Chapter 25 Pharmacology and molecular biology of octopamine receptors from different insect species

Abstract

This chapter discusses the pharmacology and molecular biology of octopamine receptors. It studies the structure and pharmacology of octopamine receptors using two different radioligands. In addition to the natural agonist octopamine, the phenlyiminoimidazolidine derivative 3 H-NC-SZ served as the second radioligand. Because it has a higher affinity and it is not degraded by endogenous enzymes, it is much better suited for ligand-binding studies. Using these radioligands, the octopamine receptor of the locusts, Schistocerca gregaria and Locusta migratoria , and the honey bee Apis mellifera are studied in detail in the chapter. In all these preparations, octopamine receptors are present in relatively high concentrations. In the desert locust—for example, Schistocerca gregaria—the maximal concentration of binding sites is approx. 10-times higher if compared with 5-HT and 20-times higher if compared with dopamine receptors. Only the neuronal histamine H1-like receptor has a slightly higher concentration of binding sites. This indicates the important role of octopamine in the nervous system of insects. Most pharmacological studies of insect neuronal octopamine receptors have been performed using locusts. High-affinity antagonists are well suited for physiological studies. The most important among them are the tetracyclic substances, mianserin and, with even higher affinity, the structurally related substance, maroxepine.