Name: Author Spotlight: Exploring Microglial Interactions with Stress-Response Circuitry Using the Limited Bedding and Nesting Model
Uploaded: 2024-07-12T14:25:00
Description: Early-life adversity (ELA), such as abuse, neglect, lack of resources, and an unpredictable home environment, is a known risk factor for developing ...

This work was supported by NIMH K99/R00 Pathway to Independence Award #MH120327, Whitehall Foundation Grant #2022-08-051, and NARSAD Young Investigator Grant #31308 from the Brain &#38; Behavior Research Foundation and The John and Polly Sparks Foundation. The authors would like to thank the Division of Animal Resources at Georgia State University for providing exceptional care to our animals., and Ryan Sleeth for his excellent technical support in setting up and maintaining our video management system. Dr. Bolton would also like to thank Dr. Tallie Z. Baram for excellent training in the proper implementation of the LBN model during her postdoctoral fellowship.

All of the procedures involving animals were performed in compliance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals, and approved by the Institutional Animal Care and Use Committee from Georgia State University&#160;(approval number A24011). The mice were bred and maintained in the Animal Facilities at Georgia State University. The experiments were performed on a C57BL/6J strain during the perinatal period (postnatal day [P] 2-10) and included males and females. The reagents and e...

Modeling Early-Life Adversity in Mice Using Limited Bedding and Nesting

This article provides a detailed protocol to apply the LBN model in mice. This model is an important tool for understanding how an ethologically and translationally relevant form of chronic stress in early life contributes to the development of neuropsychiatric disorders in the offspring13. It is also useful for studying maternal behavior and any changes in the dams&#39; brain from a molecular, neuroendocrine, or circuit-based perspective24. For these types of questions, mu...

The early postnatal period is a critical developmental window in which environmental influences can shift the trajectory of development. For example, early-life adversity (ELA) can alter brain development to provoke long-term changes in cognitive and emotional function. Examples of ELA include physical or emotional abuse, neglect, inadequate resources, and an unpredictable home environment occurring during childhood or adolescence1. It is known that ELA is a risk factor for developing disorders such as depression, substance use disorder, post-traumatic stress disorder (PTSD), and anxiety2,3,4,5. This is important given that the levels of childhood poverty in the US have more than doubled recently, from 5.2% in 2021 to 12.4% in 20226, and although poverty itself is not necessarily ELA, it does increase the probability of various types of ELA7.
Animal models have long been essential for understanding the effects of early-life stress on brain development and adult outcomes. The two main animal models used in recent years to dissect this phenomenon are maternal separation (MS) and an impoverished environment induced by limited bedding and nesting materials (LBN). MS was developed as a model of parental deprivation8. In it, rodent dams are taken away from their pups, usually for several hours, every day until weaning8. The MS paradigm has been found to result in depressive- and anxiety-like behaviors in adulthood9, as well as an aberrant response to chronic stress10,11. On the other hand, the LBN model, first developed in the Baram laboratory12, does not separate the dam from the pups, but rather modifies the environment in which the pups are reared, mimicking a low-resource environment12,13. Decreasing the amount of nesting material and preventing direct access to the bedding in this model results in disrupted maternal care from the dams3. Since robust and predictable maternal care is required for the proper development of cognitive and emotional brain circuits14, fragmented maternal care from LBN can result in a range of outcomes, including an over-active Hypothalamic-Pituitary-Adrenal (HPA) axis, shifted excitatory-inhibitory balance in multiple brain regions, increased corticotropin-releasing hormone (CRH) levels, and depressive-like behavior in the offspring13,15,16,17,18,19.
The exact mechanism by which ELA results in increased risk for neuropsychiatric disorders is not completely understood. It is thought to be related to alterations in the HPA axis circuitry19,20, and recent evidence shows that this may be caused by changes in microglial synaptic pruning19. The LBN model has been shown to be a crucial tool for understanding the perinatal environment&#39;s impact on brain development and long-term behavioral outcomes. Although this model was initially developed for rats, it has also been adapted for mice in order to take advantage of the existing transgenic tools12,13. Notably, the model is very similar in both species and provokes highly convergent outcomes, such as alterations in the HPA axis, cognitive deficits,&#160;and depressive-like behavior, thus highlighting its cross-species utility and translational potential. This article will provide a detailed description of how to employ the limited bedding and nesting model in mice, collecting and analyzing maternal behavior and offspring outcomes to validate the model&#39;s efficacy and the expected results.

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limited bedding and nesting as a model for early-life adversity in mice

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&#160;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.

Author Spotlight: Exploring Microglial Interactions with Stress-Response Circuitry Using the Limited Bedding and Nesting Model

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

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 probe 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.

The representative results demonstrate how ELA, imposed by an impoverished environment in LBN cages, affects maternal care from dams and offspring physiological outcomes. The daily entropy in maternal care behavior is higher in LBN across days P3-P6 (F1,58 = 7.21, p = 0.0094; Figure 2A), as well as the average entropy of each dam from this time period (t15 = 3.03, p = 0.0085; Figure 2B). Notably, there is no significant di...

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.

Early-life adversity (ELA), such as abuse, neglect, lack of resources, and an unpredictable home environment, is a known risk factor for developing ...

limited-bedding-nesting-as-model-for-early-life-adversity

Research

JoVE Journal

Neuroscience

Inducing Early-Life Adversity Using the Limited Bedding and Nesting Paradigm in Mouse Models

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.