Subtraction autoradiography of opiate receptor subtypes in human brain

Opiate binding sites in sections of human brain were labelled with [3H]etorphine. Many brain areas contained high levels of [3H]etorphine binding sites although the globus pallidus was an exception. Subtraction autoradiography was performed using selective displacement of [3H]etorphine with opioid agonists to visualise mu-, delta- and kappa-opiate receptor subtypes. mu-Receptors were most abundant in the thalamus, caudate nucleus, putamen and the superficial layers of the cerebral cortex. Kappa receptors were concentrated in the deep layers of the cortex, the claustrum and the caudate nucleus. Human brain contained very few delta-receptors. Some brain areas with high concentrations of endogenous opioid peptides have many receptors, but in other areas, for example the globus pallidus, there is a mismatch between peptide concentration and receptor density.