Schema of the Spicule Insertion Circuit Figure 3. Circuit diagram of cells that control spicule movement and model of prolonged vulval contact coupling to rhythmic protractor contractions. Gubernacular erector (GER), gubernacular retractor (GRT), anterior oblique (AOB), posterior oblique (POB), dorsal spicule protractor (DSP), ventral spicule protractor (VSP) and anal depressor (ADP). Arrows and bars indicate chemical synapses and gap junctions, respectively. Bi-directional arrows refer to cells that make reciprocal chemical synapses. Bi-directional arrows embedded in bars refer to cells that make gap junctions in addition to reciprocal chemical synapses. The green circles refer to cholinergic neurons. (A) Bilateral electrical and chemical connectivity diagram of male neurons and muscles that control the movements of the spicules [adapted from [25], and the Male Wiring Project]. (B) Abbreviated cartoon of limited connections between neurons and muscles discussed in this work. Refer to (Male Wiring Project, Albert Einstein College of Medicine, http://worms.aecom.yu.edu/pages/male_wiring_project.htm) for a more complete list of connections to other cells in the male. (C) Cartoon depicting changes in male tail muscles upon vulval contact. Left panel depicts relative locations and electrical junctions between the male sex muscles. The right panel depicts the shortening of the AOB and POB muscles causing a curvature in the posterior male tail (red arrow) upon chemical stimulation from the PCA, PCB and PCC neurons. Stimulated GER muscles relay their signals to the spicule protractor muscles causing rhythmic contractions (blue arrow). doi:10.1371/journal.pgen.1001326.g003 found that ablations of any neuronal pair do not obviously affect the males’ ability to locate the precise position of the vulva, since the other two pairs can compensate (data not shown). However, like the unc-29(lf);acr-16(0) males, the operations significantly reduced the duration of vulval contact (Figure 4A; Figure S2B), suggesting that each pair of p.c.s. neurons is used to sustain contact between the cloacal opening and the hermaphrodite’s vulva. Among these neurons, the PCB and PCC neurons are cholinergic PLoS Genetics | www.plosgenetics.org 5 March 2011 | Volume 7 | Issue 3 | e1001326