ABSTRACT
Among compounds from natural sources ergolines are of paramount importance as ligands for serotonin (5-hydroxytryptamine, 5-HT) receptors, dopamine receptors, and adrenoceptors. The tetracyclic structure of the ergolines contains the essential features of the monoamine neurotransmitters 5-HT, dopamine, and noradrenaline, and it is not surprising that many naturally occurring and (semi) synthetic ergolines have been shown to act as agonists, partial agonists or antagonists at receptors for these neurotransmitters. It is difficult to explain the complexity of the pharmacological profile of the ergolines without encountering the issue of receptor heterogeneity. The extent of the multiplicity of 5-HT receptors, dopamine receptors and adrenoceptors became fully apparent in the early 1990s, since at least 14 distinct subtypes of 5-HT receptors (Hoyer et al., 1994; Martin and Humphrey, 1994; Boess and Martin, 1994), 5 subtypes of dopamine receptors (Sibley and Monsma, 1992; Strange, 1993; Seeman and Van Tol, 1994), and at least 10 subtypes of adrenoceptors (Bylund et al., 1994; Hieble et al., 1995a, b) could be identified on the basis of structural, transductional and operational information obtained from molecular biological, second messenger and radioligand binding as well as functional studies.
