Mild Hypoxic-ischemic Injury Research Articles

Blockade of connexin hemichannels with tonabersat protects against mild hypoxic ischemic brain injury in neonatal rats

Background and purposeThere is growing evidence that infants with mild hypoxic-ischemic (HI) encephalopathy have increased risk of brain injury and adverse neurodevelopmental outcomes. Currently, there is no approved treatment for these infants. It was previously shown that blocking connexin 43 hemichannels is neuroprotective in models of moderate to severe HI injury. However, it is yet to be established whether these channels play a role in the evolution of mild HI brain injury, and whether blocking these channels after mild HI is neuroprotective. MethodsHI was induced in postnatal day 10 rats of both sexes by right carotid artery ligation followed by 80 min of hypoxia in 8% oxygen. Pups receiving HI were randomised to receive intraperitoneal injections of either saline, vehicle (2-hydroxypropyl-beta-cyclodextrin polyethylene glycol-400), or tonabersat (2 mg/kg), at 60 min, 24 h, and 48 h after hypoxia. Seven days after HI, brains were harvested for measurement of volume loss and histological analysis. ResultsHI resulted in a significant reduction in hemispheric, hippocampal, and white matter volumes, which were significantly attenuated after treatment with tonabersat. HI was also associated with a significant reduction in numbers of neurons in the CA1 and CA3 hippocampal regions, a reduction in the numbers of oligodendrocytes in the corpus callosum, and an increase in the number of astrocytes in both regions, which were significantly attenuated by tonabersat treatment. There were no differences in rectal temperatures between tonabersat- and vehicle-treated rat pups. ConclusionsBlockade of connexin hemichannels with tonabersat significantly reduced mild HI injury in the hippocampus and white matter, without causing hypothermia.

Mild Hypoxic-Ischemic Injury in the Neonatal Rat Brain: Longitudinal Evaluation of White Matter Using Diffusion Tensor MR Imaging

Selective white matter (WM) damage is a known sequela of mild hypoxic-ischemic (HI) injury in the neonatal rat model. The aim of this study was to evaluate longitudinally mild HI-induced WM damage (represented by the external capsule [EC]) by diffusion tensor MR imaging (DTI) and to correlate the findings with histology. Seven-day-old Sprague-Dawley rats (n = 19) underwent unilateral ligation of the left common carotid artery followed by hypoxia for 50 minutes to create mild HI injury. DTI was performed longitudinally at 5 time points from day 1 to day 90 postinjury (n = 19, 16, 13, 11, 9, respectively), and fractional anisotropy (FA), trace, radial diffusivity (lambda( perpendicular)), and axial diffusivity (lambda(//)) of the injury and control contralateral ECs were quantified. Rats were randomly sacrificed (n = 15, in total), and the corresponding ECs were stained with hematoxylin-eosin, Luxol fast blue (LFB), and neurofilament (NF) to evaluate morphologic changes, amount of myelin, and axonal count at every time point. A paired t test was applied to evaluate statistical differences between both ECs, and the Pearson correlation test was used to evaluate the relationships between DTI indices and histologic evaluations. In addition, longitudinal changes in DTI indices and histologic evaluations were analyzed by a linear mixed model and an analysis of variance test, respectively. We demonstrated significantly decreased FA, increased lambda( perpendicular), and similar lambda(//) in the injury compared with the control EC, which was persistent through all time points. Histologic evaluation by LFB and NF staining showed reduced myelin stain intensity in the injury EC and similar axonal counts in both ECs. Longitudinally, there was an increase in FA, a decrease in lambda( perpendicular) and trace, and stability in lambda(//) in both ECs. Also, there was progressive reduction in the differences in FA, trace, and lambda( perpendicular) between the injury and control EC, especially between day 1 and day 7 postinjury and in tandem with changes in myelin stain. FA was significantly correlated with myelin stain (r = 0.681, P < .01) and axonal count (r = 0.673, P < .01), whereas lambda( perpendicular) was significantly correlated with myelin stain only (r = -0.528, P < .01), and lambda(//), with axonal count only (r = 0.372, P = .043). Diffusion indices can reflect dysmyelination in mild HI injury, continual myelination of both injury and control ECs with growth, and the partial recovery of myelin postinjury. We propose that diffusion indices may be used as biomarkers to monitor noninvasively the longitudinal changes of mild HI-induced WM damage.

Glial responses to neonatal hypoxic–ischemic injury in the rat cerebral cortex

Neurogenesis is nearly completed after birth, whereas gliogenic activities remain intense during the postnatal period in the developing rat cortex. These include involution of radial glia, proliferation of astrocytes and oligodendrocytes and myelin formation. Little is known about the effects of hypoxic–ischemic (HI) injury on these critical postnatal processes. Here we explored the glial reactions to mild HI injury of the neonatal rat cerebral cortex at P3. We show that the HI lesion results in disruption of the normal radial glia architecture, which was paralleled by an increase in GFAP immunopositive reactive astrocytes. The morphology of these latter cells and the fact that they were immunolabelled for both nestin and GFAP suggest an accelerated transformation of radial glia into astrocytes. In addition, BrdU/GFAP immunostaining revealed a significant increase of double-labelled cells indicating an acute proliferation of astrocytes after HI. This enhanced proliferative activity of astrocytes persisted for several weeks. We found an elevated number and increased mitotic activity of both NG2-positive oligodendrocyte progenitors and RIP-positive oligodendrocytes after injury. These findings imply that glial responses are central to cortical tissue remodelling following neonatal ischemia and represent a potential target for therapeutic approaches.