Limited Bedding and Nesting as a Model for Early-Life Adversity in Mice
July 12th, 2024
This protocol describes an animal model for studying how early-life adversity, provoked by an impoverished environment and unpredictable maternal care during the early postnatal period, affects brain development and the future risk of mental disorders.
In our lab, we are trying to understand how early life adversity affects brain development and later risk for mental disorders, like depression and addiction. We are particularly interested in how microglia interacting with stress sensitive neurons in multiple brain regions may be the mechanism by which the circuit rewiring occurs. We previously found that this model for ELA provokes aberrant stress responses in adulthood.
This was caused by dysfunctional microglial synaptic pruning of excitatory synapses onto corticotropin releasing hormone expressing neurons in the paraventricular nucleus of the hypothalamus and thus hyperactivation of this stress responsive brain region. Although we know adverse early life experiences increase the risk of developing all kinds of health problems in humans, the limited bedding and nesting model allows us to prove the mechanisms for how these occurs in laboratory rodents. And there has never been a video protocol of this model published before.
The limited bedding and nesting model is very ecologically and translationally relevant because the low resource environment causes unpredictable maternal care, a phenomenon that can also be studied in humans. It also requires minimal experimental intervention and has been successfully implemented by multiple laboratories around the world. To begin, take a mesh divider cut according to the dimensions of a mouse cage, leaving an excess of three centimeters on the longer sides.
Fold the edges to create a platform that fits the cage edges perfectly with 2.5 centimeters above the floor. After setting up the cameras, check the video manager software interface for continuous recording. Next, pair one to four females with a single house male breeder mouse.
After 17 days of gestation or once visibly pregnant, separate the females into their own standard plexiglass cages. Place a cotton nestlet into the cage to allow the females to build a nest. After a couple of days, when the females give birth, record the date of birth.
On postnatal day two, transfer the pups into a clean new cage. Separate the males and the females into groups and count. Record the number of males and females in each litter.
To set up a control condition, fill a standard size mouse shoebox cage with about 220 grams of corn cob bedding. Add one standard square cotton nestlet. To help the mice acclimate to this unfamiliar environment, place one of their fecal pellets from their old cage in each corner of the new cage.
Transfer a small amount of used cotton nestlet from the previous cage over the new nestlet. To set up the LBN, or limited bedding and nesting condition, weigh 110 grams of corn cob bedding. Then, fill a standard shoebox cage with the corn cob and place the prepared mesh divider into the cage.
Finally, add half of a cotton nestlet square and repeat the same acclimation steps as in control cage. Now add the pups to their respective cages, placing them on top of the nestlet. Place the dam in the cage facing the pups.
Position a camera on a tripod in front of the cage with a clear side view of the dam and her pups. On postnatal day 10, transfer the dam first to standard caging conditions. Then, weigh the pups as they are transferred one by one to the standard cage.
Pups that were reared in LBN conditions were significantly smaller at postnatal day 10 than the control pups.
Overview
This study investigates how early-life adversity, induced by an impoverished environment and unpredictable maternal care, impacts brain development and the risk of later mental disorders. Using a limited bedding and nesting model in laboratory rodents, the research aims to elucidate the mechanisms, particularly the role of microglia and stress-sensitive neurons, involved in these processes.
Key Study Components
Area of Science
- Neuroscience
- Developmental Biology
- Behavioral Science
Background
- Early life adversity can increase the risk of mental health issues, including depression and addiction.
- The limited bedding and nesting (LBN) model reflects ecological and translational relevance.
- This model mimics low resource environments associated with unpredictable maternal care.
- No video protocol for this model has been previously published.
Purpose of Study
- To elucidate the biological mechanisms linking early life adversity to later mental disorders.
- To explore the role of microglia in stress responses and neuronal circuit rewiring.
- To validate a laboratory model that correlates with human experiences of early adversity.
Methods Used
- The limited bedding and nesting model was established in laboratory rodents.
- Microglia and neurons were the focus, assessing how stress influences synaptic pruning.
- Key timelines included separation of pups into clean cages and monitoring weights on postnatal day 10.
- Details included setting up control and LBN conditions with specific bedding amounts and nesting materials.
Main Results
- Pups reared in LBN conditions were significantly smaller at postnatal day 10 than controls.
- Dysfunctional microglial synaptic pruning resulted in aberrant stress responses in adulthood.
- The model demonstrated how early adversity can lead to hyperactivation of the stress response brain region.
Conclusions
- This study demonstrates the significant impact of early-life conditions on later mental health.
- The LBN model proves useful for understanding neuronal mechanisms of adversity.
- The findings may inform future research on mental disorders related to early life stress.
Frequently Asked Questions
Executive Industry Relevance
The Limited Bedding and Nesting (LBN) model provides a robust, translationally relevant system for interrogating the biological impact of early-life adversity on neurodevelopment and long-term stress responsivity. By modeling unpredictable maternal care and resource scarcity, this approach enables mechanistic de-risking of stress pathway targets and supports predictive confidence in neuropsychiatric disease modeling. Its adoption enhances portfolio decision-making at the intersection of target validation and preclinical model selection for CNS drug discovery.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Enables interrogation of stress pathway mechanisms and microglial-neuronal interactions relevant to neuropsychiatric risk.
- Supports functional target validation by linking early-life stress to circuit-level changes and behavioral phenotypes.
- Facilitates predictive confidence in selecting and triaging CNS targets based on mechanistic evidence.
Screening & Assay Development
- Provides a validated in vivo system for quantifying stress-induced phenotypes and neurodevelopmental outcomes.
- Supports reproducible measurement of quantitative outputs such as pup weight and basal corticosterone levels.
- Enables standardization of behavioral and physiological assays for downstream compound evaluation.
Translational & Preclinical Research
- Aligns with disease-relevant models of early-life adversity for translational biomarker exploration.
- Ensures continuity from mechanistic discovery to preclinical validation of stress-modulating interventions.
- De-risks advancement decisions by providing predictive data on long-term behavioral and physiological outcomes.
Pipeline & Workflow Integration
The LBN model integrates into the discovery continuum from early mechanistic studies through preclinical validation, supporting both target de-risking and translational alignment in CNS portfolios.
- Discovery Biology: Enables hypothesis testing on the impact of early-life adversity on stress circuitry and microglial function.
- Screening: Provides reproducible, quantitative endpoints for evaluating intervention efficacy in stress-related phenotypes.
- Analytics: Delivers measurable outputs such as pup weight and corticosterone for robust statistical comparison.
- Translational Research: Bridges preclinical findings to human-relevant models of adversity and stress vulnerability.
- Enterprise Reuse: Offers a standardized, scalable model for repeated use across CNS discovery programs.
Operational & Enterprise Impact
- Scientific Value: Increases predictive confidence and reduces mechanistic ambiguity in neuropsychiatric target validation.
- Operational Value: Promotes standardization, reproducibility, and scalability in stress-related model systems.
- Strategic Value: Informs go/no-go decisions and enhances capital efficiency by de-risking early CNS targets.
- Portfolio Impact: Supports risk-adjusted prioritization and advancement of CNS assets with translational relevance.
Implementation Considerations
- Requires expertise in rodent behavioral neuroscience and stress physiology.
- Needs access to specialized caging, video monitoring, and analytical infrastructure for behavioral and hormonal assays.
- Demands rigorous cross-team standardization of environmental and procedural variables.
- Adaptation across mouse strains and experimental paradigms may require protocol optimization.
- Limitations include partial recapitulation of human adversity and potential variability in maternal behavior.
