Assessment of infant physiology and neuronal development using magnetic resonance imaging

Intrauterine growth restriction due to uteroplacental insufficiency decreased white matter and altered NMDAR subunit composition in juvenile rat hippocampi

Uteroplacental insufficiency (UPI), the major cause of intrauterine growth restriction (IUGR) in developed nations, predisposes to learning impairment. The underlying mechanism is unknown. Neuronal N-methyl-d-aspartate receptors (NMDARs) are critical for synaptogenesis and learning throughout life. We hypothesized that UPI-induced IUGR alters rat hippocampal NMDAR NR2A/NR2B subunit ratio and/or NR1 mRNA isoform expression and synaptic density at day 21 (P21). To test this hypothesis, IUGR was induced by bilateral uterine artery ligation of the late-gestation Sprague-Dawley dam. At P21, hippocampal NMDAR subunit mRNA and protein were measured, as were levels of synaptophysin. Neuronal, synaptic, and glial density in CA1, CA3, and dentate gyrus (DG) was assessed by immunofluorescence. IUGR increased NR1 mRNA isoform NR1-3a and 1-3b expression in both sexes. In P21 males, IUGR increased protein levels of NR1 C2′ and decreased NR1 C2, NR2A, and the NR2A-to-NR2B ratio, whereas in females, IUGR increased NR2B protein. In males, IUGR was associated with decreased myelin basic protein-to-neuronal nuclei ratio in CA1, CA3, and DG. We conclude that IUGR has sex-specific effects and that neither neuronal loss nor decreased synaptic density appears to account for the changes in NMDAR subunits. Rather, it is possible that synaptic NMDAR subunit composition is altered. Our results suggest that apparent recovery in the IUGR hippocampus may be associated with synaptic hyperexcitability. We speculate that the NMDAR plays an important role in IUGR-associated cognitive impairment.

fMRI mapping of cortical centers following visual stimulation in postnatal pigs of different ages

Classical studies have demonstrated that the visual centers in primates consist of cortical areas V1, V2 and V4 and their branches. However, nothing is known about how these visual areas change in postnatal development. In the present studies, therefore, pigs aged 2, 4, and 6 months old, were stimulated visually with a colored checker board and the active sites in the cortex, cerebellum and brainstem recorded using functional magnetic resonance imaging (fMRI). In pigs aged 2 months old, visual stimulation induced an increase in activation of sites in the V2 and V4 cortical areas, as well as in the areas of the inferior aspect of the parietal and middle aspect of the temporal cortices, but not in the medial and caudal occipital cortex (V1 area). At 4 months old, the V1 area was also activated, and by 6 months old, an inferior sector in the prefrontal cortex was also activated. As the pigs aged, functional active sites were further demonstrated in the cerebellum and the brainstem, which probably had to do with action memory, and the control of the ocular muscles, respectively. It is concluded that the visual pathway of the pig mainly involves cortical areas that mature at 6 months of age.

Myelination of the Pig’s Brain: A Correlated MRI and Histological Study

Minipigs, 2, 4, 6 months old, were used to evaluate the relationship between myelination in the fiber tracts of the central nervous system (CNS) of this animal during development. Histological results showed an increased density of the myelinated fibers as well as branching of these fibers in the areas studied, including the cortical white matter, olfactory tract, the corticospinal tract, the fasciculus cuneatus and the spinal V nucleus from 2 to 6 months old. By 6 months, the pig was sexually matured. Concomitantly, there was an increase in high signal-intensity regions (sites) in the magnetic resonance T(1)-weighted images as myelination progressed. There is a good correlation between the histologically observed progress of myelination and the T(1)-weighted images in the development of the CNS of the pig.

Abnormal retinal optic nerve morphology in young adults after intrauterine growth restriction

Intrauterine growth restriction (IUGR) is a recognized risk factor for neurologic deficits later in life. Abnormal fetal blood flow in the presence of fetal growth retardation helps to distinguish true fetal growth impairment from small but normally grown infants. The present study aimed to investigate the influence of IUGR with abnormal fetal blood flow on retinal optic nerve morphology at 18 y of age. A prospective study was performed in 19 subjects with IUGR [abnormal fetal aortic blood flow velocity; median birth weight deviation of -31% (-22 to -42%; median (range)] and in 23 subjects with a normal birth weight for gestational age [normal fetal aortic blood flow velocity; median birth weight deviation of -2% (-10 to 22%)]. All subjects were previously examined concerning minor neurologic dysfunction (MND) at 7 y of age. The ocular fundus was examined by ophthalmoscopy, and the optic nerve morphology was evaluated by digital image analysis. Decrease in neuroretinal rim area at 18 y of age was associated with increasing negative birth weight deviation (r = 0.71, p < 0.0001). The subjects with severe MND at 7 y had a reduced neuroretinal rim area [median (range), 1.57 mm(2) (1.37-1.78 mm(2))] compared with those with less severe MND [1.94 mm(2) (1.33-2.71 mm(2))] and with those with normal neurologic function [2.18 mm(2) (1.75-2.70 mm(2)); p < 0.05 and p < 0.0001, respectively]. A decrease in neuroretinal rim area reflects either a reduction in axonal volume or a decrease in the number of axons in the optic nerve. It is yet unclear whether this finding represents neuronal changes within other cerebral regions in subjects with IUGR.