Loss of HCN/h channel function in mouse forebrain during a critical period of striatal synaptogenesis results in somatomotor dysfunctions and antipsychotics-responsive hyperactivity

Andrea Merseburg1, Steffi Sandke2, Igor Jakovcevski1, Axel Neu3, Zhuo Huang4, Mala Shah4, Stephan Marguet1, Ricardo Melo Neves1, Jochen Roeper5, Fabio Morellini6, Dirk Isbrandt1

1 German Center for Neurodegenerative Diseases (DZNE), 53175 Bonn, Germany
2 Dept. Internal Med. III, University Hospital Heidelberg, 69120 Heidelberg, Germany
3 Center for Molecular Neurobiology, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany
4 Department of Pharmacology, The School of Pharmacy, University of London, London WC1N 1AX, United Kingdom
5 Institute for Neurophysiology, Goethe University Frankfurt, 60590 Frankfurt, Germany
6 Center for Molecular Medicine Cologne, University of Cologne, 50937 Cologne, Germany

Hyperpolarization-activated, cyclic nucleotide-gated subunits (HCN) 1 to 4 mediate Ih, which is suggested to contribute to development-dependent network activity and maturation of the CNS. De novo mutations in HCN1 are associated with early infantile epileptic encephalopathies (EIEE) and neurodevelopmental co-morbidities. HCN channels are subject to developmental regulation, including subunit composition, subcellular location and underlying current properties. Yet, due to limitations of knockout mouse models targeting specific subunits of the HCN1-4 channel family and lacking the ability of temporal regulation, studies aimed at investigating Ih during brain development are sparse. Here, we present an approach to functionally and conditionally ablate Ih, independent of subunit composition, by controlling the expression of a dominant-negative HCN subunit with the Tet-off doxycycline system and CaMKIIα promoter in forebrain projection neurons. We show that lifelong Ih loss is associated with impaired somatomotor development in neonatal mutants and psychomotor disturbances, including behavioral hyperactivity paired with stereotyped circling, and motor deficits in adult mutants. Notably, restricting Ih loss to an early postnatal period had more severe consequences than lifelong ablation of Ih in that these mice also exhibited cognitive symptoms, indicating the presence of developmental changes that are not reversible by simple re-introduction of Ih. The locomotor hyperactivity could not be ameliorated by the administration of the psychostimulant methylphenidate which is a common treatment for ADHD hyperactivity. Instead, mutants responded to antipsychotics. In addition, chemogenetic activation of indirect-pathway medium spiny neurons in the striatum of mutant animals strongly ameliorated the locomotor hyperactivity. Our results suggest that developmental Ih loss in forebrain projection neurons caused persistent changes in cortico‑basal ganglia circuits, resulting in a phenotype that is reminiscent of neurodevelopmental co-morbidities in disorders such as EIEE.