Early-life stress affects the structural and functional plasticity of the medial prefrontal cortex in adolescent rats

Prefrontal control of superior colliculus modulates innate escape behavior following adversity

Innate defensive responses, though primarily instinctive, must also be highly adaptive to changes in risk assessment. However, adaptive changes can become maladaptive, following severe stress, as seen in posttraumatic stress disorder (PTSD). In a series of experiments, we observed long-term changes in innate escape behavior of male mice towards a previously non-threatening stimulus following an adverse shock experience manifested as a shift in the threshold of threat response. By recording neural activity in the superior colliculus (SC) while phototagging specific responses to afferents, we established the crucial influence of input arriving at the SC from the medial prefrontal cortex (mPFC), both directly and indirectly, on escape-related activity after adverse shock experience. Inactivating these specific projections during the shock effectively abolished the observed changes. Conversely, optogenetically activating them during encounters controlled escape responses. This establishes the necessity and sufficiency of those specific mPFC inputs into the SC for adverse experience related changes in innate escape behavior.

Impaired monoamine neural system in the mPFC of SHRSP/Ezo as an animal model of attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is the most common childhood-onset psychiatric disorder. We investigated the effects of systemic administration of monoamine reuptake inhibitors on long-term potentiation (LTP) formation and monoamine release in the medial prefrontal cortex (mPFC) of the stroke-prone spontaneously hypertensive rat (SHRSP)/Ezo, an animal model of ADHD, and its genetic control, Wistar Kyoto (WKY)/Ezo, to elucidate the functional changes in the mPFC monoamine neural system. Methylphenidate (dopamine (DA) and noradrenaline (NA) reuptake inhibitor) and desipramine (NA reuptake inhibitor) improved LTP formation defects in the mPFC of SHRSP/Ezo, suggesting that NA or both DA and NA are required for improvement of impaired LTP. Methylphenidate increased mPFC DA in both WKY/Ezo and SHRSP/Ezo, but the increase was greater in the former. GBR-12909 (DA reuptake inhibitor) increased mPFC DA in WKY/Ezo but had no effect in SHRSP/Ezo. This may be because DA transporter in SHRSP/Ezo is functionally impaired and contributes less to DA reuptake, so its inhibition did not increase DA level. Meanwhile, basal DA levels in the mPFC of SHRSP/Ezo were paradoxically decreased. These results suggest that functional changes in the DA and NA neural system in the frontal lobe are involved in the pathology of ADHD.

A Randomized Controlled Trial of a Parenting Intervention During Infancy Alters Amygdala-Prefrontal Circuitry in Middle Childhood

OBJECTIVE

Early adverse parenting predicts various negative outcomes, including psychopathology and altered development. Animal work suggests that adverse parenting might change amygdala-prefrontal cortex (PFC) circuitry, but work in humans remains correlational. The present study leveraged data from a randomized controlled trial examining the efficacy of an early parenting intervention targeting parental nurturance and sensitivity (Attachment and Biobehavioral Catch-up [ABC]) to test whether early parenting quality causally affects amygdala-PFC connectivity later in life.

METHOD

Participants (N = 60, mean age = 10.0 years) included 41 high-risk children whose parents were referred by Child Protective Services and randomly assigned to receive either ABC (n = 21) or a control intervention (n = 20) during the children's infancy and a comparison sample of low-risk children (n = 19). Amygdala-PFC connectivity was assessed via functional magnetic resonance imaging while children viewed fearful and neutral faces.

RESULTS

Across facial expressions, ABC produced different changes than the control intervention in amygdala-PFC connectivity in response to faces. The ABC group also exhibited greater responses than the control intervention group to faces in areas classically associated with emotion regulation, including the orbitofrontal cortex and right insula. Mediation analysis suggested that the effect of ABC on PFC activation was mediated by the intervention's effect on amygdala-PFC connectivity.

CONCLUSION

Results provide preliminary causal evidence for the effect of early parenting intervention on amygdala-PFC connectivity and on PFC responses to face viewing. Findings also highlight amygdala-PFC connectivity as a potential mediator of the effects of early parenting intervention on children's emotion regulation development.

CLINICAL TRIAL REGISTRATION INFORMATION

Intervening Early With Neglected Children; https://clinicaltrials.gov/; NCT02093052.

DIVERSITY & INCLUSION STATEMENT

We worked to ensure sex and gender balance in the recruitment of human participants. We worked to ensure race, ethnic, and/or other types of diversity in the recruitment of human participants. We worked to ensure that the study questionnaires were prepared in an inclusive way. One or more of the authors of this paper self-identifies as a member of one or more historically underrepresented racial and/or ethnic groups in science. One or more of the authors of this paper self-identifies as a member of one or more historically underrepresented sexual and/or gender groups in science. One or more of the authors of this paper received support from a program designed to increase minority representation in science. While citing references scientifically relevant for this work, we also actively worked to promote sex and gender balance in our reference list.

Socioeconomic Disparities in Hypothalamic-Pituitary-Adrenal Axis Regulation and Prefrontal Cortical Structure

Socioeconomic disadvantage during childhood predicts an increased risk for mental health problems across the life span. Socioeconomic disadvantage shapes multiple aspects of children's proximal environments and increases exposure to chronic stressors. Drawing from multiple literatures, we propose that childhood socioeconomic disadvantage may lead to adaptive changes in the regulation of stress response systems including the hypothalamic-pituitary-adrenal (HPA) axis. These changes, in turn, affect the development of prefrontal cortical (PFC) circuitry responsible for top-down control over cognitive and emotional processes. Translational findings indicate that chronic stress reduces dendritic complexity and spine density in the medial PFC and anterior cingulate cortex, in part through altered HPA axis regulation. Socioeconomic disadvantage has frequently been associated with reduced gray matter in the dorsolateral and ventrolateral PFC and anterior cingulate cortex and lower fractional anisotropy in the superior longitudinal fasciculus, cingulum bundle, and uncinate fasciculus during middle childhood and adolescence. Evidence of socioeconomic disparities in hair cortisol concentrations in children has accumulated, although null findings have been reported. Coupled with links between cortisol levels and reduced gray matter in the PFC and anterior cingulate cortex, these results support mechanistic roles for the HPA axis and these PFC circuits. Future longitudinal studies should simultaneously consider multiple dimensions of proximal factors, including cognitive stimulation, while focusing on epigenetic processes and genetic moderators to elucidate how socioeconomic context may influence the HPA axis and PFC circuitry involved in cognitive and emotional control. These findings, which point to modifiable factors, can be harnessed to inform policy and more effective prevention strategies.

Maternal separation modifies spontaneous synaptic activity in the infralimbic cortex of stress-resilient male rats

Glutamate and GABA signaling systems are necessary to maintain proper function of the central nervous system through excitation/inhibition (E/I) balance. Alteration of this balance in the medial prefrontal cortex (mPFC), as an effect of early-life stress, may lead to the development of anxiety and depressive disorders. Few studies exist in the infralimbic division of the mPFC to understand the effect of early-life stress at different ages, which is the purpose of the present work. Newborn Sprague Dawley male rats were subjected to maternal separation (MS) for two weeks. First, tests measuring anxiety- and depression-like behaviors were performed on adolescent and adult rats subjected to MS (MS-rats). Then, to establish a relationship with behavioral results, electrophysiological recordings were performed in neurons of the infralimbic cortex in acute brain slices of infant, adolescent, and adult rats. In the behavioral tests, there were no significant differences in MS-rats compared to control rats at any age. Moreover, MS had no effect on the passive membrane properties nor neuronal excitability in the infralimbic cortex, whereas spontaneous synaptic activity in infralimbic neurons was altered. The frequency of spontaneous glutamatergic synaptic events increased in infant MS-rats, whereas in adolescent MS-rats both the frequency and the amplitude of spontaneous GABAergic events increased without any effect on glutamatergic synaptic responses. In adult MS-rats, these two parameters decreased in spontaneous GABAergic synaptic events, whereas only the frequency of glutamatergic events decreased. These data suggest that rats subjected to MS did not exhibit behavioral changes and presented an age-dependent E/I imbalance in the infralimbic cortex, possibly due to differential changes in neurotransmitter release and/or receptor expression.

Early life stress impairs VTA coordination of BLA network and behavioral states

Motivated behaviors, such as social interactions, are governed by the interplay between mesocorticolimbic structures, such as the ventral tegmental area (VTA), basolateral amygdala (BLA), and medial prefrontal cortex (mPFC). Adverse childhood experiences and early life stress (ELS) can impact these networks and behaviors, which is associated with increased risk for psychiatric illnesses. While it is known that the VTA projects to both the BLA and mPFC, the influence of these inputs on local network activity which govern behavioral states - and whether ELS impacts VTA-mediated network communication - remains unknown. Our study demonstrates that VTA inputs influence BLA oscillations and mPFC activity, and that ELS weakens the ability of the VTA to coordinate BLA network states, likely due to ELS-induced impairments in dopamine signaling between the VTA and BLA. Consequently, ELS mice exhibit increased social avoidance, which can be recapitulated in control mice by inhibiting VTA-BLA communication. These data suggest that ELS impacts social reward via the VTA-BLA dopamine network.

mPFC DUSP1 mediates adolescent cocaine exposure-induced higher sensitivity to drug in adulthood

Adolescent cocaine abuse increases the risk for developing addiction in later life, but the underlying molecular mechanism remains poorly understood. Here, we establish adolescent cocaine-exposed (ACE) male mouse models. A subthreshold dose of cocaine (sdC) treatment, insufficient to produce conditioned place preference (CPP) in adolescent mice, induces CPP in ACE mice during adulthood, along with more activated CaMKII-positive neurons, higher dual specificity protein kinase phosphatase-1 (Dusp1) mRNA, lower DUSP1 activity, and lower DUSP1 expression in CaMKII-positive neurons in the medial prefrontal cortex (mPFC). Overexpressing DUSP1 in CaMKII-positive neurons suppresses neuron activity and blocks sdC-induced CPP in ACE mice during adulthood. On the contrary, depleting DUSP1 in CaMKII-positive neurons activates more neurons and further enhances sdC-induced behavior in ACE mice during adulthood. Also, ERK1/2 might be a downstream signal of DUSP1 in the process. Our findings reveal a role of mPFC DUSP1 in ACE-induced higher sensitivity to the drug in adult mice. DUSP1 might be a potential pharmacological target to predict or treat the susceptibility to addictive drugs caused by adolescent substance use.

Loss of spines in the prelimbic cortex is detrimental to working memory in mice with early-life adversity

Adverse experiences in early life can shape neuronal structures and synaptic function in multiple brain regions, leading to deficits of distinct cognitive functions later in life. Focusing on the pyramidal cells of the prelimbic cortex (PrL), a main subregion of the medial prefrontal cortex, the impact of early-life adversity (ELA) was investigated in a well-established animal model generated by changing the rearing environment during postnatal days 2 to 9 (P2-P9), a sensitive developmental period. ELA has enduring detrimental impacts on the dendritic spines of PrL pyramidal cells, which is most apparent in a spatially circumscribed region. Specifically, ELA affects both thin and mushroom-type spines, and ELA-provoked loss of spines is observed on selective dendritic segments of PrL pyramidal cells in layers II-III and V-VI. Reduced postsynaptic puncta represented by postsynaptic density protein-95 (PSD-95), but not synaptophysin-labelled presynaptic puncta, in ELA mice supports the selective loss of spines in the PrL. Correlation analysis indicates that loss of spines and postsynaptic puncta in the PrL contributes to the poor spatial working memory of ELA mice, and thin spines may play a major role in working memory performance. To further understand whether loss of spines affects glutamatergic transmission, AMPA- and NMDA-receptor-mediated synaptic currents (EPSCs) were recorded in a group of Thy1-expressing PrL pyramidal cells. ELA mice exhibited a depressed glutamatergic transmission, which is accompanied with a decreased expression of GluR1 and NR1 subunits in the PrL. Finally, upregulating the activation of Thy1-expressing PrL pyramidal cells via excitatory DREADDs can efficiently improve the working memory performance of ELA mice in a T-maze-based task, indicating the potential of a chemogenetic approach in restoring ELA-provoked memory deficits.

Susceptibility to arecoline in male C57BL/6J mice correlates with age factor

Epidemiological investigations and clinical studies have confirmed that human chewing of betel nut is an addictive behavior, and the proportion of teenagers chewing betel nut is increasing. Previous studies have shown that adolescence shows higher sensitivity to many addictive substances compared with adulthood, and that adult susceptibility to addictive substances is usually changed after exposure to addictive substances during adolescence. However, there are no reports of age-related animal experiments on betel nut or dependence to its active ingredients. Therefore, the two-bottle choice (TBC) (experiment 1 and 2) and conditioned place preference (CPP) (experiment 3 and 4) models with mice were used in this study to explore age-related differences in intake and preference of arecoline, the alkaloid in betel nut with highest content, and to explore the effect of arecoline exposure during adolescence on the re-exposure of arecoline in adulthood in mice. The results of experiment 1 showed that the intake of 80μg/ml arecoline in adolescent mice was significantly higher than that in adult mice. However, there was no significant difference between adult and adolescent mice in preference for arecoline at any tested concentration (5-80μg/ml), which may be due to the significantly higher intake of total fluid in adolescent mice compared to adult mice. The preference of arecoline in adolescent mice peaked at 20μg/ml, and in adult mice peaked at 40μg/ml. The results of experiment 2 showed that oral arecoline (5-80μg/ml) in mice during adolescence caused a significant increase in the intake (days 3-16) and preference (days 5-8) for 40μg/ml arecoline in adulthood. The results of experiment 3 showed that the doses of 0.03 or 0.1mg/kg of arecoline produced the highest CPP response in adolescent or adult mice, respectively. The results of experiment 4 showed that mice exposed to arecoline in adolescence had significantly increased the CPP scores induced by arecoline in adulthood compared to mice that were not exposed. These data suggested that adolescent mice were more sensitive to arecoline, and exposure of mice to arecoline during adolescence increased the susceptibility to arecoline in adulthood.

Activation of RhoA pathway participated in the changes of emotion, cognitive function and hippocampal synaptic plasticity in juvenile chronic stress rats

Neuropsychiatric diseases are related to early life stress (ELS), patients often have abnormal learning, memory and emotion. But the regulatory mechanism is unclear. Hippocampal synaptic plasticity (HSP) changes are important mechanism. RhoA pathway is known to regulate HSP by modulating of dendritic spines (DS), whether it's involved in HSP changes in ELS hasn't been reported. So we investigated whether and how RhoA participates in HSP regulation in ELS. The ELS model was established by separation-rearing in juvenile. Results of IntelliCage detection etc. showed simple learning and memory wasn't affected, but spatial, punitive learning and memories reduced, the desire to explore novel things reduced, the anxiety-like emotion increased. We further found hippocampus was activated, the hippocampal neurons dendritic complexities reduced, the proportion of mature DS decreased. The full-length transcriptome sequencing techniques was used to screen for differentially expressed genes involved in regulating HSP changes, we found RhoA gene was up-regulated. We detected RhoA protein, RhoA phosphorylation and downstream molecules expression changes, results shown RhoA and p-RhoA, p-ROCK2 expression increased, p-LIMK, p-cofilin expression and F-actin/G-actin ratio decreased. Our study revealed HSP changes in ELS maybe regulate by activation RhoA through ROCK2/LIMK/cofilin pathway regulated F-actin/G-actin balance and DS plasticity, affecting emotion and cognition.

Acute stress modulates noradrenergic signaling in the ventral tegmental area-amygdalar circuit

Noradrenergic neurotransmission is a critical mediator of stress responses. In turn, exposure to stress induces noradrenergic system adaptations, some of which are implicated in the etiology of stress-related disorders. Adrenergic receptors (ARs) in the ventral tegmental area (VTA) have been demonstrated to regulate phasic dopamine (DA) release in the forebrain, necessary for behavioral responses to conditional cues. However, the impact of stress on noradrenergic modulation of the VTA has not been previously explored. We demonstrate that ARs in the VTA regulate dopaminergic activity in the VTA-BLA (basolateral amygdala) circuit, a key system for processing stress-related stimuli; and that such control is altered by acute stress. We utilized fast-scan cyclic voltammetry to assess the effects of intra-VTA microinfusion of α₁ -AR and α₂ -AR antagonists (terazosin and RX-821002, respectively), on electrically evoked phasic DA release in the BLA in stress-naïve and stressed (unavoidable electric shocks - UES) anesthetized male Sprague-Dawley rats. In addition, we used western blotting to explore UES-induced alterations in AR protein level in the VTA. Intra-VTA terazosin or RX-821002 dose-dependently attenuated DA release in the BLA. Interestingly, UES decreased the effects of intra-VTA α₂ -AR blockade on DA release (24 h but not 7 days after stress), while the effects of terazosin were unchanged. Despite changes in α₂ -AR physiological function in the VTA, UES did not alter α₂ -AR protein levels in either intracellular or membrane fractions. These findings demonstrate that NA-ergic modulation of the VTA-BLA circuit undergoes significant alterations in response to acute stress, with α₂ -AR signaling indicated as a key target.

Modulation of the endoplasmic reticulum stress and unfolded protein response mitigates the behavioral effects of early-life stress

BACKGROUND

Early-life stress (ELS) affects brain development and increases the risk of mental disorders associated with the dysfunction of the medial prefrontal cortex (mPFC). The mechanisms of ELS action are not well understood. Endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) are cellular processes involved in brain maturation through the regulation of pro-survival or proapoptotic processes. We hypothesized that ER stress and the UPR in the mPFC are involved in the neurobiology of ELS.

METHODS

We performed a maternal separation (MS) procedure from postnatal days 1 to 14 in rats. Before each MS, pups were injected with an inhibitor of ER stress, salubrinal or a vehicle. The mRNA and protein expression of UPR and apoptotic markers were evaluated in the mPFC using RT-qPCR and Western blot methods, respectively. We also estimated the numbers of neurons and glial cells using stereological methods. Additionally, we assessed behavioral phenotypes related to fear, anhedonia and response to psychostimulants.

RESULTS

MS slightly enhanced the activation of the UPR in juveniles and modulated the expression of apoptotic markers in juveniles and preadolescents but not in adults. Additionally, MS did not affect the numbers of neurons and glial cells at any age. Both salubrinal and vehicle blunted the expression of UPR markers in juvenile and preadolescent MS rats, often in a treatment-specific manner. Moreover, salubrinal and vehicle generally alleviated the behavioral effects of MS in preadolescent and adult rats.

CONCLUSIONS

Modulation of ER stress and UPR processes may potentially underlie susceptibility or resilience to ELS.

Early-life stress affects peripheral, blood-brain barrier, and brain responses to immune challenge in juvenile and adult rats

Early-life stress (ELS) may affect brain maturation and neuroimmune interactions and, consequently, the inflammatory response to subsequent environmental factors later in life. Recently, the coexistence of blood-brain barrier (BBB) dysfunction and inflammation has been implicated in the etiology and progression of mental and/or neurodegenerative diseases. There are sex differences in the prevalence and outcomes of these disorders. The number of studies reporting the effects of ELS and sex on BBB functioning and neuroinflammatory processes in response to immune challenge is very limited, and the data are inconsistent. In the present study, we examined whether ELS, based on the maternal separation (MS) paradigm in rats, can condition male and female subjects to subsequent lipopolysaccharide (LPS)-induced immune challenge in juvenility or adulthood. Twenty-four hours after acute LPS injection, serum proinflammatory cytokines were measured, and BBB permeability in the medial prefrontal cortex (mPFC) and hippocampus (HP) was evaluated. Additionally, the mRNA expression of neuroinflammatory markers and BBB-related genes was also studied. We found that a single LPS challenge induced a proinflammatory response both in the periphery and in the mPFC and HP and increased BBB permeability in a sex-dependent fashion. Moreover, MS enhanced the neuroinflammatory response to LPS challenge in males (especially juveniles), whereas MS females showed no difference or a blunted central response to LPS compared with control females, mainly during adulthood. These results suggest that ELS may precondition individuals to subsequent environmental factors later in life in a sex-specific manner and potentially determine their susceptibility or resilience to mental and/or neurodegenerative diseases.

Aberrant cortical projections to amygdala GABAergic neurons contribute to developmental circuit dysfunction following early life stress

Early life stress (ELS) results in enduring dysfunction of the corticolimbic circuitry, underlying emotional and social behavior. However, the neurobiological mechanisms involved remain elusive. Here, we have combined viral tracing and electrophysiological techniques to study the effects of maternal separation (MS) on frontolimbic connectivity and function in young (P14-21) rats. We report that aberrant prefrontal inputs to basolateral amygdala (BLA) GABAergic interneurons transiently increase the strength of feed-forward inhibition in the BLA, which raises LTP induction threshold in MS treated male rats. The enhanced GABAergic activity after MS exposure associates with lower functional synchronization within prefrontal-amygdala networks in vivo. Intriguingly, no differences in these parameters were detected in females, which were also resistant to MS dependent changes in anxiety-like behaviors. Impaired plasticity and synchronization during the sensitive period of circuit refinement may contribute to long-lasting functional changes in the prefrontal-amygdaloid circuitry that predispose to neuropsychiatric conditions later on in life.

Epidemiology of Childhood Witnessing Domestic Violence and Exploration of Its Relationships With Affective Lability and Suicide Attempts in Chinese Young Adults

Childhood witnessing domestic violence (CWDV) exerts short- and long-term negative impacts on emotional and behavioral health. The present study investigated the epidemiological features of CWDV, and its negative impact on psychological outcomes in a sample of Chinese college students. The mediating role of emotion regulation strategies on CWDV associations with psychological outcomes and gender differences in these relationships were examined. A total of 3,126 respondents (1,034 males; 2,086 females; 6 missing data in gender) completed the study questionnaire, which included demographic characteristics, CWDV, and suicide attempt history items as well as the Emotion Regulation Questionnaire (ERQ) and Affect Lability Scale-18 (ALS-18). Overall, 43.03% of the respondents reported CWDV, including 44.87% of males and 42.09% of females. Higher frequencies of CWDV were found to be related to the following factors: unstable marital status of parents; not being an only child; being a left-behind child, family financial difficulties, consumption of alcohol in the past year, and being in relatively poor physical condition. Among males, ERQ suppression scores were significantly higher for those men who experienced "often or every day" CWDV than for men who indicated that they did not have any history of CWDV (Bonferroni-corrected p = 0.047). More frequent CWDV was associated with higher ALS-18 scores and increased risk of suicide attempts in males and females (p < 0.05), and emotion regulation (suppression) was found to mediate the association between CWDV and affective lability among males. This study revealed high rates of CWDV, and serious impacts of CWDV on mental health in male and female Chinese college students. In males, but not females, emotion regulation strategy use, use of suppression, was found to act as a mediator in the association of CWDV with affective lability. Our findings suggest that interventions for individuals with CWDV should focus on the emotional regulation, which may help them improve mental health, especially in males.

Adolescent chronic unpredictable stress leads to increased anxiety and attention deficit/hyperactivity-like symptoms in adulthood

BACKGROUND

Early-life adversities during development (e.g., child abuse and neglect) are linked to multiple behavioral and cognitive dysfunctions, such as attention deficit/hyperactivity disorder (ADHD) and anxiety disorders, which have high comorbidity. However, the impact of adversities during adolescence, a crucial period in early life for these disorders, is understudied. Using a chronic unpredictable stress (CUS) model in rats, we investigated whether adversities in adolescence could lead to increased anxiety and ADHD-like symptoms in adulthood.

METHODS

Mid- to late-adolescent (5-7-week-old) male and female Sprague-Dawley rats underwent a mild CUS procedure for 2 weeks. Various stressors were applied in an unpredictable way. Rats of both sexes were then trained with a 2-choice reaction time (2-CRT) task during adulthood, which are designed to detect ADHD-like symptoms, including increased impulsivity and lapse of attention. In addition, an open field test was conducted to examine if CUS resulted in a persistent increase in anxiety-like behavior during adulthood.

RESULTS

Both male and female rats with CUS exposure travelled shorter distances in the open field and spent less time in the center zone, indicating increased anxiety. In the 2-CRT task, rats of both sexes with CUS exposure showed increased impulsivity. Augmented lapses of attention were observed in female but not male rats.

CONCLUSION

Chronic unpredictable stress during adolescence increases anxiety and leads to ADHD-like symptoms in both male and female rats in adulthood. The deficits are more severe in females than in males. These observations support that adversities during adolescence persistently increase anxiety, which is comorbid with attention deficits.

Central and peripheral neuropeptide RFRP-3: A bridge linking reproduction, nutrition, and stress response

This article is an amalgamation of the current status of RFRP-3 (GnIH) in reproduction and its association with the nutrition and stress-mediated changes in the reproductive activities. GnIH has been demonstrated in the hypothalamus of all the vertebrates studied so far and is a well-known inhibitor of GnRH mediated reproduction. The RFRP-3 neurons interact with the other hypothalamic neurons and the hormonal signals from peripheral organs for coordinating the nutritional, stress, and environmental associated changes to regulate reproduction. RFRP-3 has also been shown to regulate puberty, reproductive cyclicity and senescence depending upon the nutritional status. A favourable nutritional status and the environmental cues which are permissive for the successful breeding and pregnancy outcome keep RFRP-3 level low, whereas unfavourable nutritional status and stressful conditions increase the expression of RFRP-3 which impairs the reproduction. Still our knowledge about RFRP-3 is incomplete regarding its therapeutic application for nutritional or stress-related reproductive disorders.

Early Life Stress Induces Different Behaviors in Adolescence and Adulthood May Related With Abnormal Medial Prefrontal Cortex Excitation/Inhibition Balance

Early life stress is thought to be a risk factor for emotional disorders, particularly depression and anxiety. Although the excitation/inhibition (E/I) imbalance has been implicated in neuropsychiatric disorders, whether early life stress affects the E/I balance in the medial prefrontal cortex at various developmental stages is unclear. In this study, rats exposed to maternal separation (MS) that exhibited a well-established early life stress paradigm were used to evaluate the E/I balance in adolescence (postnatal day P43-60) and adulthood (P82-100) by behavior tests, whole-cell recordings, and microdialysis coupled with high performance liquid chromatography-mass spectrometry (HPLC-MS) analysis. First, the behavioral tests revealed that MS induced both anxiety- and depressive-like behaviors in adolescent rats but only depressive-like behavior in adult rats. Second, MS increased the action potential frequency and E/I balance of synaptic transmission onto L5 pyramidal neurons in the prelimbic (PrL) brain region of adolescent rats while decreasing the action potential frequency and E/I balance in adult rats. Finally, MS increases extracellular glutamate levels and decreased the paired-pulse ratio of evoked excitatory postsynaptic currents (EPSCs) of pyramidal neurons in the PrL of adolescent rats. In contrast, MS decreased extracellular glutamate levels and increased the paired-pulse ratio of evoked EPSCs of pyramidal neurons in the PrL of adult rats. The present results reveal a key role of E/I balance in different MS-induced disorders may related to the altered probability of presynaptic glutamate release at different developmental stages.

FKBP5 and early life stress affect the hippocampus by an age-dependent mechanism

Early life stress (ELS) adversely affects the brain and is commonly associated with the etiology of mental health disorders, like depression. In addition to the mood-related symptoms, patients with depression show dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, increased peripheral inflammation, and structural brain alterations. Although the underlying causes are unknown, polymorphisms in the FK506-binding protein 5 (FKBP5) gene, a regulator of glucocorticoid receptor (GR) activity, interact with childhood adversities to increase vulnerability to depressive disorders. We hypothesized that high FKBP5 protein levels combined with early life stress (ELS) would alter the HPA axis and brain, promoting depressive-like behaviors. To test this, we exposed males and females of a mouse model overexpressing FKBP5 in the brain (rTgFKBP5 mice), or littermate controls, to maternal separation for 14 days after birth. Then, we evaluated neuroendocrine, behavioral, and brain changes in young adult and aged mice. We observed lower basal corticosterone (CORT) levels in rTgFKBP5 mice, which was exacerbated in females. Aged, but not young, rTgFKBP5 mice showed increased depressive-like behaviors. Moreover, FKBP5 overexpression reduced hippocampal neuron density in aged mice, while promoting markers of microglia expression, but these effects were reversed by ELS. Together, these results demonstrate that high FKBP5 affects basal CORT levels, depressive-like symptoms, and numbers of neurons and microglia in the hippocampus in an age-dependent manner.

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High FKBP5 reduces basal corticosterone levels in mice, especially in females.

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ELS prevents FKBP5-induced susceptibility to depressive-like behavior in aged mice.

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FKBP5 overexpression reduces hippocampal neuron density in aged mice, while increasing microglial markers.

Effects of early-life stress and sex on blood-brain barrier permeability and integrity in juvenile and adult rats

Early-life stress (ELS) is considered a relevant etiological factor for neurodegenerative and mental disorders. In the present study, we hypothesized that ELS may persistently and sex dependently influence blood-brain barrier (BBB) integrity and function during critical periods of brain development and consequently determine susceptibility to and sex-related prevalence of chronic diseases in adult life. We used the maternal separation (MS) procedure in rats to model ELS and evaluated BBB permeability and gene expression of selected tight junction (TJ) proteins, glucose transporter type 1 (Slc2a1) and aquaporin 4 (Aqp4) in the medial prefrontal cortex (mPFC), dorsal striatum (dSTR) and hippocampus of juvenile and adult rats. Serum concentrations of a peripheral marker of BBB function (S100β) and proinflammatory cytokines were also assessed. We observed developmental sealing of the BBB and sex differences in the permeability of the BBB and the mRNA expression of TJ proteins and Slc2a1. Adult females showed lower BBB permeability and higher levels of Cldn3, Cldn5, Ocln, and Slc2a1 in the mPFC and dSTR than males. MS temporarily increased BBB permeability in the dSTR of juvenile males and affected mRNA expression of the majority of studied proteins related to BBB function in age-, region- and sex-dependent manners. Additionally, MS sex dependently decreased serum S100β levels and did not affect proinflammatory cytokine concentrations. In general, our study did not reveal a clear or strong negative effect of MS on BBB integrity. However, the results suggest that ELS may induce adaptive/maladaptive changes or compensatory mechanisms within the BBB of unknown yet consequences.

Glia Not Neurons: Uncovering Brain Dysmaturation in a Rat Model of Alzheimer's Disease

Sporadic Alzheimer's disease (AD) is a severe disorder of unknown etiology with no definite time frame of onset. Recent studies suggest that middle age is a critical period for the relevant pathological processes of AD. Nonetheless, sufficient data have accumulated supporting the hypothesis of "neurodevelopmental origin of neurodegenerative disorders": prerequisites for neurodegeneration may occur during early brain development. Therefore, we investigated the development of the most AD-affected brain structures (hippocampus and prefrontal cortex) using an immunohistochemical approach in senescence-accelerated OXYS rats, which are considered a suitable model of the most common-sporadic-type of AD. We noticed an additional peak of neurogenesis, which coincides in time with the peak of apoptosis in the hippocampus of OXYS rats on postnatal day three. Besides, we showed signs of delayed migration of neurons to the prefrontal cortex as well as disturbances in astrocytic and microglial support of the hippocampus and prefrontal cortex during the first postnatal week. Altogether, our results point to dysmaturation during early development of the brain-especially insufficient glial support-as a possible "first hit" leading to neurodegenerative processes and AD pathology manifestation later in life.

Venlafaxine and L-Thyroxine Treatment Combination: Impact on Metabolic and Synaptic Plasticity Changes in an Animal Model of Coexisting Depression and Hypothyroidism

The clinical effectiveness of supportive therapy with thyroid hormones in drug-resistant depression is well-known; however, the mechanisms of action of these hormones in the adult brain have not been fully elucidated to date. We determined the effects of venlafaxine and/or L-thyroxine on metabolic parameters and markers involved in the regulation of synaptic plasticity and cell damage in an animal model of coexisting depression and hypothyroidism, namely, Wistar Kyoto rats treated with propylthiouracil. In this model, in relation to the depression model itself, the glycolysis process in the brain was weakened, and a reduction in pyruvate dehydrogenase in the frontal cortex was normalized only by the combined treatment with L-thyroxine and venlafaxine, whereas changes in pyruvate and lactate levels were affected by all applied therapies. None of the drugs improved the decrease in the expression of mitochondrial respiratory chain enzymes. No intensification of glucocorticoid action was shown, while an unfavorable change caused by the lack of thyroid hormones was an increase in the caspase-1 level, which was not reversed by venlafaxine alone. The results indicated that the combined administration of drugs was more effective in normalizing glycolysis and the transition to the Krebs cycle than the use of venlafaxine or L-thyroxine alone.

Neuroplasticity: A Key Player in the Antidepressant Action of Chinese Herbal Medicine

Traditional Chinese medicine (TCM) is a systematic medicine. It provides alternative strategies for the treatment of depression with its clinical experience, comprehensive diagnosis, and treatment theory. Chinese herbal medicine (CHM) is the major form of TCM prescription, and numerous CHMs have been demonstrated to possess remarkable antidepressant-like properties. A diversity of mechanisms have been implicated in CHM-associated antidepressant property. This paper reviewed the neuroplastic mechanisms underlying the antidepressant actions of CHM, finding that CHM repairs neuroplasticity by improving neurogenesis, neurotrophic factors, synaptic spine morphology, cell signaling, glutamatergic system, monoamine neurotransmitters, and neural apoptosis. CHM thereby exerts an antidepressant effect, attempting to offer a better understanding of the mechanisms implicated in TCM-related antidepressant-like efficacy and laying a foundation for the scientific evaluation and development of TCM in treating depression.

A Search for Biomarkers of Early-life Stress-related Psychopathology: Focus on 70-kDa Heat Shock Proteins

Clinical studies clearly indicate that early-life stress (ELS) may cause physical and mental health problems later in life. Therefore, the identification of universal biomarkers of ELS-related diseases is very important. The 70-kDa heat shock proteins (HSP70s), specifically HSPA5 and HSPA1B, have been recently shown to be potentially associated with occurrence of anxiety, mood disorders, and schizophrenia; thus, we hypothesized that HSP70s are potential candidate biomarkers of ELS-induced psychopathologies. A maternal separation (MS) procedure in rats was used to model ELS, and the expression of HSPA5 and HSPA1B was investigated in the blood, medial prefrontal cortex (mPFC), and hippocampus of juvenile, preadolescent, and adult animals. We also studied the effects of MS on the long-term potentiation (LTP) and behavioral phenotypes of adult rats. We found that MS enhanced the expression of HSPA1B mRNA in the blood and mPFC of juvenile and preadolescent rats. This increase was accompanied by an increase in the HSPA1A/1B protein levels in the mPFC and hippocampus of juvenile rats that persisted in the mPFC until adulthood. MS juvenile and adult rats showed enhanced HSPA5 mRNA expression in the blood and increased HSPA5 protein expression in the mPFC (juveniles) and hippocampus (adults). Concurrently, MS adult rats exhibited aberrations in LTP in the mPFC and hippocampus and a less anxious behavioral phenotype. These results indicate that MS may produce enduring overexpression of HSPA1B and HSPA5 in the brain and blood. Therefore, both HSP70 family members may be potential candidate peripheral and brain biomarkers of ELS-induced changes in brain functioning.

Sex-dependent and ontogenetic effects of low dose ethanol on social behavioral deficits induced by mouse maternal separation

Early life stress can induce lifelong emotional and social behavioral deficits that may in some cases be alleviated by drugs or alcohol. A model for early life stress, rodent maternal separation, recapitulates these behavioral sequelae, which are not limited to potentiated anxiety-like behavior, attenuated social motivation, and altered reward-seeking. Here we employed mouse maternal separation with early weaning (MSEW), consisting of pup-dam separation lasting 4-8 hours on postnatal days (PD) 2-16, with early weaning on PD 17. Prior MSEW studies have limited subjects by age or sex, so we more comprehensively investigated MSEW effects in both sexes, during adolescence and adulthood. We found universal effects of MSEW to include lifelong enhancement of anxiety-like and despair behavior, as well as deficits in social motivation. We also observed some sex-dependent effects of MSEW, namely that female MSEW mice exhibited social habituation to a greater degree than their male counterparts. Low dose ethanol administration had no major effects on the social behavior of non-stressed mice. But interestingly, MSEW-induced social habituation was counteracted by low dose ethanol in adolescent female mice, and potentiated in adolescent male mice. These effects were absent in adult animals, suggesting that ethanol may exert differential effects on the developing brain in such a manner to produce age-, sex-, and stress-dependent effects upon social behavior. Together, results indicate that MSEW reliably produces long-lasting impairments in emotional and social behaviors in both sexes and across the lifespan, but may exert more salient social behavioral effects on female animals.

Social defeat stress in adult mice causes alterations in gene expression, alternative splicing, and the epigenetic landscape of H3K4me3 in the prefrontal cortex: An impact of early-life stress

Chronic stress is the leading risk factor of a broad range of severe psychopathologies. Nonetheless, the molecular mechanisms triggering these pathological processes are not well understood. In our study, we investigated the effects of 15-day social defeat stress (SDS) on the genome-wide landscape of trimethylation at the 4th lysine residue of histone H3 (H3K4me3) and on the transcriptome in the prefrontal cortex of mice that were reared normally (group SDS) or subjected to maternal separation early in life (group MS+SDS). The mice with the history of stress early in life showed increased susceptibility to SDS in adulthood and demonstrated long-lasting genome-wide alterations in gene expression and splicing as well as in the H3K4me3 epigenetic landscape in the prefrontal cortex. Thus, the high-throughput techniques applied here allowed us to simultaneously detect, for the first time, genome-wide epigenetic and transcriptional changes in the murine prefrontal cortex that are associated with both chronic SDS and increased susceptibility to this stressor.

Maternal separation increases cocaine intake through a mechanism involving plasticity in glutamate signalling

Early-life stress (ELS) is associated with negative consequences, including maladaptive long-lasting brain effects. These alterations seem to increase the likelihood of developing substance use disorders. However, the molecular consequences of ELS are poorly understood. In the present study, we tested the impact of ELS induced by maternal separation with early weaning (MSEW) in CD1 male mice at different phases of cocaine self-administration (SA). We also investigated the subsequent alterations on GluR2, GluR1, cAMP response element-binding (CREB), and CREB-phosphorylation (pCREB) in ventral tegmental area (VTA) and nucleus accumbens (NAc) induced by both MSEW and cocaine SA. Our results show that MSEW animals expressed a higher cocaine intake, an increased vulnerability to the acquisition of cocaine SA, and incapacity to extinguish cocaine SA behaviour. MSEW mice showed decreased GluR2 and increased GluR1 and pCREB in NAc. Also, results displayed reduction of basal levels of GluR1 and CREB and an elevation of GluR1/GluR2 ratio in the VTA. Such results hint at an enhanced glutamatergic function in NAc and increased excitability of VTA DA neurons in maternally separated mice. Altogether, our results suggest that MSEW induces molecular alterations in the brain areas related to reward processing, increasing the vulnerability to depression and cocaine-seeking behaviour.

The burden of early life stress on the nociceptive system development and pain responses

For a long time, the capacity of the newborn infant to feel pain was denied. Today it is clear that the nociceptive system, even if still immature, is functional enough in the newborn infant to elicit pain responses. Unfortunately, pain is often present in the neonatal period, in particular in the case of premature infants which are subjected to a high number of painful procedures during care. These are accompanied by a variety of environmental stressors, which could impact the maturation of the nociceptive system. Therefore, the question of the long-term consequences of early life stress is a critical question. Early stressful experience, both painful and non-painful, can imprint the nociceptive system and induce long-term alteration in brain function and nociceptive behavior, often leading to an increase sensitivity and higher susceptibility to chronic pain. Different animal models have been developed to understand the mechanisms underlying the long-term effects of different early life stressful procedures, including pain and maternal separation. This review will focus on the clinical and preclinical data about early life stress and its consequence on the nociceptive system.

Trajectories of Mother-Infant Communication: An Experiential Measure of the Impacts of Early Life Adversity

Caretaking stability in the early life environment supports neurobehavioral development, while instability and neglect constitute adverse environments that can alter maturational processes. Research in humans suggests that different types of early life adversity (ELA) can have differential effects on caretaker relationships and later cognitive and social development; however, identifying mechanistic underpinnings will require animal models with translational validity. Two common rodent models, maternal separation (MS) and limited bedding (LB), influence the mother-infant relationship during a critical window of development. We hypothesized that these paradigms may affect the development of communication strategies on the part of the pup. Ultrasonic vocalizations (USVs) are a care-eliciting mechanism and ethologically relevant response to stressors in the rat pup. USV emission rates and acoustic parameters change throughout early development, presenting the opportunity to define developmental milestones in USVs that would reflect neurobehavioral aberrations if disrupted. This study investigated the effects of MS or LB on the dam-pup relationship by quantifying pup USVs, maternal behavior, and the relationship between the two. First, we used a generalized additive model approach to establish typical developmental trajectories of USV acoustic properties and determine windows of change in MS or LB rearing. Additionally, we quantified maternal behaviors and the predictability of maternal care sequences using an entropy rate calculation. MS and LB each shifted the developmental trajectories of USV acoustic parameters and call types in a sex-specific manner. MS more often impacted male USVs, while LB impacted female USVs. MS dams spent more time passive nursing, and LB dams spent more time on the nest. The predictability of maternal care was associated with the rate of USV emissions exclusively in females. Taken together, findings demonstrate sex- and model-specific effects of rearing environments on a novel developmental trajectory involving the mother-infant relationship, facilitating the translation of animal ELA paradigms to assess later-life consequences.

Psychosocial Crowding Stress-Induced Changes in Synaptic Transmission and Glutamate Receptor Expression in the Rat Frontal Cortex

This study demonstrates how exposure to psychosocial crowding stress (CS) for 3, 7, and 14 days affects glutamate synapse functioning and signal transduction in the frontal cortex (FC) of rats. CS effects on synaptic activity were evaluated in FC slices of the primary motor cortex (M1) by measuring field potential (FP) amplitude, paired-pulse ratio (PPR), and long-term potentiation (LTP). Protein expression of GluA1, GluN2B mGluR1a/5, VGLUT1, and VGLUT2 was assessed in FC by western blot. The body’s response to CS was evaluated by measuring body weight and the plasma level of plasma corticosterone (CORT), adrenocorticotropic hormone (ACTH), and interleukin 1 beta (IL1B). CS 3 14d increased FP and attenuated LTP in M1, while PPR was augmented in CS 14d. The expression of GluA1, GluN2B, and mGluR1a/5 was up-regulated in CS 3d and downregulated in CS 14d. VGLUTs expression tended to increase in CS 7d. The failure to blunt the effects of chronic CS on FP and LTP in M1 suggests the impairment of habituation mechanisms by psychosocial stressors. PPR augmented by chronic CS with increased VGLUTs level in the CS 7d indicates that prolonged CS exposure changed presynaptic signaling within the FC. The CS bidirectional profile of changes in glutamate receptors’ expression seems to be a common mechanism evoked by stress in the FC.

Long term effects of early life stress on HPA circuit in rodent models

Adaptation to environmental challenges represents a critical process for survival, requiring the complex integration of information derived from both external cues and internal signals regarding current conditions and previous experiences. The Hypothalamic-pituitary-adrenal axis plays a central role in this process inducing the activation of a neuroendocrine signaling cascade that affects the delicate balance of activity and cross-talk between areas that are involved in sensorial, emotional, and cognitive processing such as the hippocampus, amygdala, Prefrontal Cortex, Ventral Tegmental Area, and dorsal raphe. Early life stress, especially early critical experiences with caregivers, influences the functional and structural organization of these areas, affects these processes in a long-lasting manner and may result in long-term maladaptive and psychopathological outcomes, depending on the complex interaction between genetic and environmental factors. This review summarizes the results of studies that have modeled this early postnatal stress in rodents during the first 2 postnatal weeks, focusing on the long-term effects on molecular and structural alteration in brain areas involved in Hypothalamic-pituitary-adrenal axis function. Moreover, a brief investigation of epigenetic mechanisms and specific genetic targets mediating the long-term effects of these early environmental manipulations and at the basis of differential neurobiological and behavioral effects during adulthood is provided.

Role of Polyinosinic:Polycytidylic Acid-Induced Maternal Immune Activation and Subsequent Immune Challenge in the Behaviour and Microglial Cell Trajectory in Adult Offspring: A Study of the Neurodevelopmental Model of Schizophrenia

Multiple lines of evidence support the pathogenic role of maternal immune activation (MIA) in the occurrence of the schizophrenia-like disturbances in offspring. While in the brain the homeostatic role of neuron-microglia protein systems is well documented, the participation of the CX3CL1-CX3CR1 and CD200-CD200R dyads in the adverse impact of MIA often goes under-recognized. Therefore, in the present study, we examined the effect of MIA induced by polyinosinic:polycytidylic acid (Poly I:C) on the CX3CL1-CX3CR1 and CD200-CD200R axes, microglial trajectory (MhcII, Cd40, iNos, Il-1β, Tnf-α, Il-6, Arg1, Igf-1, Tgf-β and Il-4), and schizophrenia-like behaviour in adult male offspring of Sprague-Dawley rats. Additionally, according to the “two-hit” hypothesis of schizophrenia, we evaluated the influence of acute challenge with Poly I:C in adult prenatally MIA-exposed animals on the above parameters. In the present study, MIA evoked by Poly I:C injection in the late period of gestation led to the appearance of schizophrenia-like disturbances in adult offspring. Our results revealed the deficits manifested as a diminished number of aggressive interactions, presence of depressive-like episodes, and increase of exploratory activity, as well as a dichotomy in the sensorimotor gating in the prepulse inhibition (PPI) test expressed as two behavioural phenotypes (MIA_PPI-low and MIA_PPI-high). Furthermore, in the offspring rats subjected to a prenatal challenge (i.e., MIA) we noticed the lack of modulation of behavioural changes after the additional acute immune stimulus (Poly I:C) in adulthood. The important finding reported in this article is that MIA affects the expression and levels of the neuron-microglia proteins in the frontal cortex and hippocampus of adult offspring. We found that the changes in the CX3CL1-CX3CR1 axis could affect microglial trajectory, including decreased hippocampal mRNA level of MhcII and elevated cortical expression of Igf-1 in the MIA_PPI-high animals and/or could cause the up-regulation of an inflammatory response (Il-6, Tnf-α, iNos) after the “second hit” in both examined brain regions and, at least in part, might differentiate behavioural disturbances in adult offspring. Consequently, the future effort to identify the biological background of these interactions in the Poly I:C-induced MIA model in Sprague-Dawley rats is desirable to unequivocally clarify this issue.

Chronic Lorcaserin Treatment Reverses the Nicotine Withdrawal-Induced Disruptions to Behavior and Maturation in Developing Neurons in the Hippocampus of Rats

Preclinical data have shown that treatment with serotonin (5-HT)_2C receptor agonists inhibits the behavioral effects of nicotine, including self-administration, reinstatement, and locomotor responses to nicotine. Since the data on the effects of 5-HT_2C receptor agonism on nicotine withdrawal signs are limited, we aimed to investigate whether 5-HT_2C receptor agonism alleviated the behavioral and neurobiochemical (hippocampal neurogenesis) consequences of nicotine withdrawal in Sprague-Dawley rats. Our data indicate that withdrawal from nicotine self-administration induced locomotor hyperactivity, lengthened immobility time (the forced swim test), induced ‘drug-seeking’ behavior and deficits in cognition-like behavior (the novel object recognition task). A two-week exposure to the 5-HT_2C receptor agonist lorcaserin attenuated locomotor hyperactivity and induced recovery from depression-like behavior. Analyses of brain slices from nicotine-withdrawn animals revealed that lorcaserin treatment recovered the reduced number of doublecortin (DCX)-positive cells, but it did not affect the number of K_i-67- or 5-bromo-2’-deoxyuridine (BrdU)-positive cells or the maturation of proliferating neurons in drug-weaned rats. To summarize, we show that lorcaserin alleviated locomotor responses and depression-like state during nicotine withdrawal. We propose that the modulatory effect of lorcaserin on the ‘affective’ aspects of nicotine cessation may be linked to the positive changes caused by the compound in hippocampal neurogenesis during nicotine withdrawal.

Long-term Effects of Maternal Separation on Anxiety-Like Behavior and Neuroendocrine Parameters in Adult Balb/c Mice

Introduction: Disruption of maternal care using maternal separation (MS) models has provided significant evidence of the deleterious long-term effects of early life stress. Several preclinical studies investigating MS showed multiple behavioral and biomolecular alterations. However, there is still conflicting results from MS studies, which represents a challenge for reliability and replicability of those findings. Objective: To address that, this study was conducted to investigate whether MS would affect anxiety-like behaviors using a battery of classical tasks, as well as central and peripheral stress-related biomarkers. Methods: Male Balb/c mice were exposed to MS from postnatal day (PND) 2 to 14 for 180-min per day. Two independent cohorts were performed to evaluate both baseline and anxiety-like behavior responses to MS at PND60. We performed composite scores to evaluate MS effects on anxiety and risk assessment phenotypes. Also, we assessed mRNA gene expression in the medial pre-frontal cortex (mPFC) of glucocorticoid and mineralocorticoid receptors (GR and MR) using real-time PCR and peripheral corticosterone levels (CORT) to investigate possible neurobiological correlates to anxiety behaviors. Results: We found increased anxiety-like behavior and decreased risk assessment and exploratory behaviors in MS mice. The animals exposed to MS also presented a decrease in MR mRNA expression and higher levels of CORT compared to controls. Conclusions: Our findings reinforce the body of evidence suggesting that long-term MS induces effects on anxiety and risk assessment phenotypes following the exposure to a standardized MS protocol. Moreover, MS affected the expression of MR mRNA and induced significant changes on CORT response. This data highlights that the reprograming MS effects on HPA axis could be mediate by MR gene expression in mPFC and chronic overactivity of peripheral CORT levels.

Long-Term Decreases in the Expression of Calcineurin and GABAA Receptors Induced by Early Maternal Separation Are Associated with Increased Anxiety-Like Behavior in Adult Male Rats

INTRODUCTION

Early life stress is a well-described risk factor of anxiety disorders in adulthood. Dysfunction in GABA/glutamate receptors and their functional regulator, calcineurin, is linked to anxiety disorders. Here, we investigated the effect of early life stress, such as repeated maternal separation (MS; 3 h per day from postnatal day [P] 2 to 11), on changes in the expression of calcineurin as well as the ionotropic glutamatergic and GABAergic receptors including α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), N-methyl-D-aspartate (NMDA) and GABAA receptors in the hippocampus and prefrontal cortex (PFC) of adolescent (P35) and adult (P62) male Wistar rats and their correlations with anxiety-like behavior in adulthood.

METHODS

The protein levels were assessed by Western blot analysis. Anxiety-like behavior was measured in the elevated plus maze (EPM) and open field (OF) tests.

RESULTS

MS induced a regional transient decrease of glutamate receptors expression at P35, with decreased NMDA and AMPA receptor levels, respectively, in the hippocampus and PFC, suggesting a possible decrease in excitatory synaptic strength. In contrast to glutamate receptors, MS had long-lasting influence on GABAA receptor and calcineurin levels, with reduced expression of GABAA receptor and calcineurin in both brain regions at P35 that continued into adulthood. These results were accompanied by increased anxiety behavior in adulthood, shown by lower percentage of number of total entries and time spent in the open arms of the EPM, and by lower time spent and number of entries in the OF central area.

CONCLUSIONS

Together, our study suggests that GABAA receptors via calcineurin-dependent signaling pathways may play an important role in the expression of stress-induced anxiety-like behavior.

Negative relationship between brain α1A-AR neurotransmission and βArr2 levels in anxious adolescent rats subjected to early life stress

Early-life stress is correlated with the development of anxiety-related behavior in adolescence, but underlying mechanisms remain poorly known. The α_1A-adrenergic receptor (AR) is linked to mood regulation and its function is assumed to be regulated by β-arrestins (βArrs) via desensitization and downregulation. Here, we investigated correlation between changes in α_1A-AR and βArr2 levels in the prefrontal cortex (PFC) and hippocampus of adolescent and adult male rats subjected to maternal separation (MS) and their relationship with anxiety-like behavior in adolescence. MS was performed 3 h per day from postnatal days 2-11 and anxiety-like behavior was evaluated in the elevated plus-maze and open field tests. The protein levels were examined using western blot assay. MS decreased α_1A-AR expression and increased βArr2 expression in both brain regions of adolescent rats, while induced reverse changes in adulthood. MS adolescent rats demonstrated higher anxiety-type behavior and lower activity in behavioral tests than controls. Decreased α_1A-AR levels in MS adolescence strongly correlated with reduced time spent in the open field central area, consistent with increased anxiety-like behavior. An anxiety-like phenotype was mimicked by acute and chronic treatment of developing rats with prazosin, an α_1A-AR antagonist, suggesting α_1A-AR downregulation may facilitate anxiety behavior in MS adolescent rats. Together, our results indicate a negative correlation between α_1A-AR neurotransmission and βArr2 levels in both adults and anxious-adolescent rats and suggest that increased βArr2 levels may contribute to posttranslational regulation of α_1A-AR and modulation of anxiety-like behavior in adolescent rats. This may provide a path to develop more effective anxiolytic treatments.

Age-dependent shift in spontaneous excitation-inhibition balance of infralimbic prefrontal layer II/III neurons is accelerated by early life stress, independent of forebrain mineralocorticoid receptor expression

In this study we tested the hypothesis i) that age-dependent shifts in the excitation-inhibition balance of prefrontal neurons are accelerated by early life stress, a risk factor for the etiology of many psychiatric disorders; and if so, ii) that this process is exacerbated by genetic forebrain-specific downregulation of the mineralocorticoid receptor, a receptor that was earlier found to be a protective factor for negative effects of early life stress in both rodents and humans. In agreement with the literature, an age-dependent downregulation of the excitation-inhibition balance was found both with regard to spontaneous and evoked synaptic currents. The age-dependent shift in spontaneous excitatory relative to inhibitory currents was significantly accelerated by early life stress, but this was not exacerbated by reduction in mineralocorticoid receptor expression. The age-dependent changes in the excitation-inhibition balance were mirrored by similar changes in receptor subunit expression and morphological alterations, particularly in spine density, which could thus potentially contribute to the functional changes. However, none of these parameters displayed acceleration by early life stress, nor depended on mineralocorticoid receptor expression. We conclude that, in agreement with the hypothesis, early life stress accelerates the developmental shift of the excitation-inhibition balance but, contrary to expectation, there is no evidence for a putative protective role of the mineralocorticoid receptor in this system. In view of the modest effect of early life stress on the excitation-inhibition balance, alternative mechanisms potentially underlying the development of psychiatric disorders should be further explored.

Corticotropin-releasing factor infusion in the bed nucleus of the stria terminalis of lactating mice alters maternal care and induces behavioural phenotypes in offspring

The peripartum period is accompanied by numerous physiological and behavioural adaptations organised by the maternal brain. These changes are essential for adequate expression of maternal behaviour, thereby ensuring proper development of the offspring. The corticotropin-releasing factor (CRF) plays a key role in a variety of behaviours accompanying stress, anxiety, and depression. There is also evidence that CRF contributes to maladaptations during the peripartum period. We investigated the effects of CRF in the bed nucleus of the stria terminalis (BNST) of lactating mice during maternal care and analysed locomotor activity and anxiety-like behaviour in the offspring. The BNST has been implicated in anxiety behaviour and regulation of the stress response. The effects of intra-BNST CRF administration were compared with those induced by the limited bedding (LB) procedure, a model that produces altered maternal behaviour. BALB/cJ dams were exposed to five infusions of CRF or saline into the BNST in the first weeks after birth while the LB dams were exposed to limited nesting material from postnatal days (P) 2–9. Maternal behaviour was recorded in intercalated days, from P1-9. Offspring anxiety-like behaviour was assessed during adulthood using the open-field, elevated plus-maze, and light/dark tests. Both intra-BNST CRF and LB exposure produced altered maternal care, represented by decreased arched-back nursing and increased frequency of exits from the nest. These changes in maternal care resulted in robust sex-based differences in the offspring’s behavioural responses during adulthood. Females raised by CRF-infused dams exhibited increased anxiety-like behaviour, whereas males presented a significant decrease in anxiety. On the other hand, both males and females raised by dams exposed to LB showed higher locomotor activity. Our study demonstrates that maternal care is impaired by intra-BNST CRF administrations, and these maladaptations are similar to exposure to adverse early environments. These procedures, however, produce distinct phenotypes in mice during young adulthood and suggest sex-based differences in the susceptibility to poor maternal care.

Repeated maternal separation causes transient reduction in BDNF expression in the medial prefrontal cortex during early brain development, affecting inhibitory neuron development

It is widely accepted that maternal separation (MS) induces stress in children and disrupts neural circuit formation during early brain development. Even though such disruption occurs transiently early in life, its influence persists after maturation, and could lead to various neurodevelopmental disorders. Our recent study revealed that repeated MS reduces the number of inhibitory neurons and synapses in the medial prefrontal cortex (mPFC) and causes mPFC-related social deficits after maturation. However, how MS impedes mPFC development during early brain development remains poorly understood. Here, we focused on brain-derived neurotrophic factor (BDNF) involved in the development of inhibitory neurons, and examined time-dependent BDNF expression in the mPFC during the pre-weaning period in male rats exposed to MS. Our results show that MS attenuates BDNF expression only around the end of the first postnatal week. Likewise, mRNA expression of activity-regulated cytoskeleton-associated protein (Arc), an immediate-early gene whose expression is partly regulated by BDNF, also decreased in the MS group along with the reduction in BDNF expression. On the contrary, mRNA expression of tropomyosin-related kinase B (TrkB), which is a BDNF receptor, was scarcely altered, while its protein expression decreased in the MS group only during the weaning period. In addition, MS reduced mRNA levels of glutamic acid decarboxylase (GAD) 65, a GABA synthesizing enzyme, only during the weaning period. Our results suggest that repeated MS temporarily attenuates BDNF signaling in the mPFC during early brain development. BDNF plays a crucial role in the development of inhibitory neurons; therefore, transient attenuation of BDNF signaling may cause delays in GABAergic neuron development in the mPFC.

The prenatal challenge with lipopolysaccharide and polyinosinic:polycytidylic acid disrupts CX3CL1-CX3CR1 and CD200-CD200R signalling in the brains of male rat offspring: a link to schizophrenia-like behaviours

BACKGROUND

The bidirectional communication between neurons and microglia is fundamental for the homeostasis and biological function of the central nervous system. Maternal immune activation (MIA) is considered to be one of the factors affecting these interactions. Accordingly, MIA has been suggested to be involved in several neuropsychiatric diseases, including schizophrenia. The crucial regulatory systems for neuron-microglia crosstalk are the CX3CL1-CX3CR1 and CD200-CD200R axes.

METHODS

We aimed to clarify the impact of MIA on CX3CL1-CX3CR1 and CD200-CD200R signalling pathways in the brains of male Wistar rats in early and adult life by employing two neurodevelopmental models of schizophrenia based on the prenatal challenge with lipopolysaccharide (LPS) and polyinosinic:polycytidylic acid (Poly I:C). We also examined the effect of MIA on the expression of microglial markers and the profile of cytokines released in the brains of young offspring, as well as the behaviour of adult animals. Moreover, we visualized the localization of ligand-receptor systems in the hippocampal regions (CA1, CA3 and DG) and the frontal cortex of young rats exposed to MIA. The differences between groups were analysed using Student's t test.

RESULTS

We observed that MIA altered developmental trajectories in neuron-microglia communication in the brains of young offspring, as evidenced by the disruption of CX3CL1-CX3CR1 and/or CD200-CD200R axes. Our data demonstrated the presence of abnormalities after LPS-induced MIA in levels of Cd40, Il-1β, Tnf-α, Arg1, Tgf-β and Il-10, as well as IBA1, IL-1β and IL-4, while after Poly I:C-generated MIA in levels of Cd40, iNos, Il-6, Tgf-β, Il-10, and IBA1, IL-1β, TNF-α, IL-6, TGF-β and IL-4 early in the life of male animals. In adult male rats that experienced prenatal exposure to MIA, we observed behavioural changes resembling a schizophrenia-like phenotype.

CONCLUSIONS

Our study provides evidence that altered CX3CL1-CX3CR1 and/or CD200-CD200R pathways, emerging after prenatal immune challenge with LPS and Poly I:C, might be involved in the aetiology of schizophrenia.

Maternal Immune Activation Sensitizes Male Offspring Rats to Lipopolysaccharide-Induced Microglial Deficits Involving the Dysfunction of CD200-CD200R and CX3CL1-CX3CR1 Systems

Early life challenges resulting from maternal immune activation (MIA) may exert persistent effects on the offspring, including the development of psychiatric disorders, such as schizophrenia. Recent evidence has suggested that the adverse effects of MIA may be mediated by neuron-microglia crosstalk, particularly CX3CL1-CX3CR1 and CD200-CD200R dyads. Therefore, the present study assessed the behavioural parameters resembling schizophrenia-like symptoms in the adult male offspring of Sprague-Dawley rats that were exposed to MIA and to an additional acute lipopolysaccharide (LPS) challenge in adulthood, according to the "two-hit" hypothesis of schizophrenia. Simultaneously, we aimed to clarify the role of the CX3CL1-CX3CR1 and CD200-CD200R axes and microglial reactivity in the brains of adult offspring subjected to MIA and the "second hit" wit LPS. In the present study, MIA generated a range of behavioural changes in the adult male offspring, including increased exploratory activity and anxiety-like behaviours. The most intriguing finding was observed in the prepulse inhibition (PPI) test, where the deficit in the sensorimotor gating was age-dependent and present only in part of the rats. We were able to distinguish the occurrence of two groups: responsive and non-responsive (without the deficit). Concurrently, based on the results of the biochemical studies, MIA disrupted mainly the CD200-CD200R system, while the changes of the CX3CL1-CX3CR1 axis were less evident in the frontal cortex of adult non-responsive offspring. MIA markedly affected the immune regulators of the CD200-CD200R pathway as we observed an increase in cortical IL-6 release in the responsive group and IL-4 in the non-responsive offspring. Importantly, the "second hit" generated disturbances at the behavioural and biochemical levels mostly in the non-responsive adult animals. Those offspring were characterized both by disturbed PPI and "priming" microglia. Altogether, the exposure to MIA altered the immunomodulatory mechanisms, including the CD200-CD200R axis, in the brain and sensitized animals to subsequent immunological challenges, leading to the manifestation of schizophrenia-like alterations.

Imipramine Ameliorates Depressive Symptoms by Blocking Differential Alteration of Dendritic Spine Structure in Amygdala and Prefrontal Cortex of Chronic Stress-Induced Mice

Previous studies have shown disrupted synaptic plasticity and neural activity in depression. Such alteration is strongly associated with disrupted synaptic structures. Chronic stress has been known to induce changes in dendritic structure in the basolateral amygdala (BLA) and medial prefrontal cortex (mPFC), but antidepressant effect on structure of these brain areas has been unclear. Here, the effects of imipramine on dendritic spine density and morphology in BLA and mPFC subregions of stressed mice were examined. Chronic restraint stress caused depressive-like behaviors such as enhanced social avoidance and despair level coincident with differential changes in dendritic spine structure. Chronic stress enhanced dendritic spine density in the lateral nucleus of BLA with no significant change in the basal nucleus of BLA, and altered the proportion of stubby or mushroom spines in both subregions. Conversely, in the apical and basal mPFC, chronic stress caused a significant reduction in spine density. The proportion of stubby or mushroom spines in these subregions overall reduced while the proportion of thin spines increased after repeated stress. Interestingly, most of these structural alterations by chronic stress were reversed by imipramine. In addition, structural changes caused by stress and blocking the changes by imipramine were corelated well with altered activation and expression of synaptic plasticity-promoting molecules such as phospho-CREB, phospho-CAMKII, and PSD-95. Collectively, our data suggest that imipramine modulates stress-induced changes in synaptic structure and synaptic plasticity-promoting molecules in a coordinated manner although structural and molecular alterations induced by stress are distinct in the BLA and mPFC.

How Early Life Adversity Influences Defensive Circuitry

Childhood maltreatment increases the likelihood of developing anxiety disorders in humans. Early life adversity (ELA) paradigms in rodents produce lasting increases in avoidant and inhibitory responses to both immediate and nonspecific threats, collectively referred to as defensive behaviors. This approach provides an opportunity to thoroughly investigate the underlying mechanisms, an effort that is currently under way. In this review, we consider the growing literature indicating that ELA alters the rhythmic firing of neurons in brain regions associated with defensive behavior, as well as potential neuronal, glial, and extracellular matrix contributions to functional changes in this circuitry. We also consider how ELA studies in rodents may inform us about both susceptible and resilient outcomes in humans.

Maternal Separation Early in Life Alters the Expression of Genes Npas4 and Nr1d1 in Adult Female Mice: Correlation with Social Behavior

Early-life stress affects neuronal plasticity of the brain regions participating in the implementation of social behavior. Our previous studies have shown that brief and prolonged separation of pups from their mothers leads to enhanced social behavior in adult female mice. The goal of the present study was to characterize the expression of genes (which are engaged in synaptic plasticity) Egr1, Npas4, Arc, and Homer1 in the prefrontal cortex and dorsal hippocampus of adult female mice with a history of early-life stress. In addition, we evaluated the expression of stress-related genes: glucocorticoid and mineralocorticoid receptors (Nr3c1 and Nr3c2) and Nr1d1, which encodes a transcription factor (also known as REVERBα) modulating sociability and anxiety-related behavior. C57Bl/6 mice were exposed to either maternal separation (MS, 3 h once a day) or handling (HD, 15 min once a day) on postnatal days 2 through 14. In adulthood, the behavior of female mice was analyzed by some behavioral tests, and on the day after the testing of social behavior, we measured the gene expression. We found increased Npas4 expression only in the prefrontal cortex and higher Nr1d1 expression in both the prefrontal cortex and dorsal hippocampus of adult female mice with a history of MS. The expression of the studied genes did not change in HD female mice. The expression of stress-related genes Nr3c1 and Nr3c2 was unaltered in both groups. We propose that the upregulation of Npas4 and Nr1d1 in females with a history of early-life stress and the corresponding enhancement of social behavior may be regarded as an adaptation mechanism reversing possible aberrations caused by early-life stress.

Early Adversity and the Neotenous Human Brain

Human brain development is optimized to learn from environmental cues. The protracted development of the cortex and its connections with subcortical targets has been argued to permit more opportunity for acquiring complex behaviors. This review uses the example of amygdala-medial prefrontal cortex circuitry development to illustrate a principle of human development-namely, that the extension of the brain's developmental timeline allows for the (species-expected) collaboration between child and parent in co-construction of the human brain. The neurobiology underlying affective learning capitalizes on this protracted timeline to develop a rich affective repertoire in adulthood. Humans are afforded this luxuriously slow development in part by the extended period of caregiving provided by parents, and parents aid in scaffolding the process of maturation during childhood. Just as adequate caregiving is a potent effector of brain development, so is adverse caregiving, which is the largest environmental risk factor for adult mental illness. There are large individual differences in neurobiological outcomes following caregiving adversity, indicating that these pathways are probabilistic, rather than deterministic, and prolonged plasticity in human brain development may also allow for subsequent amelioration by positive experiences. The extant research indicates that the development of mental health cannot be considered without consideration of children in the context of their families.

Vulnerable and resilient cognitive performance related to early life stress: The potential mediating role of dopaminergic receptors in the medial prefrontal cortex of adult mice

RATIONALE

Exposure to early life stress (ELS) is known to have pronounced effects on the prefrontal cortex (PFC). However, not all individuals exposed to ELS manifest the same neurobiological and cognitive phenotypes when adults. Dopamine signaling could be a key factor in understanding the effects of stress on PFC-related cognitive function.

OBJECTIVES

We aimed to investigate the differential effects of ELS on cognitive performance of adult mice and the dopaminergic receptors expression in the PFC.

METHODS

BALB/c males were exposed to the maternal separation (MS) procedure and their cognitive performance on the eight-arm radial maze (8-RAM) were assessed during adulthood. For molecular-level assessments, we performed mRNA expression analyses for dopamine receptors-DRD1, DRD2, DRD3-and Hers1 expression in the medial PFC.

RESULTS

While MS produced an overall impairment on 8-RAM, the stressed animals could be divided in two groups based on their performance: those with impaired cognitive performance (vulnerable to maternal separation, V-MS) and those without any impairment (resilient to maternal separation, R-MS). V-MS animals showed increased DRD1 and DRD2 expression in comparison with other groups. Errors on 8-RAM were also positively correlated with DRD1 and DRD2 mRNA expression.

CONCLUSIONS

Our findings suggest a potential role of the dopaminergic system in the programming mechanisms of cognitive vulnerability and resilience related to ELS.