Fastigiovestibular projections in the rat: retrograde tracing coupled with gammaamino-butyric acid and glutamate immunohistochemistry.

In this study, a double labeling technique using retrograde tracing with protein-gold complex (gold-HRP) in conjunction with a gammaamino-butyric acid (GABA) and glutamate immunohistochemical procedure was performed to identify GABA (GABA-IR) and glutamate (Glu-IR) immunoreactive neurons in the cerebellar fastigial nucleus (FN) that projects to the vestibular nuclei (VN). The results show that FN neurons projecting to the VN consist of both GABA-IR and Glu-IR neurons with a predominance of glutamatergic ones. Because GABAergic neurons in the cerebellar nuclei project to the inferior olive (IO), double retrograde labeling experiments were performed with injections of gold-HRP in the IO and of biotilynated dextran amine in the VN. This showed that the GABA-IR fastigiovestibular neurons project by axon collaterals to both the VN and the IO.