The pharmacology of the gut of the desert locust Schistocerca gregaria and other insects

Abstract

1. The pentapeptide proctolin is likely to be the main excitatory neuromuscular transmitter in the fore- and hindgut of most insect species. 2. 5-Hydroxytryptamine relaxes the gut of Schistocerca gregaria by activating 5-HT 2-like receptors but is reported to contract tissues isolated from other species. 3. Octopamine reduced gut contractility of most insect species. In Schistocerca gregaria this is achieved by activation of adenylate cyclase-linked OA 2 receptors. 4. The role of acetylcholine in the insect gut is unclear but in the desert locust there is evidence of relaxation mediated via nicotinic receptors. 5. FMRFamide-related peptides modulate the effects of 5-hydroxytryptamine and proctolin in the gut of Schistocerca gregaria by activating naloxone-sensitive receptors. Work on Leucophaea maderae suggests that other peptides, including leucomyosuppressin and the leucokinins, are also involved in regulation of gut muscle function.