Patricia Boksa

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

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.

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

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 μCi of iodinated LPS (125I-LPS) and its distribution was assessed in maternal/fetal tissues (1–8 h). In addition, induction of the inflammatory cytokines, TNF-α, IL-1β and IL-6, was measured in maternal/fetal tissues following maternal LPS challenge (0.05 mg/kg, i.p.) (2–8 h). 125I-LPS was detected in maternal tissues and placenta, but not the fetus. This distribution was accompanied by significant increases in TNF-α, IL-1β and IL-6 in maternal plasma and placenta, but not in fetal liver or brain. A significant increase in IL-1β 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.

Effects of prenatal infection on prepulse inhibition in the rat depend on the nature of the infectious agent and the stage of pregnancy

Maternal infection during pregnancy is a risk factor for some psychiatric illnesses of neurodevelopmental origin such as schizophrenia and autism. In experimental animals, behavioral and neuropathological outcomes relevant to schizophrenia have been observed in offspring of infected dams. However, the type of infectious agent used and gestational age at time of administration have varied. The objective of the present study was to compare the effects of prenatal challenge with different immune agents given at different time windows during gestation on behavioral outcomes in offspring. For this, pregnant rats were administered bacterial endotoxin (lipopolysaccharide, LPS), the viral mimic polyinosinic: polycytidylic acid (poly I:C), or turpentine, an inducer of local inflammation, at doses known to produce fever, at three different stages in pregnancy: embryonic day (E)10-11, E15-16 and E18-19. Prepulse inhibition of acoustic startle (PPI) was later measured in male adult offspring. PPI was significantly decreased in offspring after prenatal LPS treatment at E15-16 and E18-19. Intramuscular injection of pregnant dams with turpentine at E15-16 also decreased PPI in adult offspring. Maternal poly I:C administration had no significant effect on PPI in offspring. In contrast to prenatal LPS exposure, acute LPS administration to naive adult males had no effect on PPI. Thus, prenatal exposure both to a systemic immunogen and to local inflammation at brief periods during later pregnancy produced lasting deficits in PPI in rat offspring. These findings support the idea that maternal infection during critical windows of pregnancy could contribute to sensorimotor gating deficits in schizophrenia.

Birth insult interacts with stress at adulthood to alter dopaminergic function in animal models: possible implications for schizophrenia and other disorders

Altered subcortical dopaminergic activity is thought to be involved in the pathophysiology of several disorders including schizophrenia, substance abuse and attention deficit hyperactivity disorder. Epidemiological studies have implicated perinatal insults, particularly obstetric complications involving fetal or neonatal hypoxia, as etiological risk factors for schizophrenia. This suggests the possibility that perinatal hypoxia might have lasting effects on dopaminergic function. In animal models, dopaminergic systems appears to be particularly vulnerable to a wide range of perinatal insults, resulting in persistent alterations in function of mesolimbic and mesostriatal pathways. This review summarizes recent work characterizing long-term changes in dopaminergic function and biochemistry in models of Caesarean section (C-section) birth and of C-section birth with added global anoxia in the rat and guinea pig. C-section birth and C-section with anoxia appear to be two distinct hypoxic birth insults, with somewhat differing patterns of lasting effects on dopamine systems. In addition, birth insult alters the manner in which dopaminergic function is regulated by stress at adulthood. The possible relevance of these finding to effects of human birth procedures is discussed.

Interleukin-2 Modulates Evoked Release of [3H]Dopamine in Rat Cultured Mesencephalic Cells

Abstract: Mesencephalic cell cultures were used as a model to investigate the effects of interleukin‐2 (IL‐2) on evoked release of [3H]dopamine ([3H]DA) and γ‐[3H]‐aminobutyric acid ([3H]GABA). At low concentrations (10−13‐10−12M), IL‐2 potentiated [3H]DA release evoked by the excitatory amino acids N‐methyl‐D‐aspartate (NMDA) and kainate, whereas higher IL‐2 concentrations (10−9‐10−8M) had no effect. IL‐2 (10−14‐10−8M) modulated K+‐evoked [3H]DA release in a biphasic manner, with low concentrations (10−12‐10−11M) of IL‐2 potentiating and higher concentrations (10−9‐10−8M) inhibiting K+‐induced [3H]DA release. IL‐2 (10−14‐10−8M) by itself failed to alter spontaneous [3H]DA release. The inhibition by IL‐2 of K+‐evoked [3H]DA release was reversible and not due to neurotoxicity, as preexposure to IL‐2 (10−8M) had no significant effect on the subsequent ability of dopaminergic cells to take up and to release [3H]DA. Under our experimental conditions, IL‐2 (10−8 M) did not alter Ca2+‐independent [3H]GABA release evoked by either K+ or NMDA. The results of this study indicate that IL‐2 is able to potentiate [3H]DA release evoked by a number of different stimuli, including K+ depolarization and activation of both NMDA and non‐NMDA receptor subtypes in mesencephalic cell cultures. IL‐2 is active at very low concentrations, a finding that indicates a potent effect of IL‐2 on dopaminergic neurons and implicates a physiological role for this cytokine in the modulation of DA release.

Effects of prenatal immune activation on hippocampal neurogenesis in the rat

Maternal infection during pregnancy has been associated with an increased risk for the development of schizophrenia, a disorder characterized by abnormalities in hippocampal morphology and function. Neurogenesis occurs in the hippocampus throughout development into adulthood and is believed to modulate hippocampal function. This study used a rat model in which bacterial endotoxin, lipopolysaccharide (LPS), is administered to pregnant dams, to test if prenatal immune activation has acute and/or long term effects on various phases of neurogenesis (proliferation, survival, differentiation) in the hippocampal dentate gyrus of offspring. When LPS was administered to dams on gestation days (GD) 15 and 16, there was decreased proliferation of dentate cells at postnatal day (PD) 14 and decreased survival of cells generated at PD14 in offspring. When prenatal exposure to LPS was later in pregnancy (GD 18 and 19), offspring showed decreased survival of cells generated both at the time of LPS exposure and at PD14. There was no change in cell proliferation or survival in adult offspring at PD60, with prenatal LPS exposure. Co-administration of the cyclo-oxygenase inhibitor, ibuprofen (IBU), together with prenatal LPS on GD 15 and 16, was unable to prevent the deficit in neuronal survival at PD14. IBU blocked LPS-induced fever but did not block LPS-induced increases in plasma cytokines and corticosterone in the pregnant dam. This indicates that deficits in neurogenesis caused by prenatal LPS are not mediated by LPS-induced fever or eicosanoid induction, but could be mediated by LPS-induced increases in maternal cytokines or corticosterone.

Desensitization to Nicotinic Cholinergic Agonists and K+, Agents That Stimulate Catecholamine Secretion, in Isolated Adrenal Chromaffin Cells

Abstract: Desensitization of catecholamine (CA) release from cultured bovine adrenal chromaffin cells was studied to characterize the phenomenon of desensitization and to attempt an elucidation of the mechanism(s) involved in this phenomenon at the level of the isolated chromaffin cell. Prior exposure of chromaffin cells to nicotinic cholinergic agonists [acetylcholine (ACh) or nicotine] caused a subsequent depression or desensitization of CA release during restimulation of the cells with the same agonists. Rates of development of and recovery from nicotinic desensitization were in the minute time range and the magnitude of nicotinic desensitization of CA release was greater at 37°C than at 23°C. ACh‐ (or nicotine)‐induced desensitization was shown to be the result of two processes: (1) a Ca2+‐dependent component of desensitization, possibly due to a depletion of intracellular CA stores and (2) a Ca2+‐independent, depletion‐independent component of desensitization. Prior exposure of cultured chromaffin cells to an elevated concentration of K+ also resulted in desensitization of K+‐induced CA release in these cells. K+‐induced desensitization was completely Ca2+‐dependent and was shown to be the result, at least in part, of a mechanism that is independent of depletion of CA stores.

Prenatal and postnatal animal models of immune activation: Relevance to a range of neurodevelopmental disorders

Epidemiological evidence has established links between immune activation during the prenatal or early postnatal period and increased risk of developing a range of neurodevelopment disorders in later life. Animal models have been used to great effect to explore the ramifications of immune activation during gestation and neonatal life. A range of behavioral, neurochemical, molecular, and structural outcome measures associated with schizophrenia, autism, cerebral palsy, and epilepsy have been assessed in models of prenatal and postnatal immune activation. However, the epidemiology‐driven disease‐first approach taken by some studies can be limiting and, despite the wealth of data, there is a lack of consensus in the literature as to the specific dose, timing, and nature of the immunogen that results in replicable and reproducible changes related to a single disease phenotype. In this review, we highlight a number of similarities and differences in models of prenatal and postnatal immune activation currently being used to investigate the origins of schizophrenia, autism, cerebral palsy, epilepsy, and Parkinsons disease. However, we describe a lack of synthesis not only between but also within disease‐specific models. Our inability to compare the equivalency dose of immunogen used is identified as a significant yet easily remedied problem. We ask whether early life exposure to infection should be described as a disease‐specific or general vulnerability factor for neurodevelopmental disorders and discuss the implications that either classification has on the design, strengths and limitations offuture experiments.

Characterization and quantitative autoradiographic distribution of [3H]acetylcholine muscarinic receptors in mammalian brain. Apparent labelling of an M2-like receptor sub-type

[3H]Acetylcholine receptor binding characteristics (under muscarinic conditions) have been investigated using membrane binding assays and in vitro receptor autoradiography. In rat, guinea-pig and monkey brain membrane preparations, [3H]acetylcholine binds with high affinity (25-50 nM) to an apparently single class of sites which is differentially distributed across brain regions. The ligand selectivity pattern reveals that the potency of (-)quinuclidinyl benzylate is greater than (greater than) atropine greater than scopolamine greater than oxotremorine greater than carbamylcholine greater than pirenzepine greater than methylcarbamyl-choline = nicotine in competing for [3H]acetylcholine binding sites, indicating that [3H]acetylcholine selectively binds to muscarinic sites under these incubation conditions. Moreover, the low potency of pirenzepine suggests that [3H]acetylcholine does not label a significant proportion of the M1 receptor sub-type but most likely binds to putative M2-like receptor sites. This hypothesis is also supported by the autoradiographic distribution of [3H]acetylcholine binding sites in all species studied here. High densities of [3H]acetylcholine binding sites are seen in various nuclei of the medulla and pons, certain thalamic nuclei, medial septum, laminae III, V and VI of the cortex and just above the pyramidal cell layer of the hippocampus. Such localization is much different from that seen with the non-selective antagonist [3H]quinuclidinyl benzylate and the selective M1 receptor ligand [3H]pirenzepine, although it resembles that of the selective M2 receptor antagonist [3H]AF-DX 116. Thus, [3H]acetylcholine apparently mostly binds with high affinity mainly to non-M1 muscarinic receptor types in mammalian brain tissues. Moreover, the ligand selectivity pattern and in vitro receptor autoradiographic data suggest that at low concentrations (10-20 nM) most of [3H]actylcholine labelled sites are of the M2-like receptor class.

Long-Term Reciprocal Changes in Dopamine Levels in Prefrontal Cortex versus Nucleus Accumbens in Rats Born by Caesarean Section Compared to Vaginal Birth

Epidemiological evidence indicates a higher incidence of pregnancy and birth complications among individuals who later develop schizophrenia, a disorder linked to alterations in mesolimbic dopamine (DA) function. Two birth complications usually included in these epidemiological studies, and still frequently encountered in the general population, are birth by Caesarean section (C-section) and fetal asphyxia. To test the hypothesis that birth complications can produce long-lasting changes in DA systems, the present study examined the effects of Caesarean birth, with or without an added period of anoxia, on steady state monoamine levels and metabolism in various brain regions in a rat model. Pups born vaginally served as controls. At 2 months of age, in animals born by rapid C-section, steady state levels of DA were decreased by 53% in the prefrontal cortex and increased by 40% in both the nucleus accumbens and striatum, in comparison to the vaginally born group. DA turnover increased in the prefrontal cortex, decreased in the nucleus accumbens, and showed no significant change in the striatum, in the C-section group. Thus, birth by a Caesarean procedure produces long-term reciprocal changes in DA levels and metabolism in the nucleus accumbens and prefrontal cortex. This is consistent with the known inhibitory effect of increased prefrontal cortex DA activity on DA release in the nucleus accumbens. By contrast to birth by rapid C-section alone, young adult animals, that had been born by C-section with 15 min of added anoxia, showed no change in steady state DA levels in the prefrontal cortex, nucleus accumbens, or striatum and a significant decrease in DA turnover only in the nucleus accumbens, in comparison to the vaginally born group. Levels of norepinephrine, serotonin, and its metabolite, 5-hydroxyindole acetic acid, were unchanged in all groups, indicating relatively specific effects on DA systems. Although appearing robust at birth on gross observation, more subtle measurements revealed that rat pups born by C-section show altered respiratory rates and activity levels and increased levels of whole brain lactate, suggestive of low grade brain hypoxia, during the first 24 h of life, in comparison to vaginally born controls. Pups born by C-section with 15 min of added acute anoxia were pale, hypotonic, and inactive at birth and showed reduced respiration and high brain lactate levels. However, these alterations resolved by 1-5 h after birth and, with few exceptions, animals in the anoxic group remained normal with respect to these parameters during the remainder of the first 24 h of life. Immediately after birth, levels of plasma epinephrine, a hormone known to play a role in neonatal adaptation to extrauterine life and protection against hypoxia, were decreased in pups born by C-section but increased in pups born by C-section with 15 min added anoxia, in comparison to levels measured in vaginally born controls. These early developmental alterations could contribute to long-term alterations in dopaminergic parameters observed in rats born by C-section, with or without added anoxia. It is concluded that C-section birth is sufficient perturbation to produce long-lasting effects on DA levels and metabolism in the central nervous system of the rat. These findings highlight the sensitivity of DA pathways to variations in birth procedure and support the notion that birth complications might contribute to the pathophysiology of disorders involving central dopaminergic neurons, such as schizophrenia.