ABSTRACT

During the past several years, with the development of more selective ligands and the increased sophistication of methodologies, there has been a proliferation of binding studies describing new types and subtypes of opioid receptors. Not surprisingly, a consensus has not yet been reached regarding the classification of all of the novel sites and, consequently, inconsistencies in nomenclature have emerged. Thus, different laboratories have adopted different names for what is likely to be the same binding site or, conversely, the same name for apparently different binding sites, making communication and evaluation of findings cumbersome. In addition, selective ligands are not yet available for some receptors and, therefore, a variety of different non-selective ligands and assay conditions have been utilized. Under such conditions, a lack of complete agreement about receptor characteristics is not surprising.