Viral and Non-viral Tracing of Cerebellar Corticonuclear and Vestibulorubral Projections in the Mouse

Previously reported multisynaptic tracing of the mouse eyeblink circuit [1] revealed characteristic spatiotemporal patterns in cerebellar labelling that suggested well-defined corticonuclear pathways. This project further explores the connectivity of these circuits in the cerebellum and in downstream motor structures. Cerebellar cortical projections to the deep cerebellar nuclei were traced with retrograde virus, which was allowed to propagate through one infection cycle (synapse). Further downstream motor circuits were traced with electroporated dextran dye and fluorescent microbeads. Distinct, coherent pathways were uncovered from ansiform lobule to the dentate nucleus, from the lobule simplex to the anterior interpositus, from anterior vermis to posterior interpositus, and from posterior vermis to fastigial nucleus. There were no crossprojections observed between the corticonuclear projections to different cerebellar nuclei. The first two pathways have been implicated in classical conditioning, while the third is likely involved in cerebellar modulation of reflexes, as well as in the control and enhancement of conditioned responses. Little is known about the fourth, and its potential motor outputs were further explored by tracing from the fastigiovestibular tract to the red nucleus and vice versa, establishing the existence of a previously unexplored vestibulorubral pathway in the mouse.