Insects have an open circulatory system that transports nutrients, waste, hormones, immune factors and other molecules to all regions of the body. This circulatory system is composed of hemolymph (insect blood), the hemocoel (open body cavity) and several contractile pumps. The pump that distributes hemolymph throughout the main body cavity is the dorsal vessel, but additional pumps, called accessory pulsatile organs or auxiliary hearts, propel hemolymph into narrow areas of the body, or areas that are distant from the dorsal vessel.

This study assessed the hormonal control of the antennal hearts of mosquitoes, and used intravital video imaging to show that:

1. 1.The neuropeptides crustacean cardioactive peptide (CCAP), FMRFamide and SALDKNFMRFamide increase the contraction rates of both the antennal accessory pulsatile organs and the heart.
   

2. 2.CCAP, FMRFamide and SALDKNFMRFamide increase hemolymph velocity in the antennal space.
   

Article citation:

Suggs, J.M., T.H. Jones, S.C. Murphree, and J.F. Hillyer. 2016. CCAP and FMRFamide-like peptides accelerate the contraction rate of the antennal accessory pulsatile organs (auxiliary hearts) of mosquitoes. Journal of Experimental Biology. 219(15): 2388-2395. (PMID: 27247317) (See it in JEB) (Email me for a pdf copy)

Graphical abstract:

Article abstract:

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.