Neuroanatomy and Brain Histological Atlas of the South American Plains Vizcacha

Brains could be classified as lissencephalic or gyrencephalic according to the presence of sulci and gyri. In recent years, studies of the physiology and anatomy of wild species like the South American plains vizcacha, Lagostomus maximus, a hystricomorph rodent that inhabits Argentina, Bolivia, and Paraguay, have shown an increased interest. However, very few reports have investigated its neuroanatomy. This chapter describes the neuroanatomy and histology of the brain of the plains vizcacha and establishes the location of its main brain areas and nuclei. Adult vizcacha shows a 14 g weight, 3.8 cm length, and 3.2 cm width gyrencephalic brain, with a dorsoventrally flattened pyramidal shape. It shows a deep longitudinal fissure between both hemispheres and three pairs of sulci in the cortex (the rostral-lateral, the intraparietal, and the transversal sulci). For a histological inspection of the location of different areas and nuclei, the brain was divided into 12 coronal sections with a rostrocaudal orientation (according to Sigman’s plates), and Nissl and Klüver Barrera, together with immunohistochemistry and immunofluorescence histological techniques, were used. Around the 4th coronal section, the rostral diencephalic septum plate has the preoptic area and regionalized striatum with the presence of an internal capsule, among other areas and nuclei. Then, in the 6th coronal section, the rostral diencephalon plate has the thalamic reticular and paraventricular nuclei and the hypothalamic median eminence among others. More caudally, in the 7th coronal section, the caudal diencephalon plate has the midbrain occupying the largest portion of this section, together with the mammillary structures and the mid-hippocampus formation with well-developed subiculum, horns of Ammon, and dentate gyrus. Finally, at the level of the 8th coronal section, the mesencephalon main dopaminergic structures substantia nigra and ventral tegmental area, connected by the interpeduncular nucleus, are found. The present chapter represents a significant advancement in our understanding of the neuroanatomy and histology of the South American plains vizcacha being a valuable tool for future neurological studies. In addition, the findings shed light on distinctive structural features of the brain, which are closely linked to its colonial and burrowing way of life.