Inferior olive: All ins and outs

Abstract

The inferior olive provides all climbing fibers to the Purkinje cells in the cerebellar cortex and thereby has a strong impact on cerebellar output. As a consequence, the integration of inputs to olivary neurons as well as their intrinsic properties are critical for cerebellar function. In this chapter, all issues that are relevant for their ultimate function are addressed. This chapter starts by reviewing developmental aspects such as the origin and migratory routes of inferior olivary neurons and a description of their axonal outgrowth into climbing fibers innervating Purkinje cells. Subsequently, a detailed description of the olivary subdivisions and the ultrastructure of their neuropil is provided. This is characterized by the presence of dendro-dendritic gap junctions located in glomeruli and by the consistently combined excitatory and inhibitory innervation of their coupled spines. Furthermore, the electrophysiological behavior of olivary neurons is described and discussed. Finally, these unique properties are integrated in cellular and system models. Both type of models show that the inferior olive is very well able to control both rate coding and spatiotemporal pattern coding of their postsynaptic target neurons in the cerebellar cortex, cerebellar nuclei, and vestibular nuclei. Abnormalities in their firing properties can contribute to syndromes such as Ataxia, palatomyoclonus, and possibly also autism.