The frontal ganglion and associated neuronal pathways in larvae of the noctuid moth Helicoverpa armigera have been studied immunocytochemically with antisera against the endogenous neuropeptides, the allatostatins (helicostatins), and allatotropin. Two pairs of large ganglionic neurones contain allatostatin immunoreactivity, with the anteriormost of these pairs showing colocalisation with allatotropin. Allatostatin and allatotropin axons exit the frontal ganglion in the recurrent nerve and traverse the surface of the crop to give terminal arborisations around the stomodeal valve. There is a greater degree of lateral branching of allatotropin axons compared with allatostatin axons over the crop musculature. In vitro experiments show that the two types of peptides have antagonistic effects on the spontaneous myoactivity of the crop musculature. Allatotropin is myostimulatory at concentrations as low as 10(-16) M, enhancing both frequency and amplitude of peristaltic waves of contraction. All members of the helicostatin family inhibit peristalsis completely at concentrations of 10(-7)-10(-6) M and, to varying degrees, at 10(-10)-10(-8) M. On the basis of this evidence, it is suggested that peptidergic neurones of the frontal ganglion play a major part in regulating foregut motility through the antagonistic actions of the allatostatins and allatotropin.
Copyright 1999 Wiley-Liss, Inc.