Synergistic Effect between Maternal Infection and Adolescent Cannabinoid Exposure on Serotonin 5HT1A Receptor Binding in the Hippocampus: Testing the "Two Hit" Hypothesis for the Development of Schizophrenia

Lack of interactions between prenatal immune activation and Δ9-tetrahydrocannabinol exposure during adolescence in behaviours relevant to symptom dimensions of schizophrenia in rats

The causality in the association between cannabis use and the risk of developing schizophrenia has been the subject of intense debate in the last few years. The development of animal models recapitulating several aspects of the disease is crucial for shedding light on this issue. Given that maternal infections are a known risk for schizophrenia, here, we used the maternal immune activation (MIA) model combined with THC exposure during adolescence to examine several behaviours in rats (working memory in the Y maze, sociability in the three-chamber test, sucrose preference as a measure, prepulse inhibition and formation of incidental associations) that are similar to the different symptom clusters of the disease. To this end, we administered LPS to pregnant dams and when the offspring reached adolescence, we exposed them to a mild dose of THC to examine their behaviour in adulthood. We also studied several parameters in the dams, including locomotor activity in the open field, elevated plus maze performance and their response to LPS, that could predict symptom severity of the offspring, but found no evidence of any predictive value of these variables. In the adult offspring, MIA was associated with impaired working memory and sensorimotor gating, but surprisingly, it increased sociability, social novelty and sucrose preference. THC, on its own, impaired sociability and social memory, but there were no interactions between MIA and THC exposure. These results suggest that, in this model, THC during adolescence does not trigger or aggravate symptoms related to schizophrenia in rats.

Prenatal risk factors and postnatal cannabis exposure: Assessing dual models of schizophrenia-like rodents

Schizophrenia (SCZ) is a multifactorial neurodevelopmental disorder caused by genetic and environmental alterations, especially during prenatal stages. On the other hand, cannabis consumption in adolescence has been also linked to an increased risk of developing SCZ. The combination of both hits has been proposed as the dual hit hypothesis of SCZ. We systematically reviewed prenatal environmental alterations and cannabis consumption during adolescence that are associated with an increased risk of SCZ, following the PRISMA model. The analysis focused on dual animal models where the first hit is prenatal environmental exposure and the second hit consists of postnatal cannabis exposure. The articles were evaluated by three independent reviewers based on inclusion criteria. We extracted the first author´s name, year, model species, sex and analysis. The articles reported on dual murine models and their effects on weight, behavior, genetics, electrophysiology and brain structure and function. We conclude that the defects caused by the dual hits depend on the sex of the model, as well as type of hits.

Modeling psychotic disorders: Environment x environment interaction

Schizophrenia is a major psychotic disorder with multifactorial etiology that includes interactions between genetic vulnerability and environmental risk factors. In addition, interplay of multiple environmental adversities affects neurodevelopment and may increase the individual risk of developing schizophrenia. Consistent with the two-hit hypothesis of schizophrenia, we review rodent models that combine maternal immune activation as the first hit with other adverse environmental exposures as the second hit. We discuss the strengths and pitfalls of the current animal models of environment x environment interplay and propose some future directions to advance the field.

Maternal infection during pregnancy aggravates the behavioral response to an immune challenge during adolescence in female rats

Prenatal and early postnatal infection have been associated with changes in microglial activity and the development of psychiatric disorders. Here, we investigated the effect of prenatal immune activation and postnatal immune challenge, alone and combined, on behavior and microglial cell density in female Wistar rats. Pregnant rats were injected with poly I:C to induce a maternal immune activation (MIA). Their female offspring were subsequently exposed to a lipopolysaccharide (LPS) immune challenge during adolescence. Anhedonia, social behavior, anxiety, locomotion, and working memory were measured with the sucrose preference, social interaction, open field, elevated-plus maze, and Y-maze test, respectively. Microglia cell density was quantified by counting the number of Iba-1 positive cells in the brain cortex. Female MIA offspring were more susceptible to the LPS immune challenge during adolescence than control offspring as demonstrated by a more pronounced reduction in sucrose preference and body weight on the days following the LPS immune challenge. Furthermore, only the rats exposed to both MIA and LPS showed long-lasting changes in social behavior and locomotion. Conversely, the combination MIA and LPS prevented the anxiety induced by MIA alone during adulthood. MIA, LPS, or their combination did not change microglial cell density in the parietal and frontal cortex of adult rats. The results of our study suggest that the maternal immune activation during pregnancy aggravates the response to an immune challenge during adolescence in female rats.

Interaction of the pre- and postnatal environment in the maternal immune activation model

Adverse influences during pregnancy are associated with a range of unfavorable outcomes for the developing offspring. Maternal psychosocial stress, exposure to infections and nutritional imbalances are known risk factors for neurodevelopmental derangements and according psychiatric and neurological manifestations later in offspring life. In this context, the maternal immune activation (MIA) model has been extensively used in preclinical research to study how stimulation of the maternal immune system during gestation derails the tightly coordinated sequence of fetal neurodevelopment. The ensuing consequence of MIA for offspring brain structure and function are majorly manifested in behavioral and cognitive abnormalities, phenotypically presenting during the periods of adolescence and adulthood. These observations have been interpreted within the framework of the "double-hit-hypothesis" suggesting that an elevated risk for neurodevelopmental disorders results from an individual being subjected to two adverse environmental influences at distinct periods of life, jointly leading to the emergence of pathology. The early postnatal period, during which the caregiving parent is the major determinant of the newborn´s environment, constitutes a window of vulnerability to external stimuli. Considering that MIA not only affects the developing fetus, but also impinges on the mother´s brain, which is in a state of heightened malleability during pregnancy, the impact of MIA on maternal brain function and behavior postpartum may importantly contribute to the detrimental consequences for her progeny. Here we review current information on the interaction between the prenatal and postnatal maternal environments in the modulation of offspring development and their relevance for the pathophysiology of the MIA model.

Investigating the "two-hit hypothesis": Effects of prenatal maternal immune activation and adolescent cannabis use on neurodevelopment in mice

Prenatal exposure to maternal immune activation (MIA) and chronic adolescent cannabis use are both risk factors for neuropsychiatric disorders. However, exposure to a single risk factor may not result in major mental illness, indicating that multiple exposures may be required for illness onset. Here, we examine whether combined exposure to prenatal MIA and adolescent delta-9-tetrahydrocannabinol (THC), the main psychoactive component of cannabis, lead to enduring neuroanatomical and behavioural changes in adulthood. Mice were prenatally exposed to viral mimetic, poly I:C (5 mg/kg), or vehicle at gestational day (GD) 9, and postnatally exposed to chronic THC (5 mg/kg, intraperitoneal) or vehicle during adolescence (postnatal day [PND]28-45). Longitudinal magnetic resonance imaging (MRI) was performed pre-treatment, PND 25, post-treatment, PND 50, and in adulthood, PND85, followed by behavioural tests for anxiety-like, social, and sensorimotor gating. Post-mortem assessment of cannabinoid (CB)1 and 2 receptor expressing cells was performed in altered regions identified by MRI (anterior cingulate and somatosensory cortices, striatum, and hippocampus). Subtle deviations in neurodevelopmental trajectory and subthreshold anxiety-like behaviours were observed in mice exposed to both risk factors. Sex-dependent effects were observed in patterns of shared brain-behaviour covariation, indicative of potential sex differences in response to MIA and THC. Density of CB1 and CB2 receptor positive cells was significantly decreased in all mice exposed to MIA, THC, or both. These findings suggest that there may be a cumulative effect of risk factor exposure on gross neuroanatomical development, and that the endocannabinoid system may be sensitive to both prenatal MIA, adolescent THC, or the combination.

The dual hit hypothesis of schizophrenia: Evidence from animal models

Schizophrenia is a heterogeneous psychiatric disorder, which can severely impact social and professional functioning. Epidemiological and clinical studies show that schizophrenia has a multifactorial aetiology comprising genetic and environmental risk factors. Although several risk factors have been identified, it is still not clear how they result in schizophrenia. This knowledge gap, however, can be investigated in animal studies. In this review, we summarise animal studies regarding molecular and cellular mechanisms through which genetic and environmental factors may affect brain development, ultimately causing schizophrenia. Preclinical studies suggest that early environmental risk factors can affect the immune, GABAergic, glutamatergic, or dopaminergic system and thus increase the susceptibility to another risk factor later in life. A second insult, like social isolation, stress, or drug abuse, can further disrupt these systems and the interactions between them, leading to behavioural abnormalities. Surprisingly, first insults like maternal infection and early maternal separation can also have protective effects. Single gene mutations associated with schizophrenia did not have a major impact on the susceptibility to subsequent environmental hits.

Early or Late Gestational Exposure to Maternal Immune Activation Alters Neurodevelopmental Trajectories in Mice: An Integrated Neuroimaging, Behavioral, and Transcriptional Study

BACKGROUND

Exposure to maternal immune activation (MIA) in utero is a risk factor for neurodevelopmental disorders later in life. The impact of the gestational timing of MIA exposure on downstream development remains unclear.

METHODS

We characterized neurodevelopmental trajectories of mice exposed to the viral mimetic poly I:C (polyinosinic:polycytidylic acid) either on gestational day 9 (early) or on day 17 (late) using longitudinal structural magnetic resonance imaging from weaning to adulthood. Using multivariate methods, we related neuroimaging and behavioral variables for the time of greatest alteration (adolescence/early adulthood) and identified regions for further investigation using RNA sequencing.

RESULTS

Early MIA exposure was associated with accelerated brain volume increases in adolescence/early adulthood that normalized in later adulthood in the striatum, hippocampus, and cingulate cortex. Similarly, alterations in anxiety-like, stereotypic, and sensorimotor gating behaviors observed in adolescence normalized in adulthood. MIA exposure in late gestation had less impact on anatomical and behavioral profiles. Multivariate maps associated anxiety-like, social, and sensorimotor gating deficits with volume of the dorsal and ventral hippocampus and anterior cingulate cortex, among others. The most transcriptional changes were observed in the dorsal hippocampus, with genes enriched for fibroblast growth factor regulation, autistic behaviors, inflammatory pathways, and microRNA regulation.

CONCLUSIONS

Leveraging an integrated hypothesis- and data-driven approach linking brain-behavior alterations to the transcriptome, we found that MIA timing differentially affects offspring development. Exposure in late gestation leads to subthreshold deficits, whereas exposure in early gestation perturbs brain development mechanisms implicated in neurodevelopmental disorders.

Associations Between Maternal Prenatal C-Reactive Protein and Risk Factors for Psychosis in Adolescent Offspring: Findings From the Northern Finland Birth Cohort 1986

Prenatal infection is associated with brain structural and functional abnormalities and may increase the risk for psychosis through a direct effect on neurodevelopment. Various infections may exert their effect through a proinflammatory immune response but studies of prenatal maternal inflammatory markers and offspring neurodevelopment are scarce. Using the longitudinal Northern Finland Birth Cohort 1986 study, we examined the associations of maternal prenatal C-reactive protein (CRP) levels with psychosis risk factors in adolescent offspring. CRP was measured in maternal sera collected in pregnancy. In offspring, school performance was measured at age 7 years, while school performance, psychotic experiences, and cannabis use were measured at age 16 years. We tested associations of CRP with offspring measures using regression analysis controlling for offspring sex, maternal education level, and prenatal maternal body mass index, smoking and alcohol use in pregnancy, place of birth, maternal psychiatric admission, paternal psychiatric admission, mothers age at birth, and gestational week of CRP sample. We also tested if adolescent cannabis use mediated the associations between maternal CRP and offspring outcomes. Controlling for covariates, maternal CRP was associated with academic performance at age 16 years (beta = .062, 95% CI = 0.036-0.088), but not with possible psychotic experiences at 16 years (odds ratio [OR] = 1.09, 95% CI = 0.96-1.24). Maternal CRP was also associated with adolescent cannabis use (OR = 1.24, 95% CI = 1.07-1.43). These findings suggest that prenatal inflammation may influence later mental illness risk by affecting neurodevelopment and also indirectly by increasing the risk of exposure to cannabis.

The independent and combined effects of cannabis use and systemic inflammation during the early stages of psychosis: exploring the two-hit hypothesis

BACKGROUND

Cannabis consumption is a modifiable risk factor associated with psychosis, but not all cannabis users develop psychosis. Animal studies suggest that an antecedent active immune system interacts with subsequent cannabis exposure and moderates the cannabis-psychosis association, supporting the two-hit hypothesis. The clinical investigations are few, and it is unclear if the immune system is a biological candidate moderating the cannabis-psychosis association or whether cannabis increases inflammation, which in turn, augments psychosis likelihood.

METHODS

We explored the mediating and moderating role of blood inflammation using PROCESS macro. We used data from a cross-sectional study, including 153 first-episode psychosis patients and 256 community-based controls. Participants answered the Cannabis Experience Questionnaire (cannabis frequency, age of onset, and duration), and plasma cytokines were measured [interleukin (IL)-1β, IL-6, IL-4, IL-10, tumour necrosis factor-α (TNF-α), interferon-γ (IFN-γ), transforming growth factor-β (TGF-β); multiplex]. We computed an inflammatory composite score (ICS) to represent the systemic inflammatory state. Confounders included sex, age, ethnicity, educational level, body mass index, tobacco smoking, lifetime use of other drugs, and antipsychotic treatment.

RESULTS

Mediation: Cannabis consumption was not associated with increased inflammation, thus not supporting a mediating effect of inflammation. Moderation: Daily use and age of onset <17 interacted significantly with the ICS to increase the odds of psychosis beyond their individual effects and were only associated with psychosis among those scoring medium-high in the ICS.

CONCLUSIONS

Immune dysregulation might be part of the pathophysiology of psychosis, not explained by cannabis use or other confounders. We provide the first and initial evidence that immune dysregulation modifies the cannabis-psychosis association, in line with a two-hit hypothesis.

Gestational poly(I:C) attenuates, not exacerbates, the behavioral, cytokine and mTOR changes caused by isolation rearing in a rat 'dual-hit' model for neurodevelopmental disorders

Many psychiatric illnesses have a multifactorial etiology involving genetic and environmental risk factors that trigger persistent neurodevelopmental impairments. Several risk factors have been individually replicated in rodents, to understand disease mechanisms and evaluate novel treatments, particularly for poorly-managed negative and cognitive symptoms. However, the complex interplay between various factors remains unclear. Rodent dual-hit neurodevelopmental models offer vital opportunities to examine this and explore new strategies for early therapeutic intervention. This study combined gestational administration of polyinosinic:polycytidylic acid (poly(I:C); PIC, to mimic viral infection during pregnancy) with post-weaning isolation of resulting offspring (to mirror adolescent social adversity). After in vitro and in vivo studies required for laboratory-specific PIC characterization and optimization, we administered 10 mg/kg i.p. PIC potassium salt to time-mated Lister hooded dams on gestational day 15. This induced transient hypothermia, sickness behavior and weight loss in the dams, and led to locomotor hyperactivity, elevated striatal cytokine levels, and increased frontal cortical JNK phosphorylation in the offspring at adulthood. Remarkably, instead of exacerbating the well-characterized isolation syndrome, gestational PIC exposure actually protected against a spectrum of isolation-induced behavioral and brain regional changes. Thus isolation reared rats exhibited locomotor hyperactivity, impaired associative memory and reversal learning, elevated hippocampal and frontal cortical cytokine levels, and increased mammalian target of rapamycin (mTOR) activation in the frontal cortex - which were not evident in isolates previously exposed to gestational PIC. Brains from adolescent littermates suggest little contribution of cytokines, mTOR or JNK to early development of the isolation syndrome, or resilience conferred by PIC. But notably hippocampal oxytocin, which can protect against stress, was higher in adolescent PIC-exposed isolates so might contribute to a more favorable outcome. These findings have implications for identifying individuals at risk for disorders like schizophrenia who may benefit from early therapeutic intervention, and justify preclinical assessment of whether adolescent oxytocin manipulations can modulate disease onset or progression.

The effect of 17β-estradiol on maternal immune activation-induced changes in prepulse inhibition and dopamine receptor and transporter binding in female rats

Maternal immune activation (MIA) during pregnancy is associated with an increased risk of development of schizophrenia in later life. 17β-estradiol treatment may improve schizophrenia symptoms, but little is known about its efficacy on MIA-induced psychosis-like behavioural deficits in animals. Therefore, in this study we used the poly(I:C) neurodevelopmental model of schizophrenia to examine whether MIA-induced psychosis-like behavioural and neurochemical changes can be attenuated by chronic treatment (2-6 weeks) with 17β-estradiol. Pregnant rats were treated with saline or the viral mimetic, poly(I:C), on gestational day 15 and adult female offspring were tested for changes in prepulse inhibition (PPI) and density of dopamine D1 and D2 receptors and dopamine transporters in the forebrain compared to control offspring. Poly(I:C)-treated offspring exhibited significantly disrupted PPI, an effect which was reversed by chronic treatment with 17β-estradiol. In control offspring, but not poly(I:C) offspring, PPI was significantly reduced by acute treatment with either the dopamine D1/D2 receptor agonist, apomorphine, or dopamine releaser, methamphetamine. 17β-estradiol restored the effect of apomorphine, but not methamphetamine, on PPI in poly(I:C) offspring. There was a strong trend for a dopamine D2 receptor binding density increase in the nucleus accumbens core region in poly(I:C) offspring, and this was reversed by chronic 17β-estradiol treatment. No changes were found in the nucleus accumbens shell, caudate putamen or frontal cortex or in the density of dopamine D1 receptors or transporters. These findings suggest that 17β-estradiol may improve some symptoms of schizophrenia, an effect that may be mediated by selective changes in dopamine D2 receptor density.

Adolescent cannabinoid exposure interacts with other risk factors in schizophrenia: A review of the evidence from animal models

Many factors and their interaction are linked to the aetiology of schizophrenia, leading to the development of animal models of multiple risk factors and adverse exposures. Differentiating between separate and combined effects for each factor could better elucidate schizophrenia pathology, and drive development of preventative strategies for high-load risk factors. An epidemiologically valid risk factor commonly associated with schizophrenia is adolescent cannabis use. The aim of this review is to evaluate how early-life adversity from various origins, in combination with adolescent cannabinoid exposure interact, and whether these interactions confer main, synergistic or protective effects in animal models of schizophrenia-like behavioural, cognitive and morphological alterations. Patterns emerge regarding which models show consistent synergistic or protective effects, particularly those models incorporating early-life exposure to maternal deprivation and maternal immune activation, and sex-specific effects are observed. It is evident that more research needs to be conducted to better understand the risks and alterations of interacting factors, with particular interest in sex differences, to better understand the translatability of these preclinical models to humans.

Investigating the gut-brain axis in a neurodevelopmental rodent model of schizophrenia

Background

Although the aetiology of schizophrenia remains unknown, it has been suggested that it might occur in response to alterations in the gut-brain axis (GBA), the bi-directional communication system between the gut and the brain. The current study aimed to determine whether the “two-hit” animal model of neuropsychopathology (maternal immune activation combined with adolescent cannabinoid exposure), produced abnormalities in the GBA

Method

Pregnant Wistar rats were administered the viral mimetic polyI:C on gestational day 19 and offspring were administered the synthetic cannabinoid HU210 from postnatal days 35–48. Evidence of GBA activation was assessed in the hypothalamus, colon and fecal samples from male and female offspring at adolescence and adulthood

Results

Findings were sex-specific with adolescent female offspring exhibiting an increased hypothalamic inflammatory profile, increased hypothalamic CRHR1 mRNA, and decreased fecal expression of Bifidobacterium longum, however, no changes were detected in colonic inflammation or integrity.

Conclusion

These results indicate that the rat two-hit model, documented to produce behavioural and neuroanatomical abnormalities, also produces hypothalamic and microbiota abnormalities. The results also demonstrate significant sex differences, suggesting that this model may be useful for investigating the role of the GBA in the aetiology of neurodevelopmental disorders such as schizophrenia.

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Combined MIA and ACE induces sex-specific alterations in hypothalamic inflammation.

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Combined MIA and ACE increases hypothalamic CRHR1 expression.

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Combined MIA and ACE decreases fecal expression of Bifidobacterium longum.

Consequences of Perinatal Cannabis Exposure

Cannabis exposure during the perinatal period results in varied and significant consequences in affected offspring. The prevalence of detrimental outcomes of perinatal cannabis exposure is likely to increase in tandem with the broadening of legalization and acceptance of the drug. As such, it is crucial to highlight the immediate and protracted consequences of cannabis exposure on pre- and postnatal development. Here, we identify lasting changes in neurons' learning flexibility (synaptic plasticity) and epigenetic misregulation in animal models of perinatal cannabinoid exposure (using synthetic cannabinoids or active components of the cannabis plant), in addition to significant alterations in social behavior and executive functions. These findings are supported by epidemiological data indicating similar behavioral outcomes throughout life in human offspring exposed to cannabis during pregnancy. Further, we indicate important lingering questions regarding accurate modeling of perinatal cannabis exposure as well as the need for sex- and age-dependent outcome measures in future studies.

Modelling gene-environment interaction in first episodes of psychosis

INTRODUCTION

Recent research demonstrates the heterogeneous etiology of psychotic disorders, where gen-environment (GxE) interaction plays a key role. Large genetic studies have linked many genetic variants with schizophrenia, but each variant is only associated with a small effect and the GxE interaction contribution has not been evaluated.

METHODS

The PEPs Project was designed to carefully collect a large amount of genetic and environmental exposure data of 335 FEP patients and 253 matched healthy controls.780single-nucleotide polymorphisms (from 159 candidate genes)and 16 environmental variables previously reported as the main psychosis non-genetic risk factors were analyzed together using entropy-based measures of information gain.

RESULTS

Our analyses identified an interaction between nine SNPs and the exposition to the environmental risk factors of psychosis, showing a clear enrichment of genes linked to serotonin neurotransmission and neurodevelopmental processes.

CONCLUSIONS

This study has allowed the identification of several GxE-environment interactions involved in the risk of presenting a FEP. Our results highlight the importance of serotonin neurotransmission interacting with certain environmental stimuli. The serotoninergic system may be playing a key role in the regulatory network of stress and other systems implicated in the emergence and development of psychotic disorders.

Alteration of transcriptional networks in the entorhinal cortex after maternal immune activation and adolescent cannabinoid exposure

Maternal immune activation (MIA) and adolescent cannabinoid exposure (ACE) have both been identified as major environmental risk factors for schizophrenia. We examined the effects of these two risk factors alone, and in combination, on gene expression during late adolescence. Pregnant rats were exposed to the viral infection mimic polyriboinosinic-polyribocytidylic acid (poly I:C) on gestational day (GD) 15. Adolescent offspring received daily injections of the cannabinoid HU210 for 14days starting on postnatal day (PND) 35. Gene expression was examined in the left entorhinal cortex (EC) using mRNA microarrays. We found prenatal treatment with poly I:C alone, or HU210 alone, produced relatively minor changes in gene expression. However, following combined treatments, offspring displayed significant changes in transcription. This dramatic and persistent alteration of transcriptional networks enriched with genes involved in neurotransmission, cellular signalling and schizophrenia, was associated with a corresponding perturbation in the expression of small non-coding microRNA (miRNA). These results suggest that a combination of environmental exposures during development leads to significant genomic remodeling that disrupts maturation of the EC and its associated circuitry with important implications as the potential antecedents of memory and learning deficits in schizophrenia and other neuropsychiatric disorders.

Striatal but not frontal cortical up-regulation of the epidermal growth factor receptor in rats exposed to immune activation in utero and cannabinoid treatment in adolescence

In utero maternal immune activation (MIA) and cannabinoid exposure during adolescence constitute environmental risk factors for schizophrenia. We investigated these risk factors alone and in combination ("two-hit") on epidermal growth factor receptor (EGFR) and neuregulin-1 receptor (ErbB4) levels in the rat brain. EGFR but not ErbB4 receptor protein levels were significantly increased in the nucleus accumbens and striatum of "two-hit" rats only, with no changes seen at the mRNA level. These findings support region specific EGF-system dysregulation as a plausible mechanism in this animal model of schizophrenia pathogenesis.

Individual and combined effects of maternal anemia and prenatal infection on risk for schizophrenia in offspring

BACKGROUND

Maternal iron deficiency and infection during pregnancy have individually been associated with increased risk of schizophrenia in the offspring, but possible interactions between the two remain unidentified thus far. Therefore, we determined the individual and combined effects of maternal infection during pregnancy and prepartum anemia on schizophrenia risk in the offspring.

METHODS

We conducted a population-based study with individual record linkage of the Danish Civil Registration System, the Danish Hospital Register, and the Central Danish Psychiatric Register. In a cohort of Danish singleton births 1,403,183 born between 1977 and 2002, 6729 developed schizophrenia between 1987 and 2012. Cohort members were considered as having a maternal history of anemia if the mother had received a diagnosis of anemia at any time during the pregnancy. Maternal infection was defined based on infections requiring hospital admission during pregnancy.

RESULTS

Maternal anemia and infection were both associated with increased risk of schizophrenia in unadjusted analyses (1.45-fold increase for anemia, 95% CI: 1.14-1.82; 1.32-fold increase for infection, 95% CI: 1.17-1.48). The effect of maternal infection remained significant (1.16-fold increase, 95% CI: 1.03-1.31) after adjustment for possible confounding factors. Combined exposure to anemia and an infection increased the effect size to a 2.49-fold increased schizophrenia risk (95% CI: 1.29-4.27). The interaction analysis, however, failed to provide evidence for multiplicative interactions between the two factors.

CONCLUSION

Our findings indicate that maternal anemia and infection have additive but not interactive effects, and therefore, they may represent two independent risk factors of schizophrenia.

Synergistic stress exacerbation in hippocampal neurons: Evidence favoring the dual-hit hypothesis of neurodegeneration

The dual-hit hypothesis of neurodegeneration states that severe stress sensitizes vulnerable cells to subsequent challenges so that the two hits are synergistic in their toxic effects. Although the hippocampus is vulnerable to a number of neurodegenerative disorders, there are no models of synergistic cell death in hippocampal neurons in response to combined proteotoxic and oxidative stressors, the two major characteristics of these diseases. Therefore, a relatively high-throughput dual-hit model of stress synergy was developed in primary hippocampal neurons. In order to increase the rigor of the study and strengthen the interpretations, three independent, unbiased viability assays were employed at multiple timepoints. Stress synergy was elicited when hippocampal neurons were treated with the proteasome inhibitor MG132 followed by exposure to the oxidative toxicant paraquat, but only after 48 h. MG132 and paraquat only elicited additive effects 24 h after the final hit and even loss of heat shock protein 70 activity and glutathione did not promote stress synergy at this early timepoint. Dual hits of MG132 elicited modest glutathione loss and slightly synergistic toxic effects 48 h after the second hit, but only at some concentrations and only according to two viability assays (metabolic fitness and cytoskeletal integrity). The thiol N-acetyl cysteine protected hippocampal neurons against dual MG132/MG132 hits but not dual MG132/paraquat hits. These findings support the view that proteotoxic and oxidative stress propel and propagate each other in hippocampal neurons, leading to synergistically toxic effects, but not as the default response and only after a delay. The neuronal stress synergy observed here lies in contrast to astrocytic responses to dual hits, because astrocytes that survive severe proteotoxic stress resist additional cell loss following second hits. In conclusion, a new model of hippocampal vulnerability was developed for the testing of therapies, because neuroprotective treatments that are effective against severe, synergistic stress are more likely to succeed in the clinic. © 2016 Wiley Periodicals, Inc.

Fetal programming of schizophrenia: select mechanisms

Mounting evidence indicates that schizophrenia is associated with adverse intrauterine experiences. An adverse or suboptimal fetal environment can cause irreversible changes in brain that can subsequently exert long-lasting effects through resetting a diverse array of biological systems including endocrine, immune and nervous. It is evident from animal and imaging studies that subtle variations in the intrauterine environment can cause recognizable differences in brain structure and cognitive functions in the offspring. A wide variety of environmental factors may play a role in precipitating the emergent developmental dysregulation and the consequent evolution of psychiatric traits in early adulthood by inducing inflammatory, oxidative and nitrosative stress (IO&NS) pathways, mitochondrial dysfunction, apoptosis, and epigenetic dysregulation. However, the precise mechanisms behind such relationships and the specificity of the risk factors for schizophrenia remain exploratory. Considering the paucity of knowledge on fetal programming of schizophrenia, it is timely to consolidate the recent advances in the field and put forward an integrated overview of the mechanisms associated with fetal origin of schizophrenia.

Brain in flames - animal models of psychosis: utility and limitations

The neurodevelopmental hypothesis of schizophrenia posits that schizophrenia is a psychopathological condition resulting from aberrations in neurodevelopmental processes caused by a combination of environmental and genetic factors which proceed long before the onset of clinical symptoms. Many studies discuss an immunological component in the onset and progression of schizophrenia. We here review studies utilizing animal models of schizophrenia with manipulations of genetic, pharmacologic, and immunological origin. We focus on the immunological component to bridge the studies in terms of evaluation and treatment options of negative, positive, and cognitive symptoms. Throughout the review we link certain aspects of each model to the situation in human schizophrenic patients. In conclusion we suggest a combination of existing models to better represent the human situation. Moreover, we emphasize that animal models represent defined single or multiple symptoms or hallmarks of a given disease.

Maternal immune activation and abnormal brain development across CNS disorders

Epidemiological studies have shown a clear association between maternal infection and schizophrenia or autism in the progeny. Animal models have revealed maternal immune activation (mIA) to be a profound risk factor for neurochemical and behavioural abnormalities in the offspring. Microglial priming has been proposed as a major consequence of mIA, and represents a critical link in a causal chain that leads to the wide spectrum of neuronal dysfunctions and behavioural phenotypes observed in the juvenile, adult or aged offspring. Such diversity of phenotypic outcomes in the mIA model are mirrored by recent clinical evidence suggesting that infectious exposure during pregnancy is also associated with epilepsy and, to a lesser extent, cerebral palsy in children. Preclinical research also suggests that mIA might precipitate the development of Alzheimer and Parkinson diseases. Here, we summarize and critically review the emerging evidence that mIA is a shared environmental risk factor across CNS disorders that varies as a function of interactions between genetic and additional environmental factors. We also review ongoing clinical trials targeting immune pathways affected by mIA that may play a part in disease manifestation. In addition, future directions and outstanding questions are discussed, including potential symptomatic, disease-modifying and preventive treatment strategies.

Effect of maternal immune activation on the kynurenine pathway in preadolescent rat offspring and on MK801-induced hyperlocomotion in adulthood: amelioration by COX-2 inhibition

Infections during pregnancy and subsequent maternal immune activation (MIA) increase risk for schizophrenia in offspring. The progeny of rodents injected with the viral infection mimic polyI:C during gestation display brain and behavioural abnormalities but the underlying mechanisms are unknown. Since the blood kynurenine pathway (KP) of tryptophan degradation impacts brain function and is strongly regulated by the immune system, we tested if KP changes occur in polyI:C offspring at preadolescence. We also tested whether MK801-induced hyperlocomotion, a behaviour characteristic of adult polyI:C offspring, is prevented by adolescent treatment with celecoxib, a COX-2 inhibitor that impacts the KP. Pregnant rats were treated with polyI:C (4mg/kg, i.v.) or vehicle on gestational day 19. Serum levels of KP metabolites were measured in offspring of polyI:C or vehicle treated dams at postnatal day (PND) 31-33 using HPLC/GCMS. Additional polyI:C or vehicle exposed offspring were given celecoxib or vehicle between PND 35 and 46 and tested with MK801 (0.3mg/kg) in adulthood (PND>90). Prenatal polyI:C resulted in increases in the serum KP neurotoxic metabolite quinolinic acid at PND 31-33 (105%, p=0.014). In contrast, the neuroprotective kynurenic acid and its precursor kynurenine were significantly decreased (28% p=0.027, and 31% p=0.033, respectively). Picolinic acid, another neuroprotective KP metabolite, was increased (31%, p=0.014). Adolescent treatment with celecoxib (2.5 and 5mg/kg/day, i.p.) prevented the development of MK801-induced hyperlocomotion in adult polyI:C offspring. Our study reveals the blood KP as a potential mechanism by which MIA interferes with postnatal brain maturation and associated behavioural disturbances and emphasises the preventative potential of inflammation targeting drugs.

Alteration of imprinted Dlk1-Dio3 miRNA cluster expression in the entorhinal cortex induced by maternal immune activation and adolescent cannabinoid exposure

A significant feature of the cortical neuropathology of schizophrenia is a disturbance in the biogenesis of short non-coding microRNA (miRNA) that regulate translation and stability of mRNA. While the biological origin of this phenomenon has not been defined, it is plausible that it relates to major environmental risk factors associated with the disorder such as exposure to maternal immune activation (MIA) and adolescent cannabis use. To explore this hypothesis, we administered the viral mimic poly I:C to pregnant rats and further exposed some of their maturing offsprings to daily injections of the synthetic cannabinoid HU210 for 14 days starting on postnatal day 35. Whole-genome miRNA expression analysis was then performed on the left and right hemispheres of the entorhinal cortex (EC), a region strongly associated with schizophrenia. Animals exposed to either treatment alone or in combination exhibited significant differences in the expression of miRNA in the left hemisphere, whereas the right hemisphere was less responsive. Hemisphere-associated differences in miRNA expression were greatest in the combined treatment and highly over-represented in a single imprinted locus on chromosome 6q32. This observation was significant as the syntenic 14q32 locus in humans encodes a large proportion of miRNAs differentially expressed in peripheral blood lymphocytes from patients with schizophrenia, suggesting that interaction of early and late environmental insults may affect miRNA expression, in a manner that is relevant to schizophrenia.

Immune system: a possible nexus between cannabinoids and psychosis

BACKGROUND

Endocannabinoid system is involved in the regulation of the brain-immune axis. Cannabis consumption is related with the development, course, and severity of psychosis. The epidemiological evidence for increased occurrence of immunological alterations in patients with psychosis has not been sufficiently addressed. The aim of this review is to establish whether there is any scientific evidence of the influence of cannabinoids on aspects of immunity that affect susceptibility to psychotic disorder induction.

METHODS

A comprehensive search of PubMed/MEDLINE, EMBASE and ISI Web of Knowledge was performed using combinations of key terms distributed into three blocks: "immune", "cannabinoid", and "endocannabinoid receptor". Studies were considered to be eligible for the review if they were original articles, they reported a quantitative or qualitative relation between cannabinoid ligands, their receptors, and immune system, and they were carried out in vitro or in mammals, included humans. All the information was systematically extracted and evaluated.

RESULTS

We identified 122 articles from 446 references. Overall, endocannabinoids enhanced immune response, whereas exogenous cannabinoids had immunosuppressant effects. A general change in the immune response from Th1 to Th2 was also demonstrated for cannabinoid action. Endogenous and synthetic cannabinoids also modulated microglia function and neurotransmitter secretion.

CONCLUSION

The actions of cannabinoids through the immune system are quite regular and predictable in the peripheral but remain fuzzy in the central nervous system. Despite this uncertainty, it may be hypothesized that exposure to exocannabinoids, in particular during adolescence might prompt immunological dysfunctions that potentially cause a latent vulnerability to psychosis. Further investigations are warranted to clarify the relationship between the immunological effects of cannabis and psychosis.

Prenatal poly I:C age-dependently alters cannabinoid type 1 receptors in offspring: a longitudinal small animal PET study using [(18)F]MK-9470

Evidence suggests that there is a link between the endocannabinoid system (ECS) and neuropsychiatric illnesses, including schizophrenia. Whilst the ECS has been shown to be involved in immune system regulation in various ways, it is known that infections during pregnancy can modulate the immune system of the mother and increase the risk for schizophrenia in offspring. In animal studies, maternal immune activation following administration of viral or bacterial mimics has been shown to reproduce many key structural, behavioural, and pharmacological abnormalities in offspring that resemble schizophrenia. In the present study, we used Positron Emission Tomography (PET) and [(18)F]MK-9470, a selective high-affinity inverse agonist radioligand for cannabinoid type 1 receptors (CB1R), to longitudinally assess CB1R expression in the progeny of female rats exposed to the viral mimic polyriboinosinic-polyribocytidilic acid (poly I:C) (4mg/kg i.v.) or vehicle at gestational day 15 (GD 15). PET scans were performed in offspring at postnatal days (PND) 32-42 (adolescence) and in the same animals again at PNDs 75-79 (adulthood). Sixteen regions of interest were assessed, encompassing the whole rat brain. At adolescence, offspring exposed prenatally to poly I:C had significantly lower CB1R relative Standard Uptake Values (rSUV) compared to controls in the globus pallidus (p=0.046). In adulthood, however, poly I:C exposed offspring had higher levels of CB1R rSUV in sensory cortex (p=0.034) and hypothalamus (p=0.032) compared to controls. Our results suggest that prenatal poly I:C leads to long term alterations in the integrity of the ECS that are age and region-specific. The increased CB1R expression in adulthood following poly I:C mirrors the increased CB1R observed in patients with schizophrenia in post-mortem and in vivo PET studies.

Protracted maturation of forebrain afferent connections of the ventral tegmental area in the rat

The mesocorticolimbic dopamine system has long attracted the interest of researchers concerned with the unique gamut of behavioral and mental health vulnerabilities associated with adolescence. Accordingly, the development of the mesocorticolimbic system has been studied extensively, but almost exclusively with regard to dopaminergic output, particularly in the nucleus accumbens and medial prefrontal cortex. To the contrary, the ontogeny of inputs to the ventral tegmental area (VTA), the source of mesocorticolimbic dopamine, has been neglected. This is not a trivial oversight, as the activity of VTA neurons, which reflects their capacity to transmit information about salient events, is sensitively modulated by inputs. Here, we assessed the development of VTA afferent connections using the β subunit of cholera toxin (Ctβ) as a retrograde axonal tracer in adolescent (postnatal day 39) and early adult (8-9-week-old) rats. After intra-VTA injections of Ctβ, adolescent and early adult animals exhibited qualitatively similar distributions of retrogradely labeled neurons in the sense that VTA-projecting neurons were present at all of the same rostrocaudal levels in all of the same structures in both age groups. However, quantitation of retrogradely labeled neurons revealed that adolescent brains, compared with early adult brains, had significantly fewer VTA-projecting neurons preferentially within an interconnected network of cortical and striatopallidal forebrain structures. These findings provide a novel perspective on the development of the mesocorticolimbic dopamine system and may have important implications for age-dependent specificity in the function of this system, particularly with regard to adolescent impulsivity and mental health vulnerabilities.

Inflammation and the two-hit hypothesis of schizophrenia

The high societal and individual cost of schizophrenia necessitates finding better, more effective treatment, diagnosis, and prevention strategies. One of the obstacles in this endeavor is the diverse set of etiologies that comprises schizophrenia. A substantial body of evidence has grown over the last few decades to suggest that schizophrenia is a heterogeneous syndrome with overlapping symptoms and etiologies. At the same time, an increasing number of clinical, epidemiological, and experimental studies have shown links between schizophrenia and inflammatory conditions. In this review, we analyze the literature on inflammation and schizophrenia, with a particular focus on comorbidity, biomarkers, and environmental insults. We then identify several mechanisms by which inflammation could influence the development of schizophrenia via the two-hit hypothesis. Lastly, we note the relevance of these findings to clinical applications in the diagnosis, prevention, and treatment of schizophrenia.