Late prenatal immune activation causes hippocampal deficits in the absence of persistent inflammation across aging.

BACKGROUND: Prenatal exposure to infection and/or inflammation is increasingly recognized to play an important role in neurodevelopmental brain disorders. It has recently been postulated that prenatal immune activation, especially when occurring during late gestational stages, may also induce pathological brain aging via sustained effects on systemic and central inflammation. Here, we tested this hypothesis using an established mouse model of exposure to viral-like immune activation in late pregnancy. METHODS: Pregnant C57BL6/J mice on gestation day 17 were treated with the viral mimetic polyriboinosinic-polyribocytidilic acid (poly(I:C)) or control vehicle solution. The resulting offspring were first tested using cognitive and behavioral paradigms known to be sensitive to hippocampal damage, after which they were assigned to quantitative analyses of inflammatory cytokines, microglia density and morphology, astrocyte density, presynaptic markers, and neurotrophin expression in the hippocampus throughout aging (1, 5, and 22 months of age). RESULTS: Maternal poly(I:C) treatment led to a robust increase in inflammatory cytokine levels in late gestation but did not cause persistent systemic or hippocampal inflammation in the offspring. The late prenatal manipulation also failed to cause long-term changes in microglia density, morphology, or activation, and did not induce signs of astrogliosis in pubescent, adult, or aged offspring. Despite the lack of persistent inflammatory or glial anomalies, offspring of poly(I:C)-exposed mothers showed marked and partly age-dependent deficits in hippocampus-regulated cognitive functions as well as impaired hippocampal synaptophysin and brain-derived neurotrophic factor (BDNF) expression. CONCLUSIONS: Late prenatal exposure to viral-like immune activation in mice causes hippocampus-related cognitive and synaptic deficits in the absence of chronic inflammation across aging. These findings do not support the hypothesis that this form of prenatal immune activation may induce pathological brain aging via sustained effects on systemic and central inflammation. We further conclude that poly(I:C)-based prenatal immune activation models are reliable in their effectiveness to induce (hippocampal) neuropathology across aging, but they appear unsuited for studying the role of chronic systemic or central inflammation in brain aging.

Prenatal immune activation interacts with genetic Nurr1 deficiency in the development of attentional impairments.

Prenatal exposure to infection has been linked to increased risk of neurodevelopmental brain disorders, and recent evidence implicates altered dopaminergic development in this association. However, since the relative risk size of prenatal infection appears relatively small with respect to long-term neuropsychiatric outcomes, it is likely that this prenatal insult interacts with other factors in shaping the risk of postnatal brain dysfunctions. In the present study, we show that the neuropathological consequences of prenatal viral-like immune activation are exacerbated in offspring with genetic predisposition to dopaminergic abnormalities induced by mutations in Nurr1, a transcription factor highly essential for normal dopaminergic development. We combined a mouse model of heterozygous genetic deletion of Nurr1 with a model of prenatal immune challenge by the viral mimetic poly(I:C) (polyriboinosinic polyribocytidilic acid). In our gene-environment interaction model, we demonstrate that the combination of the genetic and environmental factors not only exerts additive effects on locomotor hyperactivity and sensorimotor gating deficits, but further produces synergistic effects in the development of impaired attentional shifting and sustained attention. We further demonstrate that the combination of the two factors is necessary to trigger maldevelopment of prefrontal cortical and ventral striatal dopamine systems. Our findings provide evidence for specific gene-environment interactions in the emergence of enduring attentional impairments and neuronal abnormalities pertinent to dopamine-associated brain disorders such as schizophrenia and attention deficit/hyperactivity disorder, and further emphasize a critical role of abnormal dopaminergic development in these etiopathological processes.

A longitudinal examination of the neurodevelopmental impact of prenatal immune activation in mice reveals primary defects in dopaminergic development relevant to schizophrenia.

Prenatal exposure to infection is a significant environmental risk factor in the development of schizophrenia and related disorders. Recent evidence indicates that disruption of functional and structural dopaminergic development may be at the core of the developmental neuropathology associated with psychosis-related abnormalities induced by prenatal exposure to infection. Using a mouse model of prenatal immune challenge by the viral mimic polyriboinosinic-polyribocytidilic acid, the present study critically evaluated this hypothesis by longitudinally monitoring the effects of maternal immune challenge during pregnancy on structural and functional dopaminergic development in the offspring from fetal to adult stages of life. Our study shows that prenatal immune challenge leads to dopaminergic maldevelopment starting as early as in the fetal stages of life and produces a set of postnatal dopaminergic abnormalities that is dependent on postnatal maturational processes. Furthermore, our longitudinal investigations reveal a striking developmental correspondence between the ontogeny of specific dopaminergic neuropathology and the postnatal onset of distinct forms of dopamine-dependent functional abnormalities implicated in schizophrenia. Prenatal immune activation thus appears to be a significant environmental risk factor for primary defects in normal dopaminergic development and facilitates the expression of postnatal dopamine dysfunctions involved in the precipitation of psychosis-related behavior. Early interventions targeting the developing dopamine system may open new avenues for a successful attenuation or even prevention of psychotic disorders following neurodevelopmental disruption of dopamine functions.

Nurr1 is not essential for the development of prepulse inhibition deficits induced by prenatal immune activation.

Inflammation-induced disruption of fetal neurodevelopmental processes has been linked to the precipitation of long-lasting behavioral abnormalities and associated neuropathology. Recent longitudinal investigations in prenatal immune activation models have revealed developmental correspondences between the ontogeny of specific dopaminergic neuropathology and the postnatal onset of distinct forms of dopamine-dependent functional abnormalities implicated in schizophrenia. Two examples of such developmental correspondences are increased expression of the orphan nuclear receptor Nurr1 (NR4A2) in ventral midbrain areas and disruption of prepulse inhibition of the acoustic startle reflex, with both the neuroanatomical and behavioral effects emerging only in adult but not pre-pubertal subjects exposed to prenatal maternal inflammation. In the present study, we tested the hypothesis that Nurr1 may be a critical molecular mediator of prepulse inhibition deficits induced by prenatal immune activation. To this end, we compared the effects of prenatal immune challenge on adult PPI in wild-type (wt) mice and mice with a heterozygous constitutive deletion of Nurr1 (Nurr1+/-) using a well established mouse model of maternal immune activation by exposure to the viral mimetic poly(I:C) (=polyriboinosinic-polyribocytidilic acid). We found that prenatal poly(I:C) treatment on gestation day 9 was similarly effective in disrupting prepulse inhibition in adult wt and Nurr1+/- mice. Prenatal poly(I:C) treatment also generally increased midbrain Nurr1-positive cells and counteracted the genetically driven Nurr1 deficit in the substantia nigra. Our data thus suggest that at least under the present experimental conditions, Nurr1 is not essential for the development of prepulse inhibition deficits induced by prenatal immune activation.

An extended drawing test for the assessment of arm and hand function with a performance invariant for healthy subjects.

Impaired hand motor function resulting from neurological, psychiatric or orthopaedic disorders affects patients of all ages. Existing hand function assessment methods, e.g. rating scales, accelerometers and electromyographical devices, are often time-consuming to administer, subjective in interpretation and/or expensive. Graphonomic tests are gaining popularity as a way of avoiding these drawbacks while relating directly to writing and drawing. Here we present a computerized Extended Drawing Test (EDT), which improves on an earlier Drawing Test for stroke patients in three ways. First, it assesses isolated proximal arm movement using a graphics pen in a puck-like pen holder, and in addition combined arm and finger dexterity in movements using a normal writing grip. Secondly, we calibrated our test against 186 healthy subjects (3-70 years), finding significant age- and handedness-related differences in both speed and accuracy of drawing. Thirdly, to simplify assessment we devised an overall performance measure using a variant of Fitts' Law combining speed and accuracy, which we found to be age-independent for healthy subjects above 3 years of age. This result enables us to provide age-independent performance norms using both hands, with and without the pen holder. These norms may assist quantification of specific arm dysfunction by comparing patient performance with the healthy norms, and also by comparing within-patient performance in the dominant and non-dominant hands with and without the pen holder. Using our freely available software, this new test will allow clinicians to rapidly assess arm and hand function across a wide range of patient categories and ages.

Maternal Vitamin D Prevents Abnormal Dopaminergic Development and Function in a Mouse Model of Prenatal Immune Activation.

Dysfunction in dopamine (DA) systems is a prominent feature in schizophrenia patients and may result from the abnormal development of mesencephalic (mes)DA systems. Maternal immune activation (MIA) and developmental vitamin D (DVD)-deficiency both induce schizophrenia-relevant dopaminergic abnormalities in adult offspring. In this study, we investigated whether maternal administration of the vitamin D hormone (1,25OHD, VITD) could prevent MIA-induced abnormalities in DA-related behaviors and mesDA development. We administrated the viral mimetic polyriboinosinic-polyribocytidylic (poly (I:C)) simultaneously with 1,25OHD and/or their vehicles, to pregnant mouse dams at gestational day 9. Maternal treatment with VITD prevented MIA-induced hypersensitivity to acute DA stimulation induced by amphetamine, whereas it failed to block prepulse inhibition deficiency in MIA-exposed offspring. MIA and VITD both reduced fetal mesDA progenitor (Lmx1a + Sox2+) cells, while VITD treatment increased the number of mature (Nurr1 + TH+) mesDA neurons. Single-cell quantification of protein expression showed that VITD treatment increased the expression of Lmx1a, Nurr1 and TH in individual mesDA cells and restored normal mesDA positioning. Our data demonstrate that VITD prevents abnormal dopaminergic phenotypes in MIA offspring possibly via its early neuroprotective actions on fetal mesDA neurons. Maternal supplementation with the dietary form of vitamin D, cholecalciferol may become a valuable strategy for the prevention of MIA-induced neurodevelopmental abnormalities.

Vitamin D treatment during pregnancy prevents autism-related phenotypes in a mouse model of maternal immune activation.

BACKGROUND: Prenatal exposure to infection is a recognized environmental risk factor for neuropsychiatric disorders of developmental origins such as autism or schizophrenia. Experimental work in animals indicates that this link is mediated by maternal immune activation (MIA) involving interactions between cytokine-associated inflammatory events, oxidative stress, and other pathophysiological processes such as hypoferremia and zinc deficiency. Maternal administration of the viral mimic polyriboinosinic-polyribocytidylic acid (poly(I:C)) in mice produces several behavioral phenotypes in adult offspring of relevance to autism spectrum disorder (ASD) and other neurodevelopmental disorders. METHODS: Here, we investigated whether some of these phenotypes might also present in juveniles. In addition, given the known immunomodulatory and neuroprotective effects of vitamin D, we also investigated whether the co-administration of vitamin D could block MIA-induced ASD-related behaviors. We co-administered the hormonally active form of vitamin D, 1α,25 dihydroxy vitamin D3 (1,25OHD), simultaneously with poly(I:C) and examined (i) social interaction, stereotyped behavior, emotional learning and memory, and innate anxiety-like behavior in juveniles and (ii) the levels of the pro-inflammatory cytokines IL-1ß, IL-6 and TNF-α in maternal plasma and fetal brains. RESULTS: We show that like adult offspring that were exposed to MIA, juveniles display similar deficits in social approach behavior. Juvenile MIA offspring also show abnormal stereotyped digging and impaired acquisition and expression of tone-cued fear conditioning. Importantly, our study reveals that prenatal administration of 1,25OHD abolishes all these behavioral deficits in poly(I:C)-treated juveniles. However, prenatal administration of vitamin D had no effect on pro-inflammatory cytokine levels in dams or in fetal brains suggesting the anti-inflammatory actions of vitamin D are not the critical mechanism for its preventive actions in this ASD animal model. CONCLUSIONS: This work raises the possibility that early dietary supplementation with vitamin D may open new avenues for a successful attenuation or even prevention of neurodevelopmental disorders following maternal inflammation during pregnancy.

An Anti-ß-Amyloid Vaccine for Treating Cognitive Deficits in a Mouse Model of Down Syndrome.

In Down syndrome (DS) or trisomy of chromosome 21, the ß-amyloid (Aß) peptide product of the amyloid precursor protein (APP) is present in excess. Evidence points to increased APP gene dose and Aß as playing a critical role in cognitive difficulties experienced by people with DS. Particularly, Aß is linked to the late-life emergence of dementia as associated with neuropathological markers of Alzheimer's disease (AD). At present, no treatment targets Aß-related pathogenesis in people with DS. Herein we used a vaccine containing the Aß 1-15 peptide embedded into liposomes together with the adjuvant monophosphoryl lipid A (MPLA). Ts65Dn mice, a model of DS, were immunized with the anti-Aß vaccine at 5 months of age and were examined for cognitive measures at 8 months of age. The status of basal forebrain cholinergic neurons and brain levels of APP and its proteolytic products were measured. Immunization of Ts65Dn mice resulted in robust anti-Aß IgG titers, demonstrating the ability of the vaccine to break self-tolerance. The vaccine-induced antibodies reacted with Aß without detectable binding to either APP or its C-terminal fragments. Vaccination of Ts65Dn mice resulted in a modest, but non-significant reduction in brain Aß levels relative to vehicle-treated Ts65Dn mice, resulting in similar levels of Aß as diploid (2N) mice. Importantly, vaccinated Ts65Dn mice showed resolution of memory deficits in the novel object recognition and contextual fear conditioning tests, as well as reduction of cholinergic neuron atrophy. No treatment adverse effects were observed; vaccine did not result in inflammation, cellular infiltration, or hemorrhage. These data are the first to show that an anti-Aß immunotherapeutic approach may act to target Aß-related pathology in a mouse model of DS.

Relationship between sensorimotor gating deficits and dopaminergic neuroanatomy in Nurr1-deficient mice.

Nurr1 (NR4A2) is an orphan nuclear receptor highly essential for the development and maintenance of dopaminergic neurons. Reduced expression of Nurr1 has been linked to the etiopathogenesis of Parkinson's disease and other dopamine-related disorders such as schizophrenia. Recent experimental work in mice with a heterozygous constitutive deletion of Nurr1 has revealed that this genetic manipulation leads to the presence of sensorimotor gating dysfunctions in the form of reduced prepulse inhibition of the acoustic startle reflex. However, the neuronal substances for this behavioral manifestation remain essentially unknown. Since converging evidence supports a key role of the central dopamine system in the regulation of prepulse inhibition, we hypothesized that the emergence of prepulse inhibition deficits in adult Nurr1-deficient mice may be linked to dopaminergic neuroanatomical changes. To test this hypothesis, we followed a within-subject approach in which sensorimotor gating performance was correlated with post-mortem expression of several dopaminergic markers in relevant striatal and midbrain regions. We found that prepulse inhibition deficits in Nurr1-deficient mice were paralleled by reduced numbers of substantia nigra dopamine cells expressing tyrosine hydroxylase, and by decreased tyrosine hydroxylase and dopamine transporter immunoreactivity in ventral parts of the striatum. Most interestingly, we also revealed a striking negative correlation between prepulse inhibition levels and tyrosine hydroxylase immunoreactivity in Nurr1-deficient mice in dorsal striatal regions (caudate putamen) and ventral striatal regions (nucleus accumbens core and shell). Our findings thus suggest that the emergence of prepulse inhibition deficits induced by heterozygous constitutive deletion of Nurr1 is, at least in part, related to alterations in presynaptic components of the striatal dopamine system. The constellation of neuroanatomical and behavioral alterations in Nurr1-deficient mice observed here confirms previous impressions that the consequences of Nurr1 down-regulation capture neuronal and behavioral pathologies relevant especially for (but not limited to) Parkinson's disease.