The cerebellar and vestibular nuclear complexes in the turtle. II. Projections to the prosencephalon.

Prosencephalic projections from the cerebellar and vestibular nuclear complexes in the turtle Pseudemys scripta elegans were investigated with anterograde tracing. Following injections of 35S-methionine at various locations within the cerebellar and vestibular nuclear complexes, labeled ascending fibers were found to arise from the lateral cerebellar and the rostral (superior and/or dorsolateral) vestibular nuclei. The great majority of these fibers coursed within the ipsilateral ascending periventricular tract. There were possible terminations in the hypothalamosuprapeduncular region, the ovalis-complex, and the nucleus commissuralis anterior, but scarcely any indication of terminal labeling within the dorsal thalamus. The labeled fibers, however, continued rostralward, entered the lateral forebrain bundle, and terminated in the anterior dorsal ventricular ridge--in all but one case, exclusively ipsilaterally. The terminal area within the lateral division (referred to as area L) of the anterior dorsal ventricular ridge was sharply delimited, being situated ventrolateral to the visually oriented area D of the anterior dorsal ventricular ridge (Balaban and Ulinski, '81), medial to the lateral cortex, and ventral to the pallial thickening (motor pallium of Johnston, '16). The findings are compared with related ones in mammals, particularly those pertaining to telencephalic somatosensorimotor regions and their interactions with the vestibular nuclear complex and the cerebellum.