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  • Title: II. Localization and characterization of dopamine D4 binding sites in rat and human brain by use of the novel, D4 receptor-selective ligand [3H]NGD 94-1.
    Author: Primus RJ, Thurkauf A, Xu J, Yevich E, McInerney S, Shaw K, Tallman JF, Gallagher DW.
    Journal: J Pharmacol Exp Ther; 1997 Aug; 282(2):1020-7. PubMed ID: 9262371.
    Abstract:
    The dopamine D4 selective ligand, [H]NGD 94-1, was used in these studies to characterize binding sites in rat and human brain tissue by membrane binding and autoradiography techniques. Autoradiographic analysis of rat brain showed that specific [3H]NGD 94-1 binding was greatest in entorhinal cortex, lateral septal nucleus, hippocampus and the medial preoptic area of the hypothalamus. This nonstriatal distribution of [3H]NGD 94-1 binding was distinct from the autoradiographic distribution of dopamine D2 and D3 receptor subtypes. In homogenate preparations from rat brain regions, [3H]NGD 94-1 binding sites were low in density (<30.0 fmol/mg protein). The low density of D4 binding sites was corroborated by autoradiographic comparisons in which binding density for D4 receptors as measured by [3H]NGD 94-1 was only 1/7 of D2 and 1/5 of D3 receptor densities, despite corrections for differing radioligand binding characteristics. Pharmacological evaluation showed high affinity at rat [3H]NGD 94-1 binding sites for compounds with known D4 receptor affinity and little displacement by compounds with affinity for dopamine D1/D2/D3 receptor subtypes. Specific, high-affinity [3H]NGD 94-1 binding was also present in several human brain regions, including hippocampus, hypothalamus, dorsal medial thalamus, entorhinal cortex, prefrontal cortex and lateral septal nucleus. High-affinity [3H]NGD 94-1 binding was not present in any human striatal region examined. The pharmacological profile of [3H]NGD 94-1 binding sites in human brain was consistent with that previously demonstrated for cloned human D4 receptors expressed in mammalian cells. These findings suggest that specific, high-affinity [3H]NGD 94-1 binding exists in rat and human brain and that these sites reflect populations of dopamine D4 receptors with a distribution unique among dopamine receptor subtypes.
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