Mesolimbic dopaminergic activity responding to acute stress is blunted in adolescent rats that experienced neonatal maternal separation

Impacts of maternal separation stress on ethanol-related responses, anxiety- and depressive-like behaviors in adolescent mice

The present work evaluated the consequences of chronic maternal separation (MS), an animal model of early-life stress, on ethanol intake and striatal Fos expression induced by ethanol consumption. Furthermore, we analyzed MS impacts on anxiety- and depressive-like behaviors and on locomotor and plasma corticosterone responses to intraperitoneal treatment with ethanol in adolescent mice. For that, male and female C57BL/6J mice were exposed or not to MS stress, for 3 h per day, from postnatal day (PND) 1 to 14, and submitted to behavioral tests from PND 28. In Experiment 1, MS and control groups of mice were submitted to an involuntary ethanol intake protocol, and striatal Fos expression following ethanol exposure was analyzed. In Experiment 2, mice behavior was assessed in elevated plus-maze, sucrose splash, saccharin preference, and open field tests. Locomotor and plasma corticosterone responses induced by a systemic dose of ethanol (1.75 g/kg) were also evaluated. Our results demonstrated that MS increased ethanol intake only in an acute manner and did not impact ethanol-induced Fos expression in the dorsal striatum and nucleus accumbens (NAc) core and shell subregions. MS did not change the parameters analyzed during elevated plus-maze, sucrose splash, preference for saccharin, and open field tests. MS did not affect locomotor activity following ethanol injection nor plasma corticosterone response to the drug. Thus, our data showed that MS transiently increased ethanol intake. However, early-life stress did not impact Fos, locomotor, or plasma corticosterone responses to the drug. In addition, MS did not affect anxiety- and depressive-like behaviors in adolescent mice.

Lasting impact of postnatal maternal separation on the developing BNST: Lifelong socioemotional consequences

Nearly one percent of children in the US experience childhood neglect or abuse, which can incite lifelong emotional and behavioral disorders. Many studies investigating the neural underpinnings of maleffects inflicted by early life stress have largely focused on dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis. Newer veins of evidence suggest that exposure to early life stressors can interrupt neural development in extrahypothalamic areas as well, including the bed nucleus of the stria terminalis (BNST). One widely used approach in this area is rodent maternal separation (MS), which typically consists of separating pups from the dam for extended periods of time, over several days during the first weeks of postnatal life - a time when pups are highly dependent on maternal care for survival. MS has been shown to incite myriad lasting effects not limited to increased anxiety-like behavior, hyper-responsiveness to stressors, and social behavior deficits. The behavioral effects of MS are widespread and thus unlikely to be limited to hypothalamic mechanisms. Recent work has highlighted the BNST as a critical arbiter of some of the consequences of MS, especially socioemotional behavioral deficits. The BNST is a well-documented modulator of anxiety, reward, and social behavior by way of its connections with hypothalamic and extra-hypothalamic systems. Moreover, during the postnatal period when MS is typically administered, the BNST undergoes critical neural developmental events. This review highlights evidence that MS interferes with neural development to permanently alter BNST circuitry, which may account for a variety of behavioral deficits seen following early life stress. This article is part of the Special Issue on 'Fear, Anxiety and PTSD'.

Effects of prenatal opioid exposure on synaptic adaptations and behaviors across development

In this review, we focus on prenatal opioid exposure (POE) given the significant concern for the mental health outcomes of children with parents affected by opioid use disorder (OUD) in the view of the current opioid crisis. We highlight some of the less explored interactions between developmental age and sex on synaptic plasticity and associated behavioral outcomes in preclinical POE research. We begin with an overview of the rich literature on hippocampal related behaviors and plasticity across POE exposure paradigms. We then discuss recent work on reward circuit dysregulation following POE. Additional risk factors such as early life stress (ELS) could further influence synaptic and behavioral outcomes of POE. Therefore, we include an overview on the use of preclinical ELS models where ELS exposure during key critical developmental periods confers considerable vulnerability to addiction and stress psychopathology. Here, we hope to highlight the similarity between POE and ELS on development and maintenance of opioid-induced plasticity and altered opioid-related behaviors where similar enduring plasticity in reward circuits may occur. We conclude the review with some of the limitations that should be considered in future investigations. This article is part of the Special Issue on 'Opioid-induced addiction'.

Sex differences in addiction-relevant behavioral outcomes in rodents following early life stress

In humans, exposure to early life stress (ELS) is an established risk factor for the development of substance use disorders (SUDs) during later life. Similarly, rodents exposed to ELS involving disrupted mother-infant interactions, such as maternal separation (MS) or adverse caregiving due to scarcity-adversity induced by limited bedding and nesting (LBN) conditions, also exhibit long-term alterations in alcohol and drug consumption. In both humans and rodents, there is a range of addiction-related behaviors that are associated with drug use and even predictive of subsequent SUDs. In rodents, these include increased anxiety-like behavior, impulsivity, and novelty-seeking, altered alcohol and drug intake patterns, as well as disrupted reward-related processes involving consummatory and social behaviors. Importantly, the expression of these behaviors often varies throughout the lifespan. Moreover, preclinical studies suggest that sex differences play a role in how exposure to ELS impacts reward and addiction-related phenotypes as well as underlying brain reward circuitry. Here, addiction-relevant behavioral outcomes and mesolimbic dopamine (DA) dysfunction resulting from ELS in the form of MS and LBN are discussed with a focus on age- and sex-dependent effects. Overall, these findings suggest that ELS may increase susceptibility for later life drug use and SUDs by interfering with the normal maturation of reward-related brain and behavioral function.

Dissecting early life stress-induced adolescent depression through epigenomic approach

Early life stress (ELS), such as abuse and neglect during childhood, can lead to psychiatric disorders in later life. Previous studies have suggested that ELS can cause profound changes in gene expression through epigenetic mechanisms, which can lead to psychiatric disorders in adulthood; however, studies on epigenetic modifications associated with ELS and psychiatric disorders in adolescents are limited. Moreover, how these epigenetic modifications can lead to psychiatric disorders in adolescents is not fully understood. Commonly, DNA methylation, histone modification, and the regulation of noncoding RNAs have been attributed to the reprogramming of epigenetic profiling associated with ELS. Although only a few studies have attempted to examine epigenetic modifications in adolescents with ELS, existing evidence suggests that there are commonalities and differences in epigenetic profiling between adolescents and adults. In addition, epigenetic modifications are sex-dependent and are influenced by the type of ELS. In this review, we have critically evaluated the current evidence on epigenetic modifications in adolescents with ELS, particularly DNA methylation and the expression of microRNAs in both preclinical models and humans. We have also clarified the impact of ELS on psychiatric disorders in adolescents to predict the development of neuropsychiatric disorders and to prevent and recover these disorders through personalized medicine.

Early life stress induces visual dysfunction and retinal structural alterations in adult mice

Early life stress (ELS) is defined as a period of severe and/or chronic trauma, as well as environmental/social deprivation or neglect in the prenatal/early postnatal stage. Presently, the impact of ELS on the retina in the adult stage is unknown. The long-term consequences of ELS at retinal level were analyzed in an animal model of maternal separation with early weaning (MSEW), which mimics early life maternal neglect. For this purpose, mice were separated from the dams for 2 h at postnatal days (PNDs) 4-6, for 3 h at PNDs 7-9, for 4 h at PNDs 10-12, for 6 h at PNDs 13-16, and weaned at PND17. At the end of each separation period, mothers were subjected to movement restriction for 10 min. Control pups were left undisturbed from PND0, and weaned at PND21. Electroretinograms, visual evoked potentials, vision-guided behavioral tests, retinal anterograde transport, and retinal histopathology were examined at PNDs 60-80. MSEW induced long-lasting functional and histological effects at retinal level, including decreased retinal ganglion cell function and alterations in vision-guided behaviors, likely associated to decreased synaptophysin content, retina-superior colliculus communication deficit, increased microglial phagocytic activity, and retinal ganglion cell loss through a corticoid-dependent mechanism. A treatment with mifepristone, injected every 3 days between PNDs 4 and16, prevented functional and structural alterations induced by MSEW. These results suggest that retinal alterations might be included among the childhood adversity-induced threats to life quality, and that an early intervention with mifepristone avoided ELS-induced retinal disturbances.

Epigenetic Mechanism of Early Life Stress-Induced Depression: Focus on the Neurotransmitter Systems

Depression has an alarmingly high prevalence worldwide. A growing body of evidence indicates that environmental factors significantly affect the neural development and function of the central nervous system and then induce psychiatric disorders. Early life stress (ELS) affects brain development and has been identified as a major cause of depression. It could promote susceptibility to stress in adulthood. Recent studies have found that ELS induces epigenetic changes that subsequently affect transcriptional rates of differentially expressed genes. The epigenetic modifications involved in ELS include histone modifications, DNA methylation, and non-coding RNA. Understanding of these genetic modifications may identify mechanisms that may lead to new interventions for the treatment of depression. Many reports indicate that different types of ELS induce epigenetic modifications of genes involved in the neurotransmitter systems, such as the dopaminergic system, the serotonergic system, the gamma-aminobutyric acid (GABA)-ergic system, and the glutamatergic system, which further regulate gene expression and ultimately induce depression-like behaviors. In this article, we review the effects of epigenetic modifications on the neurotransmitter systems in depression-like outcomes produced by different types of ELS in recent years, aiming to provide new therapeutic targets for patients who suffer from depression.

Potentiation of glutamatergic synaptic transmission onto lateral habenula neurons following early life stress and intravenous morphine self-administration in rats

Early life stress presents an important risk factor for drug addiction and comorbid depression and anxiety through persistent effects on the mesolimbic dopamine pathways. Using an early life stress model for child neglect (a single 24 h episode of maternal deprivation, MD) in rats, recent published works from our lab show that MD induces dysfunction in the ventral tegmental area and its negative controller, the lateral habenula (LHb). MD-induced potentiation of glutamatergic synaptic transmission onto LHb neurons shifts the coordination of excitation/inhibition (E/I) balance towards excitation, resulting in an increase in the overall spontaneous neuronal activity with elevation in bursting and tonic firing, and in the intrinsic excitability of LHb neurons in early adolescent male rats. Here, we explored how MD affects intravenous morphine self-administration (MSA) acquisition and sucrose preference as well as glutamatergic synaptic function in LHb neurons of adult male rats self-administering morphine. We found that MD-induced increases in LHb neuronal and glutamatergic synaptic activity and E/I ratio persisted into adulthood. Moreover, MD significantly reduced morphine intake, triggered anhedonia-like behaviour in the sucrose preference test and was associated with persistent glutamatergic potentiation 24 h after the last MSA session. MSA also altered the decay time kinetics of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor (AMPAR) currents in LHb neurons of control rats during this time period. Our data highlight that early life stress-induced glutamatergic plasticity in LHb may dampen the positive reinforcing and motivational properties of both natural rewards and opioids, and may contribute to the development of anhedonia and dysphoric states associated with opioids.

Maternal Separation Stress Affects Voluntary Ethanol Intake in a Sex Dependent Manner

Maternal separation (MS) stress is a predictive animal model for evaluating the effects of early stress exposure on alcohol use disorders (AUD). The extended amygdala (AMY) is a complex circuit involved in both stress- and ethanol-related responses. We hypothesized that MS stress may increase ethanol consumption in adulthood, as well as augment neuronal activity in extended AMY, in a sex-dependent manner. We aimed to investigate the influence of MS stress on the ethanol consumption of male and female mice, and the involvement of extended amygdala sub-nuclei in this process. The C57BL/6J pups were subjected to 180min of MS, from postnatal day (PND) 1 to 14. The control group was left undisturbed. On PND 45, mice (n=28) in cages were exposed to a bottle containing 20% ethanol (w/v) for 4h during the dark period of the light-dark cycle, for 3weeks. Afterward, mice underwent ethanol self-administration training in operant chambers under fixed ratio (FR) schedule. Then, subjects were tested under 2h sessions of a progressive-ratio (PR) schedule of reinforcement (the last ratio achieved was considered the breaking point), and at the end, a 4h session of FR schedule (binge-intake). An immunohistochemistry assay for Fos protein was performed in Nucleus Accumbens (NAcc), Bed Nucleus of Stria Terminalis (BNST), and AMY. Our results showed that in the third week of training, the female MS group consumed more ethanol than the respective control group. The MS group presented increased breakpoint parameters. Female control group and male MS group were more resistant to bitter quinine taste. Increased Fos-immunoreactive neurons (Fos-IR) were observed in the central nucleus of AMY, but not in NAcc nor BNST in male maternal-separated mice. Maternal separation stress may influence ethanol intake in adulthood, and it is dependent on the sex and reinforcement protocol.

Impact of Early Life Stress on Reward Circuit Function and Regulation

Early life stress - including experience of child maltreatment, neglect, separation from or loss of a parent, and other forms of adversity - increases lifetime risk of mood, anxiety, and substance use disorders. A major component of this risk may be early life stress-induced alterations in motivation and reward processing, mediated by changes in the nucleus accumbens (NAc) and ventral tegmental area (VTA). Here, we review evidence of the impact of early life stress on reward circuit structure and function from human and animal models, with a focus on the NAc. We then connect these results to emerging theoretical models about the indirect and direct impacts of early life stress on reward circuit development. Through this review and synthesis, we aim to highlight open research questions and suggest avenues of future study in service of basic science, as well as applied insights. Understanding how early life stress alters reward circuit development, function, and motivated behaviors is a critical first step toward developing the ability to predict, prevent, and treat stress-related psychopathology spanning mood, anxiety, and substance use disorders.

Sex-Specific Effects of Stress on Respiratory Control: Plasticity, Adaptation, and Dysfunction

As our understanding of respiratory control evolves, we appreciate how the basic neurobiological principles of plasticity discovered in other systems shape the development and function of the respiratory control system. While breathing is a robust homeostatic function, there is growing evidence that stress disrupts respiratory control in ways that predispose to disease. Neonatal stress (in the form of maternal separation) affects "classical" respiratory control structures such as the peripheral O₂ sensors (carotid bodies) and the medulla (e.g., nucleus of the solitary tract). Furthermore, early life stress disrupts the paraventricular nucleus of the hypothalamus (PVH), a structure that has emerged as a primary determinant of the intensity of the ventilatory response to hypoxia. Although underestimated, the PVH's influence on respiratory function is a logical extension of the hypothalamic control of metabolic demand and supply. In this article, we review the functional and anatomical links between the stress neuroendocrine axis and the medullary network regulating breathing. We then present the persistent and sex-specific effects of neonatal stress on respiratory control in adult rats. The similarities between the respiratory phenotype of stressed rats and clinical manifestations of respiratory control disorders such as sleep-disordered breathing and panic attacks are remarkable. These observations are in line with the scientific consensus that the origins of adult disease are often found among developmental and biological disruptions occurring during early life. These observations bring a different perspective on the structural hierarchy of respiratory homeostasis and point to new directions in our understanding of the etiology of respiratory control disorders. © 2021 American Physiological Society. Compr Physiol 11:1-38, 2021.

Early Life Stress and Risks for Opioid Misuse: Review of Data Supporting Neurobiological Underpinnings

A robust body of research has shown that traumatic experiences occurring during critical developmental periods of childhood when neuronal plasticity is high increase risks for a spectrum of physical and mental health problems in adulthood, including substance use disorders. However, until recently, relatively few studies had specifically examined the relationships between early life stress (ELS) and opioid use disorder (OUD). Associations with opioid use initiation, injection drug use, overdose, and poor treatment outcome have now been demonstrated. In rodents, ELS has also been shown to increase the euphoric and decrease antinociceptive effects of opioids, but little is known about these processes in humans or about the neurobiological mechanisms that may underlie these relationships. This review aims to establish a theoretical model that highlights the mechanisms by which ELS may alter opioid sensitivity, thereby contributing to future risks for OUD. Alterations induced by ELS in mesocorticolimbic brain circuits, and endogenous opioid and dopamine neurotransmitter systems are described. The limited but provocative evidence linking these alterations with opioid sensitivity and risks for OUD is presented. Overall, the findings suggest that better understanding of these mechanisms holds promise for reducing vulnerability, improving prevention strategies, and prescribing guidelines for high-risk individuals.

Long-Term Effects of Maternal Deprivation on the Volume of Dopaminergic Nuclei and Number of Dopaminergic Neurons in Substantia Nigra and Ventral Tegmental Area in Rats

Early life adversities leave long-lasting structural and functional consequences on the brain, which may persist later in life. Dopamine is a neurotransmitter that is extremely important in mood and motor control. The aim of this study was to investigate the effect of maternal deprivation during the ninth postnatal day on the volume of dopaminergic nuclei and the number of dopaminergic neurons in adolescence and adulthood. Maternally deprived and control Wistar rats were sacrificed on postnatal day 35 or 60, and the dopaminergic neurons were stained in coronal histological sections of ventral midbrain with the tyrosine hydroxylase antibody. The volume of dopaminergic nuclei and the number of dopaminergic neurons in the substantia nigra (SN) and ventral tegmental area (VTA) were analyzed in three representative coordinates. Maternal deprivation caused weight loss on postnatal day 21 (weaning) and corticosterone blood level elevation on postnatal days 35 and 60 in stressed compared to control rats. In maternally deprived animals, the volumes of SN and VTA were increased compared to the controls. This increase was accompanied by an elevation in the number of dopaminergic neurons in both nuclei. Altogether, based on somatic and corticosterone level measurements, maternal deprivation represents a substantial adversity, and the phenotype it causes in adulthood includes increased volume of the dopaminergic nuclei and number of dopaminergic neurons.

Maternal deprivation induces persistent adaptations in putative dopamine neurons in rat ventral tegmental area: in vivo electrophysiological study

Early life aversive experiences can trigger persistent deficits in neuronal signaling within the mesolimbic pathway, most notably in the dopamine (DA) neurons of the ventral tegmental area (VTA). The identity of such cellular mechanisms currently appears as an important issue. To address this concern, we investigated whether early life maternal deprivation (MD) would affect the electrical activity of VTA DA neurons, via in vivo extracellular single-unit recording. Male Wistar rats were deprived of their dams for 3 h per day from postnatal days (PND) 1-14. Thereafter, the adult animals (PND 70-80) were tested for the discharge activity of putative VTA DA neurons. The VTA DA neurons displayed a decrease in firing rate and an increase in the variability of baseline discharge activity in deprived animals. MD also caused a decrease in burst firing of VTA DA neurons compared to control subjects. In summary, early life MD induces a hypoactive VTA DA system, which may contribute to lifespan psychopathologies.

Effects of Early-Life Stress on the Brain and Behaviors: Implications of Early Maternal Separation in Rodents

Early-life stress during the prenatal and postnatal periods affects the formation of neural networks that influence brain function throughout life. Previous studies have indicated that maternal separation (MS), a typical rodent model equivalent to early-life stress and, more specifically, to child abuse and/or neglect in humans, can modulate the hypothalamic-pituitary-adrenal (HPA) axis, affecting subsequent neuronal function and emotional behavior. However, the neural basis of the long-lasting effects of early-life stress on brain function has not been clarified. In the present review, we describe the alterations in the HPA-axis activity-focusing on serum corticosterone (CORT)-and in the end products of the HPA axis as well as on the CORT receptor in rodents. We then introduce the brain regions activated during various patterns of MS, including repeated MS and single exposure to MS at various stages before weaning, via an investigation of c-Fos expression, which is a biological marker of neuronal activity. Furthermore, we discuss the alterations in behavior and gene expression in the brains of adult mice exposed to MS. Finally, we ask whether MS repeats itself and whether intergenerational transmission of child abuse and neglect is possible.

Facilitation of dopamine-dependent long-term potentiation in the medial prefrontal cortex of male rats follows the behavioral effects of stress

The effect of stress on animal behavior and brain activity has been attracting growing attention in the last decades. Stress dramatically affects several aspects of animal behavior, including motivation and cognitive functioning, and has been used to model human pathologies such as post-traumatic stress disorder. A key question is whether stress alters the plastic potential of synaptic circuits. In this work, we evaluated if stress affects dopamine (DA)-dependent synaptic plasticity in the medial prefrontal cortex (mPFC). On male adolescent rats, we characterized anxiety- and depressive-like behaviors using behavioral testing before and after exposure to a mild stress (elevated platform, EP). After the behavioral protocols, we investigated DA-dependent long-term potentiation (DA-LTP) and depression (DA-LTD) on acute slices of mPFC and evaluated the activation of DA-producing brain regions by western and dot blot analysis. We show that exposure to the EP stress enhances DA-LTP and that desipramine (DMI) treatment abolishes this effect. We also found that DA-LTD is not affected by EP stress unless when this is followed by DMI treatment. In addition, EP stress reduces anxiety, an effect abolished by both DMI and ketamine, while motivation is promoted by previous exposure to EP stress independently of pharmacological treatments. Finally, this form of stress reduces the expression of the early gene cFOS in the ventral tegmental area. These findings support the idea that mild stressors can promote synaptic plasticity in PFC through a dopaminergic mechanism, an effect that might increase the sensitivity of mPFC to subsequent stressful experiences.

Early life stress-induced alterations in the activity and morphology of ventral tegmental area neurons in female rats

Childhood maltreatment, which can take the form of physical or psychological abuse, is experienced by more than a quarter of all children. Early life stress has substantial and long-term consequences, including an increased risk of drug abuse and psychiatric disorders in adolescence and adulthood, and this risk is higher in women than in men. The neuronal mechanisms underlying the influence of early life adversities on brain functioning remain poorly understood; therefore, in the current study, we used maternal separation (MS), a rodent model of early-life neglect, to verify its influence on the properties of neurons in the ventral tegmental area (VTA), a brain area critically involved in reward and motivation processing. Using whole-cell patch-clamp recordings in brain slices from adolescent female Sprague-Dawley rats, we found an MS-induced increase in the excitability of putative dopaminergic (DAergic) neurons selectively in the medial part of the VTA. We also showed an enhancement of excitatory synaptic transmission in VTA putative DAergic neurons. MS-induced alterations in electrophysiology were accompanied by an increase in the diameter of dendritic spine heads on lateral VTA DAergic neurons, although the overall dendritic spine density remained unchanged. Finally, we reported MS-related increases in basal plasma ACTH and corticosterone levels. These results show the long-term consequences of early life stress and indicate the possible neuronal mechanisms of behavioral disturbances in individuals who experience early life neglect.

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Adversity in early life is a predisposing factor for psychiatric disorders.

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Maternal separation (MS) increases excitability of dopaminergic VTA neurons.

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Early life stress enhances excitatory synaptic transmission in the VTA.

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MS changes morphology of dendritic spine heads on VTA dopaminergic neurons.

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Early life stress increases basal ACTH and corticosterone levels in adulthood.

Histone deacetylase inhibition reduces ventral tegmental area dopamine neuronal hyperexcitability involving AKAP150 signaling following maternal deprivation in juvenile male rats

Traumatic early life stress (ELS) is linked to dopamine (DA) dysregulation which increases the probability of developing psychiatric disorders in adolescence and adulthood. Our prior studies demonstrated that a severe early life stressor, a 24-hr maternal deprivation (MD) in juvenile male rats, could lead to altered DA signaling from the ventral tegmental area (VTA) due to impairment of GABAergic synaptic plasticity (promoting GABAergic long-term depression, LTD) with concomitant changes in the abundance of synaptic regulators including A-kinase anchoring protein (AKAP150). Importantly, these MD-induced synaptic changes in the VTA were accompanied by upregulation of histone deacetylase 2, histone hypoacetylation, and were reversible by HDAC inhibition. Using cell-attached and whole-cell patch clamp recordings, we found that MD stress also increased spontaneous VTA DA neuronal activity and excitability in juvenile male rats without affecting intrinsic excitability. Postsynaptic chemical disruption of AKAP150 and protein kinase A interaction increased VTA DA neuronal excitability in control non-MD rats mimicking the effects of MD on DA cell excitability with similar changes in membrane properties. Interestingly, this disruption decreased MD-induced VTA DA hyperexcitability. This MD-induced DA neuronal hyperexcitability could also be normalized at 24 hr after injection of the class 1 HDAC inhibitor, CI-994. Altogether, our data suggest that AKAP150 plays a critical role in the regulation of VTA DA neuronal excitability and that HDAC-mediated targeting of AKAP150 signaling could normalize VTA DA dysfunction following ELS thereby providing novel therapeutic targets for prevention of later life psychopathology.

The impacts of maternal separation experience and its pattern on depression and dysfunctional attitude in middle school students in rural China

BACKGROUND

In China, because of the growth of economically driven rural-to-urban migration, there are lots of children in rural area who are separating or have separation experience with their parents. Until now, few studies focused on solely maternal separation and no research studied whether its pattern will affect children's later psychological status.

AIM

The aim of this study was to determine whether early or late maternal separation affects depression and dysfunctional attitude in middle school students and what is the role of cumulative duration and meeting frequency.

METHODS

Maternal separation experience was obtained by using questionnaires. We got early maternal separation group first. Then, late maternal separation and control group were obtained with the same number by matching grade, sex and family socioeconomic status. All the students in the three groups completed the scales of Children's Depression Inventory (CDI) and Dysfunctional Attitude Scale (DAS).

RESULTS

Both CDI and DAS scores of early separation group are higher than the other two groups. When we split the data by sex, only females presented the same results. When cumulative duration is short, there is significant difference in both scores of CDI and DAS among the three groups, which showed the scores of early separation group are higher than the other two groups. When the cumulative duration is long, there is no significant difference among the three groups. When meeting frequency is high, there is no significant difference among the three groups. When it is low, there is significant difference among the three groups, which showed the CDI and DAS scores of early separation group are higher than the other two groups. Furthermore, the same results are also found in females.

CONCLUSION

Early maternal separation may exert negative influence on student's depression and dysfunctional attitude. The sex, cumulative duration and meeting frequency may also play important roles in the effect.

Alterations in adolescent dopaminergic systems as a function of early mother-toddler attachment: A prospective longitudinal examination

Early experiences have the potential for outsized influence on neural development across a wide number of domains. In humans, many of the most important such experiences take place in the context of the mother-child attachment relationship. Work from animal models has highlighted neural changes in dopaminergic systems as a function of early care experiences, but translational research in humans has been limited. Our goal was to fill this gap by examining the longitudinal associations between early attachment experiences (assessed at 2.5 years) and neural responses to risk and rewards during adolescence (assessed at 13 years). Adolescence is a developmental period where sensitivity to rewards has important implications for behavior and long-term outcomes, providing an important window to study potential influences of early attachment experiences on reward processing. In order to address this question, 50 adolescents completed a risk and reward task during an fMRI scan, allowing us to assess differences in neural sensitivity to changes in risk level and reward amount as a function of early attachment experiences. Adolescents with insecure attachment histories showed blunted sensitivity to increasing risk levels in regions of the dorsal striatum, while also showing heightened sensitivity to increasing reward levels in the same region. These results highlight the importance of early attachment experiences for long-term neural development. Specifically, early exposure to more maladaptive relationships with caregivers may confer dual risks prospectively for adolescents, sensitizing them to rewarding outcomes while de-sensitizing them to potential risks associated with those behaviors, perhaps due to stress-related dopaminergic changes early in development.

Sex-dependent effects of early unstable post-natal environment on response to positive and negative stimuli in adult mice

Alterations in early environmental conditions that interfere with the creation of a stable mother-pup bond have been suggested to be a risk factor for the development of stress-related psychopathologies later in life. The long-lasting effects of early experiences are mediated by changes in various cerebral circuits, such as the corticolimbic system, which processes aversive and rewarding stimuli. However, it is evident that the early environment is not sufficient per se to induce psychiatric disorders; interindividual (eg, sex-based) differences in the response to environmental challenges exist. To examine the sex-related effects that are induced by an early experience on later events in adulthood, we determine the enduring effects of repeated cross-fostering (RCF) in female and male C57BL/6J mice. To this end, we assessed the behavioral phenotype of RCF and control (male and female) mice in the saccharine preference test and cocaine-induced conditioned place preference to evaluate the response to natural and pharmacological stimuli and in the elevated plus maze test and forced swimming test to measure their anxiety- and depression-like behavior. We also evaluated FST-induced c-Fos immunoreactivity in various brain regions that are engaged in the response to acute stress exposure (FST). Notably, RCF has opposing effects on the adult response to these tests between sexes, directing male mice toward an "anhedonia-like" phenotype and increasing the sensitivity for rewarding stimuli in female mice.

Chronic light exposure alters serotonergic and orexinergic systems in the rat brain and reverses maternal separation-induced increase in orexin receptors in the prefrontal cortex

Maternal separation (MS) is a well-established rodent model of depression. Chronic constant light (CCL) treatment during adolescence has been shown to reverse the depression-like behaviour induced by MS. We aimed to further delineate the antidepressant effect of light by investigating the involvement of the dopaminergic, serotonergic and orexinergic systems. MS was used to induce changes in adult male Sprague-Dawley rats, some of whom were also treated with CCL for 3 weeks during adolescence. At P80, rats were decapitated and brain tissue collected for analysis of glutamate- and potassium-stimulated dopamine release in the nucleus accumbens (NAc) using an in vitro superfusion technique. Enzyme-linked immunosorbent assays were employed to measure 5-hydroxytryptamine (5-HT) levels in the hypothalamus and prefrontal cortex (PFC). Western blotting was used to measure orexin receptor 1 (OXR-1) and 2 (OXR-2) in the PFC. MS did not affect 5-HT levels in these rats. However, CCL increased hypothalamic 5-HT and reduced 5-HT levels in the PFC. CCL had opposite effects on OXR levels in the PFC of maternally separated and non-separated rats. MS increased OXR-1 and OXR-2 levels in the PFC, an effect that was normalized by CCL treatment. MS reduced glutamate-stimulated dopamine release in the NAc, an effect that was not reversed by CCL. The present results suggest that CCL treatment affects 5-HT and orexinergic systems in the MS model while not affecting the MS-induced decrease in dopamine release in the NAc. The reversal of changes in the orexinergic system may be of particular relevance to the antidepressant effect of CCL in depression.

Unstable Maternal Environment Affects Stress Response in Adult Mice in a Genotype-Dependent Manner

Early postnatal events exert powerful effects on development, inducing persistent functional alterations in different brain network, such as the catecholamine prefrontal-accumbal system, and increasing the risk of developing psychiatric disorders later in life. However, a vast body of literature shows that the interaction between genetic factors and early environmental conditions is crucial for expression of psychopathologies in adulthood. We evaluated the long-lasting effects of a repeated cross-fostering (RCF) procedure in 2 inbred strains of mice (C57BL/6J, DBA/2), known to show a different susceptibility to the development and expression of stress-induced psychopathologies. Coping behavior (forced swimming test) and preference for a natural reinforcing stimulus (saccharine preference test) were assessed in adult female mice of both genotypes. Moreover, c-Fos stress-induced activity was assessed in different brain regions involved in stress response. In addition, we evaluated the enduring effects of RCF on catecholamine prefrontal-accumbal response to acute stress (restraint) using, for the first time, a new "dual probes" in vivo microdialysis procedure in mouse. RCF experience affects behavioral and neurochemical responses to acute stress in adulthood in opposite direction in the 2 genotypes, leading DBA mice toward an "anhedonic-like" phenotype and C57 mice toward an increased sensitivity for a natural reinforcing stimulus.

Isolation-induced vocalization in the infant rat depends on the nucleus accumbens

Mammalian infants vocalize when socially isolated. Vocalization guides the return of the caregiver and thereby maintains an environment critical to the infant's survival. Although the role of the periaqueductal gray area (PAG) in these vocalizations is established, other aspects of the relevant neural circuitry remain under-studied. Here we report that output from the nucleus accumbens (Acb) is necessary for isolation-induced vocalizations of infant rats aged postnatal days (PND) 11-13. Local inhibition via infusion of the GABA_A agonist muscimol (.8 μg/side) of the Acb, but not the dorsolateral striatum, blocked isolation-induced vocalizations, independent of whether the isolation was at room temperature, followed a brief reunion with the dam, or occurred in a cool (10 °C) environment. These findings highlight a possible anatomical area mediating the mammalian infant response to social separation and, more generally, to the development of social attachment.

Negative childhood experiences alter a prefrontal-insular-motor cortical network in healthy adults: A preliminary multimodal rsfMRI-fMRI-MRS-dMRI study

Research in humans and animals has shown that negative childhood experiences (NCE) can have long-term effects on the structure and function of the brain. Alterations have been noted in grey and white matter, in the brain's resting state, on the glutamatergic system, and on neural and behavioural responses to aversive stimuli. These effects can be linked to psychiatric disorder such as depression and anxiety disorders that are influenced by excessive exposure to early life stressors. The aim of the current study was to investigate the effect of NCEs on these systems. Resting state functional MRI (rsfMRI), aversion task fMRI, glutamate magnetic resonance spectroscopy (MRS), and diffusion magnetic resonance imaging (dMRI) were combined with the Childhood Trauma Questionnaire (CTQ) in healthy subjects to examine the impact of NCEs on the brain. Low CTQ scores, a measure of NCEs, were related to higher resting state glutamate levels and higher resting state entropy in the medial prefrontal cortex (mPFC). CTQ scores, mPFC glutamate and entropy, correlated with neural BOLD responses to the anticipation of aversive stimuli in regions throughout the aversion-related network, with strong correlations between all measures in the motor cortex and left insula. Structural connectivity strength, measured using mean fractional anisotropy, between the mPFC and left insula correlated to aversion-related signal changes in the motor cortex. These findings highlight the impact of NCEs on multiple inter-related brain systems. In particular, they highlight the role of a prefrontal-insular-motor cortical network in the processing and responsivity to aversive stimuli and its potential adaptability by NCEs.

Functional Uncoupling NMDAR NR2A Subunit from PSD-95 in the Prefrontal Cortex: Effects on Behavioral Dysfunction and Parvalbumin Loss after Early-Life Stress

Exposure to early-life stress increases vulnerability to psychiatric disorders, including depression, schizophrenia, and anxiety. Growing evidence implicates aberrant development of the prefrontal cortex (PFC) in the effects of early-life stress, which often emerge in adolescence or young adulthood. Specifically, early-life stress in the form of maternal separation (MS) in rodents has been shown to decrease parvalbumin (PVB)-positive interneurons in the adolescent PFC; however, the mechanism underpinning behavioral dysfunction and PVB loss is not yet known. We recently reported that MS causes overexpression of the NMDA subunit NR2A in the PFC of adolescent rats. Elevated PFC NR2A is also found in developmental models of schizophrenia and is correlated with behavioral deficits, acting largely through its association with the postsynaptic protein PSD-95. In addition, adolescent maturation of PVB-positive interneurons relies on NR2A-driven NMDA activity. Therefore, it is possible that the NR2A/PSD-95 signaling complex has a role in adolescent MS effects. Here, we aimed to determine whether a discrete manipulation of PFC NR2A could prevent MS effects on PFC-controlled behaviors, including cognition, anxiety, and novelty-induced hyperlocomotion, as well as PVB loss in adolescence. We intracranially infused the NR2A-specific blocking peptide TAT2A in order to uncouple NR2A from PSD-95 in the early-adolescent PFC, without antagonizing the NMDA receptor. We demonstrated that MS rats treated with TAT2A during early adolescence were protected from MS-induced PVB loss and exhibited less anxious behavior than those infused with control peptide. These data implicate NR2A-related N-methyl-D-aspartate receptor development in adolescent behavioral and neural consequences of early-life stress.

Beneficial Effects of Highly Palatable Food on the Behavioral and Neural Adversities induced by Early Life Stress Experience in Female Rats

This study examined the effects of highly palatable food during adolescence on the psycho-emotional and neural disturbances caused by early life stress experience in female rats. Female Sprague-Dawley pups were separated from dam for 3 h daily during the first two weeks of birth (MS) or left undisturbed (NH). Half of MS females received free access to chocolate cookies in addition to ad libitum chow from postnatal day 28. Pups were subjected to the behavioral tests during young adulthood. The plasma corticosterone response to acute stress, ΔFosB and brain-derived neurotrophic factor (BDNF) levels in the brain regions were analyzed. Total caloric intake and body weight gain during the whole experimental period did not differ among the experimental groups. Cookie access during adolescence and youth improved anxiety-/depression-like behaviors by MS experience. ΔFosB expression was decreased, but BDNF was increased in the nucleus accumbens of MS females, and ΔFosB expression was normalized and BDNF was further increased following cookie access. Corticosterone response to acute stress was blunted by MS experience and cookie access did not improve it. Results suggest that cookie access during adolescence improves the psycho-emotional disturbances of MS females, and ΔFosB and/or BDNF expression in the nucleus accumbens may play a role in its underlying neural mechanisms.

The dopaminergic response to acute stress in health and psychopathology: A systematic review

Previous work in animals has shown that dopamine (DA) in cortex and striatum plays an essential role in stress processing. For the first time, we systematically reviewed the in vivo evidence for DAergic stress processing in health and psychopathology in humans. All studies included (n studies=25, n observations=324) utilized DA D2/3 positron emission tomography and measured DAergic activity during an acute stress challenge. The evidence in healthy volunteers (HV) suggests that physiological, but not psychological, stress consistently increases striatal DA release. Instead, increased medial prefrontal cortex (mPFC) DAergic activity in HV was observed during psychological stress. Across brain regions, stress-related DAergic activity was correlated with the physiological and psychological intensity of the stressor. The magnitude of stress-induced DA release was dependent on rearing conditions, personality traits and genetic variations in several SNPs. In psychopathology, preliminary evidence was found for stress-related dorsal striatal DAergic hyperactivity in psychosis spectrum and a blunted response in chronic cannabis use and pain-related disorders, but results were inconsistent. Physiological stress-induced DAergic activity in striatum in HV may reflect somatosensory properties of the stressor and readiness for active fight-or-flight behavior. DAergic activity in HV in the ventral striatum and mPFC may be more related to expectations about the stressor and threat evaluation, respectively. Future studies with increased sample size in HV and psychopathology assessing the functional relevance of stress-induced DAergic activity, the association between cortical and subcortical DAergic activity and the direct comparison of different stressors are necessary to conclusively elucidate the role of the DA system in the stress response.

Stress and the social brain: behavioural effects and neurobiological mechanisms

Stress often affects our social lives. When undergoing high-level or persistent stress, individuals frequently retract from social interactions and become irritable and hostile. Predisposition to antisocial behaviours - including social detachment and violence - is also modulated by early life adversity; however, the effects of early life stress depend on the timing of exposure and genetic factors. Research in animals and humans has revealed some of the structural, functional and molecular changes in the brain that underlie the effects of stress on social behaviour. Findings in this emerging field will have implications both for the clinic and for society.

Progesterone Receptor Expression in the Developing Mesocortical Dopamine Pathway: Importance for Complex Cognitive Behavior in Adulthood

BACKGROUND

Numerous psychiatric and behavioral disorders such as autism, attention deficit disorder and schizophrenia may involve disruptions in the development of the mesocortical dopamine pathway, consisting of dopaminergic projections from the midbrain ventral tegmental area (VTA) to the medial prefrontal cortex (mPFC). Nuclear steroid hormone receptors are powerful transcription factors and can profoundly and permanently alter fundamental processes of neural development. Nuclear progesterone receptor (PR) is transiently expressed in both the VTA and the PFC of rodents during perinatal life, suggesting that PR may regulate the normal development of this important behavioral circuit.

METHODS AND RESULTS

Here, we demonstrate that virtually all PR-immunoreactive (PR-ir) cells in the VTA also express tyrosine hydroxylase immunoreactivity (TH-ir). In addition, retrograde tract tracing reveals that many PR-ir cells in the VTA project to the mPFC. Administration of a PR antagonist to rats during the neonatal period decreased TH-ir fiber density in the prelimbic mPFC of juveniles (postnatal day 25) and decreased levels of TH-ir in the VTA of adults. Neonatal treatment with a PR antagonist impaired adult performance on a passive inhibitory avoidance task and an attentional set-shifting task, measures of behavioral inhibition/impulsivity and cognitive flexibility, respectively. TH-ir levels in the VTA were reduced and cognitive flexibility was impaired in PR knockout mice as well.

CONCLUSIONS

These findings provide novel insights into a potential role for PR in the developmental etiology of behavioral disorders that involve impairments in complex cognitive behaviors and have implications for the use of synthetic progestins in humans during critical neurodevelopmental periods.

Interaction between parental psychosis and early motor development and the risk of schizophrenia in a general population birth cohort

Background

Delayed motor development in infancy and family history of psychosis are both associated with increased risk of schizophrenia, but their interaction is largely unstudied.

Aim

To investigate the association of the age of achieving motor milestones and parental psychosis and their interaction in respect to risk of schizophrenia.

Methods

We used data from the general population-based prospective Northern Finland Birth Cohort 1966 (n = 10,283). Developmental information of the cohort members was gathered during regular visits to Finnish child welfare clinics. Several registers were used to determine the diagnosis of schizophrenia among the cohort members and psychosis among the parents. Altogether 152 (1.5%) individuals had schizophrenia by the age of 46 years, with 23 (15.1%) of them having a parent with psychosis. Cox regression analysis was used in analyses.

Results

Parental psychosis was associated (P < 0.05) with later achievement of holding the head up, grabbing an object, and walking without support. In the parental psychosis group, the risk for schizophrenia was increased if holding the head up (hazard ratio [HR]: 2.46; degrees of freedom [df] = 1; 95% confidence interval [95% CI]: 1.07–5.66) and touching the thumb with the index finger (HR: 1.84; df = 1; 95% CI: 1.11–3.06) was later. In the group without parental psychosis, a delay in the following milestones increased the risk of schizophrenia: standing without support and walking without support. Parental psychosis had an interaction with delayed touching thumb with index finger (HR: 1.87; df = 1; 95% CI: 1.08–3.25) when risk of schizophrenia was investigated.

Conclusions

Parental psychosis was associated with achieving motor milestones later in infancy, particularly the milestones that appear early in a child's life. Parental psychosis and touching the thumb with the index finger had a significant interaction on risk of schizophrenia. Genetic risk for psychosis may interact with delayed development to raise future risk of schizophrenia, or delayed development may be a marker of other risk processes that interact with genetic liability to cause later schizophrenia.

Effect of acute swim stress on plasma corticosterone and brain monoamine levels in bidirectionally selected DxH recombinant inbred mouse strains differing in fear recall and extinction

Stress-induced changes in plasma corticosterone and central monoamine levels were examined in mouse strains that differ in fear-related behaviors. Two DxH recombinant inbred mouse strains with a DBA/2J background, which were originally bred for a high (H-FSS) and low fear-sensitized acoustic startle reflex (L-FSS), were used. Levels of noradrenaline, dopamine, and serotonin and their metabolites 3,4-dihydroxyphenyacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) were studied in the amygdala, hippocampus, medial prefrontal cortex, striatum, hypothalamus and brainstem. H-FSS mice exhibited increased fear levels and a deficit in fear extinction (within-session) in the auditory fear-conditioning test, and depressive-like behavior in the acute forced swim stress test. They had higher tissue noradrenaline and serotonin levels and lower dopamine and serotonin turnover under basal conditions, although they were largely insensitive to stress-induced changes in neurotransmitter metabolism. In contrast, acute swim stress increased monoamine levels but decreased turnover in the less fearful L-FSS mice. L-FSS mice also showed a trend toward higher basal and stress-induced corticosterone levels and an increase in noradrenaline and serotonin in the hypothalamus and brainstem 30 min after stress compared to H-FSS mice. Moreover, the dopaminergic system was activated differentially in the medial prefrontal cortex and striatum of the two strains by acute stress. Thus, H-FSS mice showed increased basal noradrenaline tissue levels compatible with a fear phenotype or chronic stressed condition. Low corticosterone levels and the poor monoamine response to stress in H-FSS mice may point to mechanisms similar to those found in principal fear disorders or post-traumatic stress disorder.

Effects of early life adverse experiences on the brain: implications from maternal separation models in rodents

During postnatal development, adverse early life experiences affect the formation of neuronal networks and exert long-lasting effects on neural function. Many studies have shown that daily repeated maternal separation (MS), an animal model of early life stress, can regulate the hypothalamic-pituitary-adrenal axis (HPA axis) and affect subsequent brain function and behavior during adulthood. However, the molecular basis of the long-lasting effects of early life stress on brain function has not been fully elucidated. In this mini review, we present various cases of MS in rodents and illustrate the alterations in HPA axis activity by focusing on corticosterone (CORT). We then show a characterization of the brain regions affected by various patterns of MS, including repeated MS and single time MS at various stages before weaning, by investigating c-Fos expression. These CORT and c-Fos studies suggest that repeated early life stress may affect neuronal function in region- and temporal-specific manners, indicating a critical period for habituation to early life stress. Next, we introduce how early life stress can impact behavior, namely by inducing depression, anxiety or eating disorders, and alterations in gene expression in adult mice subjected to MS.

History of childhood adversity is positively associated with ventral striatal dopamine responses to amphetamine

RATIONALE

Childhood exposure to severe or chronic trauma is an important risk factor for the later development of adult mental health problems, such as substance abuse. Even in nonclinical samples of healthy adults, persons with a history of significant childhood adversity seem to experience greater psychological distress than those without this history. Evidence from rodent studies suggests that early life stress may impair dopamine function in ways that increase risks for drug abuse. However, the degree to which these findings translate to other species remains unclear.

OBJECTIVES

This study was conducted to examine associations between childhood adversity and dopamine and subjective responses to amphetamine in humans.

METHODS

Following intake assessment, 28 healthy male and female adults, aged 18-29 years, underwent two consecutive 90-min positron emission tomography studies with high specific activity [(11)C]raclopride. The first scan was preceded by intravenous saline; the second by amphetamine (AMPH 0.3 mg/kg).

RESULTS

Consistent with prior literature, findings showed positive associations between childhood trauma and current levels of perceived stress. Moreover, greater number of traumatic events and higher levels of perceived stress were each associated with higher ventral striatal dopamine responses to AMPH. Findings of mediation analyses further showed that a portion of the relationship between childhood trauma and dopamine release may be mediated by perceived stress.

CONCLUSIONS

Overall, results are consistent with preclinical findings suggesting that early trauma may lead to enhanced sensitivity to psychostimulants and that this mechanism may underlie increased vulnerability for drug abuse.

Highly Palatable Food during Adolescence Improves Anxiety-Like Behaviors and Hypothalamic-Pituitary-Adrenal Axis Dysfunction in Rats that Experienced Neonatal Maternal Separation

BACKGROUND

This study was conducted to examine the effects of ad libitum consumption of highly palatable food (HPF) during adolescence on the adverse behavioral outcome of neonatal maternal separation.

METHODS

Male Sprague-Dawley pups were separated from dam for 3 hours daily during the first 2 weeks of birth (maternal separation, MS) or left undisturbed (nonhandled, NH). Half of MS pups received free access to chocolate cookies in addition to ad libitum chow from postnatal day 28 (MS+HPF). Pups were subjected to behavioral tests during young adulthood. The plasma corticosterone response to stress challenge was analyzed by radioimmunoassay.

RESULTS

Daily caloric intake and body weight gain did not differ among the experimental groups. Ambulatory activities were decreased defecation activity and rostral grooming were increased in MS controls (fed with chow only) compared with NH rats. MS controls spent less time in open arms, and more time in closed arms during the elevated plus maze test, than NH rats. Immobility duration during the forced swim test was increased in MS controls compared with NH rats. Cookie access normalized the behavioral scores of ambulatory and defecation activities and grooming, but not the scores during the elevated plus maze and swim tests in MS rats. Stress-induced corticosterone increase was blunted in MS rats fed with chow only, and cookie access normalized it.

CONCLUSION

Prolonged access to HPF during adolescence and youth partly improves anxiety-related, but not depressive, symptoms in rats that experienced neonatal maternal separation, possibly in relation with improved function of the hypothalamic-pituitary-adrenal (HPA) axis.

Modulation of early stress-induced neurobiological changes: a review of behavioural and pharmacological interventions in animal models

Childhood adversity alters the predisposition to psychiatric disorders later in life. Those with psychiatric conditions and a history of early adversity exhibit a higher incidence of treatment resistance compared with individuals with no such history. Modulation of the influence early stress exerts over neurobiology may help to prevent the development of psychiatric disorders in some cases, while attenuating the extent of treatment resistance in those with established psychiatric disorders. This review aims to critically evaluate the ability of behavioural, environmental and pharmacologic interventions to modulate neurobiological changes induced by early stress in animal models. Databases were systematically searched to locate literature relevant to this review. Early adversity was defined as stress that resulted from manipulation of the mother-infant relationship. Analysis was restricted to animal models to enable characterisation of how a given intervention altered specific neurobiological changes induced by early stress. A wide variety of changes in neurobiology due to early stress are amenable to intervention. Behavioural interventions in childhood, exercise in adolescence and administration of epigenetic-modifying drugs throughout life appear to best modulate cellar and behavioural alterations induced by childhood adversity. Other pharmacotherapies, such as endocannabinoid system modulators, anti-inflammatories and antidepressants can also influence these neurobiological and behavioural changes that result from early stress, although findings are less consistent at present and require further investigation. Further work is required to examine the influence that behavioural interventions, exercise and epigenetic-modifying drugs exert over alterations that occur following childhood stress in human studies, before possible translational into clinical practice is possible.

Stress-mediated modulations in dopaminergic system and their subsequent impact on behavioral and oxidative alterations: an update

CONTEXT

Stress-induced changes in the dopaminergic system and subsequent enhancement of oxidative load and behavior are associated with a wide range of central and peripheral nervous disorders. Dopamine acts as a key neurotransmitter in the brain plays an important role in the regulation of motor and limbic functions.

OBJECTIVE

This article reviews the effect of stress on central dopaminergic system and its subsequent impact on the alterations in behavior and oxidative stress.

METHODS

A literature survey in PubMed (Bethesda, MD), Scopus (Philadelphia, PA), SciFinder (Columbus, OH) and Google Scholar (PMV, CA) was performed to gather information regarding the role of stress on central dopaminergic system and its associated behavioral and oxidative alterations.

RESULTS

Our collective data on behavioral studies and oxidative distress in stressful conditions show the functional reduction in dopaminergic neuronal system that could be one of the factors for the development of stress-induced motor suppression. Collectively, stress caused significant behavioral and oxidative alterations via suppression of neuronal functions of the central dopaminergic system.

CONCLUSIONS

This study provides an insight into the overall pathophysiological alterations in neuronal functions of the central dopaminergic system caused by acute and chronic unpredictable stress that, in our opinion, represent optimal utility as future therapeutic targets for neurodegenerative disorders.

Increased depression-like behaviors with dysfunctions in the stress axis and the reward center by free access to highly palatable food

This study was conducted to examine the behavioral consequences of unlimited consumption of highly palatable food (HPF) and investigate its underlying neural mechanisms. Male Sprague-Dawley rats had free access to chocolate cookie rich in fat (HPF) in addition to ad libitum chow and the control group received chow only. Rats were subjected to behavioral tests during the 2nd week of food condition; i.e. ambulatory activity test on the 8th, elevated plus maze test (EPM) on the 10th and forced swim test (FST) on the 14th day of food condition. After 8 days of food condition, another group of rats were placed in a restraint box and tail bloods were collected at 0, 20, 60, and 120 time points during 2h of restraint period, used for the plasma corticosterone assay. At the end of restraint session, rats were sacrificed and the tissue sections of the nucleus accumbens (NAc) were processed for c-Fos immunohistochemistry. Ambulatory activities and the scores of EPM were not significantly affected by unlimited cookie consumption. However, immobility duration during FST was increased, and swim decreased, in the rats received free cookie access compared with control rats. Stress-induced corticosterone increase was exaggerated in cookie-fed rats, while the stress-induced c-Fos expression in the NAc was blunted, compared to control rats. Results suggest that free access to HPF may lead to the development of depression-like behaviors in rats, likely in relation with dysfunctions in the hypothalamic-pituitary-adrenal axis and the reward center.