Western blot analysis from the brain stem of PDE4D- and PDE4B-deficient mice and their wild-type littermates. Left: Expression of PDE4D proteins in the brain stem of PDE4D-deficient mice (–/–) and their wild-type littermates (+/+). A mixture of recombinant PDE4D3 and PDE4D5 (Rec) was loaded for control. Right: Expression of PDE4B proteins in the brain stem of PDE4B-deficient mice (–/–) and their wild-type littermates (+/+).