Modulation of adult hippocampal neurogenesis by early-life environmental challenges triggering immune activation

Decreased hippocampal neurite density in late middle-aged adults following prenatal exposure to higher levels of maternal inflammation

In animal models, exposure to heightened maternal inflammation in utero is associated with altered offspring hippocampal development, including reduced dendritic arborization and density. However, the effects of prenatal maternal inflammation (PNMI) on offspring hippocampal microstructure in humans remains unclear. Here, we examined the relationship between exposure to PNMI and neurite density in the hippocampus and its subfields among offspring during late middle age. Participants included 72 mother-offspring dyads from the Child Health and Development Studies (CHDS) cohort. Data for four inflammatory biomarkers (IL-6, IL-8, IL-1 receptor antagonist [IL-1RA], and soluble TNF receptor-II [sTNF-RII]) were available from first and second trimester maternal sera. Neurite density in the offspring hippocampus and its subfields was estimated using microstructural modeling of offsprings' diffusion-weighted Magnetic Resonance Imaging data (mean age of offspring at imaging = 59 years; 51% male). We estimated the relationship between each biomarker and region-of-interest's neurite density. Higher first trimester maternal IL-1RA and IL-6 levels were associated with lower offspring hippocampal neurite density. These relationships were specific to the CA3, CA4, dentate gyrus, and subiculum subfields. In addition, higher second trimester IL-6 was associated with lower subiculum neurite density. Our findings reveal that exposure to heightened prenatal levels of maternal inflammation is linked to altered offspring hippocampal microstructure in late middle age, which could have implications for memory decreases during this period and may be relevant for understanding risk of aging-related cognitive changes.

Gene expression changes in Brodmann's Area 46 differentiate epidermal growth factor and immune system interactions in schizophrenia and mood disorders

How early in life stress-immune related environmental factors increase risk predisposition to schizophrenia remains unknown. We examined if pro-inflammatory changes perturb the brain epidermal growth factor (EGF) system, a system critical for neurodevelopment and mature CNS functions including synaptic plasticity. We quantified genes from key EGF and immune system pathways for mRNA levels and eight immune proteins in post-mortem dorsolateral prefrontal (DLPFC; Brodmann's Area (BA) 46) and orbitofrontal (OFC; BA11) cortices from people with schizophrenia, mood disorders and neurotypical controls. In BA46, 64 genes were differentially expressed, predominantly in schizophrenia, where attenuated expression of the MAPK-ERK, NRG1-PI3K-AKT and mTOR cascades indicated reduced EGF system signalling, and similarly diminished immune molecular expression, notably in TLR, TNF and complement pathways, along with low NF-κB1 and elevated IL12RB2 protein levels were noted. There was nominal evidence for altered convergence between ErbB-PI3K-AKT-mTOR and TLR pathways in BA46 in schizophrenia. Comparatively minimal changes were noted in BA11. Overall, distinct pathway gene expression changes may reflect variant pathological processes involving immune and EGF system signalling between schizophrenia and mood disorder, particularly in DLPFC. Further, the abnormal convergence between innate immune signalling and candidate EGF signalling pathways may indicate a pathologically important interaction in the developing brain in response to environmental stressors.

High-intensity interval training ameliorates postnatal immune activation-induced mood disorders through KDM6B-regulated glial activation

Postnatal immune activation (PIA) induces persistent glial activation in the brain and causes various neuropathologies in adults. Exercise training improves stress-related mood disorders; however, the role of exercise in psychiatric disorders induced by early-life immune activation and the association between exercise training and glial activation remain unclear. We compared the effects of different exercise intensities on the PIA model, including high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT). Both HIIT and MICT in adolescent mice inhibited neuroinflammation, remodeled synaptic plasticity, and improved PIA-induced mood disorders in adulthood. Importantly, HIIT was superior to MICT in terms of reducing inflammation and increasing body weight. RNA-seq of prefrontal cortex (PFC) tissues revealed a gene expression pattern, confirming that HIIT was more effective than MICT in improving brain glial cell activation through epigenetic modifications of KDM6B. We investigated the role of KDM6B, a specific histone lysine demethylation enzyme - histone 3 lysine 27 demethylase, in inhibiting glial activation against PIA-induced depression and anxiety by regulating the expression of IL-4 and brain-derived neurotrophic factor (BDNF). Overall, our data support the idea that HIIT improves PIA-induced mood disorders by regulating KDM6B-mediated epigenetic mechanisms and indicate that HIIT might be superior to MICT in improving mood disorders with PIA in mice. Our findings provide new insights into the treatment of anxiety and depression disorders.

Effects of different types of induced neonatal inflammation on development and behavior of C57BL/6 and BTBR mice

Neuroinflammation in the early postnatal period can disturb trajectories of the completion of normal brain development and can lead to mental illnesses, such as depression, anxiety disorders, and personality disorders later in life. In our study, we focused on evaluating short- and long-term effects of neonatal inflammation induced by lipopolysaccharide, poly(I:C), or their combination in female and male C57BL/6 and BTBR mice. We chose the BTBR strain as potentially more susceptible to neonatal inflammation because these mice have behavioral, neuroanatomical, and physiological features of autism spectrum disorders, an abnormal immune response, and several structural aberrations in the brain. Our results indicated that BTBR mice are more sensitive to the influence of the neonatal immune activation (NIA) on the formation of neonatal reflexes than C57BL/6 mice are. In these experiments, the injection of lipopolysaccharide had an effect on the formation of the cliff aversion reflex in female BTBR mice. Nonetheless, NIA had no delayed effects on either social behavior or anxiety-like behavior in juvenile and adolescent BTBR and C57BL/6 mice. Altogether, our data show that NIA has mimetic-, age-, and strain-dependent effects on the development of neonatal reflexes and on exploratory activity in BTBR and C57BL/6 mice.

Neonatal kaempferol exposure attenuates impact of cerebral palsy model on neuromotor development, cell proliferation, microglia activation, and antioxidant enzyme expression in the hippocampus of rats

OBJECTIVES

This study aims to assess the effect of neonatal treatment with kaempferol on neuromotor development, proliferation of neural precursor cells, the microglia profile, and antioxidant enzyme gene expression in the hippocampus.

METHODS

A rat model of cerebral palsy was established using perinatal anoxia and sensorimotor restriction of hindlimbs during infancy. Kaempferol (1 mg/ kg) was intraperitoneally administered during the neonatal period.

RESULTS

Neonatal treatment with kaempferol reduces the impact of the cerebral palsy model on reflex ontogeny and on the maturation of physical features. Impairment of locomotor activity development and motor coordination was found to be attenuated by kaempferol treatment during the neonatal period in rats exposed to cerebral palsy. Neonatal treatment of kaempferol in cerebral palsy rats prevents a substantial reduction in the number of neural precursor cells in the dentate gyrus of the hippocampus, an activated microglia profile, and increased proliferation of microglia in the sub-granular zone and in the granular cell layer. Neonatal treatment with kaempferol increases gene expression of superoxide dismutase and catalase in the hippocampus of rats submitted to the cerebral palsy model.

DISCUSSION

Kaempferol attenuates the impact of cerebral palsy on neuromotor behavior development, preventing altered hippocampal microglia activation and mitigating impaired cell proliferation in a neurogenic niche in these rats. Neonatal treatment with kaempferol also increases antioxidant defense gene expression in the hippocampus of rats submitted to the cerebral palsy model.

Microglial Caspase-3 is essential for modulating hippocampal neurogenesis

Adult hippocampal neurogenesis (AHN) is a process involved in numerous neurodegenerative diseases. Many researchers have described microglia as a key component in regulating the formation and migration of new neurons along the rostral migratory stream. Caspase-3 is a cysteine-aspartate-protease classically considered as one of the main effector caspases in the cell death program process. In addition to this classical function, we have identified the role of this protein as a modulator of microglial function; however, its action on neurogenic processes is unknown. The aim of the present study is to identify the role of Caspase-3 in neurogenesis-related microglial functions. To address this study, Caspase-3 conditional knockout mice in the microglia cell line were used. Using this tool, we wanted to elucidate the role of this protein in microglial function in the hippocampus, the main region in which adult neurogenesis takes place. After the reduction of Caspase-3 in microglia, mutant mice showed a reduction of microglia in the hippocampus, especially in the dentate gyrus region, a region inherently associated to neurogenesis. In addition, we found a reduction in doublecortin-positive neurons in conditional Caspase-3 knockout mice, which corresponds to a reduction in neurogenic neurons. Furthermore, using high-resolution image analysis, we also observed a reduction in the phagocytic capacity of microglia lacking Caspase-3. Behavioral analysis using object recognition and Y-maze tests showed altered memory and learning in the absence of Caspase-3. Finally, we identified specific microglia located specifically in neurogenic niche positive for Galectin 3 which colocalized with Cleaved-Caspase-3 in control mice. Taken together, these results showed the essential role of Caspase-3 in microglial function and highlight the relevant role of this specific microglial phenotype in the maintenance of AHN in the hippocampus.

Maternal Immune Activation Induced by Prenatal Lipopolysaccharide Exposure Leads to Long-Lasting Autistic-like Social, Cognitive and Immune Alterations in Male Wistar Rats

Several studies have supported the association between maternal immune activation (MIA) caused by exposure to pathogens or inflammation during critical periods of gestation and an increased susceptibility to the development of various psychiatric and neurological disorders, including autism and other neurodevelopmental disorders (NDDs), in the offspring. In the present work, we aimed to provide extensive characterization of the short- and long-term consequences of MIA in the offspring, both at the behavioral and immunological level. To this end, we exposed Wistar rat dams to Lipopolysaccharide and tested the infant, adolescent and adult offspring across several behavioral domains relevant to human psychopathological traits. Furthermore, we also measured plasmatic inflammatory markers both at adolescence and adulthood. Our results support the hypothesis of a deleterious impact of MIA on the neurobehavioral development of the offspring: we found deficits in the communicative, social and cognitive domains, together with stereotypic-like behaviors and an altered inflammatory profile at the systemic level. Although the precise mechanisms underlying the role of neuroinflammatory states in neurodevelopment need to be clarified, this study contributes to a better understanding of the impact of MIA on the risk of developing behavioral deficits and psychiatric illness in the offspring.

Psychosocial factors and hippocampal subfields: The Medea-7T study

Specific subfields within the hippocampus have shown vulnerability to chronic stress, highlighting the importance of looking regionally within the hippocampus to understand the role of psychosocial factors in the development of neurodegenerative diseases. A systematic review on psychosocial factors and hippocampal subfield volumes was performed and showed inconsistent results, highlighting the need for future studies to explore this relationship. The current study aimed to explore the association of psychosocial factors with hippocampal (subfield) volumes, using high-field 7T MRI. Data were from the Memory Depression and Aging (Medea)-7T study, which included 333 participants without dementia. Hippocampal subfields were automatically segmented from T2-weighted images using ASHS software. Generalized linear models accounting for correlated outcomes were used to assess the association between subfields (i.e., entorhinal cortex, subiculum, Cornu Ammonis [CA]1, CA2, CA3, dentate gyrus, and tail) and each psychosocial factor (i.e., depressive symptoms, anxiety symptoms, childhood maltreatment, recent stressful life events, and social support), adjusted for age, sex, and intracranial volume. Neither depression nor anxiety was associated with specific hippocampal (subfield) volumes. A trend for lower total hippocampal volume was found in those reporting childhood maltreatment, and a trend for higher total hippocampal volume was found in those who experienced a recent stressful life event. Among subfields, low social support was associated with lower volume in the CA3 (B = -0.43, 95% CI: -0.72; -0.15). This study suggests possible differential effects among hippocampal (subfield) volumes and psychosocial factors.

Maternal immune activation primes deficiencies in adult hippocampal neurogenesis

Neurogenesis, the process in which new neurons are generated, occurs throughout life in the mammalian hippocampus. Decreased adult hippocampal neurogenesis (AHN) is a common feature across psychiatric disorders, including schizophrenia, depression- and anxiety-related behaviours, and is highly regulated by environmental influences. Epidemiological studies have consistently implicated maternal immune activation (MIA) during neurodevelopment as a risk factor for psychiatric disorders in adulthood. The extent to which the reduction of hippocampal neurogenesis in adulthood may be driven by early life exposures, such as MIA, is however unclear. We therefore reviewed the literature for evidence of the involvement of MIA in disrupting AHN. Consistent with our hypothesis, data from both in vivo murine and in vitro human models of AHN provide evidence for key roles of specific cytokines induced by MIA in the foetal brain in disrupting hippocampal neural progenitor cell proliferation and differentiation early in development. The precise molecular mechanisms however remain unclear. Nonetheless, these data suggest a potential latent vulnerability mechanism, whereby MIA primes dysfunction in the unique hippocampal pool of neural stem/progenitor cells. This renders offspring potentially more susceptible to additional environmental exposures later in life, such as chronic stress, resulting in the unmasking of psychopathology. We highlight the need for studies to test this hypothesis using validated animal models of MIA, but also to test the relevance of such data for human pathology at a molecular basis through the use of patient-derived induced pluripotent stem cells (hiPSC) differentiated into hippocampal progenitor cells.

Modulation of Neural Networks by Interleukin-1

Interleukin-1 (IL-1) is an inflammatory cytokine that has been shown to modulate neuronal signaling in homeostasis and diseases. In homeostasis, IL-1 regulates sleep and memory formation, whereas in diseases, IL-1 impairs memory and alters affect. Interestingly, IL-1 can cause long-lasting changes in behavior, suggesting IL-1 can alter neuroplasticity. The neuroplastic effects of IL-1 are mediated via its cognate receptor, Interleukin-1 Type 1 Receptor (IL-1R1), and are dependent on the distribution and cell type(s) of IL-1R1 expression. Recent reports found that IL-1R1 expression is restricted to discrete subpopulations of neurons, astrocytes, and endothelial cells and suggest IL-1 can influence neural circuits directly through neuronal IL-1R1 or indirectly via non-neuronal IL-1R1. In this review, we analyzed multiple mechanisms by which IL-1/IL-1R1 signaling might impact neuroplasticity based upon the most up-to-date literature and provided potential explanations to clarify discrepant and confusing findings reported in the past.

A systematic review of neurogenesis in animal models of early brain damage: Implications for cerebral palsy

Brain damage during early life is the main factor in the development of cerebral palsy (CP), which is one of the leading neurodevelopmental disorders in childhood. Few studies, however, have focused on the mechanisms of cell proliferation, migration, and differentiation in the brain of individuals with CP. We thus conducted a systematic review of preclinical evidence of structural neurogenesis in early brain damage and the underlying mechanisms involved in the pathogenesis of CP. Studies were obtained from Embase, Pubmed, Scopus, and Web of Science. After screening 2329 studies, 29 studies, covering a total of 751 animals, were included. Prenatal models based on oxygen deprivation, inflammatory response and infection, postnatal models based on oxygen deprivation or hypoxic-ischemia, and intraventricular hemorrhage models showed varying neurogenesis responses according to the nature of the brain damage, the time period during which the brain injury occurred, proliferative capacity, pattern of migration, and differentiation profile in neurogenic niches. Results mainly from rodent studies suggest that prenatal brain damage impacts neurogenesis and curbs generation of neural stem cells, while postnatal models show increased proliferation of neural precursor cells, improper migration, and reduced survival of new neurons.

Neonatal Immune Activation May Provoke Long-term Depressive Attributes

BACKGROUND

Studies have shown the relationship between neuroinflammation and depressive- like parameters. However, research still has not been carried out to evaluate neuroinflammation in the neonatal period and psychiatric disorders in adulthood.

OBJECTIVE

To verify the association between neonatal immune activation and depressive-like parameters in adulthood using an animal model.

METHODS

Two days old C57BL/6 animals were exposed to lipopolysaccharides (LPS) or phosphate- buffered saline (PBS). When the animals were 46 days old, they received PBS or Imipramine at 14 days. At 60 days, the consumption of sucrose; immobility time; adrenal gland and the hippocampus weight; levels of plasma corticosterone and hippocampal Brain-derived neurotrophic factor (BDNF) were evaluated.

RESULTS

It was observed that the animals exposed to LPS in the neonatal period and evaluated in adulthood decreased the consumption of sucrose and had reducted hippocampus weight. Also, the exposed animals presented an increase of immobility time, adrenal gland weight and plasma levels of corticosteroids. The use of imipramine did not only modify the decreased hippocampal weight. On the other hand, there were no alterations in the BDNF levels in the hippocampus with or without the use of imipramine.

CONCLUSION

These results suggest that neonatal immune activation may be associated with depressive- like parameters in adulthood. It is believed that endotoxemia may trigger physiological and behavioral alterations, increasing vulnerability for the development of depression in adulthood.

The Anti-Depressive Effects of Hesperidin and the Relative Mechanisms Based on the NLRP3 Inflammatory Signaling Pathway

There is increasing evidence showing that inflammation is associated with depression in humans. Hesperidin, a natural bioflavonoid, has performed excellent effects on depression. The aim of this research was to investigate the therapeutic effect of hesperidin on chronic unpredictable mild stress (CUMS)-induced rats. The sucrose preference test (SPT), forced swimming test (FST), and open field test (OFT) were performed to measure the depression-related symptoms. The enzyme-linked immunosorbent assay (ELISA) was used to determine the concentrations of interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α in the prefrontal cortex (PFC) of rats and cellular supernatant. PCR and Western blot were used to monitor the differences of NLRP3, caspase-1, ASC activation in the levels of genes and proteins in the PFC of rats and microglia. The activation of microglia was determined using immunofluorescence staining and flow cytometry assay. Our results show that hesperidin treatment significantly relieved depressive like behaviors in CUMS rats. In addition, hesperidin decreased the expression levels of IL-1β, IL-6, TNF-α, NLRP3, caspase-1, and ASC in the PFC and microglia. This study investigated that hesperidin treatment ameliorated CUMS-induced depression by suppressing microglia and inflammation.

The Appendix in Parkinson's Disease: From Vestigial Remnant to Vital Organ?

Parkinson's disease (PD) has long been considered a brain disease, but studies now point to the gastrointestinal (GI) tract as a potential starting point for PD. In particular, the human vermiform appendix has been implicated in PD. The appendix is a tissue rich in immune cells, serving as part of the gut-associated lymphoid tissue and as a storehouse for the gut microbiome. The functions of the appendix converge with recent evidence demonstrating that gut inflammation and shifts in the microbiome are linked to PD. Some epidemiological studies have linked removal of the appendix to lowered PD risk, though there is controversy among these associations. What is apparent is that there is an abundance of aggregated forms of α-synuclein in the appendix relevant to PD pathology. α-Synuclein pathology is thought to propagate from gut to brain via the vagus nerve, which innervates GI tract locations, including the appendix. Remarkably, α-synuclein aggregates in the appendix occur not only in PD patients, but are also present in healthy individuals. This has led to the proposal that in the appendix α-synuclein aggregates are not unique to PD. Moreover, the molecular events leading to PD and the mechanisms by which α-synuclein aggregates transfers from gut to brain may be identifiable in the human appendix. The influence of the appendix on GI inflammation, autoimmunity, microbiome storage, and the lymphatic system may be yet unexplored mechanisms by which the appendix contributes to PD. Overall, the appendix represents a promising tissue site to advance our understanding of PD pathobiology.

Exercising New Neurons to Vanquish Alzheimer Disease

Alzheimer disease (AD) is the most common type of dementia in individuals over 65 years of age. The neuropathological hallmarks of the condition are Tau neurofibrillary tangles and Amyloid-β senile plaques. Moreover, certain susceptible regions of the brain experience a generalized lack of neural plasticity and marked synaptic alterations during the progression of this as yet incurable disease. One of these regions, the hippocampus, is characterized by the continuous addition of new neurons throughout life. This phenomenon, named adult hippocampal neurogenesis (AHN), provides a potentially endless source of new synaptic elements that increase the complexity and plasticity of the hippocampal circuitry. Numerous lines of evidence show that physical activity and environmental enrichment (EE) are among the most potent positive regulators of AHN. Given that neural plasticity is markedly decreased in many neurodegenerative diseases, the therapeutic potential of making certain lifestyle changes, such as increasing physical activity, is being recognised in several non-pharmacologic strategies seeking to slow down or prevent the progression of these diseases. This review article summarizes current evidence supporting the putative therapeutic potential of EE and physical exercise to increase AHN and hippocampal plasticity both under physiological and pathological circumstances, with a special emphasis on neurodegenerative diseases and AD.

Maternal immune and affiliative biomarkers and sensitive parenting mediate the effects of chronic early trauma on child anxiety

BACKGROUND

Chronic early trauma alters children's stress reactivity and increases the prevalence of anxiety disorders; yet the neuroendocrine and immune mechanisms underpinning this effect are not fully clear. Animal studies indicate that the mother's physiology and behavior mediate offspring stress in a system-specific manner, but few studies tested this external-regulatory maternal role in human children exposed to chronic stress.

METHODS

We followed a unique cohort of children exposed to continuous wartime trauma (N = 177; exposed; N = 101, controls; N = 76). At 10 years, maternal and child's salivary immunoglobulin A (s-IgA) and oxytocin (OT), biomarkers of the immune and affiliation systems, were assayed, maternal and child relational behaviors observed, mother and child underwent psychiatric diagnosis, and child anxiety symptoms assessed.

RESULTS

War-exposed mothers had higher s-IgA, lower OT, more anxiety symptoms, and their parenting was characterized by reduced sensitivity. Exposed children showed higher s-IgA, more anxiety disorders and post traumatic stress disorder, and more anxiety symptoms. Path analysis model defined three pathways by which maternal physiology and behavior impacted child anxiety; (a) increasing maternal s-IgA, which led to increased child s-IgA, augmenting child anxiety; (b) reducing maternal OT, which linked with diminished child OT and social repertoire; and (c) increasing maternal anxiety, which directly impacted child anxiety.

CONCLUSIONS

Our findings, the first to measure immune and affiliation biomarkers in mothers and children, detail their unique and joint effects on children's anxiety in response to stress; highlight the relations between chronic stress, immune activation, and anxiety in children; and describe how processes of biobehavioral synchrony shape children's long-term adaptation.

Release of interleukin-10 and neurotrophic factors in the choroid plexus: possible inductors of neurogenesis following copolymer-1 immunization after cerebral ischemia

Copolymer-1 (Cop-1) is a peptide with immunomodulatory properties, approved by the Food and Drug Administration of United States in the treatment of multiple sclerosis. Cop-1 has been shown to exert neuroprotective effects and induce neurogenesis in cerebral ischemia models. Nevertheless, the mechanism involved in the neurogenic action of this compound remains unknown. The choroid plexus (CP) is a network of cells that constitute the interphase between the immune and central nervous systems, with the ability to mediate neurogenesis through the release of cytokines and growth factors. Therefore, the CP could play a role in Cop-1-induced neurogenesis. In order to determine the participation of the CP in the induction of neurogenesis after Cop-1 immunization, we evaluated the gene expression of various growth factors (brain-derived neurotrophic factor, insulin-like growth factor 1, neurotrophin-3) and cytokines (tumor necrosis factor alpha, interferon-gamma, interleukin-4 (IL-4), IL-10 and IL-17), in the CP at 14 days after ischemia. Furthermore, we analyzed the correlation between the expression of these genes and neurogenesis. Our results showed that Cop-1 was capable of stimulating an upregulation in the expression of the genes encoding for brain-derived neurotrophic factor, insulin-like growth factor 1, neurotrophin-3 and IL-10 in the CP, which correlated with an increase in neurogenesis in the subventricular and subgranular zone. As well, we observed a downregulation of IL-17 gene expression. This study demonstrates the effect of Cop-1 on the expression of growth factors and IL-10 in the CP, in the same way, presents a possible mechanism involved in the neurogenic effect of Cop-1.

The genome-wide expression effects of escitalopram and its relationship to neurogenesis, hippocampal volume, and antidepressant response

Antidepressant-induced hippocampal neurogenesis (AHN) is hypothesized to contribute to increases in hippocampal volume among major depressive disorder patients after long-term treatment. Furthermore, rodent studies suggest AHN may be the cellular mechanism mediating the therapeutic benefits of antidepressants. Here, we perform the first investigation of genome-wide expression changes associated with AHN in human cells. We identify gene expression networks significantly activated during AHN, and we perform gene set analyses to probe the molecular relationship between AHN, hippocampal volume, and antidepressant response. The latter were achieved using genome-wide association summary data collected from 30,717 individuals as part of the ENIGMA Consortium (genetic predictors of hippocampal volume dataset), and data collected from 1,222 major depressed patients as part of the NEWMEDS Project (genetic predictors of response to antidepressants dataset). Our results showed that the selective serotonin reuptake inhibitor, escitalopram evoked AHN in human cells; dose-dependently increasing the differentiation of cells into neuroblasts, as well as increasing gliogenesis. Activated genome-wide expression networks relate to axon and microtubule formation, and ribosomal biogenesis. Gene set analysis revealed that gene expression changes associated with AHN were nominally enriched for genes predictive of hippocampal volume, but not for genes predictive of therapeutic response.

Adult neurogenesis and neurodegenerative diseases: A systems biology perspective

New neurons are generated throughout adulthood in two regions of the brain, the olfactory bulb and dentate gyrus of the hippocampus, and are incorporated into the hippocampal network circuitry; disruption of this process has been postulated to contribute to neurodegenerative diseases including Alzheimer's disease and Parkinson's disease. Known modulators of adult neurogenesis include signal transduction pathways, the vascular and immune systems, metabolic factors, and epigenetic regulation. Multiple intrinsic and extrinsic factors such as neurotrophic factors, transcription factors, and cell cycle regulators control neural stem cell proliferation, maintenance in the adult neurogenic niche, and differentiation into mature neurons; these factors act in networks of signaling molecules that influence each other during construction and maintenance of neural circuits, and in turn contribute to learning and memory. The immune system and vascular system are necessary for neuronal formation and neural stem cell fate determination. Inflammatory cytokines regulate adult neurogenesis in response to immune system activation, whereas the vasculature regulates the neural stem cell niche. Vasculature, immune/support cell populations (microglia/astrocytes), adhesion molecules, growth factors, and the extracellular matrix also provide a homing environment for neural stem cells. Epigenetic changes during hippocampal neurogenesis also impact memory and learning. Some genetic variations in neurogenesis related genes may play important roles in the alteration of neural stem cells differentiation into new born neurons during adult neurogenesis, with important therapeutic implications. In this review, we discuss mechanisms of and interactions between these modulators of adult neurogenesis, as well as implications for neurodegenerative disease and current therapeutic research. © 2016 Wiley Periodicals, Inc.

Effects of Chronic Social Stress and Maternal Intranasal Oxytocin and Vasopressin on Offspring Interferon-γ and Behavior

Recent studies support the hypothesis that the adverse effects of early-life adversity and transgenerational stress on neural plasticity and behavior are mediated by inflammation. The objective of the present study was to investigate the immune and behavioral programing effects of intranasal (IN) vasopressin (AVP) and oxytocin (OXT) treatment of chronic social stress (CSS)-exposed F1 dams on F2 juvenile female offspring. It was hypothesized that maternal AVP and OXT treatment would have preventative effects on social stress-induced deficits in offspring anxiety and social behavior and that these effects would be associated with changes in interferon-γ (IFNγ). Control and CSS-exposed F1 dams were administered IN saline, AVP, or OXT during lactation and the F2 juvenile female offspring were assessed for basal plasma IFNγ and perseverative, anxiety, and social behavior. CSS F2 female juvenile offspring had elevated IFNγ levels and exhibited increased repetitive/perseverative and anxiety behaviors and deficits in social behavior. These effects were modulated by AVP and OXT in a context- and behavior-dependent manner, with OXT exhibiting preventative effects on repetitive and anxiety behaviors and AVP possessing preventative effects on social behavior deficits and anxiety. Basal IFNγ levels were elevated in the F2 offspring of OXT-treated F1 dams, but IFNγ was not correlated with the behavioral effects. These results support the hypothesis that maternal AVP and OXT treatment have context- and behavior-specific effects on peripheral IFNγ levels and perseverative, anxiety, and social behaviors in the female offspring of early-life social stress-exposed dams. Both maternal AVP and OXT are effective at preventing social stress-induced increases in self-directed measures of anxiety, and AVP is particularly effective at preventing impairments in overall social contact. OXT is specifically effective at preventing repetitive/perseverative behaviors, yet is ineffective at preventing deficits in overall social behavior.

Oxidative stress: a potential link between emotional wellbeing and immune response

Emotional wellbeing is central to normal health and good living. Persistent psychological stress often disrupts emotional wellbeing and triggers onset of neuropsychiatric ailments. An integrated, multisystemic stress response involving neuroinflammatory, neuroendocrine and metabolic cascades seem to have some causative links. Of particular interest are the neuroinflammatory processes. Psychological stress has been suggested to negatively affect normal functioning of the immune system contributing to the pathophysiology of some neuropsychiatric conditions. Thus examination of the interaction between the immune system and the central nervous system is likely to reveal molecular targets critical for development of potential therapeutic and preventive measures. This review is a summarized discussion of evidence linking impact of psychological stress on the immune system, with a particular emphasis on oxidative stress mechanisms by which mental stress potentially impacts immune function leading to activation of multiple cascades resulting in subsequent manifestation of psychiatric symptomologies.

Toddler temperament and prenatal exposure to lead and maternal depression

BACKGROUND

Temperament is a psychological construct that reflects both personality and an infant's reaction to social stimuli. It can be assessed early in life and is stable over time Temperament predicts many later life behaviors and illnesses, including impulsivity, emotional regulation and obesity. Early life exposure to neurotoxicants often results in developmental deficits in attention, social function, and IQ, but environmental predictors of infant temperament are largely unknown. We propose that prenatal exposure to both chemical and non-chemical environmental toxicants impacts the development of temperament, which can itself be used as a marker of risk for maladaptive neurobehavior in later life. In this study, we assessed associations among prenatal and early life exposure to lead, mercury, poverty, maternal depression and toddler temperament.

METHODS

A prospective cohort of women living in the Mexico City area were followed longitudinally beginning in the second trimester of pregnancy. Prenatal exposure to lead (blood, bone), mercury, and maternal depression were assessed repeatedly and the Toddler Temperament Scale (TTS) was completed when the child was 24 months old. The association between each measure of prenatal exposure and performance on individual TTS subscales was evaluated by multivariable linear regression. Latent profile analysis was used to classify subjects by TTS performance. Multinomial regression models were used to estimate the prospective association between prenatal exposures and TTS performance.

RESULTS

500 mother-child pairs completed the TTS and had complete data on exposures and covariates. Three latent profiles were identified and categorized as predominantly difficult, intermediate, or easy temperament. Prenatal exposure to maternal depression predicted increasing probability of difficult toddler temperament. Maternal bone lead, a marker of cumulative exposure, also predicted difficult temperament. Prenatal lead exposure modified this association, suggesting that joint exposure in pregnancy to both was most toxic.

CONCLUSIONS

Maternal depression predicts difficult temperament and concurrent prenatal exposure to maternal depression and lead predicts a more difficult temperament phenotype in 2 year olds. The role of temperament as an intermediate variable in the path from prenatal exposures to neurobehavioral deficits and other health effects deserves further study.

Resveratrol: A Potential Hippocampal Plasticity Enhancer

The search for molecules capable of restoring altered hippocampal plasticity in psychiatric and neurological conditions is one of the most important tasks of modern neuroscience. It is well established that neural plasticity, such as the ability of the postnatal hippocampus to continuously generate newly functional neurons throughout life, a process called adult hippocampal neurogenesis (AHN), can be modulated not only by pharmacological agents, physical exercise, and environmental enrichment, but also by “nutraceutical” agents. In this review we focus on resveratrol, a phenol and phytoalexin found in the skin of grapes and red berries, as well as in nuts. Resveratrol has been reported to have antioxidant and antitumor properties, but its effects as a neural plasticity inducer are still debated. The current review examines recent evidence implicating resveratrol in regulating hippocampal neural plasticity and in mitigating the effects of various disorders and diseases on this important brain structure. Overall, findings show that resveratrol can improve cognition and mood and enhance hippocampal plasticity and AHN; however, some studies report opposite effects, with resveratrol inhibiting aspects of AHN. Therefore, further investigation is needed to resolve these controversies before resveratrol can be established as a safe coadjuvant in preventing and treating neuropsychiatric conditions.

Transgenerational Social Stress, Immune Factors, Hormones, and Social Behavior

A social signal transduction theory of depression has been proposed that states that exposure to social adversity alters the immune response and these changes mediate symptoms of depression such as anhedonia and impairments in social behavior The exposure of maternal rats to the chronic social stress (CSS) of a male intruder depresses maternal care and impairs social behavior in the F1 and F2 offspring of these dams. The objective of the present study was to characterize basal peripheral levels of several immune factors and related hormone levels in the adult F2 offspring of CSS exposed dams and assess whether changes in these factors are associated with previously reported deficits in allogrooming behavior. CSS decreased acid glycoprotein (α1AGP) and intercellular adhesion molecule-1 (ICAM-1) in F2 females, and increased granulocyte macrophage-colony stimulating factor (GM-CSF) in F2 males. There were also sex dependent changes in IL-18, tissue inhibitors of metalloproteinases 1 (TIMP-1), and vascular endothelial growth factor (VEGF). Progesterone was decreased and alpha melanocyte stimulating hormone (α-MSH) was increased in F2 males, and brain-derived neurotrophic factor (BDNF) was decreased in F2 females. Changes in α1AGP, GM-CSF, progesterone, and α-MSH were correlated with decreased allogrooming in the F2 offspring of stressed dams. These results support the hypothesis that transgenerational social stress affects both the immune system and social behavior, and also support previous studies on the adverse effects of early life stress on immune functioning and stress associated immunological disorders, including the increasing prevalence of asthma. The immune system may represent an important transgenerational etiological factor in disorders which involve social and/or early life stress associated changes in social behavior, such as depression, anxiety, and autism, as well as comorbid immune disorders. Future studies involving immune and/or endocrine assessments and manipulations will address specific questions of function and causation, and may identify novel preventative measures and treatments for the growing number of immune mediated disorders.

Regulation of Adult Neurogenesis and Plasticity by (Early) Stress, Glucocorticoids, and Inflammation

Exposure to stress is one of the best-known negative regulators of adult neurogenesis (AN). We discuss changes in neurogenesis in relation to exposure to stress, glucocorticoid hormones, and inflammation, with a particular focus on early development and on lasting effects of stress. Although the effects of acute and mild stress on AN are generally brief and can be quickly overcome, chronic exposure or more severe forms of stress can induce longer lasting reductions in neurogenesis that can, however, in part, be overcome by subsequent exposure to exercise, drugs targeting the stress system, and some antidepressants. Exposure to stress, particularly during the sensitive period of early life, may (re)program brain plasticity, in particular, in the hippocampus. This may increase the risk to develop cognitive or anxiety symptoms, common to brain diseases like dementia and depression in which plasticity changes occur, and a normalization of neurogenesis may be required for a successful treatment response and recovery.

Ketamine and phencyclidine: the good, the bad and the unexpected

The history of ketamine and phencyclidine from their development as potential clinical anaesthetics through drugs of abuse and animal models of schizophrenia to potential rapidly acting antidepressants is reviewed. The discovery in 1983 of the NMDA receptor antagonist property of ketamine and phencyclidine was a key step to understanding their pharmacology, including their psychotomimetic effects in man. This review describes the historical context and the course of that discovery and its expansion into other hallucinatory drugs. The relevance of these findings to modern hypotheses of schizophrenia and the implications for drug discovery are reviewed. The findings of the rapidly acting antidepressant effects of ketamine in man are discussed in relation to other glutamatergic mechanisms.

Hippocampal Proteomic and Metabonomic Abnormalities in Neurotransmission, Oxidative Stress, and Apoptotic Pathways in a Chronic Phencyclidine Rat Model

Schizophrenia is a neuropsychiatric disorder affecting 1% of the world's population. Due to both a broad range of symptoms and disease heterogeneity, current therapeutic approaches to treat schizophrenia fail to address all symptomatic manifestations of the disease. Therefore, disease models that reproduce core pathological features of schizophrenia are needed for the elucidation of pathological disease mechanisms. Here, we employ a comprehensive global label-free liquid chromatography-mass spectrometry proteomic (LC-MS(E)) and metabonomic (LC-MS) profiling analysis combined with the targeted proteomics (selected reaction monitoring and multiplex immunoassay) of serum and brain tissues to investigate a chronic phencyclidine (PCP) rat model in which glutamatergic hypofunction is induced through noncompetitive NMDAR-receptor antagonism. Using a multiplex immunoassay, we identified alterations in the levels of several cytokines (IL-5, IL-2, and IL-1β) and fibroblast growth factor-2. Extensive proteomic and metabonomic brain tissue profiling revealed a more prominent effect of chronic PCP treatment on both the hippocampal proteome and metabonome compared to the effect on the frontal cortex. Bioinformatic pathway analysis confirmed prominent abnormalities in NMDA-receptor-associated pathways in both brain regions, as well as alterations in other neurotransmitter systems such as kainate, AMPA, and GABAergic signaling in the hippocampus and in proteins associated with neurodegeneration. We further identified abundance changes in the level of the superoxide dismutase enzyme (SODC) in both the frontal cortex and hippocampus, which indicates alterations in oxidative stress and substantiates the apoptotic pathway alterations. The present study could lead to an increased understanding of how perturbed glutamate receptor signaling affects other relevant biological pathways in schizophrenia and, therefore, support drug discovery efforts for the improved treatment of patients suffering from this debilitating psychiatric disorder.

Early life stress and hippocampal neurogenesis in the neonate: sexual dimorphism, long term consequences and possible mediators

Adverse early life experience decreases adult hippocampal neurogenesis and results in increased vulnerability to neuropsychiatric disorders. Despite that the effects of postnatal stress on neurogenesis have been widely studied in adult individuals, few efforts have been done to evaluate its immediate effects on the developing hippocampus. Moreover, it is not clear whether postnatal stress causes a differential impact in hippocampus development in male and female neonates that could be related to emotional deficits in adulthood. It has been proposed that the long term effects of early stress exposure rise from a persistent HPA axis activation during sensitive time windows; nevertheless the exact mechanisms and mediators remain unknown. Here, we summarize the immediate and late effects of early life stress on hippocampal neurogenesis in male and female rat pups, compare its later consequences in emotionality, and highlight some relevant mediator peptides that could be potentially involved in programming.

The interplay of early-life stress, nutrition, and immune activation programs adult hippocampal structure and function

Early-life adversity increases the vulnerability to develop psychopathologies and cognitive decline later in life. This association is supported by clinical and preclinical studies. Remarkably, experiences of stress during this sensitive period, in the form of abuse or neglect but also early malnutrition or an early immune challenge elicit very similar long-term effects on brain structure and function. During early-life, both exogenous factors like nutrition and maternal care, as well as endogenous modulators, including stress hormones and mediator of immunological activity affect brain development. The interplay of these key elements and their underlying molecular mechanisms are not fully understood. We discuss here the hypothesis that exposure to early-life adversity (specifically stress, under/malnutrition and infection) leads to life-long alterations in hippocampal-related cognitive functions, at least partly via changes in hippocampal neurogenesis. We further discuss how these different key elements of the early-life environment interact and affect one another and suggest that it is a synergistic action of these elements that shapes cognition throughout life. Finally, we consider different intervention studies aiming to prevent these early-life adversity induced consequences. The emerging evidence for the intriguing interplay of stress, nutrition, and immune activity in the early-life programming calls for a more in depth understanding of the interaction of these elements and the underlying mechanisms. This knowledge will help to develop intervention strategies that will converge on a more complete set of changes induced by early-life adversity.

Influences of prenatal and postnatal stress on adult hippocampal neurogenesis: the double neurogenic niche hypothesis

Adult hippocampal neurogenesis (AHN) is involved in learning, memory, and stress, and plays a significant role in neurodegenerative and psychiatric disorders. As an age-dependent process, AHN is largely influenced by changes that occur during the pre- and postnatal stages of brain development, and constitutes an important field of research. This review examines the current knowledge regarding the regulators of AHN and the influence of prenatal and postnatal stress on later AHN. In addition, a hypothesis is presented suggesting that each kind of stress influences a specific neurogenic pool, developmental or postnatal, that later becomes a precursor with important repercussions for AHN. This hypothesis is referred to as "the double neurogenic niche hypothesis." Discovering what receptors, transcription factors, or genes are specifically activated by different stressors is proposed as an essential line of future research in the field. Such knowledge shall constitute an important starting point toward the goal of modifying AHN in neurodegenerative or psychiatric diseases.