there is ample evidence from studies of peripheral isolated organs , binding of opiate receptor ligands to brain membranes and behavioural experiments that opiate receptors are not homogeneous but consist of different types such as the mu- ( = morphine ) , delta- ( = enkephalin ) , kappa- ( = ketocyclazocine ) and the epsilon- ( = beta-endorphin ) receptors .
C0006104
brain
C0004927
behavioural