Selective labelling of high affinity 5-hydroxytryptamine1 receptors in whole rat brain

In synaptic membranes prepared from whole rat brain, cinanserin produced a relatively shallow inhibition curve of [3H] 5-HT binding with Hill slope of 0.68, as compared with that observed in the [3H]spiperone binding (Hill slope = 0.99). Furthermore, nonlinear regression analysis demonstrated that the former inhibition curve is best fitted by a two-site model. Regional and Scatchard analyses both clearly revealed that, in rat brain, at least two populations of binding sites were labelled by [3H]5-HT; however, high affinity binding sites (K(D) = 1.90 nM, Bmax = 0.188 pmoles/mg protein) could apparently be differentiated from the others by the action of 5 nM cinanserin.