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Insight into the Anatomy of the Poor Visual system in the Adult African Giant Rat ( Cricetomys gambianus Waterhouse)
Author(s) -
Alawa Judith Nkiruka,
Amuzor Stella,
Sambo Samaila J,
Alawa Clement Barikuma
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.779.3
Subject(s) - anatomy , ciliary body , retina , biology , cornea , iris (biosensor) , nocturnal , lens (geology) , retinal , neuroscience , biochemistry , computer security , computer science , biometrics , ecology , paleontology
The African giant rat (AGR) is microptic with poor day time vision, known to be nocturnal and depends on olfactory, auditory and tactile systems. This study investigated the morphometry, morphology and histology of the eyes of male and female adult AGRs to ascertain the anatomical basis of these adaptations. Results showed that the eye of the AGR is intermediate between nocturnal and diurnal mammals sharing close similarities in several features between them. The eye showed normal mammalian characteristics with mean diameter of 3.3 ± 0.02 mm and constituted 2% of body weight. Histologically, the lens is large and round occupying most of the vitreous chamber. The ciliary body is small with branching processes and lacking circular constrictor or radial dilator muscle bundles necessary for accommodation. This is suggestive of an inability to accommodate. The cornea is large relative to the eye size which is compensatory to increase visual sensitivity to low light levels and consistent with nocturnal vision. The AGR lacks Harderian glands and shows a separation between the posterior pigmented iris and the ciliary body which are features similar to the human eye. The retina showed characteristic lamination consistent with ability to detect low levels of light. This is evidenced by thick inner plexiform layer, thick outer nuclear layer and lack of fovea suggestive of poor visual acuity. Also observed was a high concentration of rods photoreceptors suggestive of peripheral vision and lack of colour as well as a monolayer of ganglionic cells suggestive of a small optic nerve. These unique anatomical features of the eyes of the AGR give credence to the poor vision and microptic nature of the AGR and these may have evolved as an adaptation to their dark habitats. Support or Funding Information Ahmadu Bello University, Zaria, Kaduna State. Nigeria