Identification and distribution of neurons presumed to give rise to cerebellar climbing fibers in turtle. A retrograde axonal flow study using radioactive D-aspartate as a marker.

Radioactive D-aspartate and horseradish peroxidase were injected into the cerebellar cortex in turtle, Pseudemys scripta elegans. While neurons retrogradely labeled with horseradish peroxidase were found in various regions of the spinal cord and brainstem, labeled cells following aspartate injections were only observed in circumscribed regions of the caudal medulla. In rat it was recently reported that climbing fibers, but no other cerebellar afferents, were retrogradely labeled with D-aspartate (Wiklund et al.12). It is suggested that the aspartate-positive neurons in turtle also give rise to climbing fibers.