Regulation of lepidopteran foregut movement by allatostatins and allatotropin from the frontal ganglion

The frontal ganglion and associated neuronal pathways in larvae of the noct uid moth Helicoverpa armigera have been studied immunocytochemically with a ntisera against the endogenous neuropeptides, the allatostatins, (helicosta tins), and allatotropin. Two pairs of large ganglionic neurones contain all atostatin immunoreactivity, with the anteriormost of these pairs showing co localisation with allatotropin. Allatostatin and allatotropin axons exit th e frontal ganglion in the recurrent nerve and traverse the surface of the c rop to give terminal arborisations around the stomodeal valve. There is a g reater degree of lateral branching of allatotropin axons compared with alla tostatin axons over the crop musculature, In vitro experiments show that th e two types of peptides have antagonistic effects on the spontaneous myoact ivity of the crop musculature. Allatotropin is myostimulatory at concentrat ions as low as 10(-16) M, enhancing both frequency and amplitude of perista ltic waves of contraction. All members of the helicostatin family inhibit p eristalsis 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 suggeste d that peptidergic neurones of the frontal ganglion play a major part in re gulating foregut motility through the antagonistic actions of the allatosta tins and allatotropin. (C) 1999 Wiley-Liss, Inc.