Fetal inflammation is associated with persistent systemic and hippocampal inflammation and dysregulation of hippocampal glutamatergic homeostasis

Abstract

BACKGROUND:Inflammation is a major cause of preterm birth and often results in a fetal inflammatory response syndrome (FIRS). Preterm infants with FIRS have a higher childhood incidence of neurodevelopmental disability than preterm infants without FIRS. The mechanisms connecting FIRS to neurodevelopmental disability in formerly preterm infants are not fully understood, but the effect on premature gray matter may have an important role.METHODS:Fetal rats were exposed to intra-amniotic (i.a.) LPS two days prior to birth to model FIRS. On postnatal day 7, expression of inflammatory mediators was measured in the liver, lung and brain. Activation of microglia and expression of glutamatergic receptor subunits and transporters were measured in the hippocampus and cortex.RESULTS:LPS caused persistent systemic inflammatory mediators gene expression. In the brain, there was corresponding activation of microglia in the hippocampus and cortex. Expression of inflammatory mediators persisted in the hippocampus, but not the cortex, and was associated with altered glutamatergic receptor subunits and transporters.CONCLUSION:Hippocampal inflammation and dysregulation of glutamate metabolism persisted well into the postnatal period following i.a. LPS. Poor neurodevelopmental outcomes after FIRS in preterm infants may result in part through glutamatergically-driven gray matter injury to the neonatal hippocampus.

Fetal inflammation induces acute immune tolerance in the neonatal rat hippocampus

“…On gestational day 20 (term = 22 days) dams underwent laparotomy to facilitate intra-amniotic (i.a.) injections to model FIRS as previously reported [ 26 ]. Dams were premedicated with long-acting buprenorphine (1.2 mg/kg) 4 h prior to surgery.…”

“…Incisions were treated along their lengths with bupivacaine (2 mg/kg s.c.). Delivery was performed operatively on gestational day 22 as reported [ 26 ]; dams were under general anesthesia with isoflurane. Following delivery, dams were killed using an overdose of sodium pentobarbital (100 mg/kg, i.p.).…”

“…For pups used for qPCR and protein analysis, the brain was removed and both hippocampi were quickly dissected on ice, flash-frozen in liquid nitrogen, and stored at – 80 °C until analysis. Pups used for immunohistochemistry underwent transcardial perfusion-fixation before removal of brain as previously described [ 26 ]. Microglia were isolated from whole brain tissue using the Gentle MACS Octo Dissociator with Heaters and Neural Tissue Dissociation Kit (Miltenyi Biotech, Auburn, CA).…”

“…qPCR experiments were performed as previously described ( n = 6–8) [ 26 ]. Total RNA was isolated from hippocampi or isolated microglia using an RNA extraction kit (Thermo Fischer Scientific, Waltham, MA and Qiagen Inc., Germantown, MD, respectively) and cDNA was obtained using 500 ng of RNA in a high capacity RNA to cDNA kit (Applied Biosystems, Foster City, CA).…”

“…To address this question, we previously studied the inflammatory response of the hippocampus to a prenatal inflammatory event in a rat model of FIRS and reported persistent postnatal altered expression of pro-inflammatory genes and microglial activation associated with gray matter dysregulation [ 26 ]. In the current study, we assessed how a postnatal inflammatory challenge in the setting of FIRS would affect the hippocampus with the hypothesis that a prenatal inflammatory event would modulate the response to the postnatal event.…”