The anterior stomach of larval mosquitoes (Aedes aegypti):effects of neuropeptides on transepithelial ion transport and muscular motility

Abstract

SUMMARY The present investigation studied the influence of a number of neuropeptides on semi-open preparations of the isolated and perfused anterior stomach of larval Aedes aegypti. Effects of peptides were observed on the lumen negative transepithelial voltage (Vte) that is present with serotonin in the bath; this voltage most likely reflects active HCO3– secretion involved in alkalization of the larval anterior stomach. The five different A. aegypti allatostatins(allatostatin A 1–5) all affected Vte in almost identical ways, causing a 10–15% reduction of the voltage at 10–7 mol l–1. A. aegyptineuropeptide F and proctolin reduced Vte at submicromolar concentrations. At 10–6 mol l–1,neuropeptide F reduced Vte by 30% and proctolin reduced Vte by 50%. In contrast, A. aegypti allatotropin, A. aegypti head peptides I and III and A. aegypti short neuropeptide F were without effect on Vte. During the investigation it was observed that the peristaltic contractions of the preparations caused a dynamic component of Vte. Peristaltic contractions and the correlated voltage fluctuations depended on the presence of serotonin. Peristaltic activity and Vtedeflections were progressively inhibited by A. aegypti head peptides I and III by A. aegypti short neuropeptide F and by A. aegypti neuropeptide F when the peptide concentrations were increased from 10–8 to 10–6 mol l–1. These observations show that physiological concentrations of some of the tested neuropeptides affect two processes that require coordination: ion transport and motility of the larval anterior stomach.

Allatostatin A-like immunoreactivity in the nervous system and gut of the larval midge, Chironomus riparius (Meigen): Modulation of hindgut motility, rectal K+ transport and implications for exposure to salinity

“…In the cockroach, ASTs have been shown to decrease food consumption (Aguilar et al, 2003). There is increasing evidence that ASTs modulate ion transport of various regions of the gut (Onken et al, 2004;Vanderveken and O'Donnell, 2014). An important group of insects in which ASTs have not been studied are the midges.…”

“…Studies have shown that AST modulates gut muscle activity (Sarkar et al, 2003;Duve et al, 2000). Studies have also provided evidence that AST directly modulates ion transport activities in gut epithelia (Onken et al, 2004;Vanderveken and O'Donnell, 2014). By simultaneously and perhaps independently modulating transit time of hindgut luminal contents and the magnitude of epithelial ion reabsorption through direct neural control, the midge would greatly increase its ability to fine-tune the reabsorptive and excretory functions of the hindgut.…”

“…This suggests that the hindgut muscle expresses receptors for AST. Many previous studies have demonstrated that AST is a myoinhibitory peptide in insects (Sarkar et al, 2003;Lange et al, 1993;Onken et al, 2004;Duve et al, 2000). A dose of 1 pmol l −1 non-native AST on the foregut and hindgut of Lacanobia oleracea and Rhodnius prolixus, respectively (Sarkar et al, 2003;Duve et al, 2000), is effective at inhibiting muscle contractions.…”

The neural and peptidergic control of gut contraction in Locusta migratoria: the effect of an FGLa/AST

“…It is possible that FGLa/ASTs can affect both muscle contractility and reabsorption because FGLa/ASTs have been shown to alter ion transport in other insect species (Onken et al, 2004). Future work will examine the role that FGLa/ASTs play in locust gut ion transport to further elucidate the physiological roles that this peptide family plays in digestion.…”

Organization, ultrastructure, and development of midgut visceral muscle in larval Aedes aegypti

“…The present studies of the structure and ultrastructure of the muscularis of this organ in the 2 nd , 3 rd and 4 th larval instars were prompted by our interest in understanding the mechanisms by which the multiple functions of the midgut are controlled and integrated by neurotransmitters and hormones. Previously, we had found that both alkali secretion and motility of the isolated, perfused anterior stomach were stimulated by serotonin (Clark et al, 2000;Onken et al, 2004;Onken et al, 2004a), and that the midgut receives an extensive serotonergic innervation that is derived from a small number of bilateral neurons (Moffett & Moffett, 2005). Several Aedes neuropeptides were found to have inhibitory effects on motility, ion transport, or both functions (Onken et al 2004a), and these effects may be reflected by an apparent peptidergic innervation of the gut and by the presence of a substantial population of enteroendocrine cells (Moffett & Moffett, 2005).…”