Helicostatins: Brain-gut peptides of the moth,Helicoverpa armigera (Lepidoptera: Noctuidae)

Abstract

Gene expression and immunolocalisation studies have determined that the helicostatins are brain-gut peptides in larvae of the lepidopteran, Helicoverpa armigera. Mapping of the distribution of these peptides in the nervous system and alimentary canal has provided evidence for multifunctional regulatory roles. In situ hybridisation studies have shown that the helicostatin precursor gene is expressed in neurones of the central and stomatogastric nervous systems, and endocrine cells of the midgut demonstrating that the helicostatins are true brain-gut peptides. Antisera raised against Leu-callatostatin 3 (ANRYGFGL-NH(2)), a peptide isolated from the blowfly, Calliphora vomitoria was used to map the distribution of allatostatin-like immunoreactive (Ast-ir) material in H. armigera to elucidate possible functions of the helicostatins. In situ hybridisation studies verified that the helicostatin precursor gene is expressed in neurones shown to contain Ast-ir, providing strong evidence that the Ast-ir material is helicostatins. Extensive immunoreactive axonal projections into complex regions of neuropile indicate that the helicostatins may have a neuromodulatory role in the brain and segmental ganglia of the ventral nerve cord. The presence of large amounts of immunoreactive material in axons within the corpora cardiaca (CC) and transverse nerves of the perisympathetic nervous system, two known neurohaemal organs, provides evidence for a neurohormonal role. The corpora allata (CA) were innervated only sparsely by Ast-ir axons suggesting that the CA are not a neurohaemal release site or a target. Thus, it is unlikely that the helicostatins regulate juvenile hormone (JH) biosynthesis or release. Ast-ir axons extended from the frontal ganglion through the recurrent nerve and many branches were closely associated with muscles of the foregut, stomodeal valve, and anterior midgut, implicating helicostatins in regulation of foregut motility. Ast-ir material was also present in nerves associated with muscles of the pyloric valve and rectum, and in endocrine cells of the midgut.