Sex differences in associations between maternal deprivation and alterations in hippocampal calcium-binding proteins and cognitive functions in rats

Quercetin-loaded nanophytosome ameliorates early life stress-induced hippocampal oxido-inflammatory damages

Phytosome-based nanocarriers have emerged as innovative drug delivery systems in recent years, demonstrating significant potential in the treatment of neurodegenerative disorders. This study aimed to evaluate the therapeutic efficacy of quercetin-loaded nanophytosome (QNP) in modulating the oxido-inflammatory response in a rat model of early life stress (ELS) induced by maternal isolation (MI). To establish the ELS model, male rat pups were isolated from their dam for 3 hours daily from postnatal days 1-9. Following the lactation period (postpartum days 1-21), treatments with quercetin (10 and 40 mg/kg) and QNP (10 and 40 mg/kg) were administered continuously for 21 days. Cognitive behaviors, oxidative stress markers, hippocampal dopamine levels, and mRNA expression of TNF-α and IL-6 were assessed after ELS induction. Treatment with QNP (40 mg/kg) significantly improved cognitive function (P < 0.01), increased hippocampal dopamine levels (P < 0.001), and reduced oxidative stress (P < 0.01) as well as the expression of TNF-α (P < 0.001) and IL-6 (P < 0.001). In conclusion, QNP demonstrates potent hippocampal anti-oxidoinflammatory effects, making it a promising therapeutic candidate for mitigating the adverse effects of maternal isolation-induced early life stress.

A single 24 h maternal separation at PND 9 promotes behavioral resilience of female C57BL/6J mice and the possible role of hippocampal Homer1a

Early life stress (ELS) has been thought to increase vulnerability to developing psychiatric disorders later in life, while some researchers have found that adversity early in life may promote stress resilience. Studies investigating the resilient effect of maternal separation (MS) are still relatively few, and the underlying mechanisms remain unknown. In the current study, the effect of a single 24 h MS paradigm at postnatal day 9 (PND 9) in female C57BL/6J mice was investigated by assessing behavioral performance in middle adolescence. We demonstrated that, mice in MS group displayed decreased anxiety-like behavior and increased exploratory behavior than controls in the open field test and elevated plus maze test. Furthermore, MS mice exhibited improved hippocampal-dependent spatial learning in the Morris water maze test. This performance indicated behavioral resilience to early life stress. The protein expression levels of Homer1 isoforms, which are implicated in a variety of neuropsychiatric disorders, were evaluated using Western blot analysis. A significant increase in hippocampal Homer1a protein expression was observed immediately after MS, which subsequently decreased until adolescence (PND 27-42), when a significant increase was observed again. This distinctive change of hippocampal Homer1a protein expression pattern indicated that hippocampal Homer1a might play a role in behavioral resilience to MS in female C57BL/6J mice. In conclusion, this study demonstrated that exposure to a single 24 h MS at PND 9 promoted behavioral resilience of female C57BL/6J mice in middle adolescence. This behavioral resilience might be related to increased expression of hippocampal Homer1a.

Neonatal stress disrupts the glymphatic system development and increases the susceptibility to Parkinson's disease in later life

INTRODUCTION

Neonatal stress disrupts brain development and increases the risk of neurological disorders later in life. However, the impact of neonatal stress on the development of the glymphatic system and susceptibility to Parkinson's disease (PD) remains largely unknown.

METHODS

Neonatal maternal deprivation (NMD) was performed on mice for 14 consecutive days to model chronic neonatal stress. Adeno-associated virus expressing A53T-α-synuclein (α-syn) was injected into the substantia nigra to establish PD model mice. Glymphatic activity was determined using in vivo magnetic resonance imaging, ex vivo fluorescence imaging and microplate assay. The transcription and expression of aquaporin-4 (AQP4) and other molecules were evaluated by qPCR, western blotting, and immunofluorescence. Animal's responses to NMD and α-syn overexpression were observed using behavioral tests.

RESULTS

Glymphatic activity was impaired in adult NMD mice. AQP4 polarization and platelet-derived growth factor B (PDGF-B) signaling were reduced in the frontal cortex and hippocampus of both young and adult NMD mice. Furthermore, exogenous α-syn accumulation was increased and PD-like symptoms were aggravated in adult NMD mice.

CONCLUSION

The results demonstrated that NMD could disrupt the development of the glymphatic system through PDGF-B signaling and increase the risk of PD later in life, indicating that alleviating neonatal stress could be beneficial in protecting the glymphatic system and reducing susceptibility to neurodegeneration.

Early life adversity as a risk factor for cognitive impairment and Alzheimer's disease

Neurological conditions, including cognitive impairment and Alzheimer's disease (AD), impose a huge burden on society, affecting millions of people globally. In addition to genetic factors, recent studies indicate that environmental and experiential factors may contribute to the pathogenesis of these diseases. Early life adversity (ELA) has a profound impact on brain function and health later in life. In rodent models, exposure to ELA results in specific cognitive deficits and aggravated AD pathology. Extensive concerns have been raised regarding the higher risk of developing cognitive impairments in people with a history of ELA. In this review, we scrutinize findings from human and animal studies focusing on the connection of ELA with cognitive impairment and AD. These discoveries suggest that ELA, especially at early postnatal stages, increases susceptibility to cognitive impairment and AD later in life. In terms of mechanisms, ELA could lead to dysregulation of the hypothalamus-pituitary-adrenal axis, altered gut microbiome, persistent inflammation, oligodendrocyte dysfunction, hypomyelination, and aberrant adult hippocampal neurogenesis. Crosstalks among these events may synergistically contribute to cognitive impairment later in life. Additionally, we discuss several interventions that may alleviate adverse consequences of ELA. Further investigation into this crucial area will help improve ELA management and reduce the burden of related neurological conditions.

Resource scarcity but not maternal separation provokes unpredictable maternal care sequences in mice and both upregulate Crh-associated gene expression in the amygdala

Early life adversity (ELA) is a major risk factor for the development of pathology, including anxiety disorders. Neurodevelopmental and behavioral outcomes following ELA are multifaceted and are influenced heavily by the type of adversity experienced and sex of the individual experiencing ELA. It remains unclear what properties of ELA portend differential neurobiological risk and the basis of sex-differences for negative outcomes. Predictability of the postnatal environment has emerged as being a core feature supporting development, with the most salient signals deriving from parental care. Predictability of parental care may be a distinguishing feature of different forms of ELA, and the degree of predictability afforded by these manipulations may contribute to the diversity of outcomes observed across models. Further, questions remain as to whether differing levels of predictability may contribute to differential effects on neurodevelopment and expression of genes associated with risk for pathology. Here, we tested the hypothesis that changes in maternal behavior in mice would be contingent on the type of ELA experienced, directly comparing predictability of care in the limited bedding and nesting (LBN) and maternal separation (MS) paradigms. We then tested whether the predictability of the ELA environment altered the expression of corticotropin-releasing hormone (Crh), a sexually-dimorphic neuropeptide that regulates threat-related learning, in the amygdala of male and female mice. The LBN manipulation reliably increased the entropy of maternal care, a measure that indicates lower predictability between sequences of dam behavior. LBN and MS rearing similarly increased the frequency of nest sorties and licking of pups but had mixed effects on other aspects of dam-, pup-, and nest-related behaviors. Increased expression of Crh-related genes was observed in pups that experienced ELA, with gene expression measures showing a significant interaction with sex and type of ELA manipulation. Specifically, MS was associated with increased expression of Crh-related genes in males, but not females, and LBN primarily increased expression of these genes in females, but not males. The present study provides evidence for predictability as a distinguishing feature of models of ELA and demonstrates robust consequences of these differing experience on sex-differences in gene expression critically associated with stress responding and sex differences in risk for pathology.

Sex-dependence and comorbidities of the early-life adversity induced mental and metabolic disease risks: Where are we at?

Early-life adversity (ELA) is a major risk factor for developing later-life mental and metabolic disorders. However, if and to what extent ELA contributes to the comorbidity and sex-dependent prevalence/presentation of these disorders remains unclear. We here comprehensively review and integrate human and rodent ELA (pre- and postnatal) studies examining mental or metabolic health in both sexes and discuss the role of the placenta and maternal milk, key in transferring maternal effects to the offspring. We conclude that ELA impacts mental and metabolic health with sex-specific presentations that depend on timing of exposure, and that human and rodent studies largely converge in their findings. ELA is more often reported to impact cognitive and externalizing domains in males, internalizing behaviors in both sexes and concerning the metabolic dimension, adiposity in females and insulin sensitivity in males. Thus, ELA seems to be involved in the origin of the comorbidity and sex-specific prevalence/presentation of some of the most common disorders in our society. Therefore, ELA-induced disease states deserve specific preventive and intervention strategies.

Effects of early life adversities upon memory processes and cognition in rodent models

Exposure to stressors in early postnatal life induces long-lasting modifications in brainfunction.Thisplasticity,an essential characteristic of the brain that enables adaptation to the environment, may also induce impairments in some psychophysiological functions, including learning and memory. Early life stress (ELS) has long-term effects on thehypothalamic-pituitary-adrenal axisresponse to stressors, and has been reported to lead toneuroinflammation,altered levelsof neurotrophic factors, modifications inneurogenesis andsynaptic plasticity,with changes in neurotransmitter systems and network functioning. In this review, we focus on early postnatal stress in animal models and their effects on learning and memory.Many studies have reported ELS-induced impairments in different types of memories, including spatial memory, fear memory, recognition (both for objects and social) memory, working memory and reversal learning. Studies are not always in agreement, however, no effects, or sometimes facilitation, being reported, depending on the nature and intensity of the early intervention, as well as the age when the outcome was evaluated and the sex of the animals. When considering processes occurring after consolidation, related with memory maintenance or modification, there are a very reduced number of reports. Future studies addressing the mechanisms underlying memory changes for ELS should shed some light on the understanding of the different effects induced by stressors of different types and intensities on cognitive functions.

Impact of stress on inhibitory neuronal circuits, our tribute to Bruce McEwen

This manuscript is dedicated to the memory of Bruce S. McEwen, to commemorate the impact he had on how we understand stress and neuronal plasticity, and the profound influence he exerted on our scientific careers. The focus of this review is the impact of stressors on inhibitory circuits, particularly those of the limbic system, but we also consider other regions affected by these adverse experiences. We revise the effects of acute and chronic stress during different stages of development and lifespan, taking into account the influence of the sex of the animals. We review first the influence of stress on the physiology of inhibitory neurons and on the expression of molecules related directly to GABAergic neurotransmission, and then focus on specific interneuron subpopulations, particularly on parvalbumin and somatostatin expressing cells. Then we analyze the effects of stress on molecules and structures related to the plasticity of inhibitory neurons: the polysialylated form of the neural cell adhesion molecule and perineuronal nets. Finally, we review the potential of antidepressants or environmental manipulations to revert the effects of stress on inhibitory circuits.

Deficits in hippocampal-dependent memory across different rodent models of early life stress: systematic review and meta-analysis

Exposure to early life stress (ELS) causes abnormal hippocampal development and functional deficits in rodents and humans, but no meta-analysis has been used yet to quantify the effects of different rodent models of ELS on hippocampal-dependent memory. We searched PubMed and Web of Science for publications that assessed the effects of handling, maternal separation (MS), and limited bedding and nesting (LBN) on performance in the Morris water maze (MWM), novel object recognition (NOR), and contextual fear conditioning (CFC). Forty-five studies met inclusion criteria (n = 451-763 rodents per test) and were used to calculate standardized mean differences (Hedge's g) and to assess heterogeneity, publication bias, and the moderating effects of sex and species (rats vs. mice). We found significantly lower heterogeneity in LBN compared to handling and MS with no consistent effects of sex or species across the three paradigms. LBN and MS caused similar cognitive deficits in tasks that rely heavily on the dorsal hippocampus, such as MWM and NOR, and were significantly different compared to the improved performance seen in rodents exposed to handling. In the CFC task, which relies more on the ventral hippocampus, all three paradigms showed reduced freezing with moderate effect sizes that were not statistically different. These findings demonstrate the utility of using meta-analysis to quantify outcomes in a large number of inconsistent preclinical studies and highlight the need to further investigate the possibility that handling causes different alterations in the dorsal hippocampus but similar outcomes in the ventral hippocampus when compared to MS and LBN.

Modified limited bedding and nesting is a model of early-life stress that affects reproductive physiology and behavior in female and male Long-Evans rats

We used a modification of the limited bedding and nesting (LBN) model to evaluate the effects of early-life stress (ELS) on female and male reproductive physiology and behavior in Long-Evans rats. On postnatal day (PD) 2, dams and pups were transferred to a cage containing 100 mL of bedding (LBN condition) or to a cage containing 500 mL of bedding (control condition); bedding conditions remained until PD 10. In female rats, we measured vaginal opening, estrous cyclicity, female sexual behavior and motivation, and anxiety-like behavior. In male rats, we measured preputial separation, the development of male copulatory behavior, sexual motivation, and anxiety-like behavior. We found that relative to controls, female rats reared with LBN experienced precocious puberty and enhanced sexual motivation, but normal estrous cyclicity. Relative to controls, male rats reared with LBN experienced delayed puberty and enhanced sexual motivation, but normal development of copulatory behavior. Anxiety-like behavior was not affected by LBN in either female or male rats. In summary, the ELS of being reared with LBN affected the onset of puberty in the opposite direction in females and males, but enhanced sexual motivation in both. The current study is the first to examine the effects of ELS on sexual motivation using the LBN model. These findings further support the hypothesis that maternal care affects the development of sexual maturation and sexual motivation.

Sex-Specific Cognitive Deficits Following Space Radiation Exposure

The radiation fields in space define tangible risks to the health of astronauts, and significant work in rodent models has clearly shown a variety of exposure paradigms to compromise central nervous system (CNS) functionality. Despite our current knowledge, sex differences regarding the risks of space radiation exposure on cognitive function remain poorly understood, which is potentially problematic given that 30% of astronauts are women. While work from us and others have demonstrated pronounced cognitive decrements in male mice exposed to charged particle irradiation, here we show that female mice exhibit significant resistance to adverse neurocognitive effects of space radiation. The present findings indicate that male mice exposed to low doses (≤30 cGy) of energetic (400 MeV/n) helium ions (⁴He) show significantly higher levels of neuroinflammation and more extensive cognitive deficits than females. Twelve weeks following ⁴He ion exposure, irradiated male mice demonstrated significant deficits in object and place recognition memory accompanied by activation of microglia, marked upregulation of hippocampal Toll-like receptor 4 (TLR4), and increased expression of the pro-inflammatory marker high mobility group box 1 protein (HMGB1). Additionally, we determined that exposure to ⁴He ions caused a significant decline in the number of dendritic branch points and total dendritic length along with the hippocampus neurons in female mice. Interestingly, only male mice showed a significant decline of dendritic spine density following irradiation. These data indicate that fundamental differences in inflammatory cascades between male and female mice may drive divergent CNS radiation responses that differentially impact the structural plasticity of neurons and neurocognitive outcomes following cosmic radiation exposure.

Post-weaning infant-to-mother bonding in nutritionally independent female mice

Infant-parent attachment is highly selective and continues beyond essential care in primates, most prominently in humans, and the quality of this attachment crucially determines cognitive and emotional development of the infant. Altricial rodent species such as mice (Mus musculus) display mutual recognition and communal nursing in wild and laboratory environments, but parental bonding beyond the nursing period has not been reported. We presently demonstrated that socially and nutritionally independent mice still prefer to interact selectively with their mother dam. Furthermore, we observed gender differences in the mother-infant relationship, and showed disruption of this relationship in haploinsufficient Nbea+/- mice, a putative autism model with neuroendocrine dysregulation. To our knowledge, this is the first observation of murine infant-to-mother bonding beyond the nursing period.

Sex-dependent effects of paternal deprivation and chronic variable stress on novel object recognition in adult California mice (Peromyscus californicus)

Early-life stress exposure can confer vulnerability for development of psychiatric illnesses and impaired cognition in adulthood. It is well-known that early-life stress can dysregulate the hypothalamic-pituitary-adrenal (HPA) axis in a sex-dependent manner. Specifically, uniparental rodent models of prolonged disrupted mother-offspring relationships (e.g., maternal separation) have demonstrated greater alterations in stress responsivity in adult males, compared to females. Also, chronic early-life stressors (e.g., limited bedding model) impair cognitive function in males more than females. However, the sex-dependent effects of early-life stress and later-life chronic HPA axis activation on cognition have not been well-characterized. Here, we utilized the biparental California mouse (Peromyscus californicus) to model the early-life adversity of paternal deprivation (PD). Fathers either remained in the nest (biparental care) or were permanently removed (PD) on postnatal day (PND) 1. Adult offspring were exposed to daily handling (control) or chronic variable stress (CVS; three stressors for seven days). Twenty-four hours after the final stressor, the novel object recognition (NOR) task commenced, followed by serum collection for corticosterone (CORT) analysis. Independent of sex or rearing, CVS increased CORT. Exploration during acquisition for the NOR task was increased as a result of CVS and PD. During NOR testing, non-stressed females exhibited greater difference scores (i.e., increased recognition memory), compared to non-stressed males. However, the addition of CVS diminished difference scores in females - an effect not observed in CVS-exposed males. Overall, these data suggest that neonatal paternal experience, sex, and chronic stress contribute to exploratory behavior, cognition, and stress hormone concentrations in a biparental species.