Maternal Separation Combined With Limited Bedding Increases Anxiety-Like Behavior and Alters Hypothalamic-Pituitary-Adrenal Axis Function of Male BALB/cJ Mice

Abstract

Early life stress (ELS) is considered a risk factor for the development of psychiatric conditions, including depression and anxiety disorder. Individuals that live in adverse environments are usually exposed to multiple stressors simultaneously, such as maternal neglect, maltreatment, and limited resources. Nevertheless, most pre-clinical ELS models are designed to explore the impact of these events separately. For this reason, this study aims to investigate the effects of a combined model of ELS on anxiety-like behavior and hypothalamic-pituitary-adrenal (HPA) axis related targets. From PND 2 to PND 15 BALB/cJ mice were exposed simultaneously to maternal separation (MS; 3 h per day) and limited bedding (LB; ELS group) or left undisturbed (CT group). Maternal behavior was recorded in intercalated days, from PND 1 to PND 9. Male offspring were tested for anxiety-like behavior from PND 53 to PND 55 in the open field test (OF), elevated plus-maze (EPM), and light/dark test (LD). After behavioral testing, animals were euthanized, and glucocorticoid receptor ( Nr3c1) , corticotrophin-releasing hormone ( Crh ), and its receptor type 1 ( Crhr1 ) gene expression in the hypothalamus were measured. Moreover, plasma corticosterone levels were analyzed. We observed that ELS dams presented altered quality of maternal care, characterized by a decrease in arched-back nursing, and an increase in passive nursing. Stressed dams also showed an increase in the number of exits from the nest when compared to CT dams. Furthermore, ELS animals showed increased anxiety-like behavior in the OF, EPM, and LD. Regarding gene expression, we identified an increase in hypothalamus Crh levels of ELS group when compared to CT animals, while no differences in Nr3c1 and Crhr1 expression were observed. Finally, stressed animals showed decreased levels of plasma corticosterone when compared to the CT group. In conclusion, we observed an alteration in maternal behavior in ELS dams. Later in life, animals exposed to the combined model of ELS showed increased levels of anxiety-like behavior. Moreover, the central and peripheral HPA measures observed could indicate a dysregulation in HPA function provoked by ELS exposure.

Anxiety, aggression, reward sensitivity, and forebrain dopamine receptor expression in a laboratory rat model of early‐life disadvantage

“…Studies involving only males found that previous Limited Bedding & Nesting produced higher anxiety in a light-dark box, but not in an open field (Bolton et al, 2018;Yang et al, 2015) or EPM (Wearick-Silva et al, 2019). Perhaps multiple early-life insults are needed to produce clear effects of limited bedding on later offspring anxiety (Orso et al, 2020), although the present results indicate that lead acetate is not one of them. In any case, our findings contribute to this literature by demonstrating that a prolonged postpartum Scarcity model alone can differentially affect anxiety-related behavior in female and male laboratory rats, although more research is needed to clarify this literature.…”

“…A handful of laboratory rodent studies have introduced multiple early‐life risk factors to be one step closer to the human condition (e.g., Amancio‐Belmont et al., 2020; Bassey & Gondré‐Lewis, 2019; Cory‐Slechta et al., 2013; Graham et al., 2011; Holman et al., 2021; Lehmann et al., 2000; Orso et al., 2020; Sprowles et al., 2018; Strzelewicz et al., 2021; Verstraeten et al., 2019; Zimmerberg & Brown, 1998), sometimes uncovering interesting interactive effects. For instance, prenatal nicotine exacerbates the negative effects of daily preweaning maternal deprivation on later rat offspring behavioral despair in a forced swim test (Bassey & Gondré‐Lewis, 2019), and only the combination of prenatal ethanol and early postnatal limited nesting material impairs social discrimination in late‐adolescent male rats (Holman et al., 2021).…”

Early Life Stress-Induced Epigenetic Programming of Hippocampal NPY-Y2 Receptor Gene Expression Changes in Response to Adult Stress

“…A more detailed mechanistic understanding of the longterm consequences of ELS and how ELS exposure may affect stress responses and behavior later in life can only be obtained by exposing individuals to multiple and also different types of stressors at different life spans (Orso et al, 2020). This led to the "two-(or multiple) hit" concept, which claims that early life adversities may exert a "programming" effect on the behavioral and on the cellular/molecular level and thereby increase or decrease stress sensitivity later in life (Lupien et al, 2009;Gruber et al, 2015;Lesse et al, 2017;Santarelli et al, 2017;Jaric et al, 2019).…”

Postnatal melatonin administration to stressed dams for ameliorating risk‐taking behaviour in rat pups through maternal care improvement

“…According to the study findings, the rats in the SG spent significantly less time in the open arms than those in the CG, and the percentage of their entries into the open arms reduced. Previous research had further suggested that early‐life stress, such as maternal separation combined with limited nesting stress within 2 weeks of birth, could cause anxiety and depression disorders in male rats (Orso et al, 2020). In the OF test decreased crossing numbers and rearing might be a sign for increased anxiety‐like behaviour in the offspring.…”