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

The regulation of insect gut physiology is complex and involves the interactions of a number of mechanisms, including the neural regulation of gut contraction by altering neural input and the modulation of gut contractions by neuropeptides directly affecting the muscle. The FGLa-type allatostatins (FGLa/ASTs) are known brain/gut peptides with numerous physiological roles, including modulation of gut contraction and neural input. To further investigate the pleiotropic roles of FGLa/AST peptides in Locusta migratoria, we have examined the role of a locust FGLa/AST (Scg-AST-6) in the gut. Proctolin and Scg-AST-6 have opposing effects on gut contraction, where proctolin dose-dependently increases gut muscle tension, while Scg-AST-6 inhibits both muscle tension and spontaneous and neurogenic contractions in a dose-dependent manner. Results from neurophysiological recordings indicate that there may be a central pattern generator (CPG) within the ventricular ganglia regulated by descending inhibition, and the addition of Scg-AST-6 dose-dependently modulates this ventricular ganglion CPG. This work provides a comprehensive picture of how FGLa/ASTs may modulate and coordinate each region of the locust gut, and shows that FGLa/ASTs have both central effects, on the ventricular ganglion CPG, and peripheral effects on the gut muscle. Overall, this study shows how FGLa/ASTs contribute to the complex regulation and fine tuning of gut contraction.