Neuroimaging with diffusion-weighted imaging is routinely used for clinical diagnosis/prognosis. Its quantitative parameter, the apparent diffusion coefficient (ADC), is thought to reflect water mobility in brain tissues. After injury, reduced ADC values are thought to be secondary to decreases in the extracellular space caused by cell swelling. However, the physiological mechanisms associated with such changes remain uncertain. Aquaporins (AQPs) facilitate water diffusion through the plasma membrane and provide a unique opportunity to examine the molecular mechanisms underlying water mobility. Because of this critical role and the recognition that brain AQP4 is distributed within astrocytic cell membranes, we hypothesized that AQP4 contributes to the regulation of water diffusion and variations in its expression would alter ADC values in normal brain. Using RNA interference in the rodent brain, we acutely knocked down AQP4 expression and observed that a 27% AQP4-specific silencing induced a 50% decrease in ADC values, without modification of tissue histology. Our results demonstrate that ADC values in normal brain are modulated by astrocytic AQP4. These findings have major clinical relevance as they suggest that imaging changes seen in acute neurologic disorders such as stroke and trauma are in part due to changes in tissue AQP4 levels.

Purpose: To develop and compare an automated detection system for ischemic lesions in a neonatal model of bilateral carotid artery occlusion with hypoxia (BCAO-H) from T2 weighted MRI (T2WI) to the currently used ''gold standard'' of manual segmentation.Materials and Methods: Forty-three P10 BCAO-H rat pups and 8 controls underwent T2WI at 1 day and 28 days. A computational imaging method, Hierarchical Region Splitting (HRS), was developed to automatically and rapidly detect and quantify 3D lesion and normal appearing brain matter (NABM) volumes.Results: HRS quantified lesion and NABM volumes within 15 s in comparison to 3 h for its manual counterpart, with a high correlation for injury (r 2 ¼ 0. 95; P ¼ 8.6 Â 10 À7 ) and NABM (r 2 ¼ 0. 92; P ¼ 1.4 Â 10 À22 ). Average lesion volumes for mild, moderate, and severe injuries were 3.85%, 28.85%, and 52.98% for HRS and 0.51%, 24.22%, and 48.74% for manual detection. Lesion volumes and locations were similar for both methods (sensitivity: 0.82, specificity: 0.86, and similarity: 1.47). Conclusion:HRS is an accurate, objective, and rapid method to quantify injury evolution in neonatal hypoxic ischemic injury models.

We report a new clinically relevant model of neonatal hypoxic-ischemic injury in a 10-day-old rat pup. Bilateral carotid artery occlusion and 8% hypoxia (1 to 15 mins, BCAO-H) was induced with varying degrees of injury (mild, moderate, severe), which was quantified using magnetic resonance imaging including diffusion-weighted and T2-weighted imaging at 24 h and 21/28 days. We developed a magnetic resonance imaging-based rat pup severity score and compared 3D ischemic injury volumes/rat pup severity score with histology and behavioral testing. At 24 h, hypoxicischemic injury was observed in 17/27 animals; long-term survival was 81%. Magnetic resonance imaging lesion volumes did not correlate with hypoxia duration but correlated with rat pup severity score, which was used to classify animals into mild (n = 21), moderate (n = 6), and severe (n = 10) groups with average brain lesion volumes of 0.9%, 33.2%, and 56.3%, respectively. Histology confirmed lesion location and histologic scoring correlated with the rat pup severity score. We also found excellent correlation between injury severity and multiple behavioral tasks. Bilateral carotid artery occlusion and hypoxia in the P10 rat pup is an excellent model of neonatal hypoxic-ischemic injury because it induces diffuse global injury similar to the term infant. This model can produce graded injury severity, similar to that seen in human neonates, but manipulation with hypoxia duration is unpredictable.