An opiate binding site in the rat brain is highly selective for 4,5-epoxymorphinans

Science  16 Sep 1983:
Vol. 221, Issue 4616, pp. 1198-1201
DOI: 10.1126/science.6310750


In vitro binding studies have demonstrated the existence of multiple opiate receptor types. An additional site in the rat brain (termed the lambda site) is distinct from the established types by its selectivity for 4,5-epoxymorphinans (such as naloxone and morphine). While the lambda site displays a high affinity for naloxone in vivo and in vitro in fresh brain membrane homogenates, these sites rapidly convert in vitro to a state of low affinity. The regional distribution of the lambda site in the brain is strikingly different from that of the classic opiate receptor types.