Histomorphological Characterization of the Visual Pathway Structures of an African Rodent Species (Cricetomys gambianus - Waterhouse 1840; African Giant Rats)

Sensory information for vision is transmitted from the eye (retina) through the optic nerves to other brain regions, in mammalian species including rodents. The Cricetomys gambianus (African giant rat, AGRs) share several structural morphological similarities with higher mammals including humans, particularly in their nervous system and sensory processing mechanisms. This study assessed the histomorphological features of visual pathway structures in AGR. Four male AGRs (926 ± 133.0 g) were captured from the wild and used for this study. The AGRs were sedated, perfused transcardially, decapitated, and dissected to expose the intact eyeball and brain for histological processing and assessment. The AGR eyeball and brain sections were stained with Hematoxylin and Eosin (H & E) and assessed at varying magnifying powers using a light microscope. Sections of AGR eyeball demonstrated three distinct layers: the sclera-corneal, uvea, and retina layers. The retina revealed laminarizations with different cellular orientations and densities. Brain sections revealed a tear-shaped, pseudo-laminarized structure, the dorsal lateral geniculate nucleus, with transversing fasciculi through its parenchyma oriented mediolaterally. The midbrain section revealed a rostrally-situated superior colliculus (SC) that relates caudally with the inferior colliculus. The SC parenchyma revealed two distinct layers; narrow superficial (dorsal) and wide deep (ventral) layers. The primary visual cortex revealed a laminar organization having six cellular layers. Histomorphological features of structures of the visual pathway showed similarity with that of other rodent species providing evolutionary advantage for survival in its natural habitat. Hence a potential neuroscience research tool.

Key Words: African giant rats; Brain; Laminarization; Retina; Optic nerve