Comparative Neuroanatomical Characterization of Ventral Midbrain Grey Matter of Some Small Laboratory Mammals

Empirical assessments of the similarities and variations of neurobiological structures in animals are the basis of comparative neuroanatomy. Animal models including small laboratory mammals are indispensable tools for neuroanatomical research. The mammalian midbrain has been described with grey matter structures including red nucleus (RN), and substantia nigra (SN) involved in important brain functions like regulation of motor and related activities. This study comparatively characterized the neuroanatomical features of the ventral midbrain grey matter (RN and SN) of three small laboratory mammals: Wistar rat, guinea pig (Cavia porcellus) and rabbit (Oryctolagus cuniculus). The laboratory mammals (n=3/species) were obtained and weighed. The brains of species were harvested and measured, and sections of RN and SN were processed for histologic and histometric assessments. Data obtained were compared among species using statistical (IBM SPSS v21) and imaging (MPP, AmScope, and ImageJ, US) software. Results revealed higher (p<0.05) values for body and brain weights with rabbits. Histologic examinations of the RN and SN pars compacta (SNc) revealed similarities and some variations in the species; RN and SNc presented with a variety of cell morphologies. The histometric characteristics (pyramidal cell soma area and perimeter) of the RN showed no significant difference between the species. However, SNc histometric characteristics were different (p<0.05) with lower mean values for guinea pigs. In conclusion, the assessed small laboratory mammalian species demonstrated similarities and variations in neuroanatomical characteristics of the ventral midbrain grey matter (SN and RN). Similarities of cytoarchitectural characteristics could be attributed to the commonality of the species’ ancestry as mammals.