Microglial Activation in Perinatal Rabbit Brain Induced by Intrauterine Inflammation: Detection with 11C-(R)-PK11195 and Small-Animal PET

Abstract

Intrauterine infection can lead to a fetal inflammatory response syndrome that has been implicated as one of the causes of perinatal brain injury leading to periventricular leukomalacia (PVL) and cerebral palsy. The presence of activated microglial cells has been noted in autopsy specimens of patients with PVL and in models of neonatal hypoxia and ischemia. Activated microglial cells can cause oligodendrocyte damage and white matter injury by release of inflammatory cytokines and production of excitotoxic metabolites. We hypothesized that exposure to endotoxin in utero leads to microglial activation in the fetal brain that can be monitored in vivo by 11 positron-emitting ligand that binds peripheral benzodiazepine receptor sites in activated microglia-using small-animal PET. Methods: Pregnant New Zealand White rabbits underwent laparotomy and were injected with 20 and 30 mg/kg of Escherichia coli lipopolysaccharide along the length of the uterus on day 28 of gestation. The pups were born spontaneously at term (31 d) and were scanned using small-animal PET after intravenous administration of 11 C-(R)-PK11195 and by MRI on postnatal day 1. The standard uptake values (SUVs) of the tracer were calculated for the whole brain at 10-min intervals for 60 min after tracer injection. The pups were euthanized after the scan, and brains were fixed, sectioned, and stained for microglial cells using biotinylated tomato lectin. Results: There was increased brain retention of 11 C-(R)-PK11195-as determined by a significant difference in the slope of the SUV over time-in the endotoxintreated pups when compared with that of age-matched controls. Immunohistochemical staining showed dose-dependent changes in activated microglia (increased number and morphologic changes) in the periventricular region and hippocampus of the brain of newborn rabbit pups exposed to endotoxin in utero. Conclusion: Intrauterine inflammation leads to activation of microglial cells that may be responsible for the development of brain injury and white matter damage in the perinatal period.PET with the tracer 11 C-(R)-PK11195 can be used as a noninvasive, sensitive tool for determining the presence and progress of neuroinflammation due to perinatal insults in newborns.

Models of Fetal Brain Injury, Intrauterine Inflammation, and Preterm Birth

“…Impaired development of the sensory cortex and decreased serotonin are seen in patients with ASD. 44,[55][56][57] These studies indicate that ongoing activation of microglial cells may be responsible for the development of white matter and neuronal injury in infants exposed to intrauterine infections/inflammation (Fig. 2).…”

“…In our animal model of maternal inflammation-mediated injury in the rabbit kits, we have observed microglial infiltration into the white matter region of the brain followed by decreased myelination and motor deficits on postnatal day 1. 43,44 Chorioamnionitis at term has a higher incidence of CP compared with preterm infants. 32 A mouse model of intrauterine inflammation was created by intrauterine injection of lipopolysaccharide (LPS; an endotoxin and a component of a cell wall of gram-negative bacteria) on gestational day 18.5 (corresponding to the end of murine gestation).…”

Decreased Cortical Serotonin in Neonatal Rabbits Exposed to Endotoxin in Utero

“…The pregnant rabbits were divided into three groups: (1) control-saline (n = 4), (2) endotoxin (n = 5), and (3) control-no intervention (n = 4). Pregnant rabbits in the control saline and endotoxin groups underwent laparotomy at gestational day 28 (term pregnancy 31 to 32 days) and were injected with 1 mL of saline or 1 mL saline containing 20 mg/kg of Escherichia coli endotoxin (E. coli serotype O127:B8; Sigma Aldrich, St Louis, MO, USA) along the length of the uterus as previously described (Kannan et al, 2007). The control-no intervention group included pregnant rabbits that had no surgery or intervention and was added to determine the effect of the stress of surgery or exposure to anesthetic agents in utero.…”

Magnitude of [¹¹C]PK11195 Binding Is Related to Severity of Motor Deficits in a Rabbit Model of Cerebral Palsy Induced by Intrauterine Endotoxin Exposure

“…New Zealand white rabbits with timed pregnancies (CoVance Research Products Inc., Kalamazoo, Mich., USA) underwent laparotomy on gestation day 28 (term pregnancy: 31–32 days) and were injected with 1 ml of saline solution (control saline group: n = 5) or 1 ml of saline containing 20 µg/kg of lipopolysaccharide (endotoxin group: n = 6; Escherichia coli serotype O127:B8; Sigma Aldrich, St. Louis, Mo., USA) along the length of the uterus between the fetuses, as previously described [8,36]. A third group comprised animals that had no surgical intervention (control-no intervention: n = 3).…”