Ex vivo diffusion-weighted MRI tractography of the Göttingen minipig limbic system.

The limbic system encompasses a collection of brain areas primarily involved in higher cognitive and emotional processing. Altered function in the limbic circuitry may play a major role in various psychiatric disorders. This study aims to provide a high-quality ex vivo diffusion-weighted MRI (DWI) tractographic overview of the Göttingen minipig limbic system pathways, which are currently not well described. This may facilitate future translational large animal studies. The study used previously obtained post-mortem DWI scans in 3 female Göttingen minipigs aging 11-15 months. The tractography performed on the DWI data set was made using a probabilistic algorithm, and regions of interest (ROIs) were defined in accordance with a histological atlas. The investigated pathways included the fornix, mammillothalamic tract, stria terminalis, stria medullaris, habenulo-interpeduncular tract, and cingulum. All the investigated limbic connections could be visualized with a high detail yielding a comprehensive three-dimensional overview, which was emphasized by the inclusion of video material. The minipig limbic system pathways displayed using tractography closely resembled what was previously described in both human studies and neuronal tracing studies from other mammalian species. We encountered well-known inherent methodological challenges of tractography, e.g., partial volume effects and complex white matter regions, which may have contributed to derouted false-positive streamlines and the failure to visualize some of the minor limbic pathway ramifications. This underlines the importance of preexisting anatomical knowledge. Conclusively, we have, for the first time, provided an overview and substantial insight of the Göttingen minipig limbic system.

The porcine corticospinal decussation: A combined neuronal tracing and tractography study.

BACKGROUND: Pigs and minipigs are increasingly used as non-primate large animal models for preclinical research on nervous system disorders resulting in motor dysfunction. Knowledge of the minipig pyramidal tract is therefore essential to support such models. AIM AND METHODS: This study used 5 female Göttingen minipigs aging 11-15 months. The Göttingen minipig corticospinal tract was investigated, in the same animals, with in vivo neuronal tracing and with postmortem diffusion weighted MRI tractography to provide a thorough insight in the encephalic distribution of this primary motor pathway and its decussation at the craniocervical junction. RESULTS: The two methods similarly outlined the course of the pyramidal tract from its origin in the motor cortex down through the internal capsule to the craniocervical junction, where both methods displayed an axonal crossover at the pyramid decussation. The degree of crossover was quantified with unbiased stereology, where 81-93% of the traced corticospinal fibers crossed to the contralateral spinal cord. Accordingly, in the upper cervical spinal cord the corticospinal tract is primarily distributed in the contralateral lateral funiculus and in close relation to the gray matter, wherein some direct terminations on large ventral column gray matter neurons could be identified. DISCUSSION: The combination of neuronal tracing and tractography exploited the strengths of the respective methods to gain a better understanding of the encephalic distribution and craniocervical decussation of the Göttingen minipig corticospinal tract. Moreover, a quantification of the crossing fibers was obtained from the tracing data, which was not possible with tractography. Our data indicate that the porcine corticospinal system is quite lateralized down to the investigated upper cervical levels. However, further elucidation of this point will require a full examination of the corticospinal tracing pattern into the caudal spinal cord combined with an analysis of the direct versus indirect termination pattern on the lower motor neurons.

A fiducial skull marker for precise MRI-based stereotaxic surgery in large animal models.

BACKGROUND: Stereotaxic neurosurgery in large animals is used widely in different sophisticated models, where precision is becoming more crucial as desired anatomical target regions are becoming smaller. Individually calculated coordinates are necessary in large animal models with cortical and subcortical anatomical differences. NEW METHOD: We present a convenient method to make an MRI-visible skull fiducial for 3D MRI-based stereotaxic procedures in larger experimental animals. Plastic screws were filled with either copper-sulfate solution or MRI-visible paste from a commercially available cranial head marker. The screw fiducials were inserted in the animal skulls and T1 weighted MRI was performed allowing identification of the inserted skull marker. RESULTS: Both types of fiducial markers were clearly visible on the MRÍs. This allows high precision in the stereotaxic space. COMPARISON WITH EXISTING METHOD: The use of skull bone based fiducial markers gives high precision for both targeting and evaluation of stereotaxic systems. There are no metal artifacts and the fiducial is easily removed after surgery. CONCLUSION: The fiducial marker can be used as a very precise reference point, either for direct targeting or in evaluation of other stereotaxic systems.

Exposure of the Pig CNS for Histological Analysis: A Manual for Decapitation, Skull Opening, and Brain Removal.

Pigs have become increasingly popular in large-animal translational neuroscience research as an economically and ethically feasible substitute to non-human primates. The large brain size of the pig allows the use of conventional clinical brain imagers and the direct use and testing of neurosurgical procedures and equipment from the human clinic. Further macroscopic and histological analysis, however, requires postmortem exposure of the pig central nervous system (CNS) and subsequent brain removal. This is not an easy task, as the pig CNS is encapsulated by a thick, bony skull and spinal column. The goal of this paper and instructional video is to describe how to expose and remove the postmortem pig brain and the pituitary gland in an intact state, suitable for subsequent macroscopic and histological analysis.