Localization of kappa opioid receptor binding sites in human forebrain using [3H]U69,593: Comparison with [3H]bremazocine

1. The autoradiographic distribution of kappa opioid receptor binding sites in human brain was examined using two radiolabeled probes, namely 3H]U69,593 and 3H]bremazocine. 2. 3H]U69,593 binding was performed in the absence of blockers for other sites, while 3H]bremazocine binding was investigated in the presence of saturating concentrations of mu and delta blockers to ensure selective labeling of kappa opioid receptors. 3. Our results show that the autoradiographic distribution of 3H]U69,593 and 3H]bremazocine (plus blockers) binding sites is identical, with high densities of sites found in deep cortical layers and claustrum. 4. This indicates that 3H]U69,593 is a highly selective ligand of the kappa opioid receptor type.