Induction of Long-Term Depression at Flocculus Purkinje Cells in Juvenile Mice

Abstract

Cerebellum is a brain region important in motor control. Cerebellum can be subdivided into cerebrocerebellum, spinocerebellum and vestibulocerebellum. Spinocerebellum receives inputs from spinal cord and auditory system, while vestibulocerebellum receives vestibular inputs from semicircular canals and vestibular nuclei. Vestibular ocular reflex (VOR) learning is usually used to test cerebellar functions. Flocculus, a part of vestibulocerebellum, is supposed to be the initial place of VOR learning and long-term depression (LTD) is the underlying mechanism for it. However, LTD had not been observed directly in floccular slices. Here whole-cell recordings were made at lobules III to V of cerebellar vermis and lobule X and flocculus, which are known to be the spinocerebellum and vestibulocerebellum, respectively. Data were analyzed them for LTD and other electrophysiological properties. First, AMPA receptor-mediated fast excitatory post-synaptic current (EPSC) showed no difference in input-output curve and paired pulse ratio among three groups, meaning they have similar presynaptic properties. Second, Second, flocculus showed metabotropic glutamate receptor (mGluR)-mediated slow EPSC measured in the presence of NBQX and its amplitude was not significantly different from that in lobule III to V. However, lobule X which is also a part of vestibulocerebellum as flocculus, showed much smaller amplitude in slow EPSC. Third, it was possible to record LTD at flocculus with similar amplitude of LTD, while much smaller LTD was recorded from lobule X. The result suggests that LTD is normally induced at flocculus and it can be underlying cellular mechanisms for VOR learning.