Guest lecture by Zong Peng Sun (Uni Tübingen)BrainLinks-BrainTools is inviting all members, colleagues and friends to a guest lecture given by Dr. Zong Peng Sun from the Eberhard-Karls-Universität Tübingen:
Cerebellar control of different types of eye movements Intracellular trafficking and secretion of CDNF
Part 1: Cerebellar control of different types of eye movements - from cerebellar cortex to cerebellar nuclei: Visual perception is one of the most important sources of information entering the brain. To achieve clear vision, two major types of eye movements, saccades and pursuits, must be precisely controlled. It is known that oculomotor vermis (OMV) of the cerebellar cortex and its major target, caudal fastigial nucleus (cFN), are dedicated to saccades and smooth pursuit eye movements (SPEM). Furthermore, it has been shown that individual neurons in OMV and cFN can be involved in both tasks; however, it remains vague how the same neuron contributes to controlling these two different types of movements considering their dramatically different kinematics. To address this question, we applied the multiple regression analysis to the electrophysiological data recorded from Purkinje cells in OMV and neurons in cFN. We found that the cerebellar cortical computational principles for saccades and pursuits are different at the level of OMV. Surprisingly, the kinematic preference is different in cFN compared with that in OMV, which indicates that cFN is not just a relay and that some local computation is performed in cFN. Given that the cerebellar substrates, both OMV and cFN, are shared by saccades and SPEM, it is reasonable to speculate that learning process within one type of eye movement would affect the kinematics of the other. The aim of another study of ours was to test behaviorally whether an adaptation of saccades influences the SPEM initiation. We observed no effect of the consistent saccadic adaptation on the SPEM initiation, little change of SPEM parameters were observed during a random saccadic error paradigm. We interpret these findings as an evidence for greatly distinct neural substrates that are responsible for saccade and SPEM adaptation which has little overlap at the level of cerebellar structures. Additionally, our eyes are not still even during fixation. Microsaccades, small saccades having an amplitude of <1° down to a few minutes of arc, can be seen during fixation. Recent studies have demonstrated that microsaccades are well controlled goal-directed movements, ensuring that the retinal image is moved from the foveal periphery into the rod-free foveola. We are interested to know how cerebellar nuclei contribute to the precisely controlled eye movement. Our work showed that individual cFN neurons process control signals for saccades that are continuous across micro- and macrosaccades. Furthermore, response features of cFN neurons suggested a neural mechanism linking microsaccades and the optimization of visual fixation.
Part 2: Intracellular trafficking and secretion of CDNF: Cerebral dopamine neurotrophic factor (CDNF) is a recently discovered evolutionary conserved protein. The role of CDNF in protecting and restoring the function of dopaminergic neurons in the animal model of Parkinson’s disease (PD) makes it an important candidate for the treatment of PD. However, the mechanism underlying the secretion of CDNF remains unclear. In this study, we found that CDNF could be secreted primarily via the regulated secretory pathway in PC12 cells. The glycosylation of CDNF is not required for its secretion. Moreover, we identified a key subdomain and an important peptide sequence in CDNF which are important for its intracellular localization and secretion.
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