Axonal quantification of the white matter association fasciculi in cerebral hemispheres of cow (Bos taurus), pig (Sus scrofa domesticus) and rabbit (Oryctolagus cuniculus)

Cerebral white matter consists mainly of axons surrounded by myelin sheaths, which are grouped to form association, commissural, and projection fasciculi. The aim of our work was to quantify and compare under the microscope the axons of the white matter association fasciculi in the cerebral hemispheres of cow (Bos taurus), pig (Sus scrofa domesticus) and rabbit (Oryctolagus cuniculus) indirectly by identification of their myelin sheaths. The samples were taken from 30 cerebral hemispheres: 10 cow, 10 pig and 10 rabbit (15 right and 15 left). They were obtained following a protocol based on the Talairach-Tournoux coordinate system for human and primate brains. The slides were stained with Luxol Fast Blue, observed by optical microscopy, and photographed at 600x. Samples were also prepared for observation in scanning transmission electron microscopy (STEM) with osmium tetroxide. The myelin sheaths/axons were counted with the ImageJ software. Statistically significant differences in the number of myelin sheaths per 410 µm² were found in the inferior and superior longitudinal fasciculi between the left and right hemispheres of cows, with predominance of the right hemisphere; and in the inferior occipitofrontal fasciculus of the rabbit with predominance of the left hemisphere. The use of animal models for experiments in the cerebral fasciculi, especially pig, could give us a greater understanding of the behavior of demyelinating and neurodegenerative diseases in humans.