Abstract
Circuitry of the cerebellar cortex is regionally and functionally specialized. Unipolar brush cells (UBCs), and Purkinje cell (PC) synapses made by axon collaterals in the granular layer, are both enriched in areas that control balance and eye movement. Here, we find a link between these specializations in mice: PCs preferentially inhibit metabotropic glutamate receptor type 1 (mGluR1)-expressing UBCs that respond to mossy fiber (MF) inputs with long lasting increases in firing, but PCs do not inhibit mGluR1-lacking UBCs. PCs inhibit about 29% of mGluR1-expressing UBCs by activating GABAA receptors (GABAARs) and inhibit almost all mGluR1-expressing UBCs by activating GABAB receptors (GABABRs). PC to UBC synapses allow PC output to regulate the input layer of the cerebellar cortex in diverse ways. Based on optogenetic studies and a small number of paired recordings, GABAAR-mediated feedback is fast and unreliable. GABABR-mediated inhibition is slower and is sufficiently large to strongly influence the input-output transformations of mGluR1-expressing UBCs.
Highlights
Different lobules of the cerebellar cortex are engaged in diverse motor and non-motor behaviors
Annotated Purkinje cell (PC) synapses were colored in cyan, and the PC and molecular layers are shown in grey based on the synaptophysin-tdTomato signal (Figure 1B)
PC to Unipolar brush cells (UBCs) synapses provides a new way for PC outputs to dynamically regulate the temporal transformations by UBC populations within the input layer
Summary
Different lobules of the cerebellar cortex are engaged in diverse motor and non-motor behaviors Mossy fibers (MFs) provide excitatory inputs to granule cells (Delvendahl & Hallermann, 2016; DiGregorio et al, 2002; Huang et al, 2013; Sotelo, 2008), which in turn excite Purkinje cells (PCs) that provide the output of the cerebellar cortex. Regional synaptic and cellular specializations exist beyond this basic circuit motif, presumably to meet the computational demands associated with specific behaviors (DiÑO et al, 1999; Guo et al, 2016; Kozareva et al, 2020; Sekerková et al, 2014; Suvrathan et al, 2016)
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