Maternal separation with early weaning impairs neuron-glia integrity: non-invasive evaluation and substructure demonstration

TREK-1 inhibition promotes synaptic plasticity in the prelimbic cortex

Synaptic plasticity is one of the putative mechanisms involved in the maturation of the prefrontal cortex (PFC) during postnatal development. Early life stress (ELS) affects the shaping of cortical circuitries through impairment of synaptic plasticity supporting the onset of mood disorders. Growing evidence suggests that dysfunctional postnatal maturation of the prelimbic division (PL) of the PFC might be related to the emergence of depression. The potassium channel TREK-1 has attracted particular interest among many factors that modulate plasticity, concerning synaptic modifications that could underlie mood disorders. Studies have found that ablation of TREK-1 increases the resilience to depression, while rats exposed to ELS exhibit higher TREK-1 levels in the PL. TREK-1 is regulated by multiple intracellular transduction pathways including the ones activated by metabotropic receptors. In the hippocampal neurons, TREK-1 interacts with the serotonergic system, one of the main factors involved in the action of antidepressants. To investigate possible mechanisms related to the antidepressant role of TREK-1, we used brain slice electrophysiology to evaluate the effects of TREK-1 pharmacological blockade on synaptic plasticity at PL circuitry. We extended this investigation to animals subjected to ELS. Our findings suggest that in non-stressed animals, TREK-1 activity is required for the reduction of synaptic responses mediated by the 5HT1A receptor activation. Furthermore, we demonstrate that TREK-1 blockade promotes activity-dependent long-term depression (LTD) when acting in synergy with 5HT1A receptor stimulation. On the other hand, in ELS animals, TREK-1 blockade reduces synaptic transmission and facilitates LTD expression. These results indicate that TREK-1 inhibition stimulates synaptic plasticity in the PL and this effect is more pronounced in animals subjected to ELS during postnatal development.

The mineralocorticoid receptor and extra-synaptic NMDA receptor in the lateral habenula involve in the vulnerability to early life stress in the maternal separation model

The lateral habenula (LHb) plays a pivotal role in regulating emotional responses during stress reactions, and its hyperactivity has been associated with depression. Recently it has been demonstrated that chronic early-life stress results in individual differences in stress vulnerability among rodents. However, how synaptic function in the LHb varies between susceptibility and resilience to early life stress remains elusive. In this study, we used a maternal separation model to assign animals with different stress vulnerabilities into groups and investigated the synaptic responses in the LHb. Our findings indicate that synaptic long-term depression (LTD) was impaired and extra-synaptic LTD was enhanced in the LHb of the susceptible group. To mimic the synaptic alteration in stress situations, when administered corticosterone, a stress hormone, the intervention appeared to impair synaptic LTD in the LHb of the control group, through the activation of mineralocorticoid receptors (MR). Indeed, there was an up-regulation of MR mRNA observed in the susceptible group. Following there was an up-regulation of both NR2A and NR2B subunits in the LHb. These results indicated that MR and extra-synaptic NMDA receptors in LHb are critically engaged in the susceptibilities to stress. Furthermore, our findings propose potential therapeutic targets for alleviating stress-related symptoms.

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.

Oligodendrocytes matter: a review of animal studies on early adversity

Exposure to adversities in early life appears to affect the development of white matter, especially oligodendrocytes. Furthermore, altered myelination is present in regions subjected to maturation during the developmental time when early adversities are experienced. In this review, studies applying two well-established animal models of early life adversity, namely maternal separation and maternal immune activation, focusing on oligodendrocyte alterations and resulting implications for psychiatric disorders are discussed. Studies revealed that myelination is reduced as a result of altered oligodendrocyte expression. Furthermore, early adversity is associated with increased cell death, a simpler morphology, and inhibited oligodendrocyte maturation. However, these effects seem to be region- specific as some brain regions show increased expression while others show decreased expression of oligodendroglia-related genes, and they occur especially in regions of ongoing development. Some studies furthermore suggest that early adversity leads to premature differentiation of oligodendrocytes. Importantly, especially early exposure results in stronger oligodendrocyte-related impairments. However, resulting alterations are not restricted to exposure during the early pre- and postnatal days as social isolation after weaning leads to fewer internodes and branches and shorter processes of oligodendrocytes in adulthood. Eventually, the found alterations may lead to dysfunction and long-lasting alterations in structural brain development associated with psychiatric disorders. To date, only few preclinical studies have focused on the effects of early adversity on oligodendrocytes. More studies including several developmental stages are needed to further disentangle the role of oligodendrocytes in the development of psychiatric disorders.

Maternal Separation Alters Ethanol Drinking and Reversal Learning Processes in Adolescent Rats: The Impact of Sex and Glycine Transporter Type 1 (GlyT1) Inhibitor

Adverse early life experiences are associated with an enhanced risk for mental and physical health problems, including substance abuse. Despite clinical evidence, the mechanisms underlying these relationships are not fully understood. Maternal separation (MS) is a commonly used animal model of early neglect. The aim of the current study is to determine whether the N-methyl-D-aspartate receptor (NMDAR)/glycine sites are involved in vulnerability to alcohol consumption (two-bottle choice paradigm) and reversal learning deficits (Barnes maze task) in adolescent rats subjected to the MS procedure and whether these effects are sex dependent. By using ELISA, we evaluated MS-induced changes in the NMDAR subunits (GluN1, GluN2A, GluN2B) expression, especially in the glycine-binding subunit, GluN1, in the prefrontal cortex (PFC) and ventral striatum (vSTR) of male/female rats. Next, we investigated whether Org 24598, a glycine transporter 1 (GlyT1) inhibitor, was able to modify ethanol drinking in adolescent and adult male/female rats with prior MS experience and reversal learning in the Barnes maze task. Our findings revealed that adolescent MS female rats consumed more alcohol which may be associated with a substantial increase in GluN1 subunit of NMDAR in the PFC and vSTR. Org 24598 decreased ethanol intake in both sexes with a more pronounced decrease in ethanol consumption in adolescent female rats. Furthermore, MS showed deficits in reversal learning in both sexes. Org 24598 ameliorated reversal learning deficits, and this effect was reversed by the NMDAR/glycine site inhibitor, L-701,324. Collectively, our results suggest that NMDAR/glycine sites might be targeted in the treatment of alcohol abuse in adolescents with early MS, especially females.

Alpha-Asaronol Alleviates Dysmyelination by Enhancing Glutamate Transport Through the Activation of PPARγ-GLT-1 Signaling in Hypoxia-Ischemia Neonatal Rats

Preterm white matter injury (PWMI) is the most common form of brain damage in premature infants caused by hypoxia-ischemia (HI), inflammation, or excitotoxicity. It is characterized by oligodendrocyte precursor cell (OPC) differentiation disorder and dysmyelination. Our previous study confirmed that alpha-asarone (α-asaronol), a major compound isolated from the Chinese medicinal herb Acorus gramineus by our lab, could alleviate neuronal overexcitation and improve the cognitive function of aged rats. In the present study, we investigated the effect and mechanism of α-asaronol on myelination in a rat model of PWMI induced by HI. Notably, α-asaronol promoted OPC differentiation and myelination in the corpus callosum of PWMI rats. Meanwhile, the concentration of glutamate was significantly decreased, and the levels of PPARγ and glutamate transporter 1 (GLT-1) were increased by α-asaronol treatment. In vitro, it was also confirmed that α-asaronol increased GLT-1 expression and recruitment of the PPARγ coactivator PCG-1a in astrocytes under oxygen and glucose deprivation (OGD) conditions. The PPARγ inhibitor GW9662 significantly reversed the effect of α-asaronol on GLT-1 expression and PCG-1a recruitment. Interestingly, the conditioned medium from α-asaronol-treated astrocytes decreased the number of OPCs and increased the number of mature oligodendrocytes. These results suggest that α-asaronol can promote OPC differentiation and relieve dysmyelination by regulating glutamate levels via astrocyte PPARγ-GLT-1 signaling. Although whether α-asaronol binds to PPARγ directly or indirectly is not investigated here, this study still indicates that α-asaronol may be a promising small molecular drug for the treatment of myelin-related diseases.

Glia-Driven Brain Circuit Refinement Is Altered by Early-Life Adversity: Behavioral Outcomes

Early-life adversity (ELA), often clinically referred to as "adverse childhood experiences (ACE)," is the exposure to stress-inducing events in childhood that can result in poor health outcomes. ELA negatively affects neurodevelopment in children and adolescents resulting in several behavioral deficits and increasing the risk of developing a myriad of neuropsychiatric disorders later in life. The neurobiological mechanisms by which ELA alters neurodevelopment in childhood have been the focus of numerous reviews. However, a comprehensive review of the mechanisms affecting adolescent neurodevelopment (i.e., synaptic pruning and myelination) is lacking. Synaptic pruning and myelination are glia-driven processes that are imperative for brain circuit refinement during the transition from adolescence to adulthood. Failure to optimize brain circuitry between key brain structures involved in learning and memory, such as the hippocampus and prefrontal cortex, leads to the emergence of maladaptive behaviors including increased anxiety or reduced executive function. As such, we review preclinical and clinical literature to explore the immediate and lasting effects of ELA on brain circuit development and refinement. Finally, we describe a number of therapeutic interventions best-suited to support adolescent neurodevelopment in children with a history of ELA.

Alpha lipoic acid ameliorates detrimental effects of maternal lipopolysaccharides exposure on prefrontal white matter in adult male offspring rats

BACKGROUND

Activation of the maternal immune system by lipopolysaccharide (LPS) increases the production of proinflammatory cytokines, free radicals, and reactive oxygen species (ROS), all of which play a significant role in the pathogenesis of many offspring neurodevelopmental disorders. Alpha Lipoic Acid (ALA) is a natural compound that has anti-inflammatory and antioxidant properties. This study was performed to assess the effect of prenatal exposure to LPS on the prefrontal white matter of rat offspring and evaluate the potential protective effects of ALA co-administration during pregnancy.

METHODS

Pregnant Wistar rats were randomly divided into six groups (n = 6 each group): (1) control, (2) received LPS (100 μg/kg, intraperitoneally (IP) on gestational day 9.5 (GD 9.5), (3) received ALA (20 mg/kg) from GD1 to GD11, (4) LPS+ALA received LPS on GD9.5 and ALA from GD1 to GD11, (5 and 6) received LPS and ALA vehicle respectively. In each group, 21-day old male offspring (2 male pups from each mother) was harvested, and then their prefrontal white matter was separated and prepared for the ultrastructural, stereological, and molecular assays.

RESULTS

In utero exposure to LPS led to a significant decrease in nerve cell counts, ultrastructural alterations in myelinated axons, and abnormal changes in genes expression of Sox10,Olig1,yrf,Wnt in the prefrontal of the rat offspring. Co-administration of ALA resulted in amelioration of those abnormal changes in the LPS rat offspring.

CONCLUSION

The findings of our preclinical study, explore that prenatal ALA treatment efficiently protects the nervous system against LPS induced abnormal changes in the offspring.