Olivocerebellar connections in the Atlantic stingray

The morphology of the cerebellum in cartilaginous fishes varies from a smooth, relatively simple bi-lobed structure, to an undulated and complex multi-lobed configuration. Little is known about the anatomical connections and functions of the cerebellum in species with a complex cerebellar morphology, such as the Atlantic stingray, which possesses a tri-lobed cerebellum. The forces that drove this elaboration of the cerebellum in stingrays remain unclear. The inferior olive is a major neural center that is found in all vertebrates. Studies in mammals and other vertebrates indicate that the inferior olive has strong neural connections with, and functional influence on, the cerebellum. Therefore, the elaboration of the cerebellar structure in the Atlantic stingray may have been paralleled by an elaboration of the inferior olive inputs to the cerebellum in this species. In the present study the organization of the neural connections between the inferior olive and the three different lobes of the cerebellum in the Atlantic stingray were revealed using neuroanatomical tracing techniques. Compared to studies of the olivo-cerebellar connections in elasmobranch species with a bi-lobed cerebellar structure, there appears to have been an increase in complexity of these connections in the Atlantic stingray. The results of this research contribute to our understanding of the evolution of the brain in cartilaginous fishes, as well as other vertebrates.