Mesodiencephalic junction Gabaergic inputs are processed separately from motor cortical inputs in the basilar pons

Abstract

The basilar pontine nuclei (bPN) receive inputs from the entire neocortex and constitute the main source of mossy fibers to the cerebellum. Despite their critical position in the cortico-cerebellar pathway, it remains unclear if and how the bPN process inputs. An important unresolved question is whether the bPN strictly receives excitatory inputs or also receives inhibitory inputs. In the present study, we identified the mesodiencephalic junction as a prominent source of GABAergic afferents to the bPN. We combined optogenetics and whole-cell patch clamp recordings and confirmed that the bPN indeed receives monosynaptic GABA inputs from this region. Furthermore, we found no evidence that these inhibitory inputs converge with motor cortex (M1) inputs at the single neuron level. We also found no evidence of any connectivity between bPN neurons, suggesting the absence of a local circuit. Finally, rabies tracings revealed that GABAergic MDJ neurons themselves receive prominent inputs from neocortical output neurons. Our data indicates that inhibition from the MDJ, and excitation from the neocortex remain separate streams of information through the bPN. It is therefore unlikely that inhibition in the bPN has a gating function, but rather shapes an appropriate output of the bPN during behavior.