Nomenclature of central and peripheral dopaminergic sites and receptors.

The recommendation of this personal commentary is that dopaminergic sites and states be defined by the rank order of the effective absolute molarities (in vitro) for the principal dopaminergic congeners. This recommendation can serve to define the receptors in both the central nervous system and peripheral tissues and will assist in communicating the following fundamental and controversial issues in the biochemical pharmacology of dopamine receptors. First, the central question is whether or not there is more than one type of functional dopamine receptor. The different biological effects of dopamine [1-6] may occur because the same dopamine receptor may be located on different types of cells, or because there may be different types of dopamine receptors. An extreme view, for example, stated by Laduron [2], is that there is only one type of dopamine receptor, postsynaptic in location and having D2-type properties (see later), which fully accounts for the central actions of dopamine, including both the postsynaptic and autoreceptor actions of dopamine. Second, it is now clear that the "state" of a receptor can be altered by GTP [7-9]. That is, GTP lowers the affinity of the receptor for its agonist. The question then arises: are there different dopamine receptor sites in addition to these different states, or can all the data fit into the idea of a single receptor with two different states? Third, this fundamental issue of "states" and/or "sites" has, therefore, resulted in a variety of nomenclatures for classifying dopamine receptors. These variations in terminology are confusing, a point recently emphasized by others [10]. Hence, do the different names or terms refer to the same site or state? Is it possible to compare nomenclatures, despite the different conditions and 3H-ligands used? Which nomenclature is useful? Fourth, particularly difficult is the question of whether or not the central and peripheral dopamine receptors are the same. Is it possible to have a single nomenclature for both central and peripheral dopamine receptors?