Dendritic potassium channel dysfunction may contribute to dendrite degeneration in spinocerebellar ataxia type 1

Purkinje neuron dendritic degeneration precedes cell loss in cerebellar ataxia, but the basis for dendritic vulnerability in ataxia remains poorly understood. Recent work has suggested that potassium (K+) channel dysfunction and consequent spiking abnormalities contribute to Purkinje neuron degeneration, but little attention has been paid to how K+ channel dysfunction impacts dendritic excitability and the role this may play in the degenerative process. We examined the relationship between K+ channel dysfunction, dendritic excitability and dendritic degeneration in spinocerebellar ataxia type 1 (SCA1). Examination of published RNA sequencing data from SCA1 mice revealed reduced expression of several K+ channels that are important regulators of excitability in Purkinje neuron dendrites. Patch clamp recordings in Purkinje neurons from SCA1 mice identified increased dendritic excitability in the form of enhanced back-propagation of action potentials and an increased propensity to produce dendritic calcium spikes. Dendritic excitability could be rescued by restoring expression of large-conductance calcium-activated potassium (BK) channels and activating other K+ channels with baclofen. Importantly, this treatment combination improves motor performance and mitigates dendritic degeneration in SCA1 mice. These results suggest that reduced expression of K+ channels results in persistently increased dendritic excitability at all stages of disease in SCA1, which in turn may contribute to the dendritic degeneration that precedes cell loss.