PURKINJE CELL COMPLEX SPIKES AND NEUROPROTECTIVE MOLECULAR IDENTITY IN SPINOCEREBELLAR ATAXIA TYPE 13

Spinocerebellar Ataxia Type 13 (SCA13) is an autosomal dominant neurodegenerative disorder caused by point mutations in KCNC3, which encodes the high-voltage–gated potassium channel subunit Kv3.3. The R420H mutation, identified in a large Filipino kindred disrupts the voltage-sensing domain of Kv3.3, and is associated with late-onset progressive cerebellar ataxia and degeneration of cerebellar Purkinje neurons, the sole output neurons of the cerebellar cortex. To investigate disease mechanisms, we generated a novel CRISPR-Cas9 knock-in mouse line expressing the human R420H mutation.
Purkinje neurons integrate excitatory inputs from parallel fiber and climbing fiber synapses, generating functionally distinct action potentials: simple spikes and complex spikes, respectively. Both firing modes require Kv3.3 mediated fast membrane repolarization. Using whole-cell patch-clamp recordings in acute cerebellar slices from mice aged 1-6 months, we observed a progressive prolongation of simple spike duration in homozygous R420H Purkinje neurons compared with wild-type littermates. Notably, Purkinje neurons located in the Floccular and Parafloccular node did not degenerate nor exhibit changes in simple spike duration despite expressing the R420H mutation in Kv3.3.
By immunohistochemical analyses we identified a robust expression of a molecular marker in the Flocculus/Paraflocculus node and other surviving clusters of neurons throughout the Cerebellum. This suggests a neuroprotective function associated with this molecular Purkinje Neuron identity. We aim to characterize the simple and complex spike properties of Purkinje neurons in both genotypes to determine whether electrophysiological differences correlate with the molecular marker and its associated neuroresistance.