Huntington Disease/physiopathology; Neostriatum/cytology; Neostriatum/physiopathology; Neurons/physiology; Potassium Channels/physiology; Age Factors; Analysis of Variance; Animals; Cesium/pharmacology; Disease Models, Animal; Dose-Response Relationship, Radiation; Electric Stimulation; Gene Expression Regulation/physiology; Huntington Disease/genetics; Huntington Disease/metabolism; Immunohistochemistry/methods; In Vitro Techniques; Membrane Potentials/drug effects; Membrane Potentials/physiology; Membrane Potentials/radiation effects; Mice; Mice, Transgenic; Neostriatum/metabolism; Neurons/drug effects; Neurons/radiation effects; Patch-Clamp Techniques/methods; Potassium Channel Blockers/pharmacology; Potassium Channels/drug effects; Potassium Channels/radiation effects; Tetraethylammonium/pharmacology