Three-dimensional reconstruction of the rubrocerebellar premotor network of the turtle

Neuroanatomical studies have demonstrated that the organization of the reptilian rubrocerebellar limb premotor network is similar to that of mammals. This network is composed of prominent recurrent connections among the red nucleus, lateral cerebellar nucleus and lateral reticular nucleus. In this paper the rubrocerebellar system of the turtle was three-dimensionally reconstructed to permit detailed examination of its anatomical organization. Each nucleus and its major efferent pathway was imaged and reconstructed from separate anatomical cases. Section images were used to draw tissue boundaries, mark cell positions and locate axonal trajectories. For each nucleus, drawings of section images containing labeled cells were stacked in the rostrocaudal direction using anatomical landmarks, and a graphic model of the surface was constructed using the method of triangulation. An ellipsoid of equal concentration was computed for each nucleus to ascertain their three-dimensional boundaries and location within the brainstem. To examine the entire rubrocerebellar network, a template of the turtle brainstem and cerebellum was constructed. The component nuclei of the rubrocerebellar network and their axonal projections were then spatially warped onto the template reconstruction on a section by section basis. The final three-dimensional reconstruction of the turtle rubrocerebellar limb premotor network could be rotated in space, allowing proper visualization of the anatomical details of this system. Furthermore, we were able to mathematically section through the reconstruction to obtain brainstem slices with differing orientations and thickness.