Characteristics of high affinity binding of [3H]N-acetylserotonin in rat brain

Evidence that the putative pineal hormone, N-acetylserotonin (NAS), is present in diverse areas of the brain of the rat and that this compound is biologically active, prompted a study of its central binding characteristics. [3H]N-acetylserotonin [( 3H]-NAS) exhibits specific, saturable and high affinity binding in synaptosomal fractions from the brain of the rat. In fresh CNS membranes, [3H]N-acetylserotonin appeared to bind to a single population of high affinity sites with a dissociation constant (Kd) of 3-5 nM and a maximal binding site concentration (Bmax) of 250-400 fmol mg-1 protein. A comparison of the regional distribution of the binding of [3H]N-acetylserotonin and [3H]-5-hydroxytryptamine [( 3H]-5-HT) indicated that both radioligands exhibited the greatest binding in the striatum and frontal cortex, while relatively more [3H]N-acetylserotonin was bound in the cerebellum and brainstem. The structural specificity of the binding suggests that [3H]N-acetylserotonin labelled serotonergic receptors in the frontal cortex.