Fig. 2. Generation of mice lacking α^2A-adrenergic (α^2A-KO) and α^2B-adrenergic (α^2B-KO) receptors. (a ) Schematic representation of the murine α^2A- and α^2B-KO alleles that were targeted for deletion by insertion of a neomycin cassette. Gray areas  indicate location of the sequences encoding for transmembrane regions of the α²-receptors. Arrowheads  show location of polymerase chain reaction primers used for genotyping. (b ) Representative polymerase chain reactions to detect wild-type (WT) and KO alleles for the α^2A(upper panel ) and the α^2B-receptor (lower panel ). (c ) α^2AB-KO mice were derived from crosses of double heterozygous mice at the expected Mendelian frequency.