Prenatal Hypoxia–Ischemia Induces Abnormalities in CA3 Microstructure, Potassium Chloride Co-Transporter 2 Expression and Inhibitory Tone

Abstract

Infants who suffer perinatal brain injury, including those with encephalopathy of prematurity, are prone to chronic neurological deficits, including epilepsy, cognitive impairment, and behavioral problems, such as anxiety, inattention, and poor social interaction. These deficits, especially in combination, pose the greatest hindrance to these children becoming independent adults. Cerebral function depends on adequate development of essential inhibitory neural circuits and the appropriate amount of excitation and inhibition at specific stages of maturation. Early neuronal synaptic responses to γ-amino butyric acid (GABA) are initially excitatory. During the early postnatal period, GABAAR responses switch to inhibitory with the upregulation of potassium-chloride co-transporter KCC2. With extrusion of chloride by KCC2, the Cl− reversal potential shifts and GABA and glycine responses become inhibitory. We hypothesized that prenatal hypoxic–ischemic brain injury chronically impairs the developmental upregulation of KCC2 that is essential for cerebral circuit formation. Following late gestation hypoxia–ischemia (HI), diffusion tensor imaging in juvenile rats shows poor microstructural integrity in the hippocampal CA3 subfield, with reduced fractional anisotropy and elevated radial diffusivity. The loss of microstructure correlates with early reduced KCC2 expression on NeuN-positive pyramidal neurons, and decreased monomeric and oligomeric KCC2 protein expression in the CA3 subfield. Together with decreased inhibitory post-synaptic currents during a critical window of development, we document for the first time that prenatal transient systemic HI in rats impairs hippocampal CA3 inhibitory tone. Failure of timely development of inhibitory tone likely contributes to a lower seizure threshold and impaired cognitive function in children who suffer perinatal brain injury.

Imaging and serum biomarkers reflecting the functional efficacy of extended erythropoietin treatment in rats following infantile traumatic brain injury

“…9,32,68,76,92,99 Loss of KCC2 expression occurs with epilepsy, 31 gliomas, 15,65 trauma, 11,12,67 and perinatal brain injury. 37,36,79 Developmentally regulated molecules essential for cerebral function are vulnerable to calpain including KCC2, 37,39,72,108 myelin basic protein, and phosphorylated neurofilament. 39 A better understanding of the pattern of excess CNS calpain activity following infant TBI will guide the dosing of therapeutic interventions.…”

“…34,35 A similar strategy was used to estimate the sample sizes needed to detect group differences in mRNA and protein levels from the brain for EPOR levels, 53 cytokines and calpain DPs, 37,107 serum cytokine changes following TBI, 98 and microstructural DTI alterations on ex vivo MRI. 36 A sample size of 6 per group would be expected to detect a 20% difference with a Type 1 error of 0.05 with a SD of 20% of the mean. Given the high resource intensity of these studies, this initial pilot study was not powered to detect sex differences in the degree of injury or EPO responsiveness.…”

Extended Combined Neonatal Treatment With Erythropoietin Plus Melatonin Prevents Posthemorrhagic Hydrocephalus of Prematurity in Rats

“…Brains were post-fixed in 4% PFA for 1 week and embedded in 2% agarose containing 3 mM sodium azide. A T2 multi-slice multi-echo (MSME) sequence was performed with a TR of 3000 ms and TE of 12 ms. FOV was 3 cm × 3 cm, with a slice thickness of 1 mm, 12 slices total, and matrix of 256 × 256, as previously published ( Jantzie et al, 2015a ; Robinson et al, 2016 ). Echo-planar diffusion tensor imaging (EP-DTI) images of twelve contiguous coronal 1 mm slices was obtained with a FOV of 3.…”

Acute oligodendrocyte loss with persistent white matter injury in a third trimester equivalent mouse model of fetal alcohol spectrum disorder

“…For scanning, brains were embedded in 2% agarose containing 3 mM sodium azide. Images were acquired, as previously described (Jantzie et al 2015a; Robinson et al 2016), on a Bruker 4.7T BioSpec 47/40 Ultra-Shielded Refrigerated nuclear MRI system equipped with a quadrature RF coil (72 mm I.D.) and a small-bore (12 cm I.D.)…”

“…For scanning, brains were embedded in 2% agarose containing 3 mM sodium azide. Images were acquired, as previously described(Jantzie et al, 2015a;Robinson et al, Third trimester-equivalent ethanol exposure in nestin-CreER T2 :tdTomato mice Nestin-CreER T2 :tdTomato bitransgenic mice were used across all treatment groups to distinguish mature OLs and OPCs originating from the postnatal SVZ from those originating earlier in embryonic development.…”