Neonatal Neurobehavior and Diffusion MRI Changes in Brain Reorganization Due to Intrauterine Growth Restriction in a Rabbit Model

Abstract

BackgroundIntrauterine growth restriction (IUGR) affects 5–10% of all newborns and is associated with a high risk of abnormal neurodevelopment. The timing and patterns of brain reorganization underlying IUGR are poorly documented. We developed a rabbit model of IUGR allowing neonatal neurobehavioral assessment and high resolution brain diffusion magnetic resonance imaging (MRI). The aim of the study was to describe the pattern and functional correlates of fetal brain reorganization induced by IUGR.Methodology/Principal FindingsIUGR was induced in 10 New Zealand fetal rabbits by ligation of 40–50% of uteroplacental vessels in one horn at 25 days of gestation. Ten contralateral horn fetuses were used as controls. Cesarean section was performed at 30 days (term 31 days). At postnatal day +1, neonates were assessed by validated neurobehavioral tests including evaluation of tone, spontaneous locomotion, reflex motor activity, motor responses to olfactory stimuli, and coordination of suck and swallow. Subsequently, brains were collected and fixed and MRI was performed using a high resolution acquisition scheme. Global and regional (manual delineation and voxel based analysis) diffusion tensor imaging parameters were analyzed. IUGR was associated with significantly poorer neurobehavioral performance in most domains. Voxel based analysis revealed fractional anisotropy (FA) differences in multiple brain regions of gray and white matter, including frontal, insular, occipital and temporal cortex, hippocampus, putamen, thalamus, claustrum, medial septal nucleus, anterior commissure, internal capsule, fimbria of hippocampus, medial lemniscus and olfactory tract. Regional FA changes were correlated with poorer outcome in neurobehavioral tests.ConclusionsIUGR is associated with a complex pattern of brain reorganization already at birth, which may open opportunities for early intervention. Diffusion MRI can offer suitable imaging biomarkers to characterize and monitor brain reorganization due to fetal diseases.

Programming the brain: Common outcomes and gaps in knowledge from animal studies of IUGR

“…Volume ↓ cerebrum, E60 [162] ↓cerebellum E60 [142,162] Myelination ↓cerebrum, cerebellum, CA1 hippocampus, dorsal fornix, dorsal fimbria, corpus callosum, periventricular white matter, parasagittal white matter [119,121,143,206] =/↓ spine, age dependent [119] = subcortical white matter, d65 [143] Delayed maturation of myelin [162] ↓cerebral cortex, striatum [108] Thinner sheaths, signs of degeneration [108] Damage + lesions in cerebrum [108] + lesions, gliosis, axonal degeneration [109] Oligodendrocytes ↑ numbers in cerebellum [162] ASTROGLIOSIS Cerebrum = E52 [119] ↑E60, E62 [119,162] = E65 [143] ↑cortex [108,109] Striatum ↑ [108] Cerebellum = [119] ↑ E60 [162] Hippocampus = E65 [143] [79] ↓11% [90] ↓17.3% [128,129] ↓10-18% [116,212] = [125] Forebrain ↓10-15% [79,85] ↓ [129] ↓13-16% [145,162] ↓19% [212] = [125] Cortex ↓31% [128] ↓20% [217] Striatum ↓12% [212] Hippocampus = …”

“…Brain ↓ [116] Cerebrum = [162] = [125] Corpus callosum ↓d7 [112,218] ↓d14 [222] Preoligodendrocytes ↓cingulum and CC d7 [112,218] Oligodendrocytes ↓ CC d14 [218,222] ↑↓ cingulum, p7, dependent on severity [218] ↑↓ CA1, sex specific [220] = immature oligodendrocytes, CA3, DG, d0 [220] ASTROGLIOSIS Cerebrum + parietal, frontal and temporal lobes [125] Hypothalamus ↓ [90] Hippocampus ↑CA3, males, d0 [220] Dentate gyrus ↑males, d0 [220] Corpus callosum ↑d21 [222] Cingulum ↑d7, d13, d14, d21, adults [112,114,218] Internal capsule ↑d7, d14 [112] External capsule = [112] Table 5 -Adolescent and adult neurodevelopmental outcomes in animal models of IUGR. Gestational age is shown in days of gestation, eg d20 for day 20 of gestation.…”

“…Axonal density ↓ left hemispheric anxiety and memory pathways [117] Axonal degeneration + cingulate and somatosensory cortices, internal capsule, pontocerebellar tract [115] Microstructural reorganisation + [163] MYELINATION Cerebrum = [162] ↓ [117] Corpus callosum = [222] ↓ d60 [40] Cingulum ↓ d60 [112] Internal and external capsule = d60 [112] Astrogliosis Hippocampus ↑CA1 [113,115] Dentate gyrus ↑ [113,115] Entorhinal cortex ↑ [113,115] Cingulum ↑ [113,115] = [94] Fornix ↑ [113] Motor cortex = [115] Somatosensory cortex ↑ [115] Neonatal neurobehaviour = reflexes [79] ↓ righting reflex, d3-4 males, d3 females [87] ↓cliff avoidance, d7 females, d8, both sexes [87] ↓negative geotaxis, d7-8 males [87] = reflexes d10-21 [165] ↓surface righting, d2-9 ↓ negative geotaxis d 4-15 [129] ↓righting reflexes, locomotion, head turning and smell test scores as d1 neonates [116] Neuromotor ↓ grip strength adult males [165] ↓ motor learning, males [129] ↓motor learning, adults [222] Spatial learning = adult males [95] = adults [97,165] = adult males [167] ↓initial simple maze tests (lambs) [122] = extended simple maze testing, obstacle course tasks, tmaze tasks (lambs) [122] ↓initial simple maze tests (male lambs and young adults) [150] Revers...…”

A New Rabbit Model of Pediatric Traumatic Brain Injury

“…20 We also fed the kits rabbit milk with a syringe attached to an artificial nipple and assessed suck and swallow and head turn during feeding on a scale of 0-3 (worst-best). 20,21 Olfaction was tested by the intensity of aversive response to a cotton swab soaked with 100% ethanol. 21,22 We assessed the righting reflex by placing the kits on their backs and recording the number of times they turned from the supine to the prone position in 10 tries.…”

“…20,21 Olfaction was tested by the intensity of aversive response to a cotton swab soaked with 100% ethanol. 21,22 We assessed the righting reflex by placing the kits on their backs and recording the number of times they turned from the supine to the prone position in 10 tries. The hops and steps were scaled at 0-4 (0, no step or hop; 4, ‡ 10 steps or 4 hops).…”