(Poole, UK) and were of the highest purity available. The radioligands: [3H]DAMGO, [3H][Ile5,6]deltorphin-2, and [3H]nor-binaltorphimine ([3H]nor-BNI) were from Perkin Elmer (Massachusetts, USA). Tested compounds: KGOP01, Dmt-DALDA, SBL-OPNK-4, SBL-OPNK-5, SBL-OPNK-6,...