Serotonin Inhibits Protein Feeding in the Blow Fly, Phormia regina (Meigen)

Serotonin is an important signaling molecule involved in the control of feeding in flies and other animals. In this study, a potential neurohemal release site for serotonin and the effects of exogenous serotonin on protein feeding were examined in the black blow fly, Phormia regina. A dense network of varicose neural processes exhibiting serotonin-like immunoreactivity was identified on the dorsal region of the thoracico-abdominal ganglion in P. regina. This dorsal region of the central nervous system is a likely site for the release of serotonin into the hemolymph. Circulating serotonin may have multiple systemic effects on fly physiology, including modulating or regulating feeding related processes and diuresis. Injections of exogenous serotonin reduced protein meal size in female flies at all doses and at all time points examined within a 24 h period relative to control and saline injected flies. Similar results were observed in serotonin-injected males at 35 min post injection. The injection of 50 μg serotonin resulted in the greatest amount of protein feeding inhibition. Serotonin injected flies also experienced greater weight loss than control or saline-injected flies during the 24 h post-injection period, possibly due to increased diuresis.