Peptidergic control of the heart of the stick insect, Baculum extradentatum

SUMMARYCrustacean cardioactive peptide (CCAP) is a highly conserved arthropod neurohormone that is involved in ecdysis, hormone release and the modulation of muscle contractions. Here, we determined the CCAP gene structure in the malaria mosquito Anopheles gambiae, assessed the developmental expression of CCAP and its receptor and determined the role that CCAP plays in regulating mosquito cardiac function. RACE sequencing revealed that the A. gambiae CCAP gene encodes a neuropeptide that shares 100% amino acid identity with all sequenced CCAP peptides, with the exception of Daphnia pulex. Quantitative RT-PCR showed that expression of CCAP and the CCAP receptor displays a bimodal distribution, with peak mRNA levels in second instar larvae and pupae. Injection of CCAP revealed that augmenting hemocoelic CCAP levels in adult mosquitoes increases the anterograde and retrograde heart contraction rates by up to 28%, and increases intracardiac hemolymph flow velocities by up to 33%. Partial CCAP knockdown by RNAi had the opposite effect, decreasing the mosquito heart rate by 6%. Quantitative RT-PCR experiments showed that CCAP mRNA is enriched in the head region, and immunohistochemical experiments in newly eclosed mosquitoes detected CCAP in abdominal neurons and projections, some of which innervated the heart, but failed to detect CCAP in the abdomens of older mosquitoes. Instead, in older mosquitoes CCAP was detected in the pars lateralis, the subesophageal ganglion and the corpora cardiaca. In conclusion, CCAP has a potent effect on mosquito circulatory physiology, and thus heart physiology in this dipteran insect is under partial neuronal control. Supplementary material available online at

Section: −7mentioning

confidence: 63%

Section: Discussionmentioning

confidence: 99%

Cardioacceleratory function of the neurohormone CCAP in the mosquito Anopheles gambiae

Estévez‐Lao

Boyce

Honegger

et al. 2013

“…In cockroaches, two types of neuropeptides are known to accelerate the antennal APO contraction rate: proctolin and three FLPs (Hertel et al, 1985(Hertel et al, , 2012Hertel and Penzlin, 1992;Lange et al, 1993;Predel et al, 2004). Proctolin stimulates the contraction of visceral, skeletal and cardiac muscle, and modulates digestion, egg laying, and both sexual and feeding behaviors (Konopinska and Rosinski, 1999;Isaac et al, 2004;Ejaz and Lange, 2008). However, a search of the genomes of A. gambiae, Aedes aegypti and Culex quinquefasciatus (via www.vectorbase.org) reveals that neither proctolin nor the proctolin receptor is encoded in the mosquito lineage.…”

Section: Discussionmentioning

confidence: 99%

“…In cockroaches and some polyneopterans (lower Neoptera), the neuropeptide proctolin and three FMRFamide-like peptides (FLPs) accelerate the contraction rate of the antennal APOs, whereas the neuropeptide allatostatin and another FLP do not (Hertel et al, 1985(Hertel et al, , 2012Hertel and Penzlin, 1992;Lange et al, 1993;Predel et al, 2004). Whether these or other factors accelerate the contraction rate of the antennal APOs of nonpolyneopteran insects remains unknown; however, proctolin and certain FLPs are cardioacceleratory in diverse insect species (Cuthbert and Evans, 1989;Robb and Evans, 1990;Zornik et al, 1999;Sliwowska et al, 2001;Nichols, 2006;Ejaz and Lange, 2008;Hillyer et al, 2014). Thus, it is likely that other cardiomodulatory factors affect the contraction rate of the antennal APOs of insects.…”

Section: Introductionmentioning

confidence: 99%

CCAP and FMRFamide-like peptides accelerate the contraction rate of the antennal accessory pulsatile organs (auxiliary hearts) of mosquitoes

Suggs

Jones

Murphree

et al. 2016

Insects rely on specialized accessory pulsatile organs (APOs), also known as auxiliary hearts, to propel hemolymph into their antennae. In most insects, this is accomplished via the pulsations of a pair of ampulla located in the head, each of which propels hemolymph across an antenna via an antennal vessel. Once at the distal end of the appendage, hemolymph returns to the head via the antennal hemocoel. Although the structure of the antennal hearts has been elucidated in various insect orders, their hormonal modulation has only been studied in cockroaches and other hemimetabolous insects within the superorder Polyneoptera, where proctolin and FMRFamide-like peptides accelerate the contraction rate of these auxiliary hearts. Here, we assessed the hormonal modulation of the antennal APOs of mosquitoes, a group of holometabolous (Endopterygota) insects within the order Diptera. We show that crustacean cardioactive peptide (CCAP), FMRFamide and SALDKNFMRFamide increase the contraction rate of the antennal APOs and the heart of Anopheles gambiae. Both antennal hearts are synchronously responsive to these neuropeptides, but their contractions are asynchronous with the contraction of the heart. Furthermore, we show that these neuropeptides increase the velocity and maximum acceleration of hemolymph within the antennal space, suggesting that each contraction is also more forceful. To our knowledge, this is the first report demonstrating that hormones of a holometabolous insect modulate the contraction dynamics of an auxiliary heart, and the first report that shows that the hormones of any insect accelerate the velocity of hemolymph in the antennal space.

“…In both mosquitoes and cockroaches, there is no correlation between the contraction rate of the antennal hearts and the dorsal vessel, but different from what we observed for the wing heart, the antennal hearts contract at a significantly slower rate than the dorsal vessel (Hertel et al, 1985;Boppana and Hillyer, 2014;Suggs et al, 2016). Furthermore, some cardioacceleratory peptides, such as CCAP, FMRFamides and proctolin, are known to modulate the contraction dynamics of both the dorsal vessel and the antennal hearts of insects (Cuthbert and Evans, 1989;Predel et al, 2004;Ejaz and Lange, 2008;Hertel et al, 2012;Estevez-Lao et al, 2013;Suggs et al, 2016). Whether these same factors also modulate the rhythmicity of the wing heart remains to be determined.…”

Section: Discussionmentioning

confidence: 56%

Hemolymph circulation in insect flight appendages: physiology of the wing heart and circulatory flow in the wings of the mosquito,Anopheles gambiae

Chintapalli

Hillyer

2016

The wings of insects are composed of membranes supported by interconnected veins. Within these veins are epithelial cells, nerves and tracheae, and their maintenance requires the flow of hemolymph. For this purpose, insects employ accessory pulsatile organs (auxiliary hearts) that circulate hemolymph throughout the wings. Here, we used correlative approaches to determine the functional mechanics of hemolymph circulation in the wings of the malaria mosquito Anopheles gambiae. Examination of sectioned tissues and intravital videos showed that the wing heart is located underneath the scutellum and is separate from the dorsal vessel. It is composed of a single pulsatile diaphragm (indicating that it is unpaired) that contracts at 3 Hz and circulates hemolymph throughout both wings. The wing heart contracts significantly faster than the dorsal vessel, and there is no correlation between the contractions of these two pulsatile organs. The wing heart functions by aspirating hemolymph out of the posterior wing veins, which forces hemolymph into the wings via anterior veins. By tracking the movement of fluorescent microspheres, we show that the flow diameter of the wing circulatory circuit is less than 1 µm, and we present a spatial map detailing the flow of hemolymph across all the wing veins, including the costa, sub-costa, ambient costa, radius, media, cubitus anterior, anal vein and crossveins. We also quantified the movement of hemolymph within the radius and within the ambient costa, and show that hemolymph velocity and maximum acceleration are higher when hemolymph is exiting the wing.