Autoradiographic distribution of mu and delta opiate receptors in rat brain using highly selective ligands

We have characterized the autoradiographic distribution of mu and delta opiate receptors in rat brain using [3H]-Tyr-D-Ala-Gly-NMe-Phe-Gly-ol (DAGO) and [3H]D-Thr2, Thr6leu-enkephalin (DTLET), two highly selective ligands for mu and delta opiate receptors, respectively. Both ligands label an apparent single class of sites. Ligand selectivity shows that [3H]DAGO and [3H]DTLET are more selective ligands for their respective receptors than [3H]dihydromorphine (DHM) and [3H][D-Ala2,D-Leu5]enkephalin (DADLE). Autoradiographically, mu opiate receptors are highly discretely distributed in certain areas. High densities are found in "patches" in caudate-putamen, nucleus accumbens, cingulate cortex, habenula, various thalamic nuclei, amygdala, superior colliculus, and interpeduncular nucleus. Delta opiate receptors are mostly concentrated in the external plexiform layers of the olfactory bulb, caudate-putamen, olfactory tubercule, claustrum, and deep layers (layers V and VI) of the cortex. Since [3H]DAGO and [3H]DTLET are more selective ligands for their respective opiate receptor subtypes, they should be better ligands to characterize the fine distribution of mu and delta opiate receptors.