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

Influence of Early-Life Stress on the Excitability of Dynorphin Neurons in the Adult Mouse Dorsal Horn

While early-life adversity has been associated with a higher risk of developing chronic pain in adulthood, the cellular and molecular mechanisms by which chronic stress during the neonatal period can persistently sensitize developing nociceptive circuits remain poorly understood. Here, we investigate the effects of early-life stress (ELS) on synaptic integration and intrinsic excitability in dynorphin-lineage (DYN) interneurons within the adult mouse superficial dorsal horn (SDH), which are important for inhibiting mechanical pain and itch. The administration of neonatal limited bedding between postnatal days (P)2 and P9 evoked sex-dependent effects on spontaneous glutamatergic signaling, as female SDH neurons exhibited a higher amplitude of miniature excitatory postsynaptic currents (mEPSCs) after ELS, while mEPSC frequency was reduced in DYN neurons of the male SDH. Furthermore, ELS decreased the frequency of miniature inhibitory postsynaptic currents selectively in female DYN neurons. As a result, ELS increased the balance of spontaneous excitation versus inhibition (E:I ratio) in mature DYN neurons of the female, but not male, SDH network. Nonetheless, ELS weakened the total primary afferent-evoked glutamatergic drive onto adult DYN neurons selectively in females, without modifying afferent-evoked inhibitory signaling onto the DYN population. Finally, ELS failed to significantly change the intrinsic membrane excitability of mature DYN neurons in either males or females. Collectively, these data suggest that ELS exerts a long-term influence on the properties of synaptic transmission onto DYN neurons within the adult SDH, which includes a reduction in the overall strength of sensory input onto this important subset of inhibitory interneurons. PERSPECTIVE: This study suggests that chronic stress during the neonatal period influences synaptic function within adult spinal nociceptive circuits in a sex-dependent manner. These findings yield new insight into the potential mechanisms by which early-life adversity might shape the maturation of pain pathways in the central nervous system (CNS).

Microglial type I interferon signaling mediates chronic stress-induced synapse loss and social behavior deficits

Inflammation and synapse loss have been associated with deficits in social behavior and are involved in pathophysiology of many neuropsychiatric disorders. Synapse loss, characterized by reduction in dendritic spines can significantly disrupt synaptic connectivity and neural circuitry underlying social behavior. Chronic stress is known to induce loss of spines and dendrites in the prefrontal cortex (PFC), a brain region implicated in social behavior. However, the underlying mechanisms are not well understood. In the present study, we investigated the role of type I Interferon (IFN-I) signaling in chronic unpredictable stress (CUS)-induced synapse loss and behavior deficits in mice. We found increased expression of type I IFN receptor (IFNAR) in microglia following CUS. Conditional knockout of microglial IFNAR in adult mice rescued CUS-induced social behavior deficits and synapse loss. Bulk RNA sequencing data show that microglial IFNAR deletion attenuated CUS-mediated changes in the expression of genes such as Keratin 20 (Krt20), Claudin-5 (Cldn5) and Nuclear Receptor Subfamily 4 Group A Member 1 (Nr4a1) in the PFC. Cldn5 and Nr4a1 are known for their roles in synaptic plasticity. Krt20 is an intermediate filament protein responsible for the structural integrity of epithelial cells. The reduction in Krt20 following CUS presents a novel insight into the potential contribution of cytokeratin in stress-induced alterations in neuroplasticity. Overall, these results suggest that microglial IFNAR plays a critical role in regulating synaptic plasticity and social behavior deficits associated with chronic stress conditions.

Can computational models help elucidate the link between complex trauma and hallucinations?

Recently, a number of predictive coding models have been proposed to account for post-traumatic stress disorder (PTSD)'s symptomatology, including intrusions, flashbacks and hallucinations. These models were usually developed to account for traditional/type-1 PTSD. We here discuss whether these models also apply or can be translated to the case of complex/type-2 PTSD and childhood trauma (cPTSD). The distinction between PTSD and cPTSD is important because the disorders differ in terms of symptomatology and potential mechanisms, how they relate to developmental stages, but also in terms of illness trajectory and treatment. Models of complex trauma could give us insights on hallucinations in physiological/pathological conditions or more generally on the development of intrusive experiences across diagnostic classes.

An enriched environment ameliorates the reduction of parvalbumin-positive interneurons in the medial prefrontal cortex caused by maternal separation early in life

Early child maltreatment, such as child abuse and neglect, is well known to affect the development of social skills. However, the mechanisms by which such an adverse environment interrupts the development of social skills remain unelucidated. Identifying the period and brain regions that are susceptible to adverse environments can lead to appropriate developmental care later in life. We recently reported an excitatory/inhibitory imbalance and low activity during social behavior in the medial prefrontal cortex (mPFC) of the maternal separation (MS) animal model of early life neglect after maturation. Based on these results, in the present study, we investigated how MS disturbs factors related to excitatory and inhibitory neurons in the mPFC until the critical period of mPFC development. Additionally, we evaluated whether the effects of MS could be recovered in an enriched environment after MS exposure. Rat pups were separated from their dams on postnatal days (PDs) 2-20 (twice daily, 3 h each) and compared with the mother-reared control (MRC) group. Gene expression analysis revealed that various factors related to excitatory and inhibitory neurons were transiently disturbed in the mPFC during MS. A similar tendency was found in the sensory cortex; however, decreased parvalbumin (PV) expression persisted until PD 35 only in the mPFC. Moreover, the number of PV+ interneurons decreased in the ventromedial prefrontal cortex (vmPFC) on PD 35 in the MS group. Additionally, perineural net formation surrounding PV+ interneurons, which is an indicator of maturity and critical period closure, was unchanged, indicating that the decreased PV+ interneurons were not simply attributable to developmental delay. This reduction of PV+ interneurons improved to the level observed in the MRC group by the enriched environment from PD 21 after the MS period. These results suggest that an early adverse environment disturbs the development of the mPFC but that these abnormalities allow room for recovery depending on the subsequent environment. Considering that PV+ interneurons in the mPFC play an important role in social skills such as empathy, an early rearing environment is likely a very important factor in the subsequent acquisition of social skills.

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.

Si-Ni-San alleviates early life stress-induced depression-like behaviors in adolescence via modulating Rac1 activity and associated spine plasticity in the nucleus accumbens

Background: Early life stress (ELS) is a major risk factor for depression in adolescents. The nucleus accumbens (NAc) is a key center of the reward system, and spine remodeling in the NAc contributes to the development of depression. The Si-Ni-San formula (SNS) is a fundamental prescription for treating depression in traditional Chinese medicine. However, little is known about the effects of SNS on behavioral abnormalities and spine plasticity in the NAc induced by ELS. Purpose: This study aimed to investigate the therapeutic effect and the modulatory mechanism of SNS on abnormal behaviors and spine plasticity in the NAc caused by ELS. Methods: We utilized a model of ELS that involved maternal separation with early weaning to explore the protective effects of SNS on adolescent depression. Depressive-like behaviors were evaluated by the sucrose preference test, the tail suspension test, and the forced swimming test; anxiety-like behaviors were monitored by the open field test and the elevated plus maze. A laser scanning confocal microscope was used to analyze dendritic spine remodeling in the NAc. The activity of Rac1 was detected by pull-down and Western blot tests. Viral-mediated gene transfer of Rac1 was used to investigate its role in ELS-induced depression-like behaviors in adolescence. Results: ELS induced depression-like behaviors but not anxiety-like behaviors in adolescent mice, accompanied by an increase in stubby spine density, a decrease in mushroom spine density, and decreased Rac1 activity in the NAc. Overexpression of constitutively active Rac1 in the NAc reversed depression-related behaviors, leading to a decrease in stubby spine density and an increase in mushroom spine density. Moreover, SNS attenuated depression-like behavior in adolescent mice and counteracted the spine abnormalities in the NAc induced by ELS. Additionally, SNS increased NAc Rac1 activity, and the inhibition of Rac1 activity weakened the antidepressant effect of SNS. Conclusion: These results suggest that SNS may exert its antidepressant effects by modulating Rac1 activity and associated spine plasticity in the NAc.

Activation of cell-free mtDNA-TLR9 signaling mediates chronic stress-induced social behavior deficits

Inflammation and social behavior deficits are associated with a number of neuropsychiatric disorders. Chronic stress, a major risk factor for depression and other mental health conditions is known to increase inflammatory responses and social behavior impairments. Disturbances in mitochondria function have been found in chronic stress conditions, however the mechanisms that link mitochondrial dysfunction to stress-induced social behavior deficits are not well understood. In this study, we found that chronic restraint stress (RS) induces significant increases in serum cell-free mitochondrial DNA (cf-mtDNA) levels in mice, and systemic Deoxyribonuclease I (DNase I) treatment attenuated RS-induced social behavioral deficits. Our findings revealed potential roles of mitophagy and Mitochondrial antiviral-signaling protein (MAVS) in mediating chronic stress-induced changes in cf-mtDNA levels and social behavior. Furthermore, we showed that inhibition of Toll-like receptor 9 (TLR9) attenuates mtDNA-induced social behavior deficits. Together, these findings show that cf-mtDNA-TLR9 signaling is critical in mediating stress-induced social behavior deficits.

The Effects of Early-Life Stress on Liver Transcriptomics and the Protective Role of EPA in a Mouse Model of Early-Life-Stress-Induced Adolescent Depression

Early-life stress (ELS) was found to increase the risk of adolescent depression, and clinical evidence indicated that eicosapentaenoic acid (EPA) was decreased in patients with adolescent depression, but the underlying mechanisms are unclear. Here, we utilized an ELS model of maternal separation with early weaning to explore the protective role of EPA in adolescent depression. We found that that ELS induced depression-like behavior rather than anxiety-like behavior in adolescent mice. RNA-sequencing results showed that ELS changed the transcription pattern in the liver, including 863 upregulated genes and 971 downregulated genes, especially those related to the biosynthesis of unsaturated fatty acids metabolism in the liver. Moreover, ELS decreased the expression of the rate-limiting enzymes, fatty acid desaturases 1/2 (FADS1/2), involved in the biosynthesis of EPA in the liver. Additionally, ELS reduced the levels of EPA in the liver, serum, and hippocampus, and EPA administration improved depression-like behavior-induced by ELS. Our results provide transcriptomic evidence that ELS increases the risk of adolescent depression by reducing the synthesis of unsaturated fatty acids in the liver, especially EPA, and suggest that supplementation with EPA should be investigated as a potential treatment for adolescent depression.

The impact of environmental factors during maternal separation on the behaviors of adolescent C57BL/6 mice

Neonatal maternal separation is a widely used method to construct an early-life stress model in rodents. In this method, pups are separated from their mothers for several hours every day during the first 2 weeks of life, which results in adverse early-life events. It is a known fact that maternal separation can exert a significant impact on the behavior and psychological health, such as anxiety and depression, in adolescent offspring. However, environmental conditions during maternal separation can differ such as the presence of other animals or by placing pups in a different dam. To investigate the differential effects of various conditions of maternal separation on the behavior of adolescent mice, we created the following groups: (1) iMS group: pups were moved to an isolated room with no other adult mice in a nearby cage, (2) eDam group: the pups randomly exchanged their dams, (3) OF group: pups were shifted to another cage with the bedding material containing maternal odor (olfactory stimulation), and (4) MS group: pups were shifted to another vivarium. From postnatal day (PND) 2-20 (i.e., 19 consecutive days), pups were separated from the dam daily for 4 h and exposed to various environments (MS, iMS, eDam, and OF) or were left undisturbed [control (CON) group]. A series of behavioral assessments were conducted to evaluate locomotion, anxiety, recognition, learning, and memory in adolescent offspring. The results showed that neonatal maternal separation led to impaired recognition memory, motor coordination, and motor skill learning across all groups. However, the iMS group exhibited anxiety-like behavior in the elevated plus maze test and enhanced the extinction of fear memory in the auditory fear conditioning test. The OF and eDam groups displayed partially recovered short-term working memory in the Y-maze test but exhibited opposite exploratory behaviors. The OF group spent more time in the center, while the eDam group spent less time. These findings demonstrated that exposure to different environmental conditions during maternal separation causes behavioral alterations in adolescent offspring, providing a potential explanation for the variation in behavioral phenotypes observed in the early-life stress models.

Electroacupuncture alleviated depression‐like behaviors in ventromedial prefrontal cortex of chronic unpredictable mild stress‐induced rats: Increasing synaptic transmission and phosphorylating dopamine transporter

AIMS

Electroacupuncture (EA) shows advantages in both clinical practice and depression animal models. Dopaminergic-related dysfunction in the prefrontal cortex (PFC) may be a hidden antidepressant mechanism of EA, where dopamine transporter (DAT) plays an essential role. This study aimed to investigate the synaptic transmission and DAT-related changes of EA in depression.

METHODS

Male Sprague-Dawley rats were subjected to 3-week chronic unpredictable mild stress (CUMS). The successfully modeled rats were then randomly and equally assigned to CUMS, selective serotonin reuptake inhibitor (SSRI), and EA or SSRI + EA groups, followed by a 2-week treatment respectively. After monitoring body weight and behavioral tests of all rats, the ventromedial PFC (vmPFC) tissue was collected for electrophysiology and the expression detection of DAT, phosphorylated DAT (p-DAT), cyclic adenosine monophosphate (cAMP), protein kinase A (PKA), and trace amine-associated receptor 1 (TAAR1).

RESULTS

Depressive-like behaviors induced by CUMS were alleviated by EA, SSRI, and SSRI + EA treatments through behavioral tests. Compared with CUMS group, EA improved synaptic transmission in vmPFC by upregulating spontaneous excitatory postsynaptic currents amplitude. Molecularly, EA reversed the increased total DAT and p-DAT expression as well as the decreased ratio of p-DAT/total DAT along with the activation of TAAR1, cAMP, and PKA in vmPFC.

CONCLUSION

We speculated that the antidepressant effect of EA was associated with enhanced synaptic transmission in vmPFC, and the upregulated phosphorylation of DAT relevant to TAAR1, cAMP, and PKA may be the potential mechanism.

Effect of developmental stress on the in vivo neuronal circuits related to excitation-inhibition balance and mood in adulthood

INTRODUCTION

Traumatic events in early life have a deleterious effect on the development of normal brain developments, which may be a cause of various psychiatric disorders in adulthood. Most prior studies focused on molecular biological aspects, and research on functional changes in neural circuits is still limited. We aimed to elucidate the effect of early life stress on in vivo excitation-inhibition and serotonergic neurotransmission in the adulthood using non-invasive functional molecular imaging (positron emission tomography, PET).

METHODS

To compare the effect of stress intensity, early life stress animal models were divided into single trauma (MS) and double trauma groups (MRS). MS was derived from maternal separation, whereas MRS was derived from maternal separation and restraint stress after birth. And to evaluate the stress vulnerability on the sex, we used male and female rats.

RESULTS

The MRS group showed greater weight loss and more severe depressive/anxiety-like behaviors than the MS and control groups. Corticosterone levels in MRS showed a greater extent of decline than in the MS group; however, there was no significant difference in the change of T3 and T4 between MS and MRS. In the PET, the stress exposure groups showed lower brain uptake for GABAergic, glutamatergic, and serotonergic systems compared with the control group. The excitatory/inhibitory balance, which was derived by dividing glutamate brain uptake into GABAergic uptake, increased as stress intensity increased. Neuronal degeneration in the stress exposure groups was confirmed by immunohistochemistry. In the sex comparison, female showed the greater changes of body weight, corticosterone level, depressive/anxiety-like behavior, and neurotransmission systems than those in male.

CONCLUSION

Taken together, we demonstrated that developmental stress induces dysfunction of neurotransmission in vivo, and that females are more vulnerable to stress than males.

Maternal separation affects Anxiety like behavior begin in adolescence continue through adulthood and related to Dnmt3a expression

Early life stress, including maternal separation, is among one of the main causes of anxiety in adolescents. DNA methyltransferase 3A (Dnmt3a) is a key molecule that regulates DNA methylation and is found to be associated with anxiety-like behavior. It is not clear whether maternal separation affects anxiety levels in mice at different developmental stages, or whether Dnmt3a plays a role in this process. Here, by using open field test to exploring the effect of maternal separation on anxiety-like behavior in mice of different age, it was found that maternal separation could successfully induce anxiety-like behavior in adolescent mice, and which continued through adulthood. By using western blot, we found the levels of Dnmt3a in the hippocampus and cortex have shown different trends in maternal separation mice on P17. Further, by using immunostaining, we have found that the expression levels of Dnmt3a in the cortex and hippocampus were significantly different, and decreased to varying degrees with the age of mice, which being the reason for different trends. Our results provide an experimental basis for further development of anxiety/depression treatment programs more suitable for adolescence.

Distinct neuronal excitability alterations of medial prefrontal cortex in early-life neglect model of rats

OBJECT

Early-life neglect has irreversible emotional effects on the central nervous system. In this work, we aimed to elucidate distinct functional neural changes in medial prefrontal cortex (mPFC) of model rats.

METHODS

Maternal separation with early weaning was used as a rat model of early-life neglect. The excitation of glutamatergic and GABAergic neurons in rat mPFC was recorded and analyzed by whole-cell patch clamp.

RESULTS

Glutamatergic and GABAergic neurons of mPFC were distinguished by typical electrophysiological properties. The excitation of mPFC glutamatergic neurons was significantly increased in male groups, while the excitation of mPFC GABAergic neurons was significant in both female and male groups, but mainly in terms of rest membrane potential and amplitude, respectively.

CONCLUSIONS

Glutamatergic and GABAergic neurons in medial prefrontal cortex showed different excitability changes in a rat model of early-life neglect, which can contribute to distinct mechanisms for emotional and cognitive manifestations.