Perinatal infections and brain injury: current treatment options

Systemic endotoxin induces gene expression of inducible nitric oxide synthase in fetal rat brain

BACKGROUND

Few studies have examined the response of the fetus under stress, such as with maternal infection. Recent work has indicated that nitric oxide (NO) modulates corticotropin-releasing hormone (CRH) secretion by the hypothalamus, but details of the action of NO on the fetus remain unclear. Therefore, we investigated the expression of inducible nitric oxide synthase (iNOS) mRNA and the response pattern following lipopolysaccharide (LPS) loading using a rat model of fetal infection.

METHODS

Fetuses were delivered by cesarean section on day 20 of gestation and immediately placed in a chamber maintained at 37 degrees C and 100% relative humidity. The LPS group (n=12) was given 400 microg of LPS/100 g body weight, and the physiologic saline group (n=12) was given physiologic saline. Fetuses were then incubated for a further 3 hours. Fetuses were decapitated, the trunk blood was collected immediately after cesarean section or after 3 hours of incubation, and the fetal brains were fixed in formaldehyde and cryopreserved. Coronal cryosections of the brains were prepared, and a (35)S-uridine triphosphate-labeled antisense RNA probe for iNOS was then prepared. In situ hybridization was performed, and iNOS expression was evaluated semiquantitatively on the basis of optical density. In both groups, plasma corticosterone levels were determined with radioimmunoassay.

RESULTS

Expression of iNOS mRNA was not noted in the physiologic saline group (3 hours postpartum). In the LPS group, iNOS mRNA expression was observed in the subfornical organ, but not in the paraventricular nucleus. Plasma corticosterone levels were significantly elevated in the LPS group.

CONCLUSIONS

In 20-day-old rat fetuses, the hypothalamic-pituitary-adrenal axis was already mobilized in response to LPS-induced stress. These results suggest that iNOS is not involved in the acute response of the hypothalamic-pituitary-adrenal axis to LPS challenge in 20-day-old rat fetuses.

Disorders of the fetomaternal unit: hematologic manifestations in the fetus and neonate

Histoarchitectural characteristics of the human placenta place the fetus at a high risk of growth restriction, abnormal fetomaternal cell traffic, and vertical transmission of pathogens. These abnormalities of the fetomaternal unit are frequently associated with hematological abnormalities in the fetus/neonate and may be the first, most common, or the only clinical manifestations of these conditions. This article reviews the pathophysiology and characteristic hematological manifestations of these conditions in the fetus and the neonate.

Estradiol modulation of kainic acid-induced calcium elevation in neonatal hippocampal neurons

The developing hippocampus of both males and females is exposed to high levels of the gonadal steroid estradiol. The impact of this estradiol exposure on developing hippocampal neurons is essentially unknown. In the rat, the newborn hippocampus is relatively insensitive to excitotoxic brain injury, which in adults is associated with the release of amino acids, in particular glutamate, resulting in a significant increase in intracellular calcium and eventual cell death. We have shown previously in the rat that administration of the glutamate agonist, kainic acid (KA), on the day of birth results in limited hippocampal damage, which is ameliorated by treatment with the gonadal steroid, estradiol. We now show that KA induces an increase in intracellular calcium through L-type voltage-sensitive calcium channels early in development and, later in development, through polyamine-sensitive alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors with a modest increase through N-methyl-D-aspartate receptors. Pretreatment with the gonadal steroid, estradiol, decreases the percentage of neurons responding to KA and decreases the peak amplitude of the calcium transient early in development but has no effect later in development. Taken together, these data suggest that there is a developmental shift in the route of KA-induced intracellular calcium and estradiol modulates KA-induced intracellular calcium to a time restricted to early development, but whether this is the basis of the neuroprotective effect of estradiol remains to be determined.

Antenatal risk factors for cerebral palsy

Two of every 1000 live-born children develop cerebral palsy (CP). The aetiology of CP is often unclear and because CP is a symptom complex rather than a disease, clinically defined at 4-5 years of age, it is not surprising that there are considerable problems associated with epidemiological studies of its aetiology. The only reason for the CP concept is that it emanates from an insult to a growing, developing brain and a dynamic clinical picture from static pathology. Evidence suggests that 70-80% of CP cases are due to prenatal factors and that birth asphyxia plays a relatively minor role (<10%). Some antenatal risk factors are repeatedly observed to be related to CP: low gestational age, male gender, multiple gestation, intrauterine viral infections and maternal thyroid abnormalities. Recently, intrauterine infection/inflammation with a maternal response (consisting of chorioamnionitis) and a fetal inflammatory response (consisting of funicitis or elevated interleukin-6 in fetal plasma) has been found to be related to white matter injury and CP. Some risk factors are associated with CP at all gestational ages whereas others mostly affect term or preterm infants, e.g. intrauterine growth restriction seems to be a risk factor in term infants. There also seems to be an association between autoimmune and coagulation disorders and CP.

Maternal LPS induces cytokines in the amniotic fluid and corticotropin releasing hormone in the fetal rat brain

Perinatal infections are a risk factor for fetal neurological pathologies, including cerebral palsy and schizophrenia. Cytokines that are produced as part of the inflammatory response are proposed to partially mediate the neurological injury. This study investigated the effects of intraperitoneal injections of lipopolysaccharide (LPS) to pregnant rats on the production of cytokines and stress markers in the fetal environment. Gestation day 18 pregnant rats were treated with LPS (100 μg/kg body wt ip), and maternal serum, amniotic fluid, placenta, chorioamnion, and fetal brain were harvested at 1, 6, 12, and 24 h posttreatment to assay for LPS-induced changes in cytokine protein (ELISA) and mRNA (real-time RT-PCR) levels. We observed induction of proinflammatory cytokines interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α) as well as the anti-inflammatory cytokine IL-10 in the maternal serum within 6 h of LPS exposure. Similarly, proinflammatory cytokines were induced in the amniotic fluid in response to LPS; however, no significant induction of IL-10 was observed in the amniotic fluid. LPS-induced mRNA changes included upregulation of the stress-related peptide corticotropin-releasing factor in the fetal whole brain, TNF-α, IL-6, and IL-10 in the chorioamnion, and TNF-α, IL-1β, and IL-6 in the placenta. These findings suggest that maternal infections may lead to an unbalanced inflammatory reaction in the fetal environment that activates the fetal stress axis.