Maternal Separation Modifies the Activity of Social Processing Brain Nuclei Upon Social Novelty Exposure

Disrupted maternal behavior in morphine-dependent pregnant rats and anhedonia in their offspring

It is currently estimated that every 15 minutes an infant is born with opioid use disorder and undergoes intense early life trauma due to opioid withdrawal. Clinical research on the long-term consequences of gestational opioid exposure reports increased rates of social, conduct, and emotional disorders in these children. Here, we investigate the impact of perinatal opioid exposure (POE) on behaviors associated with anhedonia and stress in male and female Sprague Dawley rats. Young adult female rats were administered morphine via programmable, subcutaneous micro-infusion pumps before, during, and through one week post gestation. For the first two postnatal weeks, maternal behavior was examined for fragmentation and unpredictability. Unpredictable behavioral patterns were quantitatively characterized as entropy scores. Offspring were assessed for sucrose preference, social behavior, and stress responsivity. Overall, dams that received morphine across gestation displayed significantly less pup-directed behavior with increased fragmentation for nursing and higher entropy scores. In adolescence, male and female rat offspring exposed to morphine displayed reduced sucrose preference and, as adults, spent significantly less time interacting with familiar conspecifics. Changes in social behaviors were linked to increased activity in nondopaminergic cells of mesolimbic reward brain regions. Although no treatment effects were observed in forced swim test performance, corticosterone levels were significantly increased in POE adult males. Together, these results suggest that perinatal morphine exposure promotes anhedonic behavior, possibly due to fragmented and unpredictable maternal behavior in opioid-dependent dams.

Cerebrolysin Induces Dendritic Tree Plastic Changes and BDNF Increase in the Amygdala of Male Rats with Maternal Deprivation

Several psychopathologies may be triggered, among other factors, by stress or trauma in childhood. The maternal deprivation model (MD) replicates some of the core factors that may induce the onset of different psychopathologies like structural and plasticity defects. Among other brain regions, the amygdala is susceptible to stress and trauma and plays a key role in integrating social behavior. Several molecules, such as Cerebrolysin® (CBL), have been used to treat different symptoms by reversing the underlying neurobiological plasticity-related changes. In this study, maternal deprivation (MD) was conducted on 9-day-old male Sprague-Dawley rats (n = 28; 7 rats per group: Intact, Intact + CBL, MD, and MD + CBL). At 25 postnatal days (PND), CBL treatment was administered for 10 consecutive days, and social behavior was evaluated in a three-chamber social test at 35 PND. Moreover, Sholl analysis and immunohistochemistry were carried out for dendritic intersection and brain-derived neurotrophic factor (BDNF) presence in the amygdala, respectively. CBL treatment had an augmentative effect on intact animals in terms of social behavior and incidences, but no differences between MD and CBL-treated animals. Moreover, dendritic intersections and BDNF decreased after the MD protocol but increased by CBL treatment in MD animals. Our results show that CBL could be part of the treatment in case of a traumatic or stressful event in neurodevelopment, especially in the youth age. According to this preclinical study, CBL could help reverse symptoms of different psychopathologies caused by stress or trauma, with neurobiological changes underlying its effect.

Animal Model of Autism Induced by Valproic Acid Combined with Maternal Deprivation: Sex-Specific Effects on Inflammation and Oxidative Stress

Autism spectrum disorder (ASD) etiology probably involves a complex interplay of both genetic and environmental risk factors, which includes pre- and perinatal exposure to environmental stressors. Thus, this study evaluated the effects of prenatal exposure to valproic acid (VPA) combined with maternal deprivation (MD) on behavior, oxidative stress parameters, and inflammatory state at a central and systemic level in male and female rats. Pregnant Wistar rats were exposed to VPA during gestation, and the offspring were submitted to MD. Offspring were tested for locomotor and social behavior; rats were euthanized, where the cerebellum, posterior cortex, prefrontal cortex, and peripheric blood were collected for oxidative stress and inflammatory analysis. It was observed that young rats (25-30 days old) exposed only to VPA presented a lower social approach when compared to the control group. VPA + MD rats did not present the same deficit. Female rats exposed to VPA + MD presented oxidative stress in all brain areas analyzed. Male rats in the VPA and VPA + MD groups presented oxidative stress only in the cerebellum. Regarding inflammatory parameters, male rats exposed only to MD exhibited an increase in pro-inflammatory cytokines in the blood and in the cortex total. The same was observed in females exposed only to VPA. Animals exposed to VPA + MD showed no alterations in the cytokines analyzed. In summary, gestational (VPA) and perinatal (MD) insults can affect molecular mechanisms such as oxidative stress and inflammation differently depending on the sex and brain area analyzed. Combined exposition to VPA and MD triggers oxidative stress especially in female brains without evoking an inflammatory response.

Maternal exposure to buprenorphine, but not methadone, during pregnancy reduces social play behavior across two generations of offspring

RATIONALE

The prevalence of newborns exposed to medications for opioid use disorder (MOUD), such as methadone or buprenorphine, during pregnancy is increasing. The opioid system plays a crucial role in regulating and shaping social behavior, and children prenatally exposed to opioids face an increased risk of developing behavioral problems. However, the impact of prenatal exposure to MOUD on offspring's social behavior during adolescence and adulthood, as well as potential intergenerational effects, remains largely unexplored.

OBJECTIVES

Our study employed a translationally relevant animal model to investigate how maternal (F0) exposure to MOUD during pregnancy affects social behavior in young and adult rats across the first (F1) and second (F2) generation of offspring.

METHODS

Female Sprague-Dawley rats were implanted with an osmotic minipump delivering methadone (10 mg/kg/day), buprenorphine (1 mg/kg/day), or sterile water, prior to mating with drug-naïve males. Adult F1 females were mated with treatment-matched F1 males to generate F2 offspring. We assessed social play behavior in juvenile offspring, and social interaction behavior in a three-chamber social interaction test in young adults of the F1 and F2 generations.

RESULTS

Maternal exposure to buprenorphine, but not methadone, during pregnancy reduced social play behavior in both F1 and F2 offspring, expressed by a reduced number of pounces and pins, which are the two most characteristic parameters of social play in rats. Adult social interactions were unaffected by prenatal MOUD exposure across both generations.

CONCLUSIONS

Maternal exposure to buprenorphine during pregnancy may have adverse effects on social play behavior across two generations of offspring.

Sex-specific changes in voluntary alcohol consumption and nucleus accumbens synaptic plasticity in C57BL/6J mice exposed to neonatal maternal separation

The long-term influence of early-life stress on brain neurophysiology has been extensively investigated using different animal models. Among these, repeated maternal separation (RMS) in rodents is one of the most commonly adopted. In this study, we elucidated the long-lasting effects of exposure to postnatal RMS in C57BL/6J adult mice on voluntary alcohol consumption and nucleus accumbens (NAc) neurophysiology. Mice were separated from their dam for 360 min daily from postnatal day 2 (PND2) to PND17, and experiments were then performed in adult (PND60) animals. In addition, as recent evidence showed that circulating estrogens may play a protective role against stress effects on brain function, including the organization and activation of neuronal structures, we also evaluated the effect of a single injection of β-estradiol 3-benzoate (EB) at PND2, which is known to disrupt male sex differentiation, in male RMS mice. The RMS exposure was associated with an increased voluntary alcohol consumption and preference in male mice, but not in female mice or male mice treated with a single injection of EB. Patch clamp experiments conducted in NAc medium spiny neurons (MSNs) revealed that excitatory but not inhibitory synaptic transmission and long-term plasticity of glutamatergic synapses were significantly impaired in male but not in female mice exposed to the RMS protocol. This effect was again prevented in RMS male mice treated with EB. Our findings strengthen the idea of a sex-dependent influence of early-life stress on long-lasting modifications in synaptic transmission and plasticity in brain areas involved in goal-directed behavior and alcohol intake.

Disrupted Maternal Behavior in Morphine-Dependent Pregnant Rats and Anhedonia in their Offspring

It is currently estimated that every 15 minutes an infant is born with opioid use disorder and undergoes intense early life trauma due to opioid withdrawal. Clinical research on the long-term consequences of gestational opioid exposure reports increased rates of social, conduct, and emotional disorders in these children. Here, we investigate the impact of perinatal opioid exposure (POE) on behaviors associated with anhedonia and stress in male and female Sprague Dawley rats. Young adult female rats were administered morphine via programmable, subcutaneous micro-infusion pumps before, during, and through one week post gestation. Maternal behavior was examined for fragmentation and entropy for the first two postnatal weeks; offspring were assessed for sucrose preference, social behavior, and stress responsivity. Overall, dams that received morphine across gestation displayed significantly less pup-directed behavior with increased fragmentation for nursing and higher entropy scores. In adolescence, male and female rat offspring exposed to morphine displayed reduced sucrose preference and, as adults, spent significantly less time socially interacting with familiar conspecifics. Changes in social behaviors were linked to increased activity in nondopaminergic mesolimbic reward brain regions. Although no treatment effects were observed in forced swim test performance, corticosterone levels were significantly increased in POE adult males. Together, these results suggest that perinatal morphine exposure results in anhedonic behavior, possibly due to fragmented and unpredictable maternal behavior in opioid-dependent dams.

Activity-Dependent Synaptic Plasticity in the Medial Prefrontal Cortex of Male Rats Underlies Resilience-Related Behaviors to Social Adversity

Individuals considered resilient can overcome adversity, achieving normal physical and psychological development, while those deemed vulnerable may not. Adversity promotes structural and functional alterations in the medial prefrontal cortex (mPFC) and hippocampus. Moreover, activity-dependent synaptic plasticity is intricately linked to neuronal shaping resulting from experiences. We hypothesize that this plasticity plays a crucial role in resilience processes. However, there is a notable absence of studies investigating this plasticity and behavioral changes following social adversity at different life stages. Consequently, we evaluated the impact of social adversity during early postnatal development (maternal separation [MS]), adulthood (social defeat [SD]), and a combined exposure (MS + SD) on behavioral outcomes (anxiety, motivation, anhedonia, and social interaction). We also examined cFos expression induced by social interaction in mPFC and hippocampus of adult male rats. Behavioral analyses revealed that SD-induced anhedonia, whereas MS + SD increased social interaction and mitigated SD-induced anhedonia. cFos evaluation showed that social interaction heightened plasticity in the prelimbic (PrL) and infralimbic (IL) cortices, dentate gyrus (DG), CA3, and CA1. Social interaction-associated plasticity was compromised in IL and PrL cortices of the MS and SD groups. Interestingly, social interaction-induced plasticity was restored in the MS + SD group. Furthermore, plasticity was impaired in DG by all social stressors, and in CA3 was impaired by SD. Our findings suggest in male rats (i) two adverse social experiences during development foster resilience; (ii) activity-dependent plasticity in the mPFC is a foundation for resilience to social adversity; (iii) plasticity in DG is highly susceptible to social adversity.

Effect of a multi-strain probiotic mixture consumption on anxiety and depression symptoms induced in adult mice by postnatal maternal separation

BACKGROUND

Intestinal microbial composition not only affects the health of the gut but also influences centrally mediated systems involved in mood, through the "gut-brain" axis, a bidirectional communication between gut microbiota and the brain. In this context, the modulation of intestinal microbiota and its metabolites through the administration of probiotics seems to represent a very promising approach in the treatment of the central nervous system alterations. Early postnatal life is a critical period during which the brain undergoes profound and essential modulations in terms of maturation and plasticity. Maternal separation (MS), i.e., the disruption of the mother-pup interaction, represents a pivotal paradigm in the study of stress-related mood disorders, by inducing persistent changes in the immune system, inflammatory processes, and emotional behavior in adult mammals.

RESULTS

We conducted experiments to investigate whether sustained consumption of a multi-strain probiotic formulation by adult male mice could mitigate the effects of maternal separation. Our data demonstrated that the treatment with probiotics was able to totally reverse the anxiety- and depressive-like behavior; normalize the neuro-inflammatory state, by restoring the resting state of microglia; and finally induce a proneurogenic effect. Mice subjected to maternal separation showed changes in microbiota composition compared to the control group that resulted in permissive colonization by the administered multi-strain probiotic product. As a consequence, the probiotic treatment also significantly affected the production of SCFA and in particular the level of butyrate.

CONCLUSION

Gut microbiota and its metabolites mediate the therapeutic action of the probiotic mix on MS-induced brain dysfunctions. Our findings extend the knowledge on the use of probiotics as a therapeutic tool in the presence of alterations of the emotional sphere that significantly impact on gut microbiota composition. Video Abstract.

Maternal Substance Use and Early-Life Adversity: Inducing Drug Dependence in Offspring, Interactions, Mechanisms, and Treatments

The likelihood of substance dependency in offspring is increased in cases when there is a family history of drug or alcohol use. Mothering is limited by maternal addiction because of the separation. Maternal separation (MS) leads to the development of behavioural and neuropsychiatric issues in the future. Despite the importance of this issue, empirical investigations of the influences of maternal substance use and separation on substance use problems in offspring are limited, and studies that consider both effects are rare. This study aims to review a few studies on the mechanisms, treatments, genetics, epigenetics, molecular and psychological alterations, and neuroanatomical regions involved in the dependence of offspring who underwent maternal addiction and separation. The PubMed database was used. A total of 95 articles were found, including the most related ones in the review. The brain's lateral paragigantocellularis (LPGi), nucleus accumbens (NAc), caudate-putamen (CPu), prefrontal cortex (PFC), and hippocampus, can be affected by MS. Dopamine receptor subtype genes, alcohol biomarker minor allele, and preproenkephalin mRNA may be affected by alcohol or substance use disorders. After early-life adversity, histone acetylation in the hippocampus may be linked to brain-derived neurotrophic factor (BDNF) gene epigenetics and glucocorticoid receptors (GRs). The adverse early-life experiences differ in offspring›s genders and rewire the brain›s dopamine and endocannabinoid circuits, making offspring more susceptible to dependence. Related psychological factors rooted in early-life stress (ELS) and parental substance use disorder (SUD). Treatments include antidepressants, histone deacetylase inhibitors, lamotrigine, ketamine, choline, modafinil, methadone, dopamine, cannabinoid 1 receptor agonists/antagonists, vitamins, oxytocin, tetrahydrocannabinol, SR141716A, and dronabinol. Finally, the study emphasizes the need for multifaceted strategies to prevent these outcomes.

Chronic Stress in Early Development and Effects on Traumatic Brain Injury Outcome

In recent years, significant advances have been made in the study of mild traumatic brain injury (mTBI). Complete recovery from mTBI normally requires days to weeks, yet a subset of the population suffers from symptoms for weeks to months after injury. The risk factors for these prolonged symptoms have not yet been fully understood. In this chapter, we address one proposed risk factor, early life stress (ELS) and its influence on mTBI recovery. To study the effects of ELS on mTBI recovery, accepted animal models of ELS, including maternal separation, limited bedding and nesting, and chronic unpredictable stress, have been implemented. Combining these ELS models with standardized mTBI models, such as fluid percussion injury or controlled cortical impact, has allowed for a deeper understanding of the neuronal, hormonal, and cognitive changes that occur after mTBI following ELS. These preclinical findings are being used to understand how adverse childhood experiences may predispose a subset of individuals to poorer recovery after mTBI.

The impact of early life stress and schizophrenia on motor and cognitive functioning: an experimental study

Background

Early life stress (ELS) and parental psychopathology, such as schizophrenia (SZ), have been associated with altered neurobiological and behavioral outcomes later in life. Previous studies have investigated the effects of ELS and parental SZ on various aspects of behavior, however, we have studied the combined effects of these stressors and how they interact, as individuals in real-life situations may experience multiple stressors simultaneously.

Objective

The aim of this study was to investigate the impact of ELS and schizophrenia on locomotor activity, anxiety-like behavior, exploratory tendencies, and spatial memory in Sprague Dawley (SD) rats.

Methods

Male and female SD pups were randomly assigned to eight groups: control, ELS, schizophrenia, and ELS + schizophrenia. ELS was induced by prenatal stress (maternal stress) and maternal separation (MS) during the first 2 weeks of life, while SZ was induced by subcutaneous administration of ketamine. Behavioral tests included an open field test (OFT) for motor abilities and a Morris water maze (MWM) for cognitive abilities. ANOVA and post hoc Tukey tests were utilized to analyze the data.

Results

Our results show that ELS and parental psychopathology had enduring effects on SZ symptoms, particularly psychomotor retardation (p < 0.05). The OFT revealed increased anxiety-like behavior in the ELS group (p = 0.023) and the parental psychopathology group (p = 0.017) compared to controls. The combined ELS and parental psychopathology group exhibited the highest anxiety-like behavior (p = 0.006). The MWM analysis indicated impaired spatial memory in the ELS group (p = 0.012) and the combined ELS and parental psychopathology group (p = 0.003) compared to controls. Significantly, the exposure to ELS resulted in a decrease in the population of glial fibrillary acidic protein-positive (GFAP+) astrocytes. However, this effect was reversed by positive parental mental health.

Conclusion

Our findings highlight the interactive effects of ELS and parental psychopathology on anxiety-like behavior and spatial memory in rats. ELS was linked to increased anxiety-like behavior, while SZ was associated with anhedonia-like behavior. Positive parenting augments neuroplasticity, synaptic function, and overall cognitive capacities.

Communal nesting differentially attenuates the impact of pre-weaning social isolation on behavior in male and female rats during adolescence and adulthood

Introduction

Early social isolation (ESI) disrupts neurodevelopmental processes, potentially leading to long-lasting emotional and cognitive changes in adulthood. Communal nesting (CN), i.e., the sharing of parental responsibilities between multiple individuals in a nest, creates a socially enriching environment known to impact social and anxiety-related behaviors.

Methods

This study examines the effects of (i) the CN condition and of (ii) ESI during the 3rd week of life (i.e., pre-weaning ESI) on motor, cognitive, and emotional domains during adolescence and adulthood in male and female rats reared in the two different housing conditions, as well as (iii) the potential of CN to mitigate the impact of ESI on offspring.

Results

We found that in a spontaneous locomotor activity test, females exhibited higher activity levels compared to males. In female groups, adolescents reared in standard housing (SH) condition spent less time in the center of the arena, suggestive of increased anxiety levels, while the CN condition increased the time spent in the center during adolescence, but not adulthood, independently from ESI. The prepulse inhibition (PPI) test showed a reduced PPI in ESI adolescent animals of both sexes and in adult males (but not in adult females), with CN restoring PPI in males, but not in adolescent females. Further, in the marble burying test SH-ESI adolescent males exhibited higher marble burying behavior than all other groups, suggestive of obsessive-compulsive traits. CN completely reversed this stress-induced effect. Interestingly, ESI and CN did not have a significant impact on burying behavior in adult animals of both sexes.

Discussion

Overall, our findings (i) assess the effects of ESI on locomotion, sensorimotor gating, and compulsive-like behaviors, (ii) reveal distinct vulnerabilities of males and females within these domains, and (iii) show how early-life social enrichment may successfully counteract some of the behavioral alterations induced by early-life social stress in a sex-dependent manner. This study strengthens the notion that social experiences during early-life can shape emotional and cognitive outcomes in adulthood, and points to the importance of social enrichment interventions for mitigating the negative effects of early social stress on neurodevelopment.

Whole-brain mapping of neuronal activity evoked by maternal separation in neonatal mice: An association with ultrasound vocalization

Neonatal mice emit ultrasonic vocalizations (USVs) when separated from their mothers. Since the USVs attract their mothers' attention and trigger maternal retrieval, they are considered to serve as social signals for communication. We have modeled paternal aging effects on the vocal communication of offspring in mice. However, little is known about the neural basis underlying neonatal USV production. To identify responsible brain regions driving the vocal behavior, we comprehensively mapped the neuronal activity associated with USV production in the entire brain of mice at postnatal day 6 (P6). Using an expression of immediate-early gene c-Fos as a neuronal activity marker, correlations between the numbers of USVs and c-Fos positive neurons were analyzed. We identified 23 candidate brain regions associated with USV production in the mice at P6. Our study would be a first step toward comprehensively understanding the neuronal mechanisms that regulate and develop vocal behaviors in neonatal mice.

Sex-dependent changes of hippocampal synaptic plasticity and cognitive performance in C57BL/6J mice exposed to neonatal repeated maternal separation

The repeated maternal separation (RMS) is a useful experimental model useful in rodents to study the long-term influence of early-life stress on brain neurophysiology. We here investigated the influence of RMS exposure on hippocampal inhibitory and excitatory synaptic transmission, long-term synaptic plasticity and the related potential alterations in learning and memory performance in adult male and female C57Bl/6J mice. Mice were separated daily from their dam for 360 min, from postnatal day 2 (PND2) to PND17, and experiments were performed at PND 60. Patch-clamp recordings in hippocampal CA1 pyramidal neurons revealed a significant enhancement of GABAergic miniature IPSC (mIPSC) frequency, and a decrease in the amplitude of glutamatergic mEPSCs in male mice exposed to RMS. Only a slight but significant reduction in the amplitude of GABAergic mIPSCs was observed in females exposed to RMS compared to the relative controls. A marked increase in long-term depression (LTD) at CA3-CA1 glutamatergic synapses and in the response to the CB1r agonist win55,212 were detected in RMS male, but not female mice. An impaired spatial memory and a reduced preference for novelty was observed in males exposed to RMS but not in females. A single injection of β-ethynyl estradiol at PND2, prevented the changes observed in RMS male mice, suggesting that estrogens may play a protective role early in life against the exposure to stressful conditions. Our findings strengthen the idea of a sex-dependent influence of RMS on long-lasting modifications in synaptic transmission, effects that may be relevant for cognitive performance.

Early Life Adversity and Neuropsychiatric Disease: Differential Outcomes and Translational Relevance of Rodent Models

It is now well-established that early life adversity (ELA) predisposes individuals to develop several neuropsychiatric conditions, including anxiety disorders, and major depressive disorder. However, ELA is a very broad term, encompassing multiple types of negative childhood experiences, including physical, sexual and emotional abuse, physical and emotional neglect, as well as trauma associated with chronic illness, family separation, natural disasters, accidents, and witnessing a violent crime. Emerging literature suggests that in humans, different types of adverse experiences are more or less likely to produce susceptibilities to certain conditions that involve affective dysfunction. To investigate the driving mechanisms underlying the connection between experience and subsequent disease, neuroscientists have developed several rodent models of ELA, including pain exposure, maternal deprivation, and limited resources. These studies have also shown that different types of ELA paradigms produce different but somewhat overlapping behavioral phenotypes. In this review, we first investigate the types of ELA that may be driving different neuropsychiatric outcomes and brain changes in humans. We next evaluate whether rodent models of ELA can provide translationally relevant information regarding links between specific types of experience and changes in neural circuits underlying dysfunction.

The influence of early-life and adulthood stressors on brain neuropeptide-S system

Central administered neuropeptide-S (NPS) was shown to reduce stress response in rodents. This study aimed to investigate the alterations in NPS system upon chronic exposure to early-life and adulthood stressors. Newborn pups underwent maternal separation (MS) from postnatal day 1 to 14 comprised of daily 3-h separations. In the adulthood, 90-min of restraint stress was loaded to males as an acute stress (AS) model. For chronic homotypic stress (CHS), same stressor was applied for 5 consecutive days. The changes in the expression and the release of NPS were monitored by immunohistochemistry and microdialysis, respectively. Throughout the CHS, heart rate variability (HRV) was analyzed on a daily basis. The immunoreactivity for NPS receptor (NPSR) was detected in basolateral amygdala (BLA) and hypothalamic paraventricular nucleus (PVN) by immunofluorescence staining. The NPS expression in the brainstem was increased upon AS which was more prominent following CHS, whereas these responses were found to be blunted in MS counterparts. Similar to histological data, the stress-induced release of NPS in BLA was attenuated in MS rats. CHS-induced elevations in sympatho-vagal balance were alleviated in control rats; which was not observed in MS rats. The expression of NPSR in BLA and PVN was down-regulated in MS rats. The brain NPS/NPSR system appears to be susceptible to the early-life stressors and the subsequent chronic stress exposure in adulthood which results in altered autonomic outflow.