The neuropeptide cerebellin is a marker for two similar neuronal circuits in rat brain

We report here that the neuropeptide cerebellin, a known marker of cerebellar Purkinje cells, has only one substantial extracerebellar location, the dorsal cochlear nucleus (DCoN). By reverse-phase high-performance liquid chromatography and radioimmunoassay, cerebellum and DCoN in rat were found to contain similar concentrations of this hexadecapeptide. Immunocytochemistry with our rabbit antiserum C1, raised against synthetic cerebellin, revealed that cerebellin-like immunoreactivity in the cerebellum is localized exclusively to Purkinje cells, while in the DCoN, it is found primarily in cartwheel cells and in the basal dendrites of pyramidal neurons. Some displaced Purkinje cells were also stained. Although cerebellum and DCoN receive their inputs from different brain regions, their organizations show several similarities, with many neuronal cell types present in one having their presumed homologue in the other. Cerebellin is present in Purkinje and cartwheel cells throughout the cerebellum and the DCoN without site predilection. This should be viewed together with recent data indicating that these two classes of neurons share a similar fate in several murine mutations ("nervous," "lurcher," "Purkinje cell degeneration," and "staggerer"). This situation leads us to conclude that cerebellin represents a marker for a small number of spatially related neuronal cell classes, and that it may play a role in an as yet unknown aspect of a circuit function worthy of further exploration.