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Cracking the Nucleo-Olivary Code

Periodic Reporting for period 1 - CraNOC (Cracking the Nucleo-Olivary Code)

Reporting period: 2016-03-01 to 2018-02-28

For animals and humans to be successful in their environments, their motor and cognitive behavior must be adjusted to the constantly changing reality at a millisecond-timescale. For example, it is fairly simple for a brain to determine which muscles need to be activated to catch a falling object, but much harder to determine when and for how long. Without correct timing of the executive brain functions, as happens in some neurological disorders such as ataxia, the individual is unable to produce smooth and accurate movements and will also have difficulties with a range of cognitive functions requiring orchestration of distinct mental operations. The tripartite olivo-cerebellar system (OCS), which is formed by the inferior olive (IO), cerebellar cortex (CCTX) and cerebellar nuclei (CN), is considered critical for generating proper timing for many motor and cognitive operations. Interestingly, all three areas, IO, CTX and CN, have intrinsic oscillatory properties and together they constitute a reverberating microcircuit, beating with well-timed responses to requests from the sensorimotor system. The ultimate timing of the output of this system, by which it imposes its effects upon the rest of the brain, is mediated by the CN. Indeed, decades of research on the OCS has resulted in detailed concepts as to how it may generate and control computations with high temporal complexity. However, due to methodological difficulties the function of the nucleo-olivary (NO) pathway, which links the CN with the IO, has been neglected, hindering completion of the cerebellar theory and thereby reaching additional goals in motor disorder-related clinical research. The first aim of the project was to develop means and protocols for precise, reliable and efficient control and experimentation on the NO pathway, so that its function in healthy and diseased brain could be elucidated.
During the initial part of the project (March 2016 - late 2016), two aspects of the nucleo-olivary system were examined. Notably, in May 2016 the grantee (Dr. Uusisaari) was informed of being accepted as a research faculty in OIST, Japan; therefore, starting from summer 2016 the project works were gradually shifted so that the main lab work is done by other researchers at Erasmus MC, while the grantee retains the coordinating position even after the MSCA grant is terminated.

First, we screened a library of AAV viral vectors (purchased from Penn Vector core) for their suitability for targeting specific pathways in the olivo-cerebellar system and introducing optogenetic tools into the neurons, as well as tested specific mutant mouse lines with knock-in cre expression. The work involved targeted viral injections into the inferior olive and cerebellar nuclei in juvenile and adult mice, anatomical confirmation with confocal microscopy as well as pilot experiments demonstrating the function and usability of the optogenetic tools in awake, behaving animals. These tools, still unpublished, as well as the protocols for their use are now established, and they are being used in experiments examining the function of the OCS.
The optogenetic toolbox developed during the project will open new opportunities for novel experimental questions related to the olivo-cerebellar system computation to be addressed. Due to the short period of work, only the initial aims (developing the tools for future optogenetic work) have been extensively worked on.