Abstract: | The regional distribution of 3H]idazoxan and 3H]rauwolscine was studied autoradiographically in human brain. 3H]Idazoxan binds with high affinity to α2 adrenoceptors as well as to non-adrenergic sites (NAIBS). 3H]Rauwolscine, besides binding to α2 adrenoceptors, also binds to 5-HT1A receptors. Both radioligands labelled the same population of α2 adrenoceptors, defined as the epinephrine-displaceable binding component. The highest densities of α2 adrenoceptors occur in the leptomeninges, cerebral cortex and claustrum; lower densities were visualised in the basal ganglia, thalamus, pons, substantia nigra, cerebellum and medulla oblongata; no α2 adrenoceptors were detected in amygdala and nucleus ruber. NAIBS were present in all the examined brain areas, with the highest densities found in the basal ganglia and substantia nigra. The finding that certain brain regions, such as the amygdala, contained NAIBS but no detectable α2 adrenoceptors, suggests that the binding sites are independent from each other. The regional distribution of 5-HT1A receptors labelled by 3H]rauwolscine is in agreement with previous studies using 3H]8-OH-DPAT. |