High resolution MRI anatomy of the cat brain at 3 Tesla

Clinical and biochemical abnormalities in a feline model of GM2 activator deficiency

Though it has no catalytic activity toward GM2 ganglioside, the GM2 activator protein (GM2A) is essential for ganglioside hydrolysis by facilitating the action of lysosomal ß-N-acetylhexosaminidase. GM2A deficiency results in death in early childhood due to rapid central nervous system deterioration similar to the related GM2 gangliosidoses, Tay-Sachs disease and Sandhoff disease. This manuscript further characterizes a feline model of GM2A deficiency with a focus on clinical and biochemical parameters that may be useful as benchmarks for translational therapeutic research. The GM2A deficient cat has clinical features consistent with the human condition, including isointensity of gray and white matter of the brain on T2-weighted MRI; MR spectroscopic changes of brain metabolites consistent with gliosis, neuronal injury and demyelination; rhythmical slowing of cerebral cortical activation on electroencephalography; and elevation of aspartate aminotransferase and lactate dehydrogenase in cerebrospinal fluid. Biochemically, the brain of GM2A deficient cats has storage of GM2 and GA2 ganglioside coincident with increased hexosaminidase activity toward a standard synthetic substrate. Also, the brain of GM2A deficient cats has increased levels of lyso-platelet activating factor and lyso-phosphatidylcholine, which may serve as novel biomarkers of disease progression and provide insights into pathogenic mechanisms.

Study of the Normal Crested Porcupine (Hystrix cristata) Nasal Cavity and Paranasal Sinuses by Cross-Sectional Anatomy and Computed Tomography

This study utilized CT imaging to investigate the rostral part of the head of the crested porcupine's head. By combining CT images with anatomical cross-sections, we have provided a detailed description of the structures in this area. This information could be useful for diagnosing disorders and improving their treatment in the nasal cavity and paranasal sinuses of crested porcupines.

Beyond the surface: how ex-vivo diffusion-weighted imaging reveals large animal brain microstructure and connectivity

Diffusion-weighted Imaging (DWI) is an effective and state-of-the-art neuroimaging method that non-invasively reveals the microstructure and connectivity of tissues. Recently, novel applications of the DWI technique in studying large brains through ex-vivo imaging enabled researchers to gain insights into the complex neural architecture in different species such as those of Perissodactyla (e.g., horses and rhinos), Artiodactyla (e.g., bovids, swines, and cetaceans), and Carnivora (e.g., felids, canids, and pinnipeds). Classical in-vivo tract-tracing methods are usually considered unsuitable for ethical and practical reasons, in large animals or protected species. Ex-vivo DWI-based tractography offers the chance to examine the microstructure and connectivity of formalin-fixed tissues with scan times and precision that is not feasible in-vivo. This paper explores DWI's application to ex-vivo brains of large animals, highlighting the unique insights it offers into the structure of sometimes phylogenetically different neural networks, the connectivity of white matter tracts, and comparative evolutionary adaptations. Here, we also summarize the challenges, concerns, and perspectives of ex-vivo DWI that will shape the future of the field in large brains.

Life-Limiting Peripheral Organ Dysfunction in Feline Sandhoff Disease Emerges after Effective CNS Gene Therapy

OBJECTIVE

GM2 gangliosidosis is usually fatal by 5 years of age in its 2 major subtypes, Tay-Sachs and Sandhoff disease. First reported in 1881, GM2 gangliosidosis has no effective treatment today, and children succumb to the disease after a protracted neurodegenerative course and semi-vegetative state. This study seeks to further develop adeno-associated virus (AAV) gene therapy for human translation.

METHODS

Cats with Sandhoff disease were treated by intracranial injection of vectors expressing feline β-N-acetylhexosaminidase, the enzyme deficient in GM2 gangliosidosis.

RESULTS

Hexosaminidase activity throughout the brain and spinal cord was above normal after treatment, with highest activities at the injection sites (thalamus and deep cerebellar nuclei). Ganglioside storage was reduced throughout the brain and spinal cord, with near complete clearance in many regions. While untreated cats with Sandhoff disease lived for 4.4 ± 0.6 months, AAV-treated cats lived to 19.1 ± 8.6 months, and 3 of 9 cats lived >21 months. Correction of the central nervous system was so effective that significant increases in lifespan led to the emergence of otherwise subclinical peripheral disease, including megacolon, enlarged stomach and urinary bladder, soft tissue spinal cord compression, and patellar luxation. Throughout the gastrointestinal tract, neurons of the myenteric and submucosal plexuses developed profound pathology, demonstrating that the enteric nervous system was inadequately treated.

INTERPRETATION

The vector formulation in the current study effectively treats neuropathology in feline Sandhoff disease, but whole-body targeting will be an important consideration in next-generation approaches. ANN NEUROL 2023;94:969-986.

Increased Resting-State Positron Emission Tomography Activity After Cochlear Implantation in Adult Deafened Cats

OBJECTIVES

Cochlear implants are widely used for hearing rehabilitation in patients with profound sensorineural hearing loss. However, Cochlear implants have variable.

RESULTS

and central neural plasticity is considered to be a reason for this variability. We hypothesized that resting-state cortical networks play a role in conditions of profound hearing loss and are affected by cochlear implants. To investigate the resting-state neuronal networks after cochlear implantation, we acquired 18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) images in experimental animals.

METHODS

Eight adult domestic cats were enrolled in this study. The hearing threshold of the animals was within the normal range, as measured by auditory evoked potential. They were divided into control (n=4) and hearing loss (n=4) groups. Hearing loss was induced by co-administration of ethacrynic acid and kanamycin. FDG-PET was performed in a normal hearing state and 4 and 11 months after the deafening procedure. Cochlear implantation was performed in the right ear, and electrical cochlear stimulation was performed for 7 months (from 4 to 11 months after the deafening procedure). PET images were compared between the two groups at the three time points.

RESULTS

Four months after hearing loss, the auditory cortical area's activity decreased, and activity in the associated visual area increased. After 7 months of cochlear stimulation, the superior marginal gyrus and cingulate gyrus, which are components of the default mode network, showed hypermetabolism. The inferior colliculi showed hypometabolism.

CONCLUSION

Resting-state cortical activity in the default mode network components was elevated after cochlear stimulation. This suggests that the animals' awareness level was elevated after hearing restoration by the cochlear implantation.

Diffusion tensor imaging tractography in the one-humped camel (Camelus dromedarius) brain

Introduction

Tractography is a technique used to trace the pathways of the brain using noninvasive diffusion tensor imaging (DTI) data. It is becoming increasingly popular for investigating the brains of domestic mammals and other animals with myelinated fibers but the principle of DTI can also apply for those with unmyelinated fibers. In the case of camels, DTI tractography is a promising method for enhancing current knowledge of the brain's structural connectivity and identifying white-matter tract changes potentially linked to neurodegenerative pathologies. The present study was therefore designed to describe representative white-matter tracts in the one-humped camel DTI tractography.

Methods

Post mortem DTI was used to obtain images of two one-humped camel brains using a 3 Tesla system. T2-weighted images were also acquired to identify regions of interest for each fiber tract and a fiber dissection technique was used to complement the DT images. The main association, commissural, and projection fibers were reconstructed and superimposed on T2-weighted images or fractional anisotropy maps.

Results

The results of the present study show the reconstruction of the most representative tracts, ie the cingulum, the corpus callosum and the internal capsule, in the one-humped camel brain using DTI data acquired post mortem. These DTI results were compared to those from fiber dissection.

Discussion

Anatomy of the cingulum, corpus callosum and internal capsule correlates well with the description in anatomical textbooks and appears to be similar to fibers describe in large animals. Further research will be required to improve and validate these findings and to generate a tractography atlas based on MRI and histological data, as such an atlas would be a valuable resource for future neuroimaging research.

Cranial Investigations of Crested Porcupine (Hystrix cristata) by Anatomical Cross-Sections and Magnetic Resonance Imaging

This paper aimed to describe an atlas of the crested porcupine (Hystrix cristata) head by applying advanced imaging techniques such as MRI. Furthermore, by combining the images acquired through these techniques with anatomical sections, we obtained an adequate description of the structures that form the CNS and associated structures of this species. This anatomical information could serve as a valuable diagnostic tool for the clinical evaluation of different pathological processes in porcupines, such as abscesses, skull malformations, fractures, and neoplasia.

Ex vivo susceptibility-weighted imaging anatomy of canine brain–comparison of imaging and histological sections

Now that access of large domestic mammals to high-field MRI becomes more common, techniques initially implemented for human patients can be used for the structural and functional study of the brain of these animals. Among them, susceptibility-weighted imaging (SWI) is a recent technique obtained from gradient echo (GE) imaging that allow for an excellent anatomical tissue contrast and a non-invasive assessment of brain iron content. The goal of this study was to design an optimal GE SWI imaging protocol to be used in dogs undergoing an MRI examination of the brain in a 3-Tesla scanner. This imaging protocol was applied to ex vivo brains from four dogs. The imaging protocol was validated by visual inspection of the SWI images that provided a high anatomical detail, as demonstrated by their comparison with corresponding microscopic sections. As resolvable brain structures were labeled, this study is the first to provide an anatomic description of SWI images of the canine brain. Once validated in living animals, this GE SWI imaging protocol could be easily included in routine neuroimaging protocols to improve the diagnosis of various intracranial diseases of dogs, or be used in future comparative studies aiming at evaluating brain iron content in animals.

GM1 Gangliosidosis: Mechanisms and Management

The lysosomal storage disorder, GM1 gangliosidosis (GM1), is a neurodegenerative condition resulting from deficiency of the enzyme β-galactosidase (β-gal). Mutation of the GLB1 gene, which codes for β-gal, prevents cleavage of the terminal β-1,4-linked galactose residue from GM1 ganglioside. Subsequent accumulation of GM1 ganglioside and other substrates in the lysosome impairs cell physiology and precipitates dysfunction of the nervous system. Beyond palliative and supportive care, no FDA-approved treatments exist for GM1 patients. Researchers are critically evaluating the efficacy of substrate reduction therapy, pharmacological chaperones, enzyme replacement therapy, stem cell transplantation, and gene therapy for GM1. A Phase I/II clinical trial for GM1 children is ongoing to evaluate the safety and efficacy of adeno-associated virus-mediated GLB1 delivery by intravenous injection, providing patients and families with hope for the future.

A neuroanatomical study of the feline brain using MRI and mulligan staining: functional and pathological considerations

BACKGROUND

Despite multiple studies describing accurate diagnoses using advanced neuroimaging techniques, low and mid-field magnetic resonance imaging (MRI) are still the most frequent scanners in veterinary clinics. To date, these studies in cats do not show a clear distinction of nerve centres in MRI data.

AIMS

The objective of this study is to determine the efficacy of Mulligan histological staining as a tool in facilitating the location and identification of the main structures of the feline brain in MRI. This study aims to facilitate the interpretation of MRI obtained with these types of scanners.

METHODS

A total of 10 feline brains were used. One specimen was used for MRI (T2 sequence using a 1.5T scanner). The other 9 brains were sectioned and stained with the three Mulligan staining techniques (Mulligan, Le Masurier and Robert).

RESULTS

The uptake of stain by the grey matter in these sections allowed the determination of the location and the limits of these nervous structures within the brain. The histological location of these structures was correlated with the MRI scans, leading to the successful identification of many small, indistinct nuclei.

CONCLUSION

Mulligan staining is proposed as a tool that facilitates the location of nerve structures in comparison with data from the most frequently-used MRI scanners in veterinary clinics.

Diffusion Tensor Imaging Tractography of White Matter Tracts in the Equine Brain

Tractography, a noninvasive technique tracing brain pathways from diffusion tensor magnetic resonance imaging (DTI) data, is increasingly being used for brain investigation of domestic mammals. In the equine species, such a technique could be useful to improve our knowledge about structural connectivity or to assess structural changes of white matter tracts potentially associated with neurodegenerative diseases. The goals of the present study were to establish the feasibility of DTI tractography in the equine brain and to provide a morphologic description of the most representative tracts in this species. Postmortem DTI and susceptibility-weighted imaging (SWI) of an equine brain were acquired with a 3-T system using a head coil. Association, commissural, and projection fibers, the three fiber groups typically investigated in tractography studies, were successfully reconstructed and overlaid on SWI or fractional anisotropy maps. The fibers derived from DTI correlate well with their description in anatomical textbooks. Our results demonstrate the feasibility of using postmortem DTI data to reconstruct the main white matter tracts of the equine brain. Further DTI acquisitions and corresponding dissections of equine brains will be necessary to validate these findings and create an equine stereotaxic white matter atlas that could be used in future neuroimaging research.

Delineation of the Feline Hippocampal Formation: A Comparison of Magnetic Resonance Images With Anatomic Slices

The hippocampal formation (HF) is a relevant brain structure that is involved in several neurological and psychiatric diseases. In cats, structural changes of the HF are associated with epilepsy. The knowledge of a detailed anatomy of this brain region may lead to the accurate diagnosis and development of better therapies. There are, however, discrepancies among the research findings, which may be due to different definitions being used, according to anatomical guidelines and boundaries, as well as different magnetic resonance (MR) protocols. The aim of this study is to evaluate the anatomical borders of the HF on transverse MR images and the correlated anatomic sections in three cats. The boundaries of the HF were mostly visible in the formalin fixed anatomic sections, except in the areas where the hippocampus proper exchanges into the subicular complex. Also, the delineation of the anteroventral part and the latero-caudal borders of the HF were not clearly defined. Based on our preliminary results these problems are reinforced on MR images, and further histological and anatomical research must be done to find a way to delineate these neurological structures accurately.

The Brain Anatomy of the Brown Bear (Carnivora, Ursus arctos L., 1758) Compared to That of Other Carnivorans: A Cross-Sectional Study Using MRI

In this study, we aimed to provide a neuroanatomy atlas derived from cross-sectional and magnetic resonance imaging (MRI) of the encephalon of the brown bear (Ursus arctos). A postmortem brain analysis using magnetic resonance imaging (MRI - 1,5T; a high-resolution submillimeter three-dimensional T1-3D FFE) and cross-sectional macroscopic anatomy methods revealed major embryological and anatomical subdivisions of the encephalon, including the ventricular system. Most of the internal structures were comparably identifiable in both methods. The tractus olfactorius medialis, corpus subthalamicum, brachium colliculi rostralis, fasciculus longitudinalis medialis, nuclei vestibulares, velum medullare rostrale, nucleus fastigii, fasciculi cuneatus et gracilis were identified entirely by cross-sectional macroscopic analysis. However, the glandula pinealis, lemniscus lateralis and nuclei rhaphe were visualized only with MRI. Gross neuroanatomic analysis provided information about sulci and gyri of the cerebral hemispheres, components of the vermis and cerebellar hemispheres, and relative size and morphology of constituents of the rhinencephalon and cerebellum constituents. Similarities and discrepancies in identification of structures provided by both methods, as well as hallmarks of the structures facilitating identification using these methods are discussed. Finally, we compare the brown bear encephalon with other carnivores and discuss most of the identified structures compared to those of the domestic dog, the domestic cat, Ursidae and Mustelidae families and Pinnipedia clade.

Shape of the feline cerebellum and occipital bone related to breed on MRI of 200 cats

Objectives The MRI features of the feline cerebellum and occipital bone have not previously been described in the literature. The aims of this study were three-fold. Firstly, to document variations in cerebellar shape on MRI in neurologically normal cats to support our hypothesis that crowding of the contents of the caudal fossa or herniation of the cerebellar vermis through the foramen magnum occurs frequently as an anatomical variant. Secondly, to document variations in the morphology of the occipital bone. Thirdly, to see whether these variations in shape of the feline cerebellum and occipital bone could be associated with head conformation, such as brachycephaly. Methods The imaging records of the small animal clinic at the Animal Health Trust between 2000 and 2013 were searched retrospectively to identify adult cats that had undergone high-field (1.5 T) MRI investigation which included the brain. Exclusion criteria included evidence of intracranial disease or the presence of cervical syringomyelia. Midline sagittal T2-weighted and transverse images were used to assess the occipital bone morphology and cerebellar shape, and to measure the width to length ratio of the cranial cavity. Results Fourteen different breeds were represented. A cerebellar shape consistent with crowding of the contents of the caudal fossa, or herniation through the foramen magnum was present in 40% of the entire population. Persians (recognised as a brachycephalic breed) had a higher proportion of cerebellar crowding or herniation than all other breeds. There was no significant difference in the distribution of occipital bone morphology between these breed groups. Conclusions and relevance It is important to recognise morphological variations of the feline cerebellum and occipital bone in order to avoid false-positive diagnoses of raised intracranial pressure and pathological herniation on MRI.

Stimulation Efficiency With Decaying Exponential Waveforms in a Wirelessly Powered Switched-Capacitor Discharge Stimulation System

The purpose of this study was to test the feasibility of using a switched-capacitor discharge stimulation (SCDS) system for electrical stimulation, and, subsequently, determine the overall energy saved compared to a conventional stimulator. We have constructed a computational model by pairing an image-based volume conductor model of the cat head with cable models of corticospinal tract (CST) axons and quantified the theoretical stimulation efficiency of rectangular and decaying exponential waveforms, produced by conventional and SCDS systems, respectively. Subsequently, the model predictions were tested in vivo by activating axons in the posterior internal capsule and recording evoked electromyography (EMG) in the contralateral upper arm muscles. Compared to rectangular waveforms, decaying exponential waveforms with time constants >500 μs were predicted to require 2%-4% less stimulus energy to activate directly models of CST axons and 0.4%-2% less stimulus energy to evoke EMG activity in vivo. Using the calculated wireless input energy of the stimulation system and the measured stimulus energies required to evoke EMG activity, we predict that an SCDS implantable pulse generator (IPG) will require 40% less input energy than a conventional IPG to activate target neural elements. A wireless SCDS IPG that is more energy efficient than a conventional IPG will reduce the size of an implant, require that less wireless energy be transmitted through the skin, and extend the lifetime of the battery in the external power transmitter.

Functional MRI-based identification of brain regions activated by mechanical noxious stimulation and modulatory effect of remifentanil in cats

This study was conducted to identify the brain regions corresponding to mechanical noxious stimulation in cats using functional magnetic resonance imaging (fMRI) and to investigate the modulatory effect of remifentanil on the activation of these regions. Six healthy cats were anesthetized using a constant-rate infusion of alfaxalone. Cats were allocated to one of three treatment groups: remifentanil 0 (saline), 0.25, and 0.5μg/kg/min. A 3.0-T MRI unit was used to collect fMRI data. During the fMRI scanning, mechanical noxious stimulation was applied by tail clamping. The brain regions activated by the stimulation were identified based on blood oxygenation level-dependent (BOLD) responses. The modulatory effects of remifentanil were evaluated using a region of interest (ROI) analysis comparing signal changes in each brain region. Increased activity from noxious stimulation was observed in the somatosensory area (the postcruciatus gyrus, the anterior part of the marginalis gyrus, and the anterior part of the ectomarginalis gyrus), the parietal association area (the middle part of the marginalis gyrus and the middle part of the ectomarginalis gyrus), the cingulate cortex, the hippocampus, and the cerebellum. The results of the ROI analysis indicated that activations in the somatosensory area, the cingulate cortex, the hippocampus, and the cerebellum were significantly modulated (P<0.05) by remifentanil. In cats, activation patterns evoked by mechanical noxious stimulation were observed in several brain regions thought to be involved in various aspects of pain processing, including sensory discrimination and integration, affect, and motor response. These brain responses were modulated by remifentanil.

A novel imaging method for correlating 2D light microscopic data and 3D volume data based on block-face imaging

We have developed an imaging method designated as correlative light microscopy and block-face imaging (CoMBI), which contributes to improve the reliability of morphological analyses. This method can collect both the frozen sections and serial block-face images in a single specimen. The frozen section can be used for conventional light microscopic analysis to obtain 2-dimensional (2D) anatomical and molecular information, while serial block-face images can be used as 3-dimensional (3D) volume data for anatomical analysis. Thus, the sections maintain positional information in the specimen, and allows the correlation of 2D microscopic data and 3D volume data in a single specimen. The subjects can vary in size and type, and can cover most specimens encountered in biology. In addition, the required system for our method is characterized by cost-effectiveness. Here, we demonstrated the utility of CoMBI using specimens ranging in size from several millimeters to several centimeters, i.e., mouse embryos, human brainstem samples, and stag beetle larvae, and present successful correlation between the 2D light microscopic images and 3D volume data in a single specimen.

The Sleeping Cerebellum

We sleep almost one-third of our lives and sleep plays an important role in critical brain functions like memory formation and consolidation. The role of sleep in cerebellar processing, however, constitutes an enigma in the field of neuroscience; we know little about cerebellar sleep-physiology, cerebro-cerebellar interactions during sleep, or the contributions of sleep to cerebellum-dependent memory consolidation. Likewise, we do not understand why cerebellar malfunction can lead to changes in the sleep-wake cycle and sleep disorders. In this review, we evaluate how sleep and cerebellar processing may influence one another and highlight which scientific routes and technical approaches could be taken to uncover the mechanisms underlying these interactions.

Translational models for vascular cognitive impairment: a review including larger species

BACKGROUND

Disease models are useful for prospective studies of pathology, identification of molecular and cellular mechanisms, pre-clinical testing of interventions, and validation of clinical biomarkers. Here, we review animal models relevant to vascular cognitive impairment (VCI). A synopsis of each model was initially presented by expert practitioners. Synopses were refined by the authors, and subsequently by the scientific committee of a recent conference (International Conference on Vascular Dementia 2015). Only peer-reviewed sources were cited.

METHODS

We included models that mimic VCI-related brain lesions (white matter hypoperfusion injury, focal ischaemia, cerebral amyloid angiopathy) or reproduce VCI risk factors (old age, hypertension, hyperhomocysteinemia, high-salt/high-fat diet) or reproduce genetic causes of VCI (CADASIL-causing Notch3 mutations).

CONCLUSIONS

We concluded that (1) translational models may reflect a VCI-relevant pathological process, while not fully replicating a human disease spectrum; (2) rodent models of VCI are limited by paucity of white matter; and (3) further translational models, and improved cognitive testing instruments, are required.

Comparison of Feline Brain Anatomy in 0.25 and 3 Tesla Magnetic Resonance Images

The intention of the comparison of both low and high field was to examine which anatomical brain structures of cats were visible on low field images, as in clinical veterinary practice, 3 Tesla (T) magnets were of limited availability. The research was performed on 20 European short-haired male and female cats, aged 1-3 years, with body weight of 2-4 kg. 0.25 T magnetic resonance images of neurocranium were acquired in all using T2-weighted fast spin echo sequences with repetition time (TR) of 4010 ms and echo time (TE) of 90 ms in dorsal and transverse plane, and T2-weighted fast spine echo sequences with TR of 4290 ms and TE of 120 ms in sagittal plane. Based on a detailed catalogue of feline brain structures visible at 3 T in previously published studies, it was examined which structures were visible on low field images. Anatomic structures were identified and compared to assess the reliability of diagnoses made based on low-field magnetic resonance imaging. In low-field scans, 92 structures were identified. Elements of auditory, visual, motor pathways, hippocampus and cerebral ventricular system were distinguished. Low-field as well as high-field magnetic resonance imaging support the identification of local tissue lesions, metastasis, focal ischaemia and haemorrhage, disorders associated with ventricular system dilation and hydrocephalus. It also produced accurate images of the hippocampus, which contributes to reliable diagnoses of various forms of epilepsy in cats. Due to technical limitations, a low-field scanner is unlikely to visualize microtraumas, local inflammations, small haematomas or metastatic tumours.

Mucopolysaccharidosis-like phenotype in feline Sandhoff disease and partial correction after AAV gene therapy

Sandhoff disease (SD) is a fatal neurodegenerative disease caused by a mutation in the enzyme β-N-acetylhexosaminidase. Children with infantile onset SD develop seizures, loss of motor tone and swallowing problems, eventually reaching a vegetative state with death typically by 4years of age. Other symptoms include vertebral gibbus and cardiac abnormalities strikingly similar to those of the mucopolysaccharidoses. Isolated fibroblasts from SD patients have impaired catabolism of glycosaminoglycans (GAGs). To evaluate mucopolysaccharidosis-like features of the feline SD model, we utilized radiography, MRI, echocardiography, histopathology and GAG quantification of both central nervous system and peripheral tissues/fluids. The feline SD model exhibits cardiac valvular and structural abnormalities, skeletal changes and spinal cord compression that are consistent with accumulation of GAGs, but are much less prominent than the severe neurologic disease that defines the humane endpoint (4.5±0.5months). Sixteen weeks after intracranial AAV gene therapy, GAG storage was cleared in the SD cat cerebral cortex and liver, but not in the heart, lung, skeletal muscle, kidney, spleen, pancreas, small intestine, skin, or urine. GAG storage worsens with time and therefore may become a significant source of pathology in humans whose lives are substantially lengthened by gene therapy or other novel treatments for the primary, neurologic disease.

Magnetic resonance imaging anatomy of the rabbit brain at 3 T

BACKGROUND

Rabbits are widely accepted as an animal model in neuroscience research. They also represent very popular pet animals, and, in selected clinical cases with neurological signs, magnetic resonance imaging (MRI) may be indicated for imaging the rabbit brain. Literature on the normal MRI anatomy of the rabbit brain and associated structures as well as related reference values is sparse. Therefore, it was the purpose of this study to generate an MRI atlas of the normal rabbit brain including the pituitary gland, the cranial nerves and major vessels by the use of a 3 T magnet.

RESULTS

Based on transverse, dorsal and sagittal T2-weighted (T2w) and pre- and post-contrast 3D T1-weighted (T1w) sequences, 60 intracranial structures were identified and labeled. Typical features of a lissencephalic brain type were described. In the 5 investigated rabbits, on T1w images a crescent-shaped hyperintense area caudodorsally in the pituitary gland most likely corresponded to a part of the neurohypophysis. The optic, trigeminal, and in part, the facial, vestibulocochlear and trochlear nerves were identified. Mild contrast enhancement of the trigeminal nerve was present in all rabbits. Absolute and relative size of the pituitary gland, midline area of the cranial and caudal cranial fossa and height of the tel- and diencephalon, 3rd and 4th ventricles were also determined.

CONCLUSIONS

These data established normal MRI appearance and measurements of the rabbit brain. Results provide reference for research studies in rabbits and, in rare instances, clinical cases in veterinary medicine.

Robust methods to create ex vivo minimum deformation atlases for brain mapping

Highly detailed ex vivo 3D atlases of average structure are of critical importance to neuroscience and its current push to understanding the global microstructure of the brain. Multiple single slice histology sections can no longer provide sufficient detail of inter-slice microstructure and lack out of plane resolution. Two ex vivo methods have emerged that can create such detailed models. High-field micro MRI with the addition of contrast media has allowed intact whole brain microstructure imaging with an isotropic resolution of 15 μm in mouse. Blockface imaging has similarly evolved to a point where it is now possible to image an entire brain in a rigorous fashion with an out of plane resolution of 10 μm. Despite the destruction of the tissue as part of this process it allows a reconstructed model that is free from cutting artifacts. Both of these methods have been utilised to create minimum deformation atlases that are representative of the respective populations. The MDA atlases allow us unprecedented insight into the commonality and differences in microstructure in cortical structures in specific taxa. In this paper we provide an overview of how to create such MDA models from ex vivo data.