Prenatal immune activation causes hippocampal synaptic deficits in the absence of overt microglia anomalies

Prenatal exposure to infectious or inflammatory insults can increase the risk of developing neuropsychiatric disorder in later life, including schizophrenia, bipolar disorder, and autism. These brain disorders are also characterized by pre- and postsynaptic deficits. Using a well-established mouse model of maternal exposure to the viral mimetic polyriboinosinic–polyribocytidilic acid [poly(I:C)], we examined whether prenatal immune activation might cause synaptic deficits in the hippocampal formation of pubescent and adult offspring. Based on the widely appreciated role of microglia in synaptic pruning, we further explored possible associations between synaptic deficits and microglia anomalies in offspring of poly(I:C)-exposed and control mothers. We found that prenatal immune activation induced an adult onset of presynaptic hippocampal deficits (as evaluated by synaptophysin and bassoon density). The early-life insult further caused postsynaptic hippocampal deficits in pubescence (as evaluated by PSD95 and SynGAP density), some of which persisted into adulthood. In contrast, prenatal immune activation did not change microglia (or astrocyte) density, nor did it alter their activation phenotypes. The prenatal manipulation did also not cause signs of persistent systemic inflammation. Despite the absence of overt glial anomalies or systemic inflammation, adult offspring exposed to prenatal immune activation displayed increased hippocampal IL-1β levels. Taken together, our findings demonstrate that age-dependent synaptic deficits and abnormal pro-inflammatory cytokine expression can occur during postnatal brain maturation in the absence of microglial anomalies or systemic inflammation.     

Prenatal exposure to a pro-inflammatory stimulus causes delays in the development of the innate immune response to LPS in the offspring

Growing evidence suggests that maternal health during the prenatal period is a critical determinant of adult immuno-competence. This study aimed to characterise the innate immune response to bacterial exposure in rat offspring following maternal exposure to a pro-inflammatory stimulus. The offspring's innate immune responses were investigated at four developmental timepoints in the rat by determination of immune cell subtypes and TNF-alpha and IL-1beta response to in-vivo LPS exposure. The pre-weaned offspring of exposed dams demonstrated no immune response to the LPS challenge, whereas control offspring responded with a typical elevation in cytokine levels. In pubescence no differences were observed between the responses of the control and exposed offspring. In adulthood and senescence, offspring of endotoxin treated dams had significantly less monocytes in circulation than control offspring and differential sex effects were only evident in these older animals. The developmental profile of immune functioning following prenatal immune activation has not previously been demonstrated. This study highlights the prenatal period as one of importance in determining later immune function.     

Neonatal LPS injection alters the body weight regulation systems of rats under non-stress and immune stress conditions

It has been reported that prenatal immune stress induced by lipopolysaccharides or cytokines increases food intake and leads to obesity and other features of metabolic syndrome in adulthood. Using Sprague–Dawley rats, we evaluated whether neonatal LPS injection altered their body weight regulation systems under non-stress and immune stress conditions. On Day 10 after birth, all pups were injected with LPS (100 μg/kg, i.p.) (PND₁₀LPS) or saline (PND₁₀Saline). After weaning, body weight was significantly elevated in PND₁₀LPS compared with PND₁₀Saline. Thereafter, the rats were injected with LPS (100 μg/kg, i.p.) or saline (used as a basal condition) from 7 to 8 weeks of age. Under basal conditions, cumulative food intake were significantly higher, serum leptin concentration was significantly increased, and hypothalamic NPY mRNA expression was significantly decreased in PND₁₀LPS compared with PND₁₀Saline. Under adult LPS injected conditions, body weight gain and cumulative food intake were suppressed in both the PND₁₀LPS and PND₁₀Saline groups compared with those observed under basal adult saline-injected conditions. The suppressive effects induced by adult LPS injection were less evident in the PND₁₀LPS group than in the PND₁₀Saline group. Adult LPS injection increased the serum leptin concentration in the PND₁₀Saline rats, but not in the PND₁₀LPS rats. In addition, adult LPS injection increased the mRNA expression of anorexinergic factors (IL-1β, and TNF-α), and decreased that of the orexinergic factor NPY in both groups. However, the influence of adult LPS injection upon these factors was less evident in the PND₁₀LPS group than in the PND₁₀Saline group. These results suggest that neonatal LPS injection alters body weight regulation under both non-stress and immune stress conditions in male rats. Changes in the endocrine, neuropeptide, and cytokine regulation systems might be involved in these alterations.     

Additive effects of maternal iron deficiency and prenatal immune activation on adult behaviors in rat offspring

Both iron deficiency (ID) and infection are common during pregnancy and studies have described altered brain development in offspring as a result of these individual maternal exposures. Given their high global incidence, these two insults may occur simultaneously during pregnancy. We recently described a rat model which pairs dietary ID during pregnancy and prenatal immune activation. Pregnant rats were placed on iron sufficient (IS) or ID diets from embryonic day 2 (E2) until postnatal day 7, and administered the bacterial endotoxin, lipopolysaccharide (LPS) or saline on E15/16. In this model, LPS administration on E15 caused greater induction of the pro-inflammatory cytokines, interleukin-6 and tumor necrosis factor-α, in ID dams compared to IS dams. This suggested that the combination of prenatal immune activation on a background of maternal ID might have more adverse neurodevelopmental consequences for the offspring than exposure to either insult alone. In this study we used this model to determine whether combined exposure to maternal ID and prenatal immune activation interact to affect juvenile and adult behaviors in the offspring. We assessed behaviors relevant to deficits in humans or animals that have been associated with exposure to either maternal ID or prenatal immune activation alone. Adult offspring from ID dams displayed significant deficits in pre-pulse inhibition of acoustic startle and in passive avoidance learning, together with increases in cytochrome oxidase immunohistochemistry, a marker of metabolic activity, in the ventral hippocampus immediately after passive avoidance testing. Offspring from LPS treated dams showed a significant increase in social behavior with unfamiliar rats, and subtle locomotor changes during exploration in an open field and in response to amphetamine. Surprisingly, there was no interaction between effects of the two insults on the behaviors assessed, and few observed alterations in juvenile behavior. Our findings show that long-term effects of maternal ID and prenatal LPS were additive, such that offspring exposed to both insults displayed more adult behavioral abnormalities than offspring exposed to one alone.     

Intrauterine inflammation, insufficient to induce parturition, still evokes fetal and neonatal brain injury

Exposure to prenatal inflammation is a known risk factor for long term neurobehavioral disorders including cerebral palsy, schizophrenia, and autism. Models of systemic inflammation during pregnancy have demonstrated an association with an immune response an adverse neurobehavioral outcomes for the exposed fetus. Yet, the most common route for an inflammatory exposure to a fetus is from intrauterine inflammation as occurs with chorioamnionitis. The aims of this study were to assess the effect of intrauterine inflammation on fetal and neonatal brain development and to determine if the gestational age of exposure altered the maternal or fetal response to inflammation.CD-1 timed pregnant mice on embryonic day 15 (E15) and E18.5 were utilized for this study. Dams were randomized to receive intrauterine infusion of lipopolysaccharide (LPS, 50 μg/dam) or normal saline. Different experimental groups were used to assess both acute and long-term outcomes. For each gestational age and each treatment group, fetal brains, amniotic fluid, maternal serum and placentas were collected 6 h after intrauterine infusion. Rates of preterm birth, maternal morbidity and litter size were assessed. IL6 levels were assayed in maternal serum and amniotic fluid.An immune response was determined in the fetal brains and placentas by QPCR. Cortical cultures were performed to assess for fetal neuronal injury. Gene expression changes in postnatal day 7 brains from exposed and unexposed pups were determined.In the preterm period, low dose LPS resulted in a 30% preterm birth rate. Litter sizes were not different between the groups at either gestational age. IL6 levels were not significantly increased in maternal serum at either gestational time period. Low dose LPS increased IL6 levels in the amniotic fluid from exposed dams in the term but not preterm period. Regardless of gestational age of exposure, low dose intrauterine LPS activated an immune response in the placenta and fetal brain. Exposure to intrauterine LPS significantly decreased dendritic counts in cortical cultures from both the preterm and term period. Exposure to intrauterine inflammation altered gene expression patterns in the postnatal brain; this effect was dependent on gestational age of exposure.In conclusion, intrauterine inflammation, even in the absence of preterm parturition, can evoke fetal brain injury as evidence by alterations in cytokine expression and neuronal injury. Despite an absent or limited maternal immune response in low dose intrauterine inflammation, the immune system in the placenta is activated which is likely sufficient to induce a fetal immune response and subsequent brain injury. Changes in the fetal brain lead to changes in gene expression patterns into the neonatal period. Subclinical intrauterine inflammation can lead to fetal brain injury and is likely to be mechanistically associated with long term adverse outcomes for exposed offspring.     

Prenatal protein deprivation in rats induces changes in prepulse inhibition and NMDA receptor binding

Epidemiological studies suggest that prenatal malnutrition increases the risk of developing schizophrenia. Animal models indicate that prenatal protein deprivation (PPD) affects many aspects of adult brain function. We tested the hypothesis that PPD in rats would alter prepulse inhibition (PPI), which is an operational measure of sensorimotor gating that is deficient in schizophrenia patients. Additionally, we examined dopaminergic and glutaminergic receptor binding in the striatum and hippocampus, which have been suggested to play a role in the etiology of schizophrenia. Rat dams were fed normal (25%) or low (6%) protein diets beginning 5 weeks prior to, and throughout pregnancy. The pups were tested at postnatal days (PND) 35 and 56 for PPI. Striatal and hippocampal NMDA receptor, and striatal dopamine receptor binding were quantified post-mortem in a subset of these rats. Female rats exposed to PPD had reduced levels of PPI at PND 56, but not PND 35, suggesting the emergence of a sensorimotor gating deficit in early adulthood. Striatal NMDA receptor binding was increased in PPD females. A decrease in initial startle response (SR) was also observed in all PPD rats relative to control rats. These results suggest that PPD causes age- and sex-dependent decreases in PPI and increases in NMDA receptor binding. This animal model may be useful for the investigation of neurodevelopmental changes that are associated with schizophrenia in humans.     

Astrocyte-neuron vulnerability to prenatal stress in the adult rat brain

Chronic activation of the stress response during pregnancy has been shown to be injurious to the development of the offspring. We have previously demonstrated that restraint prenatal stress inflicted during the last week of pregnancy in rats increased dopamine and glutamate receptors in forebrain areas of the adult offsprings. In this study, the same prenatal insult was employed to assess morphological changes in astrocytes and in the dendritic arborization in frontal cortex, striatum, and hippocampus of the adult rat brain. On postnatal day 90, brains were processed for immunocytochemistry using primary antibodies to glial fibrillary acidic protein (GFAP; the main cytoskeletal astroglial protein), S100B protein (an astroglial-derived neurotrophic factor), MAP-2 (a microtubule-associated protein present almost exclusively in dendrites), and synaptophysin (Syn; one major integral protein of the synaptic vesicles membrane). The results show a significant increase in the cell area of GFAP-immunoreactive (-IR) astrocytes, with high levels of S100B protein and a significant decrease in the relative area of MAP-2-IR neuronal processes in prenatally stressed adult rats. The expression of synaptophysin decreased in all areas studied. These results demonstrate that prenatal stress induces a long-lasting astroglial reaction and a reduced dendritic arborization, with synaptic loss in the brain of adult offspring. In addition to the neurochemical alterations previously reported, these morphological changes might be underlying the behavioral and learning impairment previously observed in prenatally stressed rats.     

Neonatal lipopolysaccharide exposure attenuates the homotypic stress-induced suppression of LH secretion in adulthood in male rat

Neonatal immune challenges have a long-lasting influence on immune response. Using male Sprague–Dawley rats, we examined whether neonatal lipopolysaccharide (LPS) challenge alters the sensitivity of male reproductive function to adult LPS challenge and at which level (central or testes) the alteration occurs. We also examined the mRNA expression of proinflammatory cytokines in the hypothalamus and testes because they have a pivotal role in immune stress-induced suppression of gonadotropin secretion and testosterone synthesis. On day 10 after birth, all the pups were injected with LPS (100 μg/kg, i.p.) or saline. Thereafter, LPS (100 μg/kg, i.p.) or saline was injected in adulthood at 8 weeks of age. The serum LH concentration was decreased by LPS injection during adulthood in the neonatal saline-injected rats. This suppressive effect was not seen in the neonatal LPS-injected rats. The serum testosterone concentration was decreased by adult LPS injection in both the neonatal LPS-injected and neonatal saline-injected rats. The expression levels of KiSS-1, which encodes kisspeptin, known to have a crucial role in the regulation of gonadotropin secretion, and GnRH mRNA in the hypothalamus and LHβ mRNA in the pituitary were not influenced by neonatal or adult LPS injection. On the other hand, the expression levels of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) mRNA in the hypothalamus and testes were increased by adult LPS injection in both the neonatal LPS-injected and neonatal saline-injected rats. Furthermore, the expression levels of these factors in the hypothalamus after adult LPS injection were significantly lower in the neonatal LPS-injected rats than in the neonatal saline-injected rats. These findings indicate that neonatal LPS challenge reduces the sensitivity of male reproductive function to the suppressive effects of LPS, mainly at the central level. Attenuation of proinflammatory cytokine synthesis in the hypothalamus might be involved in this alteration.     

Polychlorinated biphenyls induce proinflammatory cytokine release and dopaminergic dysfunction: protection in interleukin-6 knockout mice

Proinflammatory cytokines are not only important mediators of brain development, but also pose an increased risk for neurodegeneration following exposure to neurotoxicants or trauma. We have used the ubiquitous environmental and occupational neurotoxicant polychlorinated biphenyls (PCBs) to investigate the putative role of inflammatory agents in mediating processes involved in basal ganglia dysfunctions. PCBs induced inflammatory responses in C57BL/6 adult male mice, significantly elevating serum levels of IL-6 (31%), IL-1beta (71%) and TNF-alpha (22%) and significantly reducing striatal dopamine (DA, 21%), tyrosine hydroxylase (TH, 26%), dopamine transporter (DAT, 39%), and synaptophysin (29%) concentrations. We also exposed mice deficient in the proinflammatory cytokine interleukin-6 (IL-6-/-) to PCBs, to explore the role of this specific cytokine in mediating PCB-induced DA neurodegeneration. Not only did the PCB-treated IL-6-/- mice exhibit a decrease in serum levels of IL-1beta and TNF-alpha, but they were also protected from PCB-induced striatal dopaminergic dysfunction, displaying no signs of toxicant-induced reductions in DA levels, or TH, DAT or synaptophysin expression. Taken together, these results suggest that: (1) PCB exposure results in a peripheral inflammatory response associated with striatal terminal degeneration; and (2) the absence of IL-6 prevents PCB-induced dopaminergic losses in the striatum.     

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.     

Presynaptic dopaminergic function is largely unaltered in mesolimbic and mesostriatal terminals of adult rats that were prenatally exposed to cocaine

Fast-scan cyclic voltammetry in brain slices and postmortem tissue content assessment were used to evaluate presynaptic dopaminergic function in the caudate putamen and nucleus accumbens of adult male rats (180+ days old) that were prenatally treated with either cocaine or saline. Experiments were carried out to test whether there were differences in dopamine release, reuptake, autoreceptor function or the tissue levels of dopamine and its metabolites between cocaine- and saline-exposed rats. We report that presynaptic dopaminergic function remains largely intact in adult rats that were prenatally exposed to cocaine. The ability of terminals in the caudate putamen and nucleus accumbens to release and regulate dopamine is unaltered by prenatal cocaine exposure. However the tissue content of dopamine in the caudate putamen was decreased, representing a diminution in the dopamine storage pool. We conclude, therefore, that behavioral changes that have previously been observed in rats that were prenatally exposed to cocaine are not mediated through alteration of presynaptic dopaminergic mechanisms in these brain regions.     

Microglia and memory: modulation by early-life infection

The proinflammatory cytokine interleukin-1β (IL-1β) is critical for normal hippocampus (HP)-dependent cognition, whereas high levels can disrupt memory and are implicated in neurodegeneration. However, the cellular source of IL-1β during learning has not been shown, and little is known about the risk factors leading to cytokine dysregulation within the HP. We have reported that neonatal bacterial infection in rats leads to marked HP-dependent memory deficits in adulthood. However, deficits are only observed if unmasked by a subsequent immune challenge [lipopolysaccharide (LPS)] around the time of learning. These data implicate a long-term change within the immune system that, upon activation with the "second hit," LPS, acutely impacts the neural processes underlying memory. Indeed, inhibiting brain IL-1β before the LPS challenge prevents memory impairment in neonatally infected (NI) rats. We aimed to determine the cellular source of IL-1β during normal learning and thereby lend insight into the mechanism by which this cytokine is enduringly altered by early-life infection. We show for the first time that CD11b(+) enriched cells are the source of IL-1β during normal HP-dependent learning. CD11b(+) cells from NI rats are functionally sensitized within the adult HP and produce exaggerated IL-1β ex vivo compared with controls. However, an exaggerated IL-1β response in vivo requires LPS before learning. Moreover, preventing microglial activation during learning prevents memory impairment in NI rats, even following an LPS challenge. Thus, early-life events can significantly modulate normal learning-dependent cytokine activity within the HP, via a specific, enduring impact on brain microglial function.     

Immune activation during mid-gestation disrupts sensorimotor gating in rat offspring

Maternal immune activation (MIA) is a newly developed animal model of schizophrenia. It has recently been reported that when MIA is induced with the cytokine inducer polyinosinic-polycytidilic acid (poly I:C) rats do not show deficits in prepulse inhibition (PPI), a test that is often considered a validity benchmark. The aim of the current experiment was to determine whether doses of poly I:C that have previously been shown to induce the behavioural features of schizophrenia can disrupt PPI in rats. Pregnant rat dams were given a single injection of poly I:C (4.0 mg/kg) or a saline injection equivalent on gestational day 15. Acoustic startle reactivity, habituation of the startle response and PPI were assessed in juvenile (34-35 day) and adult (>56 day) offspring. Prenatal immune activation did not alter startle reactivity on startle-only or prepulse-only trials. Furthermore, there was no effect of MIA on habituation of the startle response. MIA does however disrupt PPI, as PPI was reduced significantly in adult MIA offspring, and a trend was observed in the juvenile animals. Our finding that prenatal poly I:C can disrupt PPI in MIA rats further validates this procedure as an animal model.     

Prenatal inflammation impairs adult neurogenesis and memory related behavior through persistent hippocampal TGFβ1 downregulation

Prenatal exposure to inflammatory stimuli is known to influence adult brain function. In addition, adult hippocampal neurogenesis is impaired by a local pro-inflammatory microenvironment. On this basis, we hypothesized that a pro-inflammatory insult during gestation would have negative effects on adult neurogenesis in the offspring. Pregnant Wistar rats received subcutaneous injections of lipopolysaccharide (LPS; 0.5 mg/kg) or saline every other day from gestational day 14 to 20. The adult offspring prenatally treated with LPS showed a decrease in the proliferating cells and the newborn neurons of the dentate gyrus. Furthermore, prenatal LPS treatment impaired performance in the neurogenesis-dependent novel object recognition test. Maternal care was impaired by prenatal LPS administration but did not contribute to the effects of prenatal LPS on adult neurogenesis. Persistent microglial activation and downregulated expression of transforming growth factor beta-1 (TGFβ₁) occurred specifically in the adult hippocampus of animals treated prenatally with LPS. Importantly, chronic hippocampal TGFβ₁ overexpression restored neurogenesis as well as recognition memory performance to control levels.These findings demonstrate that prenatal inflammation triggered by LPS impairs adult neurogenesis and recognition memory. Furthermore, we provide a model of reduced adult neurogenesis with long-lasting defined alterations in the neurogenic niche. Finally, we show that the expression of a single cytokine (TGFβ₁) in the hippocampus can restore adult neurogenesis and its related behavior, highlighting the role of TGFβ₁ in these processes.     

Neonatal overfeeding alters hypothalamic microglial profiles and central responses to immune challenge long-term

The early life period is one of significant vulnerability to programming effects from the environment. Given the sensitivity of microglial cells to early life programming and to adult diet, we hypothesized overfeeding during the neonatal period would acutely alter microglial profiles within the developing brain, predisposing the individual to a lasting central pro-inflammatory profile that contributes to overactive immune responses long-term. We tested this idea by manipulating litter sizes in which Wistar rat pups were raised, so the pups were suckled in litters of 4 (neonatally overfed) or 12 (control). This manipulation induces obesity and susceptibility to lipopolysaccharide (LPS) long-term. We then examined microglial and central pro-inflammatory profiles during development and in adulthood as well as susceptibility to neuroimmune challenge with LPS. Neonatally overfed rats have evidence of microgliosis in the paraventricular nucleus of the hypothalamus (PVN) as early as postnatal day 14. They also show changes in hypothalamic gene expression at this time, with suppressed hypothalamic interleukin 1β mRNA. These effects persist into adulthood, with basal PVN microgliosis and increased hypothalamic toll-like receptor 4, nuclear factor κB, and interleukin 6 gene expression. These neonatally overfed rats also have dramatically exacerbated microglial activation in the PVN 24 h after an adult LPS challenge, coupled with changes in inflammatory gene expression. Thus, it appears neonatal overfeeding sensitizes PVN microglia, contributing to a basal pro-inflammatory profile and an altered response to a neuroimmune challenge throughout life. It remains to be seen if these effects can be reversed with early interventions.     

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.     

Dual role of intrauterine immune challenge on neonatal and adult brain vulnerability to hypoxia-ischemia

Epidemiologic evidence has underlined the impact of prenatal inflammation on the development of postnatal hypoxia-ischemia (HI) brain injury. To study to what extent prenatal inflammation affects CNS vulnerability later during development, C57BL/6 mice were subjected to intrauterine injection of lipopolysaccharide (LPS) at gestational day 15. At postnatal day (PND) 5, 9, and 70, the offspring were subjected to HI. It was found that, in neonatal mice, LPS-exposed brains showed markedly enhanced brain injury after HI, whereas in adult mice, LPS exposure resulted in a significant reduction in tissue loss after HI. Reduced myelin in subcortical white matter was noticed after HI in the LPS-exposed brains at PND14 and PND75. Increased activities of nuclear factor-kappaB and caspase-3 were obtained in fetal/neonatal brain after LPS administration. Conclusions were that 1) a prenatal low dose of LPS sensitized to HI-induced brain injury in neonates but confers protection in adulthood, 2) reduced myelination is seen after prenatal LPS exposure and HI in both neonatal and adult mice despite the fact that LPS reduced total tissue loss in adult mice; and 3) nuclear factor-kappaB and caspase-3 activation early after LPS exposure may play a role in the sensitization/protection (preconditioning) effects.