Mosquitoes sure know how to make their presence felt. If its not their annoying buzz, their nasty nip will certainly get your attention. But in many regions, mosquitoes aren't just annoying, they're life threatening. Although many scientists are dedicated to finding effective ways of combating mosquito borne diseases, one of the main focuses for control has been the insect larva;more specifically, the larva's digestive system. One of the gut's main functions is to generate an extreme pH, by ion transport, for digestion. Horst Onken from Washington State University explains that studying ion transport in the insect's gut is difficult and although the isolated tissue is easier to control, it loses a significant proportion of its transport activity. He adds that while serotonin can restore some of the tissue's function, the neurotransmitter never restores it entirely; some vital physiological component is missing. Wondering whether the secret ingredient could be one of the many peptide hormones secreted by the insect, Onken and his colleagues,Stacia and David Moffett, began testing various insect hormones on the larval Aedes aegypti digestive system, to see whether hormones could hold the key to restoring the tissue's function().
First the team monitored the hormones' effects on isolated gut tissue. Knowing that the pH in the anterior portion of the gut is extremely alkaline during digestion, the team decided to monitor the transepithelial voltage,which reflects ion transport activity, as an indicator of the hormone's effects. However, obtaining A. aegypti hormones was tricky; Onken explains that he couldn't buy many of the peptide hormones off the shelf as each species secretes its own specific cocktail. Fortunately, colleagues from around the world were able to supply the precious peptides, providing Onken with eleven peptides in the hope of raising the transepithelial voltage to its physiological level. But after systematically administering the hormones to isolated gut tissue, the team were in for a disappointment; none of the hormones reproduced the gut's initially high transepithelial voltage, in fact some even decreased it.
Despite this dissappointment, Stacia Moffett noticed an unexpected side effect; four of the hormones seemed to inhibit the tissue's peristaltic movement. Onken explains that when serotonin is applied to larval gut tissue,the resulting transepithelial voltage fluctuates and is accompanied by gentle rippling muscular movements, as if mixing and digesting a satisfying meal. But when the team exposed the tissue to some of the A. aegypti hormones(two forms of neuropeptide F and head peptides I and III), the transepithelial voltage fluctuations decreased and the tissue stopped rippling. Rather than modulating the gut's ion transport alone, some of the hormones also regulate the tissue's ability to mix and move its contents.
Having discovered that some hormones modulate two key aspects of the larva's gut function, Onken is very excited about the possibility of eventually being able to simulate these aspects of the gut's physiology, and the powerful role this could play in man's ceaseless battle against his relentless foe.
