In vivo analysis of synaptic activity in cerebellar nucleineurons unravels the efficacy of excitatory inputs

It is commonly agreed that the main function of the cerebellar system is to providewell-timed signals used for the execution of motor commands or prediction of sensory inputs.This function is manifested as a temporal sequence of spiking that should be expressed in thecerebellar nuclei (CN) projection neurons. Whether spiking activity is generated by excitationor release from inhibition is still a hotly debated issue. In an attempt to resolve this debate,we recorded intracellularly from CN neurons in anaesthetized mice and performed an analysisof synaptic activity that yielded a number of important observations. First, we demonstratethat CN neurons can be classified into four groups. Second, shape-index plots of the excitatoryevents suggest that they are distributed over the entire dendritic tree. Third, the rise time ofexcitatory events is linearly related to amplitude, suggesting that all excitatory events contributeequally to the generation of action potentials (APs). Fourth, we identified a temporal patternof spontaneous excitatory events that represent climbing fibre inputs and confirm the resultsby direct stimulation and analysis on harmaline-evoked activity. Finally, we demonstrate thatthe probability of excitatory inputs generating an AP is 0.1 yet half of the APs are generated byexcitatory events. Moreover, the probability of a presumably spontaneous climbing fibre inputgenerating an AP is higher, reaching a mean population value of 0.15. In view of these results, themode of synaptic integration at the level of the CN should be re-considered.

Yarden-Rabinowitz Y., Yarom Y.
Year of publication
J Physiol 595.17 (2017) pp 5945–5963