Neuroanatomy and brain histological atlas of the South American plains vizcacha

Abstract

Brains could be classified as lissencephalic or gyrencephalic according to thepresence of sulci and gyri. In recent years, studies of the physiology and anatomyof wild species like the South American plains vizcacha, Lagostomus maximus,a hystricomorph rodent that inhabits Argentina, Bolivia, and Paraguay, haveshown an increased interest. However, very few reports have investigated itsneuroanatomy. This chapter describes the neuroanatomy and histology of thebrain of the plains vizcacha and establishes the location of its main brain areasand nuclei. Adult vizcacha shows a 14 g weight, 3.8 cm length, and 3.2 cmwidth gyrencephalic brain, with a dorsoventrally flattened pyramidal shape.It shows a deep longitudinal fissure between both hemispheres and three pairsof sulci in the cortex (the rostral-lateral, the intraparietal, and the transversalsulci). 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 withimmunohistochemistry and immunofluorescence histological techniques, wereused. Around the 4th coronal section, the rostral diencephalic septum plate hasthe preoptic area and regionalized striatum with the presence of an internalcapsule, among other areas and nuclei. Then, in the 6th coronal section, therostral diencephalon plate has the thalamic reticular and paraventricular nucleiand the hypothalamic median eminence among others. More caudally, in the7th coronal section, the caudal diencephalon plate has the midbrain occupyingthe largest portion of this section, together with the mammillary structuresand the mid-hippocampusformation with well-developed subiculum, hornsof Ammon, and dentate gyrus. Finally, at the level of the 8th coronal section,the mesencephalon main dopaminergic structures substantia nigra and ventraltegmental area, connected by the interpeduncular nucleus, are found. Thepresent chapter represents a significant advancement in our understanding ofthe neuroanatomy and histology of the South American plains vizcacha beinga valuable tool for future neurological studies. In addition, the findings shedlight on distinctive structural features of the brain, which are closely linked toits colonial and burrowing way of life.