Human striatal dopamine receptors are organized in compartments

Dopamine (D2) receptors visualized in postmortem human striatum by quantitative autoradiography of [3H]spiroperidol binding are organized into circumscribed zones of low receptor density separated from other such zones by regions of higher D2 density. The D2-rich zones of the caudate nucleus and putamen contain twice the binding of D2-poor zones. The Hill coefficient, obtained from saturation analysis of [3H]spiroperidol binding to thin sections of human striatum, gave a value near unity, indicating the binding was occurring to a single type of site. The patchiness of [3H]spiroperidol binding was unaltered by postincubation removal of lipid from the tissue sections, indicating that a differential absorption of tritium in white and grey matter does not account for the heterogeneous distribution. The D2-rich and D2-poor regions appear to form labyrinths oriented in the anterior-posterior axis and are typically aligned with, respectively, acetylcholinesterase-rich and -poor compartments as visualized on stained adjacent sections. Thus, the distribution of dopamine D2 receptors conforms to the "striosomal" organization of the human caudate-putamen, a finding that suggests that this receptor subtype may mediate the influence of dopamine on distinct neurochemical compartments within the structure.