Limited Bedding and Nesting as a Model for Early-Life Adversity in Mice

Abstract

Early-life adversity (ELA), such as abuse, neglect, lack of resources, and an unpredictable home environment, is a known risk factor for developing neuropsychiatric disorders such as depression. Animal models for ELA have been used to study the impact of chronic stress on brain development, and typically rely on manipulating the quality and/or quantity of maternal care, as this is the major source of early-life experiences in mammals, including humans. Here, a detailed protocol for employing the Limited Bedding and Nesting (LBN) model in mice is provided. This model mimics a low-resource environment, which provokes fragmented and unpredictable patterns of maternal care during a critical developmental window (postnatal days 2-9) by limiting the amount of nesting materials given to the dam to build a nest for her pups and separating the mice from the bedding via a mesh platform in the cage. Representative data are provided to illustrate the changes in maternal behavior, as well as the diminished pup weights and long-term changes in basal corticosterone levels, that result from the LBN model. As adults, offspring reared in the LBN environment have been shown to exhibit an aberrant stress response, cognitive deficits, and anhedonia-like behavior. Therefore, this model is an important tool to define how the maturation of stress-sensitive brain circuits is altered by ELA and results in long-term behavioral changes that confer vulnerability to mental disorders.

Figure 1.

Example of cage setup. The cage on the left side of the image shows a standard control (CTL) cage containing a full amount of bedding and a full nestlet. The cage on the right side shows a limited bedding and nesting (LBN) setup with half the amount of bedding, half a nestlet, and a mesh divider for separating the animals from the bedding.

Figure 2.

Maternal behavior analysis. A. The daily entropy rate is higher in limited bedding and nesting (LBN) dams vs. control (CTL) as analyzed by mixed-effects model (F_1,58=7.21, p=0.0094). B. The average entropy rate is higher in LBN dams vs. CTL (t₁₅=3.025, p=0.0085). C. The average entropy rate (P3-P6) is not significantly different across multiple litters within the same dam maintained in the same treatment condition (F_1.699,4.247=0.574, p=0.58). Each line represents a single dam. D. The cumulative frequency of licking and grooming (LG) events is higher for LG dams vs. CTL (t₁₆=4.039, p=0.0010). E. The LG average bout length is shorter for LG dams vs. CTL (t₁₆=3.247, p=0.0050). F. The cumulative time spent LG is not significantly different due to LBN (t₁₆=1.521, p=0.15). Data are mean ± SEM, *p<0.05.

Figure 3.

Offspring outcomes. A. Limited bedding and nesting (LBN) decreases pup weight measured at P10, just before return to standard cages (t₆₁=6.296, p<0.0001). B. Weight is still decreased by LBN at weaning age (t₆₂=6.292, p<0.0001). C. Adult weight does not differ due to LBN (t₃₈=1.081, p=0.2864). D. The baseline concentration of corticosterone in adulthood is increased by LBN, as analyzed by Welch’s t-test (t_18.79=2.230, p=0.0381). For all graphs, females are shown with circles, and males with triangles. Data are mean ± SEM, *p<0.05.