Neonatal neurobehavior and diffusion MRI changes in brain reorganization due to intrauterine growth restriction in a rabbit model

Abstract

Background: Intrauterine 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 findings: IUGR 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.

Conclusions: IUGR 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.

Figure 1. Schematic and graphical representation of study design and methods.

PANEL 1: (A) Illustrative image of unilateral ligation of 40–50% of uteroplacental vessels at 25 days of pregnancy, (B) Scheme of surgical procedures and study groups. PANEL 2: Illustrative pictures of neurobehavioral evaluation of locomotion (C), tone (D), smelling test (E), righting reflex (F) and sucking and swallowing (G) performed at +1 postnatal day. PANEL 3: MRI acquisition. Fixed brains (H) were scanned to obtain a high resolution T1 weighted (I) images and diffusion weighted images (J). PANEL 4a: MRI global analysis. After masking brain volume, global analysis was performed to obtain average DTI parameters (FA, ADC, radial diffusivity, axial diffusivity, linearity, planarity and sphericity). PANEL 4b: Voxel based analysis was performed by elastic registration to a reference FA map. Once subject brains were registered and smoothed, diffusion-related parameters values distribution for each voxel was analyzed to identify areas with statistically significant different distribution in IUGR and the correlation of changes with neurobehavioral tests.

Figure 2. Manual delineation of regions of interest (ROIs).

Coronal slices with manual delineation of ROIs. GM structures were delineated in T1 weighted images including prefrontal cortex (PrC), caudate nucleus (Ca), putamen (Pu), thalamus (Th), cerebellar hemisphere (CHe), and vermis (V). WM structures were delineated directly in FA map including corpus callosum (CC), corona radiata (CR); internal capsule (IC), and fimbria hippocampus (Fi).

Figure 3. Fractional anisotropy values: regions showing statistically significant differences between cases and controls.

Slices of the smoothed reference FA image. Red areas have a significance of p<0.01, green areas have a significance of p<0.05. The slices displayed contain representative anatomical structures. Slice locations are shown in the T1 weighted images in the right. (A) Coronal slices from anterior to posterior. (B) Axial slices from superior to inferior.

Figure 4. Linearity, planarity and sphericity coefficients: regions showing statistically significant differences between cases and controls.

Coronal slices of the smoothed reference FA image. Red areas have a significance of p<0.01, green areas have a significance of p<0.05. Slice locations are shown in the T1 weighted images in the right. The slices displayed representative anatomical regions showing increased sphericity coefficient (A) and decreased linearity (B) and planarity (C) coefficient.

Figure 5. Correlation maps between neurobehavioral test items and fractional anisotropy values.

Coronal slices (from anterior to posterior) of the smoothed reference FA image. Colormap highlights the areas where the correlation coefficient is higher than 0.2. (A) Posture, (B) Righting reflex, (C) Tone, (D) Locomotion, (E) Circular motion, (F) Intensity, (G) Duration, (H) Lineal movement, (I) Fore-hindpaw distance, (J) Sucking and swallowing, (K) Head turn, (L) Smelling test, (M) Smelling test time.