVision. e Plots of the mean weight for control (closed) and stressed (open) male (blue) and female (red) mice across development. For weight plot, data represent means ± 1 SEM. Main effects depicted as #; #p < 0.001

Fig. 2

Early-onset depression in female mice exposed to ELS strengthens by adulthood. a For sucrose preference, animals had a choice between water or sucrose for 3 days, percent of all liquid consumed that was sucrose is reported here. b There was no main effect of sex or treatment at early adolescence. However, a trend toward decreased sucrose preference (anhedonia) was found in ELS females (n = 9) compared with ELS males (n = 8). c In adulthood, a significant main effect of sex and treatment as well as a sex × treatment interaction were found on sucrose preference, with female ELS animals (n = 9) driving these effects, drinking significantly less sucrose water than any other group (n = 7–9). In the forced swim test, d immobility on day 2 − immobility on day 1 (baseline) is reported here. e At early adolescence, an overall effect of sex was found, with females showing greater learned helplessness overall (n = 10–11). f At adulthood, a main effect of sex as well as a significant sex × treatment interaction was found, again with ELS females (n = 13) driving these effects, showing significantly greater behavioral despair compared with any other group (control F, n = 13; control and ELS M, n = 8). g In the novelty-induced hypophagia task, latency to approach the sweet milk is reported in the home and novel cage. h In early adolescence, all animals took longer to approach the sweet milk in the novel cage than their home cage. Specifically, in their home cage, ELS female mice (n = 9) took longer to approach the sweetened milk compared with all other groups (n = 8–9). i At adulthood, there were main effects of both treatment and day, with ELS animals taking longer to approach the sweetened milk than control animals, and all animals showed increased latency to approach the milk in the novel cage. There were no differences between groups in the home cage phase of the task. In the novel cage, a significant effect was found between groups specifically with ELS females (n = 12) taking longer to approach the sweetened milk than control females (n = 12). For all plots, data show means ± 1 SEM. Significance is denoted as follows: # for main effects, & for interaction effects, and * for significant post hoc comparisons; *p < 0.05, **p < 0.005. In the case of a significant one-way analysis of variance, F statistics are reported but only the significant post hoc Bonferroni comparisons are shown

Fig. 3

Early life stress does not lead to sex-selective anxiety-like behavior in early adolescence or adulthood. a, b The elevated plus maze measures anxiety as a % duration of time spent exploring the open arms (white) and number of entries into the open arms. At early adolescence (n = 10–12) and adulthood (n = 10–12), no differences were detected between groups on either measure. Additionally, there were no effects of sex or rearing condition on locomotor activity in this task. c, d The open field arena is divided into three zones: outer (light gray); middle (white); and center (dark gray). Anxiety is measured by decreased % time spent in center and increased % time spent in outer areas. c No effects of sex or rearing condition were observed on anxiety or locomotion in early adolescent mice (n = 10–12). d In adult mice, there was a significant effect of rearing condition on % time in outer arena, with ELS spending more time in this area, but no effects of sex or rearing condition on % time in center or locomotion were observed (n = 16). For all plots, data represent means ± 1 SEM. Main effects depicted as #; #p < 0.05

Fig. 4

Early life stress leads to depressive-like home cage behaviors, specifically in female mice. Ethograms presenting the mean time (minutes ± 1 SEM) engaged in a given behavior for each hour over a 24-h period, averaged over 5 days. Mice were housed on a 12:12 light:dark cycle, with shaded regions indicating periods of dark and white regions indicating periods of light. Measures are presented for male control (n = 15, closed circles) and ELS (n = 12, open circles) mice, shown in blue, as well as female control (n = 13, closed squares) and ELS (n = 18, open squares) mice, in red. a ELS females show diminished self-care, spending significantly less time grooming than control females and male animals at hours 3 (F_(3,57) = 4.860, p = 0.005), 4 (F_(3,57) = 5.151, p = 0.003), 5 (F_(3,57) = 3.315, p = 0.027), 6 (F_(3,57) = 6.347, p = 0.001), 7 (F_(3,57) = 3.386, p = 0.025), 8 (F_(3,57) = 4.747, p = 0.005), 10 (F_(3,57) = 3.042, p = 0.037), 11 (F_(3,57) = 6.581, p = 0.001), 18 (F_(3,57) = 3.234, p = 0.029, 20 (F_(3,57) = 6.033, p = 0.001), 22 (F_(3,57) = 4.473, p = 0.007), and 23 (F_(3,57) = 3.447, p = 0.023). This stress-effect was sex-selective, with ELS males performing similar grooming patterns to control males. b ELS females spent significantly more time sleeping than control females and male animals. Specifically, significant effects of group were found during hours 5 (F_(3,57) = 3.288, p = 0.027), 6 (F_(3,57) = 10.235, p < = 0.001), 7 (F_(3,57) = 3.454, p < 0.023), 12 (F_(3,57) = 3.272, p = 0.028), 20 (F_(3,57) = 9.135, p < 0.001), 21 (F_(3,57) = 4.597, p = 0.006), 22 (F_(3,57) = 10.526, p < 0.001), and 23 (F_(3,57) = 3.847, p < 0.014), which are almost all during the animals’ dark cycle. c Exclusively during dark hours, ELS females demonstrated reduced locomotion, spending significantly less time walking than control animals. Significant effects of group were found during hours 20 (F_(3,57) = 6.947, p < 0.001), 21 (F_(3,57) = 4.794, p = 0.005), 22 (F_(3,57) = 3.165, p = 0.032), and 23 (F_(3,57) = 5.994, p = 0.001). d Detailed breakdown of the percent of time that each group of animals engaged in specific behaviors over the course of 5 days in their home cage

Fig. 5

The fast-acting, atypical antidepressant, ketamine, rescues depressive-like home cage behavior in ELS female mice. a Experimental design. b Significant differences in resting behaviors exist between control and ELS females before ketamine treatment, specifically at hour 4 (t₂₉ = 2.516, p = 0.018); hour 6 (t₂₉ = 4.710, p < 0.001); hour 7 (t₂₉ = 3.579, p = 0.001); hour 12 (t₂₉ = 2.091, p = 0.045); hour 13 (t₂₉ = 2.248, p = 0.032); hour 20 (t₂₉ = 4.351, p < 0.001); hour 21 (t₂₉ = 3.612, p = 0.001); hour 22 (t₂₉ = 4.942, p < 0.001); and hour 23 (t₂₉ = 3.585, p < 0.001). c Ketamine treatment reverses disordered resting behavior in ELS females to match control animals. There only remaining effect of rearing condition exists at hour 23 (t₂₉ = 2.160, p = 0.046). d Prior to ketamine treatment, ELS females spend significantly less time grooming than control females at nearly every hour (hour 1 (t₂₉ = 2/588, p = 0.015); hour 2 (t₂₉ = 2.285, p = 0.030); hour 3 (t₂₉ = 3.793, p = 0.001); hour 4 (t₂₉ = 4.094, p < 0.001); hour 5 (t₂₉ = 3.069, p = 0.005); hour 6 (t₂₉ = 4.489, p < 0.001); hour 7 (t₂₉ = 3.645, p = 0.001); hour 8 (t₂₉ = 3.385, p = 0.002); hour 10 (t₂₉ = 3.063, p = 0.005); hour 11 (t₂₉ = 4.717, p < 0.001); hour 14 (t₂₉ = 2.693, p = 0.12); hour 15 (t₂₉ = 2.053, p = 0.049); hour 16 (t₂₉ = 2.525, p = 0.017); hour 17 (t₂₉ = 2.151, p = 0.040); hour 18 (t₂₉ = 2.906, p = 0.007); hour 19 (t₂₉ = 2.590, p = 0.015); hour 20 (t₂₉ = 4.797, p < 0.001); hour 21 (t₂₉ = 2.505, p = 0.018); hour 22 (t₂₉ = 4.074, p = < 0.001); hour 23 (t₂₉ = 3.127, p = 0.004); and hour 24 (t₂₉ = 2.648, p = 0.013)). e Following ketamine treatment, ELS females engaged in self-care (grooming) to the same extent as control females. No differences exist between groups at any hour. For all plots, data represent mean ± SEM. Significance is denoted as follows: # for main effects and & for interaction effects, ^#p < 0.05, ^##p < 0.001