Schizophrenia and autism are thought to result from the interaction between a susceptibility genotype and environmental risk factors. The offspring of women who experience infection while pregnant have an increased risk for these disorders. Maternal immune activation (MIA) in pregnant rodents produces offspring with abnormalities in behavior, histology, and gene expression that are reminiscent of schizophrenia and autism, making MIA a useful model of the disorders. However, the mechanism by which MIA causes long-term behavioral deficits in the offspring is unknown. Here we show that the cytokine interleukin-6 (IL-6) is critical for mediating the behavioral and transcriptional changes in the offspring. A single maternal injection of IL-6 on day 12.5 of mouse pregnancy causes prepulse inhibition (PPI) and latent inhibition (LI) deficits in the adult offspring. Moreover, coadministration of an anti-IL-6 antibody in the poly(I:C) model of MIA prevents the PPI, LI, and exploratory and social deficits caused by poly(I:C) and normalizes the associated changes in gene expression in the brains of adult offspring. Finally, MIA in IL-6 knock-out mice does not result in several of the behavioral changes seen in the offspring of wild-type mice after MIA. The identification of IL-6 as a key intermediary should aid in the molecular dissection of the pathways whereby MIA alters fetal brain development, which can shed new light on the pathophysiological mechanisms that predispose to schizophrenia and autism.

https://www.jneurosci.org/content/jneuro/27/40/10695.full.pdf

Maternal Immune Activation Alters Fetal Brain Development through Interleukin-6

Disturbance to early brain development is implicated in several neuropsychiatric disorders including autism, schizophrenia, and mental retardation. Epidemiological studies have indicated that the risk of developing these disorders is enhanced by prenatal maternal infection, presumably as a result of neurodevelopmental defects triggered by cytokine-related inflammatory events. Here, we demonstrate that the effects of maternal immune challenge between middle and late gestation periods in mice are dissociable in terms of fetal brain cytokine responses to maternal inflammation and the pathological consequences in brain and behavior. Specifically, the relative expression of pro- and anti-inflammatory cytokines in the fetal brains in response to maternal immune challenge may be an important determinant among other developmental factors for the precise pathological profile emerging in later life. Thus, the middle and late gestation periods correspond to two windows with differing vulnerability to adult behavioral dysfunction, brain neuropathology in early adolescence, and of the acute cytokine responses in the fetal brain.

https://www.jneurosci.org/content/jneuro/26/18/4752.full.pdf

The time of prenatal immune challenge determines the specificity of inflammation-mediated brain and behavioral pathology

Immune involvement in schizophrenia and autism: Etiology, pathology and animal models

Schizophrenia, “Just the Facts” What we know in 2008. 2. Epidemiology and etiology

Epidemiological studies with human populations indicate associations between maternal infection during pregnancy and increased risk in offspring for central nervous system (CNS) disorders including schizophrenia, autism and cerebral palsy. Since 2000, a large number of studies have used rodent models of systemic prenatal infection or prenatal immune activation to characterize changes in brain function and behavior caused by the prenatal insult. This review provides a comprehensive summary of these findings, and examines consistencies and trends across studies in an effort to provide a perspective on our current state of understanding from this body of work. Results from these animal modeling studies clearly indicate that prenatal immune activation can cause both acute and lasting changes in behavior and CNS structure and function in offspring. Across laboratories, studies vary with respect to the type, dose and timing of immunogen administration during gestation, species used, postnatal age examined and specific outcome measure quantified. This makes comparison across studies and assessment of replicability difficult. With regard to mechanisms, evidence for roles for several acute mediators of effects of prenatal immune activation has emerged, including circulating interleukin-6, increased placental cytokines and oxidative stress in the fetal brain. However, information required to describe the complete mechanistic pathway responsible for acute effects of prenatal immune activation on fetal brain is lacking, and no studies have yet addressed the issue of how acute prenatal exposure to an immunogen is transduced into a long-term CNS change in the postnatal animal. Directions for further research are discussed.

Effects of prenatal infection on brain development and behavior: A review of findings from animal models

Maternal infections with bacterial or viral agents during pregnancy are associated with an increased incidence of schizophrenia in the offspring at adulthood although little is known about the mechanism by which maternal infection might affect fetal neurodevelopment. Exposure of pregnant rodents to the bacterial endotoxin, lipopolysaccharide (LPS), results in behavioral deficits in the adult offspring that are relevant to schizophrenia. It is however unknown whether these effects are due to the direct action of the inflammatory stimulus on the developing fetus, or due to secondary immune mediators (cytokines) activated at maternal/fetal sites. In this study we sought to elucidate the site of action of LPS, following a single intraperitoneal (i.p.) injection, in pregnant rats at gestation day 18. Animals received 5 muCi of iodinated LPS ((125)I-LPS) and its distribution was assessed in maternal/fetal tissues (1-8 h). In addition, induction of the inflammatory cytokines, TNF-alpha, IL-1beta and IL-6, was measured in maternal/fetal tissues following maternal LPS challenge (0.05 mg/kg, i.p.) (2-8 h). (125)I-LPS was detected in maternal tissues and placenta, but not the fetus. This distribution was accompanied by significant increases in TNF-alpha, IL-1beta and IL-6 in maternal plasma and placenta, but not in fetal liver or brain. A significant increase in IL-1beta was however detected in fetal plasma, possibly due to transfer from the maternal circulation or placenta. Collectively, these data suggest that effects of maternal LPS exposure on the developing fetal brain are not mediated by the direct action of LPS, but via indirect actions at the level of the maternal circulation or placenta.

The role of cytokines in mediating effects of prenatal infection on the fetus: implications for schizophrenia.

Polyinosinic:polycytidylic acid (poly I:C) is a synthetic double-stranded RNA that is used experimentally to model viral infections in vivo. Previous studies investigating the inflammatory properti...

The viral mimic, polyinosinic:polycytidylic acid, induces fever in rats via an interleukin-1-dependent mechanism

Effects of prenatal immune activation on hippocampal neurogenesis in the rat.

Febrile responses to bacterial pathogens are attenuated near term of pregnancy in several mammalian species. It is unknown, however, whether this reflects a fundamental physiological adaptation of ...

Interleukin-1 receptor antagonist as a modulator of gender differences in the febrile response to lipopolysaccharide in rats

The main cause of hypoxic/ischemic brain damage in term human neonates is intrauterine asphyxia, in which the whole body is subjected to hypoxia. Inflammatory cytokines are thought to play an important role in modulating hypoxic/ischemic damage in immature brain. Evidence for this from animal models is based mainly on studies that used a model of carotid artery ligation with hypoxia in postnatal rats. However, little is known about the role of cytokines in brain injury after whole-body hypoxia at the time of birth. This study used a well-established rat model of global birth hypoxia to assess mRNA and protein expression of three key proinflammatory cytokines, interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor-alpha, (TNF-alpha) in the brain, liver, and kidney of neonates. We observed decreased IL-1beta and TNF-alpha protein, and decreased IL-6 mRNA in brains of neonates in the 2 hr after birth hypoxia but increased IL-6 and IL-1beta in liver compared with vaginally born controls. Increasing the severity of the insult by increasing the period of anoxic exposure further decreased brain IL-1beta, whereas delivering anoxia under hypothermic conditions, known to be neuroprotective, attenuated the decrease in brain IL-1beta. These data suggest that decreased brain levels of inflammatory cytokines may modulate central nervous system responses to global birth hypoxia in rats. Our findings of decreased brain cytokine expression after global birth hypoxia contrast with reports of increased brain cytokines after carotid artery ligation with hypoxia in postnatal rats; possible reasons for these differences are discussed.

Helen Ashdown

Papers

The role of cytokines in mediating effects of prenatal infection on the fetus: implications for schizophrenia.

The viral mimic, polyinosinic:polycytidylic acid, induces fever in rats via an interleukin-1-dependent mechanism

Effects of prenatal immune activation on hippocampal neurogenesis in the rat.

Interleukin-1 receptor antagonist as a modulator of gender differences in the febrile response to lipopolysaccharide in rats

Acute brain cytokine responses after global birth hypoxia in the rat.