Early-life-stress affects the homeostasis of glutamatergic synapses

Communal nesting shapes the sex-dependent glutamatergic response to early life stress in the rat prefrontal cortex

Introduction

Early social environment, either positive or negative, shapes the adult brain. Communal nesting (CN), a naturalistic setting in which 2-3 females keep their pups in a single nest sharing care-giving behavior, provides high level of peer interaction for pups. Early social isolation (ESI) from dam and siblings represents, instead, an adverse condition providing no peer interaction.

Methods

We investigated whether CN (enrichment setting) might influence the response to ESI (impoverishment setting) in terms of social behavior and glutamate system in the medial prefrontal cortex (mPFC) of adult and adolescent male and female rats.

Results

Pinning (a rewarding component of social play behavior) was significantly more pronounced in males than in females exposed to the combination of CN and ESI. CN sensitized the glutamate synapse in the mPFC of ESI-exposed male, but not female, rats. Accordingly, we observed (i) a potentiation of the glutamatergic neurotransmission in the mPFC of both adolescent and adult males, as shown by the recruitment of NMDA receptor subunits together with increased expression/activation of PSD95, SynCAM 1, Synapsin I and αCaMKII; (ii) a de-recruiting of NMDA receptors from active synaptic zones of same-age females, together with reduced expression/activation of the above-mentioned proteins, which might reduce the glutamate transmission. Whether similar sex-dependent glutamate homeostasis modulation occurs in other brain areas remains to be elucidated.

Discussion

CN and ESI interact to shape social behavior and mPFC glutamate synapse homeostasis in an age- and sex-dependent fashion, suggesting that early-life social environment may play a crucial role in regulating the risk to develop psychopathology.

Adult-onset hypothyroidism causes mechanical hypersensitivity due to peripheral nerve hyperexcitability based on voltage-gated potassium channel downregulation in male mice

Thyroid hormones play an important role in the central and peripheral nervous system functions. Approximately 50% of adult-onset hypothyroid patients have sensory symptoms including pain, possibly caused by peripheral neuropathy. However, the mechanism causing the pain has not been clarified. We generated an adult-onset hypothyroid model animal by administering 50 ppm propylthiouracil (PTU) for 5 weeks to male mice. Female mice were not tested in this study. Mechanical hypersensitivity, determined by the von Frey hair test, was observed during the PTU exposure and recovered after the exposure termination. The sciatic nerve compound action potential was also analyzed. Under single-pulse stimulation, no significant change in the threshold and conduction velocity was observed in the PTU-administered group. On the other hand, under train-pulse stimulation, the latency delay in the Aδ-fiber component was less in the PTU-administered group in Week 4 of PTU exposure, indicating relative hyperexcitability. Fluticasone, which is the anti-inflammatory agent with an ability to activate the voltage-gated potassium channel subfamily A (Kv1), restored the decrease in the latency change ratio by PTU exposure under the train-pulse stimulation supporting our hypothesis that Kv1 may be involved in the conductivity change. Kv1.1 protein level decreased significantly in the sciatic nerve of the PTU-administered group. These results indicate that adult-onset hypothyroidism causes mechanical hypersensitivity owing to hyperexcitability of the peripheral nerve and that reduction of Kv1.1 level may be involved in such alteration.

DNA methylation of Vesicular Glutamate Transporters in the mesocorticolimbic brain following early-life stress and adult ethanol exposure-an explorative study

DNA methylation and gene expression can be altered by early life stress (ELS) and/or ethanol consumption. The present study aimed to investigate whether DNA methylation of the Vesicular Glutamate Transporters (Vglut)1-3 is related to previously observed Vglut1-3 transcriptional differences in the ventral tegmental area (VTA), nucleus accumbens (Acb), dorsal striatum (dStr) and medial prefrontal cortex (mPFC) of adult rats exposed to ELS, modelled by maternal separation, and voluntary ethanol consumption. Targeted next-generation bisulfite sequencing was performed to identify the methylation levels on 61 5′-cytosine-phosphate-guanosine-3′ sites (CpGs) in potential regulatory regions of Vglut1, 53 for Vglut2, and 51 for Vglut3. In the VTA, ELS in ethanol-drinking rats was associated with Vglut1-2 CpG-specific hypomethylation, whereas bidirectional Vglut2 methylation differences at single CpGs were associated with ELS alone. Exposure to both ELS and ethanol, in the Acb, was associated with lower promoter and higher intronic Vglut3 methylation; and in the dStr, with higher and lower methylation in 26% and 43% of the analyzed Vglut1 CpGs, respectively. In the mPFC, lower Vglut2 methylation was observed upon exposure to ELS or ethanol. The present findings suggest Vglut1-3 CpG-specific methylation signatures of ELS and ethanol drinking, underlying previously reported Vglut1-3 transcriptional differences in the mesocorticolimbic brain.

Mechanisms of Shared Vulnerability to Post-traumatic Stress Disorder and Substance Use Disorders

Psychoactive substance use is a nearly universal human behavior, but a significant minority of people who use addictive substances will go on to develop an addictive disorder. Similarly, though ~90% of people experience traumatic events in their lifetime, only ~10% ever develop post-traumatic stress disorder (PTSD). Substance use disorders (SUD) and PTSD are highly comorbid, occurring in the same individual far more often than would be predicted by chance given the respective prevalence of each disorder. Some possible reasons that have been proposed for the relationship between PTSD and SUD are self-medication of anxiety with drugs or alcohol, increased exposure to traumatic events due to activities involved in acquiring illegal substances, or addictive substances altering the brain's stress response systems to make users more vulnerable to PTSD. Yet another possibility is that some people have an intrinsic vulnerability that predisposes them to both PTSD and SUD. In this review, we integrate clinical and animal data to explore these possible etiological links between SUD and PTSD, with an emphasis on interactions between dopaminergic, adrenocorticotropic, GABAergic, and glutamatergic neurobehavioral mechanisms that underlie different emotional learning styles.

Ceftriaxone modulates the acute corticosterone effects in local field potentials in the primary somatosensory cortex of anesthetized mice

Stress responses are associated with elevations in corticosterone levels and, as a consequence, increases in glutamate in the central nervous system which can lead to neurological impairment. Ceftriaxone promotes glutamate transport and has been used to reduce glutamate toxicity, but so far it is not known whether ceftriaxone is able to reverse the effects of corticosterone administration. Here we describe the separate and combined effects of acute ceftriaxone and acute corticosterone administration in local field potentials (LFPs) recorded from the somatosensory cortex (S1) of anesthetized mice. For this, LFPs were recorded from groups of anesthetized mice injected with saline, corticosterone, ceftriaxone, or both. Comparison of global state maps, and their displacements, as measured by ratios of different frequency bands (Ratio 1: 0.5–20 Hz/0.5–45 Hz; and Ratio 2: 0.5–4.5 Hz/0.5–9 Hz) revealed distinct and opposite effects for corticosterone and for ceftriaxone. Corticosterone specifically increased the displacement in Ratio 2, while ceftriaxone decreased it; in addition, when both corticosterone and ceftriaxone were injected, Ratio 2 displacement values were again similar to those of the control group. The present results suggest that ceftriaxone and corticosterone modulate specific frequency bands in opposite directions and reveal a potential role for ceftriaxone in counteracting the effects of corticosterone.

Effects of early life stress on cocaine conditioning and AMPA receptor composition are sex-specific and driven by TNF

Exposure to early life adversity can predispose adolescents to the formation of substance abuse disorders. In rodents, early stressors such as repeated maternal separation (MS) impact AMPAR activity in the prefrontal cortex (PFC) and nucleus accumbens (NAc), regions involved in drug-cue association after cocaine-induced conditioned place preference (CPP). Notably, previous reports suggest that the pro-inflammatory cytokine tumor necrosis factor (TNF) regulates AMPAR subunit composition; increased TNF levels are reported to reduce GluA2-positive AMPARs. Since MS can elevate adolescent TNF levels, the stressor may therefore alter AMPAR subunit composition via neuroimmune signaling, thereby affecting cocaine-induced CPP. We tested the specific role of soluble TNF in MS-induced GluA2 loss and cocaine-induced CPP with biologic disruption of TNF signaling. TNF gene and protein expression were elevated in both PFC and NAc of MS males, but not females. GluA2 expression was reduced in both regions in only male MS rats, and systemic treatment with either ibudilast - a phosphodiesterase inhibitor, or XPro1595 - a blood-brain barrier-permeable blocker of soluble TNF - reversed such loss. MS males also formed greater preference for a cocaine-paired environment, the expression of which returned to control levels after XPro1595 administration. These data suggest a sex-specific mechanistic link between TNF signaling and changes in GluA2 expression and drug-cue conditioning, thereby providing further evidence for a role of MS and neuro-immune activity in cortical and striatal AMPAR changes. Moreover, manipulation of the TNF signaling pathway represents a novel approach for influencing response to reinforcing effects of drug use.

Early-life stress induces motor coordination dysfunction in adult mice

Although child abuse has become a serious social problem in most countries, the neural mechanisms by which it induces adulthood mental disorders is not yet fully understood. Mice exposed to early-life stresses, such as maternal deprivation (MD) during lactation, are a good model for studying the effects of neglect of humans in early life. Early-life stress induces structural/functional changes of neurons in the hippocampus, prefrontal cortex, and amygdala, and causes mental disorders in adulthood. In this study, we found motor coordination dysfunction in male MD mice. We also found that the expression levels of the aminomethylphosphonic acid receptor subunits GluA1 and GluA3 were high in the cerebellum of male MD mice. The basal activity of the cerebellum detected by field-potential analysis was higher in male MD mice than in male control mice. Caloric stimulation increased the activity of the cerebellum of control mice, but it did not significantly increase the activity of the cerebellum in male MD mice. We concluded that early-life stress induced a functional change in the cerebellum of MD mice and that this change induced motor coordination dysfunctions.

Epigenetics of Subcellular Structure Functioning in the Origin of Risk or Resilience to Comorbidity of Neuropsychiatric and Cardiometabolic Disorders

Mechanisms controlling mitochondrial function, protein folding in the endoplasmic reticulum (ER) and nuclear processes such as telomere length and DNA repair may be subject to epigenetic cues that relate the genomic expression and environmental exposures in early stages of life. They may also be involved in the comorbid appearance of cardiometabolic (CMD) and neuropsychiatric disorders (NPD) during adulthood. Mitochondrial function and protein folding in the endoplasmic reticulum are associated with oxidative stress and elevated intracellular calcium levels and may also underlie the vulnerability for comorbid CMD and NPD. Mitochondria provide key metabolites such as nicotinamide adenine dinucleotide (NAD+), ATP, α-ketoglutarate and acetyl coenzyme A that are required for many transcriptional and epigenetic processes. They are also a source of free radicals. On the other hand, epigenetic markers in nuclear DNA determine mitochondrial biogenesis. The ER is the subcellular organelle in which secretory proteins are folded. Many environmental factors stop the ability of cells to properly fold proteins and modify post-translationally secretory and transmembrane proteins leading to endoplasmic reticulum stress and oxidative stress. ER functioning may be epigenetically determined. Chronic ER stress is emerging as a key contributor to a growing list of human diseases, including CMD and NPD. Telomere loss causes chromosomal fusion, activation of the control of DNA damage-responses, unstable genome and altered stem cell function, which may underlie the comorbidity of CMD and NPD. The length of telomeres is related to oxidative stress and may be epigenetically programmed. Pathways involved in DNA repair may be epigenetically programmed and may contribute to diseases. In this paper, we describe subcellular mechanisms that are determined by epigenetic markers and their possible relation to the development of increased susceptibility to develop CMD and NPD.

Effects of Mild Perinatal Hypothyroidism on Cognitive Function of Adult Male Offspring

Mild perinatal hypothyroidism may result from inadequate iodine intake, insufficient treatment of congenital hypothyroidism, or exposure to endocrine-disrupting chemicals. Because thyroid hormones are critical for brain development, severe hypothyroidism that is untreated in infancy causes irreversible cretinism. Milder hypothyroidism may also affect cognitive development; however, the effects of mild and/or moderate hypothyroidism on brain development are not fully understood. In this study, we examined the behavior of adult male mice rendered mildly hypothyroid during the perinatal period using low-dose propylthiouracil (PTU). PTU was administered through drinking water (5 or 50 ppm) from gestational day 14 to postnatal day 21. Cognitive performance, studied by an object in-location test (OLT), was impaired in PTU-treated mice at postnatal week 8. These results suggest that, although the hypothyroidism was mild, it partially impaired cognitive function. We next measured the concentration of neurotransmitters (glutamate, γ-aminobutyric acid, and glycine) in the hippocampus using in vivo microdialysis during OLT. The concentrations of neurotransmitters, particularly glutamate and glycine, decreased in PTU-treated mice. The expression levels of N-methyl-d-aspartate receptor subunits, which are profound regulators of glutamate neurotransmission and memory function, also were decreased in PTU-treated mice. These data indicate that mild perinatal hypothyroidism causes cognitive disorders in adult offspring. Such disorders may be partially induced secondary to decreased concentrations of neurotransmitters and receptor expression.

High prolactin concentration during lactation period induced disorders of maternal behavioral in offspring

Early-life stress during the perinatal period induces several neuropsychological disorders in adulthood. In animal studies, early-life stress during the perinatal period induces not only behavioral disorders but also other neurofunctional disorders, such as somatosensory functional disorder in adulthood. Furthermore, the offspring of an early-life-stressed parent also show disturbance of brain function in humans. Behavioral and neurological alterations in the offspring of a stressed parent have also been shown in animal studies. However, the mechanisms underlying such behavioral/neurological alterations are not yet fully understood. In this study, we found a disorder of maternal behavior in the offspring of early-life-stressed mothers. The stressed mothers showed high concentrations of serum prolactin (PRL) during pregnancy and lactation. The concentration on the day of weaning the offspring significantly correlated with the changes in the concentration of corticosterone and the neurological function of offspring. These findings indicate that PRL may be involved in the induction of transgenerational effects of early-life stress on the brain function of offspring. In addition, maternal PRL can be a good biomarker for predicting the potential risk of neurofunctional alterations in the offspring.

Early-life stress induces cognitive disorder in middle-aged mice

Early-life stress can induce several neuropsychological disorders in adulthood. However, the underlying mechanisms inducing such disorders are still not fully understood. Furthermore, the effects of early-life stress on the changes in cognitive function with age are still not clarified. In this study, we used maternal deprivation (MD) to examine the cognitive function in middle-aged mice using a touchscreen-equipped operant chamber. In the visual-discrimination task, the aged (∼1.4 years old) control mice could accurately learn to discriminate between different visual stimuli. In contrast, the correct response rate of aged MD mice increased to ∼60% by day 10; it was still significantly lower than that of the control mice (85%). In the hippocampus of aged MD mice, the expression level of the N-methyl-d-aspartate receptor subunit GluN1 decreased significantly as compared to that in control mice. On the other hand, no significant difference in GluN1 expression level was detected in young (2.5 months old) mice. These findings indicate that early-life stress accelerates cognitive impairment in middle-aged mice.

Differential impact of Met receptor gene interaction with early-life stress on neuronal morphology and behavior in mice

Early adversity in childhood increases the risk of anxiety, mood, and post-traumatic stress disorders in adulthood, and specific gene-by-environment interactions may increase risk further. A common functional variant in the promoter region of the gene encoding the human MET receptor tyrosine kinase (rs1858830 ‘C’ allele) reduces expression of MET and is associated with altered cortical circuit function and structural connectivity. Mice with reduced Met expression exhibit changes in anxiety-like and conditioned fear behavior, precocious synaptic maturation in the hippocampus, and reduced neuronal arbor complexity and synaptogenesis. These phenotypes also can be produced independently by early adversity in wild-type mice. The present study addresses the outcome of combining early-life stress and genetic influences that alter timing of maturation on enduring functional and structural phenotypes. Using a model of reduced Met expression (Met^+/−) and early-life stress from postnatal day 2–9, social, anxiety-like, and contextual fear behaviors in later life were measured. Mice that experienced early-life stress exhibited impairments in social interaction, whereas alterations in anxiety-like behavior and fear learning were driven by Met haploinsufficiency, independent of rearing condition. Early-life stress or reduced Met expression decreased arbor complexity of ventral hippocampal CA1 pyramidal neurons projecting to basolateral amygdala. Paradoxically, arbor complexity in Met^+/− mice was increased following early-life stress, and thus not different from arbors in wild-type mice raised in control conditions. The changes in dendritic morphology are consistent with the hypothesis that the physiological state of maturation of CA1 neurons in Met^+/− mice influences their responsiveness to early-life stress. The dissociation of behavioral and structural changes suggests that there may be phenotype-specific sensitivities to early-life stress.

Maternal separation stress leads to resilience against neuropathic pain in adulthood

Early life stress (ELS) leads to a permanent reprogramming of biochemical stress response cascades that may also be relevant for the processing of chronic pain states such as neuropathy. Despite clinical evidence, little is known about ELS-related vulnerability for neuropathic pain and the possibly underlying etiology.

In the framework of experimental studies aimed at investigating the respective relationships we used the established ELS model of maternal separation (MS). Rat dams and neonates were separated for 3 h/day from post-natal day 2–12. At adulthood, noxious mechanical and thermal thresholds were assessed before and during induction of neuropathic pain by chronic constriction injury (CCI). The potential involvement of spinal glutamatergic transmission, glial cells, pro-inflammatory cytokines and growth factors was studied by using qPCR.

MS per se did not modify pain thresholds. But, when exposed to neuropathic pain, MS rats exhibited a marked reduction of thermal sensitivity and a delayed development of mechanical allodynia/hyperalgesia when compared to control animals. Also, MS did not alter glucocorticoid receptor mRNA levels, but prevented the CCI-induced down-regulation of NR1 and NR2 sub-units of the NMDA receptor and of the glutamate transporter EAAT3 as observed at 21 days post-surgery. Additionally, CCI-provoked up-regulation of glial cell markers was either prevented (GFAP for astrocytes) or dampened (Iba1 for microglia) by MS. Pro-inflammatory cytokine mRNA expression was either not affected (IL-6) or reduced (IL-1β) by MS shortly after CCI. The growth factors GDNF and NGF were only slightly downregulated 4 days after CCI in the MS-treated animals. The changes in glutamatergic signaling, astroglial and cytokine activation as well as neurotrophin expression could, to some extent, explain these changes in pain behavior. Taken together, the results obtained in the described experimental conditions support the mismatch theory of chronic stress where an early life stress, rather than predisposing individuals to certain pathologies, renders them resilient.

7-Fluoro-1,3-diphenylisoquinoline-1-amine reverses the reduction in self-care behavior induced by maternal separation stress in rats by modulating glutamatergic/GABAergic systems

7-Fluoro-1,3-diphenylisoquinoline-1-amine (FDPI) is a promising isoquinoline that elicits an antidepressant-like action in rodents. In this study, an animal model of stress induced by maternal separation was used to investigate the effects of FDPI in Wistar rats of 30 and 90 days of age. It was investigated the effects of maternal separation in the self-care behavior and the contribution of glutamatergic and gamma-aminobutyric acid (GABA)ergic systems in the FDPI action. Male Wistar rats were separated from their mothers for 3 h/day from postnatal day (PND) 1-10. The rats were treated at different ages (PND-30 and PND-90) with FDPI (5 mg/kg, intragastrically/7 days) and performed the splash test. Maternal separation reduced total grooming time in the splash test, an index of motivational and self-care behavior, and FDPI treatment was effective in reversing this behavior in rats at both ages. The neurochemical parameters were differently affected, dependent on the age of rats, by maternal separation and FDPI. Maternal separation increased the GABA uptake and the excitatory amino acid transporter 1 levels in the prefrontal cortices of rats at PND-30 and FDPI was effective against these alterations. At PND-90, maternal separation decreased the glutamate uptake and increased the GABA uptake and the N-methyl-D-aspartate (NMDA) receptor 2B levels in the prefrontal cortices of rats. FDPI reversed the neurochemical alterations caused by maternal separation in the prefrontal cortices of rats at PND-90. The results of this study demonstrated that FDPI reversed the reduction in self-care behavior induced by maternal separation stress in rats by modulating the glutamatergic/GABAergic systems in rats.

Benefits of Stimulus Exposure: Developmental Learning Independent of Task Performance

Perceptual learning (training-induced performance improvement) can be elicited by task-irrelevant stimulus exposure in humans. In contrast, task-irrelevant stimulus exposure in animals typically disrupts perception in juveniles while causing little to no effect in adults. This may be due to the extent of exposure, which is brief in humans while chronic in animals. Here we assessed the effects of short bouts of passive stimulus exposure on learning during development in gerbils, compared with non-passive stimulus exposure (i.e., during testing). We used prepulse inhibition of the acoustic startle response, a method that can be applied at any age, to measure gap detection thresholds across four age groups, spanning development. First, we showed that both gap detection thresholds and gap detection learning across sessions displayed a long developmental trajectory, improving throughout the juvenile period. Additionally, we demonstrated larger within- and across-animal performance variability in younger animals. These results are generally consistent with results in humans, where there are extended developmental trajectories for both the perception of temporally-varying signals, and the effects of perceptual training, as well as increased variability and poorer performance consistency in children. We then chose an age (mid-juveniles) that displayed clear learning over sessions in order to assess effects of brief passive stimulus exposure on this learning. We compared learning in mid-juveniles exposed to either gap detection testing (gaps paired with startles) or equivalent gap exposure without testing (gaps alone) for three sessions. Learning was equivalent in both these groups and better than both naïve age-matched animals and controls receiving no gap exposure but only startle testing. Thus, short bouts of exposure to gaps independent of task performance is sufficient to induce learning at this age, and is as effective as gap detection testing.

The Regulation of GluN2A by Endogenous and Exogenous Regulators in the Central Nervous System

The NMDA receptor is the most widely studied ionotropic glutamate receptor, and it is central to many physiological and pathophysiological processes in the central nervous system. GluN2A is one of the two main types of GluN2 NMDA receptor subunits in the forebrain. The proper activity of GluN2A is important to brain function, as the abnormal regulation of GluN2A may induce some neuropsychiatric disorders. This review will examine the regulation of GluN2A by endogenous and exogenous regulators in the central nervous system.

Aberrant Cerebellar Development in Mice Lacking Dual Oxidase Maturation Factors

BACKGROUND

Thyroid hormone (TH) plays a key role in the developing brain, including the cerebellum. TH deficiency induces organizational changes of the cerebellum, causing cerebellar ataxia. However, the mechanisms causing these abnormalities are poorly understood. Various animal models have been used to study the mechanism. Lacking dual oxidase (DUOX) and its maturation factor (DUOXA) are major inducers of congenital hypothyroidism. Thus, this study examined the organizational changes of the cerebellum using knockout mice of the Duoxa gene (Duoxa-/-).

METHODS

The morphological, behavioral, and electrophysiological changes were analyzed in wild type (Wt) and Duoxa-deficient (Duoxa-/-) mice from postnatal day (P) 10 to P30. To detect the changes in the expression levels of presynaptic proteins, Western blot analysis was performed.

RESULTS

The proliferation and migration of granule cells was delayed after P15 in Duoxa-/- mice. However, these changes disappeared by P25. Although the cerebellar structure of Duoxa-/- mice was not significantly different from that of Wt mice at P25, motor coordination was impaired. It was also found that the amplitude of paired-pulse facilitation at parallel fiber-Purkinje cell synapses decreased in Duoxa-/- mice, particularly at P15. There were no differences between expression levels of presynaptic proteins regulating neurotransmitter release at P25.

CONCLUSIONS

These results indicate that the anatomical catch-up growth of the cerebellum did not normalize its function because of the disturbance of neuronal circuits by the combined effect of hypothyroidism and functional disruption of the DUOX/DUOXA complex.

Alterations of Mitochondrial DNA Copy Number and Telomere Length With Early Adversity and Psychopathology

BACKGROUND

Telomere shortening and alterations of mitochondrial biogenesis are involved in cellular aging. Childhood adversity is associated with telomere shortening, and several investigations have shown short telomeres in psychiatric disorders. Recent studies have examined whether mitochondria might be involved in neuropsychiatric conditions; findings are limited and no prior work has examined this in relation to stress exposure.

METHODS

Two-hundred ninety healthy adults provided information on childhood parental loss and maltreatment and completed diagnostic interviews. Participants were categorized into four groups based upon the presence or absence of childhood adversity and the presence or absence of lifetime psychopathology (depressive, anxiety, and substance use disorders). Telomere length and mitochondrial DNA (mtDNA) copy number were measured from leukocyte DNA by quantitative polymerase chain reaction.

RESULTS

Childhood adversity and lifetime psychopathology were each associated with shorter telomeres (p < .01) and higher mtDNA copy numbers (p < .001). Significantly higher mtDNA copy numbers and shorter telomeres were seen in individuals with major depression, depressive disorders, and anxiety disorders, as well as those with parental loss and childhood maltreatment. A history of substance disorders was also associated with significantly higher mtDNA copy numbers.

CONCLUSIONS

This study provides the first evidence of an alteration of mitochondrial biogenesis with early life stress and with anxiety and substance use disorders. We replicate prior work on telomere length and psychopathology and show that this effect is not secondary to medication use or comorbid medical illness. Finally, we show that early life stress and psychopathology are each associated with these markers of cellular aging.

Alteration of somatosensory response in adulthood by early life stress

Early life stress is well-known as a critical risk factor for mental and cognitive disorders in adulthood. Such disorders are accompanied by altered neuro- (synapto-) genesis and gene expression. Because psychosomatic disorders induced by early life stress (e.g., physical and/or sexual abuse, and neglect) have become a socio-economic problem, it is very important to clarify the mechanisms underlying these changes. However, despite of intensive clinical and animal studies, such mechanisms have not yet been clarified. Although the disturbance of glucocorticoid and glutamate homeostasis by stress has been well-documented, it has not yet been clarified whether such disturbance by early life stress persists for life. Furthermore, since previous studies have focused on the detection of changes in specific brain regions, such as the hippocampus and prefrontal cortex, it has not been clarified whether early life stress induced changes in the sensory/motor system. Thus, in this review, we introduce recent studies on functional/structural changes in the somatosensory cortex induced by early life stress. We believe that this review provides new insights into the functional alteration of the somatosensory system induced by early life stress. Such information may have clinical relevance in terms of providing effective therapeutic interventions to early life stressed individuals.

Early-life stress increases the motility of microglia in adulthood

Early-life stress may cause several neuropsychological disorders in adulthood. Such disorders may be induced as a result of instability of neuronal circuits and/or synaptic formation. However, the mechanisms underlying such instability have not yet been clearly understood. We previously reported that the mushroom spine in the somatosensory cortex (SSC) is unstable in early-life stressed mice not only in the juvenile stage but also in adulthood. In this study, we measured the number and motility of microglial processes in early-life stressed mice to understand the mechanism further. We found that the number and motility of filopodia-like protrusions of microglial processes tended to increase in the SSC of early-life stressed mice. Interestingly, the motility of protrusions correlated significantly with the nociceptive threshold level measured by the von Frey test. These results indicated that the activity of microglia affected the neuronal function in early-life stressed mice.