Allatotropin-like neuropeptide in the cockroach abdominal nervous system: Myotropic actions, sexually dimorphic distribution and colocalization with serotonin

Allatotropin (AT) was isolated from the moth Manduca sexta as a peptide sti mulating biosynthesis of juvenile hormone in the corpora allata, but has al so been shown to be cardioactive in the same species. Here, we have investi gated the presence and biological activity of AT-like peptide in the cockro aches Leucophaea maderae and Periplaneta americana with focus on abdominal ganglia and their target tissues. An antiserum to M. sexta AT was used for immunocytochemical mapping of neurons in the abdominal ganglia. A small num ber of interneurons and efferent neurons were found AT-like immunoreactive (AT-LI) in each of the abdominal ganglia. A prominent sexual dimorphism was detected in the terminal abdominal ganglion: in L. maderae the male gangli on there are approximately 18 AT-LI neurons with cell bodies posteriorly an d efferent axons in the genital nerves; in the female ganglion 4-5 AT-LI ce ll bodies (with efferent axons) were found in the same region. Correlated w ith the extra efferents in males, the male accessory glands are richly supp lied by AT-LI fibers and in females a less prominent innervation was seen i n oviduct muscle. A similar dimorphism was seen in abdominal ganglia of P. americana. A sexual dimorphism was also detected in the abdominal ganglia A 4-A6 oft. maderae. In each of these ganglia, approximately 8-10 large AT-LI neuronal cell bodies were found along the midline; in females these neuron s have significantly larger cell bodies than in males. In both sexes, and b oth cockroach species, two large dorsal midline neurons were detected in A- 5 and 6, which seem to send axons to the hindgut: the rectal pads of the hi ndgut are supplied by arborizing AT-LI axons. In males and females of both species, efferent AT-LI axons from midline neurons in A3-A6 supply the late ral heart nerves and other neurohemal release sites with arborizations. The efferent midline neurons of females contain colocalized serotonin-immunore activity. We tested the in vitro actions of M. sexta AT on muscle contracti ons in the L. maderae hindgut and the abdominal heart of both species. The frequency of contractions in the hindgut increased dose dependently when ap plying AT at 5 x 10(-8) to 5 x 10(-6) M (maximal response at 5 X 10(-7) M). Also the frequency of contractions of the heart increased by application o f AT (threshold response at 5 x 10(-9) M). This effect was more prominent i n males of both species (maximal response was a 35-40% increase in males an d 10-20% in females). In conclusion, an AT-like peptide is present in neuro ns and neurosecretory cells of cockroach abdominal ganglia and seems to pla y a role in control of contractions in the hindgut and heart and also to ha ve some function in male accessory glands and oviduct. (C) 2000 Wiley-Liss, Inc.