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Somatic calcium imaging reveals simple spike activity of cerebellar Purkinje cells : applications and limitations to in vivo research

Abstract : The cerebellum is thought to coordinate movement by processing sensorimotor information in the cerebellar cortex before relaying its output to other brain structures. Since all information processed by the cerebellar cortex converges on Purkinje cells (PCs), the ability to record the spiking output from identified populations of these cells is crucial for understanding cerebellar processing. In this thesis, we demonstrate that somatic calcium imaging in Purkine cells is a faithful reporter of sodium-dependent simple spike (SS) activity, with almost no interference coming from the dendritic calcium fluctuations of complex spikes (CS). This enabled us to optically record changes in SS firing rates from Purkinje cells in brain slices and in vivo. In cerebellar slices, the simultaneous recordings of Purkinje cell groups revealed a striking spatial organization of pauses in Purkinje cell activity inside a sagittal plane. The source of this organization is shown to be the presynaptic gamma-Aminobutyric acid producing (GABAergic) network, since blocking ionotropic GABA receptors (GABAARs) abolishes the synchrony. Concerning in vivo experiments, we tested the feasibility of this imaging method to infer Purkinje cell activity in combination with the genetically encoded calcium indicator GCaMP6f. Despite the nonlinear binding kinetics of GCaMP6f with calcium, we developed a method that allows a quantitative estimate of changes in Purkinje cell SS firing activity. This method is susceptible to open new avenues for research on cerebellar cortex output in vivo.
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Jorge Enrique Ramírez Buriticá. Somatic calcium imaging reveals simple spike activity of cerebellar Purkinje cells : applications and limitations to in vivo research. Tissues and Organs [q-bio.TO]. Université Sorbonne Paris Cité, 2018. English. ⟨NNT : 2018USPCB030⟩. ⟨tel-02493058⟩

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