MR-based statistical atlas of the Göttingen minipig brain

Combined In Vivo Microdialysis and PET Studies to Validate [11C]Yohimbine Binding as a Marker of Noradrenaline Release

The noradrenaline system attracts attention for its role in mood disorders and neurodegenerative diseases but the lack of well-validated methods impairs our understanding when assessing its function and release in vivo. This study combines simultaneous positron emission tomography (PET) and microdialysis to explore if [11C]yohimbine, a selective antagonist radioligand of the α2 adrenoceptors, may be used to assess in vivo changes in synaptic noradrenaline during acute pharmacological challenges. Anesthetised Göttingen minipigs were positioned in a head holder in a PET/CT device. Microdialysis probes were placed in the thalamus, striatum and cortex and dialysis samples were collected every 10 min. Three 90 min [11C]yohimbine scans were acquired: at baseline and at two timepoints after the administration of amphetamine (1-10 mg/kg), a non-specific releaser of dopamine and noradrenaline, or nisoxetine (1 mg/kg), a specific noradrenaline transporter inhibitor. [11C]yohimbine volumes of distribution (VT) were obtained using the Logan kinetic model. Both challenges induced a significant decrease in yohimbine VT, with time courses reflecting their different mechanisms of action. Dialysis samples revealed a significant increase in noradrenaline extracellular concentrations after challenge and an inverse correlation with changes in yohimbine VT. These data suggest that [11C]yohimbine can be used to evaluate acute variations in synaptic noradrenaline concentrations after pharmacological challenges.

Usability of the SedLine® electroencephalographic monitor of depth of anaesthesia in pigs: a pilot study

To investigate the usability of the SedLine® monitor in anaesthetized pigs. Five juvenile healthy pigs underwent balanced isoflurane-based general anaesthesia for surgical placement of a subcutaneous jugular venous port. The SedLine® was applied to continuously monitor electroencephalographic (EEG) activity and its modulation during anaesthesia. Computer tomography and magnetic resonance were performed to investigate the relationship between electrodes' positioning and anatomical structures. The pediatric SedLine® EEG-sensor could be easily applied and SedLine®-generated variables collected. An EEG Density Spectral Array (DS) was displayed over the whole procedure. During surgery, the EEG signal was dominated by elevated power in the delta range (0.5-4 Hz), with an underlying broadband signal (where power decreased with increasing frequency). The emergence period was marked by a decrease in delta power, and a more evenly distributed power over the 4-40 Hz frequency range. From incision to end of surgery, mean SedLine®-generated values (± standard deviation) were overall stable [23.0 (± 2.8) Patient State Index (PSI), 1.0% (± 3.8%) Suppression Ratio (SR), 8.8 Hz (± 2.5 Hz) Spectral Edge Frequency 95% (SEF) left, 7.7 Hz (± 2.4 Hz) SEF right], quickly changing during emergence [75.3 (± 11.1) PSI, 0.0 (± 0.0) SR, 12.5 (± 6.6) SEF left 10.4 (± 6.6) SEF right]. Based on the imaging performed, the sensor does not record EEG signals from the same brain areas as in humans. SedLine®-DSA and -generated variables seemed to reflect variations in depth of anaesthesia in pigs. Further studies are needed to investigate this correlation, as well as to define the species-specific brain structures monitored by the EEG-sensor.

Brain MR Atlas Construction Using Symmetric Deep Neural Inpainting

Modeling statistical properties of anatomical structures using magnetic resonance imaging is essential for revealing common information of a target population and unique properties of specific subjects. In brain imaging, a statistical brain atlas is often constructed using a number of healthy subjects. When tumors are present, however, it is difficult to either provide a common space for various subjects or align their imaging data due to the unpredictable distribution of lesions. Here we propose a deep learning-based image inpainting method to replace the tumor regions with normal tissue intensities using only a patient population. Our framework has three major innovations: 1) incompletely distributed datasets with random tumor locations can be used for training; 2) irregularly-shaped tumor regions are properly learned, identified, and corrected; and 3) a symmetry constraint between the two brain hemispheres is applied to regularize inpainted regions. Henceforth, regular atlas construction and image registration methods can be applied using inpainted data to obtain tissue deformation, thereby achieving group-specific statistical atlases and patient-to-atlas registration. Our framework was tested using the public database from the Multimodal Brain Tumor Segmentation challenge. Results showed increased similarity scores as well as reduced reconstruction errors compared with three existing image inpainting methods. Patient-to-atlas registration also yielded better results with improved normalized cross-correlation and mutual information and a reduced amount of deformation over the tumor regions.

Blood-Brain Barrier Transporters: Opportunities for Therapeutic Development in Ischemic Stroke

Globally, stroke is a leading cause of death and long-term disability. Over the past decades, several efforts have attempted to discover new drugs or repurpose existing therapeutics to promote post-stroke neurological recovery. Preclinical stroke studies have reported successes in identifying novel neuroprotective agents; however, none of these compounds have advanced beyond a phase III clinical trial. One reason for these failures is the lack of consideration of blood-brain barrier (BBB) transport mechanisms that can enable these drugs to achieve efficacious concentrations in ischemic brain tissue. Despite the knowledge that drugs with neuroprotective properties (i.e., statins, memantine, metformin) are substrates for endogenous BBB transporters, preclinical stroke research has not extensively studied the role of transporters in central nervous system (CNS) drug delivery. Here, we review current knowledge on specific BBB uptake transporters (i.e., organic anion transporting polypeptides (OATPs in humans; Oatps in rodents); organic cation transporters (OCTs in humans; Octs in rodents) that can be targeted for improved neuroprotective drug delivery. Additionally, we provide state-of-the-art perspectives on how transporter pharmacology can be integrated into preclinical stroke research. Specifically, we discuss the utility of in vivo stroke models to transporter studies and considerations (i.e., species selection, co-morbid conditions) that will optimize the translational success of stroke pharmacotherapeutic experiments.

Patch-based 3D U-Net and transfer learning for longitudinal piglet brain segmentation on MRI

BACKGROUND AND OBJECTIVES

In order to study neural plasticity in immature brain following early brain lesion, large animal model are needed. Because of its morphological similarities with the human developmental brain, piglet is a suitable but little used one. Its study from Magnetic Resonance Imaging (MRI) requires the development of automatic algorithms for the segmentation of the different structures and tissues. A crucial preliminary step consists in automatically segmenting the brain.

METHODS

We propose a fully automatic brain segmentation method applied to piglets by combining a 3D patch-based U-Net and a post-processing pipeline for spatial regularization and elimination of false positives. Our approach also integrates a transfer-learning strategy for managing an automated longitudinal monitoring evaluated for four developmental stages (2, 6, 10 and 18 weeks), facing the issue of MRI changes resulting from the rapid brain development. It is compared to a 2D approach and the Brain Extraction Tool (BET) as well as techniques adapted to other animals (rodents, macaques). The influence of training patches size and distribution is studied as well as the benefits of spatial regularization.

RESULTS

Results show that our approach is efficient in terms of average Dice score (0.952) and Hausdorff distance (8.51), outperforming the use of a 2D U-Net (Dice: 0.919, Hausdorff distance: 11.06) and BET (Dice: 0.764, Hausdorff distance: 25.91). The transfer-learning strategy achieves a good performance on older piglets (Dice of 0.934 at 6 weeks, 0.956 at 10 weeks and 0.958 at 18 weeks) compared to a standard training strategy with few data (Dice of 0.636 at 6 weeks, 0.907 at 10 weeks, not calculable at 18 weeks because of too few training piglets).

CONCLUSIONS

In conclusion, we provide a method for longitudinal MRI piglet brain segmentation based on 3D U-Net and transfer learning which can be used for future morphometric studies and applied to other animals.

4D magnetic resonance imaging atlas construction using temporally aligned audio waveforms in speech

Magnetic resonance (MR) imaging is becoming an established tool in capturing articulatory and physiological motion of the structures and muscles throughout the vocal tract and enabling visual and quantitative assessment of real-time speech activities. Although motion capture speed has been regularly improved by the continual developments in high-speed MR technology, quantitative analysis of multi-subject group data remains challenging due to variations in speaking rate and imaging time among different subjects. In this paper, a workflow of post-processing methods that matches different MR image datasets within a study group is proposed. Each subject's recorded audio waveform during speech is used to extract temporal domain information and generate temporal alignment mappings from their matching pattern. The corresponding image data are resampled by deformable registration and interpolation of the deformation fields, achieving inter-subject temporal alignment between image sequences. A four-dimensional dynamic MR speech atlas is constructed using aligned volumes from four human subjects. Similarity tests between subject and target domains using the squared error, cross correlation, and mutual information measures all show an overall score increase after spatiotemporal alignment. The amount of image variability in atlas construction is reduced, indicating a quality increase in the multi-subject data for groupwise quantitative analysis.

Anatomy and histology of the Göttingen minipig adenohypophysis with special emphasis on the polypeptide hormones: GH, PRL, and ACTH

The pituitary is involved in the regulation of endocrine homeostasis. Therefore, animal models of pituitary disease based on a thorough knowledge of pituitary anatomy are of great importance. Accordingly, we aimed to perform a qualitative and quantitative description of polypeptide hormone secreting cellular components of the Göttingen minipig adenohypophysis using immunohistochemistry and stereology. Estimates of the total number of cells immune-stained for adrenocorticotrophic hormone (ACTH), prolactin (PRL), and growth hormone (GH) were obtained with the optical fractionator technique using Stereo Investigator software. Moreover, 3D reconstructions of cell distribution were made. We estimated that the normal minipig adenohypophysis contains, on average, 5.6 million GH, 3.5 million PRL, and 2.4 million ACTH producing cells. The ACTH producing cells were widely distributed, while the PRL and GH producing cells were located in clusters in the central and lateral regions of the adenohypophysis. The morphology of the hormone producing cells also differs. We visualized a clear difference in the numerical density of hormone producing cells throughout the adenohypophysis. The relative proportions of the cells analyzed in our experiment are comparable to those observed in humans, primates, and rodents; however, the distribution of cells differs among species. The distribution of GH cells in the minipig is similar to that in humans, while the PRL and ACTH cell distributions differ. The volume of the pituitary is slightly smaller than that of humans. These data provide a framework for future large animal experimentation on pituitary function in health and disease.

MRI brain templates of the male Yucatan minipig

The pig is growing in popularity as an experimental animal because its gyrencephalic brain is similar to humans. Currently, however, there is a lack of appropriate brain templates to support functional and structural neuroimaging pipelines. The primary contribution of this work is an average volume from an iterative, non-linear registration of 70 five- to seven-month-old male Yucatan minipigs. In addition, several aspects of this study are unique, including the comparison of linear and non-linear template generation, the characterization of a large and homogeneous cohort, an analysis of effective resolution after averaging, and the evaluation of potential in-template bias as well as a comparison with a template from another minipig species using a "left-out" validation set. We found that within our highly homogeneous cohort, non-linear registration produced better templates, but only marginally so. Although our T1-weighted data were resolution limited, we preserved effective resolution across the multi-subject average, produced templates that have high gray-white matter contrast and demonstrate superior registration accuracy compared to an alternative minipig template.

Research Relevant Background Lesions and Conditions: Ferrets, Dogs, Swine, Sheep, and Goats

Animal models provide a valuable tool and resource for biomedical researchers as they investigate biological processes, disease pathogenesis, novel therapies, and toxicologic studies. Interpretation of animal model data requires knowledge not only of the processes/diseases being studied but also awareness of spontaneous conditions and background lesions in the model that can influence or even confound the study results. Species, breed/stock, sex, age, anatomy, physiology, diseases (noninfectious and infectious), and neoplastic processes are model features that can impact the results as well as study interpretation. Here, we review these features in several common laboratory animal species, including ferret, dog (beagle), pig, sheep, and goats.

High-resolution magnetic resonance imaging-based atlases for the young and adolescent domesticated pig (Sus scrofa)

BACKGROUND

Neurodevelopmental studies utilize the pig as a translational animal model due to anatomical and morphological similarities between the pig and human brain. However, neuroimaging resources are not as well developed for the pig as they are for humans and other animal models. We established a magnetic resonance imaging-based brain atlas at two different ages for biomedical studies utilizing the pig as a preclinical model.

NEW METHOD

Twenty artificially-reared domesticated male pigs (Sus scrofa) and thirteen sow-reared adolescent domesticated male pigs (Sus scrofa) underwent a series of scans measuring brain macrostructure, microstructure, and arterial cerebral blood volume.

RESULTS

An atlas for the 4-week-old and 12-week-old pig were created along with twenty-six regions of interest. Normative data for brain measures were obtained and detailed descriptions of the data processing pipelines were provided.

COMPARISON WITH EXISTING METHOD

Atlases at the two different ages were created for the pig utilizing newer imaging technology and software. This facilitates the performance of longitudinal studies and enables more precise volume measurements in pigs of various ages by appropriately representing the neuroanatomical features of younger and older pigs and accommodating the proportion differences of the brain over time.

CONCLUSION

Two high-resolution MRI brain atlases specific to the domesticated young and adolescent pig were created using defined image acquisition and data processing methods to facilitate the generation of high-quality normative data for neurodevelopmental research.

Creating a cross-sectional, CT and MR atlas of the Pannon minipig

PURPOSE

The purpose of this study was to create a detailed cross-sectional anatomical reference atlas of the Pannon minipig by correlating good resolution CT and MR images with high quality cross-sectional anatomical images. According to the authors knowledge, no detailed anatomical atlas is available for the minipig.

MATERIAL AND METHOD

An adult female minipig was utilized for this purpose. The animal was placed in a PVC half tube, and CT generated images of 0.6 mm slice thickness and MR images of 1.41 mm slice thickness were obtained. The images covered the whole body from the most rostral portion of the snout to the tip of the tail. The CT and MR scans were aligned with frozen anatomical sections prepared with an anatomical band saw from the same animal and significant structures were identified and labelled. The terminology employed has been referenced from the Nomina Anatomica Veterinaria 6th edition-2017.

FINDINGS AND CONCLUSIONS

The resulting atlas consists of 109 anatomical slices and the corresponding 109 CT and 109 MR scans (altogether 327 images) and the nomenclature list for each image. Although this publication contains limited images of the resulted atlas, it is a reference source for anatomy education and clinical sciences. We are of the opinion that more comprehensive and especially online available interactive atlases should be prepared using similar methodology.

Dynamic Changes in the Gut Microbiome at the Acute Stage of Ischemic Stroke in a Pig Model

Stroke is a major cause of death and long-term disability affecting seven million adults in the United States each year. Recently, it has been demonstrated that neurological diseases, associated pathology, and susceptibility changes correlated with changes in the gut microbiota. However, changes in the microbial community in stroke has not been well characterized. The acute stage of stroke is a critical period for assessing injury severity, therapeutic intervention, and clinical prognosis. We investigated the changes in the gut microbiota composition and diversity using a middle cerebral artery (MCA) occlusion ischemic stroke pig model. Ischemic stroke was induced by cauterization of the MCA in pigs. Blood samples were collected prestroke and 4 h, 12 h, 1 day, and 5 days poststroke to evaluate circulating proinflammatory cytokines. Fecal samples were collected prestroke and 1, 3, and 5 days poststroke to assess gut microbiome changes. Results showed elevated systemic inflammation with increased plasma levels of tumor necrosis factor alpha at 4 h and interleukin-6 at 12 h poststroke, relative to prestroke. Microbial diversity and evenness were reduced at 1 day poststroke compared to prestroke. Microbial diversity at 3 days poststroke was negatively correlated with lesion volume. Moreover, beta-diversity analysis revealed trending overall differences over time, with the most significant changes in microbial patterns observed between prestroke and 3 days poststroke. Abundance of the Proteobacteria was significantly increased, while Firmicutes decreased at 3 days poststroke, compared to prestroke populations. Abundance of the lactic acid bacteria Lactobacillus was reduced at 3 days poststroke. By day 5, the microbial pattern returned to similar values as prestroke, suggesting the plasticity of gut microbiome in an acute period of stroke in a pig model. These findings provide a basis for characterizing gut microbial changes during the acute stage of stroke, which can be used to assess stroke pathology and the potential development of therapeutic targets.

In vivo Population Averaged Stereotaxic T2w MRI Brain Template for the Adult Yucatan Micropig

Population averaged brain templates are an essential tool for imaging-based neuroscience research, providing investigators with information about the expected size and morphology of brain structures and the spatial relationships between them, within a demographic cross-section. This allows for a standardized comparison of neuroimaging data between subjects and provides neuroimaging software with a probabilistic framework upon which further processing and analysis can be based. Many different templates have been created to represent specific study populations and made publicly available for human and animal research. An increasingly studied animal model in the neurosciences that still lacks appropriate brain templates is the adult Yucatan micropig. In particular, T2-weighted templates are absent in this species as a whole. To address this need and provide a tool for neuroscientists wishing to pursue neuroimaging research in the adult micropig, we present the construction of population averaged (n = 16) T2-weighted MRI brain template for the adult Yucatan micropig. Additionally, we present initial analysis of T1-weighted (n = 3), and diffusion-weighted (n = 3) images through multimodal registration of these contrasts to our T2 template. The strategies used here may also be generalized to create similar templates for other study populations or species in need of template construction.

Perinatal Docosahexaenoic Acid Supplementation Improves Cognition and Alters Brain Functional Organization in Piglets

Epidemiologic studies associate maternal docosahexaenoic acid (DHA)/DHA-containing seafood intake with enhanced cognitive development; although, it should be noted that interventional trials show inconsistent findings. We examined perinatal DHA supplementation on cognitive performance, brain anatomical and functional organization, and the brain monoamine neurotransmitter status of offspring using a piglet model. Sows were fed a control (CON) or a diet containing DHA (DHA) from late gestation throughout lactation. Piglets underwent an open field test (OFT), an object recognition test (ORT), and magnetic resonance imaging (MRI) to acquire anatomical, diffusion tensor imaging (DTI), and resting-state functional MRI (rs-fMRI) at weaning. Piglets from DHA-fed sows spent 95% more time sniffing the walls than CON in OFT and exhibited an elevated interest in the novel object in ORT, while CON piglets demonstrated no preference. Maternal DHA supplementation increased fiber length and tended to increase fractional anisotropy in the hippocampus of offspring than CON. DHA piglets exhibited increased functional connectivity in the cerebellar, visual, and default mode network and decreased activity in executive control and sensorimotor network compared to CON. The brain monoamine neurotransmitter levels did not differ in healthy offspring. Perinatal DHA supplementation may increase exploratory behaviors, improve recognition memory, enhance fiber tract integrity, and alter brain functional organization in offspring at weaning.

A three-dimensional, population-based average of the C57BL/6 mouse brain from DAPI-stained coronal slices

Fluorescence imaging of immunolabeled brain slices is a key tool in neuroscience that enable mapping of proteins or DNA/RNA at resolutions not possible with non-invasive techniques, including magnetic resonance or nuclear imaging. The signal in specific regions is usually quantified after manually drawing regions of interest, risking operator-bias. Automated segmentation methods avoid this risk but require multi-sample average atlases with similar image contrast as the images to be analyzed. We here present the first population-based average atlas of the C57BL/6 mouse brain constructed from brain sections labeled with the fluorescence nuclear stain DAPI. The data set constitutes a rich three-dimensional representation of the average mouse brain in the DAPI staining modality reconstructed from coronal slices and includes an automatic segmentation/spatial normalization pipeline for novel coronal slices. It constitutes the final population-based average template, individual reconstructed brain volumes, and native coronal slices. The comprehensive data set and accompanying spatial normalization/segmentation software are provided. We encourage the community to utilize it to improve and validate methods for automated brain slice analysis.

Preclinical PET Studies of [11C]UCB-J Binding in Minipig Brain

PURPOSE

Loss of neuronal synapse function is associated with a number of brain disorders. The [¹¹C]UCB-J positron emission tomography (PET) tracer allows for in vivo examination of synaptic density, as it binds to synaptic vesicle glycoprotein 2A (SV2A) expressed in presynaptic terminals. Here, we characterise [¹¹C]UCB-J imaging in Göttingen minipigs.

PROCEDURES

Using PET imaging, we examined tracer specificity and compared kinetic models. We explored the use of a standard blood curve and centrum semiovale white matter as a reference region. We compared in vivo [¹¹C]UCB-J PET imaging to in vitro autoradiography, Western blotting and real-time quantitative polymerase chain reaction.

RESULTS

The uptake kinetics of [¹¹C]UCB-J could be described using a 1-tissue compartment model and blocking of SV2A availability with levetiracetam showed dose-dependent specific binding. Population-based blood curves resulted in reliable [¹¹C]UCB-J binding estimates, while it was not possible to use centrum semiovale white matter as a non-specific reference region. Brain [¹¹C]UCB-J PET signals correlated well with [³H]UCB-J autoradiography and SV2A protein levels.

CONCLUSIONS

[¹¹C]UCB-J PET is a valid in vivo marker of synaptic density in the minipig brain, with binding values close to those reported for humans. Minipig models of disease could be valuable for investigating the efficacy of putative neuroprotective agents for preserving synaptic function in future non-invasive, longitudinal studies.

Type of Anaesthetic Influences [11C]MDL100,907 Binding to 5HT2A Receptors in Porcine Brain

PURPOSE

Anaesthesia routinely is used in animal neuroimaging in order to reduce head motion artefacts and minimize the influence of stress. However, anaesthetics can modify radioligand binding profiles at receptor targets studied by positron emission tomography (PET). Here, we determined the effects of two routine anaesthetics on the binding of a tracer of the serotonin 5HT_2A receptors.

PROCEDURES

Isoflurane- and propofol-anesthetised Göttingen minipigs were imaged with [¹¹C]MDL100,907 PET and analysed using regions of interest and statistical non-parametric mapping.

RESULTS

The binding potentials of the tracer in striatum under isoflurane anaesthesia significantly exceeded those obtained under propofol anaesthesia, an effect we attribute to the higher blood flow in brain induced by the former.

CONCLUSIONS

Interactions between radioligands and anaesthesia must be carefully evaluated in the design of in vivo neuroimaging and interpretation of data.

Large animal ischemic stroke models: replicating human stroke pathophysiology

The high morbidity and mortality rate of ischemic stroke in humans has led to the development of numerous animal models that replicate human stroke to further understand the underlying pathophysiology and to explore potential therapeutic interventions. Although promising therapeutics have been identified using these animal models, with most undergoing significant testing in rodent models, the vast majority of these interventions have failed in human clinical trials. This failure of preclinical translation highlights the critical need for better therapeutic assessment in more clinically relevant ischemic stroke animal models. Large animal models such as non-human primates, sheep, pigs, and dogs are likely more predictive of human responses and outcomes due to brain anatomy and physiology that are more similar to humans-potentially making large animal testing a key step in the stroke therapy translational pipeline. The objective of this review is to highlight key characteristics that potentially make these gyrencephalic, large animal ischemic stroke models more predictive by comparing pathophysiological responses, tissue-level changes, and model limitations.

Selection of preclinical models to evaluate intranasal brain cooling for acute ischemic stroke

Stroke accounts for a large proportion of global mortality and morbidity. Selective hypothermia, via intranasal cooling devices, is a promising intervention in acute ischemic stroke. However, prior to large clinical trials, preclinical studies in large animal models of ischemic stroke are needed to assess the efficacy, safety, and feasibility of intranasal cooling for selective hypothermia as a neuroprotective strategy. Here, we review the available scientific literature for evidence supporting selective hypothermia and make recommendations of a preclinical, large, animal-based, ischemic stroke model that has the greatest potential for evaluating intranasal cooling for selective hypothermia and neuroprotection. We conclude that among large animal models of focal ischemic stroke including pigs, sheep, dogs, and nonhuman primates (NHPs), cynomolgus macaques have nasal anatomy, nasal vasculature, neuroanatomy, and cerebrovasculature that are most similar to those of humans. Moreover, middle cerebral artery stroke in cynomolgus macaques produces functional and behavioral deficits that are quantifiable to a greater degree of precision and detail than those that can be revealed through available assessments for other large animals. These NHPs are also amenable to extensive neuroimaging studies as a means of monitoring stroke evolution and evaluating infarct size. Hence, we suggest that cynomolgus macaques are best suited to assess the safety and efficacy of intranasal selective hypothermia through an evaluation of hyperacute diffusion-weighted imaging and subsequent investigation of chronic functional recovery, prior to randomized clinical trials in humans.

The exaggerated natriuresis of essential hypertension occurs independently of changes in renal medullary blood flow

AIMS

In patients with essential hypertension, abnormal renal sodium handling includes exaggerated natriuresis in response to extracellular volume expansion. We tested the hypothesis that exaggerated natriuresis is associated with increases in medullary and/or cortical renal blood flow.

METHODS

Patients with mild essential hypertension, but no signs of end organ damage, and control subjects were studied after 4 days of dietary standardization (<60 mmol Na⁺  day^-1 ) preceded in patients by a 14-day drug washout period. On the study day, subjects received a 4-hour intravenous volume expansion with saline (2.1% of body mass). Renal medullary and cortical blood flows were measured by PET scanning using H₂ ¹⁵ O as tracer; anatomical regions of interest were defined by contrast-enhanced CT scanning.

RESULTS

In patients, arterial blood pressure increased during volume expansion (107 ± 2-114 ± 3 mm Hg, P < 0.05) in contrast to the control group (92 ± 2-92 ± 2 mm Hg). Renal sodium excretion increased more in patients than in controls (+133 ± 31 µmol min^-1 vs +61 ± 14 µmol min^-1 , respectively, P < 0.05) confirming exaggerated natriuresis. During volume expansion, renal medullary blood flow did not change significantly in patients (2.8 ± 0.4-2.5 ± 0.5 mL (g tissue)^-1  min^-1 ) or in controls (3.2 ± 0.3-3.1 ± 0.2 mL (g tissue)^-1 min^-1 ). In control subjects, renal cortical blood flow fell during volume expansion (4.1 ± 0.3-3.7 ± 0.2 mL (g tissue)^-1  min^-1 , P < 0.05) in contrast to patients in which deviations remained insignificant.

CONCLUSION

Exaggerated natriuresis, a hallmark of essential hypertension, is not mediated by increases in regional, renal blood flow.

Electroconvulsive stimulation differentially affects [11C]MDL100,907 binding to cortical and subcortical 5HT2A receptors in porcine brain

BACKGROUND

Electroconvulsive therapy is an effective therapy of depression. We hypothesized that the beneficial effects are mediated partly by decreased serotonin receptor availability in the cortex.

AIMS

We used positron emission tomography with the serotonin 5HT_2A receptor radioligand [¹¹C]MDL100,907 to determine serotonin receptor availability in response to electroconvulsive stimulation (ECS).

METHODS

Seven Göttingen minipigs were deeply anaesthetized and imaged at baseline before the onset of ECS, and at 1-2 and 8-10 days after the end of a clinical course of ECS, consisting of 10 sessions over 3.5 weeks, and post-ECS values were compared to baseline. One additional minipig was anaesthetized over 10 sessions without ECS, as a control. We analysed images with the Ichise model for binding in cortex and hippocampus, followed by whole-brain analysis by statistical non-parametric mapping.

RESULTS

We found significantly increased binding potential of [¹¹C]MDL100,907 in the cortex and hippocampus 1-2 days after ECS, consistent with increased serotonin receptor availability compared to baseline. By 8-10 days after the final ECS, the average tracer binding had returned towards baseline. However, we also found significantly decreased tracer binding in the subcortical regions of olfactory bulb, pons, thalamus and striatum.

CONCLUSIONS

With ECS, minipigs, unlike primates but like rodents, have higher availability at cortical and hippocampal 5HT_2A receptors. Decreased tracer binding is consistent with reduced serotonin receptor availability as a differential effect of ECS on 5HT_2A receptors in subcortical regions of minipig brain.

Restoration of brain circulation and cellular functions hours post-mortem

The brains of humans and other mammals are highly vulnerable to interruptions in blood flow and decreases in oxygen levels. Here we describe the restoration and maintenance of microcirculation and molecular and cellular functions of the intact pig brain under ex vivo normothermic conditions up to four hours post-mortem. We have developed an extracorporeal pulsatile-perfusion system and a haemoglobin-based, acellular, non-coagulative, echogenic, and cytoprotective perfusate that promotes recovery from anoxia, reduces reperfusion injury, prevents oedema, and metabolically supports the energy requirements of the brain. With this system, we observed preservation of cytoarchitecture; attenuation of cell death; and restoration of vascular dilatory and glial inflammatory responses, spontaneous synaptic activity, and active cerebral metabolism in the absence of global electrocorticographic activity. These findings demonstrate that under appropriate conditions the isolated, intact large mammalian brain possesses an underappreciated capacity for restoration of microcirculation and molecular and cellular activity after a prolonged post-mortem interval.

Online histological atlas of the Göttingen minipig brain

Background

The cytoarchitecture of the Göttingen minipig telencephalon has recently been elucidated in the published article (Bjarkam et al., 2017). The aim of the current paper is to describe how such data can be presented in an online histological atlas of the Gottingen minipig brain and how this atlas was constructed.

Methods

Two sets of histological sections were used. One set was photographed in high resolution and labelled, the other set in low resolution (resized first set) was used for reference on the computer screen. The two sets of microphotographs enable, using the freely available JQuery Image Zoom Plugin, the subsequent construction of a simple HTML-based atlas web page with a “virtual microscope like” style, which allowed magnifying of the base image (low-resolution image) up to the maximum resolution of the high-resolution image. In addition, we describe how the established histological atlas can be accompanied by a set of similar T1-weighted MRI pictures.

Results and conclusion

Histological and MRI pictures are presented in atlas form on www.cense.dk/minipig_atlas/index.html. The described pipeline represent a cheap and freely available way to present histological images, in online virtual microscopic atlas form, and may thus be of general interest to anyone who would like to present histological data accordingly.

Longitudinal monoaminergic PET imaging of chronic proteasome inhibition in minipigs

Impairment of the ubiquitin proteasome system has been implicated in Parkinson’s disease. We used positron emission tomography to investigate longitudinal effects of chronic intracerebroventricular exposure to the proteasome inhibitor lactacystin on monoaminergic projections and neuroinflammation. Göttingen minipigs were implanted in the cisterna magna with a catheter connected to a subcutaneous injection port. Minipigs were imaged at baseline and after cumulative doses of 200 and 400 μg lactacystin, respectively. Main radioligands included [¹¹C]-DTBZ (vesicular monoamine transporter type 2) and [¹¹C]-yohimbine (α2-adrenoceptor). [¹¹C]-DASB (serotonin transporter) and [¹¹C]-PK11195 (activated microglia) became available later in the study and we present their results in a smaller subset of animals for information purposes only. Striatal [¹¹C]-DTBZ binding potentials decreased significantly by 16% after 200 μg compared to baseline, but the decrease was not sustained after 400 μg (n = 6). [¹¹C]-yohimbine volume of distribution increased by 18–25% in the pons, grey matter and the thalamus after 200 μg, which persisted at 400 μg (n = 6). In the later subset of minipigs, we observed decreased [¹¹C]-DASB (n = 5) and increased [¹¹C]-PK11195 (n = 3) uptake after 200 μg. These changes may mimic monoaminergic changes and compensatory responses in early Parkinson’s disease.

In vivo quantification of glial activation in minipigs overexpressing human α-synuclein

Parkinson's disease is characterized by a progressive loss of substantia nigra (SN) dopaminergic neurons and the formation of Lewy bodies containing accumulated alpha-synuclein (α-syn). The pathology of Parkinson's disease is associated with neuroinflammatory microglial activation, which may contribute to the ongoing neurodegeneration. This study investigates the in vivo microglial and dopaminergic response to overexpression of α-syn. We used positron emission tomography (PET) and the 18 kDa translocator protein radioligand, [¹¹ C](R)PK11195, to image brain microglial activation and (+)-α-[¹¹ C]dihydrotetrabenazine ([¹¹ C]DTBZ), to measure vesicular monoamine transporter 2 (VMAT2) availability in Göttingen minipigs following injection with recombinant adeno-associated virus (rAAV) vectors expressing either mutant A53T α-syn or green fluorescent protein (GFP) into the SN (4 rAAV-α-syn, 4 rAAV-GFP, 5 non-injected control minipigs). We performed motor symptom assessment and immunohistochemical examination of tyrosine hydroxylase (TH) and transgene expression. Expression of GFP and α-syn was observed at the SN injection site and in the striatum. We observed no motor symptoms or changes in striatal [¹¹ C]DTBZ binding potential in vivo or striatal or SN TH staining in vitro between the groups. The mean [¹¹ C](R)PK11195 total volume of distribution was significantly higher in the basal ganglia and cortical areas of the α-syn group than the control animals. We conclude that mutant α-syn expression in the SN resulted in microglial activation in multiple sub- and cortical regions, while it did not affect TH stains or VMAT2 availability. Our data suggest that microglial activation constitutes an early response to accumulation of α-syn in the absence of dopamine neuron degeneration.

Elevated dopamine D1 receptor availability in striatum of Göttingen minipigs after electroconvulsive therapy

Electroconvulsive therapy (ECT), a direct form of brain stimulation, is an effective antidepressant. We hypothesized that the beneficial effects of ECT are mediated by increased dopaminergic neurotransmission, in which the baseline activity of D1 receptors may predict the response to ECT. We established a novel model of brain stimulation in Göttingen minipigs based on the protocol of ECT applied in humans. With positron emission tomography (PET), we determined a measure of dopaminergic neurotransmission with the dopamine D1 receptor antagonist [¹¹C]SCH23390. Seven minipigs were anesthetized and completed PET at baseline, prior to the onset of ECT treatment, and at 24-48 h and 8-10 days after the end of a clinical course of ECT, consisting of 10 ECT sessions over a 3.5-week period. In all pigs, the binding of [¹¹C]SCH23390 to striatal D1 receptors had increased by 24-48 h after ECT, and in most, binding returned towards baseline at 8-10 days. Increased binding was observed in inverse proportion to baseline binding rates. Increased binding to dopamine D1 receptors suggests facilitation of dopaminergic neurotransmission, which may contribute to the therapeutic effects of ECT. Importantly, the baseline binding capacity of D1 receptors predicts the magnitude of increased binding, up to a maximum binding capacity.

Nigrostriatal proteasome inhibition impairs dopamine neurotransmission and motor function in minipigs

Parkinson's disease (PD) is characterized by degeneration of dopaminergic neurons in the substantia nigra leading to slowness and stiffness of limb movement with rest tremor. Using ubiquitin proteasome system inhibitors, rodent models have shown nigrostriatal degeneration and motor impairment. We translated this model to the Göttingen minipig by administering lactacystin into the medial forebrain bundle (MFB). Minipigs underwent positron emission tomography (PET) imaging with (+)-α-[¹¹C]dihydrotetrabenazine ([¹¹C]DTBZ), a marker of vesicular monoamine transporter 2 availability, at baseline and three weeks after the unilateral administration of 100 μg lactacystin into the MFB. Compared to their baseline values, minipigs injected with lactacystin showed on average a 36% decrease in ipsilateral striatal binding potential corresponding to impaired presynaptic dopamine terminals. Behaviourally, minipigs displayed asymmetrical motor disability with spontaneous rotations in one of the animals. Immunoreactivity for tyrosine hydroxylase (TH) and HLA-DR-positive microglia confirmed asymmetrical reduction in nigral TH-positive neurons with an inflammatory response in the lactacystin-injected minipigs. In conclusion, direct injection of lactacystin into the MFB of minipigs provides a model of PD with reduced dopamine neurotransmission, TH-positive neuron reduction, microglial activation and behavioural deficits. This large animal model could be useful in studies of symptomatic and neuroprotective therapies with translatability to human PD.

Radiosynthesis and evaluation of 1-substituted 3-(2,3-dihydro-1H-inden-2-yl)-6-(1-ethylpropyl)-(3R,6R)-2,5-piperazinedione derivatives as PET tracers for imaging the central oxytocinergic system

Oxytocin is known to be implicated in a variety of functions, such as learning, stress, anxiety, feeding, and pain perception. Oxytocin is also important for social memory and attachment, human bonding, sexual and maternal behaviour, and aggression. Human disorders characterized by aberrant social interactions, such as autism and schizophrenia, may also involve abnormal oxytocin levels. GSK712043, GSK711320, and GSK664004, three antagonists exhibiting subnanomolar affinity for the human oxytocin receptor (hOTR) and high selectivity over vasopressin receptors were successfully labelled with carbon-11 with suitable yields (0.5-1GBq @EOS), high molar activity (275-700 GBq/μmol), and radiochemical purities. The in vivo regional uptake of these radiotracers was determined in porcine brain. [¹¹ C]GSK711320 baseline scan showed no significant brain uptake, and limited initial uptake was observed following administration of [¹¹ C]GSK712043 or [¹¹ C]GSK664004. The [¹¹ C]GSK712043 and [¹¹ C]GSK664004 kinetics were slow and peaked at around 2%ID/L at 90 minutes post-injection. For both tracers, the distribution of activity was homogeneous throughout the brain. All the tracers showed high uptake in the pituitary gland, especially [¹¹ C]GSK711320; however, its uptake could not be blocked by pretreatment with the known OTR antagonist, L368,899. In vivo evaluation of these candidates demonstrated that they are not suitable as central OTR PET imaging agents.

Fibre Dissection and Sectional Study of the Major Porcine Cerebral White Matter Tracts

White matter anatomy is the basis for numerous applications in neurology, neurosurgery and fundamental neuroscience. Although the porcine brain is frequently used as experimental model in these fields of research, the description of its white matter is not as thorough as in the human brain or other species. Thus, the aim of this study is to describe the porcine white matter tracts in a complex manner. Two stepwise dissection protocols adapted from human anatomy were performed on six adult pig brain hemispheres prepared according to the Klingler method. Other four hemispheres were sectioned along section planes that were chosen similar to the Talairach coordinate system. As a result, three commissural tracts, seven association tracts and one projection tract were identified: corpus callosum, fornix, commissura rostralis, the short-association tracts, fasciculus longitudinalis superior, fasciculus uncinatus, fasciculus longitudinalis inferior, fasciculus occipitofrontalis inferior, cingulum, tractus mamillothalamicus and capsula interna. They were described and illustrated from multiple points of view, focusing on their trajectory, position, dimensions and anatomical relations. All in all, we achieved a three-dimensional understanding of the major tracts. The results are ready to be applied in future imagistic or experimental studies.

Quantitative [18F]Fluorodopa/PET and Histology of Fetal Mesencephalic Dopaminergic Grafts to the Striatum of MPTP-Poisoned Minipigs

The functional restoration of the dopamine innervation of striatum in MPTP-poisoned Göttingen minipigs was assessed for 6 months following grafting of fetal pig mesencephalic neurons. Pigs were assigned to a normal control group and a MPTP-poisoned group, members of which received no further treatment, or which received bilateral grafts to the striatum of tissue blocks harvested from E28 fetal pig mesencephalon with and without immunosuppressive treatment after grafting, or with additional co-grafting with immortalized rat neural cells transfected to produce GDNF. In the baseline condition, and again at 3 and 6 months postsurgery, all animals were subjected to quantitative [18F]fluorodopa PET scans and testing for motor impairment. At the end of 6 months, tyrosine hydroxylase (TH)-containing neurons were counted in the grafts by stereological methods. The MPTP poisoning persistently reduced the magnitude of k3D, the relative activity of DOPA decarboxylase in striatum, by 60%. Grafting restored the rate of [18F]fluorodopa decarboxylation to the normal range, and normalized the scores in motor function. The biochemical and functional recovery was associated with survival of approximately 100,000 TH-positive graft neurons in each hemisphere. Immunosuppression did not impart a greater recovery of [18F]fluorodopa uptake, nor were the number of TH-positive graft neurons or the volumes of the grafts increased in the immunosuppressed group. Contrary to expectation, co-grafting of transfected GDNF-expressing HiB5 cells, a rat-derived neural cell line, tended to impair the survival of the grafts with the lowest values for graft volumes, TH-positive cell numbers, behavioral scores, and relative DOPA decarboxylase activity. From the results we conclude that pig ventral mesencephalic allografts can restore functional dopamine innervation in adult MPTP-lesioned minipigs.

Cerebral 5-HT release correlates with [11C]Cimbi36 PET measures of 5-HT2A receptor occupancy in the pig brain

Positron emission tomography (PET) can, when used with appropriate radioligands, non-invasively generate temporal and spatial information about acute changes in brain neurotransmitter systems. We for the first time evaluate the novel 5-HT_2A receptor agonist PET radioligand, [¹¹C]Cimbi-36, for its sensitivity to detect changes in endogenous cerebral 5-HT levels, as induced by different pharmacological challenges. To enable a direct translation of PET imaging data to changes in brain 5-HT levels, we calibrated the [¹¹C]Cimbi-36 PET signal in the pig brain by simultaneous measurements of extracellular 5-HT levels with microdialysis and [¹¹C]Cimbi-36 PET after various acute interventions (saline, citalopram, citalopram + pindolol, fenfluramine). In a subset of pigs, para-chlorophenylalanine pretreatment was given to deplete cerebral 5-HT. The interventions increased the cerebral extracellular 5-HT levels to 2-11 times baseline, with fenfluramine being the most potent pharmacological enhancer of 5-HT release, and induced a varying degree of decline in [¹¹C]Cimbi-36 binding in the brain, consistent with the occupancy competition model. The observed correlation between changes in the extracellular 5-HT level in the pig brain and the 5-HT_2A receptor occupancy indicates that [¹¹C]Cimbi-36 binding is sensitive to changes in endogenous 5-HT levels, although only detectable with PET when the 5-HT release is sufficiently high.

Characterization of Motor and Somatosensory Evoked Potentials in the Yucatan Micropig Using Transcranial and Epidural Stimulation

Yucatan micropigs have brain and spinal cord dimensions similar to humans and are useful for certain spinal cord injury (SCI) translational studies. Micropigs are readily trained in behavioral tasks, allowing consistent testing of locomotor loss and recovery. However, there has been little description of their motor and sensory pathway neurophysiology. We established methods to assess motor and sensory cortical evoked potentials in the anesthetized, uninjured state. We also evaluated epidurally evoked motor and sensory stimuli from the T6 and T9 levels, spanning the intended contusion injury epicenter. Response detection frequency, mean latency and amplitude values, and variability of evoked potentials were determined. Somatosensory evoked potentials were reliable and best detected during stimulation of peripheral nerve and epidural stimulation by referencing the lateral cortex to midline Fz. The most reliable hindlimb motor evoked potential (MEP) occurred in tibialis anterior. We found MEPs in forelimb muscles in response to thoracic epidural stimulation likely generated from propriospinal pathways. Cranially stimulated MEPs were easier to evoke in the upper limbs than in the hindlimbs. Autopsy studies revealed substantial variations in cortical morphology between animals. This electrophysiological study establishes that neurophysiological measures can be reliably obtained in micropigs in a time frame compatible with other experimental procedures, such as SCI and transplantation. It underscores the need to better understand the motor control pathways, including the corticospinal tract, to determine which therapeutics are suitable for testing in the pig model.

The telencephalon of the Göttingen minipig, cytoarchitecture and cortical surface anatomy

During the last 20 years pigs have become increasingly popular in large animal translational neuroscience research as an economical and ethical feasible substitute to non-human primates. The anatomy of the pig telencephalon is, however, not well known. We present, accordingly, a detailed description of the surface anatomy and cytoarchitecture of the Göttingen minipig telencephalon based on macrophotos and consecutive high-power microphotographs of 15 μm thick paraffin embedded Nissl-stained coronal sections. In 1-year-old specimens the formalin perfused brain measures approximately 55 × 47 × 36 mm (length, width, height) and weighs around 69 g. The telencephalic part of the Göttingen minipig cerebrum covers a large surface area, which can be divided into a neocortical gyrencephalic part located dorsal to the rhinal fissure, and a ventral subrhinal part dominated by olfactory, amygdaloid, septal, and hippocampal structures. This part of the telencephalon is named the subrhinal lobe, and based on cytoarchitectural and sulcal anatomy, can be discerned from the remaining dorsally located neocortical perirhinal/insular, pericallosal, frontal, parietal, temporal, and occipital lobes. The inner subcortical structure of the minipig telencephalon is dominated by a prominent ventricular system and large basal ganglia, wherein the putamen and the caudate nucleus posterior and dorsally are separated into two entities by the internal capsule, whereas both structures ventrally fuse into a large accumbens nucleus. The presented anatomical data is accompanied by surface renderings and high-power macrophotographs illustrating the telencephalic sulcal pattern, and the localization of the identified lobes and cytoarchitectonic areas. Additionally, 24 representative Nissl-stained telencephalic coronal sections are presented as supplementary material in atlas form on http://www.cense.dk/minipig_atlas/index.html and referred to as S1-S24 throughout the manuscript.

An In vivo Multi-Modal Structural Template for Neonatal Piglets Using High Angular Resolution and Population-Based Whole-Brain Tractography

An increasing number of applications use the postnatal piglet model in neuroimaging studies, however, these are based primarily on T1 weighted image templates. There is a growing need for a multimodal structural brain template for a comprehensive depiction of the piglet brain, particularly given the growing applications of diffusion weighted imaging for characterizing tissue microstructures and white matter organization. In this study, we present the first multimodal piglet structural brain template which includes a T1 weighted image with tissue segmentation probability maps, diffusion weighted metric templates with multiple diffusivity maps, and population-based whole-brain fiber tracts for postnatal piglets. These maps provide information about the integrity of white matter that is not available in T1 images alone. The availability of this diffusion weighted metric template will contribute to the structural imaging analysis of the postnatal piglet brain, especially models that are designed for the study of white matter diseases. Furthermore, the population-based whole-brain fiber tracts permit researchers to visualize the white matter connections in the piglet brain across subjects, guiding the delineation of a specific white matter region for structural analysis where current diffusion data is lacking. Researchers are able to augment the tracts by merging tracts from their own data to the population-based fiber tracts and thus improve the confidence of the population-wise fiber distribution.

Computation of a high-resolution MRI 3D stereotaxic atlas of the sheep brain

The sheep model was first used in the fields of animal reproduction and veterinary sciences and then was utilized in fundamental and preclinical studies. For more than a decade, magnetic resonance (MR) studies performed on this model have been increasingly reported, especially in the field of neuroscience. To contribute to MR translational neuroscience research, a brain template and an atlas are necessary. We have recently generated the first complete T1-weighted (T1W) and T2W MR population average images (or templates) of in vivo sheep brains. In this study, we 1) defined a 3D stereotaxic coordinate system for previously established in vivo population average templates; 2) used deformation fields obtained during optimized nonlinear registrations to compute nonlinear tissues or prior probability maps (nlTPMs) of cerebrospinal fluid (CSF), gray matter (GM), and white matter (WM) tissues; 3) delineated 25 external and 28 internal sheep brain structures by segmenting both templates and nlTPMs; and 4) annotated and labeled these structures using an existing histological atlas. We built a quality high-resolution 3D atlas of average in vivo sheep brains linked to a reference stereotaxic space. The atlas and nlTPMs, associated with previously computed T1W and T2W in vivo sheep brain templates and nlTPMs, provide a complete set of imaging space that are able to be imported into other imaging software programs and could be used as standardized tools for neuroimaging studies or other neuroscience methods, such as image registration, image segmentation, identification of brain structures, implementation of recording devices, or neuronavigation. J. Comp. Neurol. 525:676-692, 2017. © 2016 Wiley Periodicals, Inc.

Miniature Swine for Preclinical Modeling of Complexities of Human Disease for Translational Scientific Discovery and Accelerated Development of Therapies and Medical Devices

Noncommunicable diseases, including cardiovascular disease, diabetes, chronic respiratory disease, and cancer, are the leading cause of death in the world. The cost, both monetary and time, of developing therapies to prevent, treat, or manage these diseases has become unsustainable. A contributing factor is inefficient and ineffective preclinical research, in which the animal models utilized do not replicate the complex physiology that influences disease. An ideal preclinical animal model is one that responds similarly to intrinsic and extrinsic influences, providing high translatability and concordance of preclinical findings to humans. The overwhelming genetic, anatomical, physiological, and pathophysiological similarities to humans make miniature swine an ideal model for preclinical studies of human disease. Additionally, recent development of precision gene-editing tools for creation of novel genetic swine models allows the modeling of highly complex pathophysiology and comorbidities. As such, the utilization of swine models in early research allows for the evaluation of novel drug and technology efficacy while encouraging redesign and refinement before committing to clinical testing. This review highlights the appropriateness of the miniature swine for modeling complex physiologic systems, presenting it as a highly translational preclinical platform to validate efficacy and safety of therapies and devices.

Neuroimaging of a minipig model of Huntington's disease: Feasibility of volumetric, diffusion-weighted and spectroscopic assessments

BACKGROUND

As novel treatment approaches for Huntington's disease (HD) evolve, the use of transgenic (tg) large animal models has been considered for preclinical safety and efficacy assessments. It is hoped that large animal models may provide higher reliability in translating preclinical findings to humans, e.g., by using similar endpoints and biomarkers.

NEW METHOD

We here investigated the feasibility to conduct MRI assessments in a recently developed tgHD model in the Libechov minipig. The model is characterized by high genetic homology to humans and a similar body mass and compartments. The minipig brain provides anatomical features that are attractive for imaging studies and could be used as endpoints for disease modifying preclinical studies similar to human HD.

RESULTS

We demonstrate that complex MRI protocols can be successfully acquired with tgHD and wild type (wt) Libechov minipigs. We show that acquisition of anatomical images applicable for volumetric assessments is feasible and outline the development of a segmented MRI brain atlas. Similarly diffusion-weighted imaging (DWI) including fiber tractography is presented. We also demonstrate the feasibility to conduct in vivo metabolic assessments using MR spectroscopy.

COMPARISON WITH EXISTING METHODS

In human HD, these MRI methods are already validated and used as reliable biomarker of disease progression even before the onset of a clinical motor phenotype.

CONCLUSIONS

The results show that the minipig brain is well suited for MRI assessments in preclinical studies. We conclude that further characterization of phenotypical differences between tg and wt animals in sufficiently powered cross-sectional and longitudinal studies is warranted.

Construction of an MRI 3D high resolution sheep brain template

Sheep is a developing animal model used in the field of neurosciences for the study of many behavioral, physiological or pathophysiological mechanisms, including for example, the central control of social behavior, brain injury or neurodegenerative diseases. However, sheep remains an orphan species in the field of magnetic resonance imaging (MRI). Therefore, a mean image (template), resulting of registrations of multiple subject images is needed and currently does not exist. In this study, we: i) computed multimodal high resolution 3D in-vivo sheep brain templates of T1 weighted (T1W) and T2W images, ii) computed gray matter (GM), white matter (WM) and cerebrospinal fluid (CSF) prior probability maps using linear and optimized non-linear registrations iii) used prior probability maps to perform the segmentation of a single brain tissues. Computed multimodal sheep brain templates showed to preserve and underline all brain patterns of a single T1W or T2W image, and prior probability maps allowed to improve the segmentation of brain tissues. Finally, we demonstrated that these templates and prior probability maps were able to be portable in other publicly available imaging software and could be used as standardized spaces for multi-institution neuroimaging studies or other neuroscience methods.

An in vivo three-dimensional magnetic resonance imaging-based averaged brain collection of the neonatal piglet (Sus scrofa)

Due to the fact that morphology and perinatal growth of the piglet brain is similar to humans, use of the piglet as a translational animal model for neurodevelopmental studies is increasing. Magnetic resonance imaging (MRI) can be a powerful tool to study neurodevelopment in piglets, but many of the MRI resources have been produced for adult humans. Here, we present an average in vivo MRI-based atlas specific for the 4-week-old piglet. In addition, we have developed probabilistic tissue classification maps. These tools can be used with brain mapping software packages (e.g. SPM and FSL) to aid in voxel-based morphometry and image analysis techniques. The atlas enables efficient study of neurodevelopment in a highly tractable translational animal with brain growth and development similar to humans.

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.

[11C]NS8880, a promising PET radiotracer targeting the norepinephrine transporter

INTRODUCTION

Positron emission tomography (PET) imaging of the norepinephrine transporter (NET) is still hindered by the availability of useful PET imaging probes. The present study describes the radiosynthesis and pre-clinical evaluation of a new compound, exo-3-(6-methoxypyridin-2-yloxy)-8-H-8-azabicyclo[3.2.1]octane (NS8880), targeting NET. NS8880 has an in vitro binding profile comparable to desipramine and is structurally not related to reboxetine.

METHODS

Labeling of NS8880 with [(11)C] was achieved by a non-conventional technique: substitution of pyridinyl fluorine with [(11)C]methanolate in a Boc-protected precursor. The isolated [(11)C]NS8880 was evaluated pre-clinically both in a pig model (PET scanning) and in a rat model (μPET scanning) and compared to (S,S)-[(11)C]-O-methylreboxetine ([(11)C]MeNER).

RESULTS

The radiolabeling technique yielded [(11)C]NS8880 in low (<10%) but still useful yields with high purity. The PET in vivo evaluation in pig and rat revealed a rapid brain uptake of [(11)C]NS8880 and fast obtaining of equilibrium. Highest binding was observed in thalamic and hypothalamic regions. Pretreatment with desipramine efficiently reduced binding of [(11)C]NS8880.

CONCLUSION

Based on the pre-clinical results obtained so far [(11)C]NS8880 displays promising properties for PET imaging of NET.

Development and characterization of a Yucatan miniature biomedical pig permanent middle cerebral artery occlusion stroke model

BACKGROUND

Efforts to develop stroke treatments have met with limited success despite an intense need to produce novel treatments. The failed translation of many of these therapies in clinical trials has lead to a close examination of the therapeutic development process. One of the major factors believed to be limiting effective screening of these treatments is the absence of an animal model more predictive of human responses to treatments. The pig may potentially fill this gap with a gyrencephalic brain that is larger in size with a more similar gray-white matter composition to humans than traditional stroke animal models. In this study we develop and characterize a novel pig middle cerebral artery occlusion (MCAO) ischemic stroke model.

METHODS

Eleven male pigs underwent MCAO surgery with the first 4 landrace pigs utilized to optimize stroke procedure and 7 additional Yucatan stroked pigs studied over a 90 day period. MRI analysis was done at 24 hrs and 90 days and included T2w, T2w FLAIR, T1w FLAIR and DWI sequences and associated ADC maps. Pigs were sacrificed at 90 days and underwent gross and microscopic histological evaluation. Significance in quantitative changes was determined by two-way analysis of variance and post-hoc Tukey's Pair-Wise comparisons.

RESULTS

MRI analysis of animals that underwent MCAO surgery at 24 hrs had hyperintense regions in T2w and DWI images with corresponding ADC maps having hypointense regions indicating cytotoxic edema consistent with an ischemic stroke. At 90 days, region of interest analysis of T1 FLAIR and ADC maps had an average lesion size of 59.17 cc, a loss of 8% brain matter. Histological examination of pig brains showed atrophy and loss of tissue, consistent with MRI, as well as glial scar formation and macrophage infiltration.

CONCLUSIONS

The MCAO procedure led to significant and consistent strokes with high survivability. These results suggest that the pig model is potentially a robust system for the study of stroke pathophysiology and potential diagnostics and therapeutics.

A neonatal piglet model for investigating brain and cognitive development in small for gestational age human infants

The piglet was investigated as a potential model for studying brain and cognitive deficits associated with being born small for gestational age (SGA). Naturally farrowed SGA (0.7-1.0 kg BW) and average for gestational age (AGA, 1.3-1.6 kg BW) piglets were obtained on postnatal day (PD) 2, placed in individual cages, and provided a nutritionally adequate milk replacer diet (285 ml/kg/d). Beginning at PD14, performance in a spatial T-maze task was assessed. At PD28, piglets were anesthetized for magnetic resonance (MR) imaging to assess brain structure (voxel-based morphometry), connectivity (diffusion-tensor imaging) and metabolites in the hippocampus and corpus callosum (proton MR spectroscopy). Piglets born SGA showed compensatory growth such that BW of SGA and AGA piglets was similar (P>0.05), by PD15. Birth weight affected maze performance, with SGA piglets taking longer to reach criterion than AGA piglets (p<0.01). Total brain volume of SGA and AGA piglets was similar (P<0.05), but overall, SGA piglets had less gray matter than AGA piglets (p<0.01) and tended to have a smaller internal capsule (p = 0.07). Group comparisons between SGA and AGA piglets defined 9 areas (≥ 20 clusters) where SGA piglets had less white matter (p<0.01); 2 areas where SGA piglets had more white matter (p<0.01); and 3 areas where SGA piglets had more gray matter (p<0.01). The impact of being born SGA on white matter was supported by a lower (p<0.04) fractional anisotropy value for SGA piglets, suggesting reduced white matter development and connectivity. None of the metabolites measured were different between groups. Collectively, the results show that SGA piglets have spatial learning deficits and abnormal development of white matter. As learning deficits and abnormalities in white matter are common in SGA human infants, the piglet is a tractable translational model that can be used to investigate SGA-associated cognitive deficits and potential interventions.