Comparative morphology of the visual and auditory reflex centres in the African grasscutter (Thryonomys swinderianus – Temminck, 1827)

Abstract

The African grasscutter is a nocturnal rodent, currently bred as a minilivestock, and research model. The present study was aimed at describing the structure of the auditory and visual reflex centres, with a view to understanding the nocturnal behaviour of the rodent. The rostral and caudal colliculi of the mesencephalic tectum were harvested from neonate, juvenile and adult African grasscutters and subjected to basic neuro-anatomical techniques. On each postnatal period, the corpora quadrigemina was bound rostrally by the 3rd ventricle and caudally by the 4th ventricle, and the caudal colliculus was grossly bigger than the rostral colliculus. The heights of the rostral and caudal colliculi in the neonates were 6.38 ± 0.28 mm and 8.78 ± 0.08 mm, respectively, and the difference was significant (P < 0.05). The values in the juveniles were 5.94 ± 0.21 mm and 11.45 ± 0.17 mm, respectively, and the difference was significant (P < 0.05). The values in the adults were 8.08 ± 0.35 mm and 16.16 ± 0.30 mm, respectively, and the difference was also significant (P < 0.05). The relative weight of rostral colliculus in the adult was significantly (P < 0.05) higher than that of the neonates, but not the juveniles. The relative weight of the caudal colliculus in the adults was significantly (P < 0.05) higher than that of the juveniles. In conclusion, the relatively bigger caudal colliculi, than the rostral colliculi, observed at all postnatal periods studied, suggests a more acute auditory than visual ability in the African grasscutter.