Purkinje cells and their target neurons operate at different coding schemes depending on the olivocerebellar module involved
Prof. Dr. Chris De Zeeuw
The output of the cerebellar cortex is provided by a layer of Purkinje cells (PCs) that deliver inhibitory projections onto cells in the cerebellar nuclei, which in turn represent the final output of the cerebellum. The overall physiological characteristics of PCs have traditionally been considered to be homogeneous. Recently, we have shown in awake mice that spiking activity of Purkinje cells (PCs), the sole output cells of the cerebellar cortex, differs between olivocerebellar modules when the animals are at rest. At rest, simple spike and complex spike frequencies co-vary concomitantly in that complex spike firing frequency is high when the simple spike firing frequency is high and vice versa. Indeed the simple spike frequency at rest is predominantly determined by the intrinsic activity of PCs, which correlates with the differential expression and distribution of proteins involved in energy consumption, glutamate clearance and effector channels of metabotropic glutamate receptors. The level of complex spike activity follows that of the simple spikes due to the PC projections to the GABAergic cells in the cerebellar nuclei that inhibit the olivary neurons establishing the baseline climbing fiber activity. The simple spike frequency at rest is not influenced by genetically blocking the excitatory or inhibitory input to PCs, neither in cells firing at high frequency nor in those showing lower firing frequencies at rest. Instead affecting these inputs to PCs does influence the regularity of simple spike firing. Thus, our results indicate that different olivo-cerebellar modules operate at different frequencies, which depend on the intrinsic constitution of PCs, and that this property is relevant for all cerebellar functions.