Dorsal raphe nuclei/ventrolateral periaqueductal grey and cerebellar fastigial nucleus interactions modulate danger response during fear learning

Fear learning and extinction are crucial for survival and lead to disease, if impaired. Recently, it has been demonstrated that the cerebellum is bidirectionally controlling fear learning via the fastigial nucleus (FN) to ventrolateral periaqueductal grey (vlPAG) pathway in rodents (Frontera et al., 2020, Lawrenson et al., 2022). The mechanisms of the cerebellar influence on fear learning still need to be elucidated. Using a combined anterograde/retrograde viral tracing strategy, we targeted a dorsal raphe nuclei (DRN)/vlPAG pathway that projects on the FN. In extracellular recordings during a modified pavlovian fear conditioning paradigm, we found facilitated threat responses in both vlPAG/DRN and the FN. We also identified cross-correlated pairs between FN and DRN/vlPAG neurons, in which vlPAG/DRN neurons seem to drive the facilitated danger response in FN, while potentially forming a functional loop between DRN/vlPAG and FN. We are now further characterizing this potential midbrain-cerebellar loop in fear learning and extinction.