Apparent regional differences in 5-HT1A binding may reflect [3H]8-OH-DPAT labeling of serotonin uptake sites.

The binding of [3H]8-OH-DPAT and [3H]paroxetine to 5-HT1A and 5-HT uptake sites (respectively) was examined in membranes prepared from bovine dorsal raphe and hippocampus. KD and Bmax values for [3H]8-OH-DPAT binding were indistinguishable in dorsal raphe nucleus and hippocampus. Competition studies with MDL 73,005EF, a selective 5-HT1A ligand, revealed a high and a low affinity site in the dorsal raphe, but only the high affinity component in hippocampal membranes. The low affinity component in the dorsal raphe was reduced in the presence of fluoxetine; saturation isotherms with [3H]paroxetine indicated a 5-fold greater concentration of 5-HT uptake sites in this region. The results are discussed in the context of earlier reports of regional differences in the pharmacology of 5-HT1A receptors and the selectivity of [3H]8-OH-DPAT binding.