the presence of multiple opioid binding sites in human fetal brain at 20 weeks gestational age was determined using the following selective tritiated ligands : d-ala2 , n-mephe4 , gly-ol5-enkephalin ( dago ) for the mu-type , d-pen2 , d-pen5-enkephalin ( dpdp ) for the delta-type and u-69,593 for the kappa-type .
C0525773
dago
C0014298
enkephalin