Neonatal maternal separation up-regulates protein signalling for cell survival in rat hypothalamus

Adolescent nonpharmacological interventions for early-life stress and their mechanisms

Those with a negative experience of psychosocial stress during the early stage of life not only have a high susceptibility of the psychiatric disorder in all phases of their life span, but they also demonstrate more severe symptoms and poorer response to treatment compared to those without a history of early-life stress. The interventions targeted to early-life stress may improve the effectiveness of treating and preventing psychiatric disorders. Brain regions associated with mood and cognition develop rapidly and own heightened plasticity during adolescence. So, manipulating nonpharmacological interventions in fewer side effects and higher acceptance during adolescence, which is a probable window of opportunity, may ameliorate or even reverse the constantly deteriorating impact of early-life stress. The present article reviews animal and people studies about adolescent nonpharmacological interventions for early-life stress. We aim to discuss whether those adolescent nonpharmacological interventions can promote individuals' psychological health who expose to early-life stress.

Deficiency in the cell-adhesion molecule dscaml1 impairs hypothalamic CRH neuron development and perturbs normal neuroendocrine stress axis function

The corticotropin-releasing hormone (CRH)-expressing neurons in the hypothalamus are critical regulators of the neuroendocrine stress response pathway, known as the hypothalamic-pituitary-adrenal (HPA) axis. As developmental vulnerabilities of CRH neurons contribute to stress-associated neurological and behavioral dysfunctions, it is critical to identify the mechanisms underlying normal and abnormal CRH neuron development. Using zebrafish, we identified Down syndrome cell adhesion molecule like-1 (dscaml1) as an integral mediator of CRH neuron development and necessary for establishing normal stress axis function. In dscaml1 mutant animals, hypothalamic CRH neurons had higher crhb (the CRH homolog in zebrafish) expression, increased cell number, and reduced cell death compared to wild-type controls. Physiologically, dscaml1 mutant animals had higher baseline stress hormone (cortisol) levels and attenuated responses to acute stressors. Together, these findings identify dscaml1 as an essential factor for stress axis development and suggest that HPA axis dysregulation may contribute to the etiology of human DSCAML1-linked neuropsychiatric disorders.

Targeting the oxytocin system to ameliorate early life depressive-like behaviors in maternally-separated rats

Oxytocin (OXT) - "the love hormone" - has been involved in the anti-depressant activity of some selective serotonin reuptake inhibitors (SSRIs). The exact mechanism underlying the OXT pathway in depression is not fully clear. This study aimed to investigate the effect of OXT analogue, carbetocin (CBT) and the SSRI, escitalopram (ESCIT) on depressive-like behaviors following maternal separation (MS). It is worthy to mention that intranasal CBT has been approved by FDA for Prader-Willi syndrome. Adolescent Wistar albino maternally-separated rats were given CBT, (100 μg/animal/day via inhalation route), and, ESCIT, (20 mg kg^-1, po) either alone or in combination for 7 days. Repeated 3-h MS demonstrated increased immobility time in forced swim test (FST) and decreased locomotor activity in open field test. MS elevated plasma level of adrenocortico-trophic hormone (ACTH) but notably reduced plasma OXT, with no effect on hippocampal OXT-R expression. Following MS, hippocampal contents of 5-hydroxytryptamine receptors (5HT1A-R), serotonin transporter (SERT) were increased. CBT and ESCIT corrected the behavioral dysfunction in FST and suppressed the high levels of ACTH. Additionally, both treatments boosted OXT level, reduced 5HT1A-R and normalized SERT contents, which reflects increased availability of serotonin. Finally, CBT markedly ameliorated the histopathological damage induced by MS and suppressed the increased glial fibrillary acidic protein. CBT and ESCIT manage depressive-like behavior by positively affecting serotonergic and oxytocinergic systems. Targeting OXT system -using CBT- ameliorated depressive like behaviors induced by maternal separation most probably via enhancing OXT plasma levels, attenuating hormonal ACTH and restoring the expression of hippocampal oxytocin and serotonin mechanisms.

Microglial synaptic pruning on axon initial segment spines of dentate granule cells: Sexually dimorphic effects of early-life stress and consequences for adult fear response

Axon initial segments (AIS) of dentate granule cells in the hippocampus exhibit prominent spines (AISS) during early development that are associated with microglial contacts. In the present study, we investigated whether developmental changes in AISS could be modified by early-life stress (ELS), specifically neonatal maternal separation (MS), through stress hormones and microglial activation and examined the potential behavioural consequences. We examined AISS at postnatal day (PND)5, 15 and 50, using Golgi-Cox staining and anatomical analysis. Neurone-microglial interaction was assessed using antibodies against ankyrin-G, PSD-95 and Iba1, for AIS, AISS and microglia visualisation, respectively, in normally reared and neonatal maternally separated male and female rats. We observed a higher density of AISS in ELS rats at both PND15 and PND50 compared to controls. Effects were more pronounced in females than males. AIS-associated microglia in ELS rats showed a hyper-ramified morphology and less co-localisation with PSD-95 compared to controls at PND15. ELS-associated alteration in microglial morphology and synaptic pruning was mimicked by treatment of acute hippocampal slices of normally reared rats with vasopressin. ELS rats exhibited increased freezing behaviour during auditory fear memory testing, which was more pronounced in female subjects and corresponded with increased Fos expression in dorsal and ventral dentate granule cells. Thus, microglial synaptic pruning in dentate AIS of hippocampus is influenced by ELS, with demonstrable sex bias regarding its anatomical characteristics and subsequent fear-induced defensive behaviours.

Proteome profiling of different rat brain regions reveals the modulatory effect of prolonged maternal separation on proteins involved in cell death-related processes

Background

Early-life stress in the form of maternal separation can be associated with alterations in offspring neurodevelopment and brain functioning. Here, we aimed to investigate the potential impact of prolonged maternal separation on proteomic profiling of prefrontal cortex, hippocampus and cerebellum of juvenile and young adult rats. A special attention was devoted to proteins involved in the process of cell death and redox state maintenance.

Methods

Long-Evans pups were separated from their mothers for 3 h daily over the first 3 weeks of life (during days 2–21 of age). Brain tissue samples collected from juvenile (22-day-old) and young adult (90-day-old) rats were used for label-free quantitative (LFQ) proteomic analysis. In parallel, selected oxidative stress markers and apoptosis-related proteins were assessed biochemically and by Western blot, respectively.

Results

In total, 5526 proteins were detected in our proteomic analysis of rat brain tissue. Approximately one tenth of them (586 proteins) represented those involved in cell death processes or regulation of oxidative stress balance. Prolonged maternal separation caused changes in less than half of these proteins (271). The observed alterations in protein expression levels were age-, sex- and brain region-dependent. Interestingly, the proteins detected by mass spectrometry that are known to be involved in the maintenance of redox state were not markedly altered. Accordingly, we did not observe any significant differences between selected oxidative stress markers, such as the levels of hydrogen peroxide, reduced glutathione, protein carbonylation and lipid peroxidation in brain samples from rats that underwent maternal separation and from the corresponding controls. On the other hand, a number of changes were found in cell death-associated proteins, mainly in those involved in the apoptotic and autophagic pathways. However, there were no detectable alterations in the levels of cleaved products of caspases or Bcl-2 family members. Taken together, these data indicate that the apoptotic and autophagic cell death pathways were not activated by maternal separation either in adolescent or young adult rats.

Conclusion

Prolonged maternal separation can distinctly modulate expression profiles of proteins associated with cell death pathways in prefrontal cortex, hippocampus and cerebellum of juvenile rats and the consequences of early-life stress may last into adulthood and likely participate in variations in stress reactivity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40659-021-00327-5.

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.

Maternal separation disturbs postnatal development of the medial prefrontal cortex and affects the number of neurons and glial cells in adolescent rats

Adolescence is a period of extensive brain maturation. In particular, the regions of the medial prefrontal cortex (mPFC) undergo intense structural and functional refinement during adolescence. Disturbances in mPFC maturation have been implicated in the emergence of multiple psychopathologies during adolescence. One of the essential risk factors for the development of mental illness in adolescence is early-life stress (ELS), which may interfere with brain maturation. However, knowledge of the mechanisms by which ELS affects mPFC maturation and functioning in adolescents is very limited. In the present study, we applied a maternal separation (MS) procedure in rats to model ELS and studied its effect on the number of neurons and glial cells in the prelimbic region of the mPFC (PLC) of adolescent rats. Moreover, the expression of markers of cell proliferation and apoptosis was also studied. We found that MS rats had more neurons, astrocytes, and NG2-glial cells in the PLC. In contrast, the number of microglial cells was reduced in MS rats. These changes were accompanied by the decreased expression of proapoptotic genes and the increased expression of some prosurvival genes. Concurrently, MS did not affect cell proliferation in adolescents. Moreover, MS induced anxiety-like behaviors, but not anhedonic-like behavior, in adolescents. These results suggest that ELS may disturb neurodevelopmental apoptosis of neurons and early-postnatal proliferation and/or apoptosis of different populations of glial cells in the PLC. ELS-induced aberrations in the postnatal maturation of the PLC may affect cortical network organization and functioning and determine vulnerability to psychopathologies in adolescents.

Modulation of the Hypothalamic-Pituitary-Adrenal Axis by Early Life Stress Exposure

Exposure to stress during critical periods in development can have severe long-term consequences, increasing overall risk on psychopathology. One of the key stress response systems mediating these long-term effects of stress is the hypothalamic-pituitary-adrenal (HPA) axis; a cascade of central and peripheral events resulting in the release of corticosteroids from the adrenal glands. Activation of the HPA-axis affects brain functioning to ensure a proper behavioral response to the stressor, but stress-induced (mal)adaptation of the HPA-axis' functional maturation may provide a mechanistic basis for the altered stress susceptibility later in life. Development of the HPA-axis and the brain regions involved in its regulation starts prenatally and continues after birth, and is protected by several mechanisms preventing corticosteroid over-exposure to the maturing brain. Nevertheless, early life stress (ELS) exposure has been reported to have numerous consequences on HPA-axis function in adulthood, affecting both its basal and stress-induced activity. According to the match/mismatch theory, encountering ELS prepares an organism for similar ("matching") adversities during adulthood, while a mismatching environment results in an increased susceptibility to psychopathology, indicating that ELS can exert either beneficial or disadvantageous effects depending on the environmental context. Here, we review studies investigating the mechanistic underpinnings of the ELS-induced alterations in the structural and functional development of the HPA-axis and its key external regulators (amygdala, hippocampus, and prefrontal cortex). The effects of ELS appear highly dependent on the developmental time window affected, the sex of the offspring, and the developmental stage at which effects are assessed. Albeit by distinct mechanisms, ELS induced by prenatal stressors, maternal separation, or the limited nesting model inducing fragmented maternal care, typically results in HPA-axis hyper-reactivity in adulthood, as also found in major depression. This hyper-activity is related to increased corticotrophin-releasing hormone signaling and impaired glucocorticoid receptor-mediated negative feedback. In contrast, initial evidence for HPA-axis hypo-reactivity is observed for early social deprivation, potentially reflecting the abnormal HPA-axis function as observed in post-traumatic stress disorder, and future studies should investigate its neural/neuroendocrine foundation in further detail. Interestingly, experiencing additional (chronic) stress in adulthood seems to normalize these alterations in HPA-axis function, supporting the match/mismatch theory.

Regulating effect of TongXie-YaoFang on colonic epithelial secretion via Cl- and HCO3- channel

AIM

To investigate the pharmacological effect of TongXie-YaoFang (TXYF) formula, a Chinese herbal formula, on Diarrhea-predominant irritable bowel syndrome (D-IBS) rats.

METHODS

In a neonatal maternal separation plus restraint stress (NMS + RS) model of D-IBS, male Sprague Dawley rats were randomly divided into two groups (NMS + RS group and TXYF-formula group) with no handlings were used as controls (NH group). Starting from postnatal day 60, rats in TXYF-formula group were administered TXYF-formula (4.92 g/100 g bodyweight) orally twice a day for 14 consecutive days while NH group and NMS + RS group were given distilled water. Using short-circuit current technology, we observed 5-HT-induced changes of current across ion channels, such as cystic fibrosis transmembrane conductance regulator (CFTR) Cl^- channel, epithelial Na⁺ channel (ENaC), Ca²⁺-dependent Cl^- channel (CACC), Na⁺-K⁺-2Cl^- co-transporter (NKCC), and Na⁺-HCO₃^- co-transporter (NBC), in the colonic epithelium of three groups after exposure to drugs and specific blockers with a Power Lab System (AD Instruments International).

RESULTS

Under basal conditions, the changes of short-circuit current (∆Isc, µA/cm²) induced by 5-HT were similar in NH group and TXYF-formula group, and both higher than NMS + RS group (70.86 µA/cm² ± 12.32 µA/cm², 67.67 µA/cm² ± 11.68 µA/cm² vs 38.8 µA/cm² ± 7.25 µA/cm², P < 0.01, respectively). When CACC was blocked by 4,4′-diisothiocyanato-stilbene-2,2′-disulfonic acid, 5-HT-induced ∆Isc was smaller in NMS + RS group than in NH group and TXYF-formula group, respectively (48.41 µA/cm² ± 13.15 µA/cm² vs 74.62 µA/cm² ± 10.73 µA/cm², 69.22 µA/cm² ± 11.7 µA/cm², P < 0.05, respectively). The similar result could be obtained when ENaC was blocked by Amiloride (44.69 µA/cm² ± 12.58 µA/cm² vs 62.05 µA/cm² ± 11.26 µA/cm², 62.11 µA/cm² ± 12.01 µA/cm², P < 0.05, respectively). However, when CFTR Cl^- channel was blocked by 1,1-dimethyl piperidinium chloride (DPC), 5-HT-induced ∆Isc did not significantly differ in three groups (42.28 µA/cm² ± 10.61 µA/cm² vs 51.48 µA/cm² ± 6.56 µA/cm² vs 47.75 µA/cm² ± 7.99 µA/cm², P > 0.05, respectively). The similar results could also be obtained in three groups when NBC and NKCC were respectively blocked by their blockers.

CONCLUSION

TXYF-formula can regulate the Cl^- and HCO₃^- secretion of colonic mucosa via CFTR Cl^- channel, Cl^-/HCO₃^- exchanger, NBC and NKCC co-transporters.

The study of traditional Chinese medical elongated-needle therapy promoting neurological recovery mechanism after spinal cord injury in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Acupuncture is a key part of traditional Chinese medicine, shown to induce favorable neuroplasticity for injuries in the central and peripheral nervous systems. Recent studies report elongated needle therapy (ENT) with BL54 and ST28 may restore acute spinal cord injury (ASCI). However, the precise mechanism for this has not been elucidated.

AIM OF THE STUDY

In our current study, we investigated the effects of ENT on inflammation and neuronal apoptosis induced by ASCI, and whether PI3K/Akt and MAPK/ERK signaling pathways are involved in the ENT restoration effect.

MATERIALS AND METHODS

Rat models of moderate SCI were established in accordance with the modified Allen's method and were treated with ENT continuously for 7 days. Spontaneous activities were evaluated by the Basso Beattie and Bresnahan locomotor scale. Levels of inflammatory cytokines, such as tumor necrosis factor alpha, interleukin-6, IL-1β, and nuclear factor kappa-β, were determined by enzyme-linked immunosorbent assay. Cell apoptosis was examined by the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. The proportions of cells with positive Bcl-2 and Bax expression were determined by immunohistochemical assays, whilst the expression profiles of p-AKT and p-ERK in spinal cord tissues were evaluated by western blotting. Furthermore, the expression profiles of Cytochrome-C (Cyt-C) and caspase-3 in vivo were analyzed by reverse transcription polymerase chain reaction. The potential inhibitory effects downstream of the Akt and ERK signaling pathways were examined by administration of specific inhibitors LY294002 and PD98059 in vivo.

RESULTS

As indicated by this study, inflammation as well as PI3K/Akt- and MAPK/ERK signaling pathway-mediated neuronal apoptosis were involved in the course of SCI in rats. The neuro-protective effect of ENT was associated with reduced Bax protein-positive neurons and increased Bcl-2 protein-positive neurons. ENT enhanced recovery of rat activities. Activation of p-Akt and p-ERK in the PI3K/Akt and MAPK/ERK signaling pathways, inhibited expression of the critical component Cyt-C. Cyt-C is required for the mitochondrial apoptosis pathway and cascade of caspase-3, which is involved in activation of neuronal apoptosis through down-regulation of Bax protein and up-regulation of Bcl-2, as determined by TUNEL. The administration of PI3K/Akt and MAPK/ERK signaling pathway specific inhibitors, LY294002 and PD98059, suppressed expression of both p-Akt and p-ERK.

CONCLUSION

ENT with BL54 and ST28 points can promote the recovery of ASCI. And the neuro-protective effect of ENT during the restoration of SCI may be associated with the suppression of both inflammation and activation of PI3K/Akt and MAPK/ERK signaling pathways, resulting from down-regulation of Bax protein, up-regulation of Bcl-2, and inhibition of the mitochondrial apoptosis pathway.

Stress and the social brain: behavioural effects and neurobiological mechanisms

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

Brain-derived neurotrophic factor (BDNF) and its precursor (proBDNF) in genetically defined fear-induced aggression

The brain-derived neurotrophic factor (BDNF), its precursor (proBDNF) and BDNF mRNA levels were studied in the brain of wild rats selectively bred for more than 70 generations for either high level or for the lack of affective aggressiveness towards man. Significant increase of BDNF mRNA level in the frontal cortex and increase of BDNF level in the hippocampus of aggressive rats was revealed. In the midbrain and hippocampus of aggressive rats proBDNF level was increased, whereas BDNF/proBDNF ratio was reduced suggesting the prevalence and increased influence of proBDNF in highly aggressive rats. In the frontal cortex, proBDNF level in aggressive rats was decreased. Thus, considerable structure-specific differences in BDNF and proBDNF levels as well as in BDNF gene expression between highly aggressive and nonaggressive rats were shown. The data suggested the implication of BDNF and its precursor proBDNF in the mechanism of aggressiveness and in the creation of either aggressive or nonaggressive phenotype.