Maternal infection: window on neuroimmune interactions in fetal brain development and mental illness

Direct viral infection of the developing brain can have disastrous consequences for the fetus. More subtle and perhaps more insidious are viral infections of the pregnant mother, which can have long-lasting effects such as an increased risk of schizophrenia in the offspring. A recent mouse model has shown that respiratory infection in the pregnant mother leads to marked behavioral and pharmacological abnormalities in the offspring, some of which are relevant for schizophrenia and autism. This effect on fetal brain development might be caused by the maternal antiviral immune response, possibly mediated by cytokines.     

Maternal high-fat diet programming of the neuroendocrine system and behavior

This article is part of a Special Issue “SBN 2014”.Maternal obesity, metabolic state, and diet during gestation have profound effects on offspring development. The prevalence of neurodevelopmental and mental health disorders has risen rapidly in the last several decades in parallel with the rise in obesity rates. Evidence from epidemiological studies indicates that maternal obesity and metabolic complications increase the risk of offspring developing behavioral disorders such as attention deficit hyperactivity disorder (ADHD), autism spectrum disorders (ASD), and schizophrenia. Animal models show that a maternal diet high in fat similarly disrupts behavioral programming of offspring, with animals showing social impairments, increased anxiety and depressive behaviors, reduced cognitive development, and hyperactivity. Maternal obesity, metabolic conditions, and high fat diet consumption increase maternal leptin, insulin, glucose, triglycerides, and inflammatory cytokines. This leads to increased risk of placental dysfunction, and altered fetal neuroendocrine development. Changes in brain development that likely contribute to the increased risk of behavioral and mental health disorders include increased inflammation in the brain, as well as alterations in the serotonergic system, dopaminergic system and hypothalamic–pituitary–adrenal (HPA) axis.     

Schizophrenia-relevant behaviors in a genetic mouse model of constitutive Nurr1 deficiency

Nurr1 (NR4A2) is an orphan nuclear receptor highly essential for the dopaminergic development and survival. Altered expression of Nurr1 has been suggested as a potential genetic risk factor for dopamine-related brain disorders, including schizophrenia. In support of this, recent experimental work in genetically modified mice shows that mice with a heterozygous constitutive deletion of Nurr1 show a facilitation of the development of schizophrenia-related behavioral abnormalities. However, the behavioral characterization of this Nurr1-deficient mouse model remains incomplete. This study therefore used a comprehensive behavioral test battery to evaluate schizophrenia-relevant phenotypes in Nurr1-deficient mice. We found that these mice displayed increased spontaneous locomotor activity and potentiated locomotor reaction to systemic treatment with the non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, dizocilpine (MK-801). In addition, male but not female Nurr1-deficient mice showed significant deficits in the prepulse inhibition and prepulse-elicited reactivity. However, Nurr1 deletion did not induce overt abnormalities in other cardinal behavioral and cognitive functions known to be impaired in schizophrenia, including social interaction and recognition, spatial recognition memory or discrimination reversal learning. Our findings thus suggest that heterozygous constitutive deletion of Nurr1 results in a restricted phenotype characteristic of schizophrenia symptomatology, which primarily relates to motor activity, sensorimotor gating and responsiveness to the psychomimetic drug MK-801. This study further emphasizes a critical role of altered dopaminergic development in the precipitation of specific brain dysfunctions relevant to human psychotic disorder.     

Maternal infection and fever during late gestation are associated with altered synaptic transmission in the hippocampus of juvenile offspring rats

Prenatal exposure to infection is known to affect brain development and has been linked to increased risk for schizophrenia. The goal of this study was to investigate whether maternal infection and associated fever near term disrupts synaptic transmission in the hippocampus of the offspring. We used LPS to mimic bacterial infection and trigger the maternal inflammatory response in near-term rats. LPS was administered to rats on embryonic days 15 and 16 and hippocampal synaptic transmission was evaluated in the offspring on postnatal days 20-25. Only offspring from rats that showed a fever in response to LPS were tested. Schaffer collateral-evoked field excitatory postsynaptic potentials (fEPSPs) and fiber volleys in CA1 of hippocampal slices appeared smaller in offspring from the LPS group compared with controls, but, when the fEPSPs were normalized to the amplitude of fiber volleys, they were larger in the LPS group. In addition, intrinsic excitability of CA1 pyramidal neurons was heightened, as antidromic field responses in the LPS group were greater than those from control. Short-, but not long-term plasticity was impaired since paired-pulse facilitation of the fEPSP was attenuated in the LPS group, whereas no differences in long-term potentiation were noted. These results suggest that LPS-induced inflammation during pregnancy produces in the offspring a reduction in presynaptic input to CA1 with compensatory enhancements in postsynaptic glutamatergic response and pyramidal cell excitability. Neurodevelopmental disruption triggered by prenatal infection can have profound effects on hippocampal synaptic transmission, likely contributing to the memory and cognitive deficits observed in schizophrenia.     

Prenatal Inflammation-Induced Hypoferremia Alters Dopamine Function in the Adult Offspring in Rat: Relevance for Schizophrenia

Maternal infection during pregnancy has been associated with increased incidence of schizophrenia in the adult offspring. Mechanistically, this has been partially attributed to neurodevelopmental disruption of the dopamine neurons, as a consequence of exacerbated maternal immunity. In the present study we sought to target hypoferremia, a cytokine-induced reduction of serum non-heme iron, which is common to all types of infections. Adequate iron supply to the fetus is fundamental for the development of the mesencephalic dopamine neurons and disruption of this following maternal infection can affect the offspring''s dopamine function. Using a rat model of localized injury induced by turpentine, which triggers the innate immune response and inflammation, we investigated the effects of maternal iron supplementation on the offspring''s dopamine function by assessing behavioral responses to acute and repeated administration of the dopamine indirect agonist, amphetamine. In addition we measured protein levels of tyrosine hydroxylase, and tissue levels of dopamine and its metabolites, in ventral tegmental area, susbtantia nigra, nucleus accumbens, dorsal striatum and medial prefrontal cortex. Offspring of turpentine-treated mothers exhibited greater responses to a single amphetamine injection and enhanced behavioral sensitization following repeated exposure to this drug, when compared to control offspring. These behavioral changes were accompanied by increased baseline levels of tyrosine hydroxylase, dopamine and its metabolites, selectively in the nucleus accumbens. Both, the behavioral and neurochemical changes were prevented by maternal iron supplementation. Localized prenatal inflammation induced a deregulation in iron homeostasis, which resulted in fundamental alterations in dopamine function and behavioral alterations in the adult offspring. These changes are characteristic of schizophrenia symptoms in humans.     

Analysis of the conserved neurotrophic factor MANF in the Drosophila adult brain

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an evolutionarily conserved neurotrophic factor that supports and protects dopaminergic neurons. The Drosophila MANF (DmMANF) null mutant animals die during early development, and DmMANF is required for the maintenance of dopamine positive neurites. The aim of this study was to investigate the role of DmMANF during later developmental stages. Here we report that DmMANF expression in the adult brain is much wider than in the embryonic and larval stages. It is expressed in both glia and neurons including dopaminergic neurons. Clonal analysis showed that DmMANF is not required cell-autonomously for the differentiation of either glia or dopaminergic neurons. In addition, DmMANF overexpression resulted in no apparent abnormal dopaminergic phenotype while DmMANF silencing in glia resulted in prolonged larval stage.     

Long-term cryopreservation of mouse sperm

The objective was to determine if mouse sperm can maintain their fertilizing ability after being frozen for >10 y and whether the offspring derived from these sperm had normal fertilizing ability and phenotype. We cryopreserved sperm from six strains of mice (C57BL/6J, DBA/2N, BALB/cA, C3H/HeJ, B6D2F1 and B6C3F1) in a solution containing 18% (w/v) raffinose and 3% (w/v) skim milk, and preserved them in liquid nitrogen for >10 y. To assess the normality and fertilizing ability of these sperms, they were thawed and used for in vitro fertilization of oocytes of the same strains. Fertilization rates for C57BL/6J, DBA/2N, BALB/cA, C3H/HeJ, B6D2F1 and B6C3F1 were 66.4, 92.3, 72.8, 32.9, 60.3 and 53.7%, respectively. Furthermore, 38.3, 15.0, 43.3, 26.1, 38.3 and 16.7% of the embryos transferred to pseudopregnant females developed and produced live offspring that had normal phenotype and fertility.     

Systemic administration of neuregulin-1β1 protects dopaminergic neurons in a mouse model of Parkinson's disease

Neuregulin-1 (Nrg1) is genetically linked to schizophrenia, a disease caused by neurodevelopmental imbalance in dopaminergic function. The Nrg1 receptor ErbB4 is abundantly expressed on midbrain dopaminergic neurons. Nrg1 has been shown to penetrate blood-brain barrier, and peripherally administered Nrg1 activates ErbB4 and leads to a persistent hyperdopaminergic state in neonatal mice. These data prompted us to study the effect of peripheral administration of Nrg1 in the context of Parkinson's disease, a neurodegenerative disorder affecting the dopaminergic system in the adult brain. We observed that systemic injections of the extracellular domain of Nrg1β(1) (Nrg1β(1)-ECD) increased dopamine levels in the substantia nigra and striatum of adult mice. Nrg1β(1)-ECD injections also significantly protected the mouse nigrostriatal dopaminergic system morphologically and functionally against 6-hydroxydopamine-induced toxicity in vivo. Moreover, Nrg1β(1)-ECD also protected human dopaminergic neurons in vitro against 6-hydroxydopamine. In conclusion, we have identified Nrg1β(1)-ECD as a neurotrophic factor for adult mouse and human midbrain dopaminergic neurons with peripheral administratability, warranting further investigation as therapeutic option for Parkinson's disease patients.     

Biogenic amines in the ponerine ant Harpegnathos saltator: serotonin and dopamine immunoreactivity in the brain

Many studies suggest a role for biogenic amines in a variety of insect behaviors including intraspecific aggression. In ants, despite a rich behavioral repertoire and prominent aggressive interactions, little is known about the potential impact of biogenic amines. This may partly be due to the general lack of information about aminergic systems in the ant brain. The present study investigates serotonergic and dopaminergic neuronal systems in the brain of the ponerine ant Harpegnathos saltator. In H. saltator, intraspecific aggression is important for the regulation of reproduction. This species, therefore, is amenable to comparative studies of aminergic neuronal effects on long-term changes in aggression. Using immunocytochemistry and confocal microscopy, we found that in the brains of sterile workers, the distributions of serotonergic and dopaminergic neuronal processes differed substantially. In addition, branching patterns of serotonergic neurons showed marked differences between males and females. Brains of workers after 3 days and 3 weeks of aggressive interactions revealed no marked differences in serotonergic and dopaminergic neurons compared to those of reproductive and non-aggressive individuals. We conclude that different levels of intraspecific aggression do not involve profound anatomical changes in serotonergic and dopaminergic neurons. Subtle changes may be masked by inter-individual variances.     

Unique properties of mesoprefrontal neurons within a dual mesocorticolimbic dopamine system

The mesocorticolimbic dopamine system is essential for cognitive and emotive brain functions and is thus an important target in major brain diseases like schizophrenia, drug addiction, and attention deficit hyperactivity disorder. However, the cellular basis for the diversity in behavioral functions and associated dopamine-release pattern within the mesocorticolimbic system has remained unclear. Here, we report the identification of a type of dopaminergic neuron within the mesocorticolimbic dopamine system with unconventional fast-firing properties and small DAT/TH mRNA expression ratios that selectively projects to prefrontal cortex and nucleus accumbens core and medial shell as well as to basolateral amygdala. In contrast, well-described conventional slow-firing dopamine midbrain neurons only project to the lateral shell of the nucleus accumbens and the dorsolateral striatum. Among this dual dopamine midbrain system defined in this study by converging anatomical, electrophysiological, and molecular properties, mesoprefrontal dopaminergic neurons are unique, as only they do not possess functional somatodendritic Girk2-coupled dopamine D2 autoreceptors.     

Prenatal Immune Challenge Is an Environmental Risk Factor for Brain and Behavior Change Relevant to Schizophrenia: Evidence from MRI in a Mouse Model

Objectives

Maternal infection during pregnancy increases risk of severe neuropsychiatric disorders, including schizophrenia and autism, in the offspring. The most consistent brain structural abnormality in patients with schizophrenia is enlarged lateral ventricles. However, it is unknown whether the aetiology of ventriculomegaly in schizophrenia involves prenatal infectious processes. The present experiments tested the hypothesis that there is a causal relationship between prenatal immune challenge and emergence of ventricular abnormalities relevant to schizophrenia in adulthood.

Method

We used an established mouse model of maternal immune activation (MIA) by the viral mimic PolyI:C administered in early (day 9) or late (day 17) gestation. Automated voxel-based morphometry mapped cerebrospinal fluid across the whole brain of adult offspring and the results were validated by manual region-of-interest tracing of the lateral ventricles. Parallel behavioral testing determined the existence of schizophrenia-related sensorimotor gating abnormalities.

Results

PolyI:C-induced immune activation, in early but not late gestation, caused marked enlargement of lateral ventricles in adulthood, without affecting total white and grey matter volumes. This early exposure disrupted sensorimotor gating, in the form of prepulse inhibition. Identical immune challenge in late gestation resulted in significant expansion of 4^th ventricle volume but did not disrupt sensorimotor gating.

Conclusions

Our results provide the first experimental evidence that prenatal immune activation is an environmental risk factor for adult ventricular enlargement relevant to schizophrenia. The data indicate immune-associated environmental insults targeting early foetal development may have more extensive neurodevelopmental impact than identical insults in late prenatal life.     

Systemic dissemination of H5N1 influenza A viruses in ferrets and hamsters after direct intragastric inoculation

Although oral exposure to H5N1 highly pathogenic avian influenza viruses is a risk factor for infection in humans, it is unclear how oral exposure to these virus results in lethal respiratory infections. To address this issue, we inoculated ferrets and hamsters with two highly pathogenic H5N1 strains. These viruses, inoculated directly into the stomach, were isolated from the large intestine and the mesenteric lymph nodes within 1 day of inoculation and subsequently spread to multiple tissues, including lung, liver, and brain. Histopathologic analysis of ferrets infected with virus via direct intragastric inoculation revealed lymph folliculitis in the digestive tract and mesenteric lymph nodes and focal interstitial pneumonia. Comparable results were obtained with the hamster model. We conclude that, in mammals, ingested H5N1 influenza viruses can disseminate to nondigestive organs, possibly through the lymphatic system of the gastrointestinal tract.     

Murine cytomegalovirus infection of neural stem cells alters neurogenesis in the developing brain

Background

Congenital cytomegalovirus (CMV) brain infection causes serious neuro-developmental sequelae including: mental retardation, cerebral palsy, and sensorineural hearing loss. But, the mechanisms of injury and pathogenesis to the fetal brain are not completely understood. The present study addresses potential pathogenic mechanisms by which this virus injures the CNS using a neonatal mouse model that mirrors congenital brain infection. This investigation focused on, analysis of cell types infected with mouse cytomegalovirus (MCMV) and the pattern of injury to the developing brain.

Methodology/Principal Findings

We used our MCMV infection model and a multi-color flow cytometry approach to quantify the effect of viral infection on the developing brain, identifying specific target cells and the consequent effect on neurogenesis. In this study, we show that neural stem cells (NSCs) and neuronal precursor cells are the principal target cells for MCMV in the developing brain. In addition, viral infection was demonstrated to cause a loss of NSCs expressing CD133 and nestin. We also showed that infection of neonates leads to subsequent abnormal brain development as indicated by loss of CD24(hi) cells that incorporated BrdU. This neonatal brain infection was also associated with altered expression of Oct4, a multipotency marker; as well as down regulation of the neurotrophins BDNF and NT3, which are essential to regulate the birth and differentiation of neurons during normal brain development. Finally, we report decreased expression of doublecortin, a marker to identify young neurons, following viral brain infection.

Conclusions

MCMV brain infection of newborn mice causes significant loss of NSCs, decreased proliferation of neuronal precursor cells, and marked loss of young neurons.     

Activation of CNTF/CNTFRα Signaling Pathway by hRheb(S16H) Transduction of Dopaminergic Neurons In Vivo

Ciliary neurotrophic factor (CNTF) is one of representative neurotrophic factors for the survival of dopaminergic neurons. Its effects are primarily mediated via CNTF receptor α (CNTFRα). It is still unclear whether the levels of CNTFRα change in the substantia nigra of Parkinson’s disease (PD) patients, but CNTF expression shows the remarkable decrease in dopaminergic neurons in the substantia nigra pars compacta (SNpc), suggesting that the support of CNTF/CNTFRα signaling pathway may be a useful neuroprotective strategy for the nigrostriatal dopaminergic projection in the adult brain. Here, we report that transduction of rat SNpc dopaminergic neurons by adeno-associated virus with a gene encoding human ras homolog enriched in brain (hRheb), with an S16H mutation [hRheb(S16H)], significantly upregulated the levels of both CNTF and CNTFRα in dopaminergic neurons. Moreover, the hRheb(S16H)-activated CNTF/CNTFRα signaling pathway was protective against 1-methyl-4-phenylpyridinium-induced neurotoxicity in the nigrostriatal dopaminergic projections. These results suggest that activation of CNTF/CNTFRα signaling pathway by specific gene delivery such as hRheb(S16H) may have therapeutic potential in the treatment of PD.     

The dopamine metabolite 3-methoxytyramine is a neuromodulator

Dopamine (3-hydroxytyramine) is a well-known catecholamine neurotransmitter involved in multiple physiological functions including movement control. Here we report that the major extracellular metabolite of dopamine, 3-methoxytyramine (3-MT), can induce behavioral effects in a dopamine-independent manner and these effects are partially mediated by the trace amine associated receptor 1 (TAAR1). Unbiased in vivo screening of putative trace amine receptor ligands for potential effects on the movement control revealed that 3-MT infused in the brain is able to induce a complex set of abnormal involuntary movements in mice acutely depleted of dopamine. In normal mice, the central administration of 3-MT caused a temporary mild hyperactivity with a concomitant set of abnormal movements. Furthermore, 3-MT induced significant ERK and CREB phosphorylation in the mouse striatum, signaling events generally related to PKA-mediated cAMP accumulation. In mice lacking TAAR1, both behavioral and signaling effects of 3-MT were partially attenuated, consistent with the ability of 3-MT to activate TAAR1 receptors and cause cAMP accumulation as well as ERK and CREB phosphorylation in cellular assays. Thus, 3-MT is not just an inactive metabolite of DA, but a novel neuromodulator that in certain situations may be involved in movement control. Further characterization of the physiological functions mediated by 3-MT may advance understanding of the pathophysiology and pharmacology of brain disorders involving abnormal dopaminergic transmission, such as Parkinson's disease, dyskinesia and schizophrenia.     

PINK1 is necessary for long term survival and mitochondrial function in human dopaminergic neurons

Parkinson's disease (PD) is a common age-related neurodegenerative disease and it is critical to develop models which recapitulate the pathogenic process including the effect of the ageing process. Although the pathogenesis of sporadic PD is unknown, the identification of the mendelian genetic factor PINK1 has provided new mechanistic insights. In order to investigate the role of PINK1 in Parkinson's disease, we studied PINK1 loss of function in human and primary mouse neurons. Using RNAi, we created stable PINK1 knockdown in human dopaminergic neurons differentiated from foetal ventral mesencephalon stem cells, as well as in an immortalised human neuroblastoma cell line. We sought to validate our findings in primary neurons derived from a transgenic PINK1 knockout mouse. For the first time we demonstrate an age dependent neurodegenerative phenotype in human and mouse neurons. PINK1 deficiency leads to reduced long-term viability in human neurons, which die via the mitochondrial apoptosis pathway. Human neurons lacking PINK1 demonstrate features of marked oxidative stress with widespread mitochondrial dysfunction and abnormal mitochondrial morphology. We report that PINK1 plays a neuroprotective role in the mitochondria of mammalian neurons, especially against stress such as staurosporine. In addition we provide evidence that cellular compensatory mechanisms such as mitochondrial biogenesis and upregulation of lysosomal degradation pathways occur in PINK1 deficiency. The phenotypic effects of PINK1 loss-of-function described here in mammalian neurons provides mechanistic insight into the age-related degeneration of nigral dopaminergic neurons seen in PD.