Figure 10.

The male defecation circuit is integrated with the male mating circuit to promote copulatory behaviors. Conceptual diagram of the male tail during defecation (A and B) and mating while at the hermaphrodite vulva (C and D). Dorsal is to the top, anterior to the left. The spicule is in dark gray. The GABAergic DVB, its processes, and neurotransmitter release are in green. Active muscle are shown in yellow, nonactive muscle in red. (A) During defecation, calcium increase in the intestine results in neuropeptide (black) release that activates the DVB, which in turn activates the enteric muscle. (B) Due to electrical connections between the anal depressor and protractor, the male sex muscle are activated following the expulsion step of defecation, resulting in spicule protraction when no hermaphrodite is present. (C) The male sex muscle, including the protractor, and the anal depressor are active while the male is prodding at the hermaphrodite vulva. (D) Neuropeptide release from the DVB is necessary for spicule insertion, a process during which both the sex muscle and anal depressor contract. The intestinal muscle squeezes the intestine, possibly to support sperm (blue) movement through the vas deferens (double headed arrow); as a consequence, the intestinal lumen volume also expands (brown). adp, anal depressor; exp, waste expelled from the cloaca; GABA, γ-aminobutyric acid; int, intestinal muscle; pro, dorsal protractor.