Hypothermic Neuroprotection Is Associated With Recovery of Spectral Edge Frequency After Asphyxia in Preterm Fetal Sheep

Abstract

At 103 to 104 days gestation, fetuses were randomly assigned to sham occlusion followed by normothermia (sham-normothermia, n=8), or whole-body cooling for 72 hours (sham-hypothermia, n=8), or umbilical cord occlusion for 25 minutes, followed by sham hypothermia (occlusion-normothermia, n=12), or whole-body cooling started from 30 minutes (occlusion-early hypothermia, n=10), or 5 hours (occlusion-delayed hypothermia, n=7) after occlusion and continued for 72 hours. Mild whole-body cooling was induced by circulating cold water through the cooling coil. Seven days after occlusion, the ewes and fetuses were killed.Mean arterial pressure, blood gases, EEG activity, and temperature were recorded throughout the experiment. EEG power and spectral Background and Purpose-Electroencephalographic recovery is predictive of outcome after perinatal hypoxia-ischemia, but it is unknown whether early changes in electroencephalographic can predict the response to therapeutic hypothermia in the preterm brain. Methods-0.7 gestation fetal sheep received umbilical cord occlusion or sham occlusion for 25 minutes, followed by sham hypothermia or whole-body cooling started either 30 minutes or 5 hours after occlusion and continued for 72 hours. Results-Early but not delayed hypothermia reduced neuronal loss and microglial induction in the striatum, with faster recovery of spectral edge frequency, reduced seizure burden, and less suppression of electroencephalographic amplitude (P<0.05). Conclusions-Recovery ImmunohistochemistryBrain sections were stained for NeuN (neuronal survival) and IB4 (activated microglia) in the caudate nucleus and putamen, and positive cells were counted stereologically. Statistical AnalysisData were evaluated by repeated measures ANCOVA (SPSS v22, SPSS Inc, IL) and Sidak post hoc analysis. The within subjects' correlation was assessed between EEG amplitude (μV) and extradural temperature. Statistical significance was accepted at P<0.05. Results Blood Composition, Arterial Pressure, and Extradural TemperatureUmbilical cord occlusion was associated with profound hypoxia, mixed metabolic and respiratory acidosis, and hypotension, with rapid recovery after release of occlusion. Hypothermia was associated with a small increase in pH and glucose and a lower PaCO 2 compared with occlusion-normothermia (Table I in the online-only Data Supplement) and no effect on mean arterial pressure (Table II in EEG Power and SEFOcclusion was associated with suppressed EEG power until 84 hours after asphyxia in the occlusion-normothermia group and 72 hours in both hypothermia groups (P<0.05; versus sham-normothermia; Figure 1). Compared with occlusionnormothermia, EEG power was reduced from 1 to 12 hours with early hypothermia, and 6 to 12 hours with delayed hypothermia (P<0.05). Delayed hypothermia was associated with suppressed EEG power compared with early hypothermia from 24 to 30 hours (P<0.05). SEF was significantly suppressed with occlusion-normothermia until 72 hours after occlusion compared with sham-normothermia (P<0.05;...

Impact of neonatal anoxia on adult rat hippocampal volume, neurogenesis and behavior

“…Takada model causes a noninvasive global asphyxia extra-uterus in a very immature brain (P1-P2 rats), which resembles the human condition experienced by premature neonates (Semple, Blomgren et al 2013;Takada, dos Santos Haemmerle et al 2015). In other species, perinatal hypoxia-ischemia has been used in sheeps (Williams, Gunn et al 1990;Bennet, Quaedackers et al 2000;Bennet, Roelfsema et al 2007;Wassink, Barrett et al 2015) and in rabbits (Derrick, Luo et al 2004;Tan, Drobyshevsky et al 2005), in which kits present cerebral palsy phenotype with limbs hypertonia.…”

Window of opportunity for human amnion epithelial stem cells to attenuate astrogliosis after umbilical cord occlusion in preterm fetal sheep

“…Although hypothermia is not used clinically for treatment of preterm infants, in preclinical studies using the same protocol as the present study, prolonged cerebral hypothermia started at 30 or 90 minutes after UCO was highly protective, 47,48 whereas white and gray matter protection was largely lost when initiation of hypothermia was delayed for 5 hours. 48 The finding that delaying hAEC administration until 24 hours after UCO, at a time when the secondary deterioration of mitochondrial function is well established in this model, 25 This finding is consistent with recent studies in fetal sheep of administration of mesenchymal stromal cell-derived extracellular vesicles 53 and MSCs after asphyxia. 54 The mechanisms of this EEG suppression by hAECs between seizures are unknown, but likely multifactorial and may include reduced inflammation, and an altered balance between inhibitory and excitatory neurotransmitters and neuromodulators, and suppression of metabolism.…”

EEG sharp waves are a biomarker of striatal neuronal survival after hypoxia-ischemia in preterm fetal sheep

“…Previous studies suggest that optimal recovery of cerebral metabolism after such severe HI is only present for the first few hours 6 , 7 . Pre-clinical studies in term-equivalent animals have shown that therapeutic hypothermia could prevent the majority of cell death when started within 3 hours after HI 45 , but hypothermic neuroprotection was largely lost if the start time of treatment was delayed until after ~6 hours 46 .…”

“…Therapeutic hypothermia after HI is neuroprotective in both preterm and term animals 7 , 8 , and is now standard care for term newborns after moderate to severe HI 9 . Hypothermia, and potentially other treatments that act through similar pathways, is only effective when started during the latent phase after HI; efficacy is rapidly lost with increasing delay after HI as previously reviewed 3 .…”