Comparative cytoarchitecture of the midbrain colliculi of defined age groups in the African giant pouched rat (Cricetomys gambianus)

Abstract

Background: The rostral and caudal colliculi of mammalian midbrain are pivotal to vision and audition, respectively. Cytoarchitecture of these midbrain  colliculi in neonate, juvenile and adult African giant pouched rats is dearth.

Objective: This study compared the histology of the nuclei, neurons and  laminations of the colliculi in these age groups.

Methods: Thirty-six captive African giant pouched rats consisting of twelve neonates, juveniles and adults were used. Thickness of the histologic layers of  the rostral colliculi and lengths of the central nucleus of the caudal colliculi were compared among the groups.

Results: the rostral colliculus  composed of an outermost stratum zonale, middle stratum griseum superficiale and innermost stratum griseum  profundus; migratory immature neurons of radial glial cells were observed in the stratum zonale of neonates, which disappeared in juveniles and adults;  the stratum griseum superficiale of neonates was characterized of already formed neurites, similar to those of the juveniles and adults. However, this  layer in adults had more oligodendrocytes than in juveniles. There was significant increase in thickness of the stratum griseum superficiale and stratum  griseum profundus, with increasing age (P < 0.05). The caudal colliculus contained a central nucleus, dorsal and lateral cortices, with significant increase  in the length of the central nucleus with increasing age (P < 0.05); there was transformation of fibre shaft in the lateral cortex of neonates into a mixture  of chain like and marshy matrix in the juveniles which completely disappeared in adults, indicative of mature lateral cortex in the later.

Conclusion: The adult African giant pouched rat may have the best auditory and visual senses, followed by juvenile. The neonate has the least acuity of  these senses.