A piglet model for detection of hypoxic-ischemic brain injury with magnetic resonance imaging

Hyperpolarized 13C magnetic resonance imaging in neonatal hypoxic-ischemic encephalopathy: First investigations in a large animal model

Early biomarkers of cerebral damage are essential for accurate prognosis, timely intervention, and evaluation of new treatment modalities in newborn infants with hypoxia and ischemia at birth. Hyperpolarized 13C magnetic resonance imaging (MRI) is a novel method with which to quantify metabolism in vivo with unprecedented sensitivity. We aimed to investigate the applicability of hyperpolarized 13C MRI in a newborn piglet model and whether this method may identify early changes in cerebral metabolism after a standardized hypoxic-ischemic (HI) insult. Six piglets were anesthetized and subjected to a standardized HI insult. Imaging was performed prior to and 2 h after the insult on a 3-T MR scanner. For 13C studies, [1-13C]pyruvate was hyperpolarized in a commercial polarizer. Following intravenous injection, images were acquired using metabolic-specific imaging. HI resulted in a metabolic shift with a decrease in pyruvate to bicarbonate metabolism and an increase in pyruvate to lactate metabolism (lactate/bicarbonate ratio, mean [SD]; 2.28 [0.36] vs. 3.96 [0.91]). This is the first study to show that hyperpolarized 13C MRI can be used in newborn piglets and applied to evaluate early changes in cerebral metabolism after an HI insult.

A novel model of acquired hydrocephalus for evaluation of neurosurgical treatments

Background

Many animal models have been used to study the pathophysiology of hydrocephalus; most of these have been rodent models whose lissencephalic cerebral cortex may not respond to ventriculomegaly in the same way as gyrencephalic species and whose size is not amenable to evaluation of clinically relevant neurosurgical treatments. Fewer models of hydrocephalus in gyrencephalic species have been used; thus, we have expanded upon a porcine model of hydrocephalus in juvenile pigs and used it to explore surgical treatment methods.

Methods

Acquired hydrocephalus was induced in 33–41-day old pigs by percutaneous intracisternal injections of kaolin (n = 17). Controls consisted of sham saline-injected (n = 6) and intact (n = 4) animals. Magnetic resonance imaging (MRI) was employed to evaluate ventriculomegaly at 11–42 days post-kaolin and to plan the surgical implantation of ventriculoperitoneal shunts at 14–38-days post-kaolin. Behavioral and neurological status were assessed.

Results

Bilateral ventriculomegaly occurred post-induction in all regions of the cerebral ventricles, with prominent CSF flow voids in the third ventricle, foramina of Monro, and cerebral aqueduct. Kaolin deposits formed a solid cast in the basal cisterns but the cisterna magna was patent. In 17 untreated hydrocephalic animals. Mean total ventricular volume was 8898 ± 5917 SD mm³ at 11–43 days of age, which was significantly larger than the baseline values of 2251 ± 194 SD mm³ for 6 sham controls aged 45–55 days, (p < 0.001). Past the post-induction recovery period, untreated pigs were asymptomatic despite exhibiting mild-moderate ventriculomegaly. Three out of 4 shunted animals showed a reduction in ventricular volume after 20–30 days of treatment, however some developed ataxia and lethargy, from putative shunt malfunction.

Conclusions

Kaolin induction of acquired hydrocephalus in juvenile pigs produced an in vivo model that is highly translational, allowing systematic studies of the pathophysiology and clinical treatment of hydrocephalus.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-021-00281-0.

No Added Neuroprotective Effect of Remote Ischemic Postconditioning and Therapeutic Hypothermia After Mild Hypoxia-Ischemia in a Piglet Model

Introduction: Hypoxic ischemic encephalopathy (HIE) is a major cause of death and disability in children worldwide. Apart from supportive care, the only established treatment for HIE is therapeutic hypothermia (TH). As TH is only partly neuroprotective, there is a need for additional therapies. Intermittent periods of limb ischemia, called remote ischemic postconditioning (RIPC), have been shown to be neuroprotective after HIE in rats and piglets. However, it is unknown whether RIPC adds to the effect of TH. We tested the neuroprotective effect of RIPC with TH compared to TH alone using magnetic resonance imaging and spectroscopy (MRI/MRS) in a piglet HIE model. Methods: Thirty-two male and female piglets were subjected to 45-min global hypoxia-ischemia (HI). Twenty-six animals were randomized to TH or RIPC plus TH; six animals received supportive care only. TH was induced through whole-body cooling. RIPC was induced 1 h after HI by four cycles of 5 min of ischemia and 5 min of reperfusion in both hind limbs. Primary outcome was Lac/NAA ratio at 24 h measured by MRS. Secondary outcomes were NAA/Cr, diffusion-weighted imaging (DWI), arterial spin labeling, aEGG score, and blood oxygen dependent (BOLD) signal measured by MRI/MRS at 6, 12, and 24 h after the hypoxic-ischemic insult. Results: All groups were subjected to a comparable but mild insult. No difference was found between the two intervention groups in Lac/NAA ratio, NAA/Cr ratio, DWI, arterial spin labeling, or BOLD signal. NAA/Cr ratio at 24 h was higher in the two intervention groups compared to supportive care only. There was no difference in aEEG score between the three groups. Conclusion: Treatment with RIPC resulted in no additional neuroprotection when combined with TH. However, insult severity was mild and only evaluated at 24 h after HI with a short MRS echo time. In future studies more subtle neurological effects may be detected with increased MRS echo time and post mortem investigations, such as brain histology. Thus, the possible neuroprotective effect of RIPC needs further evaluation.

Mean Diffusivity in Striatum Correlates With Acute Neuronal Death but Not Lesser Neuronal Injury in a Pilot Study of Neonatal Piglets With Encephalopathy

BACKGROUND

Diffusion MRI is routinely used to evaluate brain injury in neonatal encephalopathy. Although abnormal mean diffusivity (MD) is often attributed to cytotoxic edema, the specific contribution from neuronal pathology is unclear.

PURPOSE

To determine whether MD from high-resolution diffusion tensor imaging (DTI) can detect variable degrees of neuronal degeneration and pathology in piglets with brain injury induced by excitotoxicity or global hypoxia-ischemia (HI) with or without overt infarction.

STUDY TYPE

Prospective.

ANIMAL MODEL

Excitotoxic brain injury was induced in six neonatal piglets by intrastriatal stereotaxic injection of the glutamate receptor agonist quinolinic acid (QA). Three piglets underwent global HI or a sham procedure. Piglets recovered for 20-96 hours before undergoing MRI (n = 9).

FIELD STRENGTH/SEQUENCE

3.0T MRI with DTI, T₁ - and T₂ -weighted imaging.

ASSESSMENT

MD, fractional anisotropy (FA), and qualitative T₂ injury were assessed in the putamen and caudate. The cell bodies of normal neurons, degenerating neurons (excitotoxic necrosis, ischemic necrosis, or necrosis-apoptosis cell death continuum), and injured neurons with equivocal degeneration were counted by histopathology.

STATISTICAL TESTS

Spearman correlations were used to compare MD and FA to normal, degenerating, and injured neurons. T₂ injury and neuron counts were evaluated by descriptive analysis.

RESULTS

The QA insult generated titratable levels of neuronal pathology. In QA, HI, and sham piglets, lower MD correlated with higher ratios of degenerating-to-total neurons (P < 0.05), lower ratios of normal-to-total neurons (P < 0.05), and greater numbers of degenerating neurons (P < 0.05). MD did not correlate with abnormal neurons exhibiting nascent injury (P > 0.99). Neuron counts were not related to FA (P > 0.30) or to qualitative injury from T₂ -weighted MRI.

DATA CONCLUSION

MD is more accurate than FA for detecting neuronal degeneration and loss during acute recovery from neonatal excitotoxic and HI brain injury. MD does not reliably detect nonfulminant, nascent, and potentially reversible neuronal injury.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 2 J. Magn. Reson. Imaging 2020;52:1216-1226.

Prognostic value of 18F-FDG brain PET as an early indicator of neurological outcomes in a rat model of post-cardiac arrest syndrome

Predicting neurological outcomes in patients with post-cardiac arrest syndrome (PCAS) is crucial for identifying those who will benefit from intensive care. We evaluated the predictive value of 18F-FDG PET. PCAS was induced in Sprague Dawley rats. Baseline and post-3-hour images were acquired. Standardized uptake value (SUV) changes before and after PCAS induction (SUV_delta) and SUV ratios (SUVR) of regional SUV normalized to the whole brain SUV were obtained. The Morris water maze (MWM) test was performed after 2 weeks to evaluate neurological outcomes and rats were classified into two groups based on the result. Of 18 PCAS rats, 8 were classified into the good outcome group. The SUV_delta of forebrain regions were significantly decreased in good outcome group (p < 0.05), while the SUV_delta of hindbrain regions were not significantly different according to outcomes. The SUVR of forebrain regions were significantly higher and the SUVR of hindbrain regions were significantly lower in good outcome group (p < 0.05). Forebrain-to-hindbrain ratio predicted a good neurological outcome with a sensitivity of 90% and specificity of 100% using an optimal cutoff value of 1.22 (AUC 0.969, p < 0.05). These results suggest the potential utility of 18F-FDG PET in the early prediction of neurological outcomes in PCAS.

Magnetic Resonance Imaging Findings of Term and Preterm Hypoxic-Ischemic Encephalopathy: A Review of Relevant Animal Models and Correlation to Human Imaging

Background:

Neonatal hypoxic-ischemic encephalopathy is brain injury caused by decreased perfusion and oxygen delivery that most commonly occurs in the context of delivery complications such as umbilical cord compression or placental abruption. Imaging is a key component for guiding treatment and prediction of prognosis, and the most sensitive clinical imaging modality for the brain injury patterns seen in hypoxic-ischemic encephalopathy is magnetic resonance imaging.

Objective:

The goal of this review is to compare magnetic resonance imaging findings demonstrated in the available animal models of hypoxic-ischemic encephalopathy to those found in preterm (≤ 36 weeks) and term (>36 weeks) human neonates with hypoxic-ischemic encephalopathy, with special attention to the strengths and weaknesses of each model.

Methods:

A structured literature search was performed independently by two authors and the results of the searches were compiled. Animal model, human brain age equivalency, mechanism of injury, and area of brain injury were recorded for comparison to imaging findings in preterm and term human neonates with hypoxic-ischemic encephalopathy.

Conclusion:

Numerous animal models have been developed to better elicit the expected findings that occur after HIE by allowing investigators to control many of the clinical variables that result in injury. Although modeling the same disease process, magnetic resonance imaging findings in the animal models vary with the species and methods used to induce hypoxia and ischemia. The further development of animal models of HIE should include a focus on comparing imaging findings, and not just pathologic findings, to human studies.

Diffusion-weighted imaging detects early brain injury after hypothermic circulatory arrest in pigs

OBJECTIVES

Cerebral injury is a complication of surgery with deep hypothermic circulatory arrest (DHCA). This study aimed to evaluate diffusion-weighted imaging (DWI) for the early detection of brain injury after DHCA in an animal model.

METHODS

Twelve healthy, adult, male miniature pigs were randomly divided into the DHCA (to receive DHCA; n = 6) and the control (sham surgery under anaesthesia; n = 6) groups. All animals received DWI, T1-weighted imaging (T1WI) and T2WI the day before surgery, 7 h postoperatively and 24 h postoperatively. Histopathological evaluation of the brain tissues was performed in the DHCA group using the Fluoro-Jade C staining to detect neuronal degeneration, the Nissl staining to show neuronal morphology and the TUNEL assay for apoptosis. The Cohen's kappa coefficient was used to compare the results of DWI with those of the histopathological evaluation.

RESULTS

All animals survived surgery. In the control group, no new focal brain lesions were detected by postoperative DWI, T1WI or T2WI. In the DHCA group, new focal brain lesions were detected as early as 7 h postoperatively by DWI but not T1WI or T2WI. All three imaging sequences revealed abnormalities 24 h after surgery. In sections from areas showing abnormalities on DWI, the Fluoro-Jade C staining detected neuronal degeneration, the Nissl staining showed morphological abnormalities and the TUNEL assay demonstrated apoptotic cells. The Cohen's kappa statistics showed agreement between DWI findings and the results of all 3 histopathological examinations (TUNEL: kappa = 0.553; Nissl: kappa = 0.652; Fluoro-Jade C: kappa = 0.778; all P < 0.001).

CONCLUSIONS

DWI is superior to T1WI or T2WI for the early detection of neurological lesions after DHCA in pigs.

Umbilical Artery Lactate Correlates with Brain Lactate in Term Infants

Objective The objective of this study was to determine the correlation between umbilical artery lactate with brain lactate in nonanomalous term infants. Study Design We performed a nested case-control study within an on-going prospective cohort of more than 8,000 consecutive singleton term (≥ 37 weeks) nonanomalous infants. Neonates underwent cerebral magnetic resonance imaging (MRI) within the first 72 hours of life. Cases (umbilical artery pH ≤ 7.10) were gender and race matched 1:3 to controls (umbilical artery pH > 7.20). Single voxel magnetic resonance spectroscopy (MRS), lactate, and N-acetyl aspartate (NAA) for normalization were calculated using Siemens software (Plano, TX). Linear regression estimated the association between incremental change in umbilical artery lactate and brain lactate, both directly and as a ratio with NAA. Results Of 175 infants who underwent MRI with spectral sequencing, 52 infants had detectable brain lactate. The 52 infants with brain lactate peaks had umbilical artery lactate values of 1.6 to 11.4 mmol/L. For every 1.0 mmol/L increase in umbilical artery lactate, there was an increase in brain lactate of 0.02, which remained significant even when corrected for NAA. Conclusion MRS measured brain lactate is significantly correlated with umbilical artery lactate in nonanomalous term infants, which may help explain the observed association between umbilical artery lactate and neurologic morbidity.

Measurement of Lactate Content and Amide Proton Transfer Values in the Basal Ganglia of a Neonatal Piglet Hypoxic-Ischemic Brain Injury Model Using MRI

BACKGROUND AND PURPOSE

As amide proton transfer imaging is sensitive to protein content and intracellular pH, it has been widely used in the nervous system, including brain tumors and stroke. This work aimed to measure the lactate content and amide proton transfer values in the basal ganglia of a neonatal piglet hypoxic-ischemic brain injury model by using MR spectroscopy and amide proton transfer imaging.

MATERIALS AND METHODS

From 58 healthy neonatal piglets (3-5 days after birth; weight, 1-1.5 kg) selected initially, 9 piglets remained in the control group and 43 piglets, in the hypoxic-ischemic brain injury group. Single-section amide proton transfer imaging was performed at the coronal level of the basal ganglia. Amide proton transfer values of the bilateral basal ganglia were measured in all piglets. The ROI of MR spectroscopy imaging was the right basal ganglia, and the postprocessing was completed with LCModel software.

RESULTS

After hypoxic-ischemic insult, the amide proton transfer values immediately decreased, and at 0-2 hours, they remained at their lowest level. Thereafter, they gradually increased and finally exceeded those of the control group at 48-72 hours. After hypoxic-ischemic insult, the lactate content increased immediately, was maximal at 2-6 hours, and then gradually decreased to the level of the control group. The amide proton transfer values were negatively correlated with lactate content (r = -0.79, P < .05).

CONCLUSIONS

This observation suggests that after hypoxic-ischemic insult, the recovery of pH was faster than that of lactate homeostasis.

Short-term effects of cannabidiol after global hypoxia-ischemia in newborn piglets

BACKGROUND

Cannabidiol (CBD), a nonpsychoactive cannabinoid, has shown neuroprotective actions after neonatal hypoxia-ischemia (HI) in animals. We wanted to further explore the effects of CBD, alone and in conjunction with hypothermia, in a piglet model of global HI.

METHODS

Fifty-five anesthetized newborn piglets were randomized to either controls (n = 7) or HI (n = 48) by ventilation with 8% O₂ until mean arterial blood pressure reached 20 mmHg and/or base excess reached -20 mmol/l. After resuscitation piglets were randomized to either: vehicle (VEH), CBD 1mg/kg, VEH+hypothermia (H) or CBD 1mg/kg+H (each n = 12). Piglets were euthanized 9.5 h after HI and plasma, urine, cerebrospinal fluid, and brain tissue were sampled for analysis.

RESULTS

HI induced global damage with significantly increased neuropathology score, S100B in cerebrospinal fluid, hippocampal proton magnetic resonance spectroscopy biomarkers, plasma troponin-T, and urinary neutrophil gelatinase-associated lipocalin. CBD alone did not have any significant effects on these parameters while CBD+H reduced urinary neutrophil gelatinase-associated lipocalin compared with VEH+H (P < 0.05). Both hypothermic groups had significantly lower glutamate/N-acetylaspartate ratios (P < 0.01) and plasma troponin-T (P<0.05) levels compared with normothermic groups.

CONCLUSION

In contrast to previous studies, we do not find significant protective effects of CBD after HI in piglets. Evaluation of CBD in higher doses might be warranted.

Effects of Cannabidiol and Hypothermia on Short-Term Brain Damage in New-Born Piglets after Acute Hypoxia-Ischemia

Hypothermia is a standard treatment for neonatal encephalopathy, but nearly 50% of treated infants have adverse outcomes. Pharmacological therapies can act through complementary mechanisms with hypothermia improving neuroprotection. Cannabidiol could be a good candidate. Our aim was to test whether immediate treatment with cannabidiol and hypothermia act through complementary brain pathways in hypoxic-ischemic newborn piglets. Hypoxic-ischemic animals were randomly divided into four groups receiving 30 min after the insult: (1) normothermia and vehicle administration; (2) normothermia and cannabidiol administration; (3) hypothermia and vehicle administration; and (4) hypothermia and cannabidiol administration. Six hours after treatment, brains were processed to quantify the number of damaged neurons by Nissl staining. Proton nuclear magnetic resonance spectra were obtained and analyzed for lactate, N-acetyl-aspartate and glutamate. Metabolite ratios were calculated to assess neuronal damage (lactate/N-acetyl-aspartate) and excitotoxicity (glutamate/Nacetyl-aspartate). Western blot studies were performed to quantify protein nitrosylation (oxidative stress), content of caspase-3 (apoptosis) and TNFα (inflammation). Individually, the hypothermia and the cannabidiol treatments reduced the glutamate/Nacetyl-aspartate ratio, as well as TNFα and oxidized protein levels in newborn piglets subjected to hypoxic-ischemic insult. Also, both therapies reduced the number of necrotic neurons and prevented an increase in lactate/N-acetyl-aspartate ratio. The combined effect of hypothermia and cannabidiol on excitotoxicity, inflammation and oxidative stress, and on cell damage, was greater than either hypothermia or cannabidiol alone. The present study demonstrated that cannabidiol and hypothermia act complementarily and show additive effects on the main factors leading to hypoxic-ischemic brain damage if applied shortly after the insult.

Ischemic postconditioning protects against ischemic brain injury by up-regulation of acid-sensing ion channel 2a

Ischemic postconditioning renders brain tissue tolerant to brain ischemia, thereby alleviating ischemic brain injury. However, the exact mechanism of action is still unclear. In this study, a rat model of global brain ischemia was subjected to ischemic postconditioning treatment using the vessel occlusion method. After 2 hours of ischemia, the bilateral common carotid arteries were blocked immediately for 10 seconds and then perfused for 10 seconds. This procedure was repeated six times. Ischemic postconditioning was found to mitigate hippocampal CA1 neuronal damage in rats with brain ischemia, and up-regulate acid-sensing ion channel 2a expression at the mRNA and protein level. These findings suggest that ischemic postconditioning up-regulates acid-sensing ion channel 2a expression in the rat hippocampus after global brain ischemia, which promotes neuronal tolerance to ischemic brain injury.

Standard loading controls are not reliable for Western blot quantification across brain development or in pathological conditions

A frequently utilized method of data quantification in Western blot analysis is comparison of the protein of interest with a house keeping gene or control protein. Commonly used proteins include β-actin, glyceraldehyde 3 phosphate dehydrogenase (GAPDH), and α-tubulin. Various reliability issues have been raised when using this technique for data analysis-particularly when investigating protein expression changes during development and in disease states. In this study, we have demonstrated that β-actin, GAPDH, and α-tubulin are not appropriate controls in the study of development and hypoxic-ischemic induced damage in the piglet brain. We have also shown that using an in-house pooled standard, loaded on all blots is a reliable method for controlling interassay variability and data normalization in protein expression analysis.

Early postnatal respiratory viral infection induces structural and neurochemical changes in the neonatal piglet brain

Infections that cause inflammation during the postnatal period are common, yet little is known about their impact on brain development in gyrencephalic species. To address this issue, we investigated brain development in domestic piglets which have brain growth and morphology similar to human infants, after experimentally infecting them with porcine reproductive and respiratory syndrome virus (PRRSV) to induce an interstitial pneumonia Piglets were inoculated with PRRSV on postnatal day (PD) 7 and magnetic resonance imaging (MRI) was used to assess brain macrostructure (voxel-based morphometry), microstructure (diffusion tensor imaging) and neurochemistry (MR-spectroscopy) at PD 29 or 30. PRRSV piglets exhibited signs of infection throughout the post-inoculation period and had elevated plasma levels of TNFα at the end of the study. PRRSV infection increased the volume of several components of the ventricular system including the cerebral aqueduct, fourth ventricle, and the lateral ventricles. Group comparisons between control and PRRSV piglets defined 8 areas where PRRSV piglets had less gray matter volume; 5 areas where PRRSV piglets had less white matter volume; and 4 relatively small areas where PRRSV piglets had more white matter. Of particular interest was a bilateral reduction in gray and white matter in the primary visual cortex. PRRSV piglets tended to have reduced fractional anisotropy in the corpus callosum. Additionally, N-acetylaspartate, creatine, and myo-inositol were decreased in the hippocampus of PRRSV piglets suggesting disrupted neuronal and glial health and energy imbalances. These findings show in a gyrencephalic species that early-life infection can affect brain growth and development.

A Piglet Model of Neonatal Hypoxic-Ischemic Encephalopathy

Birth asphyxia, which causes hypoxic-ischemic encephalopathy (HIE), accounts for 0.66 million deaths worldwide each year, about a quarter of the world's 2.9 million neonatal deaths. Animal models of HIE have contributed to the understanding of the pathophysiology in HIE, and have highlighted the dynamic process that occur in brain injury due to perinatal asphyxia. Thus, animal studies have suggested a time-window for post-insult treatment strategies. Hypothermia has been tested as a treatment for HIE in pdiglet models and subsequently proven effective in clinical trials. Variations of the model have been applied in the study of adjunctive neuroprotective methods and piglet studies of xenon and melatonin have led to clinical phase I and II trials(1,2). The piglet HIE model is further used for neonatal resuscitation- and hemodynamic studies as well as in investigations of cerebral hypoxia on a cellular level. However, it is a technically challenging model and variations in the protocol may result in either too mild or too severe brain injury. In this article, we demonstrate the technical procedures necessary for establishing a stable piglet model of neonatal HIE. First, the newborn piglet (< 24 hr old, median weight 1500 g) is anesthetized, intubated, and monitored in a setup comparable to that found in a neonatal intensive care unit. Global hypoxia-ischemia is induced by lowering the inspiratory oxygen fraction to achieve global hypoxia, ischemia through hypotension and a flat trace amplitude integrated EEG (aEEG) indicative of cerebral hypoxia. Survival is promoted by adjusting oxygenation according to the aEEG response and blood pressure. Brain injury is quantified by histopathology and magnetic resonance imaging after 72 hr.

The domestic piglet: an important model for investigating the neurodevelopmental consequences of early life insults

Insults in the prenatal and early postnatal period increase the risk for behavioral problems later in life. One hypothesis is that pre- and postnatal stressors influence structural and functional brain plasticity. Understanding the mechanisms is important, but progress has lagged because certain studies in human infants are impossible, while others are extremely difficult. Furthermore, results from popular rodent models are difficult to translate to human infants owing to the substantial differences in brain development and morphology. Because it overcomes some of these obstacles, the domestic piglet has emerged as an important model. Piglets have a gyrencephalic brain that develops similar to the human brain and that can be assessed in vivo by using clinical-grade neuroimaging instruments. Furthermore, owing to their precocial nature, piglets can be weaned at birth and used in behavioral testing paradigms to assess cognitive behavior at an early age. Thus, the domestic piglet represents an important translational model for investigating the neurodevelopmental consequences of early life insults.

Detection of hypoxic-ischemic brain injury with 3D-enhanced T2* weighted angiography (ESWAN) imaging

OBJECTIVE

To demonstrate the use of 3D-enhanced T2* weighted angiography (ESWAN) imaging for the observation and quantification of the evolution of brain injury induced by a recently developed model of hypoxic-ischemic brain injury (HI/R) in neonatal piglets.

METHODS

For these experiments, newborn piglets were subjected to HI/R injury, during which ESWAN scanning was performed, followed by H&E staining and immunohistochemistry of AQP-4 expression.

RESULTS

In the striatum, values from T2* weighted magnetic resonance imaging (MRI) increased and reached their highest level at 3 days post injury, whereas T2* values increased and peaked at 24h in the subcortical region. The change in T2* values was concordant with brain edema. Phase values in the subcortical border region were not dependent on time post-injury. Magnitude values were significantly different from the control group, and increased gradually over time in the subcortical border region. Susceptibility-weighted images (SWI) indicated small petechial hemorrhages in the striatum and thalamus, as well as dilated intramedullary veins.

CONCLUSION

SWI images can be used to detect white and gray matter microhemorrhages and dilated intramedullary veins. The T2*, phase, and magnitude map can also reflect the development of brain injury. Our data illustrate that ESWAN imaging can increase the diagnostic sensitivity and specificity of MRI in neonatal hypoxic-ischemic encephalopathy.

Expression of N-methyl-d-aspartate receptor 1 and its phosphorylated state in basal ganglia of a neonatal piglet hypoxic-ischemic brain injury model: a controlled study of (1)H MRS

Excitatory amino acids (EAAs) and excitotoxicity medicated by receptors of these amino acids play an important role in hypoxic-ischemic brain injury (HIBI), but most studies were ex vivo experiments, the mechanism in vivo is not well understood. We sought to study the expression of N-methyl-d-aspartate receptor 1 (NR1) and phosphorylated N-methyl-d-aspartate receptor 1 (P-NR1) in basal ganglia in a piglet model of HIBI and to investigate the correlation between Glx(Glu/Gln) value measured by magnetic resonance spectroscopy (MRS) and NR1/P-NR1 expression. Multi-voxel (1)H MRS was applied to detect change in Glx in basal ganglia of the newborn piglets in vivo. Automatic amino acid analyzer was applied to accurately quantify the Glu concentration. Immunohistochemical method was used to examine the expression of NR1 and P-NR1. The NR1 receptors in basal ganglia of the newborn piglets were significantly activated after HIBI. P-NR1 expression in the basal ganglia was consistent with the change in brain Glu content, so the activation status of NMDA receptor in the brain could be indirectly reflected by β-, γ-Glx/NAA measured by (1)H MRS.

Dynamic FDG PET for assessing early effects of cerebral hypoxia and resuscitation in new-born pigs

PURPOSE

Changes in cerebral glucose metabolism may be an early prognostic indicator of perinatal hypoxic-ischaemic injury. In this study dynamic ¹⁸F-FDG PET was used to evaluate cerebral glucose metabolism in piglets after global perinatal hypoxia and the impact of the resuscitation strategy using room air or hyperoxia.

METHODS

New-born piglets (n = 16) underwent 60 min of global hypoxia followed by 30 min of resuscitation with a fraction of inspired oxygen (FiO₂) of 0.21 or 1.0. Dynamic FDG PET, using a microPET system, was performed at baseline and repeated at the end of resuscitation under stabilized haemodynamic conditions. MRI at 3 T was performed for anatomic correlation. Global and regional cerebral metabolic rates of glucose (CMRgl) were assessed by Patlak analysis for the two time-points and resuscitation groups.

RESULTS

Global hypoxia was found to cause an immediate decrease in cerebral glucose metabolism from a baseline level (mean ± SD) of 21.2 ± 7.9 to 12.6 ± 4.7 μmol/min/ 100 g (p <0.01). The basal ganglia, cerebellum and cortex showed the greatest decrease in CMRgl but no significant differences in global or regional CMRgl between the resuscitation groups were found.

CONCLUSION

Dynamic FDG PET detected decreased cerebral glucose metabolism early after perinatal hypoxia in piglets. The decrease in CMRgl may indicate early changes of mild cerebral hypoxia-ischaemia. No significant effect of hyperoxic resuscitation on the degree of hypometabolism was found in this early phase after hypoxia. Cerebral FDG PET can provide new insights into mechanisms of perinatal hypoxic- ischaemic injury where early detection plays an important role in instituting therapy.

The correlation between DTI parameters and levels of AQP-4 in the early phases of cerebral edema after hypoxic-ischemic/reperfusion injury in piglets

BACKGROUND

Brain edema during the early stages of hypoxic-ischemic/reperfusion (HI/R) injury can be determined using diffusion tensor imaging (DTI). The change in ADC values has been correlated with the change in expression of AQP-4.

OBJECTIVE

To determine cerebral edema at specific time intervals after HI/R injury using DTI modalities and discuss its relationship to the expression of aquaporin-4 (AQP-4).

MATERIALS AND METHODS

Thirty newborn piglets were divided into six groups (2, 6, 12, 24, 48 and 72 h) after HI/R injury. The control group subjected to sham surgery included five piglets. DTI scans and immunohistochemistry of AQP-4 expression were performed on piglet brain. The relationship between DTI parameters (FA and ADC values) and the optical density (OD) of AQP-4 expression was determined.

RESULTS

In the striatum, ADC values dropped and reached their lowest level at 24 h (F = 27.42, P < 0.05). In the subcortical border region, ADC values increased after a transient decrease and peaked at 48 h, demonstrating a significant difference from the control group (F = 50.25, P < 0.05). FA values in the internal capsules and subcortical white matter in HI/R models decreased continuously after HI/R, although no statistically significant difference from the control group was achieved. ADC and OD values of AQP-4 expression were positively correlated (r = 0.875, P < 0.05).

CONCLUSIONS

The change in ADC value after HI/R injury correlates with the expression of AQP-4.

Brain growth of the domestic pig (Sus scrofa) from 2 to 24 weeks of age: a longitudinal MRI study

An animal model with brain growth similar to humans, that can be used in MRI studies to investigate brain development, would be valuable. Our laboratory has developed and validated MRI methods for regional brain volume quantification in the neonatal piglet. The aim of this study was to utilize the MRI-based volume quantification technique in a longitudinal study to determine brain growth in domestic pigs from 2 to 24 weeks of age. MRI data were acquired from pigs 2-24 weeks of age using a 3-dimensional magnetization-prepared gradient echo sequence on a Magnetom Trio 3-tesla imager. Manual segmentation was performed for volume estimates of total brain, cortical, diencephalon, brainstem, cerebellar and hippocampal regions. Logistic modeling procedures were used to characterize brain growth. Total brain volume increased 130% (±12%) and 121% (±7%) from 2 to 24 weeks in males and females, respectively. The maximum increase in total brain volume occurred about the age of 4 weeks and 95% of whole brain growth occurred by the age of 21-23 weeks. Logistical modeling suggests there are sexually dimorphic effects on brain growth. For example, in females, the cortex was smaller (p = 0.04). Furthermore, the maximum growth of the hippocampus occurred about 5 weeks earlier in females than males, and the window for hippocampal growth was significantly shorter in females than males (p = 0.02, p = 0.002 respectively). These sexual dimorphisms are similar to what is seen in humans. In addition to providing important data on brain growth for pigs, this study shows pigs can be used to obtain longitudinal MRI data. The large increase in brain volume in the postnatal period is similar to that of human neonates and suggests pigs can be used to investigate brain development.

Motor deficits are triggered by reperfusion-reoxygenation injury as diagnosed by MRI and by a mechanism involving oxidants

The early antecedents of cerebral palsy (CP) are unknown but are suspected to be due to hypoxia-ischemia (H-I). In our rabbit model of CP, the MRI biomarker, apparent diffusion coefficient (ADC) on diffusion-weighted imaging, predicted which fetuses will develop postnatal hypertonia. Surviving H-I fetuses experience reperfusion-reoxygenation but a subpopulation manifested a continued decline of ADC during early reperfusion-reoxygenation, which possibly represented greater brain injury (RepReOx). We hypothesized that oxidative stress in reperfusion-reoxygenation is a critical trigger for postnatal hypertonia. We investigated whether RepReOx predicted postnatal neurobehavior, indicated oxidative stress, and whether targeting antioxidants at RepReOx ameliorated motor deficits, which included testing of a new superoxide dismutase mimic (MnTnHex-2-PyP). Rabbit dams, 79% gestation (E25), were subjected to 40 min uterine ischemia. Fetal brain ADC was followed during H-I, immediate reperfusion-reoxygenation, and 4-72 h after H-I. Endpoints were postnatal neurological outcome at E32, ADC at end of H-I, ADC nadir during H-I and reperfusion-reoxygenation, and area under ADC curve during the first 20 min of reperfusion-reoxygenation. Antioxidants targeting RepReOx were administered before and/or after uterine ischemia. The new MRI-ADC biomarker for RepReOx improved prediction of postnatal hypertonia. Greater superoxide production, mitochondrial injury, and oligodendroglial loss occurred in fetal brains exhibiting RepReOx than in those without. The antioxidants, MnTnHex-2-PyP and Ascorbate and Trolox combination, significantly decreased postnatal motor deficits and extent of RepReOx. The etiological link between early injury and later motor deficits can thus be investigated by MRI, and allows us to distinguish between critical oxidative stress that causes motor deficits and noncritical oxidative stress that does not.

Simultaneously changes in striatum dopaminergic and glutamatergic parameters following hypoxic-ischemic neuronal injury in newborn piglets

Basal ganglia injury (BGI) is a type of perinatal hypoxic-ischemic (H-I) brain injury. Both malfunctions of glutamatergic and dopaminergic pathways in striatum were suggested to contribute to BGI. In current study, we investigated the imaging profile of glutamate (Glx) levels by proton magnetic resonance spectroscopy ((1)H-MRS), and the expression of dopamine D2 receptors (D2R) and dopamine transporter (DAT) by immunohistochemical staining in a newborn piglet model of H-I brain injury. We found that the number of striatal D2R positive neurons decreased following H-I brain injury, and the decrease in positive neuron number was consistent with the degree of striatum. Following H-I brain insult, the number of striatal DAT positive neurons and glutamate level were simultaneously increased initially, followed by a gradual decline toward control level. There was a positive correlation between the changes in striatal DAT positive neurons and glutamate level following H-I brain insults in newborn piglets. Our findings suggest that following H-I brain insult, striatal D2R positive neurons decreased due to neuron death; straital DAT initially increased to compensate for dopamine uptake; and glutamatergic and dopaminergic systems in striatum may act in an interdependent way in the striatum of newborn piglets.

Magnetic resonance imaging of the neonatal piglet brain

INTRODUCTION

Appeal for the domestic pig as a preclinical model for neurodevelopmental research is increasing. One limitation, however, is lack of magnetic resonance imaging (MRI) methods for brain volume quantification in the neonatal piglet. The purpose of this study was to develop and validate MRI methods for estimating brain volume in piglets.

RESULTS

The results showed that MRI and manual segmentation reliably estimated the changes in volume of different brain regions in 2- and 5-wk-old piglets. Substantial increases in the volumes of all brain regions examined were evident during the 3-wk period.

DISCUSSION

MRI can provide accurate estimates of brain region volume during the neonatal period in piglets. A piglet model that can be used in longitudinal studies may be useful for investigating how experimental (e.g., nutrition, infection) factors affect brain growth and development.

METHODS

Anatomic MRI data (non-longitudinal) were acquired 2- and 5-wk-old piglets using a three--dimensional T1-weighted magnetization-prepared gradient echo (MPRAGE) sequence on a MAGNETOM Trio 3T imager. Manual segmentation was performed for volume estimates of total brain, cortical, diencephalon, brainstem, cerebellar, and -hippocampal regions. The MRI-based hippocampal volume estimates in 2- and 5-wk-old piglets were validated using histological techniques and the Cavalieri method.

Early in vivo MR spectroscopy findings in organophosphate-induced brain damage-potential biomarkers for short-term survival

Organophosphates are highly toxic substances, which cause severe brain damage. The hallmark of the brain injury is major convulsions. The goal of this study was to assess the spatial and temporal MR changes in the brain of paraoxon intoxicated rats. T2-weighted MRI and ¹H-MR-spectroscopy were conducted before intoxication, 3 h, 24 h, and 8 days postintoxication. T2 prolongation mainly in the thalami and cortex was evident as early as 3 h after intoxication (4-6% increase in T2 values, P < 0.05). On spectroscopy, N-acetyl aspartate (NAA)/creatine and NAA/choline levels significantly decreased 3 h postintoxication (>20% decrease, P < 0.005), and 3 h lactate peak was evident in all intoxicated animals. On the 8th day, although very little T2 changes were evident, NAA/creatine and choline/creatine were significantly decreased (>15%, P < 0.05). Animals who succumbed had extensive cortical edema, significant higher lactate levels and a significant decrease in NAA/creatine and NAA/choline levels compared to animals which survived the experiment. Organophosphates-induced brain damage is obvious on MR data already 3 h postintoxication. In vivo spectroscopic changes are more sensitive for assessing long-term injury than T2-weighted MR imaging. Early spectroscopic findings might be used as biomarkers for the severity of the intoxication and might predict early survival.

Effects of hypoxic-ischemic brain injury on striatal dopamine transporter in newborn piglets: evaluation of 11C-CFT PET/CT for DAT quantification

INTRODUCTION

Alterations of dopamine in striatal presynaptic terminals play an important role in the hypoxic-ischemic (HI) brain injury. Quantification of DAT levels in the presynaptic site using (11)C-N-2-carbomethoxy-3-(4-fluorophenyl)-tropane ((11)C-CFT) with positron emission tomography (PET) was applied in studies for Parkinson's disease. The current study investigated the changes in striatal DAT following HI brain injury in newborn piglets using (11)C-CFT PET.

METHODS

Newborn piglets were subjected to occlusion of bilateral common carotid arteries for 30 min and simultaneous peripheral hypoxia. Brain DAT imaging was performed using PET/CT with (11)C-CFT as the probe in each group (including the control group and HI insult groups). Brain tissues were collected for DAT immunohistochemical (IHC) analysis at each time point post the PET/CT procedure. Sham controls had some operation without HI procedure.

RESULTS

A few minutes after intravenous injection of (11)C-CFT, radioactive signals for DAT clearly appeared in the cortical area, striatum and cerebellum of newborn piglets of sham control group and HI insult groups. HI brain insult markedly increased striatal DAT at an early period (P<.05 vs. sham controls) when neuronal pathological changes were mild. Changes in striatal DAT were absent at later period post-HI insult when neuronal injury became more severe. (11)C-CFT PET imaging data and IHC DAT staining data were highly correlated (r=0.844, P<.05).

CONCLUSIONS

HI brain injury resulted in a transient increase in striatal DAT. (11)C-CFT PET/CT imaging data reflected the dynamic changes of DAT in the striatum in vivo.

The pig as a model animal for studying cognition and neurobehavioral disorders

In experimental animal research, a short phylogenetic distance, i.e., high resemblance between the model species and the species to be modeled is expected to increase the relevance and generalizability of results obtained in the model species. The (mini)pig shows multiple advantageous characteristics that have led to an increase in the use of this species in studies modeling human medical issues, including neurobehavioral (dys)functions. For example, the cerebral cortex of pigs, unlike that of mice or rats, has cerebral convolutions (gyri and sulci) similar to the human neocortex. We expect that appropriately chosen pig models will yield results of high translational value. However, this claim still needs to be substantiated by research, and the area of pig research is still in its infancy. This chapter provides an overview of the pig as a model species for studying cognitive dysfunctions and neurobehavioral disorders and their treatment, along with a discussion of the pros and cons of various tests, as an aid to researchers considering the use of pigs as model animal species in biomedical research.

Seizures are associated with brain injury severity in a neonatal model of hypoxia-ischemia

Hypoxia-ischemia is a significant cause of brain damage in the human newborn and can result in long-term neurodevelopmental disability. The loss of oxygen and glucose supply to the developing brain leads to excitotoxic neuronal cell damage and death; such over-excitation of nerve cells can also manifest as seizures. The newborn brain is highly susceptible to seizures although it is unclear what role they have in hypoxic-ischemic (H/I) injury. The aim of this study was to determine an association between seizures and severity of brain injury in a piglet model of perinatal H/I and, whether injury severity was related to type of seizure, i.e. sub-clinical (electrographic seizures only) or clinical (electrographic seizures+physical signs). Hypoxia (4% O(2)) was induced in anaesthetised newborn piglets for 30 min with a final 10 min period of hypotension; animals were recovered and survived to 72 h. Animals were monitored daily for seizures both visually and with electroencephalogram (EEG) recordings. Brain injury was assessed with magnetic resonance imaging (MRI), (1)H-MR spectroscopy ((1)H-MRS), EEG and by histology (haematoxylin and eosin). EEG seizures were observed in 75% of all H/I animals, 46% displayed clinical seizures and 29% sub-clinical seizures. Seizure animals showed significantly lower background amplitude EEG across all post-insult days. Presence of seizures was associated with lower cortical apparent diffusion coefficient (ADC) scores and changes in (1)H-MRS metabolite ratios at both 24 and 72 h post-insult. On post-mortem examination animals with seizures showed the greatest degree of neuropathological injury compared to animals without seizures. Furthermore, clinical seizure animals had significantly greater histological injury compared with sub-clinical seizure animals; this difference was not apparent on MRI or (1)H-MRS measures. In conclusion we report that both sub-clinical and clinical seizures are associated with increased severity of H/I injury in a term model of neonatal H/I.