Distribution of μ-, δ- and κ-opioid binding sites in membrane suspensions from rabbit brain regions

Analysis of saturation curves using selective labelling techniques in rabbit brain cortex showed that maximum binding capacities at μ-, δ- and κ-opioid binding sites were respectively 4.34, 1.68 and 5.43 pmol/g tissue and the binding affinities at the three sites were 2.98, 0.52 and 0.091 nM. The binding of single concentrations of tritiated ligands (1 x k(D) value in the cortex) was determined at μ-, δ- and κ-sites in seven rabbit brain regions. The highest content of μ-sites was in the striatum, followed by the diencephalon, mesencephalon, cerebellum and cortex; the lowest content was in the pons-medulla and the hippocampus. All regions had a content in δ-sites similar to the cortex, which had fewer δ-sites than μ- and κ-sites. The content in κ-sites was highest in the diencephalon and lowest in the mesencephalon, cerebellum hippocampus and pons-medulla.