Anatomical Demonstration of the Cognitive Ability of the Juvenile African Giant Pouched Rat (Cricetomys gambianus – Waterhouse, 1840)

Abstract

Cognitive ability in animals is determined using indices such as Encephalisation Quotient (EQ), relative brain weight, glial quotient and neuronal index. In this study, the cognitive ability of the juvenile African giant pouched rat was determined using the EQ and relative brain weight. Brain samples were routinely extracted from thirty-two juvenile (16 males and 16 females, respectively) rats and fixed in freshly prepared 10% buffered formalin. The nose-rump length, tail length absolute and relative brain weights were determined according to standard technique while the EQ was computed using the Martin’s formula. Structural observations revealed a diamond shaped lissencephalic cerebral cortex with the caudal colliculi exposed from the dorsal transverse fissure of the intact brain. An EQ of 0.75 was deduced for the juvenile African giant pouched rat from the study. Sexual dimorphic analysis revealed mean relative brain weight of 6.64 ± 0.30 and 6.90 ± 0.22 and mean EQ of 0.71 ± 0.06 and 0.78 ± 0.02, for the male and female juveniles respectively. The mean differences between the males and females were not statistically significant (P > 0.05). However, there was a significant negative correlation between nose-rump length and EQ (R2 = 0.66; p < 0.05), nose-rump length and relative brain length (r2 = 0.49; p < 0.05) as well as nose-rump length and relative weight of cerebrum (R2 = 0.61; p < 0.05). The results were compared with that of other age groups of the same rodent and other juvenile rodents. It was concluded that the juvenile African giant pouched rat may be a better choice for memory and cognitive studies than the adult.