Quantitative light microscopic localization of [3H]naltrindole binding sites in the rat brain

The binding of radiolabeled naltrindole ([3H]NTI), a selective delta-opioid antagonist, was characterized using receptor autoradiography. Receptor binding properties were established in brain paste slices which demonstrated one site receptor occupancy with an apparent Kd of 0.25 +/- 0.08 nM (Bmax of 597.5 fmol/mg protein). Autoradiographic localization of [3H]NTI binding sites in the rat brain revealed high densities of these sites in the cortex (layers 1-3 and 6), caudate putamen, accumbens, claustrum, and internal plexiform layer of the olfactory bulb. Moderate to low levels of specific binding were observed in the hippocampus, thalamus, and substantia gelatinosa of the spinal cord.