Role of HCN Channels in Motor Dysfunctions
1 DZNE Bonn
Hyperpolarization-activated cyclic nucleotide-gated (HCN) cation channels conduct the h-current (Ih), an important regulator of cellular excitability and plasticity. HCN channel dysfunction has been associated with various neurodevelopmental disorders; these disorders have motor dysfunctions as their most common comorbidity. To investigate the role of Ih in motor development in a subunit-independent manner, we developed a conditional transgenic mouse model expressing a dominant-negative HCN subunit (HCN-DN) in forebrain projection neurons. Lifelong expression of HCN-DN impaired somatomotor development and caused persistent locomotor hyperactivity in adult mice. This hyperactivity could be ameliorated by D2 receptor blockers, suggesting a dopaminergic component to the phenotype.
To identify disordered neuronal activity underlying these motor dysfunctions, we performed in-vivo silicon probe (Neuronexus, Neuropixels 1.0) recordings from sensorimotor cortex and dorsolateral striatum in adult head-fixed mice free to move a Mobile HomeCage (Neurotar). For post hoc cell identification of direct/indirect medium spiny neurons (d/iMSNs) in the striatum, we crossed HCN-DN mice with Adora-2a rM3Ds mouse (Jax Lab) to chemogenetically activate DREADDs in iSPNs using Compound 21. Detected spikes were clustered into single units (KiloSort, Klusters, Phy) which were then classified into different neuronal types (CellExplorer and custom-made MATLAB).
The analyses revealed alterations in firing rate properties for different cell types in HCN-DN-mutants compared to control animals during locomotion and immobility. Mutant mice had overall reduced cortical firing rates irrespective of locomotion state and cell type. In contrast, striatal MSNs and interneurons had varying degrees of firing rate changes, which were more pronounced during immobility