Experimental Modelling of the Consequences of Brief Late Gestation Asphyxia on Newborn Lamb Behaviour and Brain Structure

Abstract

Brief but severe asphyxia in late gestation or at the time of birth may lead to neonatal hypoxic ischemic encephalopathy and is associated with long-term neurodevelopmental impairment. We undertook this study to examine the consequences of transient in utero asphyxia in late gestation fetal sheep, on the newborn lamb after birth. Surgery was undertaken at 125 days gestation for implantation of fetal catheters and placement of a silastic cuff around the umbilical cord. At 132 days gestation (0.89 term), the cuff was inflated to induce umbilical cord occlusion (UCO), or sham (control). Fetal arterial blood samples were collected for assessment of fetal wellbeing and the pregnancy continued until birth. At birth, behavioral milestones for newborn lambs were recorded over 24 h, after which the lambs were euthanased for brain collection and histopathology assessments. After birth, UCO lambs displayed significant latencies to (i) use all four legs, (ii) attain a standing position, (iii) find the udder, and (iv) successfully suckle - compared to control lambs. Brains of UCO lambs showed widespread pathologies including cell death, white matter disruption, intra-parenchymal hemorrhage and inflammation, which were not observed in full term control brains. UCO resulted in some preterm births, but comparison with age-matched preterm non-UCO control lambs showed that prematurity per se was not responsible for the behavioral delays and brain structural abnormalities resulting from the in utero asphyxia. These results demonstrate that a single, brief fetal asphyxic episode in late gestation results in significant grey and white matter disruption in the developing brain, and causes significant behavioral delay in newborn lambs. These data are consistent with clinical observations that antenatal asphyxia is causal in the development of neonatal encephalopathy and provide an experimental model to advance our understanding of neuroprotective therapies.

Systemic and transdermal melatonin administration prevents neuropathology in response to perinatal asphyxia in newborn lambs

“…The term newborn brain is highly susceptible to hypoxic‐ischaemic injury due to immature innate defence systems, contributed by immature excitatory receptors, limited anti‐inflammatory and antioxidant capacity and a high metabolic demand for continuing brain development . In the current study, we demonstrate that MLT inhibited oxidative stress within the term brain in response to acute severe asphyxia.…”

“…Upregulation of ROS occurs within 30 minutes of asphyxia and may continue for days after reperfusion . The fetal and neonatal brain are particularly susceptible to oxidative stress due to poorly developed innate defence systems . ROS, and particularly hydroxyl radicals, compromise neuronal and glial cell structure and function by initiating lipid membrane peroxidation .…”

Ketamine decreases inflammatory and immune pathways after transient hypoxia in late gestation fetal cerebral cortex

“…Inflammatory mediators promote the recruitment, activation, and infiltration of immune cells in the brain, and contribute to the severity of the hypoxic injury (Castillo‐Melendez et al. ; Jellema et al. ).…”

Effects of Antenatal Melatonin Treatment on the Cerebral Vasculature in an Ovine Model of Fetal Growth Restriction

“…We assessed the integrity of the BBB, by examining the presence of the extravasation of albumin protein into the surrounding brain parenchyma blood vessels. We have routinely used and extensively published this method of detection of increased BBB permeability [23][24][25][26] . All qualitative analysis was carried out in all white matter regions of interest in 3 fields of view in 2 sections per animal.…”