CAST/EiJ (stock #000928) mice were purchased from the Jackson Laboratory. The hg mutation was originally identified in a selected outcross line [22] and has been introgressed onto a B6 background via nine backcrosses to create the HG strain. HG mice used in this experiment were from the 17th or later generation of inbreeding. Mice were housed in polycarbonate cages under controlled conditions of temperature (21°C ± 2°C), humidity (40–70%) and lighting (14 h light, 10 h dark, lights on at 7 AM), and managed according to the guidelines of the American Association for Accreditation of Laboratory Animal Care (AAALAC).