Neuroanatomical Studies on the Tectum of Some Selected Rodent Species

Comparative neurobiology provides empirical evidence to neuroscientists for the classification of biological species based on diversities or similarities of their neuroanatomical characteristics. Rodents are imperative neuroscience research tool, beneficial in elucidating brain pathologies and possible therapies where human subjects cannot be used. Tectum, a region of the midbrain, is composed of a set of colliculi responsible for initial processing of sensory information from the eyes and ears. This study comparatively assessed neuroanatomical features of the superior and inferior colliculi of some selected rodent species: Wistar rat, Guinea pig (Cavia porcellus) and rabbit (Oryctolagus cuniculus). Nine male rodents (n=3/species) were obtained for the study. Morphologic and microscopic assessments including body and brain weights, histologic and histochemical, and histometric examinations were conducted. Data obtained were compared amongst species using statistical (IBM SPSS v23) and imaging (AmScope, US and ImageJ, US) softwares. Results revealed remarkably (p<0.05) higher values for body and brain weights with rabbits, but lower for organosomatic index amongst the species. Microscopy revealed similarities, with slight variations in cytoarchitechture of the colliculi across species. Histometric characteristics of the colliculi revealed difference (p<0.05) in pyramidal neuronal soma size amongst the species. However, cell density in the colliculi was not different when compared. In conclusion, there exist similarities and differences in the neuroanatomic features of the tectum amongst the rodent species. These similarities are demonstrated in the morphologic and histologic features and, variations in the histometric characteristics. These findings demonstrate similar ancestry in the species and, could be beneficial in neuroscience related fields.

Key Words: Cytoarchitecture, Cell density, Histometry, Colliculi, Organosomatic index