[3H]thienyl-phencyclidine ([3H]TCP) binds to two different sites in rat brain. Localization by autoradiographic and...

A high affinity [3H]thienyl-phencyclidine ([3H]TCP) binding and its similarity to that of [3H]phencyclidine ([3H]PCP) have been demonstrated on whole rat brain homogenates. We now describe the regional distribution of the [3H]TCP binding sites in the rat brain with fixed sections and frozen slide-mounted sections visualized by autoradiography and with homogenates of 12 regions by direct binding experiments. The 3 techniques give a similar pattern for the [3H]TCP binding distribution and the biochemical study reveals that two distinct binding sites for [3H]TCP exist: one of high affinity (5-10 nM) in the forebrain, which should be responsible for the psychotropic effects and a second one of lower affinity (50-80 nM) in the hindbrain and the spinal cord, which should be involved in the extrapyramidal behavior induced by PCP and congeneers. Competition experiments have shown that muscarinic compounds interact only with the hindbrain receptor possibly in two different sites, although morphine interacts with a very low affinity with the forebrain's high affinity receptor. Results obtained with SKF-10,047 (N-allylnormetazocine) seem to indicate that TCP and sigma-receptors are different.