Relationship between age and brainstem allometry in the African grasscutter (Thryonomys swinderianus Temminck, 1827).

Allometric values of brainstem structures were evaluated in African grasscutters Thryonomys swinderianus (n = 27). Brain samples were extracted from 9 animals each of 3 days (neonates), 72 days (juveniles) and 450 days of age (adults). The midbrain, pons and medulla oblongata were separated from each brain sample and dimensions and weights obtained. The weights of the midbrain in the neonate, juvenile and adult African grasscutters were 0.33 g ± 0.01 g, 0.47 g ± 0.01 g and 0.93 g ± 0.02 g, respectively. The increase from neonate to juvenile (p = 0.002) and adult (p = 0.003) was significant. The pons lengths in the neonate, juvenile and adult were 2.05 mm ± 0.05 mm, 3.86 mm ± 0.05 mm and 4.16 mm ± 0.22 mm, respectively. There was a significant increase in the length of the pons from the neonate to the juvenile (p = 0.002), but the increase from the juvenile to the adult period was not significant (p = 0.263). There was also a significant (p < 0.05) increase in the weights and lengths of the medulla oblongata from neonate to juvenile and adult periods. In adults, the nose-rump length and the length of the medulla were significantly negatively correlated (r² = 0.47; p = 0.043). The present study concluded that the postnatal development of some brainstem structures in the African grasscutter varies with age.

Functional morphology of the brain of the African giant pouched rat (Cricetomys gambianus) Waterhouse, 1840).

A gross morphological study of the brain of the African giant pouched rat (Cricetomys gambianus Waterhouse, 1840) was undertaken in order to document its normal features and assess the structure-function paradigm. The study was conducted by direct observation of 29 adult African giant pouched rats' brains. In the telencephalon, the cerebral cortex was devoid of prominent gyri and sulci, but the large olfactory bulb and tract relaying impulses to the olfactory cortex were very prominent. The large size of the olfactory bulb correlated with the established sharp olfactory acuity of the rodent. In the mesencephalic tectum, the caudal colliculi were bigger than the rostral colliculi, indicating a more acute sense of hearing than sight. In the metencephalon, the cerebellar vermis, the flocculus and the paraflocculus were highly coiled and, thus, well developed. The myelencephalon revealed a better organised ventral surface than dorsal surface; the cuneate fascicle, the intermediate sulcus and the lateral sulcus were not evident on the dorsal surface, but there were clearly visible pyramids and olivary prominence on the ventral surface. In conclusion, the highly coiled cerebellar vermis, flocculus and paraflocculus, as well as the conspicuous pyramids and olivary prominence are indicative of a good motor coordination and balance in the African giant pouched rat.