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The chronic psychosocial stress (CGS) paradigm employs clinically relevant stressors during pregnancy in mice to model psychiatric disorders of mothers and infants. Here, we provide a step-by-step procedure of applying the CGS paradigm and downstream assessments to validate this model.
The peripartum period is considered a sensitive period where adverse maternal exposures can result in long-term negative consequences for both mother and offspring, including the development of neuropsychiatric disorders. Risk factors linked to the emergence of affective dysregulation in the maternal-infant dyad have been extensively studied. Exposure to psychosocial stress during pregnancy has consistently emerged as one of the strongest predictors. Several rodent models have been created to explore this association; however, these models rely on the use of physical stressors or a limited number of psychosocial stressors presented in a repetitive fashion, which do not accurately capture the type, intensity, and frequency of stressors experienced by women. To overcome these limitations, a chronic psychosocial stress (CGS) paradigm was generated that employs various psychosocial insults of different intensity presented in an unpredictable fashion. The manuscript describes this novel CGS paradigm where pregnant female mice, from gestational day 6.5 to 17.5, are exposed to various stressors during the day and overnight. Day stressors, two per day separated by a 2 h break, range from exposure to foreign objects or predator odor to frequent changes in bedding, removal of bedding, and cage tilting. Overnight stressors include continuous light exposure, changing cage mates, or wetting bedding. We have previously shown that exposure to CGS results in the development of maternal neuroendocrine and behavioral abnormalities, including increased stress reactivity, the emergence of fragmented maternal care patterns, anhedonia, and anxiety-related behaviors, core features of women suffering from perinatal mood and anxiety disorders. This CGS model, therefore, becomes a unique tool that can be used to elucidate molecular defects underlying maternal affective dysregulation, as well as trans-placental mechanisms that impact fetal neurodevelopment and result in negative long-term behavioral consequences in the offspring.
The mechanisms underlying increased susceptibility to neuropsychiatric disorders in mothers and infants following adverse maternal exposures in the peripartum period remain largely unknown. Substantial maternal physiological alterations occur during pregnancy and the transition to the postpartum period, including several neuroendocrine adaptations that are hypothesized to be critical not only for healthy offspring neurodevelopment but also for preserving maternal mental health1,2. At the level of the maternal hypothalamic pituitary adrenal (HPA) axis, adaptions in both circadian and stress-induced levels of glucocorticoid release are observed, including a more flattened rhythm of diurnal HPA axis activity and dampened HPA axis response to acute stressors3,4,5. Given that enhanced HPA axis activity is reported in a subset of women with postpartum affective dysregulation, including increased levels of circulating glucocorticoids and inhibited negative feedback6,7,8, exposure to stressors that result in increased postpartum stress reactivity and prevent maternal HPA axis adaptions are thought to increase susceptibility to neuropsychiatric disorders.
To elucidate the effects of stress on affective dysregulation in mothers and infants, several rodent models of stress in the peripartum period have been generated. A majority of these models are characterized by the application of physical stressors that result in homeostatic challenges and alterations in dam physiological status9, such as chronic restraint stress10 and swim stress during gestation11, or postpartum shock exposure12. Although these paradigms have been shown to result in the emergence of postpartum depressive-like behaviors and alterations in maternal care10,11,12, they have been limited by their inability to accurately capture the psychosocial nature of stressors commonly experienced by human mothers. This becomes particularly important when attempting to reveal the neuroendocrine consequences of chronic stress in the peripartum period, given that processing of different types of stressors is thought to be mediated by varying neural networks orchestrating HPA axis activation9.
In order to overcome this limitation, several groups have designed stress paradigms employing psychosocial insults or a combination of physical and psychosocial stressors. The maternal separation model, where dams are separated from her pups for several hours per day during the postpartum period13,14, and the chronic social stress model, where the dams are exposed to a male intruder in the presence of their litters15,16, have been able to reproduce the emergence of abnormalities in maternal care and depressive-like phenotypes associated with physical stress paradigms. The chronic ultramild stress paradigm, where pregnant female mice are exposed to a variety of psychosocial insults, including cage tilt and overnight illumination, as well as substantial physiological insults, such as restraint stress and food restriction, has further revealed exposure to a mixed nature of stressors results in abnormalities in maternal behavior, including impairments in maternal aggression, as well as dysregulation in the circadian activity of the HPA axis17,18. Consistent with these results, an alternating restraint stress and overcrowding model during gestation results in elevations in postpartum maternal circadian corticosterone levels as well as alterations in maternal care, although no differences are observed in HPA axis re-activity following postpartum exposure to novel acute insults1.
An expansion of this work, generating a gestational stress paradigm that employs multiple psychosocial insults presented in an unpredictable fashion and minimizes the use of physiological stressors. Studies have previously shown this chronic psychosocial stress paradigm (CGS) results in the development of maternal HPA axis dysfunction, including enhanced stress reactivity in the early postpartum period19. These changes are associated with abnormalities in maternal behavior, including alterations in the quality of maternal care received by pups, and the emergence of anhedonic and anxiety-like behaviors19, features consistent with perinatal mood and anxiety disorders20,21. Furthermore, offspring weight gain reduces during the postnatal period following in-utero exposure to CGS19, suggesting CGS may have persistent negative programming effects in future generations.
The goal in developing the CGS paradigm was to primarily utilize clinically relevant stressors, which accurately capture the type, intensity, and frequency of insults often associated with neuroendocrine dysregulation and the development of perinatal mood and anxiety disorders. Here, the study provides a detailed protocol of how to subject pregnant female mice to CGS, as well as downstream assessments that can be used to test the validity of the model.
All animal experiments described were approved by the Animal Care and Use Committee at Cincinnati Children's Medical Center and were in accordance with the National Institutes of Health guidelines. Ad libitum access to standard rodent chow and water was provided at all times to mice, including during the CGS paradigm. Mice were housed on a 14 h/10 h light-dark cycle (lights on 06:00 h) unless otherwise specified (i.e., exposure to lights overnight).
1. Preparing for timed matings
2. Setting up timed matings
3. Checking the copulatory plug, designated as gestational day 0.5 (G0.5)
4. Preparing for CGS paradigm
5. Performing the CGS paradigm
6. Monitoring the experimental mice during the CGS paradigm
7. Measuring the percentage body weight gain during gestation in the experimental mice (optional)
8. Measuring the postpartum relative adrenal gland weights in experimental mice (optional)
9. Measuring the postpartum hypothalamic pituitary adrenal (HPA) axis activity in the experimental mice (optional)
10. Measuring the postpartum behavioral changes in the experimental mice (optional)
11. Measuring the postnatal offspring weight changes (optional)
Exposing the pregnant female mice to CGS results in changes in chronic stress-relevant parameters, including a reduction in body weight gain during pregnancy (Figure 2A) and increased adrenal gland weights in the early postpartum period (Figure 2B)19. Importantly, exposure to CGS results in postpartum abnormalities in maternal neuroendocrine function. CGS dams exhibit a hyperactive HPA axis as evidenced by the increased serum corticostero...
Exposing the pregnant mice to CGS perturbs postpartum maternal neuroendocrine function, including HPA axis response to novel stressors, and is associated with various behavioral abnormalities relevant to perinatal mood and anxiety disorders. Given that the model employs utilization of an environmental risk factor, higher phenotypic variation is expected than otherwise observed in genetic models22. Nevertheless, results obtained from application of the CGS paradigm can be consistent across research...
The authors have no conflicts of interest to disclose.
The authors wish to acknowledge support from the National Institute of General Medical Sciences T32 GM063483-14 grant and Cincinnati Children's Research Foundation. For data adapted from Zoubovsky et al., 2019, Creative Common License can be found at the following location: http://creativecommons.org/licenses/by/4.0/.
Name | Company | Catalog Number | Comments |
Animal lancet | Braintree Scientific Inc. | GR4MM | |
Blunt end probe | Fine Science Tools | 10088-15 | Used to check for copulatory plugs |
Bottles for SPT | Braintree Scientific Inc. | WTRBTL S-BL | 100 mL glass water bottle with stopper and sipper ball point tube, graduted by 1 mL. |
Conical tubes (50 mL) | Corning Inc. | 352098 | Used for restraining mice to measure HPA axis response to acute stress. Make sure conical tube has small opening at the end for ventilation. |
Legos | Amazon | - | |
Marbles | Amazon | - | |
Mouse Corticosterone ELISA kit | Biovendor | RTC002R | |
Mouse EZM | TSE Systems | - | |
Reciprocal laboratory shaker | Labnet international | S2030-RC-B | |
Serum separator tubes | Becton Dickinson | 365967 | |
Static cage- bottom | Alternative Design Manufacturing and Supply Inc. | RC71D-PC | |
Static cage - filtered ventilated tops | Alternative Design Manufacturing and Supply Inc. | FT71H-PC |
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