The animals were randomly divided into four treatments : D ( 10 g kg ( -1 ) of dexmedetomidine ) , DM ( dexmedetomidine 10 g kg ( -1 ) and methadone 0.5 mg kg ( -1 ) ) ; DMO ( dexmedetomidine 10 g kg ( -1 ) and morphine 0.5 mg kg ( -1 ) ) , and DT ( dexmedetomidine 10 g kg ( -1 ) and tramadol 2 mg kg ( -1 ) ) .