Morphological Differences in Superior Colliculus of Adult and Juvenile African Grasscutter (Thryonomys swinderianus).

Abstract

Rodents have provided insight to specific aspects of neural organization including morphology, function, development, and evolution in mammalian species. The superior colliculus (SC) also referred to as rostral colliculus has been studied in several mammals, including nonhuman primates. The SC has been considered a visual motor integration center of the CNS. Under-explored species such as the African Grasscutter (AGC), a semi nocturnal rodent species, exhibits peculiar SC-regulated behaviors in the wild including arrest and freezing abilities in response to predators. This study morphologically assessed differences in the SC of adult and juvenile AGCs. Six AGCs (adult/ juvenile, n= 3) were procured for this study. Brains were harvested and morphologic characteristics including histology, histometry (pyramidal soma size and perimeter) and cell distribution in the SC of AGCs were assessed and quantified. Data obtained were analyzed using GraphPad Prism and computer running imaging software (AmScope and ImageJ, USA). Comparison of morphologic characteristics of SC revealed similarities and variations between the AGCs age groups: SC presented with similar histoarchitectural organization; pyramidal cell soma characteristics and cell distribution showed a significant (p<0.05) difference between the AGCs with higher mean value in the juvenile. This study has demonstrated a basic histoarchitectural organization of the superior colliculus in adult and juvenile African Grasscutter; thus, points to conserved architectural organization across rodent species. Observed differences could be attributed to variations in cellular functionality with response to developmental neurogenesis and synaptic refinement between the rodents. Findings are of potential benefit in understanding neurodevelopmental variations that influence functional capabilities across different age group.